| In an underwater-shock environment, cavitation, i.e., boiling, occurs as a result of reflection of the shock wave from the free surface and/or wetted structure that causes the pressure in the water to fall below its vapor pressure. If the explosion is sufficiently distant from the structure, the motion of the fluid surrounding the structure may be assumed small, which allows linearization of the governing fluid equations. Felippa and DeRuntz (1984) developed the cavitating acoustic finite element (CAFE) method for modeling this phenomenon. While their approach is robust, it is too computationally expensive for realistic 3-D simulations. In the work reported here, the efficiency and flexibility of the CAFE approach has been greatly improved by: (i) separating the total field into equilibrium, incident; and scattered components, (ii) replacing the bilinear CAFE basis functions with high-order Legendre-polynomial basis functions, which produces a cavitating acoustic spectral element (CASE) formulation, (iii) introducing a simple, non-conformal coupling method for the structure and fluid finite-element models, and (iv) introducing structure-fluid time-step subcycling. Field separation provides flexibility, as it allows the incorporation of non-acoustic incident fields, and propagates incident waves through the mesh with total fidelity. The use of CASE admits a significant reduction in the number of fluid degrees-of-freedom required to reach a given level of accuracy. The combined use of subcycling and non-conformal coupling affords order-of-magnitude savings in computational effort. The benefits provided by these improvements are illustrated with 1-D and 3-D canonical underwater-shock problems. |
