• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.3
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• pp.309-316
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• 2010

In this study, a digital particle holographic system and its application to channel-flow measurements were investigated. A double-exposure hologram recording system that is capable of recording digital holograms in a short time interval was developed. A correlation coefficient method was used to determine the focal plane of particles. The Wiener filter was used to remove noises and improve image quality. Two-threshold and image segmentation methods were used for binary image transformation. The cross-correlation method was used for particle pairing. The developed system was employed to study channel flow fields, and the axial velocities of channel flow were measured. The measurement errors are acceptable, and this proves the feasibility of using the digital particle holographic system as a good tool for flow-field measurements.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.5
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• pp.374-381
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• 2008

The correlation coefficient method, which was proposed by our research group, is applied to digital particle holography to locate the focal plane of particles. It uses the fact that the correlation coefficient is maximum at the focal plane. The factors influencing this method are discussed with a numerical simulation of holograms. For real holograms, the Wiener filter was proposed to process both recorded holograms and reconstructed images. The application results using the dot array target showed that the Wiener filter is a very effective tool for processing holography-related images. The effects of the dot size and the object distance on the errors in the determination of the focal plane by the correlation coefficient method were investigated by using the calibration target.

• Journal of ILASS-Korea
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• v.21 no.2
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• pp.88-94
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• 2016

In this study digital holographic microscopy system for measurements of 3-D velocities of particles in MR fluid is developed. Holograms are recorded using either a CCD camera with a double pulse laser or a high-speed camera with a continuous laser. To process recorded holograms, the correlation coefficient method is used for focal plane determination of particles. To remove noise and improve the quality of holograms and reconstructed images, a Wiener filter is adopted. The two-threshold and image segmentation methods are used for binary image transformation. For particle pairing, the match probability method is adopted. The developed system will be applied to measurements of the characteristics of unsteady 3-D particle velocities in MR fluids through the next stage of this study.

• Journal of ILASS-Korea
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• v.15 no.2
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• pp.53-60
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• 2010

This study presents development of digital particle holographic system and its application to spray field to measure three-dimensional velocities and sizes of spray droplets. A double exposure hologram recording system with synchronization system for time control was established and digital holograms can be recorded in a short time interval. To process recorded holograms, the correlation coefficient method was used for focal plane determination of particles. To remove noises and improve the quality of holograms and reconstructed images, the Wiener filter was adopted. The two-threshold and image segmentation methods were used in binary image transformation. For particle pairing, the match probability method was adopted. The developed system was applied to spray field and three-dimensional velocities and sizes of spray droplets were measured. The measurement results of digital holographic system were compared with those made by laser instruments, PDPA(Phase Doppler Particle Analyzer), which proved the feasibility of in-line digital particle holographic system as a good measurement tool for spray droplets.

• Journal of ILASS-Korea
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• v.18 no.3
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• pp.119-125
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• 2013

Digital holographic particle velocity measurement system can be a promising optical tool for the measurements of three dimensional particle velocities. In this research, validation experiments for the digital holographic particle velocity measurement system were conducted with measuring the velocities of glass beads on a rotating disk. Uncertainty analysis was performed to identify the sources of all relevant errors and to evaluate their magnitudes. The measurement results of particle velocities obtained with digital holographic method are compared reasonably well with the known values within acceptable range of errors. Moreover, digital holographic method showed better performance compared with that of optical holographic system.

• Journal of ILASS-Korea
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• v.12 no.4
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• pp.191-197
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• 2007

This study presents in-line digital particle holography and its application to spray droplets to measure the characteristics of spray droplets. Several important parameters at the time of hologram recording such as the object distance and the region of laser beam used were verified. The correlation coefficient method with important parameters such as the reconstruction interval and the correlation interval was used for determination of the focal planes of particles. The optimal values of all these parameters are obtained by either numerical simulation of holograms or experiments. Using these optimal parameters, double pulse digital spray holograms in a short time interval were recorded with the synchronization system for the time control. The spatial positions of droplets that are used for the evaluation of the three dimensional droplet velocities can be easily located, which proves the feasibility of the digital holographic technology for measurements of several important features of spray droplets.

• Journal of ILASS-Korea
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• v.14 no.2
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• pp.77-83
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• 2009

In this study, the effect of important parameters such as the pixel size and number of a CCD, the object distance, the wavelength of laser, and the particle diameter on the depth of focus in digital in-line particle holography were investigated. The depth of focus in several different cases was calculated using simulation holograms and detailed description of the depth of focus in digital particle holography was presented. The depth of focus is directly proportional to the object distance and the particle size. With the increase of the wavelength of laser, the depth of focus is decreased. The depth of focus is also inversely proportional to the pixel size and number of a CCD. Using the data of depth of focus from simulation holograms and a data-fitting software, we obtained the prediction equations of depth of focus for typical CCD cameras. Finally, the prediction equations of depth of focus in digital particle holography were verified by investigating real holograms of the calibration target in different cases and satisfied agreement between measured values and predicted values was confirmed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.10
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• pp.784-790
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• 2008

The feasibility and the accuracy of the correlation coefficient(CC) method for the determination of particle positions along the optical axis in digital particle holography were verified by alidation experiments. A traverse system with capable of high precision was used to move the particle objects by exact known distances between several different positions. The particle positions along the optical axis were calculated by the CC method and compared with their exact values to obtain the errors of the focal plane determination. The tested particles were 2D dots in a calibration target along with different sized glass beads and droplets that reflected and caused a three-dimensional effect. The results show that the CC method can work well for both the 2D dots and the 3D particles. The effect of other particles on the focal plane determination was also investigated. The CC method can locate the focal plane of particles with a high precision, regardless of the existence of other particles.

• 한국가시화정보학회:학술대회논문집
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• 2007.11a
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• pp.116-118
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• 2007

Three-dimensional (3D) velocity field information of a laminar flow in a curved micro tube of circular cross-section has been measured using a digital micro holographic particle tracking velocimetry (HPTV). The temporal evolution of instantaneous velocity field of a water flow in a curved micro tube of $100\;{\mu}\;m$ and $300\;{\mu}\;m$ in inner diameter was obtained. The 3D mean velocity field distribution was obtained quantitatively by statistical-averaging of instantaneous velocity fields. At low Dean number (De), a secondary flow was not generated in the curved tube. With increasing Dean number, the secondary flow constituted of two large-scale counter-rotating vortices was formed due to enhanced centrifugal force. To reveal the flow characteristics of high Dean numbers, trajectories of fluid particles were evaluated experimentally from the 3D velocity fields data measured by the HPTV technique. The present experimental results, especially the 3D particle trajectories, would be helpful to design and to understand the mixing phenomena in 3D curved passages of various curved micro-tubes or micro-channels.

• Journal of the Korean Society of Visualization
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• v.10 no.3
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• pp.11-15
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• 2012

Inertial migration phenomena of phytoplankton in pipe flows were investigated using a digital holography technique. As the Reynolds number increases, the microorganisms suspended in a pipe flow are focused at a certain radial position which is called equilibrium position or pinch point. In this study, the effects of the size of microorganism and Reynolds number in the range of 1 < Re < 78 on the inertial migration were investigated and the results are compared with those for solid particles under similar experimental conditions. As a result, the equilibrium position for the elastic microorganisms is not so distinct, compared to the solid particles. This results from deformation of elastic body shape caused by shear-gradient of surrounding flow.