Considering the tunneling effect and the Schottky effect,the metal semiconductor contact is simulated by using self consistent ensemble Monte Carlo method.Under different biases or at different barrier heights,the i...Considering the tunneling effect and the Schottky effect,the metal semiconductor contact is simulated by using self consistent ensemble Monte Carlo method.Under different biases or at different barrier heights,the investigation into the tunneling current indicates that the tunneling effect is of great importance under reverse biases.The Schottky barrier diode current due to Schottky effect is in agreement with the theoretical one.The barrier lowering is found a profound effect on the current transport at the metal semiconductor interface.展开更多
The investigation was carried out on the technical problems of finishing the inner surface of elbow parts and the action mechanism of particles in elbow precision machining by abrasive flow.This work was analyzed and ...The investigation was carried out on the technical problems of finishing the inner surface of elbow parts and the action mechanism of particles in elbow precision machining by abrasive flow.This work was analyzed and researched by combining theory,numerical and experimental methods.The direct simulation Monte Carlo(DSMC)method and the finite element analysis method were combined to reveal the random collision of particles during the precision machining of abrasive flow.Under different inlet velocity,volume fraction and abrasive particle size,the dynamic pressure and turbulence flow energy of abrasive flow in elbow were analyzed,and the machining mechanism of particles on the wall and the influence of different machining parameters on the precision machining quality of abrasive flow were obtained.The test results show the order of the influence of different parameters on the quality of abrasive flow precision machining and establish the optimal process parameters.The results of the surface morphology before and after the precision machining of the inner surface of the elbow are discussed,and the surface roughness Ra value is reduced from 1.125μm to 0.295μm after the precision machining of the abrasive flow.The application of DSMC method provides special insights for the development of abrasive flow technology.展开更多
针对火星独特的CO_(2)稀薄气体环境以及探测器高超声速进入火星过程中的高温真实气体效应,研究了CO_(2)多振动模式的激发特性。采用非结构网格和直接模拟蒙特卡洛法(Direct Simulation Monte Carlo method, DSMC),基于非谐振子振动激发...针对火星独特的CO_(2)稀薄气体环境以及探测器高超声速进入火星过程中的高温真实气体效应,研究了CO_(2)多振动模式的激发特性。采用非结构网格和直接模拟蒙特卡洛法(Direct Simulation Monte Carlo method, DSMC),基于非谐振子振动激发模型,通过将CO_(2)离解能均分到4种振动模态,进而限制各模态最高振动能级,模拟了含CO_(2)的5组分17反应的高温稀薄真实气体化学反应模型。计算了“火星探路者”在火星大气环境65 km高度、进入速度为7 453 m/s、攻角为0°下的高温化学非平衡效应流场。结果表明:CO_(2)在激波后大量分解并消耗大量能量;迎风面激波中各组分占比与探测器物面特性等均与文献结果相符,证明了本文对于CO_(2)振动激发处理方法的可行性。在此基础上加入N_2组分,模拟火星大气8组分44基元化学反应流场,通过改变来流密度与马赫数分析了流场特性的变化。结果表明:随着来流密度减小,流场温度呈现先增加后减小的趋势,物面热流密度增大;来流马赫数增加使得流场温度和压力上升,物面热流密度提高但是热流密度系数变化幅度很小。展开更多
Direct Monte Carlo(MC) simulation is a powerful probabilistic safety assessment method for accounting dynamics of the system.But it is not efficient at simulating rare events.A biasing transition rate method based on ...Direct Monte Carlo(MC) simulation is a powerful probabilistic safety assessment method for accounting dynamics of the system.But it is not efficient at simulating rare events.A biasing transition rate method based on direct MC simulation is proposed to solve the problem in this paper.This method biases transition rates of the components by adding virtual components to them in series to increase the occurrence probability of the rare event,hence the decrease in the variance of MC estimator.Several cases are used to benchmark this method.The results show that the method is effective at modeling system failure and is more efficient at collecting evidence of rare events than the direct MC simulation.The performance is greatly improved by the biasing transition rate method.展开更多
