Research On Modeling Methods Of FRF Based Substructuring Hybrid Synthesis For Full Vehicle NVH Performance

Automobile NVH(Noise,Vibration and Harshness)performance is becoming one of the important competitive focus and hotspot for automobile manufacturers across the world.The frequency response function based substructure approach(FBS)has gained more and more momentum for analysis and optimization on the NVH performance of a whole vehicle or its sub-systems,due to its many advantages such as applicable in a wide frequency range,and suitable for structures with high damping or high modal density.However,there are some difficulties occurred to the method during actual engineering applications,mainly including problems as follows: How to obtain the frequency response functions(FRFs)of substructures under a completely free boundary condition? How to eliminate the noise in the measured FRFs? How to solve the inversion of an ill-conditioned matrix of FRFs? How to deal with the absence in the FRFs of rotational degrees of freedom? Taking a micro-vehicle with in-wheel motor drives as a target,this dissertation addresses the aforementioned problems with the FBS methods,and establishes a model for NVH analysis on the full vehicle which is numerically divided into several substructures.The outputs of this study are valuable with improvement and engineering application of the FBS method.A method for inertia properties identification is proposed by incorporating modal shape modification into the modal model method.Numerical simulation and physical experiments are carried out to validate the applicability and efficiency of the proposed method.Inertia properties of the trimmed body of the target vehicle are identified by means of the method,which are then used to update the FRFs of the body in low frequency band.The FRFs of the body are then obtained under a completely free condition.Employing the eigenvalue decomposition(EVD)of the measured FRFs,a method is derived based on signal subspace approach to eliminate noise from measured FRFs.The efficiencies of the methods are demonstrated by reducing noise from a set of simulated noisy FRFs.The method is then used to successfully eliminate noise from the measured trimmed body FRFs,which will improve the accuracy of calculating the inversion of the FRFs matrix.A method of interface flexible equivalence is proposed to deal with information absence of the rotational degrees of freedom of the interface in the measured FRFs.In the method,an interface is divided into several sub-interfaces,each of which is treated as rigid.Simulation on a plate-like structure shows that the proposed flexible equivalence can significantly improve the synthesizing accuracy of the FBS method.In sequence,the method is applied to the interface between the front suspension and body of the target micro-vehicle,yielding corresponding FRFs related to the rotational degrees of freedom in the interface.A method for finite element model updating is put forward by combining the truncated singular value decomposition(SVD)and the support vector machine(SVM)response surface approaches.In the method,the impulse response functions are obtained through inverse Fourier transformation on the measured frequency response functions.By the phase space matrix re-construction and truncated SVD procedure,the features of the original FRFs are reflected.A support vector machine(SVM)response surface is constructed to replace the finite element model.An optimization problem is defined and solved by a genetic algorithm for parameter updating.The effectiveness of the method is validated by model update with a twist beam.Finally,the method is used to update the finite element model of the rear suspension of the target micro-vehicle.The target micro-vehicle is divided into three substructures,namely the trimmed body,the rear suspension and the front suspension.Regarding structural symmetry exists with the micro-vehicle,analysis was performed for the relationship among the FRFs of the related substructures,and the governing equations for FBS approach were derived for quick assembling and modeling.The FRFs of the trimmed body are obtained by physical testing with modification according to measured inertia parameters and noise elimination.Finite element models of front and rear suspensions are respectively established,and the corresponding FRFs of selected points are calculated.Using the FRFs of all the three substructures,a hybrid FBS model is constructed using the governing equation for the micro-vehicle.Physical experiments are carried out to validate the established whole vehicle model by comparing the calculated FRFs with their tested counterparts.