Underwater sound radiation by a layered infinite elastic plate with discontinuity
The underwater sound radiation from layered structu re is determined by the properties of elastic waves in the structure and by interaction between structural/structur al waves and between structural/fluidal waves. In t his paper, a model of a layered infinite plate is used to addres s how the properties and interaction influence the near field and far field characteristics of the radiated sound. In par ticular, the effect of structural discontinuity int roduced to the layered plate by a finite signal conditioning plate on unde rwater sound radiation is investigated. The scatter ing of structural waves in the layered plate by the signal conditioni ng plate is used to explain the changes in the radi ated sound due to the discontinuity.
Acoustic radiation from an insonified elastic plate with a line discontinuity
This paper deals with the development of analytic models for the prediction of the acoustic radiated field from an infinite elastic plate with a single line force and line moment impedance discontinuity due to an incident plane acoustic wave. The solution is in the form of a Fourier integral with a kernel having ten poles. The integral is evaluated by three methods. The first uses the steepest descent path (SDP) method, leading to a solution that decays as 1/(k0r)1/2. The second method used conformal transformations and the modified saddle point (MSP) method, where all ten poles of the integrand are factored out. This second method yields a solution that has complementary error functions and an asymptotic series in (k0r). The third method employs a transformation of the integrand to effect an efficient and fastly convergent numerical integration algorithm. In general, the MSP asymptotic series solution and the numerical integration yielded numerically identical results. However, while the SDP solution pre...
A spectral description of inertial effects in fluid-loaded plates
The wavenumber-based formulation of the surface variational principle (SVP) describes the surface pressure and displacement as a comparatively small set of interacting waves. It enables one to pose questions of parametric sensitivity from a global perspective. The present paper is the first application of such an approach to the question of the level of detail to which a model must be constructed. It considers a two-dimensional problem of an elastic plate in an infinite baffle, with pinned boundary conditions. A study by Feit and Johnson (1991) demonstrated that the signal scattered by the plate is significantly altered by the presence of an attached mass, and that the distribution of mass as well as the total mass, is important. In order to explore these issues, a line mass attached to the plate is replaced in the SVP formulation by a continuous spatial distribution. The functional form of this distribution is described in a spectral manner using Fourier series, whose ascending orders represent successive stages in refinement of the scale to which a modeldescribes inertial effects. The excitation applied to the plate is taken as a concentrated line harmonic force. With the excitation held fixed, the influence of each spectral component of inertial distribution on the surface response and radiated power are assessed. Evaluations carried out for a range of frequencies shed light on how small scale inertial heterogeneities can influence macroscopic radiation features