Advance

TAKEHARA Kohsei

    Department of Civil and Environmental Engineering　Professor
Last Updated :2024/04/19

Researcher Information

Degree

  • (BLANK)（Kyushu University）
  • (BLANK)（Kyushu University）

J-Global ID

Research Interests

  • 水工水理学   Hydraulic Engineering   

Research Areas

  • Social infrastructure (civil Engineering, architecture, disaster prevention) / Hydroengineering

Education

  •        - 1988  Kyushu University  工学研究科  水工土木学専攻
  •        - 1988  Kyushu University  Graduate School, Division of Engineering
  •        - 1986  Kyushu Institute of Technology  School of Engineering  開発土木工学科
  •        - 1986  Kyushu Institute of Technology  Faculty of Engineering

Association Memberships

  • 流体力学会   可視化情報学会   土木学会   

Published Papers

  • S. Abe; T. Takagi; S. Torisawa; K. Abe; H. Habe; N. Iguchi; K. Takehara; S. Masuma; H. Yagi; T. Yamaguchi; S. Asaumi
    Aquacultural Engineering Elsevier BV 93 102146 - 102146 0144-8609 2021/05 [Refereed]
  • Nguyen Hoai Ngo; Kazuhiro Shimonomura; Taeko Ando; Takayoshi Shimura; Heiji Watanabe; Kohsei Takehara; Anh Quang Nguyen; Edoardo Charbon; Takeharu Goji Etoh
    Sensors MDPI AG 21 (7) 2506 - 2506 2021/04 [Refereed]
     
    A burst image sensor named Hanabi, meaning fireworks in Japanese, includes a branching CCD and multiple CMOS readout circuits. The sensor is backside-illuminated with a light/charge guide pipe to minimize the temporal resolution by suppressing the horizontal motion of signal carriers. On the front side, the pixel has a guide gate at the center, branching to six first-branching gates, each bifurcating to second-branching gates, and finally connected to 12 (=6×2) floating diffusions. The signals are either read out after an image capture operation to replay 12 to 48 consecutive images, or continuously transferred to a memory chip stacked on the front side of the sensor chip and converted to digital signals. A CCD burst image sensor enables a noiseless signal transfer from a photodiode to the in-situ storage even at very high frame rates. However, the pixel count conflicts with the frame count due to the large pixel size for the relatively large in-pixel CCD memory elements. A CMOS burst image sensor can use small trench-type capacitors for memory elements, instead of CCD channels. However, the transfer noise from a floating diffusion to the memory element increases in proportion to the square root of the frame rate. The Hanabi chip overcomes the compromise between these pros and cons.
  • Yasuhide TAKANO; Shoma SUGAKI; Kazuyuki NAKAKITA; T. Goji ETOH; Kohsei TAKEHARA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) Japan Society of Civil Engineers 77 (2) I_919 - I_924 2021 [Refereed]
     
    To understand transportation mechanisms of materials through an ocean surface by wind, a preliminary study is conducted on a spaciotemporal wind pressure measurement on a continuous solid wavy bed by means of the pressure sensitive paint (PSP). The PSP measurement technology is close to an application stage in the field of aero-fluid-dynamics. However, the wind speed acting on the ocean surface and civil engineering structures is not high enough to apply the PSP measurement. For example, the pressure drop is only 0.54 % for a wind speed of 30 m/s. Therefore, temporal and spatial data accumulation methods are applied, such as binning of intensity data from neighboring pixels, and accumulation of data for repetitive captures of the images. The PSP luminescence intensity is sensitive to temperature changes caused by wind and illumination to the PSP. Therefore, it is necessary to accurately measure the temperature change at the same time to correct the pressure estimated from the intensity or the decay constant of the PSP luminescence.
  • Nobuyuki HISASUE; Kohsei TAKEHARA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) Japan Society of Civil Engineers 77 (2) I_817 - I_822 2021 [Refereed]
     
    A low water level operation is being carried out as one of effective utilization of existing hydroelectric power stations. In a low water level operation, a water level of a reservoir is lower than a conventional water level of a reservoir. So a submergence depth of an intake pipe is not enough, it causes an intake vortex in an intake facility of a hydroelectric power station. However, there is lack of knowledge about relationship between a submergence depth of an intake pipe and occurrence of an intake vortex in the horizontal intake facility. In this study, the hydraulic properties in horizontal intake are studied experimentally. Submergence depths of horizontal intake pipe are changed every diameter of the horizontal pipe, with other conditions, ie, a flow rate, a water depth are kept constant. As a result, it is found that the distance between the upper edge of the horizontal pipe and the water surface has a greater effect on the occurrence of vortices than the submergence depth when the upper edge of the horizontal pipe becomes shallower than half of the water depth in the intake channel.
  • Nguyen Hoai Ngo; Anh Quang Nguyen; Fabian M. Bufler; Yoshinari Kamakura; Hideki Mutoh; Takayoshi Shimura; Takuji Hosoi; Heiji Watanabe; Philippe Matagne; Kazuhiro Shimonomura; Kohsei Takehara; Edoardo Charbon; Takeharu Goji Etoh
    Sensors 20 (23) 6895 - 6895 2020 [Refereed]
  • Nobuyuki HISASUE; Kohsei TAKEHARA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) Japan Society of Civil Engineers 76 (2) I_931 - I_936 2020 [Refereed]
     
    An intake vortex is occurred in an intake facility of a hydroelectric power station. It causes damages on a facility due to an air hammer and a reduction of power generation output. The researches have been conducted on a vertical intake of a hydroelectric power station. However, it is difficult to apply those findings in the vertical intake to other intake types such as horizontal intake directly. In this study, the hydraulic properties of horizontal intake are discussed experimentally. Suction velocities of horizontal intake pipe are changed by changing diameter of the pipe, with other conditions, ie, a flow rate, a water depth and a submergence depth are kept constant. As a result, it is found that the occurrence of the intake vortex is related to the distance between the upper edge of the horizontal pipe and the water surface and the swirl flow of the horizontal plane of near free surface is occurred at narrow regions near the left and right side of the endwall of the intake channel.
  • HISASUE Nobuyuki; TAKEHARA Kohsei
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) Japan Society of Civil Engineers 75 (2) I_787 - I_792 1880-8751 2019/11 [Refereed]
     
    An intake vortex is entrained air from a water surface, and it causes problems in a hydropower facility due to equipment failure. In a previous research, the authors found that an increase of a velocity in a middle and lower layers of a flow field may be related to an occurrence of an intake vortex. It maybe a key to clarify a cause of an intake vortex. In this study, inner diameters of intake pipes are changed under a condition that a flow rate and water depth are kept constant, and examined how the flow field changes. As a result, it is found that an occurrence of a large vortex such as an intake vortex is related to a number of occurrences of a small vortex and so on.
  • Flying light captured with a multi-framing image sensor operating at 10ns
    TAKANO Yasuhide; OKINAKA Tomoo; TAKEHARA Kohsei; NAKANO Hitoshi; SHIMONOMURA Yasuhide; HAYASHI Naoki; MITSUI Yo; ETOH G. Takeharu
    可視化情報学会論文集 39 (9) 35 - 40 2019/09 [Refereed]
  • Takeharu Goji Etoh; Tomoo Okinaka; Yasuhide Takano; Kohsei Takehara; Hitoshi Nakano; Kazuhiro; Shimonomura; Taeko Ando; Nguyen Ngo; Yoshinari Kamakura; Son Dao Vu Truong; Array; Edoardo Charbon,Array; Piet De Moor; Paul Goetschalckx,Luc Haspeslagh
    Sensors 19 (10) 2247 - 2247 1424-8220 2019/05 [Refereed]
  • Vu Truong; Son Dao; Nguyen Ngo; Anh Quang Nguyen; Morimoto Kazuhiro; Shimonomura Kazuhiro; Goetschalckx Paul; Haspeslagh Luc; De Moor Piet; Takehara Kohsei; Etoh Takeharu Goji
    SENSORS 18 (9) 1424-8220 2018/09 [Refereed]
  • S. T. Thoroddsen; K. Takehara; H. D. Nguyen; T. G. Etoh
    Journal of Fluid Mechanics Cambridge University Press 848 1469-7645 2018/08 [Refereed]
     
    When a drop impacts on a deep pool at moderate velocity it forms a hemispheric crater which subsequently rebounds to the original free-surface level, often forming Worthington jets, which rise vertically out of the crater centre. Under certain impact conditions the crater collapse forms a dimple at its bottom, which pinches off a bubble and is also known to be associated with the formation of a very fast thin jet. Herein we use two ultra-high-speed video cameras to observe simultaneously the dimple collapse and the speed of the resulting jet. The fastest fine jets are observed at speeds of approximately and emerge when the dimple forms a cylinder which retracts without pinching off a bubble. We also identify what appears to be micro-bubbles at the bottom of this cylinder, which we propose are caused by local cavitation from extensional stress in the flow entering the jet. The radial collapse of the dimple does not follow capillary-inertial power laws nor is its bottom driven by a curvature singularity, as has been proposed in some earlier studies. The fastest jets are produced by pure inertial focusing and emerge at finite dimple size, bypassing the pinch-off singularity. These jets emerge from the liquid contained originally in the drop. Finally, we measure directly the compression of the central bubble following the pinch-off and the subsequent large volume oscillation, which occurs at frequencies slightly above the audible range at approximately 23 kHz.
  • Array,Son Dao Vu; Truong; Kazuhiro Shimonomura; Kohsei Takehara; Takeharu Goji Etoh
    Sensors 18 (8) 2407  1424-8220 2018/08 [Refereed]
  • HISASUE Nobuyuki; TAKEHARA Kohsei
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) Japan Society of Civil Engineers 74 (5) I_715 - I_720 2018 
    Countermeasures against an intake vortex are necessary to prevent problems such as a vibration of a water turbine generator in hydroelectric facilities. In order to study effects by position of the inclined wall, flow fields in the vertical intake facility with inclined wall have been measured by a visual observation and Particle Tracking Velocimetry(PTV). As a result, it is found to be important that whole flow fields are stabilize by the inclined wall and the space between the inclined wall and the inlet of the vertical pipe which is related the suppressing the swirling flow of free surface and the velocity of the middle and lower layer.
  • T. Goji Etoh; Kazuhiro Shimonomura; Anh Quang Nguyen; Kohsei Takehara; Yoshinari Kamakura; Paul Goetschalckx; Luc Haspeslagh; Piet De Moor; Vu Truong Son Dao; Hoang Dung Nguyen; Naoki Hayashi; Yo Mitsui; Hideo Inumaru
    Progress in Biomedical Optics and Imaging - Proceedings of SPIE SPIE 10505 1605-7422 2018 [Refereed]
     
    Two ultrahigh-speed CCD image sensors with different characteristics were fabricated for applications to advanced scientific measurement apparatuses. The sensors are BSI MCG (Backside-illuminated Multi-Collection-Gate) image sensors with multiple collection gates around the center of the front side of each pixel, placed like petals of a flower. One has five collection gates and one drain gate at the center, which can capture consecutive five frames at 100 Mfps with the pixel count of about 600 kpixels (512 x 576 x 2 pixels). In-pixel signal accumulation is possible for repetitive image capture of reproducible events. The target application is FLIM. The other is equipped with four collection gates each connected to an in-situ CCD memory with 305 elements, which enables capture of 1,220 (4 x 305) consecutive images at 50 Mfps. The CCD memory is folded and looped with the first element connected to the last element, which also makes possible the in-pixel signal accumulation. The sensor is a small test sensor with 32 x 32 pixels. The target applications are imaging TOF MS, pulse neutron tomography and dynamic PSP. The paper also briefly explains an expression of the temporal resolution of silicon image sensors theoretically derived by the authors in 2017. It is shown that the image sensor designed based on the theoretical analysis achieves imaging of consecutive frames at the frame interval of 50 ps.
  • 久末信幸; 竹原幸生
    土木学会論文集 B1(水工学)(Web) Japan Society of Civil Engineers 74 (4) I_691‐I_696(J‐STAGE) - I_696 2185-467X 2018 [Refereed]
     
    Intake vortices in hydroelectric facilities can entrap air from a water surface into a penstock and entrapped air can cause problems such as vibration of a water turbine generator. In order to study effects of the inclined wall, which is used as a vortex suppressing device in this study, flow fields in the vertical intake facility with the inclined wall have been measured by a visual observation and Particle Tracking Velocimetry (PTV). As results, the horizontal flow in the intake facility is bent smoothly into the vertical pipe by the inclined wall. For the case of the large angle of the inclined wall, submerged vortices occurred near the vertical pipe, because the clearance between the inclined wall and the vertical pipe becomes too narrow.
  • S. Abe; T. Takagi; K. Takehara; N. Kimura; T. Hiraishi; K. Komeyama; S. Torisawa; S. Asaumi
    SPIE Proceedings SPIE 0277-786X 2017/02 [Refereed]
  • 竹原幸生; 松井一彰
    土木学会論文集B1(水工学) 土木学会 73 I_673 - I_678 1880-8751 2017 [Refereed]
  • MATSUI Kazuaki; YOKOYAMA Yuichi; KAMEI Kunpei; NAKAGUCHI Yuzuru; EGUCHI Mitsuru; TANIGUCHI Akito; TAKEHARA Kohsei; FUMOTO Takayuki
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) Japan Society of Civil Engineers 73 (3) 134 - 142 2017 [Refereed]
     
     We explored the impact of combined sewer overflow (CSO) on the water quality of an urban river. We characterized the bacterial community of the Higashiyokobori-gawa waterway using next-generation DNA sequencing (Illumina Miseq). We examined bacterial 16S rRNA gene amplicons during rainfall periods. When rainfall exceeded 4 mm/h at our experimental site on the waterway, the bacterial community composition in the river water exhibited transient changes attributable to the CSO. The bacterial community composition in the waterway differed greatly from those in sewage, suggesting that the CSO had been diluted with bulk rainwater prior to discharge into the river. After a newly constructed stormwater storage pipe called Heisei-no-Taikougesui was commissioned, we found no changes in the bacterial community in river water even when rainfall exceeded 8 mm/h. This indicates that the storage pipe effectively prevented CSO discharge into the waterway. We suggest that bacterial community composition analysis is useful when evaluating/monitoring water quality.
  • TAKEHARA Kohsei
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) Japan Society of Civil Engineers 72 (4) I_571 - I_576 1880-8751 2016/02 [Refereed]
     
    In general intake facilities of hydroelectric power stations, intake vortices cause the air-hammer phenomena in the intake tunnel and the cavitation phenomena at blades of a water turbine generator by air-entrainments. In order to understand hydraulic characteristics of a vortex-suppressing device in a vertical intake facility, flow fields in the basic model of a vertical intake facility that combined a rectangular linear channel and a vertical pipe have been measured using a Particle Tracking Velocimetry (PTV). As a result, the relationship between installation positions of a vortex-suppressing device and number of occurrences of intake vortices indicates that the vortex-suppressing device installed near free surface and near vertical pipe is more effective.
  • 裏泰樹; 麓隆行; 竹原幸生
    資源・素材(Web) 2016 ROMBUNNO.3314 (WEB ONLY)  2016
  • Hoang Dung Nguyen; Okinaka Tomoo; Takano Yasuhide; Takehara Kohsei; Vu Truong; Son Dao; Etoff Takeharu Goji
    MECHANICAL ENGINEERING JOURNAL 3 (6) 2187-9745 2016 [Refereed]
  • TAKEHARA Kohsei; ETOH Goji; TAKANO Yasuhide
    Journal of applied mechanics Japan Society of Civil Engineers 70 (2) I_709 - I_716 2185-4661 2015/02 [Refereed]
     
    We have found that cavitation bubbles are generated when a sphere, which is freely falling from a height of several cm above the bottom, is impacting onto a bottom wall. The cavitation bubbles can be categorized into the following three types: 1) a single disk-like bubble generated at the impacting point, 2) multiple spherical bubbles generated away from the impacting point, and 3) multiple bubbles generated at the surface of the sphere and bottom wall. To clarify the generation mechanism of the cavitation bubbles, the following three kinds of experiments are conducted: (1) the experiment of the single free falling sphere impacting onto the flat buttom plate, (2) the experiment of the single sphere pulling up from the flat bottom plate, and (3) the experiment of impact force acting onto a half sphere fixed to a flat bottom plate. The motion of the sphere has been analyzed by using image processing techniques. The result of the experiments shows that the generation mechanisms of the cavitation bubbles are related to the acceleration of the impacting sphere and the shock pressure generated by the impact of the sphere.
  • 久末信幸; 竹原幸生; 進藤誠士郎; 高野保英
    土木学会論文集 B1(水工学)(Web) Japan Society of Civil Engineers 71 (4) I.523-I.528 (J-STAGE) - I_528 2185-467X 2015/02 [Refereed]
     
    In intake facilities of a hydroelectric power station, intake vortices cause an air-hammer in an intake tunnel and a cavitation at turbine blades of a water turbine generator by air-entrainments. In order to understand hydraulic characteristics of intake vortices in a vertical intake facility, flow fields in the basic model of a vertical intake facility that combined a rectangular linear channel and a vertical pipe have been measured using a Particle Tracking Velocimetry(PTV). In the horizontal plane near the free surface around the end of the intake channel, the results show that vortices generated at the both sidewalls move to the occurrence region of intake vortices. And in the vertical plane at the center of the intake channel, the results show that local vortices unrelated to the approach flows occur at the outer edge of the vertical pipe.
  • Kohsei Takehara; Nobuyuki Hisasue; Yasuhide Takano
    PROCEEDINGS OF THE 36TH IAHR WORLD CONGRESS IAHR-INT ASSOC HYDRO-ENVIRONMENT ENGINEERING RESEARCH 4147 - 4154 2015 [Refereed]
     
    In the hydro-electrical power station, water in the reservoir is taken into the electrical power generator through an intake facility. In the common intake facilities, the free surface flow merges into the closed pipe flow, which leads to the electrical power generator. Air entrapment by the intake vortices inside the surface intake facilities causes the deterioration of power generation, the destruction of blade in a turbine, and so on. It is very important for the hydro-electrical power station to suppress the air entrapment by the intake vortices. To suppress the air entrapment by the vortices, vortex-prevention devices have been proposed and some of them have been used in hydro-electrical power stations. Those vortex-prevention devices are effectively suppress the air entrapments in a certain hydraulic condition. However, the hydraulic properties of flow structure by those vortex-prevention devices are still unclear. In this research, the effects of the vortex-prevention devices in the surface intake facilities are investigated experimentally by using the particle tracking velocimetry (PTV). The vorticity distribution is evaluated by the Moving Least Square (MLS) method, which can accurately evaluate the vorticity from the randomly distributed velocity vectors obtained by the PTV. Three types of the surface intake facilities were tested to evaluate the effects of the vortex-prevention devices. The average velocity distribution, the turbulent properties distribution, the average vorticity distribution and statistics property distribution of vorticity are calculated from the obtained velocity distributions. The results show that the vortex-preventing devices effectively stabilize the flow in the dead water region. As a result, air-entrapment by surface vortex is suppressed by the vortex-preventing devices.
  • TAKANO Yasuhide; TAKEHARA Kohsei
    PROCEEDINGS OF THE JAPANESE CONFERENCE ON HYDRAULICS Japan Society of Civil Engineers 70 (4) 1_523 - 1_528 2185-467X 2014/02 [Refereed]
     
    To measure the falling velocities, the diameters and the aspect ratios of raindrops, consecutive images of raindrops in the open air outside of our laboratory were captured by an ultra-high-speed video camera. For automatic image capturing and avoiding the damage to the image sensor of the video camera due to the strong continuous illumination, a new trigger device was newly introduced to the capturing setup.
    As a result of the image analysis of the falling raindrops images, the following findings were obtained, when the equivalent raindrop diameter is smaller than 3mm. (1)The relationship between the falling velocity and the raindrop diameter determined by our outdoor measurement is similar to that between the terminal velocity and the water drop diameter determined by Gunn and Kinzer's indoor experiment. (2)The aspect ratios of raindrops determined by our measurement is similar to that calculated by Pruppacherr's model of raindrop.
  • TAKEHARA Kohsei; HISASUE Nobuyuki; TAKANO Yasuhide
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) Japan Society of Civil Engineers 70 (4) I_757 - I_762 1880-8751 2014/02 [Refereed]
     
    Air entrainments by vortices at water surfaces inside surface intake facilities of electrical power plants cause some problems, such as deterioration of power generation, destruction of blade in a turbine, etc. To suppress air entrainments by the vortices, some vortex-preventing devices have been proposed and have been used in many electrical power plants. The vortex-preventing devices used in the intake facilities are working effectively in many cases. However, the hydraulic properties of flow structure by the vortex-preventing devices are still unclear.
    In this paper, the effects of the vortex-preventing devices in surface intake facilities have been investigated experimentally by using the particle tracking velocimetry. The results show that the vortex-preventing devices suppress the turbulent intensity and the vorticity inside the facility.
  • M.-J. Thoraval; K. Takehara; T. G. Etoh; S. T. Thoroddsen
    JOURNAL OF FLUID MECHANICS CAMBRIDGE UNIV PRESS 724 234 - 258 0022-1120 2013/06 [Refereed]
     
