| Popis: |
One approach to modeling the resonant behavior of structures in a compressible fluid is to use finite elements to describe the structure and boundary elements to describe the fluid. The fluid loading is characterized by a complex, frequency‐dependent influence matrix that is combined with the frequency‐independent stiffness and mass matrices obtained from the finite element model. This approach works well for determining the fluid‐loaded harmonic response of the structure over a specified frequency range, if one knows the appropriate frequency range over which to perform the analysis. Since the in‐fluid resonance frequency is usually not known, the designer must choose successive frequency sets until the resonance peak is found. This paper describes a method that eliminates this guesswork by computing the in‐fluid eigenfrequency of the mode of interest using boundary elements to model the fluid loading. The procedure is iterative, beginning with the in vacuo eigenfrequency and continuing until the in‐fluid eigenvalue converges. The designer may then perform a harmonic analysis in a narrow band about the computed eigenfrequency to obtain the structural and/or acoustic response levels. The accuracy and efficiency of the technique is demonstrated with two examples: a spherical shell and a low‐frequency projector, both in water. |
