Affiliations: Mechanical and Aerospace Engineering Department, Naval
Postgraduate School, Monterey, CA, USA
Note: [] Corresponding author: J.M. Didoszak, Mechanical and Aerospace
Engineering Department, Naval Postgraduate School, 700 Dyer Road, Monterey, CA
93943, USA. E-mail: [email protected]
Abstract: Current practices for modeling the ocean floor in underwater
explosion simulations call for application of an inviscid fluid with soil
properties. A method for modeling the ocean floor as a Lagrangian solid, vice
an Eulerian fluid, was developed in order to determine its effects on
underwater explosions in shallow water using the DYSMAS solver. The Lagrangian
solid bottom model utilized transmitting boundary segments, exterior nodal
forces acting as constraints, and the application of prestress to minimize any
distortions into the fluid domain. For simplicity, elastic materials were used
in this current effort, though multiple constitutive soil models can be applied
to improve the overall accuracy of the model. Even though this method is unable
to account for soil cratering effects, it does however provide the distinct
advantage of modeling contoured ocean floors such as dredged channels and
sloped bottoms absent in Eulerian formulations. The study conducted here showed
significant differences among the initial bottom reflections for the different
solid bottom contours that were modeled. The most important bottom contour
effect was the distortion to the gas bubble and its associated first pulse
timing. In addition to its utility in bottom modeling, implementation of the
non-reflecting boundary along with realistic material models can be used to
drastically reduce the size of current fluid domains.