    We use ultra-high-speed video imaging to look at the initial contact of a drop impacting on a liquid layer. We observe experimentally the vortex street and the bubble-ring entrapments predicted numerically, for high impact velocities, by Thoraval et al. (Phys. Rev. Lett., vol. 108, 2012, article 264506). These dynamics mainly occur within 50 mu s after the first contact, requiring imaging at 1 million f.p.s. For a water drop impacting on a thin layer of water, the entrapment of isolated bubbles starts through azimuthal instability, which forms at low impact velocities, in the neck connecting the drop and pool. For Reynolds number Re above similar to 12 000, up to 10 partial bubble rings have been observed at the base of the ejecta, starting when the contact is similar to 20% of the drop size. More regular bubble rings are observed for a pool of ethanol or methanol. The video imaging shows rotation around some of these air cylinders, which can temporarily delay their breakup into micro-bubbles. The different refractive index in the pool liquid reveals the destabilization of the vortices and the formation of streamwise vortices and intricate vortex tangles. Fine-scale axisymmetry is thereby destroyed. We show also that the shape of the drop has a strong influence on these dynamics.
  • Takashi Kambe; Kohsei Takehara; Shuji Tsukiyama
    2013 IEEE 4TH LATIN AMERICAN SYMPOSIUM ON CIRCUITS AND SYSTEMS (LASCAS) IEEE 2330-9954 2013 [Refereed]
     
    The main bottleneck in system LSI performance is, in many cases, the processing overhead that occurs when arithmetic calculations are performed multiple times. The circuit size and processing time required for multiplication, division and other basic arithmetic operations are often especially large. In this paper we propose an application-specific arithmetic circuit design methodology and apply it to the design of a correlation coefficient calculation circuit for a particle tracking application. Particle tracking velocimetry (PTV) measures velocity fluctuations in fluids and gases and has been applied to a diverse range of flows. However, the algorithms are computationally intensive so to achieve real-time processing speeds implementation in hardware is essential. The computational overhead is accelerated by applying code refactoring, memory access optimization, and variable length pipelining. The processing speed and the circuit size of the design are evaluated. We show that the hardware solution is 1,000 times faster than the software solution and is able to achieve real-time processing speeds.
  • S. T. Thoroddsen; M.-J. Thoraval; K. Takehara; T. G. Etoh
    JOURNAL OF FLUID MECHANICS CAMBRIDGE UNIV PRESS 708 469 - 479 0022-1120 2012/10 [Refereed]
     
    When a drop impacts at low velocity onto a pool surface, a hemispheric air layer cushions and can delay direct contact. Herein we use ultra-high-speed video to study the rupture of this layer, to explain the resulting variety of observed distribution of bubbles. The size and distribution of micro-bubbles is determined by the number and location of the primary punctures. Isolated holes lead to the formation of bubble necklaces when the edges of two growing holes meet, whereas bubble nets are produced by regular shedding of micro-bubbles from a sawtooth edge instability. For the most viscous liquids the air film contracts more rapidly than the capillary-viscous velocity through repeated spontaneous ruptures of the edge. From the speed of hole opening and the total volume of micro-bubbles we conclude that the air sheet ruptures when its thickness approaches similar to 100 nm.
  • Micro-splashing by drop impacts
    S. T. Thoroddsen; K. Takehara; T. G. Etoh
    Physical Review Letters 706 560 - 570 2012/07 [Refereed]
  • MURATA Keiji; ARAGA Koichi; ETOH Takeharu; TAKEHARA Kohsei
    Proceedings of the Japan Society for Photoelasticity The Japanese Society for Experimental Mechanics 12 (2) 107 - 113 1346-4930 2012/06 [Refereed]
     
    This paper presents visualization of boiling phenomena and formation of the two-phase flow pattern in a mini tube which has a 0.30mm inner diameter. Test fluid is refrigerant HCFC123. ITO film is formed by vapor deposition over the outer surface of the glass tube. This film is transparent and electrically conductive. Refrigerant HCFC123 is pumped into the glass tube in liquid phase; it then is boiled away by electrical heating. Bubble formation and growth near the onset point of nucleate boiling and the two-phase flow pattern in the low-quality region is recorded via high-speed video camera (10,000 - 50,000 fps). Appearance of bubble formation and growth in a mini-tube depends on heat flux and mass flux. For low heat flux, an isolated bubble grows to occupy the whole tube cross section, and flows in a form resembling a bullet. Liquid film is not observed between this vapor bubble and the inner tube surface, and evaporation is not so dominant. For high heat flux and low mass flux, bubbles grow to coalesce immediately into a long vapor plug; and both nucleate boiling and evaporation from liquid film between the vapor plug and the inner tube surface remain dominant.
  • Marie-Jean Thoraval; Kohsei Takehara; Takeharu Goji Etoh; Stephane Popinet; Pascal Ray; Christophe Josserand; Stephane Zaleski; Sigurdur T. Thoroddsen
    PHYSICAL REVIEW LETTERS AMER PHYSICAL SOC 108 (26) 1 - 5 0031-9007 2012/06 [Refereed]
     
    The splashing of a drop impacting onto a liquid pool produces a range of different sized microdroplets. At high impact velocities, the most significant source of these droplets is a thin liquid jet emerging at the start of the impact from the neck that connects the drop to the pool. We use ultrahigh-speed video imaging in combination with high-resolution numerical simulations to show how this ejecta gives way to irregular splashing. At higher Reynolds numbers, its base becomes unstable, shedding vortex rings into the liquid from the free surface in an axisymmetric von Karman vortex street, thus breaking the ejecta sheet as it forms.
  • Keiji Murata; Koichi Araga; Takeharu Etoh; Kohsei Takehara
    ICEM15: 15TH INTERNATIONAL CONFERENCE ON EXPERIMENTAL MECHANICS INEGI-INST ENGENHARIA MECANICA E GESTAO INDUSTRIAL 2012 [Refereed]
     
    We present a visualization of boiling phenomena and formation of a two-phase flow pattern in a mini-tube with an inner diameter of 0.30 mm. An indium tin oxide (ITO) film is formed by vapor deposition over the outer surface of the glass tube through which refrigerant HCFC123 is pumped in the liquid phase and then boiled away by electrical heating. The appearance of bubble formation and the growth of vapor plugs in a mini-tube depend on the heat and mass fluxes. The different behavior observed for the cases of low and high heat flux indicates that the heat transfer mechanism near the onset point of nucleate boiling not only involves nucleate boiling but also depends on the liquid film evaporation. Also, elongation and coalescence of the vapor plugs affect the liquid flow between the plug and inner tube surface and the heat transfer performance.
  • HISASUE Nobuyuki; TAKEHARA Kohsei; TSUMORI Yusuke; MAEDA Yuji
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) Japan Society of Civil Engineers 55 (4) I_1117 - I_1122 2011/03 [Refereed]
     
    Aeration by free surface vortex in hydro-electric facilities has been investigated for many years. The studies on free surface vortex have been mainly conducted by model experiment that required many works and costs. Combination of image velocimetry and numerical simulation is a powerful tool for estimation of occurrence of aeration by free surface vortex. The knowledge of aeration by free surface vortex is necessary to designing the hydro-electric facilities quickly and efficiently. In this paper, the technique to measure the velocity field and free surface profile simultaneously has been developed by using image processing techniques. The developed technique is applied to experiments on the aeration by free surface vortex in order to clarify relationship between free surface profile and circulation of flow fields. The results show some interesting phenomena related to aeration by free surface vortex.
  • A 16 Mfps 165kpixel Backside-Illuminated CCD
    Takeharu G. Etoh; Dung H. Nguyen; Son V. T. Dao; Cuong L. Vo; Masatoshi Tanaka; Kohsei Takehara; Tomoo Okinaka; Harry van Kuijk; Wilco Klaassens; Jan Bosiers; Michael Lesser; David Ouellette; Hirotaka Maruyama; Tetsuya Hayashida; Toshiki Arai
    2011 IEEE International Solid-State Circuits Conference 12 - 14 2011/02 [Refereed]
  • DAO Vu Truong Son; ETOH Takeharu; TAKEHARA Kohsei; NGUYEN H. D.; Nishi Kenji; KURETA Masatoshi; SEGAWA Mariko; ARAI Masatoshi
    ITE Technical Report The Institute of Image Information and Television Engineers 35 9 - 12 2011 
    A new ultra-high-speed image sensor "Hybrid CMOS/CCD ISAS" is presented. ISAS stands for "Image Signal Accumulation Sensor". A folded CCD is installed in each pixel, which serves as an in-situ memory for parallel recording at all pixels. The CCD is looped so that image signals captured at plural of capturing operations are automatically accumulated on the memory CCD. A CMOS readout circuitry is also installed in the pixel for fast and flexible signal readout. By directly reading out signals through the CMOS readout circuit without recording them in the in-pixel CCD memory, the sensor works as a conventional parallel and partial readout high-speed imager as well. A set of Z-shaped electrodes is proposed to fold the CCD and fabricate it with a standard CMOS process. Therefore, the sensor can be fabricated solely with a CIS process. Technical feasibility of the sensor is confirmed through simulations.
  • ETOH Takeharu; Nguyen H. D.; Dao V. T. S.; TANAKA Masatoshi; TAKEHARA Kohsei; OKINAKA Tomoo; MARUYAMA Hirotaka; HAYASHIDA Tetsuya; ARAI Toshiki; KURETA Masatoshi; SEGAWA Mariko; ARAI Masatoshi
    ITE Technical Report The Institute of Image Information and Television Engineers 35 23 - 26 2011 [Refereed]
     
    In 2010, we developed a BSI image sensor capable of capturing images at 16Mfps. A preliminary evaluation result of the sensor is summarized. A concept of a next generation ultra-high-speed image sensor is also presented, which has a new function, image signal accumulation, in addition to the ultra-high-speed and the ultra-high-sensitivity.
  • S. T. Thoroddsen; M.-J. Thoraval; K. Takehara; T. G. Etoh
    PHYSICAL REVIEW LETTERS AMER PHYSICAL SOC 106 (3) 1 - 5 0031-9007 2011/01 [Refereed]
     
    When a drop impacts onto a liquid pool, it ejects a thin horizontal sheet of liquid, which emerges from the neck region connecting the two liquid masses. The leading section of this ejecta bends down to meet the pool liquid. When the sheet touches the pool, at an "elbow,'' it ruptures and sends off microdroplets by a slingshot mechanism, driven by surface tension. High-speed imaging of the splashing droplets suggests the liquid sheet is of submicron thickness, as thin as 300 nm. Experiments in partial vacuum show that air resistance plays the primary role in bending the sheet. We identify a parameter regime where this slingshot occurs and also present a simple model for the sheet evolution, capable of reproducing the overall shape.
  • 風波砕波下における渦運動のPTV計測
    竹原 幸生; 江藤 剛治
    ながれ 日本流体力学会 29 437 - 439 2010/12 [Invited]
  • S. T. Thoroddsen; H. D. Nguyen; K. Takehara; T. G. Etoh
    PHYSICAL REVIEW E AMER PHYSICAL SOC 82 (4) 046107  1539-3755 2010/10 [Refereed]
     
    The peeling of adhesive tape is known to proceed with a stick-slip mechanism and produces a characteristic ripping sound. The peeling also produces light and when peeled in a vacuum, even X-rays have been observed, whose emissions are correlated with the slip events. Here we present direct imaging of the detachment zone when Scotch tape is peeled off at high speed from a solid surface, revealing a highly regular substructure, during the slip phase. The typical 4-mm-long slip region has a regular substructure of transverse 220 mu m wide slip bands, which fracture sideways at speeds over 300 m/s. The fracture tip emits waves into the detached section of the tape at similar to 100 m/s, which promotes the sound, so characteristic of this phenomenon.
  • S. T. Thoroddsen; K. Takehara; T. G. Etoh
    PHYSICS OF FLUIDS AMER INST PHYSICS 22 (5) 051701  1070-6631 2010/05 [Refereed]
     
    When a viscous drop impacts onto a solid surface, it entraps a myriad of microbubbles at the interface between liquid and solid. We present direct high-speed video observations of this entrapment. For viscous drops, the tip of the spreading lamella is separated from the surface and levitated on a cushion of air. We show that the primary mechanism for the bubble entrapment is contact between this precursor sheet of liquid with the solid and not air pulled directly through cusps in the contact line. The sheet makes contact with the solid surface, forming a wetted patch, which grows in size, but only entraps a bubble when it meets the advancing contact line. The leading front of this wet patch can also lead to the localized thinning and puncturing of the liquid film producing strong splashing of droplets. (C) 2010 American Institute of Physics. [doi:10.1063/1.3407654]
  • Harald Kleine; Cuong Vo Le; Kohsei Takehara; T. Goji Etoh
    JOURNAL OF VISUALIZATION SPRINGER 13 (1) 33 - 40 1343-8875 2010/02 [Refereed]
     
    When a shock wave leaves an open-ended shock tube, it generates a vortex ring that subsequently detaches from the shock tube and follows the expanding shock front. This classical problem of shock-vortex interaction has been visualized in unprecedented detail and temporal resolution by means of time-resolved shadow, schlieren and shearing interferometry sequences obtained with a newly developed ultrahigh-speed color video camera. This device is capable of taking 144 frames with full-frame resolution of 720 x 410 pixels at rates of up to one million frames per second. Apart from shadowgraphy, the visualization techniques used in this study were direction- and magnitude-indicating color schlieren and polychrome shearing interferometry. The process was observed both with the standard normal view of the flow field and with an oblique view, which facilitated the identification of some three-dimensional flow features. The obtained results clearly show the development of individual flow elements, including some that so far have eluded a proper description. One example is the secondary, counter-rotating vortex ring, which at a later time wraps around the main vortex ring before disintegrating upon merging with the shear layer that surrounds the gas exiting from the tube.
  • Dao Vu Truong Son; Takeharu Goji Etoh; Masatoshi Tanaka; Nguyen Hoang Dung; Vo Le Cuong; Kohsei Takehara; Toshiro Akino; Kenji Nishi; Hitoshi Aoki; Junichi Nakai
    SENSORS MOLECULAR DIVERSITY PRESERVATION INTERNATIONAL-MDPI 10 (1) 16 - 35 1424-8220 2010/01 [Refereed]
     
    Our experience in the design of an ultra-high speed image sensor targeting the theoretical maximum frame rate is summarized. The imager is the backside illuminated in situ storage image sensor (BSI ISIS). It is confirmed that the critical factor limiting the highest frame rate is the signal electron transit time from the generation layer at the back side of each pixel to the input gate to the in situ storage area on the front side. The theoretical maximum frame rate is estimated at 100 Mega-frames per second (Mfps) by transient simulation study. The sensor has a spatial resolution of 140,800 pixels with 126 linear storage elements installed in each pixel. The very high sensitivity is ensured by application of backside illumination technology and cooling. The ultra-high frame rate is achieved by the in situ storage image sensor (ISIS) structure on the front side. In this paper, we summarize technologies developed to achieve the theoretical maximum frame rate, including: (1) a special p-well design by triple injections to generate a smooth electric field backside towards the collection gate on the front side, resulting in much shorter electron transit time; (2) design technique to reduce RC delay by employing an extra metal layer exclusively to electrodes responsible for ultra-high speed image capturing; (3) a CCD specific complementary on-chip inductance minimization technique with a couple of stacked differential bus lines.
  • Hitoshi Nakano; Sayoko Yokoi; Shigeru Yoshida; Makoto Yamada; Takeshi Takeuchi; Kohsei Takehara; T. Goji Etoh
    REVIEW OF SCIENTIFIC INSTRUMENTS AMER INST PHYSICS 81 (1) 13705  0034-6748 2010/01 [Refereed]
     
    Ultrahigh-speed microscopy of living specimens requires ultrabright illumination. Moreover, the duration of illumination should be sufficiently long, on the order of at least several tens of milliseconds, in order to investigate the dynamic state of living specimens. However, specimens are exposed to a high risk of damage by the intense illumination. The brightness and pulse duration of illumination have to be continuously controlled for use in the ultrahigh-speed microscopy of living specimens. Commercial or laboratory-made illumination systems do not satisfy the abovementioned requirements. In this paper, the development of a bright and long-pulse illumination system for ultrahigh-speed microscopy of living specimens is presented. A xenon flashlamp with an arc length of 1.5 mm has been used as the light source. The electrical power supply consists of a voltage-regulated circuit, a capacitor bank, and a control circuit including an insulated-gate bipolar transistor as a gating device, which provides a large rectangular current pulse with the duration in the range to the order of several tens of milliseconds. The brightness, pulse duration, and repetition rate can be easily and continuously controlled. The illumination developed in the present study is installed in an inverted fluorescence microscope equipped with a high-speed camera in order to evaluate the performance as an illumination source. A fluorescent image of the living spermatozoa of a mouse obtained at a frame rate of 8 kHz shows good contrast. Such an image cannot be obtained using a commercial illumination system.
  • S. T. Thoroddsen; K. Takehara; T. G. Etoh; C. -D. Ohl
    PHYSICS OF FLUIDS AMER INST PHYSICS 21 (11) 1 - 5 1070-6631 2009/11 [Refereed]
     
    We use high-speed video imaging to study laser disruption of the free Surface of a hemispheric drop. The drop sits on a glass surface and the Nd:YAG (yttrium aluminum garnet) laser pulse propagates through the drop and is focused near the free surface from below We focus on the evolution of the cylindrical liquid sheet and spray which emerges Out of the drop and resembles typical impact crowns. The tip of the sheet emerges at velocities over I km/s. The tip of the crown breaks up into fine spray some of which is sucked back into the growing cavity at about 100 m/s. We measure the size of the typical spray droplets to be about 3 mu m. We also show the formation of fine microjets, which are produced when the laser is focused inside the drop and the shock front hits small bubbles sitting tinder the free Surface. For water these microjets are 5-50 mu m in diameter and exit at 100-250 m/s. For higher viscosity drops. these lets call emerge at over 500 m/s. (C) 2009 American Institute of Physics [doi: 10.1063/1.3253394]
  • K. Arakawa; T. Mada; H. Komatsu; T. Shimizu; M. Satou; K. Takehara; G. Etoh
    EXPERIMENTAL MECHANICS SPRINGER 49 (4) 471 - 477 0014-4851 2009/08 [Refereed]
     
    The normal impact between a golf ball and a rigid steel target was studied to examine ball deformation and the contact force during the impact. Using high-speed video images, the normal and tangential compression ratios of the ball were measured to analyze the ball deformation quantitatively. In addition, the inbound and rebound ball velocities, contact time, and coefficient of restitution were determined as basic parameters of the impact. As the inbound ball velocity increased, the maximum normal compression ratio increased while the maximum tangential compression ratio, contact time and coefficient of restitution decreased. The ball center displacements during the impact were measured to determine the ball center velocity and acceleration, and the contact force was calculated by the product of the mass and acceleration. The contact force increased almost linearly with the inbound ball velocity, and its relationship agreed well quantitatively with the results from a load-cell, and also agreed well qualitatively with Hertz contact theory.
  • T. Tamano; M. Kanaoka; K. Takehara; N. Mizutani
    Proceedings of the 17th International Conference on Soil Mechanics and Geotechnical Engineering: The Academia and Practice of Geotechnical Engineering 1 356 - 359 2009 [Refereed]
     
    In this study, impact splitting tests were carried out by loading cylindrical granite specimens horizontally and obtaining the crack propagation velocities by an image analysis using a super-high-speed video camera, which has the fastest frame rate in the world. The relationship between the impulse and the crack propagation velocity indicates that there appears to be a critical state at which the crack propagation velocity does not exceed a certain value even if an increased impulse is applied. The critical value obtained for the granite specimens was 2.6 km/sec. © 2009 IOS Press.
  • B. W. Skews; H. Kleine; D. MacLucas; K. Takehara; H. Teranishi; T. G. Etoh
    28TH INTERNATIONAL CONGRESS ON HIGH-SPEED IMAGING AND PHOTONICS SPIE-INT SOC OPTICAL ENGINEERING 7126 0277-786X 2009 [Refereed]
     
    The visual study of unsteady shock wave dynamics has in the past predominantly been done using single-shot images. The advent of ultra-fast, good-resolution high-speed digital cameras has changed this state of affairs and allows the true development of the flow to be studied. It enables the detection of weaker features which are easily overlooked in single-shot visualizations by virtue of the fact that human vision is very sensitive to detecting the motion of an object, even if it generates only a faint optical signal. Recent application of these devices to the study of the focusing of a shock wave in a cylindrical cavity has identified a number of previously unknown features, while other features that previously had been inadequately reported could be clearly identified and explained The observation of deliberately generated weak disturbances allows the quantification of which part of the flow is influenced by which part of the boundaries encompassing it. Whilst the imaging itself is very useful it is also highly desirable to use techniques from which quantitative data can be obtained. Color, such as in direction-and magnitude-indicating color schlieren, and polychrome shearing interferometry, adds an additional dimension to such investigations.
  • S. T. Thoroddsen; K. Takehara; T. G. Etoh
    MODERN PHYSICS LETTERS B WORLD SCIENTIFIC PUBL CO PTE LTD 23 (3) 361 - 364 0217-9849 2009/01 [Refereed]
     
