• Journal of Korea Water Resources Association
• /
• v.38 no.11
• /
• pp.973-984
• /
• 2005

A three-dimensional thermal hydrodynamic model is developed for carrying out unsteady simulation of the selective withdrawal of the stably stratified flow in a geometrically complex, natural reservoir The governing equations are discretized on a non-staggered grid using a second-order accurate, finite-volume scheme. The numerical model is validated by applying it to simulate three-dimensional, turbulent, stratified, shear-layer flow case. The numerical predictions appear to capture reasonably well the general shape of velocity and temperature profiles observed in the laboratory experiments, while significant overestimation of the magnitude of velocity profiles is observed in the application to the flow in a natural reservoir. The physics of selective withdrawal as emerge from the numerical simulations are also discussed.

• Journal of the KSME
• /
• v.33 no.9
• /
• pp.803-810
• /
• 1993

벽면에서의 전단응력 분포와 유동장 내에서의 3차원 유동 요소를 추적하는 유동가시화 기법중 에서 몇 가지를 그 응용 예와 함께 살펴보았다. 3차원 유동의 주요 특징들과 한계유선(limiting streamlines)을 관찰하기 위해서는 oil and lampblack 기법이 충분하나 유속이 작거나 유동의 방향이 분명하지 않은 곳에서는 ink dot 기법을 적용하는 것이 좋다. Oil and lampblack 기법은 실험하고자 하는 유동의 조건에 따라 기름과 분말의 혼합비, 기름의 점도 등을 잘 선택하여야 한다. 안장점(Saddle point) 이나 재부착선(reattachment line)과 같이 성격상 중요한지점을 찾기 위해서는 털실 프로브(single tuft probe)가 유용하게 쓰이며, 이는 또 유동내에서 와동의 존재와 위치를 찾는데 쓰이기도 한다. 수치해석 결과 얻을 수 잇는 속도벡터와 같이 비교적 넓은 유동 장을 한눈에 관찰하기 위해서는 털실 격자망 (tuft grid)을 사용할 수 있으며 각 털실은 그 지 점세서의 유동의 방향과 그 안정성(steadiness)를 나타내준다. 이러한 유동가시화 방법들은 각 유동의 특성에 맞는 적절한 조건을 맞추기 위해서 많은 시행착오를 거쳐야 하며, 하나의 만족 스러운 결과를 얻기 위해서는 많은 기술과 시간과 연습을 요구하고 있어서 다른 정량적인 측정 기술과 더불어 커다란 노력과 관심을 기울여서 발전시켜야만 할 것이다.

• Journal of computational fluids engineering
• /
• v.3 no.1
• /
• pp.54-62
• /
• 1998

본 논문은 2차원 해면효과의 수치계산 결과를 정리하였다. 지면으로부터의 높이변화에 따른 점성유동장을 계산하기 위하여 지배방정식으로는 비압축성 RANS 방정식을, 시간에 대하여서는 음해법으로 프로그램을 구성하였다. 압력항은 가상압축성과 4차 수치확산항을 추가하는 것에 의해 계산하였으며, 높은 레이놀즈 수에서의 효과적인 계산을 위해 Baldwin- Lomax 난류모델을 도입하였다. 해면효과가 없는 무한유중에서의 NACA-0012 단면 계산결과를 실험 데이터와 비교하는 것에 의해 프로그램의 타당성을 확인하였다. NACA-6409와 두께 비 4.6%의 날개에 대하여 해면효과를 고려한 계산을 수행하였다. 계산결과, 높이의 변화에 따라 계산된 무차원계수, 압력 및 속도분포는 해면효과의 특성을 잘 보여주고 있다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.40 no.2
• /
• pp.79-89
• /
• 2022

Images taken using drones have been applied to fields that require rapid decision-making as they can quickly construct high-quality 3D spatial information for small regions. To construct spatial information based on drone images, it is necessary to determine the relationship between images by extracting keypoints between adjacent drone images and performing image matching. Therefore, in this study, three study regions photographed using a drone were selected: a region where parking lots and a lake coexisted, a downtown region with buildings, and a field region of natural terrain, and the performance of AKAZE (Accelerated-KAZE), BRISK (Binary Robust Invariant Scalable Keypoints), KAZE, ORB (Oriented FAST and Rotated BRIEF), SIFT (Scale Invariant Feature Transform), and SURF (Speeded Up Robust Features) algorithms were analyzed. The performance of the keypoints extraction algorithms was compared with the distribution of extracted keypoints, distribution of matched points, processing time, and matching accuracy. In the region where the parking lot and lake coexist, the processing speed of the BRISK algorithm was fast, and the SURF algorithm showed excellent performance in the distribution of keypoints and matched points and matching accuracy. In the downtown region with buildings, the processing speed of the AKAZE algorithm was fast and the SURF algorithm showed excellent performance in the distribution of keypoints and matched points and matching accuracy. In the field region of natural terrain, the keypoints and matched points of the SURF algorithm were evenly distributed throughout the image taken by drone, but the AKAZE algorithm showed the highest matching accuracy and processing speed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.23 no.5
• /
• pp.365-374
• /
• 2011

