Research On Underwater Acoustic Characteristics Of Helmholtz Composite Resonator

Low-frequency noise has always been one of the difficulties in the field of vibration and noise reduction due to its long wavelength and the difficulty of attenuation.Helmholtz resonant cavity is often used in the field of vibration and noise reduction due to its simple structure and remarkable acoustic characteristics.It is usually used in combination with other structural materials to improve its low-frequency characteristics,and there are few studies on the underwater characteristics of the cavity itself.This paper proposes a structural panel model based on Helmholtz cavity for underwater mid-low frequency environment.The theoretical study and numerical simulation are used to systematically study its underwater acoustic characteristics,and according to the single resonance characteristics of the cavity,a multiresonance composite is proposed.Cavity structure model.The main research contents are as follows:1.Theoretical study of Helmholtz resonator.The transfer matrix algorithm is used to calculate the acoustic characteristics of a homogeneous medium under normal incidence of sound waves.Add the Helmholtz cavity to the medium of the same thickness,and use the lowfrequency concentrated parameter model to calculate the equivalent acoustic impedance of the rigid wall and the elastic wall of the cavity respectively,so as to obtain the resonance frequency and the sound absorption coefficient of the cavity.Compare and analyze the cavity The effect of the elastic wall on the acoustic properties of the structure.Analyze the influence of cavity geometry parameters on the structural acoustic properties.2.Research on numerical simulation of Helmholtz resonator.Through the COMSOL Mutiphysics finite element software,a single Helmholtz resonator is used as a periodic unit to form a structural panel,the underwater acoustic characteristics of the structure under the normal incidence of sound waves are calculated,and the vibration mode,sound pressure distribution and mode shape of the structure are analyzed.The influence of the model's geometric parameter size on the structural acoustic properties is studied,and compared with the theoretical formula to summarize the main geometric parameters of the cavity structure.The thermal viscosity loss inside the cavity and the influence of the medium on the structural characteristics are studied respectively.3.Research on the compound structure of Helmholtz resonant cavity.Based on a single Helmholtz cavity,a variety of multi-resonance composite two-dimensional cavity structure models are designed.In order to increase the number of longitudinal cavities,non-uniformly periodic structures,increase the perforated partitions and double-layer partitions in the cavity,and study and analyze the underwater acoustic characteristics,structural vibration modes,vibration modes and distribution of the structures The cause of multi-resonance.The main size parameters are studied,and the advantages and disadvantages of the multi-resonance scheme and the practical application range are summarized.