    When a drop impacts onto a solid surface, it spreads out into a pancake shape and often forms a dry-spot at the center of the drop. We show that this dewetting at the center is sometimes produced by a small bubble of air which is entrapped on the substrate under the center of the drop. Capillary waves are generated on the surface of the pancake, during the rebounding of the lamellar edge. As these capillary waves converge at the axis of symmetry, their amplitude grows in size until a wave trough touches and merges with the entrapped bubble. This opens up a dry-patch at the center of the splash. We use state-of-the art high-speed video imaging to study this process, for a drop impacting onto a Perspex surface. The imaging is done by looking through the bottom plate to reveal the detailed motions of the capillary waves.
  • H. Kleine; S. Tepper; K. Takehara; T. G. Etoh; K. Hiraki
    SHOCK WAVES, VOL 2, PROCEEDINGS SPRINGER-VERLAG BERLIN 895 - + 2009 [Refereed]
  • Cuong Vo Le; H. D. Nguyen; V. T. S. Dao; K. Takehara; T. G. Etoh; T. Akino; K. Nishi; K. Kitamura; T. Arai; H. Maruyama
    28TH INTERNATIONAL CONGRESS ON HIGH-SPEED IMAGING AND PHOTONICS SPIE-INT SOC OPTICAL ENGINEERING 7126 0277-786X 2009 
    A feasibility study is presented for an image sensor capable of image capturing at 100 Mega-frames per second (Mfps). The basic structure of the sensor is the backside-illuminated ISIS, the in-situ storage image sensor, with slanted linear CCD memories, which has already achieved 1 Mfps with very high sensitivity. There are many potential technical barriers to further increase the frame rate up to 100 Mfps, such as traveling time of electrons within a pixel, Resistive-Capacitive (RC) delay in driving voltage transfer, heat generation, heavy electro-magnetic noises, etc. For each of the barriers, a countermeasure is newly proposed and the technical and practical possibility is examined mainly by simulations. The new technical proposals include a special wafer with n and p double epitaxial layers with smoothly changing doping profiles, a design method with curves, the thunderbolt bus lines, and digitalnoiseless image capturing by the ISIS with solely sinusoidal driving voltages. It is confirmed that the integration of these technologies is very promising to realize a practical image sensor with the ultra-high frame rate.
  • K. Takehara; T. G. Etoh; T. Tamano; M. Kanaoka; N. Mizutani
    28TH INTERNATIONAL CONGRESS ON HIGH-SPEED IMAGING AND PHOTONICS SPIE-INT SOC OPTICAL ENGINEERING 7126 0277-786X 2009 
    The authors applied an ultra-high-speed video camera to visualize crack propagation in brittle bodies, such as mortar specimens, under the impact splitting test. Strain of the brittle bodies in impact splitting tests was analyzed by means of PIV (Particle Image Velocimtery), which is usually used for measurements of flow fields with tracer particles. The results show that, when the applied impulse on the mortar specimens is increased, the crack propagation velocity reaches an upper bound. The upper bound of the crack propagation velocity was 2.6 km/sec. The horizontal tensile strain around the crack tip was estimated to be 370 mu by PIV measurement with the ultra-high-speed camera, and 270 375 mu by strain gages, respectively. Those results showed a good agreement with each other.
  • H. D. Nguyen; C. Vo-Le; V. T. S. Dao; K. Takehara; T. G. Etoh; Y. Kondo; H. Maruno; H. Tominaga; H. Soya; H. van Kuijk; J. Bosiers; W. Klaassens; G. Ingram; S. Singh; M. Lesser
    28TH INTERNATIONAL CONGRESS ON HIGH-SPEED IMAGING AND PHOTONICS SPIE-INT SOC OPTICAL ENGINEERING 7126 0277-786X 2009 
    This paper presents preliminary evaluation results of a test sensor of the backside-illuminated ISIS, an ultra-high sensitivity and ultra-high speed CCD image sensor. To achieve ultra-high sensitivity, the CCD image sensor employs the following three technologies: backside illumination, cooling and Charge Carrier Multiplication (CCM). The test sensor has been designed, fabricated and evaluated. At room temperature without cooling, the video camera has about ten-time higher sensitivity than the previous one, which was supported by a conventional front side illumination technology. Furthermore, the video camera can detect images at very low signal level, less than 5 e-, by using CCM at -40 degree C.
  • Sota Nakajo; Takaaki Shigematsu; Gozo Tsujimoto; Kohsei Takehara
    COASTAL ENGINEERING 2008, VOLS 1-5 WORLD SCIENTIFIC PUBL CO PTE LTD 4738 - + 2009 [Refereed]
     
    Turbulent flow inside a porous media in unidirectional flow was measured by PTV technique with high resolution in time and space. According to the measurement results, turbulence developed drastically after laminar flow intruding porous media and decreased gradually in the wake region downstream. Although turbulent properties and structure depended on the Reynolds number, normalized turbulent energy considering pore size inside porous media was independent of the Reynold number.
  • Sota Nakajo; Takaaki Shigematsu; Naoya Sakashita; Gozo Tsujimoto; Kohsei Takehara
    PROCEEDINGS OF COASTAL DYNAMICS 2009 WORLD SCIENTIFIC PUBL CO PTE LTD 2009 [Refereed]
  • 竹原幸生; 江藤剛治
    土木学会論文集B 65 (3) 151 - 165 1880-6031 2009 [Refereed]
  • T. Goji Etoh; Cuong Vo Le; Hiroyuki Kawano; Ikuko Ishikawa; Atshushi Miyawaki; Vu. T. S. Dao; Hoang Dung Nguyen; Sayoko Yokoi; Shigeru Yoshida; Hitoshi Nakano; Kohsei Takehara; Yoshiharu Saito
    28TH INTERNATIONAL CONGRESS ON HIGH-SPEED IMAGING AND PHOTONICS SPIE-INT SOC OPTICAL ENGINEERING 7126 0277-786X 2009 [Refereed]
     
    We are developing an ultra-high-sensitivity and ultra-high-speed imaging system for bioscience, mainly for imaging of microbes with visible light and cells with fluorescence emission. Scarcity of photons is the most serious problem in applications of high-speed imaging to the scientific field. To overcome the problem, the system integrates new technologies consisting of (1) an ultra-high-speed video camera with sub-ten-photon sensitivity with the frame rate of more than 1 mega frames per second, (2) a microscope with highly efficient use of light applicable to various unstained and fluorescence cell observations, and (3) very powerful long-pulse-strobe Xenon lights and lasers for microscopes. Various auxiliary technologies to support utilization of the system are also being developed. One example of them is an efficient video trigger system, which detects a weak signal of a sudden change in a frame under ultra-high-speed imaging by canceling high-frequency fluctuation of illumination light. This paper outlines the system with its preliminary evaluation results.
  • S. Yokoi; H. Nakano; M. Yamada; P. Karimov; K. Takehara; S. Yoshida; T. G. Etoh
    28TH INTERNATIONAL CONGRESS ON HIGH-SPEED IMAGING AND PHOTONICS SPIE-INT SOC OPTICAL ENGINEERING 7126 0277-786X 2009 
    Although we have aspired to observe dynamic changes in fluorescent images at the cellular level for a long time, the commercially available video cameras are not at all suitable for this purpose because of their low frame rates and photosensitivity. The present work tackles this issue and describes our attempt to find a solution by using our high-speed video camera and an ultrabright illumination system. We used light sources with considerably higher energy because conventional mercury lamps cannot produce sufficient brightness for our video cameras working a rate of more than 4,500 fps to obtain fluorescent images of cells. We observed that the flagellar movement of mice sperms ceased and multiple kinks developed in their tails when exposed to 2.7W of laser illumination for 1 s. In contrast, no significant alterations could be detected when the sperms were subjected to the same amount of energy by intermittent illumination. Since we found that cells can survive short-duration exposure to high-energy light, we attempted to construct an ultrabright Xenon-strobe illumination system. Our fluorescence studies are currently being extended to other types of animal cells, e. g., observation of the conduction of action potentials in the peripheral nerves of frog.
  • Kentaro Shinoda; Hideyuki Murakami; Seiji Kuroda; Kohsei Takehara; Sachio Oki
    JOURNAL OF THERMAL SPRAY TECHNOLOGY SPRINGER 17 (5-6) 623 - 630 1059-9630 2008/12 [Refereed]
     
    The authors have developed an in situ monitoring system for particle impacts under atmospheric dc plasma spraying conditions. This system utilized a high-speed video camera coupled with a long-distance microscope, and was capable of capturing the particle-impinging phenomena at one million frames per second. To understand the coating formation mechanism, two approaches were attempted, i.e., observation of the single splat formation and the subsequent coating formation. In the former case, the deformation and cooling processes of yttria-stabilized zirconia (YSZ) droplets impinging on substrates were successfully captured. In the latter case, multiple-droplet-impacting phenomena were observed as an ensemble treatment. Representing the coating process, the tower formation (0-dimensional) and bead formation (1-dimensional) were observed under typical plasma spray conditions for thermal barrier coatings using a triggering system coupled with the motion of a robot. The obtained images clearly showed the coating formation resulting from the integration of single splats.
  • NAKAJO Sota; SHIGEMATSU Takaaki; SAKASHITA Naoya; TSUJIMOTO Gozo; TAKEHARA Kosei
    Doboku Gakkai Ronbunshuu B Japan Society of Civil Engineers 第55巻 841 - 845 0916-7897 2008 [Refereed]
     
    The effect of oscillatory flow properties, the Reynolds number and the KC number, on turbulence generated by a porous media was investigated by hydraulic experiment. Violent turbulence was generated when interstitial velocity exceeded a critical level. Turbulent energy generated in pores increased as the Reynolds number increased. In a porous media, difference between minimum and maximum values of turbulent energy was increased as the KC number increased. And outside porous media, turbulent energy spread widely as the KC number increased. Under unsteady oscillatory flow, maximum turbulent energy was larger than that of unidirectional steady flow.
  • TAKEHARA Kohsei; ETOH T. Goji; SHIGEMATSU Takaaki; DAO Vu Truong Son
    Doboku Gakkai Ronbunshuu B Japan Society of Civil Engineers 第55巻 51 - 55 0916-7897 2008 [Refereed]
     
    Behavior of vortices near the wind wave surface is measured by using three high-speed video cameras and the Moving Least Square (MLS) method for vorticity estimations. The high-speed video cameras can increase the sampling rate andthe MLS method can estimate accurate vorticity profile from randomly distributed velocity profiles. The Particle Tracking Velocimetry, PTV, is applied to measure two dimensional flow fields close to the interface in detail. The vorticesare generated at the surfaces by the interaction between the wind shear and wind waves. The generated vorticesseparate from the surface and fall down to the bulk water. The generated vortex increases their spatial scale by unitingthe other vortex.
  • S. T. Thoroddsen; T. G. Etoh; K. Takehara
    ANNUAL REVIEW OF FLUID MECHANICS ANNUAL REVIEWS 40 257 - 285 0066-4189 2008 [Refereed]
     
    This review presents recent technological advances in charge-coupled-device ultrahigh-speed video cameras and their applications in experimental fluid mechanics. Following a brief review of the various high-speed camera types, we point out the advantages of the new technology. Then we show examples of how these cameras are leading to new discoveries in the study of free-surface flows, emphasizing the dynamics of drops and bubbles. We specifically review work on the basic singularities occurring when liquid masses come into contact and coalesce, or break apart during the pinch-off of drops or bubbles from a vertical nozzle. We briefly discuss the imaging of cavitation bubbles and finish by outlining future prospects for these sensors.
  • Pavel Karimov; Cuong Vo Le; Kohsei Takehara; Sayoko Yokoi; Takeharu Goji Etoh; Yoshiharu Saitoh
    REVIEW OF SCIENTIFIC INSTRUMENTS AMER INST PHYSICS 78 (11) 113702  0034-6748 2007/11 [Refereed]
     
    A phototrigger system is developed as a part of a video microscope mounting an ultrahigh-speed video camera capable of image capturing at frame rates as high as 1x10(6) frames/s. The extremely high frame rate is achieved by implementing in situ image storage. A distinguished feature of the camera is the on-chip overwriting mechanism that allows to keep in storage the latest image sequence of 103 frames; the old signals are continuously drained out of the storage. The trigger system is designed to synchronize recording operations with an occurrence of a target event within the limited image capturing duration. The target event is detected through a sudden change in the output of a sensor mounted to an optical port of the microscope. To reduce noise contribution, a two-sensor architecture is implemented. One sensor detects the target event while the one produces a reference signal used for noise reduction. Both sensors are connected to the same optical port by using a specially designed beam splitting unit. To provide high sensitivity, avalanche photodiodes are used as photoelements. System evaluation shows that its sensitivity is high and response time is less than 3 mu s. This is sufficiently fast for high-speed video-microscopy observations at 1x10(6) frames/s when using a video camera with a storage of 103 frames. As an example, the system was used in a microscopic observation of a soap film collapse. (C) 2007 American Institute of Physics.
  • S. T. Thoroddsen; B. Qian; T. G. Etoh; K. Takehara
    PHYSICS OF FLUIDS AMER INST PHYSICS 19 (7) 072110  1070-6631 2007/07 [Refereed]
     
    When two drops of different miscible liquids are brought into contact, their coalescence speed is governed by the liquid having the weaker surface tension. Marangoni waves propagate along the drop with the stronger surface tension. We present surface profiles and propagation speeds of these waves, from experiments with a pendent water drop coalescing with a flat ethanol surface or with a sessile drop of ethanol. We find in the former case that the capillary-Marangoni waves along the water drop show self-similar character when measured in terms of arc length along the original surface. The coalescence of two liquids of different viscosities is also studied. For large viscosity difference, mobility is confined to the lower viscosity fluid and a sharp corner forms where the two liquids meet along the free surface. The coalescence speed of a water drop with a much more viscous liquid is nearly independent of the strength of the viscosity difference. (c) 2007 American Institute of Physics.
  • S. T. Thoroddsen; T. G. Etoh; K. Takehara
    PHYSICS OF FLUIDS AMER INST PHYSICS 19 (5) 052101  1070-6631 2007/05 [Refereed]
     
    We present experimental observations of microjetting from an oscillating drop. The jet is generated by the focusing of axisymmetric capillary waves that overturn and collide at an apex of the drop. These jets are up to two orders of magnitude smaller than the original drops. We present two widely different configurations that produce such microjets. The first occurs on a satellite drop, produced by the pinch-off of a water drop from a vertical nozzle. The large oscillations following the contraction of the satellite bridge focus waves at the bottom, sending out a 30 mu m jet at 9.9 m/s. The second jet arises when a water drop, containing surfactants, falls onto and passes through a hemispherical soap film. The gentle deformation of the drop creates a surface wave that focuses at its top, shooting out a tiny jet and entrapping a small bubble inside the drop. This jet is 16 +/- 5 mu m in diameter and emerges at 6.3 m/s. In this configuration, the soap film wraps around the drop and acts as a sensor of the air flow, revealing that the liquid jet is preceded by a localized faster-moving air jet. The jetting in both configurations is quite robust and occurs even for slightly asymmetric conditions. These microjets appear for much lower values of the Reynolds and Weber numbers than previously observed, suggesting that free-surface jetting is not limited to the inviscid capillary-inertial regime, which has been the focus of much of the theoretical work. (c) 2007 American Institute of Physics.
  • Kentaro Shinoda; Hideyuki Murakami; Seiji Kuroda; Sachio Oki; Kohsei Takehara; Takeharu Goji Etoh
    APPLIED PHYSICS LETTERS AMER INST PHYSICS 90 (19) pp.194103-1 – 194193-3  0003-6951 2007/05 [Refereed]
     
    The authors have developed an in situ monitoring system that captures the impacting phenomena of plasma-sprayed particles at 1x10(6) frames/s. The system clearly captured deformation and cooling processes of an yttria-stabilized zirconia droplet of 50 mu m in diameter impinging at 170 m/s on a smooth quartz glass substrate kept at room temperature. The images show that the liquid sheet jetting out sideways from the droplet detached from the substrate and kept on spreading without disintegration until its maximum extent. While the sheet was spreading, the center region of the flattened droplet cooled down much more rapidly. (C) 2007 American Institute of Physics.
  • K. Arakawa; T. Mada; H. Komatsu; T. Shimizu; M. Satou; K. Takehara; G. Etoh
    EXPERIMENTAL MECHANICS SPRINGER 47 (2) 277 - 282 0014-4851 2007/04 [Refereed]
     
    The oblique impact between a golf ball and a polymethyl methacrylate (PMMA) target with smooth transparent surfaces was studied using a high-speed video camera. Video images of the impact were recorded from the backside of the target and were used to determine the contact time, contact area, and the displacement and rotation of the ball along the target. The average tangential and angular velocities were determined as functions of the inbound ball velocity. As the inbound ball velocity increased, the contact area and average tangential and angular velocities also increased while the contact time decreased. An oiled PMMA target was used to study the effect of reduced friction between the ball and target. The results were compared with earlier data for a steel target with relatively rough surfaces. The contact area and time were unaffected by friction, but the average tangential velocity increased while the average angular velocity decreased as the friction decreased.
  • S. T. Thoroddsen; T. G. Etoh; K. Takehara
    PHYSICS OF FLUIDS AMER INST PHYSICS 19 (4) pp.042101-1 ~042101-29  1070-6631 2007/04 [Refereed]
     
    A bubble is slowly grown from a vertical nozzle until it becomes unstable and pinches off. We use ultra-high-speed video imaging, at frame-rates up to 1 million fps, to study the dynamics and shape of the pinch-off neck region. For bubbles in water (Bo similar or equal to 1.0) the radius of the neck reduces with a power law behavior R similar to t(alpha), over more than 2 decades, with an exponent in the range alpha=0.57 +/- 0.03, in good agreement with other available studies, but which is slightly larger than 1/2 predicted by Rayleigh-Plesset theory. The vertical curvature in the neck increases more slowly than the azimuthal curvature, making the neck profiles more slender as pinch-off is approached. Self-similar shapes are recovered by normalizing the axial coordinate by a separate length scale which follows a different power law, L-z similar to t(gamma), where gamma=0.49 +/- 0.03. Results for air, He, and SF6 gas are identical, suggesting that the gas density plays a minimal role in the dynamics. The pinch-off in water leaves behind a tiny satellite bubble, around 5 mu m in diameter and the flow-field inside the liquid is shown to be consistent with simple sink flow. The effects of liquid viscosity on the pinch-off speed and neck shapes, are also characterized. The speed starts to slow down at a viscosity of about 10 times that of water, which corresponds to Re-mu similar or equal to 2000. This also changes the power law, increasing the exponent to alpha similar or equal to 1 for viscosities above 70 cP (Re-mu similar or equal to 40). For surrounding liquid of viscosity above 10 cP, we observe just before pinch-off, that the neck is stretched into a thin filament of air, which then breaks into a stream of microbubbles. In some cases we observe a cascade of bubble sizes. While some of the details differ, our results are in overall agreement with those of Burton, Waldrep, and Taborek [Phys. Rev. Lett. 94, 184502 (2005)], except we do not observe the rupture of the air cylinder as it reduces to 50 mu m size. For water we observe a continuous necking down to the pixel-resolution of our optical system, which at the largest frame-rates is similar to 10 mu m. (c) 2007 American Inst of Phys.
  • An experimental study on flow field in and around rubble mound river structures
    K. Michioku; K. Takehara; G.T. Etoh
    Journal of Hydroscience and Hydraulic Engineering Vol. 25 (No.2) 37 - 45 2007 [Refereed]
  • SUGIHARA Yuji; YAMASAKI Kazutaka; TSUMORI Hiromichi; MATSUNAGA Nobuhiro; TAKEHARA Kosei
    Doboku Gakkai Ronbunshuu B Japan Society of Civil Engineers 第53巻 481 - 485 0916-7897 2007 [Refereed]
     
    Brick-pattern ripples are three-dimensional ripple marks composed of transverse crests and longitudinal bridges. In this study, the formation process of brick-pattern ripples in an oscillatory flow is investigated experimentally by means of the visualization of sediment transport and particle tracking velocimetry (PTV). The experiments are made for the brick-pattern ripple formation over a model of two-dimensional ripple marks. The velocity distributions above brick pattern ripples are obtained from the PTV measurements. It is seen from the experimental results that three-dimensional separation vortices carry sediment to make the bridges larger and more stable. Thus, the formation of brick-pattern ripples may be accelerated by a certain kind of positive feedback due to the interaction between the separation vortices and sediment transports.
  • NAKAJYO Souta; SHIGEMATSU Takaaki; TSUJIMOTO Gozo; TAKEHARA Kosei
    Doboku Gakkai Ronbunshuu B Japan Society of Civil Engineers 第53巻 801 - 805 0916-7897 2007 
    The effect of Reynolds number on the properties of turbulence generated by a porous media was investigated by a hydraulic experiment. Velocity field inside and around the porous media was measured with a high resolution temporally and spatially using the Super-resolution KC method and a refractive index matching method. It is presented that some properties of turbulence can be normalized by a characteristic velocity and a diameter of the sphere which constitute the porous media.
  • ETOH T. Goji; VO LE Cuong; HASHISHIN Yuichi; OTSUKA Nao; TAKEHARA Kohsei; OHTAKE Hiroshi; HAYASHIDA Tetsuya; MARUYAMA Hirotaka
    Plasma and Fusion Research The Japan Society of Plasma Science and Nuclear Fusion Research Vol.2 pp.S1021-1-8. - S1021 1880-6821 2007 [Refereed]
     
    This paper reviews the high-speed video cameras developed by the authors. A video camera operating at 4,500 frames per second (fps) was developed in 1991. The partial and parallel readout scheme combined with fully digital memory with overwriting function enabled the world fastest imaging at the time. The basic configuration of the camera later became a de facto standard of high-speed video cameras. A video camera mounting an innovative image sensor achieved 1,000,000 fps in 2001. In-situ storage with more than 100 CCD memory elements is installed in each pixel of the sensor, which is capable of recording image signals in all pixels in parallel. Therefore, the sensor was named ISIS, the in-situ storage image sensor. The ultimate parallel recording operation promises the theoretical maximum frame rate. A sequence of more than one hundred consecutive images reproduces a smoothly moving image at 10 fps for more than 10 seconds. Currently, an image sensor with ultrahigh sensitivity is being developed in addition to the ultra-high frame rate, named PC-ISIS, the photon-counting ISIS, for microscopic biological observation. Some other technologies supporting the ultra-high-speed imaging developed are also presented.
  • Nao Otsuka; Vo Le Cuong; Pavel Karimov; Kohsei Takehara; T. Goji Etoh
    Videometrics IX SPIE-INT SOC OPTICAL ENGINEERING 6491 49111 - 49111 0277-786X 2007 [Refereed]
     
