| Modern vehicles are complex nonlinear systems,so the time domain model of road excitation is necessary to be established, which is more suitable for the analysis of nonlinear vehicle ride.Based on the frequency domain model of standard grade road--power spectral density of road roughness(PSD), the white noise filtration method, harmony supper-position method and inverse fast fourier transform(IFFT) method which based on the sampling of discrete PSD were used to establish the road model in time domain in the paper. Further, the method of power spectral estimation was used to estimate the time domain road for proving the established time domain road model is the equivalent model in frequency domain.Then, by expanding 1-dimensional PSD to 2-dimensional and using harmony supper-position method, white noise filtration method and IFFT method 2-dimensional road surface model, which was required by the Virtual Proving GroundTechnology, was established. Then for further research, the non-stationary 2-dimensional road model was obtained from the 2-dimensional stationary road model. This kind of model was more general, it could be treated as a necessary basic excitation model for deeper analysis of vehicle dynamics.Wavelet analysis is an efficient tool for time-frequency analysis, 2-dimensional wavelet analysis was used in the paper to decompose the regenerated non-stationary road exicitation signal into 5 level of wavelets, and the stationary and non-stationary components of the signal were extracted to reveal the characteristics of non-stationary road excitation. Next, for overcoming the disadvantage of traditional road irregularity PSD, which can't evaluate or describe the road exactly, the fractal characteristics of stochastic road irregularity was studied. The fractal dimension of 5 grade roads irregularity which obtained by using the time domain model method that based on PSD of the road were calculated by frequency spectral method, and then the evaluation and complexity of the road will be given by the fractal dimension. However, the fractal dimension can't describe the road separately, so the road roughness index.was taken into account. Either for the classfication, or the complete decription of the road features, it was of significance.Finally, the fractal regeneration method which based on fractal characteristics and the mesured sample data of stochastic road for the simulation of roads in arbitrary forms—the W-M function method for 1-dimensional road and random middle-point-displacement method which based on Fractional Brownian Motion(FBM) for 2-dimensional road was established, and then,the computer simulation of those methods have successfully represented the road irregularity. Therefore, more wide, more general roads were achieved by the construction of road model in arbitrary forms, and it was of important significance in enriching and improving the database of roads.The simulation practices demonstrated that the regeneration road models in time and spatial domain can truly present the actual roads, and those models can form the digital database of roads and at the same time it can be treated as the necessary environment model of virtual prototyping(VP) and virtual proving ground(VPG) Technology. |
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