A Reynolds-Averaged Navier-Stokes (RANS) method and a potential-flow method were employed in conjunction with a chimera domain decomposition technique for the prediction of hydrodynamic drag forces of submerged and floating sea caches in shallow water. The finite-analytic numerical method was used to solve unsteady RANS equations for turbulent free surface flows and Laplace equation for inviscid wave field. In order to capture the fully nonlinear free surface waves, the numerical grids were updated during the calculations to conform with the exact free surface elevations. Time-domain simulations were performed for three different sea cache configurations of rectangular, sharpedged, and round-edged shapes under strong ocean currents. Detailed velocity and pressure fields were obtained for all three sea caches which may be anchored on the sea floor, moored on the free surface, or tethered at mid-height. The drag forces were also computed to determine the optimal sea cache shape in terms of maximizing payload and minimizing drag.
The present study addresses some of the hydrodynamic issues relevant to the operation of a modular, submersible pontoon system (Sea Cache) in littoral water. Knowledge about environmental loads as well as seakeeping characteristics of pontoon based submersible structures in littoral water is limited. The primary objective of the present study is to develop a numerical method in support of the design efforts providing pontoon structures with the integrity, stability, and maneuverability required to operate in littoral environments. The sea caches may be moored on the surface as platforms for access by helicopters, anchored on the ocean floor for covert activity from below, or tethered for operation at any intermediate depth. Pertinent issues which need to be addressed include: (1) hull shape optimization in terms of maximizing payload, stability and strength, and minimizing drags;
