This paper is concerned with the design, modeling, and simulation and testing procedure of All Terrain Vehicle (ATV) fitted with SAS, which is used in BAJA SAEINDIA standards. Using CATIA V5, the model is created, whi...This paper is concerned with the design, modeling, and simulation and testing procedure of All Terrain Vehicle (ATV) fitted with SAS, which is used in BAJA SAEINDIA standards. Using CATIA V5, the model is created, which is fulfilling the guidelines of BAJA SAEINDIA rules. ATV is having the two different pairs of quarter car models of suspensions where dampers filled with MR Fluid (SAS) in front and rear wheels. In front SLA wishbone and rear McPherson Strut are fixed. The physical representation of the ATV is converted into the mathematical modeling and it is imported in MATLAB SIMULINK software and analyzed for ATV’s performance. The ATV is analyzed for its vertical, pitch and roll motions which include total number of 7 Degrees of Freedom. The road excitation modeling also incorporated with the equations. This paper, elaborates the approaching of simulation method only. The virtual model of ATV has involving greater significance of reducing the cost involved in real time testing as well as the results are replica of experimental results.展开更多
Based on the experimental data of apparent viscosity about semi-solid A356 aluminum alloy, the apparent viscosity model was developed and inserted into a commercial software Castsoft6.0, and a key-shaped component fil...Based on the experimental data of apparent viscosity about semi-solid A356 aluminum alloy, the apparent viscosity model was developed and inserted into a commercial software Castsoft6.0, and a key-shaped component filling process was simulated. The simulation results are in good agreement with the experimental filling results, which indicates that the apparent viscosity model established is effective and available. The process parameters on the cavity filling of the key-shaped components have been optimized. The injection pressure should be more than 15 MPa, the slurry flowing velocity in the in-gate should be more than 1.73 m/s, and the slurry temperature should be over 585 ℃.展开更多
The effect of injection pressure, piston velocity, and the forming temperature of semisolid slurry on the filling behavior of the semi-solid A356 aluminum alloy was investigated by simulation methods. The simulation r...The effect of injection pressure, piston velocity, and the forming temperature of semisolid slurry on the filling behavior of the semi-solid A356 aluminum alloy was investigated by simulation methods. The simulation results show that these processing parameters have an important effect on the filling behavior of the semi-solid A356 aluminum alloy. The slurry flows steadily in the cavity when the injection pressure, the piston velocity, and the forming temperature are low, but it is prone to turbulent flow when the injection pressure, the piston velocity, and the forming temperature are much higher. Therefore it is necessary to determine the appropriate processing parameters to get a steady flow of the slurry in the cavity.展开更多
To understand the flow trace of semi-solid slurry in mold cavity, some thermocouples were inserted in mold cavity, and the reaction timing of thermocouples showed the arrival of fluid. The filling time and rate were e...To understand the flow trace of semi-solid slurry in mold cavity, some thermocouples were inserted in mold cavity, and the reaction timing of thermocouples showed the arrival of fluid. The filling time and rate were estimated by comparison between the experiment and calculation. The introduction of computer simulation technique based on ADSTEFAN was to predict injectionforming process and to prevent defects during trial manufacture of various parts. By comparing the formed appearance of parts in experiment and in simulation, and observing the relationship between internal defects inspected by X-ray or microscope and the flow field obtained in simulation, it was indicated that both have quite good agreement in simulation and experiment. Right predictions for cast defects resulted from mold rilling can be carried out and proper direction was also proposed. The realization of numerical visualization for filling process during semi-solid die-cast process will play an important role in optimizing technology plan.展开更多
In the present study, in-situ Ti B2 particle-reinforced 7075 aluminum alloy was produced by adding a mixture of K2 Ti F6 and KBF4 to the molten base alloy. The effects of the addition of 4.5wt.% and 9wt.%Ti B2 on the ...In the present study, in-situ Ti B2 particle-reinforced 7075 aluminum alloy was produced by adding a mixture of K2 Ti F6 and KBF4 to the molten base alloy. The effects of the addition of 4.5wt.% and 9wt.%Ti B2 on the apparent viscosity and microstructure were investigated. The results showed that adding Ti B2 is effective for optimizing primary α-Al, but compared with the 4.5wt.%Ti B2/7075 composite, the addition of 9wt.%Ti B2 had no further significant refinement role in the 9wt.%Ti B2/7075 composite due to particle aggregation. The viscosities of semi-solid 7075 alloy and Ti B2/7075 composite slurries increased with an increase in solid fraction, but decreased with an increase in shear rate. The viscosity of 4.5wt.% Ti B2/7075 was the lowest among the three samples, and that of 7075 alloy was the highest under the same conditions. The primary α-Al grain size was decreased, and the dendritic grains grew into spherical shapes after shearing. Based on the experimental results, viscosity models of the semi-solid 7075 alloy and 4.5wt.% and 9wt.%Ti B2/7075 composites were formulated. According to the simulation results, the shrinkage porosity of the 4.5wt.%Ti B2/7075 wheel was lower than those of the 7075 alloy and 9wt.%Ti B2/7075 wheels.展开更多
