Abstract: Random vibration will take place for vehicles moving on uneven road or railway surfaces. Quick and reliable PSD (power spectral density) analysis for such random vibration is of great importance in order to improve the performance of vehicles. Due to the low efficiency and precision of the conventional random vibration algorithm, previously the vehicles have to be modeled into spring-mass systems with very low degrees of freedom, and so the analysis precision cannot be einsured. Particularly if the fatigue stress concentration is computed, very refined finite element meshes must be adopted, the computational cost will be extremely high and prohibited. In addition, when several wheels are excited simultaneously on different locations of the surface, the MIMO (multiinputmultioutput) random vibration analysis will be even more difficult. Usually, only one or a few samples of the surface unevenness were taken for direct numerical integration, the results were then used to evaluate the statistical characteristics of the vehicle random responses. Clearly, both the precision and efficiency are quite limited. In recent years, the pseudoexcitation method has received much attention in overcoming the above difficulties, and are being used and further developed by many experts in the research fields of cars, trains or even maglevs, which are briefly summarized.
Abstract: The multilevel substructure method was compared with the traditional dynamic substructural modal synthesis method (the super element method for MSC.Nastran). By using Lanczos method and technology of substructure tree travelling, the contribution of the multilevel substructure method’s internal freedom of substructure for the whole solution is considered. The result could be improved significantly, and which also had the same calculation accuracy with the overall structure without condensation. The numerical results show that the multilevel substructure method is more flexible than the traditional modal synthesis method in dividing substructure and calling multilevel substructure, which is not limited by the complex substructure and more accurate at higher frequencies.
Abstract: Direct numerical simulation of pulse disturbance in hypersonic flow over a blunt cone by using high-order accuracy finite difference method was performed. The interaction between fast acoustic wave and hypersonic flow field was studied; the evolution and development process of disturbance wave in the boundary layer was analyzed by Fourier frequency spectral analysis (FFSA). Results show that the disturbance into the flow field interacted with the shock wave and boundary layer, which makes bow shock bent obviously and disturbance enlarged, with obvious demarcations between the disturbance near the wall and in the outer boundary layer. The perturbation amplitudes on the nose are much larger than on the other locations. At the stage of the development of disturbance in the boundary layer, some perturbation modes continue to grow, some are filtered and seldom grow, even decay, and also some decay firstly and then grow. In general, the low frequency perturbation modes are dominated within a nose radius, with the disturbance development from upstream to downstream, the high frequency components increase quickly and low frequency components almost are restrained to grow.
Abstract: The transient response of turbulent enstrophy transport to opposition control in turbulent channel flow was studied with the aid of direct numerical simulation. It is found that the streamwise and spanwise enstrophy are suppressed by the attenuation of the stretching terms at first, while the vertical enstrophy is reduced by inhibiting the tilting of mean shear. During the initial period of the control, the streamwise enstrophy evolves much slower than the other two components. The vertical vorticity component exhibits a rapid monotonic decrease and also plays an important role in the attenuation of the other two components.
Abstract: Drift trash barrier was a kind of multibody system made up of float boxes and hinges. The float boxes were simplified to rigid bars, and the governing equations for them were established based on the multi-body dynamics theory. An iteration strategy was also proposed to obtain a numerical solution. To validate the proposed model and solution, a scaled model test was designed and the test results illustrated the validation of the model and the solution. Numerical example compared the results given by the proposed model and classical model. In addition, a judge method of the self-locking state of the drift trash barrier and the change process of tensile force were presented when the water level fell.
Abstract: To explore the habitat complexity and random environmental factors effects to the ecosystem, a new stochastic predation type ecosystem with habitat complexity was proposed. Both theoretical analysis and numerical analysis were explored. With the assumption of weak disturbances, the stationary probability density functions (PDF) for both species were obtained by applying the StratonovichKhasminskii averaging principle. The accuracy of the results obtained from theoretical method was demonstrated by those obtained from Monte Carlo simulation (MCS). The system mean first passage time(MFPT) was solved from the Pontryagin equation. The effects of the habitat complexity and the noise intensity were investigated via numerical calculations based on the data obtained from experiment. Results obtained show that: 1) the ecosystem with smaller habitat complexity is less stable when the system is disturbed by noises; 2) the stronger the noise intensities are, the less stable the ecosystem will be; 3) the ecosystem with bigger habitat complexity has longer MFPT; 4) the noise added to the prey natural increase rate has a bigger effect on the MFPT than that added to the predator natural death rate does.
Abstract: Hypersonic aircrafts enter across the atmosphere with high flight speed and over a long period of time, resulting in an intense aerodynamic heating load. Thermal analysis of thermal protection system (TPS) is the base of thermalmechanical coupling analysis; and the characteristics of temperature distribution affect thermal stress of corrugated sandwich structure directly. The analysis process was divided into three steps. The insulation performance of the integrated thermal protection system (ITPS) was analyzed to get the temperature distribution firstly. Then a sequence coupled numerical method was used to simulate the thermomechanical coupling performance of ITPS. Finally the stress field and displacement field of the corrugated sandwich structure unit cell were obtained and results were discussed. The calculation results show that the structure with initial size and constraints only satisfy the use of lowpressure zone, and structure will fail when the pressure is greater than 15 000 Pa.
Abstract: Based on the nonlinear isotropic elastic constitutive equations represented by tensor, a complete polynomial thermal stress constitutive equation and strain energy function of nonlinear isotropic elastic material were proposed. Just the initial temperature and the increase value were considered. As an application example, using MATLAB software, results were compared with known experimental data for hightemperature metal materials under uniaxial tension and compression of the elastic stage, which showed a good agreement with the results of the proposed theoretical model.
Abstract: The cumulative prospect theory (CPT) was applied to model travelers’route choice behavior based on bounded rationality in stochastic traffic network. Chosen meanexcess travel time considering both reliability and unreliability aspects of travel time variability as endogenous reference points, a CPT-based network equilibrium model and the equivalent variational inequality formulation were developed. The heuristic algorithm based on the method of successive average was adopted to solve the model. Then, a numerical example was proposed to illustrate the model and the solution algorithm. The effect of bounded rationality and endogenous reference points on such route choice behavior and network equilibrium was presented.
Abstract: The two classical models for transit assignment, pointing out their flaws for passenger flows assignment over congested networks were compared and analyzed. The causes leading to the results of these two models were analysed, based on which, the programming model and its algorithm of Spiess and Florian were improved.The improved model combined the ideas of "effective frequency" and "optimal strategies". The congestion was assumed to influence the waiting time at the stop only in our model, then the MSA was adopted to solve this problem. Finally these three methods were compared to solve the transit assignment problem in a simple example and the advantages of the improved model was summarized.
Abstract: To build a friction factors model of friction surface and dividing the friction factors into three levels, there were respectively the friction coefficient of surfaces of sand particles, average friction coefficient of asperities inclined plane, rocks surfaces (or macroscopic crack). The coupling of three levels the friction factors was the key determinants of the practical friction coefficient. The friction coefficient of rocks was from the friction factors of surfaces of sand particles and was amplified by the later two levels. And the selfsimilar series asperities themselves can amplify friction coefficients many times. The average angle of asperities inclined plane or fractal dimension is the key influencing factors and the key reason of the differentiation. The influencing factors of arrangements of particles are smaller relatively. The static friction coefficient is bigger than coefficient of the sliding friction caused by the average contact angle.