| Controlling of the low and medium frequency vibration and noise in vehicles has always been challenging.The appearance of phononic crystals(PCs)provides new ideas for the control of low and medium frequency vibrations and noise in vehicles.In order to further improve the band gap characteristics of PCs and make them more suitable for controlling vibration and noise in vehicles,this paper proposes a composite piezoelectric PC plate structure containing a piezoelectric tunable band gap and a structural locally resonant band gap,based on the analysis of the band gap characteristics and the sound and vibration transmission characteristics of locally resonant PC plates and piezoelectric PC plates,in order to explore their possible applications in the control of vibration and noise in vehicles.The main research work carried out in the thesis is as follows:(1)Study of band gap characteristics of locally resonant PC plates.A locally resonant PC plate structure is designed,a finite element model of the band gap characteristics of the plate is constructed,the band gap characteristics of the plate structure are studied,the influencing factors of the band gap characteristics are analyzed and the design of the plate is optimized.Studies have shown that the designed locally resonant PC plate has a bending wave band gap of 100-387 Hz;the optimized PC plate has a bending wave band gap of 70-403 Hz and a significant attenuation of sound and vibration within the band gap.(2)Study of sound and vibration transmission models for piezoelectric PC plates.Based on the constitutive equation of piezoelectric material and the equivalent material parameters of the piezoelectric plate under different external circuits,the equivalent bending stiffness of the plate structure is derived by combining the piezoelectric PC plate structure.The finite element model and numerical model of vibration transmission of piezoelectric PC plate are constructed,and the reliability of the two models is verified.The position of local resonance band gap is predicted by the variation of equivalent bending stiffness of plates.The finite element model and numerical model of sound transmission of piezoelectric PC plate are constructed,and the reliability of the two models is verified by an example.Studies have shown that the model of the piezoelectric PC plate is reliable,and the position of the locally resonant band gap can be predicted according to the change of the equivalent bending stiffness of the plate.(3)Study of sound and vibration transmission characteristics of piezoelectric PC plates.Based on the vibration and sound transmission model of piezoelectric PC plate,the sound and vibration transmission characteristics of the plate with different external circuits are studied,and the influence of circuit parameters on the sound and vibration transmission characteristics of the plate is analyzed.Studies have shown that inductors under resonant shunt circuits and positive and negative capacitors connected in parallel or in series in resonant shunt circuits have a significant effect on the sound and vibration attenuation band and amplitude of the plate.The resistor has the energy dissipation effect but can suppress the resonant effect of the circuit,so as to broaden the sound and vibration attenuation band and reduce the attenuation amplitude of the plate.When the resonant frequency is fixed,increasing the amplitude of the parallel negative capacitor can effectively broaden the sound and vibration attenuation band and increase the attenuation amplitude,while the series negative capacitor has little effect on the attenuation amplitude,but the series negative capacitor in the circuit can obviously broaden the attenuation band.(4)Study of sound and vibration transmission characteristics of composite piezoelectric PC plates.A composite piezoelectric PC plate is designed,and the finite element method is used to study the sound and vibration transmission characteristics of the plate when it is connected to different circuits.The influence of the circuit parameters on the sound and vibration transmission characteristics of the plate is analyzed,and the application of the composite piezoelectric PC plate on the body of a vehicle is discussed.Studies have shown that the composite piezoelectric PC plate has good and stable damping and sound insulation properties within the locally resonant band gap.By adjusting the inductance in the resonant shunt circuit and by connecting positive and negative capacitors in parallel or in series in the circuit,the sound and vibration attenuation band and amplitude of the plate can be adjusted outside the locally resonant band gap.In comparison,the parallel negative capacitance in the resonant shunt circuit has a more significant effect on the sound transmission characteristics of the plate,while the series negative capacitance has a more significant effect on the vibration transmission characteristics of the plate.The composite piezoelectric PC plate can effectively suppress the vibration and noise of the vehicle body plate in the studied frequency domain,and make the plate have adjustable sound and vibration transmission characteristics. |
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