Measurement and prediction of diffuse fields in structures

Abstract

Measurements and predictions of the response of a variety of plain and coupled plates when excited by a point source have been reported. Tests on plain plates showed that a diffuse field was generated within the first 30 wave transits across the plate. In plates coupled by a thin ligament, around 50 wave transits across one of the substructures was required for a diffuse field to be established in the whole system. This is equivalent to about 25 transits across the whole plate so the time required to set up a diffuse field was not significantly affected, even when the ligament width was only 2.5% of the total plate width. Tests on plates bolted or adhesively bonded together showed that in both cases, although a diffuse field was established in each of the substructures, the damping was too great for a diffuse field to be set up in the whole structure. Tests on stepped plates have shown that the measured surface amplitudes in the thinner sections tend to be much larger than those in the thick sections, but that the energy in the thinner sections is only slightly larger than that in a thick section of similar plan area. The field is not diffuse in the sense that the amplitude or energy density is the same throughout the coupled structure, but the field is diffuse in each substructure.