Papers by Author: Lei Wang

Abstract: Catalytic converter is an important device of automobile engine exhaust system. Based on Hydromechanics, the relational mathematical models of catalytic converter simulation are established and the parameters are calculated. Making use of CFD numerical simulation method, a simulation is set up for the internal flow field of catalytic converter original model using fluent software. From the simulation, the internal flow characteristic is understood. On the basis of this, through the optimization idea adding a guiding device in inlet cone of catalytic converter, the uniformity of velocity of flow is improved. The simulation analysis show that the flow uniformity for internal flow field can be improved observably in the structural optimization, the increasing degree of pressure loss is with little range. A new idea and reference may be offered for improving flow uniformity of a catalytic converter.

Abstract: The strain change characteristics of multiaxial fatigue are analyzed under the condition of the combined tension and torsion loading for thin-tube specimen. Based on the principle of multiaxial critical plane approach, a multiaxial fatigue damage parameter is established, which takes account of the effect of not only the maximum shear strain amplitude and normal strain amplitude on the critical plane but also the parameter of non-proportionality. The non-proportionality is the function of loading parameters which is closely contact with the strain change characteristics of multiaxial fatigue and it can indicate the whole material damage. The experiments under the tension-torsion proportional and non-proportional loading were conducted to verify the multiaxial fatigue life model proposed in this paper. The life prediction has a good correlation with the experimental results.

Abstract: Engineering components and structures in service are generally subjected to the multiaxial complex loads. The approach of critical plane has been widely accepted by most researchers as the best method in the multiaxial fatigue research field. It can be used well in the constant multiaxial fatigue loads, but not in the complex loads. Basis on analyzing characteristics of shear strain on material planes, the concept of weight-averaged maximum shear strain plane is proposed. A procedure is presented to determine the critical plane under multiaxial random loading. The angle values of the planes that experience peak values of maximum shear strains are averaged by employing the weight function, which is assumed to take into account the main factors of influencing the fatigue behavior, e.g. fatigue damage. The proposed algorithm is applied to the multiaxial in- and out-of-phase experiments to assess the correlation between the weight-averaged maximum shear strain direction and the position of the experimental fatigue crack initiation plane.

Abstract: In this paper, a multi-objective parameter optimization model based on experimental design and NN-GA is established. In this method, utilizing experimental design principle to deal with test project and applying NN to map and using Pareto genetic algorithm to optimize, multi-objective parameter optimization is accomplished, in which the high nonlinear mapping ability of neural network model, the global research ability of genetic algorithms and multiform choice about the test points according to experimental demand are utilized synthetically. A Pareto-optimal set can be found in specify region. The method can be applied broadly and it needn’t the concrete mathematic model for different optimizing demand. For virtual devices and products, the virtual experiments can be realized by parameter-driven characteristic.

Abstract: First, several widely used models of the multiaxial low-cycle fatigue life prediction based on the critical plane approach were presented in this paper, and the predicted results of these models for a medium carbon steel under the condition of multiaxial low-cycle fatigue loading were compared. Second, the stochastic expressions and probability density function curves of the fatigue performance parameters were obtained by probabilistic analysis of the medium carbon steel fatigue data. Finally, the probabilistic model of the multiaxial fatigue life prediction was simulated by Monte Carlo Method, which should provide a basis for the reliability analysis of engineering components subjected to the multiaxial complex loads.

Abstract: With a view to the whole digging process, a multi-objective optimization model based on digging process is established. Applying the mind of system theory and complex optimization method, taking model P&H2800XP excavator for example, the structure parameter optimization of its working device is accomplished. The rational parameters obtained from this. Comparing with an original model, optimized results are ideal comparatively and the performance is improved.

Abstract: The model of extracting a skeleton of mechanism is established from an existed three-dimensional CAD product model. Using assembly features, a recomposition of assembly information is carried out. At same time, geometric primitives are defined and classified. And according to the information, kinematic pairs are distinguished and matched. Using the given methods, a prototype system extracting and drawing a skeleton of mechanism is developed. Extracting a skeleton of mechanism from digital mockup has been realized primarily, which can deal with rotation pair, sliding pair, gear pair and multi-pair components consisting of these kinematic pairs. Finally, the paper demonstrates the feasibility of extracting a skeleton of mechanism by an application instances.

Abstract: The Fiber Reinforced Plastic (FRP) has been widely used in aircraft, spacecraft, watercraft and transportation because of its excellent mechanical characteristics. The fatigue characteristic of the composite laminate of FRP is important guarantee to the structure security and reliability. In this paper, according to the damage mechanical theory, a fatigue damage accumulation model based on stiffness degradation and the corresponding method of fatigue life prediction are presented. The composite material of T300/ epoxy-resin with high performance has been investigated. The tension-tension fatigue tests have been conducted on the composite laminates. The fatigue life prediction of the composite material is presented. It shows a good agreement to the experimental and theoretical results.

Abstract: An example of the rule-based expert system applied to the fan fault diagnosis is presented. The architecture and function of the fault diagnosis system are introduced. The expression of the fault diagnosis knowledge and the attribute of knowledge base based on the relational database have been studied. The hybrid reasoning technology was applied to the implementation of the diagnosis inference engine in the expert system. The presented fault diagnosis system is easy to modify the knowledge base with the experience accumulated in practice, and it has the advantages of expansibility, portability, concision, and high efficiency.

Abstract: The research on multiaxial fatigue life prediction methods is reviewed in the present paper from two aspects of experiment and theory. It is pointed out that the reasonable methods of the critical plane determining, multiaxial cycle counting and multiaxial fatigue damage parameter fixing are necessary if the fatigue life prediction models established under the multiaxial constant amplitude loading were applied to the life prediction of the complex multiaxial load. The shortcomings of existing researches are discussed. In the aspect of experiment, it is devoid of the multiaxial fatigue test that the loading components acted with different frequencies, and in the aspect of theory, the additional hardening effect of the multiaxial out-of-frequency loading is not considered. Both in the theoretical research and practical engineering applications, the problem of the out-of-frequency multiaxial loading is a pressing issue.