| The type of sound spectrum inside a vehicle cabin is a valuable attribute.In order to achieve the established goal of sound spectrum of the full vehicle,a coherent methodology approach to measuring and analysing was required.In order to determine how the source subsystems in the sound field affects the response of the targets,this paper uses the Power-Based Noise Reduction(PBNR)test technology,with the principle of energy superposition,and the method of transfer path analysis(vector superposition)is analogically applied to the sound source quantification and contribution analysis of Automotive airborne acoustic.The sound power of each sources is obtained by matrix-inverse method.From the experimental point of view,it is the extension of the sound power substitution method.On this basis,the internal sound spectrum of an electric vehicle is decomposed by taking the uniform speed100km/h operating condition as an example.The results show that the measured noise spectrum inside a vehicle cabin is in good agreement with the synthetic noise spectrum in the analyzed frequency range.Therefore,the sound power level radiated by each sound source under dynamic operating conditions and its corresponding static acoustic treatments effect determine the type of sound spectrum inside a vehicle cabin.In order to discuss the influence of perturbation during testing and data processing on the solution of linear equations,this paper discusses the edge problem of linear equations from the perspective of determinant,and points out that the precondition for small perturbation not causing great changes is that the determinant of coefficient matrix is not zero and the perturbation of determinant should not be an order of magnitude compared with itself.Further,it is pointed out that the division of subsystems directly affects the well-posedness of the problem.The difference and connection between the influence coefficient method and SEA are discussed.In this paper,the coupling strength between different subsystems is quantified.The main advantage is that the coupling strength between subsystems can be easily compared in the test process.It is pointed out that the number of microphones and the times of excitations can be reduced by limiting the upper bound of coupling strength,so as to shorten the test period and reduce the experimental cost.The coupling strength is normalized,and it well reflects the difficulty level of that the perturbation of the determinant exceeds the determinant itself.Therefore,it reflects the well-posedness of the problem and can be used as an alternative method of condition number which is usually used to evaluate the ill-conditioned degree of the matrix.The coupling strength depicts the similarity of the acoustic paths between the two subsystems and the other subsystems,and also reflects the proximity of the responses between the two subsystems.On this basis,with the help of cluster analysis,the subjective blindness of traditionally dividing subsystems according to experience or natural discrete methods has been changed,making the division of subsystems more reasonable.In this paper,the constrained nonlinear programming model is established as the correction basis of the influence coefficient matrix under weak coupling condition to compensate the perturbation during testing and data processing,so as to improve the ability of predicting the sound field parameters.In order to determine how energy is transmitted from a given source to any part of the system,the framework of the global transfer direct transfer formulation is applied to vehicle acoustic spectrum decomposition.Three different forms of path decomposition are given,and the results of path decomposition in different forms will lead to the same path classification.Furthermore,how to determine the path superposition solution in the form of power ratio or energy density ratio by experiments is discussed.This paper mainly focuses on the process of test and analysis,allowing NVH test engineers to divide different subsystems according to the needs of analysis,and considering the edge problems caused by data perturbation.The research of this paper provides a completely decomposed source-path-receiver environment for the test vehicle,so that NVH research and development engineers can easily create or modify the acoustic character of a vehicle and has guiding significance for vehicle platform development. |
