• Journal of the Society of Naval Architects of Korea
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• v.38 no.3
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• pp.31-40
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• 2001

Low-order panel methods are being used to design marine propellers. Since the potential value over each panel for these methods is assumed to be a constant, the accuracy of prediction is known to be limited. Therefore, a higher order boundary element method(HOBEM) has been studied to enhance the accuracy of prediction. In this paper, a HOBEM representing the body boundary surfaces and physical quantities by a 9-node Lagrangian shape function is employed to analyse the flow around marine propellers in steady potential flow. First, the numerical results for a circular wing with thickness variations are compared with Jordan's linear solution. Then, the computational results of two propellers(DTRC 4119 & DTRC 4842 propeller) are compared with the experimental and numerical results published. The pressure distribution on the surface of the propeller is also compared with experimental data.

• Journal of Ocean Engineering and Technology
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• v.14 no.3
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• pp.41-45
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• 2000

In solving the unsteady potential flow problem of the ship in waves with the panel method, in general one can consider the basic flow as the free stream or double body solution. For the double body solution, the body boundary condition has the 2nd derivatives of the velocity potential. Low order panel methods are known to suffer from the significant error in the 2nd derivatives computed at the body surface. This paper analyzes the numerical error in the 2nd derivatives for a 2-D cylinder and a 3-D sphere problem, and an extrapolation method to obtain the correct derivatives on the body surface is suggested.

• Journal of computational fluids engineering
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• v.11 no.4 s.35
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• pp.9-13
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• 2006

In the present study, a numerical analysis of transient mixer flow is performed considering free surface formation. The flow patterns and free surface shape in a mixers formed by flat paddle and pitched paddle impellers are predicted. In a flat paddle mixer, two flow circulation regions are formed due to strong radial flow, whereas one large circulation is formed in a pitched paddle mixer due to axial downward flow. These differences affect the free surface evolution and shape. It is seen from the results that a flat paddle mixer gives deeper free surface at center region than a pitched paddle mixer. The free surface of 8-blades-flat-paddle mixer is also simulated to compare with the available experimental and simulation results. The present computational results agree reasonably well with the experimental data.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.530-536
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• 2016

본 연구에서는 EDISON_CFD의 2D_YUIBM_1 해석자를 사용하여 선인장 단면 모양 실린더의 $C_D$를 가시의 개수(N)와 가시의 깊이(D)에 따른 경향성으로 나타내었다. 저 레이놀즈 수에 대한 유동 해석을 해야 하므로 레이놀즈 수 영역은 20(steady), 40(steady), 100(Unsteady)을 사용하였다. 또한, 특징적인 효과를 보이는 몇 개의 케이스를 선별해 그 모델들에서 $C_P$와 Vorticity의 분포를 조사했으며 이를 통해 저 레이놀즈 수의 선인장 모양 실린더에서 $C_D$의 변화 원인을 규명하였다. 마지막으로, 물체의 기하학적 성질과 유체의 성질을 기반으로 저 레이놀즈 수에서 $C_D$를 최적화하는 공식을 산출하였다.

• Journal of Korea Foundry Society
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• v.12 no.1
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• pp.51-61
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• 1992

주조시 주형내의 유동해석을 위해서는 시간에 따라 변화하는 자유표면 위치에 대한 정확한 정보가 요구되는 관계로 난제로 여겨져 왔다. 따라서 대부분의 연구는 초기치 속도를 정의하기 위해서 순간충입(instantaneous filling)을 가정하여 수치 해석을 하였던 것이다. 본 연구는 Modified Solution Algorithm-Volume of Fluid Method (MSOLA-VOF)를 개발하는 주조시 주형내의 유동을 수치적으로 해석하며, 유속이 수평 주조, 수직 주조의 경우에 어떤 영향을 미치는가에 대하여 연구하였다. 결론으로 응고 연구에 있어서 초기의 순간충입은 비현실적인 가정이라는 것이 밝혀졌으며, 충입시 초기 속도 분포와 결정 생성은 밀접한 관계가 있음을 알 수 있었다.

• Journal of Ocean Engineering and Technology
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• v.11 no.4
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• pp.130-140
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• 1997

원형주상체 주위의 유동을 규명하기 위해 회류수조에서 원주방향으로 24개의 위치에 대하여 압력을 계측하였으며, laser sheet을 이용하여 유동을 가시화 하였다. Reynolds수가 4800에서 40000인 범위에 대하여 실험을 수행하였다. 또한, 원형단면체 주위의 비정상 층류유동에 대한 Navier-Stokes방정식의 해를 구하는 수치해석기법을 개발하였다. 효과적인 격자배치를 위하여 H와 O-type의 중첩격자를 사용하였고, 이산화 방법으로는 정규격자시스템에서 유한차분법을 적용하였다. 실험과 수치해석결과에서 뚜렷한 와류박리현상을 볼 수 있었으며, 압력계수 (C$_{p}$ ), 항력계수(C$_{D}$), 스트로얼수(St)를 정량적으로 비교하였을 때, 비교적 잘 일치하는 것을 확인하였다.다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.334-337
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• 2008

Three-dimensional unsteady reacting flowfield generated by transverse hydrogen injection into a supersonic mainstream are numerically investigated using DES and finite-rate chemistry model. Comparisons are made with experimental results to investigate the turbulent reacting flow physics. The numerical OH distribution describes well the experimental OH-PLIF result, while the numerical ignition delay time shows some disparity due to the restricted available experimental data.

• Journal of Energy Engineering
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• v.29 no.3
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• pp.97-102
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• 2020

In this study, one-way fluid structure interaction analysis was adapted to verify the durability of the outdoor evacuation stair structure operated in the event of a fire when wind pressure caused by a typhoon was applied. To this end, flow analysis was performed with the flow field around the structure of the evacuation stair in a steady state, and the durability was analyzed through structural analysis such as structural stress, deformation, and fatigue life using these analysis results by fluid data input data for structural analysis. As a result of flow numerical analysis, the air flow was different according to the shape of the evacuation stair structure, and this flow velocity distribution generated by the total pressure on the structure surface. Through the structural analysis results calculated by this total pressure, the safety factor calculated as the maximum stress value was found to be more than the safety factor, and durability was proven by fatigue life and deformation analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.37-45
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• 2002

A two-dimensional unsteady, inviscid flow solver has been developed for the simulation of airfoil-vortex interactions on unstructured dynamically adapted meshes. The Euler solver is based on a second-order accurate implicit time integration using a point Gauss-Seidel relaxation scheme and a dual time-step subiteration. A vertex-centered, finite-volume discretization is used in conjunction with the Roe's flux-difference splitting. An unsteady solution-adaptive dynamic mesh scheme is used by adding and deleting mesh points to take account of both spatial and temporal variations of the flow field. The effect of vortex interaction on the aeroelastic displacement of an airfoil attached to the idealized two degree-of-freedom spring system is investigated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.863-878
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• 2009

Unsteady three-dimensional flowfield generated by transverse fuel injection into a supersonic mainstream is simulated with a DES turbulence model. Comparisons are made with experimental results in terms of the temporal eddy position and eddy formation frequency. The vorticity field around the jet exit is also analyzed to understand the formation mechanism of the large eddy structures. Results indicate that the DES model correctly predicts the convection characteristics of the large scale eddies. However, it is also observed that the numerical results slightly over-predict the eddy formation frequency. The large eddy structures are generated as the counter-rotating vortices are detached alternately in the upstream recirculation region.