Papers by Author: Li Liang Chen

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Authors: Sheng Yong Pang, Li Liang Chen, Ya Jun Yin, Ai Qin Duan, Jian Xin Zhou, Lun Ji Hu
Abstract: Numerical simulation provides a way to improve our understandings of the heat transfer and fluid flow behaviors of the weld pool during laser keyhole welding. However, current numerical studies are only limited to serial simulations which running on a single CPU. In this study, a parallel numerical study of the heat transfer and fluid flow of the weld pool is presented. A mathematical model considering the effect of Marangoni force, buoyancy force, friction force of the mushy zone region and the effect of keyhole is presented. A combined keyhole volume and surface heat source model is also developed. The coupled transient heat transfer and Navier-stokes equations are solved with a high order accuracy parallel projection method. The simulation code is parallelized with the OpenMP language. It is shown that 200% speedup can be achieved on a shared memory quad-core CPU using the presented parallel simulation system. The simulation results agree well with the in-situ high speed CCD video imaging experiments and the literature results.
Authors: Jing Hao, Li Liang Chen, Jian Xin Zhou
Abstract: Level Set Method is an appropriate mathematical tool for solving two-phase flow problems. The main advantage of Level Set Method is its efficiency to deal with complex interfaces, even if topology changes. In this paper, the liquid-gas two-phase flow is simulated using a combination of Level Set Method and SOLA method. SOLA is used to compute the Navier-Stokes equation, and Level Set Method is used to track the interfaces between the liquid and the gas during mold filling process. The difficulty in the simulation of two-phase flow comes from great change of physical parameters (e.g., density and viscosity) across the interfaces. Level Set Method allows for large density ratio and jump in viscosity without reconstructing the numerical grid. In this work, the forming and moving of the gas bubbles in liquid were numerically simulated by Level Set approach. The numerical simulation results and experiments suggest that Level Set Method is quite reliable and effective for the simulation of liquid-gas two-phase flow during mold filling.
Authors: Dun Ming Liao, Li Liang Chen, Jian Xin Zhou, Rui Xiang Liu
Abstract: The nonferrous alloy castings will be much demanded with the development of aerospace, light-weight weapons and automotive industry. Casting CAD/CAE technology has played an increasingly important role in foundry. It can help technician to design casting process and simulate heat transferring and molten metal flowing before actual production. Firstly, the main contents and basic principles, mathematical models of casting CAD and CAE were introduced. Secondly, the casting CAD/CAE technology route was interpreted, and then several CAD/CAE applications of casting process design and simulating were carried out on nonferrous alloys, such as aluminum, magnesium and copper. The results indicate that CAD/CAE technology can be applied to casting process design and predict casting defects which usually occur during the casting mold filling and solidification process, it can provide references to optimize casting process, so as to improve casting quality, reduce the rejection rate and shorten the development cycle of new products.
Authors: Wen Bang Gong, Li Liang Chen, Jing Hao
Abstract: The heat transfer during the casting solidification process includes: the heat radiation of the high temperature casting and the mold, the heat convection between the casting and the mold, and the heat conduction in the casting and the casting to the mold. In this paper, a formula of time step in simulation of solidification is derived, considering the heat radiation, convection and conduction based on the conservation of energy. The different heat transfer condition between the ordinary sand casting and the permanent mold casting is taken into account in this formula. The characteristic of heat transfer in the interior and surface of the casting is also considered. The numerical experiments show that this formula can avoid radiation of the computation, and can improve the computational efficiency about 20% in the simulation of solidification process.
Authors: Hao Liu, Li Liang Chen, Jian Xin Zhou
Abstract: Compared with traditional blazing furnace, the Continuous Casting-Direct Rolling is an advanced manufacturing steel technology, which can reduce energy waste, decrease pollution and enhance efficiency. The characteristics of steels during induction heating are complex, the change of material properties with temperature makes exact analysis methods very difficult to implement. Therefore, a powerful computer aided numerical tool (i.e., finite difference analysis) is selected to numerically model the induction heating process in this paper. The mathematic model coupling with electromagnetic field and thermal field was established, and it was solved by finite difference method (FDM), thus the slab temperature distribution and its variation with time were obtained, and the characteristics in whole induction heating process were studied. To validate the program feasible, the results were evaluated and compared with experiment results, which showed that the simulation results are reliable and effective. The skin effect in heating process from the two results was studied and demonstrated, the temperature change caused by different parameters such as the induced power intensity and the corner radian were also presented, which indicate that the slab temperature can be heated uniformly through adjusting these parameters, thus the continuous casting slab can meet the rolling requirement.
Authors: Dun Ming Liao, Li Liang Chen, Jian Xin Zhou, Rui Xiang Liu
Abstract: Many defects relative to stress occur during the complicate casting process, such as hot tearing, residual stress concentration and distortion. Modeling of casting thermal stress during casting solidification process is of great significance to predict and analyze casting stress defects. Involving too many complex influencing factors, the stress simulation is very difficult and retains a hot spot of macro simulation in foundry engineering. Currently most researchers adopt integrated FDM/FEM method, i.e. using finite difference method (FDM) to calculate solidification and heat transferring, while finite element method (FEM) to simulate stress. Some universal commercial FEA packages are usually adopted. This study has tried two kinds of approaches to simulate casting thermal stress. One is based on ANSYS, a well-known powerful FEA analysis software. Another is to develop an independent own copyrighted casting stress simulation system based on FDM. The routes of these two methods were given respectively. To calibrate the simulation system, a stress frame sample and a real practical casting were simulated and pouring experiment was also carried on. The results of simulation were in agreement with the experiment results and practical cases. It indicates that these two approaches can all meet demands. When adopting FDM method, thermal analysis and stress analysis can use the same FD model, which can avoid the nodes matching between different models and reduce the errors of thermal load transferring. It makes the simulation of fluid-flow field, temperature field and stress field unify into one model. This system takes full advantages of mature FDM technology and can be used to simulate the forming of residual stress and predict the occurrence of hot tearing.
Authors: Jun Xia Jiang, Zhi Chao Wu, Li Liang Chen
Abstract: In lost foam casting (LFC), the foam pattern is the key qualification, and the filling process is one of the crucial processes to ensure the high quality of the foam pattern. Filling without uniformity and denseness will cause various defects and affect the quality of the surface. The influential factors of filling process are analyzed .And optimizing filling process, enhancing efficiency, decreasing waster are obtained by the numerical simulation of filling process using computer. The governing equations of the dense compressible gas-solid two-phase flow are established, and the physical signification of each one in the equations is discussed. The filling process is solved by Euler- Euler model. In the simulation, the volume of foam bead in every governing unit at different time is calculated, and the trend of foam bead flow is obtained. The filling process of various different conditions is simulated, considering different shooting methods and the position of baffles, and recorded by digital vidicon. The characteristics and the rules of the process are summarized. By contrasting the result of the numerical simulation with the one of examination, it is found that the fluid trend of foam bead in the numerical simulation is accordant to the actual process. So the numerical simulation of filling process by applying this model is an effective method.
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