Kazuho Sato

Measurements of 3D flow in a micro-pipe via micro digital holographic particle tracking velocimetry

This paper details high time-resolution flow field measurements in a micro-pipe made by a micro digital holographic particle tracking velocimetry (micro-DHPTV) method. The system consists of an objective lens, a high-speed camera and a single high-frequency double pulsed laser. The volume of the system is 409.6 µm × 92 µm × 92 µm. It is illuminated by a laser beam with a pulse length of 58 ns, a resolution time of 100 µs and a repetition rate of 1 kHz. 104 velocity vectors could be obtained instantaneously in the micro-pipe. Particle positions in the three-dimensional field are reconstructed by a computer-generated hologram. The time evolution of a three-dimensional water flow in a micro-pipe of 92 µm inner diameter is obtained successfully using the micro-DHPTV system. The error of reconstruction in the z-direction is evaluated by analysing the traverse of particles on a glass plate and obtaining the velocity error in the z-direction by uncertainty analysis.

Special purpose computer for digital holographic particle tracking velocimetry

We have designed a special purpose computer system for digital holographic particle tracking velocimetry (DHPTV). We present the pipeline for calculating the intensity of an object from a hologram by fast Fourier transform in an FPGA chip. This system uses four FPGA chips and can make 100 reconstructed images from a 256x256-grid hologram in 266 msec. It is expected that this system will improve the efficiency of analysis in DHPTV.

Parallel computing of a digital hologram and particle searching for microdigital-holographic particle-tracking velocimetry.

We have developed a parallel algorithm for microdigital-holographic particle-tracking velocimetry. The algorithm is used in (1) numerical reconstruction of a particle image computer using a digital hologram, and (2) searching for particles. The numerical reconstruction from the digital hologram makes use of the Fresnel diffraction equation and the FFT (fast Fourier transform), whereas the particle search algorithm looks for local maximum graduation in a reconstruction field represented by a 3D matrix. To achieve high performance computing for both calculations (reconstruction and particle search), two memory partitions are allocated to the 3D matrix. In this matrix, the reconstruction part consists of horizontally placed 2D memory partitions on the x-y plane for the FFT, whereas, the particle search part consists of vertically placed 2D memory partitions set along the z axes. Consequently, the scalability can be obtained for the proportion of processor elements, where the benchmarks are carried out for parallel computation by a SGI Altix machine.

Digital Holographic Particle Tracking Velocimetry for 3-D Transient Flow around an Obstacle in a Narrow Channel

Digital holographic particle tracking velocimetry (PTV) is developed by single high-speed camera and single double pulsed laser with high frequency pulses. This system can directly capture 1000 hologram fringe images for 1 second through a camera computer memory. The 3-D particle location is made of the reconstruction by using a computer hologram algorithm in a personal computer. This system can successfully be applied to instantaneous 3-D velocity measurement in the water flow with a square obstacle, and can obtain an average of 300 instantaneous velocity vectors.

Special purpose computer system for flow visualization using holography technology

We have designed a special purpose computer system for visualizing fluid flow using digital holographic particle tracking velocimetry (DHPTV). This computer contains an Field Programmble Gate Array (FPGA) chip in which a pipeline for calculating the intensity of an object from a hologram by fast Fourier transform is installed. This system can produce 100 reconstructed images from a 1024 x 1024-grid hologram in 3.3 sec. It is expected that this system will contribute to fluid flow analysis.

Measurements of Three-Dimensional Flow in Microchannel With Complex Shape by Micro-Digital-Holographic Particle-Tracking Velocimetry

High time-resolution flow field measurement in two microchannels with a complex shape is performed by a micro-digital-holographic particle-tracking velocimetry (micro-DHPTV). The first microchannel has a Y junction that combines the flow of fluid from two inlets into one outlet. In this case, two laminar velocity profiles from the inlet regions merge into one laminar velocity profile. The second microchannel has a convergence region from where a fluid flows into a divergence region. At this region, two recirculation regions appear. Consequently, approximately 250 velocity vectors in both cases can be obtained instantaneously. For a microchannel with the convergence region, the two recirculation regions that appear at the divergence point are captured from a three-dimensional vector field, with which the axes of recircular vortices have some alignment. The reason why we can observe this phenomenon is that a three-dimensional velocity, including the depth direction, can be obtained by micro-DHPTV.

Special purpose computer system with highly parallel pipelines for flow visualization using holography technology

Abstract We have designed a PC cluster system with special purpose computer boards for visualization of fluid flow using digital holographic particle tracking velocimetry (DHPTV). In this board, there is a Field Programmable Gate Array (FPGA) chip in which is installed a pipeline for calculating the intensity of an object from a hologram by fast Fourier transform (FFT). This cluster system can create 1024 reconstructed images from a 1024 × 1024 -grid hologram in 0.77 s. It is expected that this system will contribute to the analysis of fluid flow using DHPTV.

Study on high speed parallel algorithm using PC grid environment for visualization measurements by Digital Holographic Particle Tracking Velocimetry

Abstract A micro-digital holographic particle tracking velocimetry with high-speed system is constructed by a PC grid environment that employs Windows XP with AD-POWERs as parallel tool. Two algorithms for high-speed system are evaluated under the same PC grid environment. Both methods are based on a computer-generated hologram algorithm. One method is a division algorithm based on time development for the measurements, while the other is a division algorithm based on spatial reconstruction for the measurement. In case of the former, the performance is increased by a factor of 3.3 by using 4 PCs. The present system can compute huge hologram images and output them “on-site” at an experimental facility.

Calibration plate for digital holographic particle tracking velocimetry

A calibration plate for digital holographic particle tracking velocimetry by in-line holography was developed. A quartz plate with a computer-generated hologram pattern is used to determine the distance between an image captured on the plate and a CCD camera to high accuracy. The method allows visual confirmation of the calibration. In addition, the reconstruction of the hologram of a cross marker on plates is demonstrated at distances of 35 mm and 40 mm.

High Performance Computing of Digital-Holographic PTV

We introduce the high performance computing of Digital Holographic PTV. The algorithm is used in (1) the reconstruction of particle by digital hologram for parallel computing and (2) the reconstruction of particle by digital hologram for FPGA and (3) the reconstruction of particle by digital hologram for grid computing. The numerical reconstruction from the digital hologram makes use of the Fresnel diffraction and the FFT. The visualization measurement for micro-flow are shown by these algorithms.