The Program DYSMAS/ELC and its Application on Underwater Shock Loading of Vessels

Abstract

The simulation of highly dynamic processes concerning structural response, fluid dynamics and the behavior of coupled systems can advantageously be managed by an explicit finite formulation, which is able to handle the various nonlinearities appearing in the wide field of short-time physics. The program family DYSMAS has been developed step by step in connection with a great number of projects mostly in the field of defense technology. The DYSMAS code consists of the two stand alone processors DYSMAS/L, a FE-Lagrangian code, and DYSMAS/E, a FD-Euler ian code and additionally of DYSMAS/ELC in which both are coupled together in 2D and 3D.

The code takes into account large displacements and distortions by the formulation of the basic equations. Its extensive material description allows the treatment of large plastic flow including work hardening and strain rate dependency, as well as material failure and post-failure-behavior using progressive methods such as crack-opening or erosion models. The 3D multibody contact processor enables the DYSMAS-user to simulate impact, penetration and crash problems. Especially fluid-structure-interaction phenomena are distinguished by nonlinearities present both in structure and in fluid. The low compressibility of water in compression and its cavitation properties under tension have great influence on the transient loading of vessels subjected to underwater detonations.

In the recent years DYSMAS/ELC was applied to the simulation of a lot of underwater detonations against various ships and submerged structures. As an example this report covers the evaluation of a torpedo shot in the nearfield of a frigate- sized ship. The investigation embraces the detonation shock wave and its propagation in the fluid and in the structure as well as the mechanical damage to the ship hull, caused by the shock wave and by the dynamic pressure due to the gas-bubble- expansion. The results comprise the assessment of damage on equipment based on the evaluation of the shock-spectra, which enable the analyst to make a decision about the residual serviceability of the total system or subsytems.

DYSMAS/ELC at present is also used to simulate soil-structure interaction phenomena as for instance the detonation of buried charges against a shelter structure or terminal ballistics phenomena including ricochetting of projectiles on soil or fluid.