To realize the technology of fabricating the rheologic semi-solid slurry of ZL112Y aluminum alloy via continues electromagnetic stirring process, ANSYS software was used to simulate electromagnetic force field and flu...To realize the technology of fabricating the rheologic semi-solid slurry of ZL112Y aluminum alloy via continues electromagnetic stirring process, ANSYS software was used to simulate electromagnetic force field and fluid velocity field in the alloy melt in a crucible tube in three coils. In the first section of the paper, eletromagnetic force field and fluid velocity field caused by single coil were simulated. The result of this simulation gives an average velocity of 3.2 cm/s and it is called critical velocity because a fluid velocity over it will cause a fine and spherical structure of solid primary a in a semi-solid melt. And, from this result, a reasonable temperature of semi-solid of the alloy and an electrical current intensity were established. The electrical current intensity of the result of this simulation corresponded to the current intensity used in a practice experiment, in which the primary α was obviously refined and sphericized. Based on this simulation of single coil electromagnetic stirring, in the second section of the paper, eletromagnetic force field and fluid velocity field caused by three coils were simulated. The result of the simulation shows that, 1） there is a semi-solid zone of 32 mm from bottom of the crucible tube to the upper; 2） the electrical current intensities of three coils of 400 A, 600 A, and 400 A, which were set to top range, middle range and bottom range of the tube, respectively, were the optimum parameters of electromagnetic current intensity under the condition of this investigation; and 3） under effect of these electromagnetic current intensity, the fluid velocities of the melt in the tube were 6.3 cm/s in top range, 3.75 cm/s in middle range, and 3.9 cm/s in bottom range of it, respectively.展开更多
Semi-enclosed sea basins have difficulty in recharging their waters due to limited communication with larger water bodies, with understandable consequences for their environmental status. This paper aims at the comput...Semi-enclosed sea basins have difficulty in recharging their waters due to limited communication with larger water bodies, with understandable consequences for their environmental status. This paper aims at the computational simulation of the hydrodynamic characteristics of the waters of the Pagasitikos Gulf (Greece), which has limited communication and water exchange with the Aegean Sea and is subject to intense environmental pressures The Estuary, Lake & Coastal Ocean 3d hydrodynamic Model (ELCOM 2.2) combined with its later version Aquatic Ecosystem Model-3d (AEM3D) were used for the simulation. The simulation included the topography of the area, the bay’s bottom geometry, atmospheric loadings, tides, the influence of the Coriolis force and boundary conditions. The hydrodynamic behaviour of the bay, water circulation, velocities at the surface and in depth, water recharge and residence time throughout the bay, density variation and other factors were examined to determine the impact of all these on the aquatic ecosystem.展开更多
In the process of preparation of semi-solid metal materials, a variety of factors would influence the preparing time and the morphology of non-dendritic microstructure. The aim of this work is using phase-field method...In the process of preparation of semi-solid metal materials, a variety of factors would influence the preparing time and the morphology of non-dendritic microstructure. The aim of this work is using phase-field method to simulate non-dendritic growth during preparation of AI-4Cu-Mg semi-solid alloy by electromagnetic stirring method （EMS method）. Several factors such as the disturbance intensity, anisotropy, the thickness of the interface and the ratio of diffusivity in solid and liquid were considered. It is shown that decreasing the thickness of the interface results in more circular outline of particles, and increasing the diffusivity in solid can reduce degree of microsegregation. The disturbance intensity in the model can be connected with current intensity of stator or magnetic induction density impressed. Simulation results show that the larger the disturbance intensity or magnetic induction density, the more globular morphology the original phase in the matrix.展开更多
A software code based on SOLA-VOF algorithm is developed for numerical simulation of mold filling of semi-solid metals.The semi-solid mould filling processes of A356 and AZ91D are studied based on the Power-Law viscos...A software code based on SOLA-VOF algorithm is developed for numerical simulation of mold filling of semi-solid metals.The semi-solid mould filling processes of A356 and AZ91D are studied based on the Power-Law viscosity model and constant viscosity model,respectively.Test molds with different thicknesses and shapes were chosen to validate the software code.The simulated mould filling sequence shows a good agreement with the experimental results.The viscosity distribution is also calculated and plotted with a post-processor.The results show that the software code can offer an effective understanding for semi-solid mold filling processes.展开更多
A reliable mathematical model of urea-water-solution(UWS) droplet evaporation and thermolysis is developed.The well known Abramzon–Sirignano evaporation model is corrected by introducing an adjustment coefficient con...A reliable mathematical model of urea-water-solution(UWS) droplet evaporation and thermolysis is developed.The well known Abramzon–Sirignano evaporation model is corrected by introducing an adjustment coefficient considering the different evaporation behaviors of UWS droplet at different ambient temperatures. A semidetailed kinetic scheme of urea thermolysis is developed based on Ebrahimian's work. Sequentially, the evaporation characteristics, decomposition efficiency of a single UWS droplet and deposit formation are simulated. As a result, the relation of evaporation time, relative velocity, exhaust temperature and droplet initial diameter is presented. Synchronously, it indicates that temperature is the decisive factor for urea thermolysis. Different temperatures result in different deposit components, and deposit yield is significantly influenced by temperature and decomposition time. The current work can provide guidance for designing urea injection strategy of SCR systems.展开更多
