David S. Burnett
Rm. 1A-254, AT&T Bell Labs., Whippany, NJ 07981
This new 3-D time-harmonic acoustic infinite element uses a truncated form of the exact asymptotic series solution for general scattered and/or radiated fields, providing an accurate approximation all the way to infinity. The infinite element and a companion fluid--structure coupling element have symmetric matrices that fit seamlessly into any structural finite element code, providing a structural acoustic capability as versatile and powerful as the structural code itself. Most important, this approach is several orders of magnitude faster, for the same accuracy, than the traditional and almost universally used boundary element method (BEM) for the acoustics, i.e., the surface Helmholtz integral equation, which the author also developed and used for several years. The reason is that the bandwidth of the coupled system equations is much smaller for infinite elements (being a domain method) than for the BEM. Experience with both methods has revealed that the severe computational inefficiency of the BEM limits practical problems to low frequencies and simple structures, whereas this infinite element approach can handle the full range of frequencies and structural complexities that are encountered in purely structural analyses, at little additional cost.