The new improved directional vector simulation method foranalyzing the reliability of struc- tural systems failure probabilityis researched. This paper also points out the defects of generaldirectional vector simulati...The new improved directional vector simulation method foranalyzing the reliability of struc- tural systems failure probabilityis researched. This paper also points out the defects of generaldirectional vector simulation, and gives rise to a new higheraccuracy approximate integral formula of structural systems failureprobability. A new geometric meaning of characteristic function isobtained. A new simple method of generating uniformly distributedrandom vector sample sin n-dimensional unit hyper-spherical surfaceis put forward and strictly proved. This method is easy to put intopractice. Numerical examples are given to show the applicability andeffectiveness of the suggested approach to structural systemsreliability problems.展开更多
Direct Simulation Monte Carlo(DSMC)solves the Boltzmann equation with large Knudsen number.The Boltzmann equation generally consists of three terms:the force term,the diffusion term and the collision term.While the fi...Direct Simulation Monte Carlo(DSMC)solves the Boltzmann equation with large Knudsen number.The Boltzmann equation generally consists of three terms:the force term,the diffusion term and the collision term.While the first two terms of the Boltzmann equation can be discretized by numerical methods such as the finite volume method,the third term can be approximated by DSMC,and DSMC simulates the physical behaviors of gas molecules.However,because of the low sampling efficiency of Monte Carlo Simulation in DSMC,this part usually occupies large portion of computational costs to solve the Boltzmann equation.In this paper,by Markov Chain Monte Carlo(MCMC)and multicore programming,we develop Direct Simulation Multi-Chain Markov Chain Monte Carlo(DSMC3):a fast solver to calculate the numerical solution for the Boltzmann equation.Computational results show that DSMC3 is significantly faster than the conventional method DSMC.展开更多
使用圆柱坐标系网格的三维DSMC(Direct Simulation Monte Carlo)模型,对同轴圆柱间Taylor-Couette流中Taylor涡的形成进行了数值模拟,并分析了不同计算域和边界条件下稳定流场中Taylor涡的轴向排列结构.在网格设置和流场参数不变的情况...使用圆柱坐标系网格的三维DSMC(Direct Simulation Monte Carlo)模型,对同轴圆柱间Taylor-Couette流中Taylor涡的形成进行了数值模拟,并分析了不同计算域和边界条件下稳定流场中Taylor涡的轴向排列结构.在网格设置和流场参数不变的情况下,使用轴对称DSMC模型对Taylor涡进行数值模拟,所得Taylor涡的稳定过程与三维结果一致,验证了使用三维DSMC方法来解决微尺度低速的稀薄气流问题的可行性.三维模拟结果表明Taylor涡以较大的圆周速度绕轴旋转,二维模拟则无法体现.对不同的内圆柱旋转速度进行数值模拟,确定了能够产生Taylor涡的临界速度值.展开更多
采用考虑颗粒脉动流动对气相湍流流动影响的大涡模拟(LES)研究气相湍流,采用直接模拟蒙特卡罗方法(DSMC)模拟颗粒间的碰撞。单颗粒运动满足牛顿第二定律,颗粒相和气相相间作用的双向耦合由牛顿第三定律确定,考虑超细颗粒间的van der Wa...采用考虑颗粒脉动流动对气相湍流流动影响的大涡模拟(LES)研究气相湍流,采用直接模拟蒙特卡罗方法(DSMC)模拟颗粒间的碰撞。单颗粒运动满足牛顿第二定律,颗粒相和气相相间作用的双向耦合由牛顿第三定律确定,考虑超细颗粒间的van der Waals作用力。数值模拟垂直管内超细颗粒气固两相流动,对颗粒相速度、浓度以及团聚物流动过程进行分析。展开更多
NS-DSMC(Navier Stokes-Direct Simulation Monte Carlo)耦合方法是计算连续-稀薄跨流域流动的主要方法,应用过程中如何确定连续流域和稀薄流域的界面是此方法的关键问题之一,界面位置通常通过连续失效参数来判定.为合理选择连续失效参...NS-DSMC(Navier Stokes-Direct Simulation Monte Carlo)耦合方法是计算连续-稀薄跨流域流动的主要方法,应用过程中如何确定连续流域和稀薄流域的界面是此方法的关键问题之一,界面位置通常通过连续失效参数来判定.为合理选择连续失效参数,对目前广泛使用的两种连续失效参数KnQ和B参数进行了理论上的分析和比较,表明虽然他们建立的出发点不同,但在数学形式上具有一定相似性.通过圆柱绕流问题的数值试验进一步验证了两种连续失效参数具有一定对应关系.KnQ和B两种连续失效参数在NS-DSMC耦合方法中应用效果相差不大,但KnQ的阈值0.05适用范围较广,而B参数的阈值对不同流动问题会有变化.展开更多
