Research On Noise And Vibration Control Mechanism Of A New Local Attached Impedance Structure

Vibration induces high acoustic radiation,which is a threat to people's normal life,work and health.With the development of social economy,demands for the living environments are increasing and acoustic equality gets more attraction.Referring to the difficulty in low-frequency sound reduction,this thesis presents a novel local attached impedance technology for vibration suppression and noise elimination,and corresponding investigations on function mechanism,configuration designing,model establishing of multiple mechanism combining and experiments are conducted.Firstly,based on the method of mobility and power flow in finite sub-structure,coupling model with local attached impedance suppression structure is established.Coupling governing equations of a plate with local attached impedance vibration suppression structure is derived,and solution of the vibration response including structural mobility of the sub-structure is obtained.And investigation on system vibration is developed for typical local attached impedance structure with lumped mass added and single spring-mass dynamic absorber.Local damping vibration suppression technology is an important part of local attached impedance vibration suppression.A locally constrained damping beam is presented in this thesis,and corresponding theoretical model for vibration analysis is established to obtain the vibration suppression performance.Effects of geometrical parameters on vibration performance of the system are calculated,which are applicable for guidance in configuration optimization of locally constrained damping structure.Dynamic absorber acts as a typical locally impedance vibration suppression technology.Its functional frequency band can be broadened by increasing systematic damping,which inspires us to propose a novel vibration suppression structure,combining the dynamic absorber and damping vibration reduction and applying the periodic bandgap vibration suppression thoughts.Based on the dynamic analysis of single spring-mass local resonance,multiple cascaded secondary vibration suppression structures and multiple secondary sub-vibration-suppression structure are presented to enrich the modal characteristics of local resonance structures.Theoretical derivation,configuration design and numerical simulation validation are conducted.For the sake of widening the gap width,a new combined vibration reduction structure is designed and made via integrating the damping reduction and dynamic absorption technology,and experiments of the vibration suppression are carried out.Results demonstrate that multiple band gaps of the proposed structure can be seen,within which vibration is greatly attenuated.Completion of the experiment provides effectiveness of the vibration suppression method and guidance for vibration suppression structure design in future.Noise elimination,an essential technique for noise control,is capable to attenuate the noise when noise is spreading in the air.This thesis demonstrates a new noise elimination technique by attaching mass to an elastic resonant cavity referring to the classical Helmholtz muffler noise elimination mechanism.Elasticizing the cavity wall increases multiple modals for the system and broadens the frequency range for noise elimination.In the meantime,lumped mass attached to the elastic cavity wall reduces the muffling frequency,which is good for improving the noise elimination in low frequency range.Dynamic governing equations for ceiling plate with lumped mass attached and acoustic traveling equations in the cavity are constructed.According to the continuity boundary condition,coupling model of the elastic plate and the resonance cavity is built to derive the acoustic admittance.Characteristics of noise elimination and structural design are finally accomplished.Moreover,this thesis proposed a novel structure which integrates both noise elimination and vibration control.Referring to the Rayleigh integral method and pipeline noise reduction theory,theoretical radiation model of a free plate with noise reduction and vibration suppression structure attached are established.Geomatrical parameter design of the integrated structure is implemented on an elastic plate,and both the theoretical prediction and numerical simulation is carried out for its performance of the vibration suppression and noise elimination.It is revealed that the designed integrated structure can suppress the vibration and eliminate the noise as expected and the reasonable configuration design and correct theoretical model provides good example for structural noise and vibration reduction.Eventually,the principle sample and the comparative sample are made.The principle sample is a free rectangular steel plate with periodically attached integral structures,while the comparative sample is a isotropic steel plate with equivalent weight.Test results report that compared with the comparative sample,within 100 Hz – 500 Hz,vibration response of the principle sample is attenuated about 13.8 d B,and noise radiation is reduced 12.3 d B;within 1 k Hz – 2 k Hz,the noise radiation decreases 5.6 d B.Comparison validates the correctness of the theoretical model and satisfactory performance in noise and vibration control,which is expected to be applied in practical engineering.