Interaction tools for underwater shock analysis in naval platform design

In order to satisfy the need for good quality UNDerwater EXplosion (UNDEX) response estimates of naval platforms, TNO developed two 3D simulation tools: the Simplified Interaction Tool (SIT) and the hydro/structural code 3DCAV. Both tools are an add-on to LS-DYNA. SIT is a module of user routines for generating the UNDEX loading and accounts for the strong fluid-structure interaction on the wet hull of a 3D finite element model of the platform structure by means of sophisticated physical approximation. This eliminates the need for a 3D modelling of the surrounding water, such as necessary for advanced coupled finite element/hydrocode simulations. Both the shock wave stage with reflections and cavitation and the subsequent gas bubble loading are modelled in SIT. The SIT was tuned and validated using experimental data from full-scale surface ship shock trials. 3DCAV is a module of user routines that uses LS-DYNA’s Lagrangian fluid elements as a hydrocode for performing UNDEX simulations with less physical approximations. The results from 3DCAV simulations are used for tuning and validating the more efficient SIT for new applications like submarines and non-standard UNDEX scenarios for surface ships. A typical simulation of a detailed 3D finite element model of a naval platform takes only hours for a SIT simulation of the shock wave stage against days for a comparable 3DCAV simulation. Nevertheless, 3DCAV is still much more efficient compared to coupled Eulerian-Lagrangian hydrocodes. Its simulation efficiency has made SIT a prime UNDEX simulation tool for use in platform design, while 3DCAV remains highly useful for verification, validation and further SIT development. This paper provides a short overview of the physical backgrounds of SIT and 3DCAV, a comparison of their performance and examples of applications.