A grid-based distributed hydrological model, the Block-wise use of TOPMODEL （BTOPMC）, which was developed from the original TOPMODEL, was used for hydrological daily rainfall-runoff simulation. In the BTOPMC model, ...A grid-based distributed hydrological model, the Block-wise use of TOPMODEL （BTOPMC）, which was developed from the original TOPMODEL, was used for hydrological daily rainfall-runoff simulation. In the BTOPMC model, the runoff is explicitly calculated on a cell-by-cell basis, and the Muskingum-Cunge flow concentration method is used. In order to test the model＇s applicability, the BTOPMC model and the Xin＇anjiang model were applied to the simulation of a humid watershed and a semi-humid to semi-arid watershed in China. The model parameters were optimized with the Shuffle Complex Evolution （SCE-UA） method. Results show that both models can effectively simulate the daily hydrograph in humid watersheds, but that the BTOPMC model performs poorly in semi-humid to semi-arid watersheds. The excess-infiltration mechanism should be incorporated into the BTOPMC model to broaden the model＇s applicability.展开更多
Real-time hybrid simulation is an attractive method to evaluate the response of structures under earthquake loads. The method is a variation of the pseudodynamic testing technique in which the experiment is executed i...Real-time hybrid simulation is an attractive method to evaluate the response of structures under earthquake loads. The method is a variation of the pseudodynamic testing technique in which the experiment is executed in real time, thus allowing investigation of structural systems with rate-dependent components. Real-time hybrid simulation is challenging because it requires performance of all calculations, application of displacements, and acquisition of measured forces, within a very small increment of time. Furthermore, unless appropriate compensation for actuator dynamics is implemented, stability problems are likely to occur during the experiment. This paper presents an approach for real-time hybrid simulation in which compensation for actuator dynamics is implemented using a model-based feedforward compensator. The method is used to evaluate the response of a semi-active control of a structure employing an MR damper. Experimental results show good agreement with the predicted responses, demonstrating the effectiveness of the method for structural control performance assessment.展开更多
Based on analysis of the main forming methods for double-layer tube,a new short-term forming process called thixo-co-extrusion was put forward in producing double-layer tube by combining the semi-solid forming technol...Based on analysis of the main forming methods for double-layer tube,a new short-term forming process called thixo-co-extrusion was put forward in producing double-layer tube by combining the semi-solid forming technology and multi-billet extrusion technology.By means of forward extrusion with shaft,a finite element model of thixo-co-extrusion with A356/AZ91 was constructed by ABAQUS FEM software.The distributions of temperature field and velocity field as well as the contact force during thixo-co-extrusion were studied.The diffusion on the interfaces between inner and outer metals was analyzed.The simulation results show that,in the beginning of thixo-co-extrusion,the uneven wall thickness can appear.To thickness ratio of 5:5,a double layer tube with good inner and outer wall combination can be realized if VA356 is 0.12 m/s and VAZ91 is 0.20 m/s.展开更多
Numerical simulation and experiment of thixoforming angle frame of AZ61 magnesium alloy were investigated.The results show that with the increase in punch displacement,cylinder billet firstly fills into die cavity of ...Numerical simulation and experiment of thixoforming angle frame of AZ61 magnesium alloy were investigated.The results show that with the increase in punch displacement,cylinder billet firstly fills into die cavity of angle frame from feed inlet and plastic deformation occurs in touching region between billet and die cavity.After central thin wall of angle frame is created,semi-solid billet fills toward two edges.Lastly,complete plastic deformation occurs in billet,leading to complete filling of semis-olid billet.Effective strain,effective stress and billet temperature decrease with the increase in punch displacement.Effective stress decreases with the increase in billet temperature,die temperature and punch velocity.The optimal conditions decided by numerical simulation are as follows:die temperature of 450 ℃,billet temperature of 560 ℃ and punch velocity of 30 mm/s.Angle frame components with high mechanical properties such as yield strength of 225 MPa,tensile strength of 309 MPa and elongation of 21.8% and fine microstructure could be thixoformed successfully according to process parameters decided by numerical simulation.展开更多
Moving particle semi-implicit （MPS） method is a fully Lagrangian particle method which can easily solve problems with violent free surface. Although it has demonstrated its advantage in ocean engineering application...Moving particle semi-implicit （MPS） method is a fully Lagrangian particle method which can easily solve problems with violent free surface. Although it has demonstrated its advantage in ocean engineering applications, it still has some defects to be improved. In this paper, MPS method is extended to the large eddy simulation （LES） by coupling with a sub-particle-scale （SPS） turbulence model. The SPS turbulence model turns into the Reynolds stress terms in the filtered momentum equation, and the Smagorinsky model is introduced to describe the Reynolds stress terms. Although MPS method has the advantage in the simulation of the free surface flow, a lot of non-free surface particles are treated as free surface particles