    This paper outlines a special microscope under development, named "Ultra-high-speed bionanoscope" for ultra-highspeed imaging in biological applications, and preliminary design of the image sensor, which is the key component in the system. The ultra-high-speed bionanoscope consists of two major subsystems: a video camera operating at more than 10 Mfps with ultra-high-sensitivity and the special microscope to minimize loss of light for seriously reduced illumination light energy due to the ultra-high-speed imaging. The ultra-high-frame rate is achieved by introducing a special structure of a CCD imager, the ISIS, In-situ Storage Image Sensor, invented by Etoh and Mutoh. The ISIS has an array of pixels each of which equips with a slanted linear CCD storage area for more than 100 image signals for reproduction of smoothly moving images. The ultra-high-sensitivity of the sensor of less than 10 photons is achieved by introducing three existing technologies, backside-illumination, cooling, and the CCM, Charge Carrier Multiplication invented by Hynecek.
  • K. Arakawa; T. Mada; H. Komatsu; T. Shimizu; M. Satou; K. Takehara; G. Etoh
    EXPERIMENTAL MECHANICS SPRINGER 46 (6) 691 - 697 0014-4851 2006/12 [Refereed]
     
    The oblique impact between a golf ball and a rigid steel target was studied using a high-speed video camera. Video images recorded before and after the impact were used to determine the inbound velocity vi, rebound velocity nu(r), inbound angle theta(i), rebound angle theta(r), and the coefficient of restitution e. The results showed that theta(r) and e decreased as nu(i) increased. The maximum compression ratio eta(c), contact time t(c), average angular velocity (omega) over bar, and tangential velocity (nu) over bar (t), along the target were determined from images obtained during the impact. The images demonstrated that eta(c) increased with nu(i) while t(c) decreased. In addition, (omega) over bar and (omega) over bar (t) increased almost linearly as nu(i) increased. A rigid body model was used to estimate the final angular velocity omega* and tangential velocity nu(t)* at the end of the impact; these results were then compared with experimental data.
  • S. T. Thoroddsen; T. G. Etoh; K. Takehara
    PHYSICS OF FLUIDS AMER INST PHYSICS 18 (9) p.091110  1070-6631 2006/09 [Refereed]
  • HIRAI Kosuke; OZONO Masashi; DEGUCHI Takashi; TSUBAKI Ryota; FUJITA Ichiro; MUTO Yasunori; KANDA Keiichi; TAKEHARA Kosei; TAKANO Yasuei
    Transactions of Visualization Society of Japan The Visualization Society of Japan 26 (2) 35 - 38 0916-4731 2006/09 
    The confluence region downstream of the Katsura River, the Kizu River and the Uji River in Kyoto displays complicated flow patterns depending on which watershed undergoes larger precipitations. The flow characteristics at this location have not been clarified so far due to the complexity of the combining streams. In the present study, in order to obtain the flow features in normal flow conditions, surface flow measurement by using a helicopter is performed. The surface flow is visualized by biodegradable tracers and they are videotaped from a helicopter hovering at about 300 meter height following the cloud of tracers. A high-vision video camera is used for recording the images and the velocity of the tracers are analyzed by applying PIV with subtracting background movement. At the same time, distributions of temperature, pH, and other parameters related to water quality are measured by multi-purpose instrument installed on a boat. It was found that water quality of the Ktsura River is quite different from the other rivers and the longitudinal dispersion of tracers is evident at the location.
  • Yasunori Watanabe; Yoshiyasu Hideshima; Takaaki Shigematsu; Kohsei Takehara
    Measurement Science and Technology Institute of Physics Publishing 17 (6) 1456 - 1469 1361-6501 2006/06 [Refereed]
     
    A new technique of three-dimensional hybrid stereoscopic particle image velocimetry (3D hybrid SPIV) for measuring a volumetric spatial distribution of three-dimensional velocity is presented in this paper. The accuracy and uncertainty of this technique are examined by numerical tests. The 3D hybrid SPIV has been found to be able to measure major features of velocity field involving a vortex with turbulence in a shear flow. This technique is used for measuring an instantaneous three-dimensional flow structure under breaking waves. The formation of the three-dimensional vortex structures involving roller and longitudinal vortices in breaking waves is investigated in this study. © 2006 IOP Publishing Ltd.
  • S. T. Thoroddsen; T. G. Etoh; K. Takehara
    JOURNAL OF FLUID MECHANICS CAMBRIDGE UNIV PRESS 557 63 - 72 0022-1120 2006/06 [Refereed]
     
    We present experimental observations of hole formation in ejecta crowns, when a viscous drop impacts onto a thin film of low-viscosity liquid with significantly lower surface tension than the drop liquid. The holes are promoted by Marangoni-driven flows in the sheet, resulting from a spray of fine droplets ejected from the thin film hitting the inner side of the crown. The puncturing of the sheet takes place in three distinct steps. First a circular patch of the sheet thins by Marangoni-driven flows. Then this thinner film ruptures and a hole quickly opens up spanning the patch. Finally, the hole opens up further at an accelerated rate, driven by the unbalanced surface tension at its edge. The holes grow until they meet adjacent holes, thus leaving a foam-like network of liquid filaments, which then breaks up into a cloud of droplets.
  • MADA Toshio; KOMATSU Haruo; SHIMIZU Tetsuo; SATO Masanori; TAKEHARA Kohsei; ETOH Goji; ARAKAWA Kazuo
    Proceedings of the 1992 Annual Meeting of JSME/MMD The Japan Society of Mechanical Engineers 2006 447 - 448 2006
  • ARAKAWA Kazuo; MADA Toshio; KOMATSU Haruo; SHIMIZU Tetsuo; SATOU Masanori; TAKEHARA Kohsei; ETOH Goji
    The proceedings of the JSME annual meeting The Japan Society of Mechanical Engineers 2006 869 - 870 2006 
    The normal impact between a golf ball and a rigid steel target was studied using a high-speed video camera. Video images recorded before and after impact were used to determine the inbound and rebound ball velocities. The images during impact were also employed to analyze the deformation of the ball. Displacement at the center of the ball was measured during impact to determine the instantaneous ball velocity and acceleration. Reaction force was evaluated by the product between the mass and acceleration of the ball. It was found that the force increased linearly with the inbound velocity.
  • TAKEHARA Kohsei; THORODDSEN Sigudur T.; ETOH T. Goji
    Transactions of Visualization Society of Japan The Visualization Society of Japan 26 (2) 215 - 218 0916-4731 2006 
    When a viscous drop impacts onto a thin film of ethanol on a solid surface, a lot of hole formations can be observed on the eject crown. The holes are caused by the Marangoni instabilities, which occur at a point where ethanol droplets contact at crown wall of viscous drop. The high-speed video camera, of which frame rate is a million frames per second, is employed for detailed observations.
  • OHSHIMA Kengo; KANAOKA Masanobu; MIZUTANI Natuki; TAKEHARA Kohsei; TAMANO Tomio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 26 (2) 207 - 210 0916-4731 2006 
    The purpose of this research is to explore the mechanism required for the generation of earthquake vibration on the propagation velocity of the crack in fault plane. In this research, the impact splitting tensile tests of mortar and granite were carried out, and the propagation velocity of the crack was visualized and obtained by image analysis using ultra high-speed video camera. A relationship between the impulse which is impact loading and propagation velocity of the crack was observed. There appears to be a critical state in which propagation velocity does not increase, even if impulse is increased over it. It was proven to converge in 2.6 km/sec. Next, the mechanism of the development of the dynamics of the crack by the impulse was examined from displacement vector and Particle Image Velocimetry (PIV) analysis.
  • HISASUE Nobuyuki; TAKEHARA Kohsei
    Doboku Gakkai Ronbunshuu B Japan Society of Civil Engineers 第50巻 883 - 888 0916-7374 2006 
    The electric power industries have been working on development of natural energy sources such as wind, solar, small-scale hydro-electric and biomass energy in order to reduce loads on the environment. The development of small-scale hydro-electric facilities involves making use of small elevation differences available at various sites. This means that the water depth of the reservoir relative to the generator can be shallow and may induce intake vortices causing adverse effects on the generator performance by the air hammer phenomenon of the entrained air. Since the conventional method of evaluation by counting the frequency of occurrence of vortex is not adequate, the measurement method PTV (Particle Tracking Velocimetry) has been applied to obtain detailed flow features in the intake bay with the vortex-preventing devices. From experimental investigations, it can be concluded that the structure near the free surface effectively reduce the flow speed near the surface and work effectively to suppress of the intake vortex.
  • TAKEHARA Kohsei; HISASUE Nobuyuki; ETOH T. Goji; TAKANO Yasuhide
    PROCEEDINGS OF HYDRAULIC ENGINEERING Japan Society of Civil Engineers 第50巻 715 - 720 0916-7374 2006 
    A Particle Tracking Velocimetry is applied to surface and internal flow measurements in an actual river model. New techniques are proposed for the flow measurements. In the measurements of surface flows, two CCD video cameras, which are exactly synchronized, are used in order to measure detailed flow vectors in a wide area. In this experiment, one CCD camera captures wider area for understanding global flow patterns. The other camera focuses on local area where flow geometry is complicated. In addition to the surface flow measurement techniques, an internal flow measurement technique is also proposed by using a bore lens system. The proposed techniques are applied to an experiment, in which an actual river model is used. The results show reasonable velocity distributions compared with the results of standard point measurements.
  • ST Thoroddsen; TG Etoh; K Takehara; N Ootsuka; A Hatsuki
    JOURNAL OF FLUID MECHANICS CAMBRIDGE UNIV PRESS 545 203 - 212 0022-1120 2005/12 
    We present experimental observations of the disk of air caught under a drop impacting onto a solid surface. By imaging the impact through an acrylic plate with an ultra-high-speed video camera, we can follow the evolution of the air disk as it contracts into a bubble under the centre of the drop. The initial size and contraction speed of the disk were measured for a range of impact Weber and Reynolds numbers. The size of the initial disk is related to the bottom curvature of the drop at the initial contact, as measured in free-fall. The initial contact often leaves behind a ring of micro-bubbles, marking its location. The air disk contracts at a speed comparable to the corresponding air disks caught under a drop impacting onto a liquid surface. This speed also seems independent of the wettability of the liquid, which only affects the azimuthal shape of the contact line. For some impact conditions, the dynamics of the contraction leaves a small droplet at the centre of the bubble. This arises from a capillary wave propagating from the edges of the contracting disk towards the centre. As the wave converges its amplitude grows until it touches the solid substrate, thereby pinching off the micro-droplet at the plate, in the centre of the bubble. The effect of increasing liquid viscosity is to slow down the contraction speed and to produce a more irregular contact line leaving more micro-bubbles along the initial ring.
  • ST Thoroddsen; TG Etoh; K Takehara; N Ootsuka
    PHYSICS OF FLUIDS AMER INST PHYSICS 17 (7) 1070-6631 2005/07 
    Two bubbles brought into contact will coalesce rapidly. We study experimentally the initial coalescence motions in the neck region connecting the two bubbles, using an ultrahigh-speed video camera. The air bubbles are grown in ethyl alcohol, at the ends of two opposing vertical needles, until they come into contact. The growth rate of the neck is measured and modeled with a capillary/inertial balance. The instantaneous profile in the neck forms a circular arc, with the ratio of the two principal radii of curvatures increasing linearly in time. (c) 2005 American Institute of Physics.
  • ST Thoroddsen; K Takehara; TG Etoh; Y Hatsuki
    JOURNAL OF FLUID MECHANICS CAMBRIDGE UNIV PRESS 530 295 - 304 0022-1120 2005/05 
    We present experiments, using an ultra-high-speed video camera, which indicate flow-induced buckling of a surfactant layer on the free surface of a deforming water drop. This results in the 'puncturing' of the liquid surface, sending out a narrow jet. The phenomenon is produced when a water drop falls onto and passes through a hemispherical soap film. The soap film wraps around the drop forming a closed pocket, with a thin layer of air separating the two. This occurs without initial contact between the soap film and the drop liquid, which becomes clear during the subsequent dynamics, as the original film unwraps fully from the drop surface. Under particular conditions the soap film makes contact with the top of the drop, producing a toroidal bubble, which is driven down the drop to form a hemisphere at its bottom. We propose that the resulting rapid reduction in surface area of the bubble leads to overpacking of the surfactant molecules and buckling of the surface, which allows the jet to emerge, from the bottom tip of the drop. Marangoni-driven boundary layers, converging at the bottom, may also play a role in forcing out the jet.
  • ST Thoroddsen; K Takehara; TG Etoh
    JOURNAL OF FLUID MECHANICS CAMBRIDGE UNIV PRESS 527 85 - 114 0022-1120 2005/03 
    When two liquid drops come into contact, they coalesce rapidly, owing to the large curvature and unbalanced surface-tension forces in the neck region. We use an ultra-high-speed video camera to study the coalescence of a pendent and a sessile drop, over a range of drop sizes and liquid viscosities. For low viscosity, the outward motion of the liquid contact region is successfully described by a dynamic capillary-inertial model based on the local vertical spacing between the two drop surfaces. This model applies even when the drops are of different sizes. Increasing viscosity slows down the coalescence when the Reynolds number Re-v = rho R(ave)sigma/mu(2) < 5000, where R-ave is the average of the tip radii of the two similar size drops, rho is the liquid density, sigma is the surface tension and mu the dynamic viscosity. At Re-v similar or equal to 50, the growth-rate of the neck radius has reduced by a half, which for water corresponds to a drop diameter of only 2 mu m. For the largest viscosities, the neck region initially grows in size at a constant velocity. The neck curvature also becomes progressively sharper with increasing viscosity. The results are compared to previously predicted power laws, finding slight, but significant deviations from the predicted exponents. These deviations are most probably caused by the finite initial contact radius.
  • MADA Toshio; KOMATSU Haruo; SATO Masanori; SIMIZU Tetsuo; TAKEHARA Kohsei; ETOH T. Goji; ARAKAWA Kazuo
    The proceedings of the JSME annual meeting The Japan Society of Mechanical Engineers 2005 337 - 338 2005
  • FUJITA Ichiro; HIRAI Kosuke; TSUBAKI Ryota; MUTO Yasunori; TAKEHARA Kosei; KANDA Keiichi
    Transactions of Visualization Society of Japan The Visualization Society of Japan 25 (2) 23 - 26 0916-4731 2005 
    Field measurements using an image analysis technique, the large-scale particle image velocimetry (LSPIV), are conducted for a river reach having a series of groins in the Uji River. The measurements are performed using a digital video camera from a height of 27m of the nearby tower for meteorological survey. The river reach with a streamwise length of about 150m and the width of about 60m is cover by three-angle recordings. The measurement results from each angle are successfully connected with each other, by which the general flow feature of the region can be revealed with a reasonable accuracy. The measurement by an ADCP is also performed to obtain the internal three-dimensional flow structure. In addition, a numerical simulation based on the unstructured grid system of the shallow water equation is conducted to compare with the field measurement results and to evaluate the effect of the groins to the main flow.
  • N Ootsuka; TG Etoh; K Takehara; S Oki; Y Takano; Y Hatsuki; S Thoroddsen
    26th International Congress on High Speed Photography and Photonics SPIE-INT SOC OPTICAL ENGINEERING 5580 153 - 162 0277-786X 2005 
    In 2001, an ultra-high-speed video camera of 1,000,000 frames per second was developed in Hydraulics Laboratory of Kinki University. The image sensor of the camera was the ISIS-V2, the In-situ Storage Image Sensor-Version 2. The camera has been applied to visualization of high-speed phenomena in various fields of science and engineering. We observed entrapment phenomena of bubbles resulting from thermal spraying of metals. Thermal spraying is used to improve solid surfaces by spraying melted metal or ceramic particles to the surfaces. One of the problems relating to the thermal spraying is entrapment of air bubbles under the metal or ceramic layers covering the solid surfaces. The bubbles decrease bonding strength of the layers made by the thermal spraying. The entrapment processes were successfully visualized by application of the ultra-high-speed video camera.
  • 辻本剛三; 竹原幸生; 柿木哲哉; 西畠泰司; 平井登
    海洋開発論文集 Japan Society of Civil Engineers 21 689 - 694 0912-7348 2005 [Refereed]
     
    The hydraulic characteristics of a block with perforations are studied experimentally and theoretically. The present paper is threefold: a field test to examinethe stability of block and the growth of seaweed; an experimental study to measure a reflection coefficient, a transmission coefficient and a rate of wave energy dissipation; and a numerical simulation to examine the flow field over the mound with blocks by employing the κ-ε turbulence model which has considered the perforations of blocks.
    It was found through the field test that the stability of prototype models was extremely high and many kinds of seaweed have been adhering to blocks. The number of stability could be calculated with a ratioof submerged depth of crown and a wave height. Also wave energy dissipation could be promoted over blocks. The agreement between experimental data and the calculated values by the numerical simulation for the transmission coefficient and wave profiles over the blocks is found to be good.
  • ARAKAWA Kazuo; MADA Toshio; KOMATSU Haruo; SHIMIZU Tetsuo; SATOU Masanori; TAKEHARA Kohsei; ETOH Goji
    Journal of JSEM 日本実験力学会 5 (4) 356 - 360 1346-4930 2005
  • MICHIOKU Kohji; TAKEHARA Kohsei; ETOH Takeharu; TAKAHASHI Ryosuke; NANJYO Masashi
    Doboku Gakkai Ronbunshu Japan Society of Civil Engineers (803) 105 - 114 0289-7806 2005 
    In order to design an environmentally-friendly river structure, the flow and fields around a rubble mound weir and groin were investigated. In a physical model experiment, the flow inside the structure was visualized by adjusting the refraction indexes between the working fluid and the rubble's materials. Velocity vectors were obtained by means of PIV. Mass and momentum exchange between the open channel flow and the rubbles' porous media were found to be predominant around the up- and downstream corners of the weir and the groin. Both the turbulent intensity and Reynolds stress were also significant in these areas due to intensive momentum exchange. On the other hand, in the structure, turbulence properties were mainly influenced by the arrangement of the rubble and pores in the structure.
  • ETOH Takeharu; TAKEHARA Kohsei; TAKANO Yasuhide; OKUNO Satoshi; FUJITA Ichiro; SAKAI Nobuyuki
    Doboku Gakkai Ronbunshu Japan Society of Civil Engineers (796) 39 - 52 0289-7806 2005 
    This case study aims at development of a local remote sensing technology for measurement of surface flow field of rivers and rakes by means of PTV, Particle Tracking Velocimetry. Six thousand flat rice cakes with the diameter of 15 cm were scattered on the Uji river as tracers. A video camera mounted on a helicopter, hovering at the height of 300 m, took continuous images of the flow. Many problems associated with the practical applications of PTV to natural flow fields were picked up. Among them, there was a problem in identification of tracer images in that the computer software could not separate images of light reflections due to wind-driven surface tension waves from the tracer images. Countermeasures to the problems were proposed and tested. The surface flow field was analyzed by the PTV with the countermeasures, and compared with the flow field at 20-cm below the surface measured with an ADCP, Acoustic Doppler Current Profiler.
  • K Takehara; N Ohtsuka; TG Etoh; Y Takano; G Tsujimoto; N Mizutani
    Coastal Engineering 2004, Vols 1-4 WORLD SCIENTIFIC PUBL CO PTE LTD 1060 - 1071 2005 
    In order to clarify the mechanisms of wind waves, the air and water flows close to the water surface were simultaneously measured by using the Image Velocimetry, the IV. In this study, a Particle Tracking Velocimetry, so-called PTV, was used as IV, which can measure the velocity vectors in the vicinity of the water surface. The experiments were carried out in the range where whitecaps cannot appear. From the measured planar velocity distributions, the instantaneous vorticity distributions in air and water were evaluated.
  • OKINAKA Tomoo; ETOH T. Goji; TAKEHARA Kohsei; KONDO Yasushi; MARUNO Hiromasa; SOYA Hideki
    Transactions of the Visualization Society of Japan The Visualization Society of Japan 24 (1) 1 - 8 1346-5252 2004/07 
    A post-digital processing for a convertible triple in-situ storage image sensor (ISIS) camera is developed in this work. The convertible Triple-ISIS camera is converted from three single ISIS cameras by users. The camera has the frame rate of 1Mfps, and is expected to be a powerful tool for scientific and engineering measurements, such as color imaging, imaging with different light wave bands, and so on. Position and sensitivity adjustments are required after conversion. Post-digital processing is employed for the adjustments instead of the mechanical ones, since the conversion is expected to be done by users. As the post-digital processing, an image of a test pattern for calibration is captured by the converted ISIS camera. The position and sensitivity are adjusted only from that image. Color imaging is employed as an example of applications. Images which are captured by three ISISes are adjusted by means of the proposed position and sensitivity adjustments, and are piled up. The accuracy of the adjustments are discussed through the resultant color pictures and movies captured at 125 Kfps.
  • 藤田 一郎; 川谷 健; 椿 涼太; 冨尾 恒一; 武藤 裕則; 竹原 幸生; 高野 保栄; 神田 佳一
    神戸大学都市安全研究センター研究報告 神戸大学都市安全研究センター 8 219 - 225 1342-9167 2004/03
  • TAMAI Masahiro; TAKEHARA Kohsei; ETOH Takeharu; SAKAI Nobuyuki
    PROCEEDINGS OF HYDRAULIC ENGINEERING Japan Society of Civil Engineers 48 415 - 420 0916-7374 2004 
    Yodo river park, the first government-managed river park in Japan, has annual visitors of about 5 million and has become one of the most important parks in Osaka and its neighboring prefectures. The park also plays a role to protect or preserve natural river environment and is composed of four types ofareas according to purposes. The actural condition of various functions and utilization of the park has never been investigated sufficiently since the park was open to the public. The purpose of this study is to evaluate the utilization of the park economically using a questionnaire survey result and visitors number data by the park administrator. A relation between characteristics of the areas and the benefit of the utilization is investigated. Annual benefit of the park is over 2.7 billion yen.
  • TODO Mitsugu; ARAKAWA Kazuo; MADA Toshio; TANAKA Asami; TAKEHARA Kohsei; ETO T.Goji
    Proceedings of the 1992 Annual Meeting of JSME/MMD The Japan Society of Mechanical Engineers 2004 585 - 586 2004
  • 重松孝昌; 塩足純一; 竹原幸生; 辻本剛三
    海岸工学論文集 Japan Society of Civil Engineers 第51巻 661 - 665 0916-7897 2004 
    固液混相流場における乱流特性を明らかにするための基礎的実験として, 一方向流中に設置された多孔質体の間隙部およびその近傍の流速を, 屈折率整合法およびSuper-Resolution PIV法を用いて計測した. レイノルズ数を3通りに変えて行った実験から得られたデータをもとに, 渦度, 乱れの運動エネルギー, 乱れエネルギーの散逸率などを求め, 流れが多孔質体を通過して下流域に流出する間のこれらの生成・減衰機構について考察した. その結果, 無次元化された乱れの運動エネルギーの生成・減衰過程は, レイノルズ数に依存しない形で表されることが明らかになった.
  • 出口一郎; 荒木進歩; 竹田怜史; 吉井匠; 大利桂子; 竹原幸生
    海岸工学論文集 第51巻 136 - 140 2004
  • ST Thoroddsen; TG Etoh; K Takehara; Y Takano
    JOURNAL OF FLUID MECHANICS CAMBRIDGE UNIV PRESS 499 139 - 148 0022-1120 2004/01 
    We use a novel ultra-high-speed video camera to study the initial stage of the impact of a solid sphere onto a liquid surface, finding a high-speed horizontal jet which emerges immediately following the intial contact. For Re > 2 x 10(4) the jet emerges when the horizontal contact between the sphere and the liquid is only 12% of its diameter. For the largest Reynolds numbers this Jet can travel at more than 30 times the impact velocity of the sphere. This Jetting occurs sooner and at much higher normalized velocities than has been observed previously. The breakup of the jet into a spray of droplets sometimes occurs through formation of pockets in the liquid sheet. Early in the impact, the energy transferred to the jet and the subsequent spray sheet is estimated to be much larger than the energy associated with the added mass inside the liquid pool. The jetting will therefore greatly increase the initial impact force on the sphere.
  • 竹原 幸生; 江藤 剛治; 髙野 保英; 大塚 直; 辻本 剛三; 水谷 夏樹
    海岸工学論文集 Japan Society of Civil Engineers 50 96 - 100 0916-7897 2003/11 [Refereed]
     
