ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

5aSA8. Implementation of infinite elements in adaptive multilevel substructuring for structural acoustic calculations.

Paul D. DSouza

Jeffrey K. Bennighof

Dept. of Aerospace Eng. and Eng. Mech., Univ. of Texas at Austin, Austin, TX 78712-1085

A procedure is presented for incorporating infinite element modeling of the external acoustic medium in structural acoustic calculations using adaptive multilevel substructuring. The coupled structure--fluid system is modeled using finite elements for the structure, and for the acoustic fluid external to the structure and within a circumscribing prolate spheroid, and infinite elements external to the prolate spheroid, following the formulation of Burnett (1994). The adaptive multilevel substructuring approach transforms the structure model from the original finite element one in terms of nodal displacements, to a much more efficient one in terms of responses in approximate substructure vibration modes, which are selectively included in the model to optimize accuracy per degree of freedom. This approach is also used on the finite element portion of the acoustic fluid model, and results in a high level of model reduction there. Transformation of the infinite element portion of the acoustic fluid model is not practical because of its frequency dependence. The transformation process results in a linear system that is generally reduced in order, having a sparse symmetric coefficient matrix amenable to the use of a profile solver. The procedure is demonstrated on numerical examples in three dimensions. [Work supported by ONR.]