Dowling Wall Pressure-Spectrum Analogy Applied to an Isotropic Two-Layered Elastic Medium

摘要

The Dowling analogy applies Lighthill's equation to predict the surface pressure spectrum on a single elastic layer subjected to turbulent excitation. We have extended the analogy to obtain the low wavenumber surface pressure spectrum for an infinitely long two-layered isotropic elastic media. This low wavenumber model includes the effect of turbulent surface shear stresses on the wal pressure spectrum. The surface pressure spectrum is calculated on the surface of the elastic layer in contact with the turbulent fluid and for the interface between te two different elastic layers. Water is used for the turbulent fluid on one surface of the elastic media. Air at rest is used as the fluid media in contact with the opposite surface. Pressure spectra are given first for the reduced case in which both layers are treated as steel of particular thicknesses at various frequencies. Then, we compare this to the pressure spectrum on the surface of two different viscoelastic layers applied to the steel plates. The results show that the propagation speeds of compressive, shear, and flexural waves in the elastic layers govern the location of singularities in the pressure spectra. It is also shown how damping can affect the strength of the singularities and the level of the local maxima.