    水表面での気体輸送現象に大きく関係する，水表面極近傍の気流・水流の同時計測した．
  • NANJYO Masashi; MICHIOKU Kohji; TAKEHARA Kohsei; ETOH Takeharu; HANATANI Kiyoaki
    Transactions of Visualization Society of Japan The Visualization Society of Japan 23 (1) 111 - 114 0916-4731 2003/07 
    Recently, permeable river structures such as a rubble mound weir attract attention from an environmental point of view. A permeable structure minimizes negative impact on natural environment compared to conventional solid structures made of concrete and steel. This type of weir purifies water through aeration as well as provides passage of aquatic lives in the longitudinal direction. In order to evaluate these environmental functions, it is necessary to analyze internal flow in the structure.
    In this study, flow fields in a rubble-mound weir were visualized by adjusting refractive index between solid-fluid phases. The flow velocity and turbulence are measured from image analysis, and the flow properties inside rubble-mound was analyzed. The present research will be useful in making hydraulic design of a permeable rubble mound.
  • Appliccations of a 1 Mfps Video Camera to Water Surface Fenomena
    竹原 幸生; 江藤 剛治; S. T. Thoroddsen
    The REE Societ del I’Electricite, de L’Electronique（SEE） 5 39 - 45 2003/05 
    種々の水表面での現象を100 万枚／秒のビデオカメラで詳細に観察した。
  • 竹原 幸生; 江藤 剛治; 髙野 保英; 大塚直; 水谷夏樹; 辻本剛三
    海岸工学論文集 .土木学会 50 86 - 91 0916-7897 2003/05 [Refereed]
     
    風波によるマイクロブレーキング現象の空間構造を解明するため、3 台のCCD カメラを用いて、広範囲かつ高解像度のPTV 計測を行った。波動場全体を把握した上で、水表面極近傍の詳細な計測結果が得られた。
  • ST Thoroddsen; TG Etoh; K Takehara
    JOURNAL OF FLUID MECHANICS CAMBRIDGE UNIV PRESS 478 125 - 134 0022-1120 2003/03 
    When a drop impacts on a liquid surface it entraps a small amount of air under its centre as the two liquid surfaces meet. The contact occurs along a ring enclosing a thin disk of air. We use the next-generation ultra-high-speed video camera, capable of 1 million f.p.s. (Etoh et al. 2002), to study the dynamics of this air sheet as it contracts due to surface tension, to form a bubble or, more frequently, splits into two bubbles. During the contraction of the air disk an azimuthal undulation, resembling a pearl necklace, develops along its edge. The contraction speed of the sheet is accurately described by a balance between inertia and surface tension. The average initial thickness of the air sheet decreases with higher impact Reynolds numbers, becoming less than one micron. The total volume of air entrapped depends strongly on the bottom curvature of the drop at impact. A sheet of micro-bubbles is often observed along the original interface. Oguz-Prosperetti bubble rings are also observed. For low Weber numbers (We < 20) a variety of other entrapment phenomena appear.
  • Shigematsu Takaaki; Takehara Kousei; Takano Tamotsu; Shiotari Jun-ichi; Oda Kazuki
    Doboku Gakkai Ronbunshuu B Japan Society of Civil Engineers 46 787 - 792 0916-7374 2003/02 [Refereed]
     
    A measuring method of fluid motion inside and in the vicinity of porous media made of silicon spheres is presented. Sodium iodide solution is used as the refraction index matching fluid. In order to capture pictures, a CCD camera and YAG laser are used. The velocity datum are obtained by analyzing the pictures using the superresolution PIV method. Some experimental results on the velocity field and turbulence kinematic energy are presented. Structure of the flow filed inside and in the vicinity of the porous media is discussed. Moreover generation and dissipation mechanisms of the turbulence are discussed.
  • MADA Toshio; KOMATSU Haruo; SATO Masanori; SIMIZU Tetsuo; TAKEHARA Kohsei; ETOH Goji; ARAKAWA Kazuo
    Proceedings of the 1992 Annual Meeting of JSME/MMD The Japan Society of Mechanical Engineers 2003 841 - 842 2003
  • ETOH Goji; Thoroddsen Sigurdur T.; Takehara Kohsei
    The proceedings of the JSME annual meeting The Japan Society of Mechanical Engineers 2003 295 - 296 2003 
    A newly developed 1M fps video camera was applied to the observation of drop impacts onto water surfaces. It captured the detailed mechanism of air sheet entrapment when a water drop is impacting onto water surfaces. Instability is newly found on the edge of the entrapped air sheet. The 100 consecutive images are enough to form a short movie, which is suitable for dynamic recognition
  • S. Devasenathipathy; J. G. Santiago; S. T. Wereley; C. D. Meinhart; K. Takehara
    Experiments in Fluids Springer Verlag 34 (4) 504 - 514 0723-4864 2003 [Refereed]
     
    This paper presents the design and implementation of velocimetry techniques applicable to the analysis of microfluidic systems. The application of both micron-resolution particle image velocimetry (micro-PIV) and particle tracking velocimetry (PTV) to the measurements of velocity fields within micromachined fluidic channels is presented. The particle tracking system uses epifluorescent microscopy, CCD imaging, and specialized image interrogation algorithms to provide microscale velocity measurement resolution. The flow field in a straight channel section is measured using cross-correlation micro-PIV and compared to the analytical solution of a measured mass flow rate. Velocity field measurements of the flow at the intersection of a cross-channel are also presented and compared with simulations from a commercially available flow solver, CFD-ACE+. Discussions regarding flow seeding, imaging optics, and the flow setup for measuring flows in microfabricated fluidic devices are presented. A simple process for estimating measurement uncertainty of the inplane velocity measurements caused by three-dimensional Brownian motion is described. A definition for the measurement depth for PTV measurements is proposed. The agreement between measured and predicted values lends further support to the argument that liquid microflows with characteristic dimensions of order 50-μm dimension channels follow macroscale flow theory.
  • K Takehara; ST Thoroddsen; TG Etoh
    25TH INTERNATIONAL CONGRESS ON HIGH-SPEED PHOTOGRAPHY AND PHOTONICS SPIE-INT SOC OPTICAL ENGINEERING 4948 63 - 70 0277-786X 2003 
    A 1 M fps video camera was applied to the observation of drop impacts onto water surfaces. It captured the detailed mechanism of sheet ejection from the contact region between the drop and the water surface, the small droplets separated from the ejected sheet and bubble entrapment by a drop impacting onto a water surface. The 103 consecutive images are enough to form a short movie which is suitable for dynamic recognition.
  • Uemura, M; C. Nakagawara; Y. Kawamura; S. Yoshida; T. Etoh; K. Takehara
    Cryobiology and Cryotechnology Japanese Society for Cryobiology and Cryotechnology 48 (2) 135 - 138 1340-7902 2002/12 [Refereed]
     
    Normal-speed (32 frames/sec) and high-speed (up to 4,000 frames/sec) video cameras attached with a cryomicroscope were utilized to analyze the freezing process of protoplasts isolated from Arabidopsis leaves and Jerusalem artichoke tubers. With protoplasts isolated from leaves of non-acclimated Arabidopsis seedlings, intracellular freezing was observed even when protoplasts were frozen to -10℃ at rates of 0.5 to 1.0℃/min, and the frequency increased significantly at 2.5 to 10℃/min. After cold acclimation for 1 day at 2℃, the intracellular freezing did not occur at cooling rates of 1.0℃ or slower. Cold acclimation for 2 to 7 days further resulted in a shift of the temperature range over which intracellular freezing occurred to lower temperatures. High-speed video microscopy revealed that intracellular freezing was initiated, with no exceptions, at places near the plasma membrane. However, it was not possible with techniques used in the present study to determine whether ice formation initially occurs inside or outside the cell. Nevertheless, these studies demonstrate that videomicroscopy combined with cryostage provides an insight to understand the effect of cold acclimation on the freezing process of plant protoplasts.
  • Applications of a 1M ftp video camera to water surface phenomena[Invited Lecture]
    竹原 幸生; 江藤 剛治; S. T. Thoroddsen
    Proc. of 25th International Congress on High-Speed Photography and Photonics 4948 60 - 70 2002/12 
    近畿大学で開発した１００万枚／秒の高速ビデオカメラを用いて，水表面近傍の現象を可視化した例を紹介した。
  • S Devasenathipathy; JG Santiago; K Takehara
    ANALYTICAL CHEMISTRY AMER CHEMICAL SOC 74 (15) 3704 - 3713 0003-2700 2002/08 
    We have applied particle tracking techniques to obtain spatially resolved velocity measurements in electrokinetic flow devices. Both micrometer-resolution particle image velocimetry (micro-PIV) and particle tracking velocimetry (PTV) techniques have been used to quantify and study flow phenomena in electrokinetic systems applicable to microfluidic bioanalytical devices. To make the flow measurements quantitative, we performed a series of seed particle calibration experiments. First, we measure the electroosmotic wall mobility of a borosilicate rectangular capillary (40 by 400 mum) using current monitoring. In addition to this wall mobility characterization, we apply PTV to determine the electrophoretic mobilities of more than 1000 fluorescent microsphere particles in aqueous buffer solutions. Particles from this calibrated particle/ buffer mixture are then introduced into two electrokinetic flow systems for particle tracking flow experiments. In these experiments, we use micro-PIV, together with an electric field prediction, to obtain electroosmotic flow bulk fluid velocity measurements. The first example flow system is a microchannel intersection where we demonstrate a detailed documentation of the similitude between the electrical fields and the velocity fields in an electrokinetic system with uniform zeta potential,. In the second system, we apply micro-PIV to a microchannel system with nonuniform. The latter experiment provides a simultaneous measurement of two distinct wall mobilities within the microchannel.
  • TAKANO Yasuhide; TANAKA Kenji; SHIGEMATSU Takaaki; ETOH Goji; TAKEHARA Kohsei
    Transactions of Visualization Society of Japan The Visualization Society of Japan 22 197 - 200 0916-4731 2002/07 
    Visualization of water flow around structures or in porous media requires refractivity matching of water and the transparent solid materials. The authors have developed two methods to make transparent spheres from silicon rubber; the stirring method and the casting method. Visualization experiments of water flow around a sphere coming up to the surface and in a porous medium were performed to examine the validity of the refractivity matching method. Velocity vectors of these flows were obtained from recorded particle images by a PTV algorithm, while was also developed by the authors.
  • ETOH Goji; TAKEHARA Kohsei; OKUNO Satoshi; TAKANO Yasuhide
    Transactions of Visualization Society of Japan The Visualization Society of Japan 22 357 - 360 0916-4731 2002/07 
    The Infrared PTV (Particle Tracking Velocimetry) is proposed for applications to measurements of surface velocity fields of local water bodies, such as rivers, lakes, ponds, estuaries and coastal areas. The tracers are either ice particles or soaked and frozen flat edible cakes. The cameras are infrared sensitive. PTV algorisms can be applied to the infrared particle images. The system can measure detailed surface velocity fields of floods even in the darkness. No or negligible pollutant is supplied respectively by the ice particles or the flat cakes.
  • YAMADA Hiroyuki; TSUJIMOTO Gozo; KUSAKABE Shigeyuki; TAKEHARA Kohsei
    Transactions of Visualization Society of Japan The Visualization Society of Japan 22 375 - 378 0916-4731 2002/07 
    A flow field in the man-made embayment of three types was examined by using a PIV technique. the pattern of a circulation flow inside the embayment changes with positions of an opening. Although the speed of a flow inside the embayment was late as compared with that of main flow, its intensity of turbulent kinematics energy was remarkably large. The profile of a circulation flow has not become clear gradually from the water surface to the bottom. This fact means that the flow field in here has a characteristic of three dimension. Send has accumulated on the central part mostly in the embayment, and these flow have contributed to formation of three dimensional bottom profiles.
  • TAKEHARA Kohsei; ETOH Goji; TAKANO Yasuhide
    日本流体力学会年会2002講演論文集 日本流体力学会 2002 208 - 209 2002/07 
    A method to measure surface tension of water was developed by measuring the properties of capillary waves. An advantage of this method is to be able to measure surface tension without disturbances of the surface, which usually occur in standard methods of measurement of surface tensions. Capillary waves are generated by vibrating cylinder at the center of water tank. The properties of capillary waves are measured by using high speed video camera and two laser beams.
  • ETOH T. Goji; MUTOH Hideaki; TAKEHARA Kohsei; OKINAKA Tomoo; TAKANO Yasuhide
    ITE Technical Report The Institute of Image Information and Television Engineers 26 (26) 27 - 33 1342-6893 2002/03 
    An image sensor of 1,000,000 fps with image storage for consecutive 103 images is developed, which is called ISIS, In-situ Storage Image Sensor. Various innovative ideas support this achievement. Each pixel of the sensor has its own in-situ storage area of image signals during an image capturing phase, image signals generated in the photo-sensitive areas of all pixels are simultaneously recorded in the in-situ storage areas without being readout from the sensor, which realizes parallel recording at all pixels and, thus, image capturing at the ultimate high frame rate.
  • ETOH Takeharu; MUTOH Hideaki; TAKEHARA Kohsei; TAKANO Yasuhide; OKINAKA Tomoo
    The Journal of the Institute of Television Engineers of Japan The Institute of Image Information and Television Engineers 56 (3) 483 - 486 1342-6907 2002/03 
    撮影速度100万枚/秒のビデオカメラ用撮像素子を開発した.撮影中は全画素並列で一斉に各画素の周辺に組入れられた記録領域に画像情報を蓄積するので究極の高速化が可能である。このような素子を画素周辺記録型撮像素子 (ISIS : In-situ Storage Image Sensor) と呼ぶ.開発した素子の記録要素は少し斜めに置かれた通常の直線CCDで, 非常に単純な構造である.ドレーンも組入れられており, 103枚の連続上書き撮影が可能である.試験撮影により高感度, 高画質であることも確かめられた.
  • 重松 孝昌; 渡部 靖憲; 竹原 幸生; 奥村 悠樹; 小池 敏也
    海岸工学論文集 公益社団法人 土木学会 49, 806-810 (49) 806 - 810 0916-7897 2002 
    従来, 測定が困難であった多孔質構造物間隙内の三次元流体運動を計測するシステムの構築を行っている. 構造物と流体の屈折率を調整することにより, 物体背後の構造物および流体を視認することができ, さらに, 拡張型三次元ステレオグラムPTV流速計測システムを用いることにより, 間隙内流体運動の計測が可能になっている. 新たに中立粒子の開発も行っている. 構築したシステムを用いて, 波動場におけるテトラポッド潜堤の間隙流体運動の計測を行い, 三次元流速分布および乱れエネルギーの空間分布について考察している.
  • 竹原 幸生; 真木 正弘; 辻本 剛三; 江藤 剛治; 高野 保英
    海洋工学論文集 Japan Society of Civil Engineers 49, 66-70 66 - 70 0916-7897 2002 
    大気-海洋間の物質, 熱および各種物質の輸送現象を明らかにするには, 水表面近傍の気相および水相の詳細な流れ構造を明らかにする必要がある.画像流速測定法 (Image Velocimetry, IV) の中で最も空間解像力の高い粒子追跡速度計測法 (Particle Tracking Velocimetry, PTV) を用いた, 風波発生時の水表面極近傍の気流・水流の同時計測法を開発した.開発した手法を用いて, これまで計測されていない風波発生時における水表面近傍の気流および水流のPTV同時計測に成功し, 水表面近傍の流れ構造を詳細に計測することができた.
  • NABESAKA Seishi; ETOH T. Goji; TAKEHARA Kohsei
    土木学会論文集 土木学会 705 (705) 19 - 29 0289-7806 2002
  • Kondo Yasushi; Etoh T. Goji; Takehara Kohsei; Takano Yasuhide; Maruno Hiromasa; Takubo Kenji; Soya Hideki
    PROCEEDINGS OF THE ITE ANNUAL CONVENTION The Institute of Image Information and Television Engineers 2001 338 - 338 1343-1846 2001 
    Development of High-Speed Video Camera that employ the ISIS, In-situ Storage Image Sensor, is reported. A test sensor of the ISIS successfully captured image at 1 million fps.
  • TAKEHARA Kohsei; ETOH Takeharu; SAITOH Masahiro; KUWANA Tohru
    Transactions of Visualization Society of Japan The Visualization Society of Japan 19 (2) 185 - 186 0916-4731 1999/10 
    The Particle Mask Fitting (PMF) method has been proposed to extract particle information properly from particle images. A method to evaluated initial values of parameters in PMF method is proposed. The simulation images are used for estimation of the parameters.
  • ETOH Takeharu; SHIRASU Toshinari; TAKEHARA Kohsei
    Transactions of Visualization Society of Japan The Visualization Society of Japan 19 (1) 251 - 254 0916-4731 1999/07 
    PTV( Particle Tracking Velocimetry) is applied to images with moving particle images. Properties required for image sensors to analyze movements of scattered particles are discussed. Much higher frame rate than 30 pps is essential, which is realized by parallel readout architecture. Lower descretization level and image compression effectively work to keep both high frame rate and high spatial resolution (number of pixels) for a given number of readout lines. 1) The optimum descretization level for PTV is 4 to 6 bit: 2) Image compression schemes generate weak false particle images, which can be compensated by post-processing if the scheme is not complicated.
  • OKAMOTO Koji; TAKEHARA Yukio; NISHIO Shigeru; SAGA Tetsuo
    Transactions of Visualization Society of Japan The Visualization Society of Japan 19 (2) 325 - 328 0916-4731 1999 
    Particle Image Velocimetry (PIV) offers many advantages for the study of fluid flows. The PIV has two processes, i.e., the image capture with visualization and the image analysis. In order to evaluate the image analysis system for the PIV, the Japanese PIV Standard Project (JPIV) proposed the standard images for PIV. The developed PIV standard images are distributed using the Internet, (http://www.vsj.or. jp/piv/) and CD-R. Using the PIV standard images, the sub-pixel accuracy on the PIV and PTV were evaluated. The accuracy was confirmed to be about 0.2 pixel/interval for both of PIV and PTV.
  • T Etoh; H Mutoh; K Takehara; T Okinaka
    HIGH-SPEED IMAGING AND SEQUENCE ANALYSIS SPIE-INT SOC OPTICAL ENGINEERING 3642 127 - 132 0277-786X 1999 [Refereed]
     
