Rules and methods for dimensioning embarked materials for surface ships when subjected to UNDEX

Abstract

This Master thesis is dedicated to the study of the different rules available in order to perform the analysis for surface ship during an underwater explosion (UNDEX). The document performs a review of the up-to date techniques used in order to perform an UNDEX analysis, as well as the different equations and variables which are present during this type of event, exploring the different formulation available. Since the tools used to perform a ship UNDEX analysis must take into account complex behavior, such as the fluid structure interaction and cavitation effects, formulations which are included in commercial codes are also exposed with some examples. At the same time, some comparisons are showed between numerical simulations obtained using professional codes and simplified formulation. The compare results are plastic strain, and stress levels, as well as displacement time histories obtained at some points of the structure being analyze. Furthermore the document explores the different rules available for the design of structures subjected to an UNDEX, and points out the common information between all of the documentation available. This information is then used for the construction of a new procedure that will highlight the main consideration in order to perform an UNDEX analysis. The procedure in then applied to the elastoplastic response analysis of a ship section submitted to a spherical shock wave. Bottom deflection and plastic strains, calculated by two different nonlinear finite element codes, are compared. The first code, used by STX France, is based on an implicit time integration solver, while the second one, used in ICAM, is based on an explicit one. Finally some conclusions on the obtained results are presented and some recommendations on nonlinear response analysis of naval structures submitted to underwater explosions are given.