• Journal of Advanced Marine Engineering and Technology
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• 제29권4호
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• pp.417-425
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• 2005

An experimental study is performed on the turbulent swirling flow behind a crcular cylinder using 2-D PIV technique. The Reynolds numbers investigated are 10.000, 15,000. 20.000 and 25.000. The mean velocity vector, time mean axial velocity, turbulence intensity, kinetic energy and Reynolds shear stress behind the cylinder are measured before and behind the cylinder along the test tube. A comparison is included without swirling flow behind a circular and square cylinder. The recirculation zones are shown unsymmetric profiles.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.142-152
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• 2008

SPT-Uphole method was introduced for the evaluation of near subsurface shear wave velocity (Vs) profile. In SPT-Uphole method, SPT (Standard Penetration Test) which is common in geotechnical site investigation was used as a source and several surface geophones in line were used as receivers. 1D shearwave velocity profile can be obtained in the manner of downhole method, Vs distribution map which is the triangular shape around the boring point can be developed by tomography inversion. To obtain the exact travel time information of shear wave component, a procedure using the magnitude summation of vertical and horizontal components was used based on the evaluation of particle motion at the surface. It was verified that proposed method could give reliable Vs distribution map through the numerical study using the FEM (Finite Element Method) model. Finally, SPT-Uphole method was performed and the feasibility of proposed method was verified in the field.

• 한국물환경학회지
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• 제32권3호
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• pp.243-252
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• 2016

In cases of water pollution accidents, accurate prediction for arrival time and concentration of contaminants in a river is essential to take proper measures and minimize their impact on downstream water intake facilities. It is critical to fully understand the behavior characteristics of contaminants on river surface, especially in case of oil spill accidents. Therefore, in this study, the effects of main parameters of advection and diffusion of contaminants were analyzed and validated by comparing the results of Lagrangian particle tracking (LPT) simulation of Environmental Fluid Dynamic Code (EFDC) model with those of Global Position System (GPS)-equipped drifter experiment. Prevention scenario modeling was accomplished by taking cases of movable weir operation into account. The simulated water level and flow velocity fluctuations agreed well with observations. There was no significant difference in the speed of surface particle movement between 5 and 10 layer modeling. Therefore, 5 layer modeling could be chosen to reduce computational time. It was found that full three dimensional modeling simulated wind effects on surface particle movements more sensitively than depth-averaged two dimensional modeling. The diffusion range of particles was linearly proportional to horizontal diffusivity by sensitivity analysis. Horizontal diffusivity estimated from the results of GPS-equipped drifter experiment was 0.096 m²/sec, which was considered to be valid for applying the LPT module in this area. Finally, the scenario analysis results showed that particle movements could be stagnant when discharge from the upstream weir was reduced, implying the possibility of securing time for mitigation actions such as oil boom installation and wiping oil contaminants. The outcomes of this study can help improve the prediction accuracy of particle tracking simulation to establish the most suitable mitigation plan considering the combination of movable weir operation.

• 한국지반공학회논문집
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• 제25권10호
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• pp.111-122
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• 2009

지반에 포함된 입자의 용해작용은 흙의 강도를 저하시키고, 지하구조물의 침하를 발생시킨다. 본 논문에서는 입자용해시 혼합재의 물리적 특성 변화를 조사하고자 하였다. 침하량 측정과 전단파 측정과 같은 거시적 반응을 평가하기 위해, 소금과 모래로 구성된 혼합재를 사용하였다. 또한, 광탄성(photoelastic) 디스크와 얼음 디스크 혼합재를 이용하여 힘 연결고리(force chain), 간극, 접촉점수(coordination number), 그리고 수평력 변화와 같은 미시적 거동을 분석하였다. 소금-모래 혼합재에서 전단파는 압밀셀에 설치된 다단의 벤더 엘리먼트로 측정되었고, 광탄성 디스크-얼음 디스크 혼합재의 역학적 거동은 로드셀과 디지털 이미지를 이용하여 분석되었다. 실험결과, 소금의 용해시 전단파 속도는 초기에는 감소한 후에 증가한 후 일정한 값으로 수렴하였다. 용해가능 입자의 크기가 커질수록 그리고 입자패킹이 불규칙해질수록 입자용해시 수평력의 변화가 더 커지는 것을 알 수 있었다. 용해 후, 간극비는 증가했고, 접촉점수는 감소하였다. 본 연구에서는 힘 연결고리, 간극비, 접촉점수와 같은 입자의 거동변화가 전단파 속도와 전체시스템의 수평력 변화 같은 전체적인 거동에 영향을 주는 것으로 나타났다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.727-732
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• 2001

The purpose of this study is to compare the time mean velocity distribution, the time mean kinetic energy, and the time mean turbulence intensity between vertical and horizontal flow fields in a coaxial circular pipe by PIV measurement. Experiments are performed at a Reynolds number 2,000, measuring regions divided as the section regions A, B, C, D in flow fields. The angle of the high-frequency ultrasonic is selected in the direction of $45^{\circ}$ to the flow axes and it is reflected several times. In results, it is clarified that the effect of gravity is given in the vertical flow field compared with the horizontal flow field and the ultrasonic affects the turbulence enhancement. And kinetic energy and turbulence intensity with ultrasonic are shown slightly bigger than those in flow field without it.

