Study On The Underwater Low Frequency Sound Insulation Mechanism Of Plates Connected Elastically

Underwater sound insulation has important application in the field of acoustic stealth of underwater vehicles.However,underwater sound insulation is more difficult than sound insulation in the air because of the high acoustic impedance of the water.Furthermore,the longer low-frequency wavelength makes the low-frequency sound insulation more difficult to achieve.Different from the traditional acoustic covering layer,two underwater sound insulation structures formed by elastic element support plates are proposed in the paper,one is a double-layer plate connected elastically composed of two rigid plates supported by elastic elements,and the other is a single-layer elastic support plate structure with gaps supported by elastic elements.Using the method of vibration analysis of spring vibrator,the theory of sound propagation and finite element analysis method,the theoretical model of underwater sound insulation under the plane wave incident is established,and the underwater sound insulation characteristics of two structures and the influence of structural parameters on sound insulation are analyzed.And by analyzing the vibration displacement,acoustic input impedance and the acoustic energy flow on both sides of the structure,the sound insulation mechanism of the two structures is initially revealed.Finally,through the sound tube sound insulation experiment and the free field sound insulation experiment,the sound insulation performance of the two structures is verified from the experimental point of view.The results show that the double-layer elastic support plate reduces the vibration coupling of the fluids on both sides.And at the same time,a large impedance mismatch is formed in the sound propagation path,thus resulting in good underwater broadband sound insulation.As for single-layer elastic support plate,the results show that this structure is due to the difference in the stiffness coefficients of elastic elements attached to two adjacent units,which makes the two units vibrate asynchronously.The phase of the surface vibration velocity and the phase of the sound field are almost antiphase,and the sound energy flow is constrained near the structure,resulting in a a significant narrow-band sound insulation peak in the low frequency range.