IMPLEMENTATION AND EXPERIMENTAL VALIDATION OF A NEW VISCOTHERMAL ACOUSTIC FINITE-ELEMENT FOR ACOUSTO-ELASTIC PROBLEMS

The propagation of sound waves in thin gas or fluid layers can be sign ificantly affected by viscothermal phenomena. In this paper, a new vis cothermal acoustic finite element is presented. The element includes t he effects on inertia, viscosity, compressibility and thermal conducti vity. The acoustic element can be coupled to flexible structural eleme nts. This enables fully coupled acousto-elastic calculations to be mad e for complex geometries. The model is experimentally validated with m easurements on a rigid airtight box with a flexible coverplate. Eigenf requencies, damping and mode shapes of the plate were measured and com pared with numerical results for a number of gas layer thicknesses. Th e agreement between measurements and calculations is good. The results indicate that there can be large shifts in eigenfrequency as a functi on of the layer thickness. In addition, for small layer thicknesses a high damping value is found, which can be attributed to viscous effect s in the layer. (C) 1998 Academic Press.