• Journal of Advanced Marine Engineering and Technology
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• 제28권6호
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• pp.922-930
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• 2004

An experimental investigation was performed to study on the generation of air bubble and air core with swirling flow in a horizontal cicular tube. To determine some characteristics of the flow, 2D PIV technique is employed for velocity measurement in water. The experimental rig is manufactured from an acryl tube. The test tube diameter of 80mm, and a length of 3000mm. The used algorithm is the gray leve cross-correlation method(Kimura et al. 1986). An Ar-ion laser is used and the light from the laser(500mW) passes through a probe to make two-dimensional light sheet. In order to make coded images of the tracer particles on one frame, an AOM(Acoustic-Optical Modulator) is used. The maximum axial velocities showed near the test tube wall at y/D =0.1 and y/D =0.9 along the test tube. The higher Reynolds number increase, the lower axial velocities are showed in the center of the test tube. The air bubbles are generated from Re =10,000 and developed into air core from the recirculating water pump rpm equal 30Hz. The pressure and temperature are measured across the test tube at X/D=3.33.

• International Journal of Aeronautical and Space Sciences
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• 제17권2호
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• pp.139-148
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• 2016

The passive control methods such as horizontal and vertical fences on the lower surface of the bluff body were applied to suppress the vortex shedding and enhance the aerodynamic stability of flow. For investigating the effects of the passive control methods, wind tunnel experiments on the unsteady flow field around a bluff body near a moving ground were performed. The boundary layer and velocity profiles were measured by the Hot Wire Anemometer (HWA) system and the vortex shedding patterns and flow structures in a wake region were visualized via the Particle Image Velocimetry (PIV) system. Also, it is a measuring on moving ground condition that the experimental values of the critical gap distances, Strouhal numbers and aerodynamic force FFT analyses. Through the experiments, we found that the momentum supply due to moving ground caused the vortex shedding at the lower critical gap distance rather than that of fixed ground. The horizontal and vertical fences increase the critical gap distance and it can suppress the vortex shedding. Consequently, the stability characteristics of the bluff body near a moving ground could be effectively enhanced by the simple passive control such as the vertical fences.

• Geomechanics and Engineering
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• 제27권5호
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• pp.433-445
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• 2021

Artificial ground freezing (AGF) is a commonly used geotechnical support technique that can be applied in any soil type and has low environmental impact. Experimental and numerical investigations have been conducted to optimize AGF for application in diverse scenarios. Precise simulation of groundwater flow is crucial to improving the reliability these investigations' results. Previous experimental research has mostly considered horizontal seepage flow, which does not allow accurate calculation of the groundwater flow velocity due to spatial variation of the piezometric head. This study adopted vertical seepage flow-which can maintain a constant cross-sectional area-to eliminate the limitations of using horizontal seepage flow. The closure time is a measure of the time taken for an impermeable layer to begin to form, this being the time for a frozen soil-ice wall to start forming adjacent to the freeze pipes; this is of great importance to applied AGF. This study reports verification of the reliability of our experimental apparatus and measurement system using only water, because temperature data could be measured while freezing was observed visually. Subsequent experimental AFG tests with saturated sandy soil were also performed. From the experimental results, a method of estimating closure time is proposed using the inflection point in the thermal conductivity difference between pore water and pore ice. It is expected that this estimation method will be highly applicable in the field. A further parametric study assessed factors influencing the closure time using a two-dimensional coupled thermo-hydraulic numerical analysis model that can simulate the AGF of saturated sandy soil considering groundwater flow. It shows that the closure time is affected by factors such as hydraulic gradient, unfrozen permeability, particle thermal conductivity, and freezing temperature. Among these factors, changes in the unfrozen permeability and particle thermal conductivity have less effect on the formation of frozen soil-ice walls when the freezing temperature is sufficiently low.

• 한국세라믹학회지
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• 제44권3호
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• pp.169-174
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• 2007

TRISO coated fuel particle is one of the most important materials for hydrogen production using HTGR (high temperature gas cooled reactors). It is composed of three isotropic layers: inner pyrolytic carbon (IPyC), silicon carbide (SiC), outer pyrolytic carbon (OPyC) layers. In this study, TRISO coated fuel particle layers were deposited through CVD process in a horizontal hot wall deposition system. Also the computational simulations of input gas velocity, temperature profile and pressure in the reaction chamber were conducted with varying process variable (i.e temperature and input gas ratios). As deposition temperature increased, microstructure, chemical composition and growth behavior changed and deposition rate increased. The simulation showed that the change of reactant states affected growth rate at each position of the susceptor. The experimental results showed a close correlation with the simulation results.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.1315-1320
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• 2008

An experimental study was carried out to study the solid-liquid mixture upward flow in a vertical and inclined annulus with rotating inner cylinder. Lift forces acting on a fluidized particle plays a central role in many importance applications, such as the removal of drill cuttings in horizontal drill holes, sand transport in fractured reservoirs, sediment transport and cleaning of particles from surfaces, etc. Field measurements have revealed that the pressure drop over a borehole during drilling of a slim oil well or a well with a long reach can depend significantly on the rotation speed of the drill pipe. An accurate prediction of the annular frictional pressure drop is therefore important for conditions where the annular clearance is small. Effect of annulus inclination and drill pipe rotation on the carrying capacity of drilling fluid, particle rising velocity, and pressure drop in the slim hole annulus have been measured for fully developed flows of water and of aqueous solutions.