Research On Measurement Of Absorption Coefficient Of Underwater Acoustic Materials By Reverberation Method

The sound absorption coefficient of underwater acoustic materials is one of the important parameters to evaluate the performance of sound absorbing materials.Therefore,it is an important basic work to accurately measure the absorption coefficient of underwater acoustic materials.There are many different methods for measuring the sound absorption coefficient,such as the standing wave tube method and the transfer function method,etc.However,in practical engineering,the direction of sound waves incident on the surface of the material is random,so the reverberation chamber method is a classic method for measuring the average sound absorption coefficient of the material when the sound waves are incident irregularly.Due to the large differences in the physical properties of water and air,the acoustic properties of underwater reverberation fields are quite different from those of air,Therefore,when reverberation method is used to measure the acoustic absorption coefficient of underwater acoustic materials in underwater enclosed space,the uncertainty increases.It is of great significance to carry out research on the measurement method of the sound absorption coefficient of underwater acoustic materials based on the reverberation tank method.In this paper,the acoustic field characteristics of glass tank reverberation are analyzed from three aspects: theoretical derivation,numerical simulation and experiment.The technology of measuring material absorption coefficient in air reverberation chamber is applied to reverberation tank.First,from the two aspects of wave acoustics and statistical acoustics theory,this article analyzes several basic acoustic characteristics,such as normal vibration mode,the number of normal waves in a unit frequency band,modal density,steady-state frequency response,cut-off frequency and other basic acoustic characteristics.And the calculation formula for measuring the sound absorption coefficient of underwater acoustic materials by reverberation method is derived.Next,through simulation modeling calculations,the simulation results of the sound fielddistribution under different sound source positions,the relationship between the sample area and the change of the sound field distribution are given.Finally,the simulation results are verified through experiments.The sound absorption coefficient is analyzed by the influence of factors such as the position of the sound source,the area of the test piece,the measurement distance of the hydrophone,and the calculation method of the reverberation time.And an ideal measurement method and test results(reverberation tank size 1.6m,0.75 m,1m,frequency band 8k Hz-25 k Hz range)are given.