슬로싱 영향을 동반한 해양 부유체 운동에 대한 수치해석적 연구

Abstract

The sloshing of a liquid inside an ocean floater is caused by external disturbances due to waves. To analyze the impact of sloshing within and on the floater, a coupled analysis method is used. The results of earlier research shows good agreements with large scale phenomenon such as ship motions by sloshing and linear sloshing behavior. However, the wave excitation method based on potential theory is not a good option to consider separation of break waves on a rigid body. Also, this method show difficulties in analysis of surface flows and violent sloshing because they use simple multi-phase model and moreover turbulence influences are not considered. Hence, in this study, the Volume of Fluids (VOF) method is used to analyze the multiphase flows of a strongly nonlinear sloshing problem in a cylindrical and a rectangular tank using three dimensional Computational Fluid Dynamics (CFD) techniques. For accountability purposes, the results of this study was compared with that of the earlier research - with many multiphase models such as the inhomogeneous multi-phase theory based free surface model and the mixture model. Two theories – the linear wave (Airy Wave) and the nonlinear wave (Stoke's 5th order wave) – were used to create the disturbances for the floater. In the results, the sloshing phenomenon in the floater is visually shown with change in filling rates through unsteady calculations and the motions of the floater with sloshing influences are shown with time history. The comparative results of the multi-phase models shows a constant periodic trend, both experimentally and numerically, even if under violent sloshing. Also the comparison matches visually. The pressure of each periods are approximately 1500pa. The maximum pressure values of numerical results for each period is 5% to 10% higher when compared with the experimental results. The results of the rectangular tank shows linear sloshing phenomenon. The pitch motions of periods are twice higher than the other cases at 75% filling case. The results of the cylindrical tank shows a maximum displacement of pitch motion at 0.15 radian for the 30 % filling case and also the pitch motions are twice higher than the other cases. The 60% case has the most active displacements for the heave motions. This confirms the non-repeatability of the floater motions due to sloshing phenomenon and waves.