The influence of pouring temperature and mold temperature on the fluidity and hot tearing behavior of Al-2Li-2Cu-0.5Mg-0.15Sc-0.1Zr-0.1Ti alloys was investigated by experimental investigation and simulation assessment...The influence of pouring temperature and mold temperature on the fluidity and hot tearing behavior of Al-2Li-2Cu-0.5Mg-0.15Sc-0.1Zr-0.1Ti alloys was investigated by experimental investigation and simulation assessment.The results showed that the length of the spiral fluidity sample increases from 302 to 756 mm as the pouring temperature increases from 680 to 740℃,and from 293 to 736 mm as the mold temperature increases from 200 to 400℃.The hot tearing susceptibility(HTS)firstly decreases and then increases with increasing pouring and mold temperatures,which is mainly caused by the oxide inclusion originating from the high activity of Li at excessive pouring temperature.Excessive pouring and mold temperatures easily produce oxide inclusions and holes,leading to a reduction in fluidity and an increase in HTS of the alloy.Combining the experimental and simulation results,the optimized pouring and mold temperatures are~720℃ and~300℃ for the cast Al-Li alloy,respectively.展开更多
A novel three-dimensional numerical model is proposed to investigate the effect of tool eccentricity on the coupled thermal and material flow characteristics in friction stir welding(FSW) process.An asymmetrical bound...A novel three-dimensional numerical model is proposed to investigate the effect of tool eccentricity on the coupled thermal and material flow characteristics in friction stir welding(FSW) process.An asymmetrical boundary condition at the tool-workpiece interface,and the dynamic mesh technique are both employed for the consideration of the tool eccentricity during tool rotating.It is found that tool eccentricity induces the periodical variation of the heat densities both at the tool-workpiece interface and inside the shear layer,but the fluctuation amplitudes of the heat density variations are limited.However,it is demonstrated that tool eccentricity results in significant variation of the material flow behavior in one tool rotating period.Moreover,the material velocity variation at the retreating side is particularly important for the formation of the periodic characteristics in FSW.The modeling result is found to be in good agreement with the experimental one.展开更多
The thermodynamic characterization as well as the rheological characterization of the A201 alloy were conducted.Thermodynamic simulations (CALPHAD method) and calorimetric experiments were performed to determine the s...The thermodynamic characterization as well as the rheological characterization of the A201 alloy were conducted.Thermodynamic simulations (CALPHAD method) and calorimetric experiments were performed to determine the solidus and liquidus temperatures, the melting range and the sensitivity of the solid fraction at the thixoforming temperatures.The rheology of aluminium alloy A201 was examined using a high temperature Searle rheometer.The flow behaviour was analyzed with concentric cylinders of graphite to avoid chemical interactions with the liquid or semi-solid aluminium.The rotational body was grooved to prevent a phenomenon called wall slippage.Continuous cooling experiment was used to observe the shear rate effects on the flow behaviour.It can be seen that the viscosity level decreases at higher shear rates.Shear rate jump experiment was carried out to evaluate the steady state flow curve within the analyzed shear rate range from 60 s-1 to 260 s-1.It is found that the power law indexes are-1.35 and-1.49 for 35% and 45% solid fraction, respectively.Finally, some mechanical property data of as-cast and as-thixoformed A201 alloy are included indicating the potential for high strength applications.展开更多
The flow between a grooved and a flat plate was presented to investigate the effects of groove on the behavior of hydro-viscous drive. The flow was solved by using computational fluid dynamics (CFD) code, Fluent. Para...The flow between a grooved and a flat plate was presented to investigate the effects of groove on the behavior of hydro-viscous drive. The flow was solved by using computational fluid dynamics (CFD) code, Fluent. Parameters related to the flow, such as velocity, pressure, temperature, axial force and viscous torque, are obtained. The results show that pressure at the upstream notch is negative, pressure at the downstream notch is positive and pressure along the film thickness is almost the same. Dynamic pressure peak decreases as groove depth or groove number increases, but increases as output rotary speed increases. Consequently, the groove depth is suggested to be around 0.4 mm. Both the groove itself and groove parameters (i.e. groove depth, groove number) have little effect on the flow temperature. Circumferential pressure gradient induced by the groove weakens the viscous torque on the grooved plate (driven plate) greatly. It has little change as the groove depth increases. However, it decreases dramatically as the groove number increases. The experiment results show that the trend of experimental temperature and pressure are the same with numerical results. And the output rotary speed also has relationship with input flow rate and flow temperature.展开更多
To reduce defects caused by non-homogeneous metal flow in conventional extrusion,a die with guiding angle was designed to improve the metal flow behavior. The characteristic quantities such as the second invariant of ...To reduce defects caused by non-homogeneous metal flow in conventional extrusion,a die with guiding angle was designed to improve the metal flow behavior. The characteristic quantities such as the second invariant of the deviator stress J2 and Lode's coefficient μ were employed for the division of deformation area. The results show that when the metal is extruded with the guiding angle,no metal flow interface forms at the container's bottom,the dead zone completely disappears,the deformation types of the metal in the plastic deformation area change from three types to one type of tension,and the homogeneity of the deformation as well as metal flow are greatly improved. The non-homogeneous metal flow at the final stage of extrusion is improved,reducing the shrinkage hole at the axis end. The radial stress of the furthest point from the axis is transformed from tensile stress to compressive stress and the axial stress,and decreased from 70.8 to 34.8 MPa. Therefore,the surface cracks caused by additional stress are greatly reduced.展开更多
