Research On Force Reconstruction Method Based On Vibro-acoustic Signals

Vibration and noise are both important parameters frequently used for equipment condition monitoring and fault diagnosis.Vibration and noise are the effects of excitation source inside the device acting on vibro-acoustic transfer paths,so noise and vibration responses of the equipment in same operating state will be different under different installation conditions.In such situation,it is difficult for characteristics analysis and threshold determination for condition monitoring and fault diagnosis.This paper intends to reconstruct excitation sources through eliminating the influence of noise and vibration transmission paths and to determine equipment status according to the characteristics of reconstructed excitation.As a result,new method and approach are provided for condition monitoring,fault diagnosis and control of vibration and noise.Generally,force identification method in frequency domain is suitable for linear systems,and it is hard to distinguish effectively random excitation from impulse excitation.A time domain method based on inverse system is proposed in this paper.Inverse system is modeled by transverse filter of which weight vector is adjusted by adaptive algorithm.Numerical and experimental results show that this method can be applied for sinusoidal,random and impulse inputs.This identification method is simple,and system characteristics matrix inversion is not required and ill-posed problem is avoid consequently.Additionally,this identification method is independent of state space model and it is more advantageous than existing inverse system methods even if there is lack of prior knowledge of the system.With regard to the situation of unsuitably installing contact vibration sensors,a force reconstruction method is put forward by making use of acoustic sound in the air.Normal surface velocity of elastic structure is reconstructed by applying nearfield acoustic holography(NAH)with collected radiated sound pressure,and then the excitation force action on the elastic structure is obtained based on reconstructed surface velocity.Thin plate in free field is used to explore the feasibility of the proposed.The force reconstruction theory is deduced based on NAH technology,and the uniqueness of the reconstruction solution is analyzed.Surface,line,point and combined forces acting on thin plate are reconstructed analytically and numerically.The effects of measurement aperture size,microphone spacing,standoff distance and number of vibration modes on the accuracy of force reconstruction is studied.Numerical results show that increase of aperture size and decrease of standoff distance can improve reconstruction accuracy at low frequencies;aperture size of hologram and standoff distance have no influence on reconstruction accuracy at high frequencies;reduction of microphone spacing can effectively improve reconstruction precision;the more modes are adopted,the more accurate the reconstruction results are.Regarding random disturbance in collected acoustic signals,modified Tikhonov regularization based on generalized cross validation criterion is employed for force reconstruction and the results show that it can improve the accuracy of reconstruction of the excitation source.Finally,the interrelationships among excitation source,structural vibration and acoustic radiation are studied.And the studies clarify the dynamic characteristics of the structure itself and the acoustic radiation efficiency are important factors affecting force reconstruction precision.