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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.
규칙파 중 해양구조물의 갑판침입수 충격하중에 관한 수치시뮬레이션
강의하,이영길,양인준,김기용,주영석,박정호 대한조선학회 2017 大韓造船學會 論文集 Vol.54 No.6
In the study, numerical simulation on the greenwater impact load of free surface offshore structure in the regular waves using fixed cartesian grid system and Modified Marker-Density (MMD) method were carried out and the results were reviewed. In order to compare numerical simulation and experimental results, the FPSO with the scale ratio of 1/100 model ship with fixed rectangular deck was selected and turbulence characteristic of the flow was considered by applying the Sub-Grid Scale (SGS) in laminar flow. As a result, it is reviewed how the greenwater impact load inflowed from bow in regular headsea wave influence the flow on the deck and the flow characteristic by numerical simulation and the experiment results were compared and reviewed. Based on this study, it would be useful to numerically study the effect of greenwater on offshore structure.