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 established wave tank avoids the wave reflection and re-reflection from the opening boundaries, and it works well in simulating the wave propagation and predicting the wave forces on the multi-bodies.•For the wave interaction with multiple floating structures, similar fluid resonance phenomena are observed to take place at approximately the same frequency in waves with different incident directions. The sway forces on the multi-bodies are highly dependent on the wave height in the gap, while little relationship is observed between the wave forces in other directions and the wave height in the gap.•Compared with the conventional potential model and inviscid model, the present viscous model generates much improved predictions in the wave height in the gap and the sway exciting forces on the multi-bodies.•Comparison researches between 3-D and 2-D multi-bodies show that three-dimensional effects of the multi-bodies make the resonant frequency increase but the resonant wave forces decrease. 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