文摘Considering the tunneling effect and the Schottky effect,the metal semiconductor contact is simulated by using self consistent ensemble Monte Carlo method.Under different biases or at different barrier heights,the investigation into the tunneling current indicates that the tunneling effect is of great importance under reverse biases.The Schottky barrier diode current due to Schottky effect is in agreement with the theoretical one.The barrier lowering is found a profound effect on the current transport at the metal semiconductor interface.
基金Projects(51206011,U1937201)supported by the National Natural Science Foundation of ChinaProject(20200301040RQ)supported by the Science and Technology Development Program of Jilin Province,China+1 种基金Project(JJKH20190541KJ)supported by the Education Department of Jilin Province,ChinaProject(18DY017)supported by Changchun Science and Technology Program of Changchun City,China。
文摘The investigation was carried out on the technical problems of finishing the inner surface of elbow parts and the action mechanism of particles in elbow precision machining by abrasive flow.This work was analyzed and researched by combining theory,numerical and experimental methods.The direct simulation Monte Carlo(DSMC)method and the finite element analysis method were combined to reveal the random collision of particles during the precision machining of abrasive flow.Under different inlet velocity,volume fraction and abrasive particle size,the dynamic pressure and turbulence flow energy of abrasive flow in elbow were analyzed,and the machining mechanism of particles on the wall and the influence of different machining parameters on the precision machining quality of abrasive flow were obtained.The test results show the order of the influence of different parameters on the quality of abrasive flow precision machining and establish the optimal process parameters.The results of the surface morphology before and after the precision machining of the inner surface of the elbow are discussed,and the surface roughness Ra value is reduced from 1.125μm to 0.295μm after the precision machining of the abrasive flow.The application of DSMC method provides special insights for the development of abrasive flow technology.
文摘针对火星独特的CO_(2)稀薄气体环境以及探测器高超声速进入火星过程中的高温真实气体效应,研究了CO_(2)多振动模式的激发特性。采用非结构网格和直接模拟蒙特卡洛法(Direct Simulation Monte Carlo method, DSMC),基于非谐振子振动激发模型,通过将CO_(2)离解能均分到4种振动模态,进而限制各模态最高振动能级,模拟了含CO_(2)的5组分17反应的高温稀薄真实气体化学反应模型。计算了“火星探路者”在火星大气环境65 km高度、进入速度为7 453 m/s、攻角为0°下的高温化学非平衡效应流场。结果表明:CO_(2)在激波后大量分解并消耗大量能量;迎风面激波中各组分占比与探测器物面特性等均与文献结果相符,证明了本文对于CO_(2)振动激发处理方法的可行性。在此基础上加入N_2组分,模拟火星大气8组分44基元化学反应流场,通过改变来流密度与马赫数分析了流场特性的变化。结果表明:随着来流密度减小,流场温度呈现先增加后减小的趋势,物面热流密度增大;来流马赫数增加使得流场温度和压力上升,物面热流密度提高但是热流密度系数变化幅度很小。
基金supported by the Special Projects of International Thermonuclear Experimental Reactor(2015GB116000)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDA03040000)+1 种基金the Informatizational Special Projects of Chinese Academy of Sciences(No.XXH12504-1-09)the Major/Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology(No.2014FXCX004)
文摘Direct Monte Carlo(MC) simulation is a powerful probabilistic safety assessment method for accounting dynamics of the system.But it is not efficient at simulating rare events.A biasing transition rate method based on direct MC simulation is proposed to solve the problem in this paper.This method biases transition rates of the components by adding virtual components to them in series to increase the occurrence probability of the rare event,hence the decrease in the variance of MC estimator.Several cases are used to benchmark this method.The results show that the method is effective at modeling system failure and is more efficient at collecting evidence of rare events than the direct MC simulation.The performance is greatly improved by the biasing transition rate method.
