Study On Coupling Effects Of Floating Box Motion And3D Sloshing In Waves

Ships carrying tanks with partially filled liquid in waves may experience violent internal liquid sloshing. Therefore ship motions are not only affected by wave excitation but also by internal sloshing forces and moments. This coupling effect may excite ship motion which can lead to dangerous situation or make structural damage as a result of large sloshing impact on liquid tank. So studies on ship motions coupled with sloshing in waves are indeed necessary.This article studies the wave exciting forces by boundary element method, and sets up a3D ghost boundary SPH model to simulate the internal liquid sloshing, then solves the ship motion using an impulse-response-function(IRF) method. The coupling effect of wave excitation and internal sloshing is realized and the model of ship, which is simulated by floating box, motions coupled with3D sloshing in waves is set up.The good agreement with other numerical and experimental results make present numerical model believable to simulate floating box motions affected by wave excitation coupling with internal liquid sloshing. Compared to empty box, partial liquid filled floating box may experience a peak of motion responses, which is always happened at the lowest linear natural frequency of the inside sloshing. The peak is produced by phase difference of internal sloshing force and wave exciting force. When wave frequency comes lose and not larger than the natural frequency, the phase difference is almost180degree so the sloshing effect impede the motion of floating box. And when wave frequency exceeds the natural frequency of liquid, the phases of sloshing force and exciting force is very close which promote the floating box motion.Furthermore, wider floating box with partial filled liquid is studied. The result shows that the trend of floating box motion responses will not change. The wider liquid filled box just enhances the effect of sloshing force. When the phase difference of sloshing force and exciting force is large and sloshing force is less than exciting force, the wider box impede the motions more obviously, and if the phase difference is small wider box is more easily to magnify the motion responses. Besides, studies on different outer water depth show that the water depth has little effect on motion responses to some extent.Finally, experiment considering the coupling effects of ship motion and sloshing on the roll motion is taken. Different wave amplitudes have been carried out in a wave flume and the response-amplitude-operator (RAO) results of steady-state roll motions have been analyzed. This study shows that RAO results of different wave amplitudes with fixed wave frequency are without consistency which indicates the incident wave has nonlinear influence on ship motion. The higher wave height of low frequency wave is, the smaller RAO results. The higher wave height of high frequency wave is, the bigger RAO results. Relevant research should pay attention to this phenomenon.