• Journal of the Korean Geotechnical Society
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• v.25 no.12
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• pp.119-130
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• 2009

To measure the soil deformation, two common techniques of the digital image analysis-Particle Image Velocimetry (PIV) and Digital Image Correlation (DIC)-have been used. To generally apply these techniques to the soils, the accuracy of these techniques should be evaluated under various conditions. In this study, the influence factors including the image resolution, the degree of displacement and deformation, the size of pixel subsets, and analysis techniques were analyzed. The deformation of an idealized particle assembly using the discrete element method was measured by the digital image analyses, and then the results were compared with the actual deformations. To conduct the optimal digital image analysis, various factors are systematically analyzed in terms of the degree of the displacement and the deformation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.991-996
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• 2002

This paper presents the fabrication method of a micro-riblet film (MRF) using MEMS technology and the experimental results of the drag reduction of an airfoil with MRFs. Riblets having grooved surface in the streamwise direction has been proven as an effective passive control technique of the drag reduction. A V-grooved pattern on (100) silicon wafer is etched with anisotropic bulk micromachining. The MRF is completed by replicating the V-grooved pattern with polydimethylsiloxane (PDMS). Experiments were performed by measuring a velocity field behind the trailing edge of a NACA 0012 airfoil with and without MRFs in a closed-type subsonic wind tunnel using particle image velocimetry (PlV) technique. The MRF provides about 3.8 % drag reduction compared to the drag on a smooth airfoil when the freestream velocity of wind tunnel is 3.3 m/s.

• Geomechanics and Engineering
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• v.35 no.2
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• pp.195-208
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• 2023

The nodular diaphragm wall (NDW) is a novel type of foundation with favorable engineering characteristics, which has already been utilized in high-rise buildings and high-speed railways. Compared to traditional diaphragm walls, the NDW offers significantly improved vertical bearing capacity due to the presence of nodular parts while reducing construction time and excavation work. Despite its potential, research on the vertical bearing characteristics of NDW requires further study, and the investigation and visualization of its displacement pattern and failure mode are scant. Meanwhile, the measurement of the force component acting on the nodular parts remains challenging. In this paper, the vertical bearing characteristics of NDW are studied in detail through the indoor model test, and the displacement and failure mode of the foundation is analyzed using particle image velocimetry (PIV) technology. The principles and methods for monitoring the force acting on the nodular parts are described in detail. The research results show that the nodular part plays an essential role in the bearing capacity of the NDW, and its maximum load-bearing ratio can reach 30.92%. The existence of the bottom nodular part contributes more to the bearing capacity of the foundation compared to the middle nodular part, and the use of both middle and bottom nodular parts increases the bearing capacity of the foundation by about 9~12% compared to a single nodular part of the NDW. The increase in the number of nodular parts cannot produce a simple superposition effect on the resistance born by the nodular parts since the nodular parts have an insignificant influence on the exertion and distribution of the skin friction of NDW. The existence of the nodular part changes the displacement field of the soil around NDW and increases the displacement influence range of the foundation to a certain extent. For NDWs with three different nodal arrangements, the failure modes of the foundations appear to be local shear failures. Overall, this study provides valuable insights into the performance and behavior of NDWs, which will aid in their effective utilization and further research in the field.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.6
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• pp.874-887
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• 1998

A 2-frame PTV (particle tracking velocimetry) system using the concept of match probability between two consequent image frames has been developed to obtain instantaneous velocity fields. The overall 2-frame PTV system including image pre-processing, tracking algorithm and post-processing routine was implemented to apply to real flows. The developed 2-frame PTV system has several advantages such as high recovery ratio of velocity vectors, low error ratio and small computational time compared with the conventional 4-frame PTV and the FFT-based cross-correlation PIV technique. The 2-frame PTV system was applied to a turbulent channel flow over a rectangular block to check its reliability and usefulness. Total 96 sequential image frames have been captured and processed to get both mean and fluctuating velocity vector fields over the recirculating region. The mean velocity and turbulent intensity profiles were well agreed with hte LDV measurements in the separated region behind the block. Time-averaged reattachment length is about 6.3 times of the block height.

• Journal of the Korean Society of Industry Convergence
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• v.6 no.3
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• pp.253-259
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• 2003

An experimental study was performed for turbulent flow behind a circular and a square cylinder by using 2-D PIV(Particle Image Velocimetry) technique in a cylindrical tube. The Reynolds number investigated were 10,000, 30,000 and 50,000. The measuring system consists of CCD camera. Ar-ion laser, image grabber and a host computer. The mean velocity vector, time mean axial velocity, turbulent intensity and Reynolds shear stress were measured along the test tube. The results are compared each other for the circular and the square cylinder.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.124-127
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• 2002

Ceil embolisation technique has been used to treat the intracranial aneurysms. Microcoils inserted into the aneurysm sac induce the blood flow stagnation inside the aneurysm sac, which causes the thrombus formation and embolisation of aneurysm. Since the intraaneurysmal flow patterns affect the embolisation process, we want to measure the flow field for different locations of coil inside the aneurysm sac . Lateral aneurysm models are manufactured using rapid prototyping, and the velocity fields are measured using particle image velocitimeter. Distally blocked models showed less flow into the aneurysm sac comparing to proximally blocked models. Also blocking the neck of aneurysm showed better inflow blocking comparing to blocking the dome of aneurysm. These results suggest that distal neck should be the preferred locations of coil for aneurysm embolisation.

• Journal of Ocean Engineering and Technology
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• v.25 no.3
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• pp.11-18
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• 2011

The rogue wave was generated in a two-dimensional wave tank the rogue wave kinematics was investigated including local and convective accelerations of the water particle and verification of existing prediction methods. PIV technique was applied to measure the wave kinematics near the wave crest which extended to compute the local and convective accelerations. The experimental results were compared with several analytical predictions. The convective acceleration under the crest of rogue wave has a similar magnitude with the local acceleration.

• Journal of the Korean Society of Visualization
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• v.3 no.2
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• pp.57-62
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• 2005

The flow characteristics in a confined slot jet impinging on a flat plate were investigated by using cinematic Particle Image Velocimetry technique. The jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. We found that the vortical structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Vortical structures and their temporal evolution are verified by using proper orthogonal decomposition.

• Journal of Mechanical Science and Technology
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• v.18 no.4
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• pp.671-680
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• 2004

We present numerical and experimental results of the periodic flows inside a rectangular container under a background rotation. In numerical computation, a parallel-computation technique with MPI is implemented. Flow visualization and PIV measurement are also performed to obtain velocity fields at the free surface. Through a series of numerical and experimental works, we aim to clarify the fundamental reasons of discrepancy between the two-dimensional computation and the experimental measurement, which was detected in the previous study for the same flow model. Specifically, we check if the various assumptions prerequisite for the validity of the classical Ekman pumping law are satisfied for periodic flows under a background rotation.

• Journal of the Korean Society of Industry Convergence
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• v.3 no.1
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• pp.29-36
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• 2000

In order to reduce a aerodynamic drag of the rear, body, effects of rear lower end configuration of a vehicles were investigated by measuring the pressure distribution, visual flow phenomena by the use of digital image processing technique. The use of flow visualization in recent years has improved the general understanding of structure of complex flow and has yielded valuable information for analyzing fluid flow. As the results, it was found that the shape of rear lower part vehicles not only effected on the pressure distribution of the rear part of the vehicle but also difference of the flow phenomena.