Research Of Multi-Hull Vessels' Longitudinal Motion Prediction

This paper presents a method for predicting the hydrodynamic property and motion characteristics of high-speed displacement ship based on 2.5D theory. The formulation of 2.5D theory retains forward speed effects on the free surface for the hydrodynamic calculation of fast ships. At the same time, the solution is based on two-dimension Laplace equation according to the slender body assumption. The computational precision of 2.5D is higher than strip method and the time consumption is much less than that based on three-dimensional Green's function with forward speed.2.5D theory is a potential flow theory method which neglects the viscosity of water. In this paper, the cross flow method is used to calculate the viscous effects on conventional high-speed displacement ship. Because the bow-up state of ship has a great change when the ship travels with high speed, the mean wet surface also has a great change. The effect of bow-up state on the ship's motion prediction is investigated.Trimaran and pentamaran are two kinds of unconventional displacement hull form, the performance of which are very promising for military and commercial application. Compared with the mono-hull ship, the introduction of the side hulls makes the flow field around the multi-hulls more complicated as the interaction between the hulls. In this paper, a numerical prediction method for the motion characteristics of displacement multi-hulls is presented based on 2.5D theory, and the numerical predictions are compared with experimental results. It is found that 2.5D theory can give satisfactory predictions of the motion response characteristics of multi-hulls.The characteristic of hydrodynamic interference between piece hulls of multi-hulls is studied, and the effect of various piece hulls' arrangement on seakeeping is investigated by changing the space between hulls and the longitudinal position of side hulls.