Transient sound tadiation from a clamped circular plate with viscoelastic coatings

Abstract

Sound radiation from the vibration of an elastic structure excited by impact forces is a fundamental problem in acoustics. The mechanism of sound radiation depends on the geometry and the nature of contact between the impinging objects. In general, the dynamic response of a plate by an impact forces can be divided into its forced and free vibrations. The forced response of the plate may be elastic deformation of its surface, and the free vibrations of the plate result in what is called "ringing" radiation. The increasing needs for reducing vibration and sound radiation in light weighted structural members such as aircraft and automobile components, have focused on the attenuation by employment of viscoelastic coating, as a possible solution for this problem. The flexural vibration characteristics of a composite plate consisting of one or two outer layers of a linear viscoelastic material bounded to an elastic core have been discussed because of their increasing application in various fields. Sound radiation from most mechanical systems results from various kinds of impact forces. In this paper, the transient sound radiation from the impact on the clamped circular plate with viscoelastic layers is studied both analytically and experimentally. First, the contact force applied during the collision between an elastic sphere and a composite plate is obtained by Hertz contact theory. The composite plate vibrations are obtained by using the Laplace transform, the convolution theorem, the normal mode analysis and the eigenvalues that are obtained by a Mindlin plate theory. In the classical plate theory the effects of rotary inertia and shear deformation are neglected, while in the Timoshenko-Mindlin plate theory these effects are included. The radiated sound pressure is calculated by the Rayleigh integral in the farfield. Prediction of the waveforms of sound radiating from the plate with attached layers and a method for reducing noise generation from the plate by impac...