Local Resonance For Vehicle Low Frequency Noise Control Application Of Acoustic Superstructure

Car interior noise is generally divided into airborne sound and structured sound according to the transmission path.For the noise reduction of high-frequency air sound inside the car,the measures widely adopted at home and abroad are acoustic packaging treatment.At present,the processing technology for this kind of air noise problem has been relatively mature and has achieved a relatively ideal noise reduction effect.However,the low frequency(20～200Hz)structure noise radiated by the vibration of automobile panel has always been a difficult problem in the field of automobile NVH(Noise,Vibration & Harshness).The traditional damping material or rubber damping material is not effective to control the low frequency(20～200Hz)structure noise radiated from the thin-walled parts of the automobile to the interior.There are many constraints in installation space,lightweight,durability and cost control,such as installing dynamic vibration absorber or adding ribs and reinforcing bars.Due to the local resonant acoustic superstructure has the special effect of "small size"(subwavelength structure)controlling "large wavelength"(low frequency elastic wave),it provides a new idea for vehicle low frequency noise vibration control.This subject is based on the school-enterprise cooperation project-the automotive acoustic superstructure application research project.By analyzing the vibration suppression mechanism of the local resonance acoustic superstructure and the structural characteristics of the body panel,a local resonance unit with adjustable frequency orientation,stable equivalent stiffness,lightweight and miniaturization has been creatively developed.Through simulation and testing,it has an ideal low-frequency vibration suppression effect.Then,based on the analysis results,a bandwidth extension scheme for the acoustic superstructure.Furthermore,aiming at the problem of low-frequency roaring sound radiated into the car by the 35 Hz vibration of the tailgate wall panel of a certain car,according to the problem frequency of the car and the structural characteristics of the tailgate,an acoustic superstructure with 6 local resonance units was designed.CAE and testing have verified that the acoustic superstructure has an ideal vibration and noise reduction effect.On this basis,the consistency analysis of the local resonance unit of the acoustic superstructure is carried out,and the processing and manufacturing process of the acoustic superstructure is evaluated using the principle of normal distribution.Finally,the manufacturing process of the acoustic superstructure and the directional adjustment process of the bandwidth of the local resonance unit are proposed,which provides a technical solution for the mass production and application of the acoustic superstructure.The main contents are as follows:(1)Innovative design of local resonance unit for acoustic superstructure.By analyzing the vibration suppression mechanism of the local resonance acoustic superstructure and the structural characteristics of the car body panel,a local resonance unit with adjustable frequency orientation,stable equivalent stiffness,lightweight and miniaturization has been creatively developed.The finite element software Comsol was used to calculate and analyze the band gap characteristics of the infinite-period local resonance acoustic superstructure.(2)Performance verification analysis of acoustic superstructure.Using the designed local resonance units for periodic arrangement,an acoustic superstructure with four local resonance units is constructed,and it is proposed to add a magnetic hot-melt damping layer on the back side of the acoustic superstructure base plate,so as to be directly attached to the wall structure.On this basis,an acoustic superstructure composed of four local resonance units is carried out based on the simulation analysis of the CAE vibration suppression performance of the flat panel and the test analysis of the actual structure.In response to the analysis results,a bandwidth extension scheme for the acoustic superstructure was proposed and the vibration suppression performance verification of the scheme was carried out.(3)Acoustic superstructure design and application for low-frequency noise of the car.In view of the obvious low-frequency(20-100Hz)roar of a certain car during a constant speed of 30km/h,through experimental testing and CAE simulation analysis,it was determined that the high 35 Hz noise peak in the car was the direct cause of the problem.And it is judged that this frequency peak is closely related to the vibration of the thin-walled parts of the tailgate.Furthermore,an acoustic superstructure with 6 local resonance units was developed and designed according to the structural characteristics of the wall panel and the peak frequency of the problem.Specific solutions are proposed for the layout planning of the acoustic superstructure on the whole vehicle and the arrangement and frequency design of the local resonance unit of the acoustic superstructure.(4)Acoustic superstructure and vehicle matching CAE analysis and test analysis.The CAE analysis method is used to match the acoustic superstructure with the vehicle.By comparing the noise and vibration of the two states before and after the acoustic superstructure is attached,it is verified at the simulation level that the acoustic superstructure has an ideal low-frequency vibration and noise reduction effect.On this basis,the designed acoustic superstructure was prototyped,and the local resonance unit performance of the acoustic superstructure was tested and adjusted.The transfer matrix method was used to correct and compensate the manufacturing errors of the acoustic superstructure.Then,for the sample car attached to the acoustic superstructure sample,through test and data comparison analysis,it is proved that the structure can effectively reduce low-frequency noise peaks in the car and improve the noise environment in the car.(5)Research on industrialization technology of acoustic superstructure.The local resonance unit consistency analysis of the acoustic superstructure is carried out,and the processing and manufacturing process of the acoustic superstructure is evaluated using the principle of normal distribution.Through statistics and analysis,it is found that the processing and manufacturing process of the acoustic superstructure local resonance unit is stable and controllable,the simulation results of its natural frequency are consistent with the test results,and the product quality is excellent,which provides performance guaranteed for the industrial application of the acoustic superstructure.On this basis,the manufacturing process of the acoustic superstructure and the directional adjustment process specification of the local resonance unit bandwidth are proposed,which provides a technical solution for the mass production and application of the acoustic superstructure.