Angela K. Karali
Dept. of Eng., Penn State Univ., 147 Shenango Ave., Sharon, PA 16146
Sabih I. Hayek
Penn State Univ., University Park, PA 16802
Almost all known structures are designed for low weight and high strength. For metal structures and especially aircrafts and underwater vehicles this means reinforcements in the form of ribs. This paper presents the development of analytic models that can be used in predicting the acoustic scattered field from such structures, assuming that the geometry is that of an elastic plate of infinite dimensions reinforced with a periodic double array of ribs. The plate is in contact with a homogeneous and isotropic acoustic fluid on one side only. Mindlin's plate theory is used in modeling the plate and this allows the evaluation of the nonspecular scattered field, generated at the reinforcements, at frequencies below and above the coincidence frequency of the plate. The reinforcements are assumed to exert both forces and moments on the plate and they are included in the mathematical model through their transverse and rotational impedances. A Fourier transform technique is used to evaluate the nonspecularly reflected field due to the periodic double array of ribs. Analytic solutions are obtained and implemented numerically for frequencies ranging from 1 to 15 times the classical coincidence frequency of the plate.