in the original MPS model. In this paper, we use a new free surface tracing method and the key point is ＂neighbor particle＂. In this new method, the zone around each particle is divided into eight parts, and the particle will be treated as a free surface particle as long as there are no ＂neighbor particles＂ in any two parts of the zone. As the number density parameter judging method has a high efficiency for the free surface particles tracing, we combine it with the neighbor detected method. First, we select out the particles which may be mistreated with high probabilities by using the number density parameter judging method. And then we deal with these particles with the neighbor detected method. By doing this, the new mixed free surface tracing method can reduce the mistreatment problem efficiently. The serious pressure fluctuation is an obvious defect in MPS method, and therefore an area-time average technique is used in this paper to remove the pressure fluctuation with a quite good result. With these improvements, the modified MPS-LES method is applied to simulate liquid sloshing problems with large deforming free surface. Results show that the modified MPS-LES method can simulate the large deforming free surface easily. It can not only capture the large impact pressure accurately on rolling tank wall but also can generate all physical phenomena successfully. The good agreement between numerical and experimental results proves that the modified MPS-LES method is a good CFD methodology in free surface flow simulations.展开更多
Preparation of semisolid slurry using a cooling slope is increasingly becoming popular,primarily because of the simplicity in design and ease control of the process.In this process,liquid alloy is poured down an incli...Preparation of semisolid slurry using a cooling slope is increasingly becoming popular,primarily because of the simplicity in design and ease control of the process.In this process,liquid alloy is poured down an inclined surface which is cooled from underneath.The cooling enables partial solidification and the incline provides the necessary shear for producing semisolid slurry.However,the final microstructure of the ingot depends on several process parameters such as cooling rate,incline angle of the cooling slope,length of the slope and initial melt superheat.In this work,a CFD model using volume of fluid(VOF) method for simulating flow along the cooling slope was presented.Equations for conservation of mass,momentum,energy and species were solved to predict hydrodynamic and thermal behavior,in addition to predicting solid fraction distribution and macrosegregation.Solidification was modeled using an enthalpy approach and a volume averaged technique for the different phases.The mushy region was modeled as a multi-layered porous medium consisting of fixed columnar dendrites and mobile equiaxed/fragmented grains.The alloy chosen for the study was aluminum alloy A356,for which adequate experimental data were available in the literature.The effects of two key process parameters,namely the slope angle and the pouring temperature,on temperature distribution,velocity distribution and macrosegregation were also studied.展开更多
A numerical model has been developed to study sloshing of turbulent flow in a tank with elastic baffles. The Moving-Particle Semi-implicit method(MPS) is a kind of meshless Lagrangian calculation method. The large edd...A numerical model has been developed to study sloshing of turbulent flow in a tank with elastic baffles. The Moving-Particle Semi-implicit method(MPS) is a kind of meshless Lagrangian calculation method. The large eddy simulation(LES) approach is employed to model the turbulence by using the Smagorinsky Sub-Particle Scale(SPS)closure model. This paper uses MPS-FSI method with LES to simulate the interaction between free surface flow and a thin elastic baffle in sloshing. Then, the numerical model is validated, and the numerical solution has good agreement with experimental data for sloshing in a tank with elastic baffles. Furthermore, under external excitations,the MPS is applied to viscous laminar flow and turbulent flow, with both the deformation of elastic baffles and the wave height of the free surface are compared with each other. Besides, the impact pressure with/without baffles and wave height of free surface are investigated and discussed in detail. Finally, preliminary simulations are carried out in the damage problem of elastic baffles, taking the advantage of the MPS-FSI method in computations of the fluid–structure interaction with large deformation.展开更多
The simulation of 295/80R22. 5 tire building process from tire building to curing was developed using ABAQUS software,which covered four stages: gluing of components on main drum,gluing of components on auxiliary drum...The simulation of 295/80R22. 5 tire building process from tire building to curing was developed using ABAQUS software,which covered four stages: gluing of components on main drum,gluing of components on auxiliary drum,building process of green tire and shaping process of green tire. Results showed that material distribution of the simulated structure had good consistence with the real tire structure. Therefore,the tire building process simulation can be used to judge the rationality of tire construction design and to determine the shapes of different tire components. In order to optimize the construction design,a reverse simulation method was proposed to design the semi-product components such as apex,tread,and shoulder pad. The semi-product components determined by utilizing the reverse simulation method were assembled again into a tire. Results show that the simulated material distribution is consistent with the material distribution of design tire,which proves effectiveness and reliability of the reverse simulation method.展开更多
