Numerical simulation of surface ship hull beam whipping response due to submitted to underwater explosion

Abstract

This study presents a method to evaluate the whipping response of a surface ship subjected to an underwater explosion. Within the analysis, the effects from both first shock wave and secondary bubble oscillation are considered. The analytical model “Doubly Asymptotic Approximation” (DAA) is applied to obtain the acoustic pressure. The main purpose of this study is to clarify the influence of the secondary bubble pulsation on the ship structure whipping response.

Once the method is widely described, it is implemented in two distinct numerical finite element software packages: an explicit code developed for LS-DYNA as well as an implicit code executed in ANSYS. First of all, DAA model is applied to a clamped plate and a semicylinder structure which is simulated as a simplified ship model in LS-DYNA so as to observe the structural behavior with respect to the nonlinear pressure, such as effective plastic strain and vertical deformation. Afterwards, the code is modified and applied to the same cylinder model in ANSYS by following an identic procedure; thus, the results obtained from both codes can be compared.

Finally, the presented method is applied to a frigate surface ship FEM model with a coarse mesh, provided by STX Europe. This model will be employed as the reference ship for carrying out the structural response calculation.