Study On The Active Control Of Structural Vibration And Sound Radiation Based On The Modal Analysis

The control of sound and vibration of structure recently has been received more and more attention in the field of naval architecture and ocean engineering.There are two main approaches for sound and vibtation control:passive control and active control.Compared with the passive control,the active control has the advantages of good performance in low-frequency control and convenience in modifying design,which provides an effective way for the control of low-frequency sound and vibration.Hence,the structural low-frequency vibration and noise problems may be solved with the active control.In the low frequency range,modal ansysis as an effective tool is often used to compute and analyze structural vibration and noise.Modal analysis can express the complex structure vibration and acoustic radiation response as a number of modal response superposition for simple calculating,moreover,modal parameters also can represent the inherent characteristics of structural systems,and clearly show the mechanism of structural vibration and radiation noise,which provides a theoretical basis for the control of low-frequency structural vibration and acoustic radiation.Hence,from the perspective of modal analysis,a modal parameter identification method based on sound pressure response was proposed firstly.Based on eigenstructure assignment,the active control methods of structural vibration and acoustic radiation using the measured receptances were proposed.In view of poles and minima of radiated acoustic power,a method for calculating the poles and minima of a radiated acoustic power was proposed.This study is aimed to achieve the vibration and sound radiation control of structures.The major contributions of this dissertation are as follows:1.Considering the unmeasurable vibration responses in some practical situations,two methods of modal parameter identification based on non-contact measured sound pressures were proposed.Theoretical formulas of identification based on sound pressure were derived under operational modal analysis and experimental modal analysis,respectively,and then we can identify the structural modal parameters by the proposed method.Using the measured sound responses directly,the proposed methods avoid the solving of acoustic inverse problems and the difficulty of measurement in certain unmeasurable siuation.2.In the multi-input control system,a new algorithm of the partial eigenstructure assignment with both the eigenvalues and the eigenvectors being designed for vibration control was proposed.All the parametric expressions for the partial eigenstructure assignment were derived in this algorithm.Minimizing modal energy was applied to optimize eigenvectors of partial eigenstructure assignment,as a result,the optimal eigenvectors can be automatically assigned to minimize the modal energy meanwhile the eigenvalues are assigned to the desired values.As the control distribution matrix affects the subspace of achievable eigenvectors,a preliminary work is done to discuss the control quantities of different actuator distribution matrices in this paper.3.A new approach of reducing structural sound radiation based on the eigenstructure assignment using the receptance method in multi-input-multi-output(MIMO)systems was proposed.The approach takes the advantage of receptance method in active vibration control that there is no need to know the mass,damping and stiffness matrices,hence it avoids the model errors with respect to practical structures.Also the approach does not depend upon a specific excitation mechanism,and it does not need the pre-knowledge of the excitation force which sometimes is not available.Modal suppression and modal rearrangement can both be imposed for the attenuation of sound radiation with the proposed approach.4.An experimental-numerical combined approach for active vibration control of fluid-loaded plate structures using receptance method was proposed.The in-air measurements of structural receptances and numerical simulated fluid loading computed using acoustic boundary element analysis were combined to obtain the receptances of the fluid-loaded structures.It does not require knowledge of the structural model,and receptance measurements of the fluid-loaded structures which usually are difficult and time consuming,so it is more feasible in engineering practicality.A partial pole assignment can also be achieved with the combined approach.5.The poles and minima of radiated acoustic power from structural vibration are calculated and the applications were discussed.The poles and minima of radiated acoustic power were discussed and a novel formulation for obtaining the poles and minima was presented.The poles of radiated acoustic power are coincident with the poles of vibration response,the minima of radiated acoustic power are related to the exciting force,modal radiation efficiencies,poles and modal shapes of structure.A numerical example of a simply supported plate was also presented to illustrate the formulation and provides the comparison between the minima of radiated acoustic power and the corresponding antiresonances.In addition,poles and minima assignment of radiated acoustic power were discussed for the control of acoustic radiation.