Research On Added Mass Of Cavitating Vehicles By Boundary Element Method

Added mass is an important parameter to research the maneuverabilities and vibration characteristics of underwater vehicles. Since the attached cavity may change the wetted surface area of vehicles and cavity deformation can bring great influence on the flow field, the added mass of cavitating vehicles is different from that in fully wetted flow. It depends not only on the outline of the vehicles but also on their motion history. And considering the difficulty in measuring added mass of cavitating vehicles in experiment, it’s necessary to research this problem numerically.This thesis writes the programs of the high-order BEM and studies the added mass of cavitating vehicles during rigid motions and bending vibrations. The main contents are as follows:1) The high-order BEM is built with the boundary surfaces described by non-uniform rational B-splines(NURBS), the source(sink) strength and dipole strength on the surfaces described by Bsplines, the singular integrals caculated by the cubic polynomial transformation method and the linear algebraic equations set up by the allocation method. Then, the method is verified by caculating the added mass of a series of bodies in fully wetted flow.2) The axisymmetric steady cavities and flow fields of underwater vehicles are caculated by the high-order BEM. With the initial cavity surface given by the independence principle of cavity section expansion, the iteration steps reduce largely. The present results are in good agreement with the existing experimental and numerical results. Then the influences of the cone angle of the headform and the cavity number on the cavity surface are investigated.3) The method built by Uhlman is applied to cavitating vehicles to calculate the added mass of axial translation, transverse translation and rotation. The relationships of the added mass with the oscillation frequency, cavity number and the cone angle of the headform are researched. Then a new explanation to the influences of the frequency on the added mass is presented from the effects of cavity deformation.4)The method to caculate the added mass of rigid bodies is generalized to elestic bodies. FEM is used to caculate the dry modes of bending vibration of the simplified vehicle model. Then the added mass of the bending vibration modes, inter-mode coupling and rigid-vibration coupling are researched by the generalized method. The study builds basis for researching the vibration responses of the fluid-structure coupling systems of cavitating vehicles by the dry-mode method.