An apparent viscosity model of semi-solid A356 aluminum alloy has been developed and the software Castsofl6.0 coupled with the model has been used to simulate the mould filling of an automobile master brake cylinder w...An apparent viscosity model of semi-solid A356 aluminum alloy has been developed and the software Castsofl6.0 coupled with the model has been used to simulate the mould filling of an automobile master brake cylinder with the semi-solid A356 aluminum alloy slurry. The simulation results are in agreement with the practical filling process, indicating that the apparent viscosity model is feasible and can be used to simulate the mould filling of the semisolid A356 aluminum alloy slurry and can be used to optimize the filling process and the design of dies. A higher injection pressure, a higher ingate flow velocity of the semi-solid slurry, and a higher slurry temperature are advantageous to the mould filling of the automobile master brake cylinder.展开更多
文摘This paper is concerned with the design, modeling, and simulation and testing procedure of All Terrain Vehicle (ATV) fitted with SAS, which is used in BAJA SAEINDIA standards. Using CATIA V5, the model is created, which is fulfilling the guidelines of BAJA SAEINDIA rules. ATV is having the two different pairs of quarter car models of suspensions where dampers filled with MR Fluid (SAS) in front and rear wheels. In front SLA wishbone and rear McPherson Strut are fixed. The physical representation of the ATV is converted into the mathematical modeling and it is imported in MATLAB SIMULINK software and analyzed for ATV’s performance. The ATV is analyzed for its vertical, pitch and roll motions which include total number of 7 Degrees of Freedom. The road excitation modeling also incorporated with the equations. This paper, elaborates the approaching of simulation method only. The virtual model of ATV has involving greater significance of reducing the cost involved in real time testing as well as the results are replica of experimental results.
基金Project(2006AA03Z115) supported by the National Hi-tech Research and Development Program of ChinaProject(2006CB605203) supported by the National Basic Research Program of ChinaProject(50774007) supported by the National Natural Science Foundation of China
文摘Based on the experimental data of apparent viscosity about semi-solid A356 aluminum alloy, the apparent viscosity model was developed and inserted into a commercial software Castsoft6.0, and a key-shaped component filling process was simulated. The simulation results are in good agreement with the experimental filling results, which indicates that the apparent viscosity model established is effective and available. The process parameters on the cavity filling of the key-shaped components have been optimized. The injection pressure should be more than 15 MPa, the slurry flowing velocity in the in-gate should be more than 1.73 m/s, and the slurry temperature should be over 585 ℃.
基金supported by the National High-Tech Research and Development Program of China(No.2006AA03Z115)the Major State Basic Research and Development Program of China(No.2006CB605203)
文摘The effect of injection pressure, piston velocity, and the forming temperature of semisolid slurry on the filling behavior of the semi-solid A356 aluminum alloy was investigated by simulation methods. The simulation results show that these processing parameters have an important effect on the filling behavior of the semi-solid A356 aluminum alloy. The slurry flows steadily in the cavity when the injection pressure, the piston velocity, and the forming temperature are low, but it is prone to turbulent flow when the injection pressure, the piston velocity, and the forming temperature are much higher. Therefore it is necessary to determine the appropriate processing parameters to get a steady flow of the slurry in the cavity.
基金Projects(0414) supported by the Science and Technology Development Foundation of Shanghai Automotive Industry
文摘To understand the flow trace of semi-solid slurry in mold cavity, some thermocouples were inserted in mold cavity, and the reaction timing of thermocouples showed the arrival of fluid. The filling time and rate were estimated by comparison between the experiment and calculation. The introduction of computer simulation technique based on ADSTEFAN was to predict injectionforming process and to prevent defects during trial manufacture of various parts. By comparing the formed appearance of parts in experiment and in simulation, and observing the relationship between internal defects inspected by X-ray or microscope and the flow field obtained in simulation, it was indicated that both have quite good agreement in simulation and experiment. Right predictions for cast defects resulted from mold rilling can be carried out and proper direction was also proposed. The realization of numerical visualization for filling process during semi-solid die-cast process will play an important role in optimizing technology plan.
文摘In the present study, in-situ Ti B2 particle-reinforced 7075 aluminum alloy was produced by adding a mixture of K2 Ti F6 and KBF4 to the molten base alloy. The effects of the addition of 4.5wt.% and 9wt.%Ti B2 on the apparent viscosity and microstructure were investigated. The results showed that adding Ti B2 is effective for optimizing primary α-Al, but compared with the 4.5wt.%Ti B2/7075 composite, the addition of 9wt.%Ti B2 had no further significant refinement role in the 9wt.%Ti B2/7075 composite due to particle aggregation. The viscosities of semi-solid 7075 alloy and Ti B2/7075 composite slurries increased with an increase in solid fraction, but decreased with an increase in shear rate. The viscosity of 4.5wt.% Ti B2/7075 was the lowest among the three samples, and that of 7075 alloy was the highest under the same conditions. The primary α-Al grain size was decreased, and the dendritic grains grew into spherical shapes after shearing. Based on the experimental results, viscosity models of the semi-solid 7075 alloy and 4.5wt.% and 9wt.%Ti B2/7075 composites were formulated. According to the simulation results, the shrinkage porosity of the 4.5wt.%Ti B2/7075 wheel was lower than those of the 7075 alloy and 9wt.%Ti B2/7075 wheels.
