This paper presents an elasticity theory solution for computation of acoustic radiation by a point- or line-excited fluid-loaded laminated plate, which may consist of a stack of an arbitrary number of different isotropic material layers. A one-side water-loaded three-layer sandwich plate, which consists of a hard rubber core sandwiched between two steel plates of equal thickness, was used as an example of the laminated plates. The approximated equivalent sandwich plate solutions were compared with the elasticity theory solutions. These results show that the approximated solutions are, as expected, valid only at frequencies much lower than the coincidence frequency. The numerical result also shows that, even at about one-tenth of the coincidence frequency, the approximated solutions suffer substantial error. The differences between the dry-side- and the wet-side-excited radiated fields of a single-layer uniform plate and a sandwich plate were investigated and compared, and found to be significantly different at frequencies above the coincidence frequency. [S0739-3717(00)01803-1]
An exact mathematical formalism was developed to calculate the acoustic response of a fluid-loaded, multilayer, sandwich plate subjected to a point-harmonic excitation. The plate can be fluid loaded on each side with arbitrary acoustic media. The solution was verified with asymptotic solution of a fluid-loaded thin steel plate. Numerical examples are presented for the acoustic radiation into water from various plate configurations subjected to a point force acting on its dry (air) side. The plate configurations considered are: (1) a two-layer elastic/viscoelastic plate, (2) a three-layer symmetric elastic/viscoelastic/elastic sandwich plate, and (3) a three-layer nonsymmetric elastic/viscoelastic/elastic sandwich plate with the viscoelastic layer given a range of different material properties (elastic constants, damping) and thicknesses. To elucidate the radiation mechanisms, the behavior of the modes of wave propagation in the plate is discussed. [Work supported by ONR.]
This paper presents an elasticity theory solution for computation of acoustic radiation by a point- or line-excited fluid-loaded laminated plate, which may consist of a stack of an arbitrary number of different isotropic material layers. A one-side water-loaded three-layer sandwich plate, which consists of a hard rubber core sandwiched between two steel plates of equal thickness, was used as an example of the laminated plates. The approximated equivalent sandwich plate solutions were compared with the elasticity theory solutions. These results show that the approximated solutions are, as expected, valid only at frequencies much lower than the coincidence frequency. The numerical result also shows that, even at about one-tenth of the coincidence frequency, the approximated solutions suffer substantial error. The differences between the dry-side- and the wet-side-excited radiated fields of a single-layer uniform plate and a sandwich plate were investigated and compared, and found to be significantly different at frequencies above the coincidence frequency.
One of the outstanding features of the multilayer composite plate is that it can be tailored for a specific structural-acoustic application by intelligently arranging the various layers of elastic and viscoelastic materials. In this study, the multilayer composite plate under consideration possesses a layer of viscoelastic material with high material loss factor for attenuating the propagating waves. For a fluid-loaded case, certain propagating modes dissipate their energy through radiation into surrounding fluid medium, and decreases in amplitude in the direction of propagation even if no material loss factor is assumed. Study of the wave dispersion of this composite plate indicates that the dispersion characteristics and the mode shape of the propagating wave are affected by the amount of damping in the viscoelastic material. The reasons for the aforementioned effect are discussed. Numerical examples are presented for various plate configurations with the viscoelastic layer given a range of material loss factor. [Work supported by ONR.]
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