Papers by Author: Wei Hua Zhang

Abstract: Organic matter plays an important role in soil moisture variation. In order to know the effect of organic matter on soil moisture dynamics, this study compared the infiltration and evaporation of soils with different organic matter content. The results showed that increasing the organic matter content in a certain degree can suppress evaporation and infiltration of soil moisture, and hence improving water use efficiency. When the organic matter content reaches3.2%, effect of suppressing evaporation is most obvious.

Abstract: The law of wheel wear is the basis for making turning repair cycle, and is one of the most important guarantees for the safe and stable running of train. A statistical analysis of individual wheel wear parameter was carried out based on wheel profile data of CRH2. The change law of individual wear parameter with mileage showed that wear process of wheel could be divided into two periods: the run-in period and the stable wear period. The paper has realized to research on the correlation between nominal wheel diameter abrasion value and wheel flange thickness variation based on Copula, too. Frank Copula was selected to describe correlation of the two wear parameters, the correlation index (α) of Frank Copula was estimated and the joint distribution function considering dependence was given. The value of α indicated that there was a weak positive correlation between the two wears, which can be ignored for calculating the accumulative failure rate of wheel wear. So the two wear parameters can be regarded as independent random variables during failure analysis of wheel wear.

Abstract: Based on the definition of the irrigation coefficient, we discussed the main factors which affect the irrigation coefficient as well as the measures to improve the irrigation coefficient in agriculture. According to the variation and the different features of the irrigation coefficient in different regions and conditions, this article not only explores the basic way to improve the irrigation coefficient, but also gives measures including water apportion measures, management and engineering measures. The potential ability of improving the irrigation coefficient is analyzed preliminarily in the real situation of Chinese irrigation methods and techniques.

Abstract: Reliability analysis of structure fatigue has two assignments: a. To forecast lifetime of the structure on given reliability level, b. To evaluate reliability level of the structure on given service conditions, material features and designing dimensions. It aims at evaluating the structure’s designing quality and providing a basis for designing improvement or manufacturing. At mean time, it provides instruction to updating management by parameter of failure rate under given fatigue lifetime.Lastly, in form of tables, this paper presents the predicting results of fatigue lifetime of pantograph V500 based on different reliability levels at 500km/h and the predicting results of reliability level of Pantograph V500 under lifetime of 1,200,000km which provide direction of design, manufacturing and general management for Pantograph V500.

Abstract: As the speed of train increases, flow-induced vibration of trains passing through tunnels has become a subject of discussion, to investigate this phenomenon, a simplified geometric model and a vehicle dynamics model of a high-speed train traveling through a tunnel were built. To analyze the unsteady three-dimensional flow around the train, the 3-D, transient, viscous, compressible Reynolds-averaged Navier-Stokes equations combined with the k- two-equation turbulence model were solved with the finite volume method. The motion of the train was carried out using the technique of sliding grid method. The dynamics response of the train was obtained by means of the computational multi-body dynamics calculation. Meanwhile the running safety and riding comfort of the train were analyzed. With the numerical simulation, the variation of aerodynamic forces was obtained. The research founds that, vibration of the train increases drastically during it passing through a tunnel. The running safety and riding quality of the train are reduced greatly but they are in the safe range.

Abstract: Numerical Simulation of oscillating flow over a circular cylinder is calculated when the Reynolds number is 100. The space-time finite element method is used to solving the two-dimensional incompressible Navier-Stokes equations. Considering the oscillating flow over a variation of perturbation amplitudes and frequency ratios, the trends of lift coefficient with amplitude and frequency ratio are compared respectively. Besides, the FFT of the lift coefficient curves are analyzed. There is a suddenly change in main frequency and second frequency when A=0.1. The excited frequencies of lift coefficient are discussed, which could be the combination of vortex shedding natural frequency and perturbation frequency, such as |fe－f0|, fe, 2fe－f0, fe＋f0, 2fe＋f0, etc.

Abstract: For high-speed railway carbody structure durability analysis problems in China, one integrated method based on MBS (multibody simulation) is proposed here. Firstly, one EMU (Electricity Multiple Unit) full vehicle was performed to dynamic modeling and simulation. The numerical simulation results were applied to illustrate the vehicle dynamic characteristics. And the relationships between structural strength, stiffness, and frequency characteristics were also studied. Secondly, the multidisciplinary design technique was used to solve multi-mode coupled vibration of carbody structure on the cumulative effects of local vibration and damage effects, as well as structure light-weighting and other parallel optimization problems. Finally, the effective measures were proposed to control carbody structure’s physical failure.

Abstract: Railway vehicle structure fatigue life consumption monitoring can be used to determine fatigue damage by directly or indirectly monitoring the loads placed on critical vehicle components susceptible to failure from fatigue damage. The sample locomotive carbody structure was used for this study. Firstly, the hybrid fatigue analysis method was used with Multi-Body System (MBS) simulation and Finite Element Method (FEM) for evaluating the carbody structure dynamic stress histories. Secondly, the standard fatigue time domain method was used in fatigue analysis software FE-FATIGUE and MATLAB WAFO (Wave Analysis for Fatigue and Oceanography) tools. And carbody structure fatigue life and fatigue damage were predicted. Finally, and carbody structure dynamic stress experimental data was taken from this locomotive running between Kunming-Weishe for this analysis. The data was used to validate the simulation results based on hybrid method. The analysis results show that the hybrid method prediction error is approximately 30.7%. It also illustrates that the fatigue life and durability of the locomotive can be predicted with this hybrid method. The results of this study can be modified to be representative of the railway vehicle dynamic stress test.

Abstract: In order to understand the influence of Heat-Affected Zone (HAZ) on fatigue properties of 16Mn steel, a series of cyclic torsional tests were conducted on 16Mn weld metal, the base metal, and the HAZ metal. The specimens of 2mm diameter were uniformly-spaced taken from a bulk 16Mn plate, which included a V-style welded joint in the center, and the space for each specimen was 4mm. From cyclic fatigue tests performed on specimens at different positions, one can observe that the fatigue damage evolution in the HAZ is faster than those in the weld and the base metal, i.e., HAZ has a significant effect on fatigue life of 16Mn. In addition, the peak stress decline curves of HAZ specimens in different rows are considerably diversified, but the damage evolution and fatigue properties of HAZ metal are similar in spite of their locations.

Abstract: In order to investigate the fatigue behaviors in very high cycle fatigue regime of bearing steel GCr15 (Chinese standard), cantilever-type rotary bending fatigue test was carried out, by using an hourglass-shaped specimen. As a result, the S-N data were classified into surface grinding flaw or inclusion induced fracture mode, subsurface inclusion without ‘granular-bright-facet’ (GBF) area induced fracture mode and subsurface inclusion with GBF area induced fracture mode. Formation of a GBF area was clearly observed in the vicinity of subsurface inclusion on the fracture surface ruptured at high- cycle fatigue regime. The cause of the S-N curves of GCr15 obtained by this experiment continuously decreased, which is different from the common ‘duplex S-N’ curve. Experiments on fracture surface was carried out based on the ‘dispersive decohesion of spherical carbide’ model aimed to clarify the mechanism of the formation of GBF area.