文摘To realize the technology of fabricating the rheologic semi-solid slurry of ZL112Y aluminum alloy via continues electromagnetic stirring process, ANSYS software was used to simulate electromagnetic force field and fluid velocity field in the alloy melt in a crucible tube in three coils. In the first section of the paper, eletromagnetic force field and fluid velocity field caused by single coil were simulated. The result of this simulation gives an average velocity of 3.2 cm/s and it is called critical velocity because a fluid velocity over it will cause a fine and spherical structure of solid primary a in a semi-solid melt. And, from this result, a reasonable temperature of semi-solid of the alloy and an electrical current intensity were established. The electrical current intensity of the result of this simulation corresponded to the current intensity used in a practice experiment, in which the primary α was obviously refined and sphericized. Based on this simulation of single coil electromagnetic stirring, in the second section of the paper, eletromagnetic force field and fluid velocity field caused by three coils were simulated. The result of the simulation shows that, 1） there is a semi-solid zone of 32 mm from bottom of the crucible tube to the upper; 2） the electrical current intensities of three coils of 400 A, 600 A, and 400 A, which were set to top range, middle range and bottom range of the tube, respectively, were the optimum parameters of electromagnetic current intensity under the condition of this investigation; and 3） under effect of these electromagnetic current intensity, the fluid velocities of the melt in the tube were 6.3 cm/s in top range, 3.75 cm/s in middle range, and 3.9 cm/s in bottom range of it, respectively.
文摘Semi-enclosed sea basins have difficulty in recharging their waters due to limited communication with larger water bodies, with understandable consequences for their environmental status. This paper aims at the computational simulation of the hydrodynamic characteristics of the waters of the Pagasitikos Gulf (Greece), which has limited communication and water exchange with the Aegean Sea and is subject to intense environmental pressures The Estuary, Lake & Coastal Ocean 3d hydrodynamic Model (ELCOM 2.2) combined with its later version Aquatic Ecosystem Model-3d (AEM3D) were used for the simulation. The simulation included the topography of the area, the bay’s bottom geometry, atmospheric loadings, tides, the influence of the Coriolis force and boundary conditions. The hydrodynamic behaviour of the bay, water circulation, velocities at the surface and in depth, water recharge and residence time throughout the bay, density variation and other factors were examined to determine the impact of all these on the aquatic ecosystem.
文摘In the process of preparation of semi-solid metal materials, a variety of factors would influence the preparing time and the morphology of non-dendritic microstructure. The aim of this work is using phase-field method to simulate non-dendritic growth during preparation of AI-4Cu-Mg semi-solid alloy by electromagnetic stirring method （EMS method）. Several factors such as the disturbance intensity, anisotropy, the thickness of the interface and the ratio of diffusivity in solid and liquid were considered. It is shown that decreasing the thickness of the interface results in more circular outline of particles, and increasing the diffusivity in solid can reduce degree of microsegregation. The disturbance intensity in the model can be connected with current intensity of stator or magnetic induction density impressed. Simulation results show that the larger the disturbance intensity or magnetic induction density, the more globular morphology the original phase in the matrix.
文摘A software code based on SOLA-VOF algorithm is developed for numerical simulation of mold filling of semi-solid metals.The semi-solid mould filling processes of A356 and AZ91D are studied based on the Power-Law viscosity model and constant viscosity model,respectively.Test molds with different thicknesses and shapes were chosen to validate the software code.The simulated mould filling sequence shows a good agreement with the experimental results.The viscosity distribution is also calculated and plotted with a post-processor.The results show that the software code can offer an effective understanding for semi-solid mold filling processes.
基金Supported by the National High Technology Research and Development Program of China(2013AA065301)the Fundamental Research Funds for the Central Universities(2016QNA4014)the State Key Laboratory of Clean Energy Utilization at Zhejiang University(ZJUCEU2016006)
文摘A reliable mathematical model of urea-water-solution(UWS) droplet evaporation and thermolysis is developed.The well known Abramzon–Sirignano evaporation model is corrected by introducing an adjustment coefficient considering the different evaporation behaviors of UWS droplet at different ambient temperatures. A semidetailed kinetic scheme of urea thermolysis is developed based on Ebrahimian's work. Sequentially, the evaporation characteristics, decomposition efficiency of a single UWS droplet and deposit formation are simulated. As a result, the relation of evaporation time, relative velocity, exhaust temperature and droplet initial diameter is presented. Synchronously, it indicates that temperature is the decisive factor for urea thermolysis. Different temperatures result in different deposit components, and deposit yield is significantly influenced by temperature and decomposition time. The current work can provide guidance for designing urea injection strategy of SCR systems.
