The effects of LNG-sloshing on the global responses of LNG-carriers
摘要
The coupling and interactions between ship motion and inner-tank sloshing are \ninvestigated by a potential-viscous hybrid method in time domain. For the time domain \nsimulation of vessel motion, the hydrodynamic coefficients and wave forces are obtained \nby a potential-theory-based 3D diffraction/radiation panel program in frequency domain. \nThen, the corresponding simulations of motions in time domain are carried out using the \nconvolution-integral method. The liquid sloshing in a tank is simulated in time domain by \na Navier-Stokes solver. A finite difference method with SURF scheme, assuming a singlevalued \nfree surface profile, is applied for the direct simulation of liquid sloshing. The \ncomputed sloshing forces and moments are then applied as external excitations to the ship \nmotion. The calculated ship motion is in turn inputted as the excitation for liquid sloshing, \nwhich is repeated for the ensuing time steps. For comparison, linear inner-fluid motion was \ncalculated using a 3D panel program and it is coupled with the vessel motion program in \nthe frequency domain. The developed computer programs are applied to a barge-type \nFPSO hull equipped with two partially filled tanks. The time domain simulation results \nshow reasonably good agreement when compared with MARIN's experimental results. \nThe frequency domain results qualitatively reproduce the trend of coupling effects but the \npeaks are usually over-predicted. It is seen that the coupling effects on roll motions appreciably change with filling level. The most pronounced coupling effects on roll \nmotions are the shift or split of peak frequencies. The pitch motions are much less \ninfluenced by the inner-fluid motion compared to roll motions. \nA developed program is also applied to a more realistic offloading configuration \nwhere a LNG-carrier is moored with a floating terminal in a side-by-side configurat