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2차원 Beach에서 쇄파의 시뮬레이션을 위한 수치계산기법의 비교
정광열(K. L. Jeong),이영길(Y.-G. Lee) 한국전산유체공학회 2004 한국전산유체공학회 학술대회논문집 Vol.2004 No.-
Unsteady nonlinear wave motions on the free surface over a plane beach of constant slope are numerically simulated using a finite difference method in rectangular grid system. Two-dimensional Navier-Stokes equations and the continuity equation are used for the computations. Irregular leg lengths and stars are employed near the boundaries of body and free surface to satisfy the boundary conditions. Also, the free surface which consists of markers or segments is determined every time step with the satisfaction of kinematic and dynamic free surface conditions. Moreover, marker-density method is also adopted to allow plunging jets impinging on the free surface. The second-order Stokes wave theory and solitary wave theory are employed for the generation of waves on the inflow boundary. For the simulation of wave breaking phenomena, the computations are carried out with the plane beach of constant slope in surf zone. The results are compared with each other. The marker-density method is better then the hybrid method. Also they are compared with other existing experimental results. The Agreement between the experimental data and the computation results is good.
수정된 밀도함수법을 이용한 SPILLING BREAKER의 수치시뮬레이션
정광열(K.-L. Jeong),이영길(Y.-G. Lee) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.11
The differences of physical properties of water and air are the source of instabilities of the numerical solutions considering the free surface flow. The most typical methods for the free surface such as Volume Of Fluid(VOF) and Level-Set(LS) methods impose transient zones where the physical prosperities vary gradually for the stabilities of solutions. The thickness of the transient zone is the source of the error of a solution. The marker-density method does not use such a transient zone. In the traditional marker-density method, however, the air velocities of free surface cells are extrapolated from the water velocity and the pressures on the free surface are extrapolated form the air pressures for the stability of a solution. Those extrapolations are also the source of the error of the solution. In this study, the marker-density method is modified to calculate the air velocities of free surface cells by determining the pressure and velocity on the free surface to get continuous pressure gradient and viscous stress. Two-dimensional steady spilling breakers behind of a submersed hydrofoil is simulated using INHAWAVE-II including the modified marker-density(MMD) method. The results are compared with the results of Fluent V6.3 including VOF method and published research results. Moreover, three-dimensional spilling breaker near a wedge shaped ship model is simulated using INHAWAVE-II. And the results are compared with the results of Fluent V6.3 and exist experimental data.
고정된 2차원 직사각형 격자계에서 자유동요하는 물체주위 유동의 수치시뮬레이션
정광열(K.-L. Jeong),이영길(Y.-G. Lee) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.11
In this research a numerical simulation method is developed for free surface flows around a freely oscillating body in fixed two-dimensional rectangular grid system. The non-linear free surface near the body is defined by modified marker-density method. The body boundary is defined by line segments connecting the points where the body surface and grid lines meet. Continuity equation and Navier-Stokes equations are used as governing equations and the equations are coupled with two-step projection method. The subgrid-scale turbulence model is applied in order to consider turbulence effects. To treat body movements in a fixed grid system. the volume displaced by moving body is added to the divergence of the body boundary cell. For the verification of the present numerical method, the vortex induced vibrations of an elastically mounted cylinder are calculated, and the amplitudes are compared with existing calculation results. Moreover, the free roll decay of a floating box is numerically simulated, and the results are compared with published experiment results.
고정된 직사각형 격자계에서 움직이는 물체주위 자유수면유동 계산을 위한 수치기법의 개발
정광열(K.L. Jeong),이영길(Y.G. Lee),하윤진(Y.J. Ha) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.5
In this research, a numerical simulation method is developed for moving body in free surface flows using fixed staggered rectangular grid system. The non-linear free surface near the body is defined by marker-density method. The body boundary is defined by line segment connecting the points where the body surface and grid line meet. Continuity equation and Navier-Stokes equations are used as governing equations and the equations are coupled with two-step projection method. The velocities and pressures of body boundary and free surface cells are calculated with simultaneous iterative method. To treat a body movement in a fixed grid system, the volume displaced by moving body is added to the divergence of the body boundary cell. For the verification of the present numerical method, vortex shedding period of advancing cylinder is calculated and the period is compared with existing experiment results. Moreover, added mass and damping coefficients of a vertically excited box are calculated and the computed results are compared with published experiment results. Impulsive pressure and water level variation due to sloshing phenomenon are simulated and the results are compared with published experiment results. Varying the plunger shape, the waves generated by plunging type wave maker are compared with the 2nd order Stokes wave theory. The plunger shape generating the wave that shows the best agreement with the theory is represented.