文摘The new improved directional vector simulation method foranalyzing the reliability of struc- tural systems failure probabilityis researched. This paper also points out the defects of generaldirectional vector simulation, and gives rise to a new higheraccuracy approximate integral formula of structural systems failureprobability. A new geometric meaning of characteristic function isobtained. A new simple method of generating uniformly distributedrandom vector sample sin n-dimensional unit hyper-spherical surfaceis put forward and strictly proved. This method is easy to put intopractice. Numerical examples are given to show the applicability andeffectiveness of the suggested approach to structural systemsreliability problems.
文摘Direct Simulation Monte Carlo(DSMC)solves the Boltzmann equation with large Knudsen number.The Boltzmann equation generally consists of three terms:the force term,the diffusion term and the collision term.While the first two terms of the Boltzmann equation can be discretized by numerical methods such as the finite volume method,the third term can be approximated by DSMC,and DSMC simulates the physical behaviors of gas molecules.However,because of the low sampling efficiency of Monte Carlo Simulation in DSMC,this part usually occupies large portion of computational costs to solve the Boltzmann equation.In this paper,by Markov Chain Monte Carlo(MCMC)and multicore programming,we develop Direct Simulation Multi-Chain Markov Chain Monte Carlo(DSMC3):a fast solver to calculate the numerical solution for the Boltzmann equation.Computational results show that DSMC3 is significantly faster than the conventional method DSMC.
文摘使用圆柱坐标系网格的三维DSMC(Direct Simulation Monte Carlo)模型,对同轴圆柱间Taylor-Couette流中Taylor涡的形成进行了数值模拟,并分析了不同计算域和边界条件下稳定流场中Taylor涡的轴向排列结构.在网格设置和流场参数不变的情况下,使用轴对称DSMC模型对Taylor涡进行数值模拟,所得Taylor涡的稳定过程与三维结果一致,验证了使用三维DSMC方法来解决微尺度低速的稀薄气流问题的可行性.三维模拟结果表明Taylor涡以较大的圆周速度绕轴旋转,二维模拟则无法体现.对不同的内圆柱旋转速度进行数值模拟,确定了能够产生Taylor涡的临界速度值.
文摘采用考虑颗粒脉动流动对气相湍流流动影响的大涡模拟(LES)研究气相湍流,采用直接模拟蒙特卡罗方法(DSMC)模拟颗粒间的碰撞。单颗粒运动满足牛顿第二定律,颗粒相和气相相间作用的双向耦合由牛顿第三定律确定,考虑超细颗粒间的van der Waals作用力。数值模拟垂直管内超细颗粒气固两相流动,对颗粒相速度、浓度以及团聚物流动过程进行分析。
文摘NS-DSMC(Navier Stokes-Direct Simulation Monte Carlo)耦合方法是计算连续-稀薄跨流域流动的主要方法,应用过程中如何确定连续流域和稀薄流域的界面是此方法的关键问题之一,界面位置通常通过连续失效参数来判定.为合理选择连续失效参数,对目前广泛使用的两种连续失效参数KnQ和B参数进行了理论上的分析和比较,表明虽然他们建立的出发点不同,但在数学形式上具有一定相似性.通过圆柱绕流问题的数值试验进一步验证了两种连续失效参数具有一定对应关系.KnQ和B两种连续失效参数在NS-DSMC耦合方法中应用效果相差不大,但KnQ的阈值0.05适用范围较广,而B参数的阈值对不同流动问题会有变化.
