Numerical Simulation And Application Of Ship Motions Coupled With Tank Sloshing Based On Potential Flow Theory

When ship with liquid tanks voyages in waves,tank sloshing in ship cargo is excited by ship motions while the sloshing flow induces impact load on tank wall which affects the ship motion. With the development of the special liquid carriers, such as LNG and LPG, the interaction and coupling between ship motion and tank sloshing has been more and more emphasized by people. Violent tank sloshing may do harm to the ship body, especially when the tank is partially loaded, press induced by large amplitude sloshing may cause seriously damage to the ship structure. The interaction and coupling between ship motion and tank sloshing is an important facts in the design stage of ship with liquid tank.For this kind of problem, many researchers had carried out a lot of researches. In particular, the recent studies can be categorized into two approaches: the frequency-domain approach assuming linear sloshing flow, and the time-domain approach adopting nonlinear sloshing flow. According to existing studies, it seems that the assumption of linear ship motion is adequate in the coupled analysis. Direct time-domain method is usually taken into consideration in solving the problem of ship motion, but multi-frequency calculation requires new numerical method to overcome the defects of direct time-domain method such as long runtime and low calculation efficiency. There is another method to solve the problem of ship motion in time domain. First, the hydrodynamic coefficient of the ship is got by using three-dimension frequency-domain method. And then based on the frequency-domain results, retardation function could be calculated through impulse-response function (IRF) method. Finally, the motion equation of ship in time-domain is established.The problem of sloshing in liquid tanks is a classic one in hydrodynamics, which is also a concern in both academic and engineering circles. Theoretically, there are many methods, such as Finite Element Method (FEM), Finite Difference Method (FDM), Boundary Element Method (BEM) and so forth. Compared to FEM and FDM, using BEM can convert the problem into lower dimension, which, apparently, can reduce computation complexity and shorten runtime.In this paper, both the flow fields inside of tank and outer of ship are dealt with potential flow theory respectively, a global ship motion coupled with tank sloshing is established. Three-dimension frequency domain method and impulse-response function method are used to get the wave forces acting on ship hull and the retardation function while boundary element method is used to solve the tank sloshing problem. Numerical simulations for ship model of S175 coupled with tank sloshing are conducted and verified in different cases such as head sea, beam sea conditions. Then this method is applied to analyze the effect of sloshing on ship roll motion. Numerical calculation of roll motion of 15000GT container ship model coupled with tank sloshing in beam sea is carried on and analyze the effect of sloshing on ship roll motion with different water depth in the tank .The research shows that the wave elevation and pressure can be obtained exactly by present method if highly nonlinear phenomenon such as wave break does not occur. And the coupling ship motion results clearly reflect the influence of tank sloshing on ship motion and the variation of resonant frequency band. The effect of tank sloshing on ship roll motion can also be well simulated. It indicates numerical simulation has quite high efficiency and its results are in good agreement with experiment ones. It is a rapid approach to analyze ship with fluid tanks or tank stabilizer in its pre-design stage.