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고행식(H.S. Ko),배윤혁(Y.H. Bae),조일형(I.H. Cho) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.1
In this study, the numerical simulation with OpenFOAM, an open source library in Computational Fluid Dynamics(CFD), to analyze a dynamic behavior of a floating structure in wave field is carried out. The two-dimensional numerical wave tank with a simple rectangular floating body constrained in two degree of freedom(heave and pitch) is modelled. “interDyMFoam” which solves the Reynolds-Averaged Navier-Stokes(RANS) for two incompressible phase using Volume Of Fluid(VOF) technique and dynamic mesh method for the floating body is used. Comparisons of free decay tests and heave and pitch Response Amplitude Operators (RAOs) have been made using existing experimental data performed with two dimensional wave flume in Jeju National University. Moreover, velocity field and vorticity near the floating body show how viscous damping is affected on the dynamic behavior. The results shows that the numerical wave tank with OpenFOAM can be used for the behavior analysis of the floating structure.
OpenFOAM을 이용한 편심 원형실린더 파력발전장치의 비선형 운동해석
고행식(H.S. Ko),조일형(I.H. Cho),배윤혁(Y.H. Bae) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.3
In this study, the numerical simulation with OpenFOAM, an open source library in Computational Fluid Dynamics(CFD), is conducted for analyzing a non-linear dynamic behavior of an eccentrical cylinder-type Wave Energy Converter(WEC) in wave field. Two optimal eccentrical cylinder-type WECs constrained in single degree of freedom(pitch) are analyzed with interDyMFoam which solves the Reynolds-Averaged Navier-Stokes(RANS) and deals with dynamic mesh. In addition, Arbitrary Mesh Interface(AMI) is employed to prevent the mesh from being distorted. Numerical results of free decay tests and dynamic behaviors with different wave heights and periods are compared with model-scale experimental results. A larger scale study is also performed. Pitch Response Amplitude Operator(RAO)s with a lower and a higher wave height are compared and non-linear dynamic behaviors are obviously investigated by spectrum analysis. The results show that higher order pitch harmonic motions are grown or added according as wave height is increased. Therefore, RAO with a higher wave height is smaller than a lower wave height due to the non-linear effect.
SPH법을 이용한 물기둥 붕괴의 수치모의 (Numerical Simulation of the Water Column Collapse using SPH Method)
김남형(Kim Nam Hyeong),고행식(Ko Haeng Sik) 대한토목학회 2007 대한토목학회논문집 B Vol.27 No.3B
Smoothed Particle Hydrodynamics(SPH) 법은 과거의 격자를 사용한 방법과는 달리 입자를 이용한 격자 없는 Lagrangian방법이다. 비압축 점성흐름을 풀기 위하여 Navier-Stokes 방정식을 사용하였다. 본 연구에서는 SPH법을 이용하여 2차원 물기둥 붕괴의 수치해석을 수행하였고, 그 결과를 Martin과 Moyce의 실험결과와 MPS법과 SMAC법의 계산결과와 비교하여 좋은 결과가 얻어졌다. 또한, 입자와 속도벡터를 사용하여 물기둥 붕괴현상을 가시화하였고, 가상점성의 α항과 입자수와 관련된 민감도 해석을 수행하였다. 결과적으로 이 방법은 댐 붕괴와 같은 수공구조물의 붕괴현상에 적용할 수 있음을 보여줬다. Smoothed Particle Hydrodynamics (SPH) method is a meshless Lagrangian method using the particle, which is different from previous methods using the mesh. The Navier-Stokes equations for the incompressible viscous flow is applied. In this study, the numerical analysis of two-dimensional water column collapse by SPH method is carried out, and the result is com-pared with Martin and Moyce's experimental data and the result of MPS and SMAC method. And a good result is obtained. The phenomenon of water column collapse by using the particle and velocity vector is also visualized, and the sensitive analysis on the artificial viscosity a-term and particle number is performed. Finally it is shown that this method could be applied to the breaking phenomenon of hydraulic structures such as dam break.