Gas–liquid two-phase flow is complex and has uncertainty in phase interfaces, which make the two-phase flow look very complicated. Even though the flow behavior(e.g. coalescence, crushing and separation) of single bu...Gas–liquid two-phase flow is complex and has uncertainty in phase interfaces, which make the two-phase flow look very complicated. Even though the flow behavior(e.g. coalescence, crushing and separation) of single bubble or bubble groups in the liquid phase looks random, combining some established characteristics and methodologies can find regularities among the randomness. In order to excavate the nonlinear dynamic characteristics of gas–liquid two-phase flow, the authors developed an improved matrix pencil(IMP) method to analyze the pressure difference signals of the two-phase flow. This paper elucidates the influence of signal length on MP calculation results and the anti-noise-interference ability of the MP method. An IMP algorithm was applied to the fluctuation signals of gas–liquid two-phase flow to extract the mode frequency and damping ratio, which were combined with the component energy index(CEI) entropy to identify the different flow patterns. It is also found that frequency, damping ratio, CEI entropy and stability diagram together not only identify flow patterns, but also provide a new way to examine and understand the evolution mechanism of physical dynamics embedded in flow patterns. Combining these characteristics and methods, the evolution of the nonlinear dynamic physical behavior of gas bubbles is revealed.展开更多
In this paper, the dynamics behaviors on fo-δ parameter surface is investigated for Gledzer-Ohkitani- Yamada model We indicate the type of intermittency chaos transitions is saddle node bifurcation. We plot phase dia...In this paper, the dynamics behaviors on fo-δ parameter surface is investigated for Gledzer-Ohkitani- Yamada model We indicate the type of intermittency chaos transitions is saddle node bifurcation. We plot phase diagram on fo-δ parameter surface, which is divided into periodic, quasi-periodic, and intermittent chaos areas. By means of varying Taylor-microscale Reynolds number, we calculate the extended self-similarity of velocity structure function.展开更多
Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou＇s model for Bingham fluids...Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou＇s model for Bingham fluids is solved by using the multiple- relaxation-time lattice Boltzmann model （MRT-LB）. Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou＇s model provides a good approximation of realistic Bingham plastics for values of m 〉 108. For lower values of m, Papanastasiou＇s model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems： 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fhi d force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients Co, and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.展开更多
Flexibility plays an important part in the application of the workflow management system and has become one of the major research hotspots in this field recently. When adapting a workflow process definition to specifi...Flexibility plays an important part in the application of the workflow management system and has become one of the major research hotspots in this field recently. When adapting a workflow process definition to specific needs or changing the structure of the workflow process as a result of evolutionary change, coarse-grained reuse of work- flow is of significance to the reduction of the work effort, modeling system and enhancing the reliability of their work. Based on decomposition of workflow tasks and teamwork, this paper proposes an approach to describing interoperability behavior between roles in teamwork by using activity-pattern. In activity-pattern, abstract mechanisms of activity specialization and activity aggregation are presented, enabling reuse of workflow by means of reuse of interoperability behavior between roles. The experimental system shows that our approach presented is feasible.展开更多
An SIS epidemiological model in a population of varying size with two dissimilar groups of susceptible individuals has been analyzed. We prove that all the solutions tend to the equilibria of the system. Then we use t...An SIS epidemiological model in a population of varying size with two dissimilar groups of susceptible individuals has been analyzed. We prove that all the solutions tend to the equilibria of the system. Then we use the Poincar~ Index theorem to determine the number of the rest points and their stability properties. It has been shown that bistability occurs for suitable values of the involved parameters. We use the perturbations of the pitchfork bifurcation points to give examples of all possible dynamics of the system. Some numerical examples of bistability and hysteresis behavior of the systeIn has been also provided.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.51871148,51821001)。
文摘The influence of pouring temperature and mold temperature on the fluidity and hot tearing behavior of Al-2Li-2Cu-0.5Mg-0.15Sc-0.1Zr-0.1Ti alloys was investigated by experimental investigation and simulation assessment.The results showed that the length of the spiral fluidity sample increases from 302 to 756 mm as the pouring temperature increases from 680 to 740℃,and from 293 to 736 mm as the mold temperature increases from 200 to 400℃.The hot tearing susceptibility(HTS)firstly decreases and then increases with increasing pouring and mold temperatures,which is mainly caused by the oxide inclusion originating from the high activity of Li at excessive pouring temperature.Excessive pouring and mold temperatures easily produce oxide inclusions and holes,leading to a reduction in fluidity and an increase in HTS of the alloy.Combining the experimental and simulation results,the optimized pouring and mold temperatures are~720℃ and~300℃ for the cast Al-Li alloy,respectively.
