英语写作.docx

1、英语写作Progress on numerical simulation of mold filling and solidification processes of shaped castingsXIONG Shou Mei ,LIU Bai Cheng,XU Qing Yan,KANG Jin WuDepartment of Mechanical Engineering,Tsinghua University,Beijing 100084,ChinaAbstract: The latest progress on numerical simulation of mold filling

2、and solidification processes of shaped-casting was reviewed. The composed splitting method was implemented in solidification simulation and a new method was proposed to optimize the computational area. The computational efficiency was studied by practical applications. A new criterion was proposed t

3、o predict the shrinkage defect of S. G. iron castings and a combined FDM/FEM method was proposed to predict the shrinkage defect of S. G. iron castings and a combined FDM/FEM method was used to simulate the thermal stresses of castings.Key words: castings；mold filling；solidification processes；numeri

4、cal simulation1 IntroductionThe computer simulation of mold filling and solidification process is the discipline development frontier, is the only way to transforme traditional casting industry. After decades of effort, the computer simulation of mold filling and solidification process has entered t

5、he stage of practical engineering, casting production is being used by experience to scientific theoretical guidance. The computer simulation of mold filling and solidification process can help staff detect effectivelly for all kinds of possible defects and size, location, and the time of occurrence

6、 in the casting process design stage, thus we can optimize the design of casting and ensure the quality, shorten the production cycle, reduce production costs1、2. This paper focuses on the analysis and research of mold filling and solidification process of castings and shrinkage prediction, progress

7、 of the stress.2 The fluid flow and heat transfer in filling processMold filling process have a greater influence on the quality of castings. Improper filling process can lead to casting defects such as gas volume and misrun and cold insulation. In many cases, the filling process can also influence

8、the solidification process of the subsequent. In recent years, people have made unremitting efforts in the numerical simulation of filling process. a variety of computational fluid dynamics technology is used in the simulation process, such as MAC, SMAC, and SOLA-VOF and other methods3、4. This study

9、 used the SOLA-VOF method, and has been improved on the free surface treatment, turbulence model and computational techniques etc.1.1 The governing equationIn the mold filling process, in order to get accurate speed distribution , we must solve the master equation includes the continuity equation, m

10、omentum and energy equations. Free surface treatment using an improved VOF method. For the turbulence model, the K- two-equation turbulence model is more used currently. Flow and heat transfer equations, the K equation of turbulent kinetic energy and the equation of turbulence dissipation rate in th

11、e K- turbulence model,and the Volume function equation for the free surface treatment can be expressed by a unified transport equation in the Cartesian coordinate system as follows. Xj Coordinate component; j = 1, 2, 3 uj Xj upward velocity component flux Transmission coefficient S The source term F

12、or the specific meanings of , specific and S.1.2 Parallel computing technology Because the flow control of the discrete equation solution is an iterative process, and it takes a long time. This study used a parallel computing technology to speed up the calculation process , especially for large-scal

13、e problem solving. Through the parallel processing of the improved SOLA-VOF algorithm, the fluid flow simulation time can be greatly reduced, and with the participation of the network connected in parallel computing vary the number of computers.1.3 Die Casting Parts filling process simulationIn SP2

14、parallel machine, The Motorcycle Crankcase Cover filling process of castings was simulated, and has carried on the analysis to the design of two different channel fill mode4, The results are shown in figure 1. In Figure 1(a), it shows the original gate solution eventually fill the location, at the u

15、pper left corner of the castings has a fluid region. From the improved design of the filling gate simulation results in Figure 1(b) , we can see the final fill area of the groove portion in the overflow , so that there is no gas in the casting involvement. By using the method of incomplete injection

16、, mold filling simulation of two kinds of gating scheme results were validated. (a) The original four gate process scheme (b) Improved two gate process schemeFIG.1 Result of mould-filling process simulation of motorcyle parts3 Solidification simulationAs the solidification process of casting was clo