    The ISIS, In-situ Storage Image Sensor, may achieve the frame rate higher than 1,000,000 pps. Technical targets in development of the ISIS are listed up. A layout of the ISIS is presented, which covers the major targets, by employing slanted CCD storage and amplified CMOS readout. The layout has two different sets of orthogonal axis systems: one is mechanical and the other functional. Photodiodes, CCD registers and all the gates are designed parallel to the mechanical axis system. The squares on which pixels are placed form the functional axis system. The axis systems are inclined to each other. To reproduce a moving image, at least fifty consecutive images are necessary for ten-second replay at 5 pps. The inclined design inlays the straight CCD storage registers for more than fifty images in the photo-receptive area of the sensor. The amplified CMOS readout circuits built in all the pixels eliminate line defects in reproduced images, which are inherent to CCD image sensors. FPN (Fixed Pattern Noise) introduced by the individual amplification is easily suppressed by digital post image processing, which is commonly employed in scientific and engineering applications. The yield rate is significantly improved by the elimination of the line defects.
  • T Etoh; H Mutoh; K Takehara; S Oki
    23RD INTERNATIONAL CONGRESS ON HIGH-SPEED PHOTOGRAPHY AND PHOTONICS, PT 1 SPIE-INT SOC OPTICAL ENGINEERING 3516 341 - 344 0277-786X 1999 [Refereed]
     
    An improved design is presented for an ISIS, In-situ Storage Image Sensor, previously proposed by the authors for a high frame rate video camera of 1,000,000 pps. CCD channels of the sensor play dual roles for signal storage in an image capturing phase and for signal transfer in a read-out phase, which minimizes unutilized spaces on the light receptive area The transfer direction is only vertical which simplifies the structure of the sensor and provides better quality in reproduced images. An overwriting mechanism is built in, which facilitates synchronization of cease of the image capturing phase to the occurrence of a target event The design is improved by coupling adjacent two CCD channels and two photodiodes, which provides wider spaces to place metal wires to increase rate of charge drive.
  • 北川 博巳; 竹原 幸生; 江藤 剛治; 三星 昭宏
    工学・工業教育研究講演会講演論文集 公益社団法人日本工学教育協会 9 221 - 224 1997/08
  • T Etoh; K Takehara
    ULTRAHIGH- AND HIGH-SPEED PHOTOGRAPHY AND IMAGE-BASED MOTION MEASUREMENT SPIE-INT SOC OPTICAL ENGINEERING 3173 57 - 66 0277-786X 1997 [Refereed]
     
    It costs a few million dollars to develop an innovative solid-state image sensor. Various image sensors with special useful functions have been proposed for individual scientific and engineering research purposes. However, the enormous cost hampers their development. Presented in this paper is an attempt to classify wide-range of requirements for high-speed image sensors for scientific and engineering use, and to combine them into a limited number of specific designs. This will serve to provide a rational overall development strategy and to reduce overlapping effort and cost for their development and hopefully contribute to realization of some of the designs. This is a state-of-the-art paper on development of high-speed video cameras, including: (1)classification of advanced image capturing technologies required for scientific and engineering researches, (2)performance criteria for high-speed image capturing, (3)classification and comparison of currently available high-speed image capturing technologies, (4)user's requirements for electronic high-speed imagers, obtained by questionnaires and hearings, (5)comparison of PRIS(parallel readout image sensors) and ISIS(in-situ storage image sensors), (6)current status of fabrication technology of both CCD-and CMOS-image sensors, and (7)recommendation of prototype high-speed image sensors for urgent development.
  • 北川博巳; 竹原幸生; 武田慎治; 三星昭宏; 江藤剛治; 篠原紀
    土木計画学研究・論文集 Japan Society of Civil Engineers 13 (13) 381 - 390 0913-4034 1996/08 
    Volunteer activities in Hanshin-Awaji earthquake disaster were dispatched in Kinki University civil engineering course. Volunteer work held to the civli engineering course student. And its purpose which consider environment and welfare is cultivated.
    In this study, this activities give what kind of educational effects to a student and attempt a grasp of the Volunteer welfare activities that was necessary an earthquake disaster. Also, analyzing the educational effect in the announcement meeting.
  • MARUYAMA Yoshikazu; ETOH Takeharu; TAKEHARA Koshei; AKABOSHT Takashi; NISHIMOTO Shoji
    Transactions of Visualization Society of Japan The Visualization Society of Japan 16 (1) 111 - 112 0916-4731 1996 
    Image analysis techniques are now widely applied to measurement for scientific and engineering studies. It has a great advantage in that simultaneous aerial measurement is possible. One disadvantage is that, as the aspect ratio of a TV display is about 5 : 3, it is difficult to visualize the whole span of an object with high aspect-ratio such as cables, bridges, etc. Three techniques are proposed to overcome the difficulty : (1) Employment of a cylindrical lens system, (2) Development of a proper computer algorithm, and (3) Development of a special video camera. The combination of all these three will accomplish simultaneous measurement of whole span of linear objects with satisfactory accuracy.
  • 北川 博巳; 竹原 幸生; 武田 慎治; 三星 昭宏; 江藤 剛治
    工学・工業教育研究講演会講演論文集 公益社団法人 日本工学教育協会 1996 207 - 210 1996
  • ETOH Takeharu; TAKEHARA Kosei; Kishida Yoshihiro
    Transactions of Visualization Society of Japan The Visualization Society of Japan 12 (1) 215 - 218 0916-4731 1992 
    Surface deformation by impact of a droplet and entrainment of the droplet into water arc visualized by means of a high-speed video camera developed by the authors, of which framerate is 4, 500 pps. The average diameter of droplets used in the experiment is 4.6 mm. The height of the nozzle which releases droplets is varied in the range of 5-45 cm.
    Some preliminary results are obtained as follows :
    (1) The relation between height (i.e., impact speed) and size of the crater changes for the low or high falling velocity, which implies the process is also different,
    (2) The surface deformation and entrainment processes can be clearly visualized in detail by the camera.
  • Takehara Kosei; Etoh Takeharu
    Transactions of Visualization Society of Japan The Visualization Society of Japan 12 (1) 79 - 82 0916-4731 1992 
    A new method for measuring velocity field by tracking particles is proposed. Kalman's filtering theory and the Chi-square test are applied to the algorithm. By using Kalman's filtering theory, the particle information at the (t+1)-th step is estimated by particle information at the t-th step. The Chi-square test is applied to correlate a particle image in the t-th frame with the same one in the (t+1)-th frame.
  • Matsunaga Nobuhiro; Takehara Kosei; Shibata Toshihiko; Komatsu Toshimitsu
    PROCEEDINGS OF HYDRAULIC ENGINEERING Japan Society of Civil Engineers 33 493 - 498 0913-4131 1989 
    The characteristics have been investigated experimentally of turbulence of open-channel flows on a sinusoidal solid bed. The experiments have been carried out on two kinds of flows, i. e., dune type flow and anti-dune type flow. The dune type flow forms a core region, in which the characteristics quantities of turbulence are constant in the flow direction. As for the antidune type flow, the region is not observed and the turbulent quantities vary in the flow direction. In the both flows, the vertical distribution of the Reynolds stress takes a minimum value in the region from crest to trough. This is due to the passing of an organized eddy.
  • MATSUNAGA Nobuhiro; AWAYA Yoichi; TAKEHARA Kosei
    Doboku Gakkai Ronbunshu Japan Society of Civil Engineers 1988 (393) 229 - 232 0289-7806 1988 
    It has been found experimentally that a row of two-dimensional vortices forms in an offshore zone when surface waves climb up a sloping flat bed. The vortices occur near the separation point of the Stokes layer, i. e., near the breaking point, and are transported in the offshore direction. Performing the vortex pairing, the vortices increase their length scales offshorewards. They are nearly equal to the local depth of water. In the case when the slope of the bed from the horizontal is 2.44°, the row of vortices appears when hb/Lb≤0.096. Here, hb and Lb are the mean water depth and the wavelength at the breaking point, respectively.

Conference Activities & Talks

  • 阿部悟; 高木力; 米山和良; 鳥澤眞介; 波部斉; 阿部孝司; 井口信和; 竹原幸生; 升間主計; 八木洋樹; 中井彰治; 山口武治; 浅海茂
    日本水産学会大会講演要旨集  2019/03
  • 林直樹; 三井鷹; 井口昭彦; 高野保英; 沖中知雄; 竹原幸生; 下ノ村和弘; 江藤剛治; 江藤剛治
    映像情報メディア学会技術報告  2018/06
  • 江藤剛治; 下ノ村和弘; 竹原幸生; 犬丸秀夫; 林直樹; 三井鷹; 井口昭彦; 三原勉
    映像情報メディア学会技術報告  2018/03
  • 高木力; 米山和良; 阿部悟; 鳥澤眞介; 竹原幸生; 山口武治; 浅海茂
    日本水産工学会学術講演会講演論文集  2017/05
  • 阿部悟; 高木力; 竹原幸生; 木村暢夫; 平石智徳; 米山和良; 鳥澤眞介; 山口武治; 浅海茂
    日本水産学会大会講演要旨集  2017/03
  • 久末信幸; 竹原幸生
    電気評論  2016/09
  • 裏泰樹; 麓隆行; 竹原幸生
    土木学会年次学術講演会講演概要集(CD-ROM)  2016/08
  • 裏泰樹; 麓隆行; 竹原幸生
    コンクリート工学年次論文集(CD-ROM)  2016/06
  • 麓隆行; 裏泰樹; 竹原幸生
    コンクリート工学年次論文集(CD-ROM)  2016/06
  • 阿部悟; 高木力; 竹原幸生; 木村暢夫; 平石智徳; 米山和良; 鳥澤眞介; 浅海茂
    日本水産学会大会講演要旨集  2016/03
  • 麓隆行; 竹原幸生
    可視化情報学会誌  2015/09
  • 高野保英; 竹原幸生; 江藤剛治
    可視化情報学会誌  2015/09
  • 竹原幸生; 高野保英; 杉原大仁; 江藤剛治
    高速度イメージングとフォトニクスに関する総合シンポジウム講演論文集(CD-ROM)  2015
  • HAMAHATA Takashi; UTO Satoshi; AKINO Toshiro; NISHI Kenji; TAKEHARA Kohsei; ETOH T. Goji
    IEICE technical report  2008/06  The Institute of Electronics, Information and Communication Engineers
     
    In this paper, we develop a printed circuit board having a discrete device that can drive a CCD chip with 5nF maximum load capacitance per CCD clock at a high speed of 100MHz and design a voltage source chip to generate the clock on basis of 0.18μmCMOS/SOI process. Although we are based on a set of BSIM3 model parameters from a TSMC bulk CMOS process, we modify the substrate doping from a non-uniform diffusion profile with the TSMC channel doping to a uniform profile of the same channel doping along a direction of deep SOI substrate. As we try to make a substrate terminal to be non-floating and design a compact layout in order to reduce the resistance value of substrate interconnection, we optimize the size of unified-CBiCMOS buffer circuit for a high speed and low energy operation of lateral npn-and pnp-BJTs. We fix the absolute value of threshold voltage as 0.5V and then the ratio value of 【power supply voltage/threshold voltage】 is changed from 1.5 to 4. As a result of circuit simulation, the minimum average energy of the unified-CBiCMOS buffer circuit is around at the ratio value of 2. Furthermore, we report the circuit simulation results under various conditions. It is concluded that a technical outlook of clock generation around 100MHz is established by the circuit simulation.
  • KOBAYASHI Masatoshi; AKINO Toshiro; NISHI Kenji; TAKEHARA Kohsei; ETOH T. Goji
    IEICE technical report  2008/06  The Institute of Electronics, Information and Communication Engineers
     
    We have been developing a ultra-high-speed camera by an in-situ storage image sensor (ISIS) with slanted linear CCD storage capturing 100 to 150 consecutive images at a frame rate of 100 Mfps. The CCD chip of this camera has a 8V maximum voltage supply source and a 5-nF maximum load capacitance per CCD clock. The goal of this study is to design a prototype power supply chip generating the clock, based on a 1.2-μmCMOS/SOI process having breakdown voltages of almost 32V. At first, we fit a set of LEVEL2 model parameters into the measured MOSFET current-voltage characteristics for a bulk type 1.2-μmCMOS process, and then only modify the substrate doping from a non-uniform diffusion profile with a channel doping to the uniform diffusion profile of the same channel doping along the direction of rather deep SOI substrate. As we try to make the substrate terminal to be non-floating and design a compact layout in order to reduce the resistance value of substrate interconnection, we optimize the size of unified-CBiCMOS buffer circuit for a high speed and low energy operation of lateral npn-and pnp-BJTs. Circuit simulation using 1.2-μm LEVEL-2 model parameters for the MOSFETs and a current gain of β_F=100 for the BJTs reduced the delay time of the unified-CBiCMOS buffer circuit by approximately 1/10 and slightly increased the energy of that by 103%, compared to that for an equivalent two-stage CMOS inverter circuit designed on the basis of logical effort for driving a load capacitance of 5-nF at V_<dd>=8V. Because the power supply chip with the unified-CBiCMOS buffer circuit can drive the CCD chip at a frame rate of only 8Mfps for the 5-nF load capacitance, we need further contraptions.
  • HAMAHATA Takashi; UTO Satoshi; AKINO Toshiro; NISHI Kenji; TAKEHARA Kohsei; ETOH T. Goji
    IEICE technical report  2008/06  The Institute of Electronics, Information and Communication Engineers
     
    In this paper, we develop a printed circuit board having a discrete device that can drive a CCD chip with 5nF maximum load capacitance per CCD clock at a high speed of 100MHz and design a voltage source chip to generate the clock on basis of 0.18μmCMOS/SOI process. Although we are based on a set of BSIM3 model parameters from a TSMC bulk CMOS process, we modify the substrate doping from a non-uniform diffusion profile with the TSMC channel doping to a uniform profile of the same channel doping along a direction of deep SOI substrate. As we try to make a substrate terminal to be non-floating and design a compact layout in order to reduce the resistance value of substrate interconnection, we optimize the size of unified-CBiCMOS buffer circuit for a high speed and low energy operation of lateral npn-and pnp-BJTs. We fix the absolute value of threshold voltage as 0.5V and then the ratio value of 【power supply voltage/threshold voltage】 is changed from 1.5 to 4. As a result of circuit simulation, the minimum average energy of the unified-CBiCMOS buffer circuit is around at the ratio value of 2. Furthermore, we report the circuit simulation results under various conditions. It is concluded that a technical outlook of clock generation around 100MHz is established by the circuit simulation.
  • KOBAYASHI Masatoshi; AKINO Toshiro; NISHI Kenji; TAKEHARA Kohsei; ETOH T. Goji
    IEICE technical report  2008/06  The Institute of Electronics, Information and Communication Engineers
     
    We have been developing a ultra-high-speed camera by an in-situ storage image sensor (ISIS) with slanted linear CCD storage capturing 100 to 150 consecutive images at a frame rate of 100 Mfps. The CCD chip of this camera has a 8V maximum voltage supply source and a 5-nF maximum load capacitance per CCD clock. The goal of this study is to design a prototype power supply chip generating the clock, based on a 1.2-μmCMOS/SOI process having breakdown voltages of almost 32V. At first, we fit a set of LEVEL2 model parameters into the measured MOSFET current-voltage characteristics for a bulk type 1.2-μmCMOS process, and then only modify the substrate doping from a non-uniform diffusion profile with a channel doping to the uniform diffusion profile of the same channel doping along the direction of rather deep SOI substrate. As we try to make the substrate terminal to be non-floating and design a compact layout in order to reduce the resistance value of substrate interconnection, we optimize the size of unified-CBiCMOS buffer circuit for a high speed and low energy operation of lateral npn-and pnp-BJTs. Circuit simulation using 1.2-μm LEVEL-2 model parameters for the MOSFETs and a current gain of β_F=100 for the BJTs reduced the delay time of the unified-CBiCMOS buffer circuit by approximately 1/10 and slightly increased the energy of that by 103%, compared to that for an equivalent two-stage CMOS inverter circuit designed on the basis of logical effort for driving a load capacitance of 5-nF at V_<dd>=8V. Because the power supply chip with the unified-CBiCMOS buffer circuit can drive the CCD chip at a frame rate of only 8Mfps for the 5-nF load capacitance, we need further contraptions.
  • HAMAHATA Takashi; UTO Satoshi; AKINO Toshiro; NISHI Kenji; TAKEHARA Kohsei; ETOH T. Goji
    IEICE technical report  2008/06  The Institute of Electronics, Information and Communication Engineers
     
    In this paper, we develop a printed circuit board having a discrete device that can drive a CCD chip with 5nF maximum load capacitance per CCD clock at a high speed of 100MHz and design a voltage source chip to generate the clock on basis of 0.18μmCMOS/SOI process. Although we are based on a set of BSIM3 model parameters from a TSMC bulk CMOS process, we modify the substrate doping from a non-uniform diffusion profile with the TSMC channel doping to a uniform profile of the same channel doping along a direction of deep SOI substrate. As we try to make a substrate terminal to be non-floating and design a compact layout in order to reduce the resistance value of substrate interconnection, we optimize the size of unified-CBiCMOS buffer circuit for a high speed and low energy operation of lateral npn-and pnp-BJTs. We fix the absolute value of threshold voltage as 0.5V and then the ratio value of 【power supply voltage/threshold voltage】 is changed from 1.5 to 4. As a result of circuit simulation, the minimum average energy of the unified-CBiCMOS buffer circuit is around at the ratio value of 2. Furthermore, we report the circuit simulation results under various conditions. It is concluded that a technical outlook of clock generation around 100MHz is established by the circuit simulation.
  • KOBAYASHI Masatoshi; AKINO Toshiro; NISHI Kenji; TAKEHARA Kohsei; ETOH T. Goji
    IEICE technical report  2008/06  The Institute of Electronics, Information and Communication Engineers
     
    We have been developing a ultra-high-speed camera by an in-situ storage image sensor (ISIS) with slanted linear CCD storage capturing 100 to 150 consecutive images at a frame rate of 100 Mfps. The CCD chip of this camera has a 8V maximum voltage supply source and a 5-nF maximum load capacitance per CCD clock. The goal of this study is to design a prototype power supply chip generating the clock, based on a 1.2-μmCMOS/SOI process having breakdown voltages of almost 32V. At first, we fit a set of LEVEL2 model parameters into the measured MOSFET current-voltage characteristics for a bulk type 1.2-μmCMOS process, and then only modify the substrate doping from a non-uniform diffusion profile with a channel doping to the uniform diffusion profile of the same channel doping along the direction of rather deep SOI substrate. As we try to make the substrate terminal to be non-floating and design a compact layout in order to reduce the resistance value of substrate interconnection, we optimize the size of unified-CBiCMOS buffer circuit for a high speed and low energy operation of lateral npn-and pnp-BJTs. Circuit simulation using 1.2-μm LEVEL-2 model parameters for the MOSFETs and a current gain of β_F=100 for the BJTs reduced the delay time of the unified-CBiCMOS buffer circuit by approximately 1/10 and slightly increased the energy of that by 103%, compared to that for an equivalent two-stage CMOS inverter circuit designed on the basis of logical effort for driving a load capacitance of 5-nF at V_<dd>=8V. Because the power supply chip with the unified-CBiCMOS buffer circuit can drive the CCD chip at a frame rate of only 8Mfps for the 5-nF load capacitance, we need further contraptions.
  • SHINODA Kentaro; MURAKAMI Hideyuki; KURODA Seiji; OKI Sachio; TAKEHARA Kohsei
    全国講演大会講演論文集  2007/11
  • Takehara Kohsei; Terasawa Hirokazu; Shigematsu Takaaki
    The Japan Society of Mechanical Engineers, Fluids engineering conference ...  2007/11
  • KOBAYASHI Masatoshi; HAMAHATA Takashi; AKINO Toshiro; NISHI Kenji; VO LE Cuong; TAKEHARA Kohsei; ETOH T. Goji
    IEICE technical report  2007/06  The Institute of Electronics, Information and Communication Engineers
     
    Since 2001, we have been developing an in-situ storage image sensor (ISIS) that captures 100 to 150 consecutive images at a frame rate of 1 Mfps and an ultra-high-speed video camera for use with this ISIS. Currently, basic research is continuing in an attempt to increase the frame rate up to 100 Mfps. The CCD chip of this camera has a 10 V maximum voltage supply source and a 5 nF maximum load capacitance per CCD clock. The goal of this study is to design a prototype power supply chip for generating the CCD clock and for driving the load capacitance of the CCD chip. A further goal is to verify the circuit behavior, based on a 1-μm CMOS/SOI process having breakdown voltages of almost 20 V. A lateral unified-CBiCMOS buffer circuit consists of n- and p-channel MOSEFTs that include parasitic lateral npn- and pnp-BJTs having partially depleted p- and n-base layers, respectively, on an epitaxial substrate and SOI. A forward current is applied to the base terminal of the channel MOSFET, adding a normal pull-up or pull-down MOSFET as a current source. A new device structure is designed to reduce the resistance values between the drains and the bases, while also keeping both MOSFETs inactive and activating either the lateral npn or pnp BJT. A clock generator consisting of a ring oscillator with a 21-stage CMOS inverter amplified and driven by a buffer circuit is designed. Circuit simulation using 1-μm LEVEL-3 model parameters for the MOSFETs and a current gain of β_F = 100 for the BJTs reduced the delay time of the unified-CBiCMOS buffer circuit by approximately 1/4, compared to that for an equivalent two-stage CMOS inverter circuit designed on the basis of logical effort for driving a load capacitance of 5 nF at V_<dd> = 10V. The power supply chip with the unified-CBiCMOS buffer circuit can drive the CCD chip at a frame rate of 10 Mfps for a 5-nF load capacitance.
  • SHINODA Kentaro; MURAKAMI Hideyuki; KURODA Seiji; OKI Sachio; TAKEHARA Kohsei
    全国講演大会講演論文集  2007/05
  • Toward 100 Mfps: an Innovative Ultra-High-Speed Video Camera  [Not invited]
    秋濃 俊郎; 江藤 剛治; 竹原 幸生; 西 謙二
    映像情報メディア学会  2007/01  東京  映像情報メディア学会
     