基金the financial support from the National Natural Science Foundation of China (Nos. 52005297, 52035005)the Key Research and Development Program of Shandong Province, China (No. 2021ZLGX01)。
文摘A novel three-dimensional numerical model is proposed to investigate the effect of tool eccentricity on the coupled thermal and material flow characteristics in friction stir welding(FSW) process.An asymmetrical boundary condition at the tool-workpiece interface,and the dynamic mesh technique are both employed for the consideration of the tool eccentricity during tool rotating.It is found that tool eccentricity induces the periodical variation of the heat densities both at the tool-workpiece interface and inside the shear layer,but the fluctuation amplitudes of the heat density variations are limited.However,it is demonstrated that tool eccentricity results in significant variation of the material flow behavior in one tool rotating period.Moreover,the material velocity variation at the retreating side is particularly important for the formation of the periodic characteristics in FSW.The modeling result is found to be in good agreement with the experimental one.
基金the "Ministerio de Ciencia e Innovación" and to the "Fondos FEDER",project "Integrauto" PSE-370000-2008-03the Basque Government,project "ETORTEK, Manufacturing 0.0 II",for their financial support
文摘The thermodynamic characterization as well as the rheological characterization of the A201 alloy were conducted.Thermodynamic simulations (CALPHAD method) and calorimetric experiments were performed to determine the solidus and liquidus temperatures, the melting range and the sensitivity of the solid fraction at the thixoforming temperatures.The rheology of aluminium alloy A201 was examined using a high temperature Searle rheometer.The flow behaviour was analyzed with concentric cylinders of graphite to avoid chemical interactions with the liquid or semi-solid aluminium.The rotational body was grooved to prevent a phenomenon called wall slippage.Continuous cooling experiment was used to observe the shear rate effects on the flow behaviour.It can be seen that the viscosity level decreases at higher shear rates.Shear rate jump experiment was carried out to evaluate the steady state flow curve within the analyzed shear rate range from 60 s-1 to 260 s-1.It is found that the power law indexes are-1.35 and-1.49 for 35% and 45% solid fraction, respectively.Finally, some mechanical property data of as-cast and as-thixoformed A201 alloy are included indicating the potential for high strength applications.
基金Project(50475106)supported by the National Natural Science Foundation of China
文摘The flow between a grooved and a flat plate was presented to investigate the effects of groove on the behavior of hydro-viscous drive. The flow was solved by using computational fluid dynamics (CFD) code, Fluent. Parameters related to the flow, such as velocity, pressure, temperature, axial force and viscous torque, are obtained. The results show that pressure at the upstream notch is negative, pressure at the downstream notch is positive and pressure along the film thickness is almost the same. Dynamic pressure peak decreases as groove depth or groove number increases, but increases as output rotary speed increases. Consequently, the groove depth is suggested to be around 0.4 mm. Both the groove itself and groove parameters (i.e. groove depth, groove number) have little effect on the flow temperature. Circumferential pressure gradient induced by the groove weakens the viscous torque on the grooved plate (driven plate) greatly. It has little change as the groove depth increases. However, it decreases dramatically as the groove number increases. The experiment results show that the trend of experimental temperature and pressure are the same with numerical results. And the output rotary speed also has relationship with input flow rate and flow temperature.