基金supported by the Research Fund for Commonweal Trades (Meteorology) (Grants No.GYHY200706037, GYHY (QX) 2007-6-1,GYHY200906007,and GYHY201006038)the National Natural Science Foundation of China (Grants No.50479017 and 40971016)Program for Changjiang Scholars and Innovative Research Team in University (Grant No.IRT0717)
文摘A grid-based distributed hydrological model, the Block-wise use of TOPMODEL （BTOPMC）, which was developed from the original TOPMODEL, was used for hydrological daily rainfall-runoff simulation. In the BTOPMC model, the runoff is explicitly calculated on a cell-by-cell basis, and the Muskingum-Cunge flow concentration method is used. In order to test the model＇s applicability, the BTOPMC model and the Xin＇anjiang model were applied to the simulation of a humid watershed and a semi-humid to semi-arid watershed in China. The model parameters were optimized with the Shuffle Complex Evolution （SCE-UA） method. Results show that both models can effectively simulate the daily hydrograph in humid watersheds, but that the BTOPMC model performs poorly in semi-humid to semi-arid watersheds. The excess-infiltration mechanism should be incorporated into the BTOPMC model to broaden the model＇s applicability.
基金National Science Foundation Graduate Research Fellowship
文摘Real-time hybrid simulation is an attractive method to evaluate the response of structures under earthquake loads. The method is a variation of the pseudodynamic testing technique in which the experiment is executed in real time, thus allowing investigation of structural systems with rate-dependent components. Real-time hybrid simulation is challenging because it requires performance of all calculations, application of displacements, and acquisition of measured forces, within a very small increment of time. Furthermore, unless appropriate compensation for actuator dynamics is implemented, stability problems are likely to occur during the experiment. This paper presents an approach for real-time hybrid simulation in which compensation for actuator dynamics is implemented using a model-based feedforward compensator. The method is used to evaluate the response of a semi-active control of a structure employing an MR damper. Experimental results show good agreement with the predicted responses, demonstrating the effectiveness of the method for structural control performance assessment.
基金Project (2007AA03Z119) supported by the National High Technology Research and Development Program of ChinaProjects (2102029,2072012) supported by Beijing Natural Science Foundation
文摘Based on analysis of the main forming methods for double-layer tube,a new short-term forming process called thixo-co-extrusion was put forward in producing double-layer tube by combining the semi-solid forming technology and multi-billet extrusion technology.By means of forward extrusion with shaft,a finite element model of thixo-co-extrusion with A356/AZ91 was constructed by ABAQUS FEM software.The distributions of temperature field and velocity field as well as the contact force during thixo-co-extrusion were studied.The diffusion on the interfaces between inner and outer metals was analyzed.The simulation results show that,in the beginning of thixo-co-extrusion,the uneven wall thickness can appear.To thickness ratio of 5:5,a double layer tube with good inner and outer wall combination can be realized if VA356 is 0.12 m/s and VAZ91 is 0.20 m/s.
基金Project(50605015) supported by the National Natural Science Foundation of ChinaProject(HITQNJS.2008.012) supported by Development Program for Outstanding Young Teachers in Harbin Institute of Technology, China+1 种基金Projects (20090460884,20080440849) supported by Postdoctoral Science Foundation of ChinaProjects(LBH-Z06072,LBH-Z07146,LBH-Q08104) supported by Postdoctoral Foundation of Heilongjiang Province,China
文摘Numerical simulation and experiment of thixoforming angle frame of AZ61 magnesium alloy were investigated.The results show that with the increase in punch displacement,cylinder billet firstly fills into die cavity of angle frame from feed inlet and plastic deformation occurs in touching region between billet and die cavity.After central thin wall of angle frame is created,semi-solid billet fills toward two edges.Lastly,complete plastic deformation occurs in billet,leading to complete filling of semis-olid billet.Effective strain,effective stress and billet temperature decrease with the increase in punch displacement.Effective stress decreases with the increase in billet temperature,die temperature and punch velocity.The optimal conditions decided by numerical simulation are as follows:die temperature of 450 ℃,billet temperature of 560 ℃ and punch velocity of 30 mm/s.Angle frame components with high mechanical properties such as yield strength of 225 MPa,tensile strength of 309 MPa and elongation of 21.8% and fine microstructure could be thixoformed successfully according to process parameters decided by numerical simulation.
