Study On Vibration Of Fluid Cavity In Underwater Acoustic Transducer

The fluid cavity resonant mode(also known as Helmholtz resonant mode)is a commonly used low frequency vibration mode in underwater acoustic transducers.It can transmit low-frequency acoustic wave with small size because of the low resonance frequency and high electromechanical conversion coefficient.In addition,the underwater acoustic transducer with fluid cavity can usually work in deep water,due to the native free-flooded structure.Moreover,the fluid cavity resonant mode can also be coupled with the structural vibration mode of the drive source to form a broadband transmission.So,fluid cavity is widely used in underwater acoustic transducers.At present,the theoretical analysis of the vibration of the fluid cavity in the underwater acoustic transducer usually based on lumped parameter model,lead to the analysis is confined to first vibration.At the same time,excessive hypothesis analysis introduced large errors.In this paper,the author expand the analysis object to multi-order mode by using distributed parameter model.Firstly,the study on fluid cavity vibration is carried out by using the analysis method for distributed parameter system.The sound pressure and vibration velocity distribution function are obtained by the wave equation which satisfied the vibration of the cylindrical fluid cavity.The relation between sound pressure and volume velocity is solved by boundary conditions.And then obtaining a four-terminal equivalent circuit.The influence of elastic cavity wall on the vibration of fluid cavity in practical application is studied.A method of correcting the sound velocity of the fluid in the elastic cavity is proposed which can effectively improve the accuracy of theoretical calculation.Secondly,a symmetric fluid cavity transducer and an asymmetric fluid cavity transducer excited by a piezoelectric ring transducer are designed for theoretical verification.The equivalent circuit corresponding to the transducer model to calculate the multi-order resonance frequency of the fluid cavity is given.The simulation calculation was carried out by using the finite element software COMSOL,and compared with the theoretical calculation results to verify the accuracy of the theoretical analysis.Then,based on the simulation design results,the experimental prototype of the symmetric and asymmetric fluid cavity transducer is designed.The electro-acoustic performance of the prototypes are tested in anechoic tank.Test results show good agreement with the theory and simulation results.It is proved that the theoretical method has guiding significance for designing a fluid cavitytransducer.Finally,in order to optimize the performance of the fluid cavity transducer,a conical fluid cavity radiation end and multi-excitation drive optimization method are proposed which can improve the transmission voltage response while achieving uniformity of the transmitted voltage response at the multi-order resonance frequency.The equivalent circuit corresponding to the transducer model is used to calculate the resonance frequency.Then,theoretical calculation results and performance optimization method are verified by simulation analysis.An ultra-low frequency fluid cavity transducer was designed to verify the effectiveness of the solution in low frequency,broadband and high power transmission.