    2001年に筆者らは、各画素が斜行直線CCD型メモリーを備える画素周辺記録型撮像素子(ISIS)を用いて100 万枚/秒で100枚以上の連続画像を撮影することができる超高速ビデオカメラを開発した。現在さらに1億枚/秒の撮影速度の実現を目指して基礎的検討を行っている。現時点における検討結果を報告する。(1) 1億枚/秒の撮影速度を達成する上で予想される様々の技術的課題を示した。(2) 画素レベルでの超高速撮影技術を提案した。曲線設計の積極的活用により、理論的には3億枚/秒を達成することが可能であることを示した。(3) 熱の発生は1億枚/秒を達成する上での制限要因とはならないことを示した。(4) 制限要因は駆動電源と駆動電圧の撮像素子の受光面中央部への送付技術である。これらの問題を解決するには、全く新しい概念のCCD駆動用ICの開発と、このICとISISのSystem-in-Packageとしての一体化技術の開発が必要である。
  • 実測表面流速データと数値解析を組み合わせた3次元流速分布推定法の基礎的研究  [Not invited]
    竹原 幸生; 江藤 剛治; 髙野 保英; 中井 和樹; 中井 亮; 中山 昭彦; 久末 信幸; 中村
    土木学会第60回年次学術講演会  2005/09  土木学会第60回年次学術講演会
  • PTV Measurements of Flow in Porous Medea by Using Refractivity Matching  [Not invited]
    竹原 幸生; 江藤 剛治; 髙野 保英; 田中健司; 重松孝昌
    The 7th Asian Symposium on Vsualization, 2003（シンガポール）  2003/11  The 7th Asian Symposium on Vsualization, 2003（シンガポール）
     
    多孔体中の流れ場を、屈折率整合法とPTV により計測した。
  • 土木学会第58回年次学術講演会  [Not invited]
    竹原 幸生; 江藤 剛治; 髙野 保英; 辻本 剛三; 水谷 夏樹
    2003/09
  • Simultaneous measurement of air and water flows at a wavy water surface generated by wind  [Not invited]
    竹原 幸生; 江藤 剛治; 髙野 保英; 真木正弘
    土木学会第57回年次学術講演会（札幌）  2002/09  土木学会第57回年次学術講演会（札幌）
     
    水表面を通した運動量や物質の輸送現象の解明を目的とし、水表面近傍の気体、および水の流れ場をPTV（Particle Tracking Velocometry）により同時画像計測した。

MISC

Awards & Honors

  • 2020/05 可視化情報学会 令和2年度 技術賞
  • 2017/11 High Speed Imaging Award
     
    受賞者: 竹原 幸生
  • 平成8年度 可視情報学会賞 技術賞
     JPN
  • 土木学会 平成22年度土木学会論文賞
     
    受賞者: 竹原 幸生
  • 平成18年度グッドプレゼンテーション賞（可視化情報学会）
  • Gallery of Fluid Motion 賞（アメリカ物理学会）
  • 平成１１年度可視化情報学会功労賞（可視化情報学会）

Research Grants & Projects

  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2022/04 -2025/03 
    Author : 高木 力; 鳥澤 眞介; 竹原 幸生
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2021/04 -2024/03 
    Author : 竹原 幸生; 江藤 剛治
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2020/04 -2023/03 
    Author : 鳥澤 眞介; 竹原 幸生; 高木 力
     
    賢く獲る漁業技術の開発が近年求められているが，生産手段の最適化は対象生物(魚類)の行動特性の理解なしには実現できない。したがって，魚類の群行動についての基本的理解とそのための研究は不可欠である。 本研究では，魚類が群れを形成する意味を物理的側面からアプローチすることにより，その本質的意義の解明を目指す。背景となる力学的論理基盤から群を形成したことによる移動エネルギーコストの利得が単一個体よりどの程度のアドバンテージとなり，魚群の規模によりどのような差がでるのか明らかにすることを試みている。 PTV（流体可視化計測）実験では，マアジを対象種として3尾で形成される魚群を回流水槽で巡航遊泳させるケースと実際のマアジと翼形状の魚体模型を用いて魚群のように遊泳させるケースについて，魚体後流域の流況可視化実験を2種類のレーザー光源と高速カメラを用いて実施した。当該実験で撮影した画像から流況を明かにするために，魚体後流域の流速ベクトルや渦度分布の解析および圧力分布の算定を現在実施中である。 CFD（数値流体力学）解析実験では，ビワマスを対象種としてデジタルビデオカメラで撮影した遊泳運動から魚体の遊泳運動関数を算定した後，魚群を形成する3個体の魚体モデルに遊泳運動を与えて群泳を再現し，数値流体力学解析により魚体モデルに作用する圧力とその分布を算出することで流体力学的効果を求めた。個体間の距離を全長の0.4倍から2.0倍まで変化させながら様々な配置で3個体の魚群を形成させた結果，単体で遊泳した場合と推進効率が変わらない配置と推進効率が10%程度向上する配置があることが分かった。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2019/04 -2022/03 
    Author : Shigematsu Takaaki
     
    It is found through a series of experiments for low-porosity porous media that the aspect ratio of the constituents of the porous media has a significant influence on the permeability test results and that the pore shape and its connectivity affect the hydraulic phenomena, which have been difficult to evaluate so far. In order to evaluate such phenomena more quantitatively, the boundary condition module of the Immersed Boundary Method was newly incorporated and validated by comparing the results with those of hydraulic experiments. In the case of high-porosity porous media, experiments on the migration characteristics of particulate suspensions using microfluidic channels revealed that the spreading of particulates is enhanced or inhibited by the coarse and dense structure of the pores, and that hydrodynamic diffusion can be expressed in a probabilistic manner.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2018/04 -2022/03 
    Author : 高木 力; 竹原 幸生; 鳥澤 眞介; 阿部 孝司; 米山 和良; 井口 信和
     
    生産物が水面下にある魚類養殖では，生産管理や成育状態を日常的に把握することが困難となっている。そのため，きめ細かい生産管理や効果的な養殖技術開発のためにICT導入による高度化が強く求められている。本研究では魚類養殖の成育・生産を効率化するシステムの構築を目指して，非接触で生簀内養殖魚の収容尾数や，成育状態を計測する基盤技術開発に取り組む。 【個体数計数システムの開発】養殖クロマグロを対象として遊泳する養殖魚魚群をワイドコンバージョンレンズを装着した小型民生品カメラを用いて20m直径の大型生簀内のほぼ全景を捉えることができた。セマンティックセグメンテーション（画像内の全画素にラベルやカテゴリを関連付ける深層学習アルゴリズム）を適用して個体画像を識別したところ，およそ5000枚の教師画像データデータセットを個体画像と背景画像の比率7:3で学習させることにより80%の検出性能を出すことができたが，システムのロバスト性を向上させるためには，個体を移動追跡するアルゴリズムを見直し，実海域での個体同士の重なりや懸濁物等のノイズ等の識別を確実化することが求められことがわかった。 【行動計測による養殖魚状態評価技術開発】個体計数システムの開発では，連続する画像間での同一個体の移動ベクトルをKC法を適用することにより推定することが可能となる。このベクトルの状態を分析することにより，養殖環境や適切な給餌量を評価することが実現できる可能性がある。そこで，連続する移動ベクトルのノルム差D，交差角θ，渦度に類似した指標ωの評価指標を算出し，養成環境の違いがこれらの指標に差をもたらすか分析した。給餌時と非給餌時では，θの値で有意な差が確認され，台風接近による風浪の激しい環境では，ノルム差やωの値に有意な差が現れた。養殖魚の飽食度合いや，波浪によるストレス度合をこれらの指標により評価できることが示唆された。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2018/04 -2021/03 
    Author : Takehara Kohsei
     
    K. Takehara is conducting researches on transfer processes through a sea surface. This paper targets development of a measurement technology of air pressure on a wavy surface with a PSP (pressure sensitive paint). K. Nakakita has developed PSP technologies to measure distributions of air pressure on aerofoils. T. G. Etoh has updated the world highest frame rate of high-speed cameras. These researchers in different scientific fields collaborate for evolution of the PSP measurement technologies. For a relative wind speed of about 250 m/s at which airliners fly, the PSP technology has progressed in this project to be able to measure the spatiotemporal distribution of the air pressure on a deforming aerofoil. However, for a wind speed about 30m/s, the air pressure deviation is not large enough to be measured only by the PSP measurement. Advanced technologies such as a simultaneous measurement of pressure and temperature to modify the pressure data have to be further developed.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2016/04 -2019/03 
    Author : Shigematsu Takaaki
     
    First, quantitative evaluation of the complex three-dimensional pore structure of the porous body was attempted using the X-ray Computed Tomography technique. Some new findings were obtained about the qualitative influence of the aspect ratio and shape of the component of the porous media. The same technique was applied to the measurement of the pore structure of porous concrete. It was found that the size of the coarse aggregate and volume ration of the coarse aggregate to the paste effected on the porosity and hydraulic conductivity of the porous media. Next, in order to be able to calculate the flow through the pore of the porous media with complicated shape, the boundary condition setting method of the Immersed Boundary Method was examined, and the influence of the pore shape on the porous media flow was examined. It was clarified that the effect of the pore size on the force acting on the component of porous media and on the pressure drop through the porous media.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2015/04 -2018/03 
    Author : TAKEHARA Kohsei
     
    (1) A Lifetime (LT) PSP measurement of the areal pressure distribution on a solid wing model under a periodic up-and-down motion was developed with multiple illuminations and the signal accumulation method. (2) Furthermore, the pressure distribution on a flexible wing under a high-speed air flow of Mach 0.89 was successively and successfully imaged with the LT-PSP method. (3) An image sensor operating at the time interval of 10 ns with ten consecutive frames was developed. The sensor successfully captured "The Light-in-Flight image" for the first time in the world as an silicon image sensor. (4) A pressure measurement on a small wavy model under a low speed air flow, such as 10 m/s, was tested. The PSP intensity method captured a general tendency of the pressure distribution in the flow direction.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2015/04 -2017/03 
    Author : KIMURA Nobuo; KOMEYAMA Kazuyoshi; TORISAWA Shinsuke; HIRAISHI Tomonori
     
    To develop the fundamental technique of counting number of fish individuals in an aquaculture cage, the basic algorithm for counting individuals was constructed by applying PTV (Particle Tracking Velocimetry) technique. The region above a certain area and brightness was defined as the candidate region of an individual. The movement vectors of the extracted regions were estimated by using Kalman filter, and the number of the vectors was possible to give that of individuals. When 200 individuals were put in an experimental tank, applying the algorithm showed that the averaged error was 5.9% and its availability was confirmed.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2014/04 -2017/03 
    Author : FUMOTO Takayuki
     
    In previous studies, the expand or shrinkage displacement in the concrete specimen was estimated with the theoretical models or 2-dimensional image correlation methods. To understand the practical internal displacement in concrete, we have developed the new X ray computed tomography apparatus and propose the measurement methods with the 3-dimensional image and the particle tracking velocimetry method. In this study, for the development of the proposal measurement methods, the tracer for the displacements is selected, fundamental measurement techniques are developed and the developed measurement method is applied for the internal displacements of concrete specimens. As the results, it is clarified that the best marker was the zirconia ball and the coordinate transformation decreased the mechanical errors of 3-dimensional images. We can to measure the internal displacements of the concrete specimen with the error of approximately 270u with the method proposed in this study.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2013/04 -2015/03 
    Author : ETOH TAKEHARU; DAO Vu Truong Son; TAKEHARA Kohsei
     
    The target is development of an image sensor with the highest frame rate of 1 Gfps and the photon detection sensitivity. The achievements in the two-year project period are as follows: (1) Device structure: a 3D-stacked image sensor with a sensor chip and a driver chip both with innovative structures, (2) Simulation results on the highest frame rate: 6 Gfps (the frame interval of 160 ps) can be achieved, (3) Evaluation of the test devices: the driver chip achieved the frame interval of 1 ns (the frame rate of 1 Gfps); the sensor chip was damaged in the process, which is now under re-process. Since the sensor chip is made with a CCD structure, it can achieve several-photon detectable sensitivity with deep cooling.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2010/04 -2014/03 
    Author : OKINAKA Tomoo; TAKEHARA Kousei
     
    To study the unstable crack growth mechanism under compressive loading, the experiment of two dimensional crack growth under uni-axial compression, the experiment and numerical simulation of three dimensional inner crack growth has been performed. Image analysis with ultra-high-speed camera is applied to the two dimensional unstable crack growth under quasi-static uniaxial compression. Stress field around the moving crack tip is visualized by means of photo-elastic technique and images of growing cracks and the stress field are captured with the frame rate of 250,000 fps. As a result, it is revealed that the crack growth is affected by the stress wave travelling the specimen. Image analysis with ultra-high speed camera is also applied to the three dimensional inner crack growth, and the growth is visualized successfully. Numerical analysis with PDS-FEM technique is applied to the three dimensional inner crack growth, and the result shows a good agreement with the experimental result.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2011 -2012 
    Author : TAKEHARA Kohsei
     
    To measure velocity distributions around a microbe, the three dimensional Particle Tracking Velocimetry (3D PTV) with a Differential interference contrast (DIC) microscope has been developed. In this method, the properties of out-of-focus image of particle are used for estimation of distance from particle to focal plane. In the out-of-focus image of particle, a ring like image is generated around the center of the particle image and the diameter of the ring like image increases with the distance from the particle to focus plane. Experimental results show that the diameter of the ring like image is proportional to the distance from a particle to the focal plane. The proposed method has been applied to measurements of the Brownian motion of a particle in water. The Results show a good agreement with the theoretical prediction.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2008 -2010 
    Author : TAKEHARA Kohsei; ETOH Takeharu; SUZUKI Naoya; TAKANO Yasuhide; MORI Nobuhito; MIZUTANI Natsuki; THORODDSEN Sigurdur T.
     
    In order to understand the mechanism of gas-transfer at wind waves with whitecaps, a PTV measurement technique was developed to measure flow fields under wind wave. The measurement technique was applied to flow field under white-cap which occurred by wind wave braking. The properties of air flows over wind waves and bubbles which generated by wave breaking were also measured by image processing techniques. In addition, global CO_2 exchange between air-sea by breaking waves was estimated by the field measurement data and satellite data.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2006 -2009 
    Author : OKINAKA Tomoo; TAKEHARA Kousei
     
    Unstable crack growth under the quasi-static loading condition is studied experimentally and numerically. Images of the crack growth and the stress distribution around the growing crack tip, which is visualized by using photo-elastic technique, are successfully captured by the ultra-high-speed video camera with the frame rate of 1Mfps. Next, numerical algorithm to simulate the unstable crack growth is proposed in this work. The simulation result shows a good agreement with the experimental result, and it is shown that the proposed algorithm has the sufficient accuracy.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2007 -2008 
    Author : MORI Nobuhito; WATANABE Yasunori; TAKEHARA Kousei
     
    沿岸域の砕波帯などで見られる水面波の砕波は, 時空間的に非定常かつ高速にマイクロスケールからセンチメートルスケールに渡る大きさの気泡や飛沫を多数発生させる. このような砕波により生成される気泡および飛沫を計測する手法を開発した. これを用いて, 砕波帯における気泡の計測を行い, 沿岸部における気泡の大きさや個数について調べ, 波浪条件との関係を明らかにした.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2003 -2005 
    Author : WELLS John C.; EGASHIRA Shinji; SUGIYAMA Susumu; OGAMI Yoshifumi; KAJISHIMA Takeo; TAKEHARA Kosei
     
    To contribute to research on simulation of wall turbulence, the present research project has developed relevant measurement technology, and has proposed a hybrid LES-RANS wall-stress modeling technique and a new fictitious-domain method for simulating turbulent flow with highly concentrated dispersed particles. Concerning measurement technique, we have developed Stereo PIV (Particle Image Velocimetry) as applied to an open water-channel. First, we pointed out some simple but new aspects of camera calibration. Next, we proposed a new image-processing Technique to directly measure the rate of shear at a wall, both as seen by a single camera, and as reconstructed in 3D from two camera views. This "PIV/Interface Gradiometry" technique was successfully applied to experimental images from a sinusoidal wall. Such basic contributions will facilitate application of (stereo) PIV to regions near possibly complex boundaries. To allow numerical simulation of solid-liquid two-phase flow near a sediment bed, we extended Kajishima's fictitious-domain technique to handle cases of high particle concentration. Tests on "closed" and "open" rotating drums, partially filled with glass beads, gave good agreements on bed angles and other important parameters. Following these tests, we considered a biperiodic "minimal" turbulent channel containing 1500 spherical beads. Parameters were adjusted to yield particle Reynolds number around 15, and nondimensional shear stress (Shields parameter) in the range 0.06 1.1. Over this range, results for sediment flux agreed to within 20% with the prediction of the Meyer-Peter Mueller equation. To contribute to the unresolved theoretical issues related to LES over a boundary of complex shape, the PI has also derived an equation for the pressure drag on a "patch" of wall in terms of the advection of vorticity nearby.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2003 -2005 
    Author : TAKEHARA Kohsei; ETOH Takeharu; TAKANO Yasuhide
     
    Gas transfer at sea surfaces is strongly dominated by disturbances close to the surface. White cap, which appear on the ocean surfaces when wind waves are breaking, is one of the most important processes in the gas transfer mechanisms. In the white caps, many bubbles are entrained into sea water and some of them are lifted up to surface. The bubbles at sea surfaces eventually burst and generate many small droplets. Similarly, some of the droplet fall down to sea surface again. This bubble-droplet chain process was experimentally investigated in this research. A high-speed video camera, of which frame rate is 1,000,000 fps, was developed at Kinki University in 2001. The high-speed video camera is a powerful tool for investigation of the gas transfer at sea surface. In this research, this high-speed video camera was applied to visualization of the fundamental processes of the bubble-droplets chain process. The following processes are picked up as the fundamental processes. (1)Air entrapment under an impacting drop (2)Coalescence speed of two drops (3)Coalescence speed of two bubbles (4)Crown-breakup by the formation of Marangoni holes And also the simultaneous plane measurement techniques of air and water flows close to wind wave interfaces was developed by using a Particle Tracking Velocimetry, which was developed at Kinki University.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2003 -2005 
    Author : SHIGEMATSU Takaaki; TAKEHARA Kohsei; WATANABE Yasunori
     
    The aim of this study is to develop a measurement technique for understanding three dimensional turbulence structures in liquid-solid flows. This study is composed of two processes ; one is for improvement of Super Resolution PIV developed by Takehara on time resolution and the other is for improvement of 3-D stereo PIV developed by Watanabe on space resolution. Although the super resolution PIV can measure the flow field with high space resolution by using many particle tracers for visualization, it did not have enough time resolution because we did not have enough capturing system. This problem was overcome by purchasing a high-speed video system with high resolution and wide range with great help of this scientific research fund. By using this high-speed video system the images of flow fields inside and in the vicinity of a porous body were captured. And generation and decay mechanisms of turbulence flow inside the porous body and in the downstream region have been studied in detail. Although the 3-D stereo PIV can measure the three dimensional flow structures, it needed a great investment of time to analyze if many particle tracers were seeded in fluid. This problem was overcome by improving calculation algorism. As a result the 3-D stereo PIV was reconstructed as a PIV system with high space resolution. The improved 3-Dstereo PIV was applied to a multi-phase flow under the breaking zone. It has been found that the improved 3-D stereo PIV is a useful tool for measurement of complex fluid flow and sediment motion under breaking waves. Furthermore, a new image velocimetry, called "path line connecting velocimetry", has been developed for measurement of the liquid-solid flows with high speed fluid motion and strong turbulence with three dimensional structure. The "path line connecting velocimetry" has been applied to the measurement of the flow field induced by particle motion. As a result, it was shown that the path line connecting velocimetry is a very useful tool for measurement of multi-phase flows including particles with high concentration and water surface.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2003 -2005 
    Author : DEGUCHI Ichiro; TAKEHARA Kousei; ARAKI Susumu
     
    More than 100 lives were lost by accidents during swimming in the sea every year. It is reported that large part of the accidents were caused by the rip current. If we can predict the occurrence of rip current in advance, it is possible to reduce number of accident through the warning system. However, a certain kind of rip current suddenly. comes in to existence in a very narrow region and its lifetime is not so long. It is generally impossible to predict the occurrence of this kind of rip current. It is needless to say that this kind of rip current is extremely dangerous for swimmers. At the same time, rip current becomes transporting agency of bed material in the very shallow water region towards offshore. The aim of this study is to develop a rip current observation system by using local remote sensing from the balloon and to investigate the occurrence condition of rip currents. Surface displacement measuring system by stereo-camera images and bottom topography measuring system using K-GPS are also developed. Almost all patterns of orographic rip currents reported until now can be recorded in the field observations. Some of the measured flow patterns are reproduced by the numerical simulations of wave fields and wave induced current on the measured bottom topography by K-GPS. Measuring systems of mesoscale bottom topography and wave field are also developed and verified through the field observations. These results surely set up effective procedures for measuring wave fields and wave induced current in very shallow water regions.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2002 -2004 
    Author : ETOH Takeharu; TAKEHARA Kohsei; NAKAGUCHI Yuzuru; KAJII Hironobou; TAKANO Yasuhide
     
