Acoustic radiation and modal coupling effects of finite plates considering fluid flow

Abstract

Naval and aerodynamic designers are concerned about the sound radiated from vibrating complex structures in heavy or light fluid medium excited by broadband random forces, that is, mechanical forces or turbulent boundary layer (TBL) pressure fluctuations. They wish to minimize significant noise radiation both outward to the medium and inward to the structure inside. Hence a method for computing the vibroacoustic response of structures acted by broadband random forces is of critical value to the designer by permitting him to select appropriate structural modifications (e.g. damping treatments) or to apply appropriate mechanical forces to structures to suppress structural vibration and the associated radiation of sound. Accurate methods of computation for the vibroacoustic response of the key components of complex structures such as plates and cylinders excited by random forces will provide a useful foundation extensible to more complex structures, e.g. airplane fuselage-wing systems, missiles, ribbed sonar domes, and ship-hull systems, etc. This thesis presents theoretical formulations of acoustic radiation from rectangular plates with a few ideal edge conditions in heavy and light fluid media excited by random forces, that is, arbitrary mechanical forces or turbulent boundary layer pressure fluctuations, in the presence of a uniform subsonic flow. This analysis is based on in vacuo modal expansion of both the plate vibration and the pressure fields. The plate vibration and the pressure fields described in modal domain are transformed into wavenumber-frequency domain. Numerical evaluation of the acoustic power is extremely time-consuming for broadband excitations. In order to obtain the approximate solutions, it is assumed that the broadband forcing functions have white spectra and remain unaltered due to the plate vibration and that the modal coupling is weak as long as structural damping is light. Under these assumptions, the approximate solutions for the surf...