Noise radiation from doubly periodic reinforced submerged plates

Almost all known structures are designed for low weight and high strength. For metal structures, especially aircrafts and underwater vehicles, this means reinforcement in the form of ribs. This paper presents an analytic model for the prediction of the acoustic scattered field from such rib-reinforced structures. The geometry is assumed to be that of an infinite elastic plate reinforced with a periodic double array of stiffeners. The plate is assumed to be in contact with a homogeneous and isotropic fluid on one side only, its other side being exposed to vacuum. The plate is modeled using the Mindlin plate theory which includes the effects of shear deformation and rotary inertia, thus allowing the evaluation of the scattered acoustic field at frequencies above the coincidence frequency. The reinforcements, exerting both forces and moments on the plate, are included in the model through their transverse and rotational impedances. A Fourier transform technique is used for evaluating the acoustic scattering of an incident plane acoustic wave by the fluid-loaded, reinforced plate and analytic solutions for the backscattered acoustic field are obtained. Numerical results for a wide range of frequencies are also presented.