Computation of the response of a window embedded in a 3-D enclosure to a sonic boom using FE/BE techniques

Abstract

The response of a structure to a sonic boom is posed as a structural-acoustics problem. The boom is represented by a plane acoustic wave with a propagation vector defined by the flight heading and Mach number. The box-shaped structure is rigid, except for the presence of a glass panel embedded in one of the walls. A second panel on the wall opposite that may be made to be transparent or rigid is also introduced for diagnostic purposes. The glass panel is modeled as an elastic plate and the enclosure is assumed to rest on a rigid ground plane. Finite element-boundary element techniques embodied in the computer code, NASHUA, are used to obtain the solution numerically. Structural-acoustic reciprocity is invoked to reduce computation time. The window response is computed in both the frequency and time domains. Window resonances, room modes and, with an “open” window a Helmholtz resonance, are identified and the effects of diffraction around the enclosure are described. Finally, the statistics for the response of the window over an ensemble of flight headings are computed as a function of Mach number.