The coupling motion of heave, pitch and roll of intact ship and damaged ship in waves, and the flow of flood water in damaged tank have been simulated based on viscous theory. The calculation model is a 29000 t tanker model moving at a constant speed with damaged tank in midship area. Three cosine waves including head waves, beam waves and oblique waves are simulated by boundary input method respectively and the free surface is captured by Volume Of Fluid (VOF) method. The RANS equation is solved on full hexahedral unstructured grids using moving grids technique that is rigid deformation integrated with weighted deformation. The calculation method is verified by simulating the ship model test of DTMB5512 conducted by IIHR ship hydrodynamics group. It is shown that:
the nonlinear motions of ships in waves are affected by various factors, such as the influence of encounter frequency and the coupling effect of the motions, and
the flow of flood water in damaged tank has a complex impact on ship motion and to obtain the influence the effect factors should be comprehensively considered.