For the first time, the present study has measured the velocity distribution function in circular open channel flow in a three-dimensional shape using a stereoscopic PIV system. For a given channel slope, water depth was varied from 30% to 80% of the channel diameter. Then, the characteristics of the velocity distribution function was compared according to the change of the water depth. Unlike a rectangular channel, the present experiment exhibited quite different shapes in the velocity distribution function whether the water depth is higher than 50% or not. Especially, the position of maximum velocity in the central and side wall changes in a different manner for the water depth above 50%. By differentiating the velocity distribution function, local wall friction coefficient was evaluated as a function of wall position. If the water depth goes down, the difference between the maximum and minimum values in the local wall friction coefficient increases, and the averaged value a1so increases.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.05a
• /
• pp.141-144
• /
• 2008

Atomization characteristics and spatial distribution of the spray emanating from an injector of liquid-propellant thruster are investigated by using dual-mode phase Doppler anemometry (DPDA). Spray characteristic parameters such as the mean velocity, Sauter mean diameter (SMD), and velocity fluctuation are measured at various locations along the spray axis as well as on the radial direction. Those data are quantified in radial profile and also used to scrutinize the correlation between diameter and turbulence intensity of spray droplets. For the better visual grasp, dynamic behavior of spray droplets along the spray stream is presented through the velocity vectors projected on the plane of geometric axis of nozzle orifice and radial coordinate.

• Journal of the Korean Institute of Gas
• /
• v.7 no.3 s.20
• /
• pp.44-50
• /
• 2003

The axisymmetric methane-air counterflow flame was simulated to investigate changes in the flame structure due to the fuel concentration and to evaluate the numerical method. The global strain rates $a_g=20,\;60,\;90\;s^{-1}$ and the mole fractions of methane $x_m=20,\;50,\;80\%$ in the fuel stream were taken to be numerical parameters. The axisymmetric simulation was conducted by using the Fire Dynamics Simulator (FDS) which employed a mixture fraction combustion model, and the results were compared with those of OPPDIF, which is an one-dimensional flamelet code and includes detail chemical reactions. In all the cases tested, there was good agreement in the temperature and axial velocity profiles between the axisymmetric and one-dimensional simulations. It was shown that the flame thickness and peak flame temperature increase and the flame radius decreases as the fuel concentration increases.

• Journal of the Society of Naval Architects of Korea
• /
• v.31 no.4
• /
• pp.73-81
• /
• 1994

The source and source/dipole distribution methods using 3-dimensional panel method have been widely used for ship motion analysis. When these methods are used, large errors in the predicted hydrodynamic coefficients are introduced around the irregular frequencies caused by the resonance of imaginary internal flow. Therefore, the irregular frequencies need to be removed for an accurate prediction of ship motion. This paper adopts 3-dimensional translating and oscillating Green function derived by Wu. The adaptive integration method, stretching transform and stationary phase method are used for the calculation of the calculation of Green function and the integral equation is derived by distributing the Green function n ship surface and inner free-surface. The condition of zero normal velocity, that is, wall condition on inner free-surface has been successfully used for the removal of irregular frequencies in oscillating problems. The calculations are carried out for series 60($C_B=0.7$) vessel and the results are compared with those of other theoretical analyses and experiment.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2008.05a
• /
• pp.379-383
• /
• 2008

본 연구의 목적은 3차원 수리 모델인 ELCOM(Estuary, Lake and Coastal Ocean Model)과 물질 전달모델인 CAEDYM(Computational Aquatic Ecosystem Dynamic Model)을 이용하여 성층화된 저수지로 밀도류 형태로 유입한 부유사의 이송과 확산 그리고 침강특성을 해석하는데 있다. ELCOM은 3차원 수리동력학 모델로써 시공간적인 유속과 수온변화를 예측하는데 사용되었으며, CAEDYM과 매 계산시간 마다 동적으로 연결(Dynamic coupling)되어 부유입자의 이송, 확산, 침강 과정을 모의하였다. 개발된 3차원 모델의 예측 성능은 2004년 홍수기 동안 대청호에서 실측한 자료를 사용하여 검증하였다. 모델의 모의변수는 입자크기별로 구분된 부유물질(SS) 그룹이며, 현장 실측자료인 탁도($C_T$)와 모델 변수인 SS간의 변환을 위해 저수지 지점 별로 측정한 SS-$C_T$ 상관관계를 사용함으로써 부유 입자의 크기분포의 공간적 변동 특성을 반영하였다. 모델은 탁수가 유입하는 환경에서 저수지 성층구조의 변화와 유입 탁수의 밀도류 거동특성, 유입한 부유사의 이송과 확산 그리고 침강특성을 비교적 잘 모의하였다. 저수지로 유입한 부유입자 중 입경이 $20{\mu}m$ 이상인 입자는 매우 빠른 속도로 저수지 바닥에 퇴적된 반면, $10{\mu}m$ 이하의 입자들은 중층에 오랜 시간 부유하며 장기탁수문제를 유발하는 원인이 되었다.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.12 no.5
• /
• pp.9-17
• /
• 2008

Pseudo-3D spatial distribution of spray droplets is investigated by using Dual-mode Phase Doppler Anemometry (DPDA) in order to examine the disintegration and spreading behavior of spray exiting from liquid-propellant thruster injector. Spray injected from nozzle orifice with length-to-diameter ratio ($L/d_o$) of 1.67 and under the injection pressure of 27.6 bar is aligned to the vertical. Vertical and horizontal mean velocities of droplets, Sauter Mean Diameter (SMD), and volumetric flux decrease as droplets travel from center/upstream toward outer region/downstream of spray. Although the distribution of spray characteristic parameters is symmetric against the geometric axis of nozzle orifice, their absolute values are asymmetric.