Underwater acoustic radiation by structures arbitrarily covered with acoustic coatings

Abstract

The shell structures of underwater vehicles are often covered with various acoustic coatings for the purpose of reducing the acoustic target strength or suppressing the structural vibration and underwater acoustic radiation. In engineering practice, there may be distinctions between acoustic coatings laid on different regions of the shell surface, and some bare regions may exist. For the complexity of the layout of acoustic coatings, a relevant calculation method needs to be developed to quantitively evaluate the effect of acoustic coatings on the reduction of underwater acoustic radiation. Further, the layout of acoustic coatings can be optimized on that basis. In this paper, the theory and relevant calculation method of three-dimensional sono-elasticity for ships arbitrarily covered by acoustic coatings are developed. By introducing an impedance matrix that describes the vibro-acoustic transfer between the inner and outer surfaces of the acoustic coating, boundary conditions on the interfaces of the acoustic coatings and the ambient water are derived. Expressions of the modal generalized hydrodynamic coefficients are given for the structure arbitrarily covered by acoustic coatings. Thus, the solution of vibro-acoustic and underwater acoustic radiation is obtained for the system of “ship structure-acoustic coating-water”. As an example, the acoustic radiation of a flat plate covered by acoustic coatings is numerically calculated and compared with analytical results, which verifies the correctness of the proposed method. Moreover, a series of results for the cylindrical shell structure with partial acoustic coatings are presented, which shows the interest of this method in engineering practice.