The effects of LNG-tank Sloshing on the roll responses of LNG-carriers
The coupling and interactions between ship motion and inner-tank sloshing were studied by a time-marching simulation scheme. For the time domain simulation, the hydrodynamic coefficients and wave forces were obtained by a potential-theory-based three-dimensional (3D) diffraction/radiation panel program in frequency domain. A finite difference method with SURF scheme, which assumes the single-value free surface profile, was applied for the direct simulation of liquid sloshing. For comparison, a coupling scheme was independently developed in the frequency domain using a sloshing code based on the linear potential theory. The hydrodynamic coefficients of the inner tanks were also obtained by a 3D panel program. The developed schemes were applied to a barge-type FPSO hull equipped with two partially filled tanks. The time-domain simulation results indicated similar trend when compared with MARIN's experimental results. The most pronounced coupling effects were the shift or split of peak-motion frequencies. The pattern of coupling effects between vessel motion and liquid sloshing appreciably changed with filling level. The liquid cargo could be a good vibration absorber when the resonance sloshing frequency was away from the motion natural frequency. This is an abstract of a paper presented at the 16th International Offshore and Polar Engineering Conference, ISOPE (San Francisco, CA 5/28/2006-6/2/2006).