Critical components in the study and improvement of ship survivability include the vulnerability of a ship to the impact of an underwater explosion (UNDEX) and how to incorporate this factor into early-stage ship design. When simulating surface ship early-time far-field UNDEX, the Finite Element Method (FEM) may be used to model shock wave propagation and cavitation in the fluid. This is a computationally intensive task, however, due to the large size of the fluid domain which typically requires several million degrees of freedom (DOF) in the mesh. The task is further complicated by the need to generate the fluid mesh around the irregular ship hull geometry. Ship design concept exploration requires fast simulation with minimal or no manual intervention in the mesh generation. The high-order Spectral Element Method (SEM) has proven to be a more accurate replacement for linear FEM in UNDEX modeling, but is restricted to using hexahedral elements in 3D. Therefore, the fast, automated application of the SEM in the surface ship UNDEX problem is hindered by the need to generate an effective and efficient unstructured hexahedral mesh. The research described in this paper assesses a mesh-first, automatic, all-hexahedral mesh generation scheme that provides excellent early-time UNDEX simulation results with only minimal compromise in the boundary geometry accuracy. The resulting fluid mesh is used with linear and high-order SEM elements and results are compared to an all-tetrahedral mesh generated by an automatic Delaunay refinement algorithm with linear FEM elements. The comparison is performed for both Total Field and Scattered Field Finite and Spectral Element Cavitating Acoustic fluid models. The goal of this study is to provide a method of modeling the fluid domain in early-time far-field UNDEX with sufficient efficiency and minimal mesh generation effort.

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