Research On The Bandgap Characteristics And Vibration Absorption Properties Of Chiral Acoustic Metamaterials

Vibration and noise problems have become a major obstacle to ship equipment’s high-speed development in the direction of invisibility and intelligence,and vibration level has become a criterion for evaluating submarines and other equipment’s merits: the lower the noise,the higher the invisibility and survivability of the submarines.However,the previous noise control methods have poor vibration isolation performance in the low-frequency region and cannot meet the complex vibration reduction requirements.Therefore,new theories and methods need to be developed.In recent years,the acoustic metamaterial structure has received great attention for its excellent low-frequency vibration isolation performance,but it still has many problems such as the low frequency bandgap is too sparse and the bandwidth is too narrow.The chiral structure can reduce the symmetry of the system and enhance the anisotropy,so it always brings elastic wave band gaps to the structure.Combining acoustic metamaterials and chiral structures can improve the low-frequency bandgap characteristics of the system and will provide new ideas for solving low-frequency vibration problems in structures.In this paper,the vibration characteristics of chiral acoustic metamaterials are carried out with the goal of achieving low-frequency vibration reduction,and the main research is as follows.Firstly,two-dimensional chiral acoustic metamaterial structure is designed based on the good vibration reduction characteristics of acoustic metamaterials and chiral structures,and its dispersion relations and vibration transmission characteristics were investigated using theories and simulations.The results shows that the structures without and with fillers have7420.6 Hz ～ 10309.4 Hz and 4242.6 Hz ～ 4546.4 Hz of the first bandgap,respectively,and the transmission loss is very large near the bandgaps.Narrower connecting sticks and heavier fillers can bring lower central frequency of bandgaps.The theoretical results agrees well with the simulation results,which proves the validity and accuracy of the theoretical model.Then,planer lattice chiral acoustic metamaterial structure was designed by abstracting two-dimensional chiral acoustic metamaterial structure,and investigated its dispersion relationship and vibration transmission characteristics systematically.It was found that the first bandgap’s central frequency of planer lattice chiral acoustic metamaterial structure without and with fillers were reduced 45.9% and 22.2% compared with the two-dimensional chiral acoustic metamaterial structure,respectively.The thinner the connecting sticks and the heavier the fillers,the lower the central frequency of bandgaps.Finally,the cubic chiral acoustic metamaterial structure was designed by stacking and evolving planer lattice chiral acoustic metamaterial structure,and its dispersion relationship and vibration transmission characteristics were investigated by the combination of simulations and experiments.The experimental and simulation results are in high agreement,and the accuracy of the simulation model is verified.Compared with the two-dimensional chiral acoustic metamaterial structure,the first bandgap’s central frequency of the cubic structure without and with fillers are reduced by 80.3% and 84.5%,respectively.The thicker the connecting sticks,the wider the bandwidth but the higher the central frequency of bandgaps in the structure.The angle between the connecting sticks and the plane where the acoustic metamaterial located has less effect on the bandgap characteristics of the structure.Embedding heavier fillers can reduce the central frequency of the bandgaps with little change in the bandwidth of the structure.The research results can provide theoretical support and guidance for low-frequency vibration reduction of ship equipment.