17、sely related with the shrinkage defects, since the 1960s, many studies have been focused on the use of numerical simulation on the solidification process to predict shrinkage defects ,put forward a lot of defect prediction method and criterion, and qualitatively for the actual casting. This article

18、focuses on using the fractional step method for solidification simulation analysis and the research of ductile iron shrinkage prediction.2.1 Componentwise splitting method for heat conduction problemsThe basic principle of Componentwise splitting method 5is the basic principle of the differential op

19、erator by a complex consisting of partial differential equations into a simple differential operator constituted by a series of simple partial differential equation. As in the numerical solution process requires only discrete scheme as a whole to meet the original PDE compatibility conditions and th

20、e stability condition. which can be decomposed on the basis of partial differential equations constitute a series of componentwise splitting discretization scheme, and by componentwise splitting discretization scheme as a whole to meet the conditions of the original equation of compatibility and sta

21、bility criteria. For heat conduction problem in the process of solidification follow the energy conservation equation, can be simplified as:Type A is called the thermal diffusion coefficient or guide in the temperature coefficient.For the heat conduction equation, according to the principles of the

22、Componentwise splitting method can be constructed with a weighted format Factional Step Difference Format:Formula of Ajx、Ajy、Ajz respectively when j tj+1 ;Each fractional step time step；jCalculation time step j=1, 2, 3Equation ( 3 ) is absolutely stable , with a second order accuracy , and that both

23、 can be used chasing method to solve.Since the algorithm is unconditionally stable, so heres the time step can be within a certain range ( mainly to ensure the reasonableness of calculated results ) arbitrary choice, it can greatly accelerate the calculation speed and improve computational efficienc

24、y.2.2 Solidification simulation optimization computing areaComponentwise splitting method for numerical solution because there is no time step limit, therefore, we can consider in the solidification simulation area partitioning and using different time steps to calculate so as to achieve the purpose

25、 of improving the computational efficiency. In the process of casting solidification, some closer from the casting mold units involved in the intense heat transfer process, and some relatively far away from the casting mold units heat transfer tends to weaken, Therefore, the casting mold can be divi

26、ded into two calculated areas , internal and external areas, as shown in figure 2. Internal area includes castings and casting cast around the area, internal casting area is decided by the thickness of the casting surface along the normal direction. external area is relatively far away from the cast

27、ing mold for all areas6. The external areas may use the larger time step relatived to the internal, at the same time, due to the calculated areas of the internal area is much less than the all areas, thus it will greatly improve the computational efficiency. A typical casting were simulated by using

28、 the componentwise splitting method and district computing technology. Figure 3 shows the temperature distribution after the start of solidification at a certain time, it displayed the may occur hot spot defect position of casting solidification. the author studied the effiiciency of solidification

29、simulation in three different grid conditions and calculating conditions, in order to the efficiency of the componentwise splitting method and district computing technology. The mesh size and number as shown in table 1. As is shown in table 3, the non-uniform grid can effectively reduce the total nu

30、mber of grid casting, while after using partition method in computing system internal number of grid computing area is reduced greatly.Table 3 lists the comparison of casting solidification simulation computation time and the calculated solidification time in different grid scheme and different calc

31、ulation parameters conditions. As can be seen from Table 2: under the same conditions of the grid scheme and partitioning calculations, the calculation time decreases with the time step increasing, and a relatively large time step has little effect to the results. Meanwhile, it can greatly reduce th

32、e computing time by using partition method in the same grid and time step, thus,we can improve the computational efficiency. Tab.1 Dissection scheme of the grid mesh and mesh quantity of a typical castingMesh size(mm) Total mesh Casting grid number Internal regional grid 2 2700000 40181 88238 2/5(non-uniform) 844736 40181 88238 5 172800 2589 10880Tab.2 Calculated time and resulted solidification time from different mesh scheme Project Grid scheme Internal mould External area Time Step