Study On Numerical Modeling And Computer Simulation Of Stochastic Road Of Vehicles

From the frequency domain model, the power spectrum density (PSD) function, of the standard grade roads and the measuring sample data of the nonstandard road, the time domain model of roads or road surfaces was regenerated to meet the requirement on the time history analysis of the advanced nonlinear vehicle system in the paper. The complete, systemic and deep study was made on several aspects including the basic description of stochastic road, the time domain modeling theories and methods of roads, the time domain model of one input excitation and multi-point excitation from road to vehicles, the domain model of the temporal-spatial correlation from the bilateral correlative track excitation of a road, the time series AR or ARMA model of arbitrary roads, the time domain model of 2 dimensional road surface, and the wavelet analysis on the nonstationary stochastic road process. The numerical road simulation was realized by using the time domain methods. The simulated road or road surface in time domain, equal to the model in frequency domain, was established as the basic road data and used as enviroment model in the virtual prototyping of vehicles (VP) and the virtual proving ground of vehicles (VPG).Firstly, the frequency domain model was introduced as a fundamental description to the stochastic roads. Two different expressions of road PSD were presented and their applications to the vehicle dynamics illustrated. Based on the property of the road random irregularities and combining with the expression of PSD in statistics, taking a six-wheel vehicle as an example, a matrix of PSD function with respect to multi-point excitation from road irregularities was deduced for the puopose of the analysis on a linear or linearized vehicle system.Then, in terms of the requirements of dynamics analysis in time domain on the nonlinear vehicle system, the basic pinciples of the four methods, harmony supperposition method, white noise filtration method, inverse fast Fourier transform (IFFT) method and the time series AR or ARMA modeling method, available for time domain modeling to road irregularities were illustrated. The first three methods were used to model the standard grade road and the domain model of the temporal-spatial correlation from the bilateral correlative track excitation of a road reached. Among these, the IFFT method was firstly successfully implemented in time domain model of vehicle road excitation. Morever, aiming at the low accuracy of psuedo-white noise generation, a improved algorithm to generat quality white noise was designed to rise the accuracy of the simulated roads. Followed was the two developments, one orienting to the modeling of an arbitrary road besides the standard grade road and another orienting to the modeling of 2 dimensional road surface. The former made the model data of vehicle dynamics richer and the latter provided direct model data for VPG.Using time series AR or ARMA modeling method, through the model test in time domain to the standard grade road, the time series AR or ARMA model of an arbitrary nonstandard measuring road was established and the simulation realization implemented in time domain.Based on the development of time domain model of road irregularities, the road surface model in time domain was constructed with the consistence to the frequency domain statistics of the standard grade road using harmony supperposition method, IFFT method and white noise filtration method respectively. Morever, based on the sample data from arbitrary measuring road, the road surface model of arbitrary road was established in time domain and the simulation realized.Finally, the model of nonstationary road was necessary for the deeper dynamics of vehicles. The numerical rengeneration of the nonstationary road was expediently reached based on the data from the numerical models of the stationary road or surface. In turn, the regenerated nonstationary road was analyzed using wavelet method in order to separate the nonstationary signal from the stationary signal and the high frequency signal from the low frequency signal. By doing so, the excitation feature of the nonstationary road or surface was revealed. On the other hand, nonstationary analysis on road was applied to study the excitation characteristics of roads under the condition of speed changing, starting and stoping of vehicles.In a word, through the complete and deep study on the time domain model of stochastic road or road surface, a data-base about the time domain model of stochastic road and surface was expedientlly constructed. In combining with some deterministic functions of roads or road surfaces, the excitation data from road irregularities were obtained in real time by means of integration, assembly or supperposition, according to the requirements of VP and VPG technologies.