Shock Analysis of Onboard Equipment Submitted to Underwater Explosion

Abstract

This thesis is dedicated to obtain the structural responses of the particular equipment when a surface ship is submitted to underwater explosion (UNDEX). In the analysis, the influence of first shock wave and first two bubbles pulsations are taken into account. The main purpose of the thesis is to analyze the response of the equipment in case of UNDEX. Once, the main shock analysis method for the equipment (DDAM) is explained widely for evaluation of the structural response of the equipment. The Dynamic Design Analysis Method (DDAM) is based on shock response spectrum theory. Therefore, shock response spectrum is described in the thesis and generated by two different codes ANSYS and MATLAB for given time-history responses, which are obtained from a finite element transient analysis to simplified ship model. In order to get the response of the vessel’s structure, the finite element transient analysis is performed, considering the pressure load of the explosion which is provided by STX Europe. Additionally, the analysis is carried out in an explicit solver LSDYNA for a simplified ship model (semi-cylinder hull) structure which as much as presents a frigate properties. The first DDAM analysis is performed with both ANSYS and MSC. NASTRAN for a cantilever beam by using only the specified coefficients from NRL-1396 report. Obtained numerical results are compared with an analytical solution to verify the DDAM process in a finite element solver. Afterwards, the procedure is followed by more complex beam structure analysis such as an antenna. In the analyses of the antenna, the shock response spectrum is obtained from the acceleration or displacement time-history signals for an equipment on the vessel, where equipment located, also, by specified DDAM coefficients from G.J. O’Hara R.O. Belsheim NRL 1396, which is used by US and British Navies. Finally, the responses of the equipment such as displacements, stresses are obtained for different calculations and are compared in a manner based on the theory stands.