Research On Sound Absorption Performance Of Helmholtz Resonator-Type Coupling Structure

With the rapid development of the automobile industry,NVH(Noise,Vibration and Harshness)performance has gradually attracted the attention of automobile manufacturers and consumers.High-quality NVH performance means that a car has excellent ride comfort.In order to improve the NVH performance of automobiles,solving the middle and low frequency noise of automobiles becomes the key.However,due to the long wavelength of the middle and low frequency noise,it is difficult for traditional sound absorption and insulation materials to produce a good noise reduction effect.The emergence and development of acoustic metamaterials provide new ideas and methods for noise control in the middle and low frequency range.In this paper,single-port and dual-port sound absorbing metamaterials based on Helmholtz resonator are researched.The specific contents are as follows:In the 1st chapter,the origin and development of acoustic metamaterials are briefly introduced,and the research status of Helmholtz resonator sound absorption metamaterials is summarized.In the 2nd chapter,the coupled-mode theory of single-port system and dual-port system is described.Taking Helmholtz resonator-type sound absorption system as an example,the sound absorption performance of single-port and dual-port sound absorption system constructed by a single Helmholtz resonator with the same resonance frequency but different leakage factor and loss factor is simulated and analyzed.It provides a research basis for the subsequent single-port and dual-port sound absorbing structures based on Helmholtz resonator.In the 3rd chapter,a method of constructing broadband and efficient single-port sound absorption structure is proposed.Firstly,based on the coupled-mode theory,the damping characteristics of Helmholtz resonator are evaluated by leakage factor and loss factor,including critical damping unit,over-damping unit and under-damping unit.The coupling sound absorption performance of Helmholtz resonator units with different damping characteristics is investigated and analyzed.Then,by coupling 15 Helmholtz resonator units with successively increased resonance frequencies(the same interval)and successively reduced damping,the average sound absorption coefficient in the wide frequency range of 535Hz-1128 Hz is more than 85%,and the average sound absorption coefficient in the range of 582Hz-1109 Hz is more than 90%.The thickness of the structure is only 22.5mm.The sound absorption performance is verified by experiments.In the 4th chapter,a dual-port structure which can realize asymmetric sound absorption is designed.Firstly,the asymmetric sound absorbing cell(AAC)based on two Helmholtz resonators with slightly detuned resonance frequencies and nearly the same leakage factor and loss factor is introduced.The ventilation rate(ventilation area / acoustic incident area ×100%)is 20%.The asymmetric sound absorption mechanism is explained by soft boundary theory.Then,the asymmetric sound absorber designed by parallel AACs significantly broadens the asymmetric sound absorption band.When the sound waves are incident from the left port,the sound absorption coefficient of the absorber in the wide frequency range of 970 Hz to1655Hz exceeds 70%,and the average sound absorption coefficient in the range of 1100 Hz to1630Hz exceeds 84%,which realizes the broadband and efficient sound absorption;When the sound waves are incident from the right port,the maximum sound absorption coefficient in the calculated frequency range does not exceed 60%,and the average sound absorption coefficient in the whole frequency band is less than 40%,which realizes broadband asymmetric sound absorption.Finally,the excellent broadband asymmetric sound absorption performance of the designed absorber is verified by experiments.In the 5th chapter,Helmholtz resonator type sound absorbing metamaterials are used for low-frequency noise reduction in vehicles.Firstly,through the real vehicle test,the interior noise distribution of the test vehicle under four medium and low-speed conditions at constant speed is obtained.Then,according to the method of building broadband and efficient single-port sound absorption structure proposed in chapter 3rd,Helmholtz resonator absorbing plate is designed for the low-frequency noise with prominent contribution.Finally,the prepared absorbing plate is installed on the main driving seat and its noise reduction effect is tested,which provides data support for the research results of this paper to be applied to the noise reduction in the vehicles.In the last chapter,the paper is summarized and the future development is prospected.