基金Project(RC2010QN017008) supported by the Excellent Young Teachers Program of Harbin City, China
文摘To reduce defects caused by non-homogeneous metal flow in conventional extrusion,a die with guiding angle was designed to improve the metal flow behavior. The characteristic quantities such as the second invariant of the deviator stress J2 and Lode's coefficient μ were employed for the division of deformation area. The results show that when the metal is extruded with the guiding angle,no metal flow interface forms at the container's bottom,the dead zone completely disappears,the deformation types of the metal in the plastic deformation area change from three types to one type of tension,and the homogeneity of the deformation as well as metal flow are greatly improved. The non-homogeneous metal flow at the final stage of extrusion is improved,reducing the shrinkage hole at the axis end. The radial stress of the furthest point from the axis is transformed from tensile stress to compressive stress and the axial stress,and decreased from 70.8 to 34.8 MPa. Therefore,the surface cracks caused by additional stress are greatly reduced.
基金Supported by the National Natural Science Foundation of China(51406031)Jilin City Science and Technology Plan Project(201464055)Jilin Province Education Department Science Research Project(2015-243)
文摘Gas–liquid two-phase flow is complex and has uncertainty in phase interfaces, which make the two-phase flow look very complicated. Even though the flow behavior(e.g. coalescence, crushing and separation) of single bubble or bubble groups in the liquid phase looks random, combining some established characteristics and methodologies can find regularities among the randomness. In order to excavate the nonlinear dynamic characteristics of gas–liquid two-phase flow, the authors developed an improved matrix pencil(IMP) method to analyze the pressure difference signals of the two-phase flow. This paper elucidates the influence of signal length on MP calculation results and the anti-noise-interference ability of the MP method. An IMP algorithm was applied to the fluctuation signals of gas–liquid two-phase flow to extract the mode frequency and damping ratio, which were combined with the component energy index(CEI) entropy to identify the different flow patterns. It is also found that frequency, damping ratio, CEI entropy and stability diagram together not only identify flow patterns, but also provide a new way to examine and understand the evolution mechanism of physical dynamics embedded in flow patterns. Combining these characteristics and methods, the evolution of the nonlinear dynamic physical behavior of gas bubbles is revealed.
基金supported by National Natural Science Foundation-the Science Foundation of China Academy of Engineering Physics (NSAF) under Grant No. 10576076the Major Projects of National Natural Science Foundation of China under Grant No. 10335010
文摘In this paper, the dynamics behaviors on fo-δ parameter surface is investigated for Gledzer-Ohkitani- Yamada model We indicate the type of intermittency chaos transitions is saddle node bifurcation. We plot phase diagram on fo-δ parameter surface, which is divided into periodic, quasi-periodic, and intermittent chaos areas. By means of varying Taylor-microscale Reynolds number, we calculate the extended self-similarity of velocity structure function.
基金supported by the National Key Basic Research Program of China(Grant No.2010CB731504)the Natural Science Foundation of China(Grant Nos.11034010,11272048 and 51239006)+1 种基金European Commission Marie Curie Actions(Grant No.IRSES-294976)the State Key Laboratory of Hydroscience and Engineering(Grant No.2013-KY-2)
文摘Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou＇s model for Bingham fluids is solved by using the multiple- relaxation-time lattice Boltzmann model （MRT-LB）. Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou＇s model provides a good approximation of realistic Bingham plastics for values of m 〉 108. For lower values of m, Papanastasiou＇s model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems： 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fhi d force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients Co, and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.
基金This research is supported by National Natural Science Foundation of China （60574028） the Key Projects of Natural Science Foundation of Edtication Department of Anhui Province of China （2006kj016A, 2005kj065）
文摘Flexibility plays an important part in the application of the workflow management system and has become one of the major research hotspots in this field recently. When adapting a workflow process definition to specific needs or changing the structure of the workflow process as a result of evolutionary change, coarse-grained reuse of work- flow is of significance to the reduction of the work effort, modeling system and enhancing the reliability of their work. Based on decomposition of workflow tasks and teamwork, this paper proposes an approach to describing interoperability behavior between roles in teamwork by using activity-pattern. In activity-pattern, abstract mechanisms of activity specialization and activity aggregation are presented, enabling reuse of workflow by means of reuse of interoperability behavior between roles. The experimental system shows that our approach presented is feasible.
文摘An SIS epidemiological model in a population of varying size with two dissimilar groups of susceptible individuals has been analyzed. We prove that all the solutions tend to the equilibria of the system. Then we use the Poincar~ Index theorem to determine the number of the rest points and their stability properties. It has been shown that bistability occurs for suitable values of the involved parameters. We use the perturbations of the pitchfork bifurcation points to give examples of all possible dynamics of the system. Some numerical examples of bistability and hysteresis behavior of the systeIn has been also provided.
