Abstract
Cavitation effects play an important role in the UNDEX loading of a structure. For far-field UNDEX, the structural loading is affected by the formation of local and bulk cavitation regions, and the pressure pulses resulting from the closure of the cavitation regions. A common approach to numerically modeling cavitation in far-field underwater explosions is Cavitating Acoustic Finite Elements (CAFE) and more recently Cavitating Acoustic Spectral Elements (CASE). Treatment of cavitation in this manner causes spurious pressure oscillations which must be treated by a numerical damping scheme. The focus of this paper is to investigate the severity of these oscillations on the structural response and a possible improvement to CAFE, based on the original Boris and Book Flux-Corrected Transport algorithm on structured meshes [6], to limit oscillations without the energy loss associated with the current damping schemes.
Highlights
For the past 20 years the finite element method (FEM) has been frequently used to model far-field underwater explosion (UNDEX) phenomena [12,13,18,26,27,28,30,33,34]
As in the previous section, the finite element flux-corrected transport (FE-FCT) model succeeds in reducing some of the larger oscillations that are observed in the 8th order Cavitating Acoustic Spectral Elements (CASE) results
Past work [34,35,36] has concluded that the capture of cavitation phenomena in numerical models of far-field UNDEX can be improved by applying the CASE methodology at the cost of increasing spurious oscillations in the problem domain
Summary
For the past 20 years the finite element method (FEM) has been frequently used to model far-field underwater explosion (UNDEX) phenomena [12,13,18,26,27,28,30,33,34]. Cavitation results from the pressure in the surrounding water dropping below its vapor pressure due to the motion of the ship structure (local cavitation) or the tensile shock wave reflected from the free surface (bulk cavitation) Both the incident shock wave and the cavitation regions present computational difficulties in far-field UNDEX finite element models. The need for fine meshes in far-field UNDEX FE models is a major obstacle in the ability to accurately simulate ship shock trials because far-field UNDEX models require a substantial amount of fluid to be modeled, especially in a full scale three-dimensional problem. An acoustic fluid is one in which disturbances in the fluid propagate at a constant speed and are small (geometrically linear), even if the constitutive behavior (i.e., cavitation phenomena) of the fluid is non-linear [12] Such a treatment is valid in the farfield problem, because shock and cavitation loading are early time events, occurring on the order of micro-seconds. This satisfies the conditions for acoustic treatment given in [43]
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