Dynamic analysis of underwater launched vehicle during water exit

While underwater launched vehicle crossing water free surface, the structure dynamic analysis, taking account of Fluid Structure Interaction effect, is conducted. The flight vehicle is simplified into a free-free Timoshenko beam. The FSI effect is treated as added mass varying with wet surface area, which decreases with the water exit of vehicle. Mode analysis presents step shaped frequencies increment and the variations of mode shapes. The dynamic response subjected to external load, which is mainly caused by the collapse of cavity, is calculated. Result shows the necessary of taking account of FSI and the influence of relative position between external load and water free surface on internal forces response. Besides, the effect of water exit velocity on internal force response amplitude has been studied.