Simulation study on measuring structural surface impedance in air reverberation room

摘要

Low-frequency active acoustic detection of underwater targets is of much interest both at home and abroad. The scattering field of targets is uniquely determined by its structural surface impedance, sound radiation impedance and acoustic load. Because the internal structure of targets and their surface coatings are usually extremely complicated, computations in numerical simulations are time consuming and complex, and it is difficult to acquire the structural surface impedance accurately by numerical methods such as the Finite Element Method (FEM), even at low frequencies. Therefore, W. A. Kuperman derived an experimental method of obtaining the structural surface impedance of an elastic body by placing it in an encompassing and spatially random noise field and cross-correlating the pressure and normal velocity measured on its surface. This method has been validated in reverberation tank experiments. Furthermore, structural surface impedance has its own natural characteristics that have nothing to do with the characteristic impedance of outer fluids. Compared with a reverberation tank, an air reverberation room has many advantages, such as high measuring accuracy, convenient operation and low cost, especially at low frequencies. Considering all that, we undertake a simulation study of measuring structural surface impedance in an air reverberation room. Taking a coated elastic spherical shell for example, the air reverberation field is constructed and finite element software COMSOL Multiphysics is used as a tool to simulate an experiment. The structural surface impedance is obtained by measuring sound pressure and normal velocity on its surface. Thus, the underwater scattering field can be acquired. Finally, comparative analysis of the theoretical and numerical solutions in this case shows that measuring structural surface impedance in an air reverberation room and applying it to predict underwater scattering fields are feasible.