unsteady cavitating flows surrounding the projectile during the underwater launch process are numerically and experimentally analyzed to investigate the collapse mechanism of the cavitating bubbles and its coupling effect with the vibration of the structure. We have examined the evolution of unsteady cavitation around the shoulder and tail of a rigid projectile when it is vertically launched. Navier-Stokes equations are solved with a mass transfer cavitation model using multi-block sliding mesh. Numerical results of the surface pressure change and the fluctuation in the exit-water phase have a fair agreement with the experimental data. The mechanism for the occurrence and evolution of cavitation collapse is investigated through flow field analysis. The generation of collapse pressure is simplified as the water layer accelerating and impacting the wall, and a physical model is established. In addition, from the dimensional analysis we observed that the bending fracture is the major potential damage form of structure, and the natural frequency of structure is a key factor to the coupling effect. Finally, a simplified process of the projectile with initial traverse velocity is studied by a fluid-structure interaction approach. The results demonstrate that the coupling effect between vibration deformation and collapse pressure is significant to enlarge the vibration amplitude. (C) 2014 Elsevier Ltd. All rights reserved.