Simulation of ship motions coupled with tank sloshing in frequency domain

Abstract

[Objectives] With the increase in the size of the ship with liquid tanks (LNG, FPSO, FLNG, etc.) and the improvement of work efficiency and operational safety, the coupled problem between the tank sloshing and the resulting ship motions have become more serious. Therefore, to effectively solve it,[Methods] firstly, based on 3D potential flow theory and wave radiation/diffraction theory, the simulation program using the higher-order Boundary Element Method(BEM) which can compute the load and motion of 3D floating structures induced by wave is developed. To verify the accuracy of this simulation program, the simulation results of a FPSO model is compared with the results obtained from the hydrodynamic software HYDROSTAR and AQWA. Secondly, a equation for the ship motions in frequency domain considering the effects of the tank sloshing is established to obtain the coupled motion response by combining the frequency domain solution method for the hydrodynamic coefficient of the tank sloshing with that for the ship motion. Finally, a FPSO ship with two liquid tanks is taken as an example to demonstrate the accuracy of this simulation program.[Results] By comparing the motion responses of the ship with different tank filling levels, it is found that there is a shift in the roll resonance frequency, there are multiple peaks in the coupled roll motion, and different effects are caused due to different tank filling levels.[Conclusions] This study provide a reference for the motion response design of the ship with liquid tanks.

Keywords

• ship motion
• tank sloshing
• FPSO
• coupling motion