Numerical study on fluid resonance of 3-D multi-bodies by a non-reflection numerical wave tank

By introducing mass and momentum source terms into Navier-Stokes equations, a 3-D viscous non-reflection numerical wave tank is developed to investigate the fluid resonance of 3-D multi-bodies with a small gap in waves. The numerical model is first validated by the analytical solutions of the linear monochromatic wave and the experimental data of wave forces on two side-by-side ships in beam waves. Then extensive numerical experiments are conducted to investigate the wave height in the gap, wave forces on multi-bodies, the hydrodynamic differences between the isolated single body and multi-bodies, the influences of 3-D effects, etc. Due to the existence of the small gap, fluid resonance occurs at a special wave frequency, near which large-amplitude wave oscillations and wave forces in sway (i.e., Fy) are observed. The sway forces Fy are highly dependent on the wave height in the gap, while little relationship is observed between the wave forces in other directions (i.e., Fx and Fz) and the wave height in the gap. For this reason, the conventional potential model and inviscid model over-predict the sway forces Fy but works as well as present viscous model in predicting the wave forces Fx and Fz. In addition, the comparison research conducted between the 3-D multi-bodies and the corresponding 2-D multi-bodies in beam waves show that the 3-D effects make the resonant frequency increase but the resonant wave forces decrease.