Abstract: In recent years, a double-carriage amphibious vehicle has been developed to improve the carrying capacity of amphibious vehicle. Based on the full-scale model of an amphibious vehicle, the computational fluid dynamics method and the overlapping grid technique are used to establish a numerical simulation model of multi-body motion. Two carriages are connected by a spherical joint with three-dimensional degrees of freedom. The hydrodynamic performances, such as resistance, pitching and heaving motions, of the vehicle under still water condition are calculated, and the effect of spherical joint connection on the vehicle is analyzed. The numerically calculated result is basically consistent with the total resistance of the model towing tank test. The research results show that the hydrodynamic performance of the three-dimensional vehicle can be numerically predicted based on the realizable k-ε turbulence model and multi-body overlapping grid technology. The pitch angle is kept within 1°，and the pitch performance of the amphibious vehicle is excellent during its sailing in still water. Key

Key words: amphibiousvehicle, doublecarriages, sailinginstillwater, hydrodynamicperformance, overlappingmesh, sphericaljoint, pitch