    A.Development of Application Technologies of PTV to Natural Water Bodies (1)An efficient technology was developed to detect tracer particles for PTV on surfaces of natural water bodies, such as rivers, lakes, etc. The tracers can be separated by a combination of discriminant analysis of color images and duration analysis, which removes candidates of tracer particle images disappearing within two seconds. (2)The technology was applied to measurement of the surface flow field of Yodo river, etc. The flow field was also measured with ADCP (Acoustic Doppler Current Profiler) carried by a boat. The results nicely agreed with each other. (3)A technique for simultaneous measurement of wave and flow under wind waves was developed. (4)In parallel, seasonal variations of chemical components in Yodo river were measured, especially on Nitrogen and Phosphor. B.Development of Air Samplers Carried along a Tether of a Balloon and/or a Kite (1)Air samplers attached to a tether of a balloon was developed. Several samplers can be attached to a tether to collect air samples at various heights. (2)In a weak-wind condition, the samplers were tested. A dust dome was detected as expected, which showed the maximum concentration of dusts at about 50m from the ground, and less concentration at the ground and at 100m. The dust dome was also visualized by a camera mounted on the balloon. C.Relevant Research Contributions An infrared video camera was introduced by the financial support of this project. The camera was applied to other researches relating to infrared image analyses, resulting in the following contributions : (1)Application of infrared video cameras to reduce traffic accidents at the corners and intersections of roads in night. (2)Applications to various research projects on temperature environment around human bodies.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2002 -2003 
    Author : TSUJIMOTO Gozo; NAKAO Kohichi; KAKINOKI Tetsuya; SHIGEMATSU Takaaki; TAKEHARA Kohsei; HOSOYAMADA Tokuzo
     
    To obtain some information to reproduce the disappearing seagrass field in the sea area, the laboratory experiment and the field observation have been conducted. The suspended sediment concentration among model seagrasses has been measured by using image technique. The distribution of suspended sediment and the grain size could be measured simultaneously. It turned out that the particle size was bigger than medium grain size at the beginning of its movement, the particle of a central particle size moved with the increasing of time. To consider the effect of the movement object into the numerical simulation, the wrapping judgment method was used. A measuring method of fluid motion inside and in the vicinity of porous media of silicon spheres is presented. Sodium iodide solution is used as the refraction index matching fluid. In order to capture pictures, a resolution PIV method Some experimental results on the velocity field and turbulence kinemaatic energy are presented. Structure of the flow field inside and in the vicinity of the porous media is discussed. Moreover generation and dissipation mechanism of the turbulence was discussed. A field observation has been executed over the seagrass field formed at Eigashima beach in Akeshi City. There were a lot of died seagrass because the growing thickly period had been passed at time. There are clear correlations in PH and DO, and it is thought the influence of the photosynthesis in daytime. Moreover, the decrease at flow velocity was observed by the influence of the marine forest in the bottom of the sea neighborhood
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2001 -2002 
    Author : WELLS John C.; 梶島 岳夫; 杉山 進; 江頭 進治; 山本 恭史; 竹原 幸生
     
    本研究は、流砂のマイクロメカニクスを解明するに当たり、次の三つの課題に焦点を絞り、これらを推進している。 (1)乱流と粒子運動のシミュレーション法の開発・検証、(2)force-momentマイクロセンサの開発・検証、(3)流砂の微視的挙動の解明。 課題(1)では、流水中の粒子間接触力に関する合理的なモデルを導入する必要がある。そのため、沈降する球形粒子とステンレス版の水中反発係数を測定し、それが表面粗さによって弱まることがわかった。また、同じ実験材料を用いて空気中の反発係数を測定した結果、粗さの影響は水中と同程度であった。したがって、衝突中接触している凹凸の間の液体の粘性よりも、凹凸の塑性変形などに伴う散逸が支配的であることが結論となる。DNSに関する梶島の手法に対しては、粒子の加逮度を正しく計算するような計算法を提案している。 課題(2)においては、水路床の粒子に働く力およびモーメントのすべての成分を測定できるピエゾ抵抗型マイクロセンサを開水路床に設置し、再現性のある信号を得た。また、センサーチップの設計を改善した結果、S/Nのより高い装置を実現できた。 課題(3)に関しては、滑面開水路における等流乱流の数値シミュレーションを行い、河床に設置した半球に働く流体力を梶島法で計算した結果、抗力と揚力の相関が非常に高く、また、それらと周りの主流速度成分の相関が高いことがわかった。また、縦渦の高さより小さい粒子(d+=12)に働く流体力の統計特性は大きい粒子と比べて随分違うことを明らかにした。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2000 -2002 
    Author : KAKUNO Shohachi; ASAI Kouji; ETOH Goji; SUGIHARA Yuji; TAKEHARA Kosei; YOSHIOKA Hiroshi
     
    A dual-tip void probe was developed as a extension of standard single void probe. The validity of dual-tip void probe was verified and applied to bubble characteristics induced by breaking wave in the mechanically generated wave in the flume. The amount of gas transfer flowing rate instead of traditional gas transfer velocity was proposed to estimate the gas transfer rate in the surf zone, quantitatively (Kakuno, Shigematsu and Hosoi). The characteristics of turbulence in bubbly flows were measured and analyzed in the experimental facility (Asai). The droplet collision into the water surface was measured using 1 million frame per second ultra-high speed camera. The instability of thin gas film between droplet and water surface shows clear Reynolds number and Weber number dependence (Etoh). The relationship between the surface renewal process and micro scale turbulence has been measured by Particle Image Velocimetry and Laser Induced Fluorescence in a lattice turbulence (Sugihara). The simultaneous visualizations of air and water velocities were conducted in the wind-wave flume. The organized motion of air and water flows were measured and the bursting motions of air flow into the water were observed visually (Takehara, Etoh, Shigematsu and Tsujimoto). The bubble diameter distribution and bubble source functions were measured using Phase-Doppler anemometry in the wind-wave flume. The coherent bubble diameter spectra were measured under the wind-wave breaking (Mori). The field observations of bubble distributions under the wind-wave breaking were investigated using ultra sonic sensor at the upper ocean (Yoshioka). The gas transfer model at the breaking wave interface was proposed as a summary of above results (Moog).
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1999 -2002 
    Author : IWATA Koichiro; TAKEHARA Kohsei; NOCHINO Masao; ETOH Takeharu; SUMI Hirokazu; KAWASAKI Koji; IWATA Koichiro
     
    This research aims to develop a new ultra-high speed video-camera to measure the wave breaking inception and formation and collapsing of air bubbles at the air-water interface as accurately as possible and to investigate the breaking wave-caused turbulence by means of laboratory experiments and numerical calculation. Main results obtained are as follows : (1) An In-situ Storage Image Sensor (ISIS) of 1,000,000 fps with linear Charge Coupled Device (CCD) has been newly developed and an ultra-high speed video-camera of 1,000,000 fps with high sensitivity has been successfully manufactured for the fist time in the world. (2) Kalman filtering and Chi-square Method (KC Method) has been much improved to trace the water particle motion after wave breaking. Using the new ultra-high speed video-camera (l,000,000 fps) and the improved KC Method, air bubble formation and collapsing process are filmed with very high accuracy for the first time in the world. The effect of viscosity and surface tension to the air bubble formation and collapsing are investigated. (3) Surface tension waves are formed on the front surface of wave and are grown up. The front water surface is broken by the air-wrapping effect of the grown critical surface tension wave and air bubbles are introduced in the water body. (4) FFT method and discrete wavelet analyses have revealed that high frequency components of water pressure rapidly increase after formation of air bubbles and that the sound wave is generated by the motion of air bubbles in water. (5) The sound wave pressure decays inverse proportional to the distance from air bubble formation point and its magnitude is well estimated theoretically with the theory of spherical wave propagation. (6) 3-dimensional numerical computation method DOLFIN has been newly developed, by extending CIP and SMAC methods, to evaluate the solid-water-air combined flow.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2000 -2001 
    Author : 江藤 剛治; 沖中 知雄; 甲藤 正人; 竹原 幸生
     
    1.00万枚/秒の高速ビデオカメラの開発 100万枚/秒の超高速ビデオカメラの開発に成功した。これは主として別予算を用いて開発したものであるが、レーザー・マーキングPTVにとっても必須の計測機器である。 2.高速ビデオカメラとホログラム・レーザー・ビームを用いた表面張力測定手法の開発 ホログラムを用いて、多数のレーザー・ビームを発生する方法を実際の計測に適用した。 通常の表面張力測定装置は、細い白金線で作った輪を、水中からゆっくり引き上げ、表面が瞬間的に破壊されて、輪が水面から抜ける瞬間の引っ張り力を測定して表面張力に換算する。 自然界の水面のように、水面に薄い化学物質の膜が形成されているような場合には、この方法による測定は不安定になることは研究代表者らにより指摘されている。すなわち輪が水面をわずかに持ち上げた状態では。輪を成す細線の両側に水面勾配が生じ、それにより、水面が流れ、水面の化学物質の層が薄くなる。 実験水槽の水底から多数の並行レーザー・ビームを水面に向けて照射し、水面上で多数の点として撮影する。中央付近に振動を与え表面張力波を発生させると、水面でのレーザー・ビームの屈折により多数の点像が高速で振動する。これを高速ビデオカメラで撮影し、点像をPTV解析することで、表面張力波の伝播速度や波長を計測することができる。微小振幅表面張力の理論にこれらの値を代入することで表面張力の値を逆算する。純水に対して適用した結果、この方法により、現段階でも誤差10%以内で表面張力を測定できることがわかった。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1999 -2001 
    Author : YAMASHITA Takao; ETOH Takeharu; YAMANE Takeshi; MURATA Osamu; TANAKA Yuji; TAKEHARA Yukio
     
    Disaster Prevention Research Institute(DPRI), Kyoto University has run this research project in partnership with Fisheries Laboratory of Kinki University (FISH LABO) and Shirahama Fisherman's Association to predict red tide in the Tanabe Bay. DPRI has monitoring facilities for sea states and FISH LABO has fish farming facilities in the same bay. Collaboration between these research institutes and the fishermen's society in the Tanabe Bay established a red tide prediction system as well as water quality, water circulation system and ecosystem monitoring, in this project. The followings are the main results and activities of the project. (1)Water Exchange Prediction Model : Quasi-three-dimensional numerical model for water circulation in the bay was constructed with improving POM code, where scalar transport equations were solved with TVD scheme in z-coordinates and current dynamics equations were integrated in sigma-coordinate. (2)Water Quality and Plankton Blooming : Intensive observations of plankton cells and physical, chemical and biological water qualities in summer were conducted for four years 1998-2001 by using the telemetry of Storm Surge Observation Tower and fish farming rafts. Profile measurements of water qualities and plankton cells were also conducted by observation ship in whole area of the bay. (3)A real time prediction system of phytoplankton density in the inner part of the Tanabe Bay was established with combination of coastal environmental telemetry and artificial neural network (ANN). The used learning system is the back-propagation model. Observation data and output data (cell concentration of diatoms and dinoflagellates) in 1999 and 2000 was employed for a learning of ANN. Prediction in 2001 made clear that input data of temperature, salinity, solar radiation and air temperature (dissolved oxygen) are included, the prediction system is improved. (4)All data measured in this project can be distributed with CD-ROM.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1999 -2000 
    Author : 竹原 幸生
     
    水域の環境を考える上で、酸素や二酸化炭素等の溶存気体量を精度よく評価、予測することが必要である。海洋や湖などにおいて水表面を通した気体輸送は、主に風応力が水表面に作用し、表面が乱されることにより促進される。これまでの研究では専ら上空の風速とバルクな溶存気体量から、気体輸送係数を求めており、直接風速と気体輸送係数を関係付けている。しかし、現地計測の気体輸送係数の結果は、風速に対して大きくばらつく。気体輸送量をより正確に評価、予測するには、水表面での気体輸送機構を理解する必要がある。 本研究では、以下の技術について開発を行った。 (1)水表面を通した二酸化炭素の溶入過程の直接可視化法の開発 蛍光強度のpH依存性を利用して、二酸化炭素の溶入過程の直接可視化法を開発した。水溶性の蛍光染料(ウラニン)がpH6以上では蛍光強度が変化せず、pH6以下では、pHの減少とともに蛍光強度が急激に減少減少する。この特性を利用して、アルゴンイオンレーサーを励起光として、LIF(Laser Induced Fluorescence)法により、風波発生時の二酸化炭素溶入過程の可視化に成功した。 (2)微小水滴をトレーサーとした気体PTVの開発 気流のPTV用トレーサーとして一般的に、微小油滴が用いられる。しかし、水表面での気体輸送現象を目的とした場合、水表面に油膜を作ってしまうため問題となる。本研究では、医療用ネブライザーを用いた微小水滴発生装置を試作し、PTVが可能であることを示した。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1998 -1999 
    Author : KAKUNO Shohachi; SUGIHARA Yuji; ETOH Goji; ASAI Koji; HOSOI Yoshihiko; NAKAMURA Yoshiyuki
     
    ・By visualizing breaker image taken by a special video camera, the relation between bubble characteristics and wave characteristic in the breaker zone was analyzed. ・The model formula of gas transfer velocity taking the effect of the entrained bubble in the breaker zone was proposed. ・An image analysis technology with high-accuracy for measurement of the flow field in the breaker zone was developed. ・Applying the laser induced fluorescence, the visualization of the entrainemnet process of CO_2 gas into the water-phase was succeeded. ・It was found that the penetration depth of entrained bubbles of the plunging breakers is deeper than that of the spilling breakers. ・It was found that the swell in the wind-waves promotes the gas transfer and that the effect of it becomes big as the wave period becomes shorter. ・Gas transfer velocity at the water surface under the condition of the vibrating grating turbulent flow field was evaluated. The velocity was found to be controlled by the Large Eddy Model. ・Distribution and change of CO_2 and N_2O on the subtropical equator of the Pacific Ocean were clarified. ・The modeling of the gas exchange process for the bubbles entrained in the breaker zone was made, and the validity was verified from an experiment under the condition of a single bubble. ・It was succeeded to visualize the entrainmenet process of bubbles into water by the breakers from the results of bubble observation in the field using ultrasonic wave and video image shot simultaneously. ・State of the art on the studies of air-water gas transfer phenomenon was investigated through the literature.
  • ローカルリモートセンシング技術の開発
    Date (from‐to) : 1999
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1996 -1997 
    Author : 江藤 剛治; 竹原 幸正
     
    粒子画像追跡法による流れ場計測においては,ビデオ画像等から流れの中のトレーサー粒子画像を抽出し,これを電子計算機上で自動追跡する。このとき動画像上では,肉眼で明らかに粒子と認識できるのに,画像を静止させると識別できなくなる粒子が或る。肉眼で認識できない粒子画像は電子計算機による画像解析によって抽出することはできない。そもそも現在の画像解析手法は、(1)静止した,(2)2次元の,(3)モノクロ画像の解析を積み上げる方式である。人間は,(1)動的で,(2)立体的な,(3)カラー画像を直接認識している。上述の静止画像上で粒子が消え去る現象は,主として,動的認識能力が行使できないからであると考えられる。 粒子画像は最も単純な形状であり,人間の動的認識に関する研究の材料として最適である。本研究では次の2つの方針で研究を進めている。 (1)粒子画像による人間の動的認識に関する研究 (2)動的認識に関する知見の粒子画像抽出アルゴリズムへの応用 本年度は次の研究成果を得た。 (1)動的認識に関する研究:粒子画像生成アルゴリズムと眼球画像自動解析装置を開発した。 (2)粒子画像抽出アルゴリズム:著者らの開発した粒子マスク法を,多時刻にわたって蓄積された画像情報を移動させながら積分した画像した画像情報に適用することを試みた。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1996 -1996 
    Author : 竹原 幸生
     
    自然界における水表面を通した気体輸送過程を規定する素過程のうち,水滴の水表面衝突および気泡の水表面での破裂は非常に重要な要素である。しかも,それらは互いに密接に関連して生じる現象である。例えば,海洋において荒天時に生じた砕破は水中に大量の気泡を取り込み(white cap等),その気泡は水表面で破裂し,大気中に多量の水滴を放出する。放出された水滴のうち,微細なものは大気中に拡散され,大きいサイズの水滴は再び水表面に衝突し,気泡を生じる。本研究ではそれらの相互作用に着目し,基礎的なメカニズムを明らかにするため,可視化技術により現象の観察を行うことを目的とした。 今回は特に液体の表面張力,動粘性を変化させたときに,気泡の崩壊,水滴の発生および水面での水滴の衝突,気泡の取り込みの観察を行った。作業液体としてエタノール水溶液を用いた。エタノール水溶液では濃度が10%と95%のとき,動粘性が0.022cm^2/sec程度とほぼ同じ値となり,表面張力は56.3dyn/cmと25.6dyn/cmとなる。表面張力のみを変化させて実験を行うことができる。また,エタノール水溶液40%と95%では,表面張力30dyn/cm程度とほぼ同じ値となり,動粘性は0.045cm^2/secと0.022cm^2/secと動粘性のみを変化させて実験することもできる。 結果の1例として,崩壊速度スケール(気泡の直径/崩壊にかかる時間と定義)の平均値は,表面張力が小さくなるにつれて大きくなり,動粘性が大きくなるにつれて大きくなる。ただし,崩壊パターンには種々のものがあり,他の要素(崩壊時の気泡の膜厚,膜の振動状態等)が大きく影響しており,ばらつきが大きくなった。その他,崩壊現象に関する詳細な観察を行った。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1995 -1995 
    Author : 竹原 幸生
     
    水表面での気体輸送と流れ場の同時可視化計測を目的として、炭酸ガスの溶入過程の定量可視化計測法の開発,および流れ場の高精度可視化計測法を開発した。 (1)フルオレセイン水溶液の蛍光強度のpH依存性による炭酸ガスの濃度場の可視化法の開発 水中の溶存炭酸ガス濃度と流れ場の同時可視化計測のために,フルオレセイン水溶液の蛍光強度のpH依存性を利用した溶存炭酸ガス濃度可視化計測法を開発した。 (2)光3分割撮影装置の開発 1つのレンズ系から入った画像を1/3,1/2のハーフプリズムを用いて3台のビデオカメラで撮影できる光3分割撮影装置を開発した。各カメラの受光面の前には光学フィルターをセットすることができ,光波長を分割した画像を撮影することができる。 (3)マイクロパーティクルトレーサー粒子の開発 水表面極近傍の流れ場のトレーサー粒子として,数十μmのプラスチック粒子(マイクロパーティクル)の作成法を開発した。 (4)カルマンフィルターとχ^2検定を用いた多数の粒子の自動追跡アルゴリズムの開発 PTV(Particle Tracking Velocimetry)のために,統計,確率学的基礎に基づいたカルマンフィルターとχ^2検定を用いた3次元自動粒子追跡アルゴリズムを開発した。 (5)高精度粒子画像情報抽出法(粒子マスク相関法)の開発 PTVのための高精度粒子画像情報抽出法として、粒子マスク相関法を開発した。 開発した可視化手法の適用例として,渦輪を水底より発生させ水表面に衝突させた場合の炭酸ガスの溶入過程の可視化を行った。また,比重0.95のマイクロパーティクルによる水表面の水中への取り込み過程を可視化した。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1994 -1995 
    Author : ETOH Takeharu; TAKEHARA Kohsei
     
    In experimental studies of motion of fluids by means of optical measurement, flow behind an immersed solid body can not be visualized. If the body is transparent and the refractive index is equal to that of the fluid, light from the back of the body goes straight through it into optical sensors such as a photodiode, a CCD videocamera, etc. Refractive index of water is 1.33 and that of pure silica glass is 1.48, which is lowest among those of usual glasses. Some special glasses such as F2Be-glass, which is strongly poisonous, two- or three-phase glasses of FLi, FNa, F2Mg, F2Ca and F3A1, which are difficult to make thicker than 1mm, have refractive indices lower or close to that of water. They, however, cannot be applied to practical use. Addition of some chemicals usually increases the refractive index of water. However, too much chemicals considerably changes other characteristics of water such as density, viscosity, etc. The present study found some preferable combination of additive chemicals and transparent low-refractive materials. The best among them, so far, is the combination of solution of 40%-NaI or KI of water and a low density silicon rubber ; both refractive indices are 1.40. A technology to automatically track moving immersed bodies is also developed. They are applied to measure interaction of motions of water and immersed moving bodies, coupled with high-performance PTV algorithm which have already been developed by the authors.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1992 -1993 
    Author : ETOH Takeharu; TAKEHARA Kohsei; TSUBAKI Takayuki
     
    A light beam passing through a transparent body in water bends by difference in refracitivity indices of water and the material, which restrains use of optical hydrometry such as flow visualization techniques and laser Doppler velocimetry. Mctching refractivity can be realized both by adding a solvant to water to increase the refractivity and by searching or developing lower refractive and highly tranparent materials. Solvants change physical properties of water. Some of them are pollutive when released to public water bodies after experiments. Refractive index of a material depends on temperature, light-wave frequency, etc. This research project presented a list of materials potentially applicable to refractivity matching between water and tranparent bodies with additionabal information to produce, use and treat them.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1992 -1992 
    Author : 竹原 幸生
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1991 -1991 
    Author : 竹原 幸生
  • 水表面での気体輸送
  • 流れの可視化画像計測法の開発
  • Gas transfer at water surfaces
  • Development of methods to measure flow fields by using image processing

Other link

researchmap


Copyright © MEDIA FUSION Co.,Ltd. All rights reserved.