基金supported by the National Natural Science Foundation of China(Grant No.50979059)
文摘Moving particle semi-implicit （MPS） method is a fully Lagrangian particle method which can easily solve problems with violent free surface. Although it has demonstrated its advantage in ocean engineering applications, it still has some defects to be improved. In this paper, MPS method is extended to the large eddy simulation （LES） by coupling with a sub-particle-scale （SPS） turbulence model. The SPS turbulence model turns into the Reynolds stress terms in the filtered momentum equation, and the Smagorinsky model is introduced to describe the Reynolds stress terms. Although MPS method has the advantage in the simulation of the free surface flow, a lot of non-free surface particles are treated as free surface particles in the original MPS model. In this paper, we use a new free surface tracing method and the key point is ＂neighbor particle＂. In this new method, the zone around each particle is divided into eight parts, and the particle will be treated as a free surface particle as long as there are no ＂neighbor particles＂ in any two parts of the zone. As the number density parameter judging method has a high efficiency for the free surface particles tracing, we combine it with the neighbor detected method. First, we select out the particles which may be mistreated with high probabilities by using the number density parameter judging method. And then we deal with these particles with the neighbor detected method. By doing this, the new mixed free surface tracing method can reduce the mistreatment problem efficiently. The serious pressure fluctuation is an obvious defect in MPS method, and therefore an area-time average technique is used in this paper to remove the pressure fluctuation with a quite good result. With these improvements, the modified MPS-LES method is applied to simulate liquid sloshing problems with large deforming free surface. Results show that the modified MPS-LES method can simulate the large deforming free surface easily. It can not only capture the large impact pressure accurately on rolling tank wall but also can generate all physical phenomena successfully. The good agreement between numerical and experimental results proves that the modified MPS-LES method is a good CFD methodology in free surface flow simulations.
文摘Preparation of semisolid slurry using a cooling slope is increasingly becoming popular,primarily because of the simplicity in design and ease control of the process.In this process,liquid alloy is poured down an inclined surface which is cooled from underneath.The cooling enables partial solidification and the incline provides the necessary shear for producing semisolid slurry.However,the final microstructure of the ingot depends on several process parameters such as cooling rate,incline angle of the cooling slope,length of the slope and initial melt superheat.In this work,a CFD model using volume of fluid(VOF) method for simulating flow along the cooling slope was presented.Equations for conservation of mass,momentum,energy and species were solved to predict hydrodynamic and thermal behavior,in addition to predicting solid fraction distribution and macrosegregation.Solidification was modeled using an enthalpy approach and a volume averaged technique for the different phases.The mushy region was modeled as a multi-layered porous medium consisting of fixed columnar dendrites and mobile equiaxed/fragmented grains.The alloy chosen for the study was aluminum alloy A356,for which adequate experimental data were available in the literature.The effects of two key process parameters,namely the slope angle and the pouring temperature,on temperature distribution,velocity distribution and macrosegregation were also studied.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51479116 and 11272213)
文摘A numerical model has been developed to study sloshing of turbulent flow in a tank with elastic baffles. The Moving-Particle Semi-implicit method(MPS) is a kind of meshless Lagrangian calculation method. The large eddy simulation(LES) approach is employed to model the turbulence by using the Smagorinsky Sub-Particle Scale(SPS)closure model. This paper uses MPS-FSI method with LES to simulate the interaction between free surface flow and a thin elastic baffle in sloshing. Then, the numerical model is validated, and the numerical solution has good agreement with experimental data for sloshing in a tank with elastic baffles. Furthermore, under external excitations,the MPS is applied to viscous laminar flow and turbulent flow, with both the deformation of elastic baffles and the wave height of the free surface are compared with each other. Besides, the impact pressure with/without baffles and wave height of free surface are investigated and discussed in detail. Finally, preliminary simulations are carried out in the damage problem of elastic baffles, taking the advantage of the MPS-FSI method in computations of the fluid–structure interaction with large deformation.
基金National Natural Science Foundation of China (No.51405201)
文摘The simulation of 295/80R22. 5 tire building process from tire building to curing was developed using ABAQUS software,which covered four stages: gluing of components on main drum,gluing of components on auxiliary drum,building process of green tire and shaping process of green tire. Results showed that material distribution of the simulated structure had good consistence with the real tire structure. Therefore,the tire building process simulation can be used to judge the rationality of tire construction design and to determine the shapes of different tire components. In order to optimize the construction design,a reverse simulation method was proposed to design the semi-product components such as apex,tread,and shoulder pad. The semi-product components determined by utilizing the reverse simulation method were assembled again into a tire. Results show that the simulated material distribution is consistent with the material distribution of design tire,which proves effectiveness and reliability of the reverse simulation method.
基金the National High-Tech Research and Development Program of China (No.2006AA03Z115)the Major State Basic Research Development Program of China (No.2006CB605203)the National Natural Science Foundation of China (No.50774007)
文摘An apparent viscosity model of semi-solid A356 aluminum alloy has been developed and the software Castsofl6.0 coupled with the model has been used to simulate the mould filling of an automobile master brake cylinder with the semi-solid A356 aluminum alloy slurry. The simulation results are in agreement with the practical filling process, indicating that the apparent viscosity model is feasible and can be used to simulate the mould filling of the semisolid A356 aluminum alloy slurry and can be used to optimize the filling process and the design of dies. A higher injection pressure, a higher ingate flow velocity of the semi-solid slurry, and a higher slurry temperature are advantageous to the mould filling of the automobile master brake cylinder.
