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
In gas-solid flows, particle-particle interaction （typical, particle collision） is highly significant, despite the small particles fractional volume. Widely distributed polydisperse particle population is a typical ...In gas-solid flows, particle-particle interaction （typical, particle collision） is highly significant, despite the small particles fractional volume. Widely distributed polydisperse particle population is a typical characteristic during dynamic evolution of particles （e.g., agglomeration and fragmentation） in spite of their initial monodisperse particle distribution. The conventional direct simulation Monte Carlo （DSMC） method for particle collision tracks equally weighted simulation particles, which results in high statistical noise for particle fields if there are insufficient simulation particles in less-populated regions. In this study, a new differentially weighted DSMC （DW-DSMC） method for collisions of particles with different number weight is proposed within the framework of the general Eulerian-Lagrangian models for hydrodynamics. Three schemes （mass, momentum and energy conservation） were developed to restore the numbers of simulation particle while keeping total mass, momentum or energy of the whole system unchanged respectively. A limiting case of high-inertia particle flow was numerically simulated to validate the DW-DSMC method in terms of computational precision and efficiency. The momentum conservation scheme which leads to little fluctuation around the mass and energy of the whole system performed best. Improved resolution in particle fields and dynamic behavior could be attained simultaneously using DW-DSMC, compared with the equally weighted DSMC. Meanwhile, computational cost can be largely reduced in contrast with direct numerical simulation.展开更多
As a common and extensive datum to analyze wind,wind rose is one of the most important components of the meteorological elements.In this study,a model is proposed to establish the joint probability distribution of win...As a common and extensive datum to analyze wind,wind rose is one of the most important components of the meteorological elements.In this study,a model is proposed to establish the joint probability distribution of wind speed and direction using grouped data of wind rose.On the basis of the model,an algorithm is presented to generate pseudorandom numbers of wind speed and paired direction data.Afterward,the proposed model and algorithm are applied to two weather stations located in the Liaodong Gulf.With the models built for the two cases,a novel graph representing the continuous joint probability distribution of wind speed and direction is plotted,showing a strong correlation to the corresponding wind rose.Moreover,the joint probability distributions are utilized to evaluate wind energy potential successfully.In cooperation with Monte Carlo simulation,the model can approximately predict annual directional extreme wind speed under different return periods under the condition that the wind rose can represent the meteorological characters of the wind field well.The model is beneficial to design and install wind turbines.展开更多
In this study, a novel model of photothermal conversion in a direct absorption solar collector based on the Monte Carlo and finite volume methods was built and validated and the temperatures of the novel and tradition...In this study, a novel model of photothermal conversion in a direct absorption solar collector based on the Monte Carlo and finite volume methods was built and validated and the temperatures of the novel and traditional solar collectors were compared. The sensitivity of the parameters to the radiative heat loss was investigated. Finally, the radiative heat transfer characteristics were discussed using the radiative exchange factor. The results of this study validated the advantages of the novel solar collector at both the surface and fluid temperatures. Under the conditions used in this study, the maximum temperature difference of the novel solar collector was 30 K, compared with 193 K for the traditional solar collector. Furthermore, the collector was divided into several units along the flow direction. The radiative exchange factor indicated that with an increase in the attenuation coefficient, the percentage of radiation intensity in the total solar radiation absorbed by the corresponding unit increased.Simultaneously, it decreased with an increase in the incident angle and scattering albedo. These results provide a reference for addressing the low efficiency and thermal damage caused by traditional solar collectors at high temperatures.展开更多
A new criterion is presented to detect global convergence to steady state,and to identify local transient characteristics,during rarefied gas flow simulations performed using the direct simulation Monte Carlo(DSMC)met...A new criterion is presented to detect global convergence to steady state,and to identify local transient characteristics,during rarefied gas flow simulations performed using the direct simulation Monte Carlo(DSMC)method.Unlike deterministic computational fluid dynamics(CFD)schemes,DSMC is generally subject to large statistical scatter in instantaneous flow property evaluations,which prevents the use of residual tracking procedures as are often employed in CFD simulations.However,reliable prediction of the time to reach steady state is necessary for initialization of DSMC sampling operations.Techniques currently used in DSMC to identify steady state convergence are usually insensitive to weak transient behavior in small regions of relatively low density or recirculating flow.The proposed convergence criterion is developed with the goal of properly identifying such weak transient behavior,while adding negligible computational expense and allowing simple implementation in any existing DSMC code.Benefits of the proposed technique over existing convergence detection methods are demonstrated for representative nozzle/plume expansion flow,hypersonic blunt body flow and driven cavity flow 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
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.
基金supported by the National Natural Science Foundation of China(51276077 and 51390494)the National Key Basic Research and Development Program(2010CB227004)
文摘In gas-solid flows, particle-particle interaction （typical, particle collision） is highly significant, despite the small particles fractional volume. Widely distributed polydisperse particle population is a typical characteristic during dynamic evolution of particles （e.g., agglomeration and fragmentation） in spite of their initial monodisperse particle distribution. The conventional direct simulation Monte Carlo （DSMC） method for particle collision tracks equally weighted simulation particles, which results in high statistical noise for particle fields if there are insufficient simulation particles in less-populated regions. In this study, a new differentially weighted DSMC （DW-DSMC） method for collisions of particles with different number weight is proposed within the framework of the general Eulerian-Lagrangian models for hydrodynamics. Three schemes （mass, momentum and energy conservation） were developed to restore the numbers of simulation particle while keeping total mass, momentum or energy of the whole system unchanged respectively. A limiting case of high-inertia particle flow was numerically simulated to validate the DW-DSMC method in terms of computational precision and efficiency. The momentum conservation scheme which leads to little fluctuation around the mass and energy of the whole system performed best. Improved resolution in particle fields and dynamic behavior could be attained simultaneously using DW-DSMC, compared with the equally weighted DSMC. Meanwhile, computational cost can be largely reduced in contrast with direct numerical simulation.
基金The study was supported by the National Key Research and Development Program of China(No.2016YFC0303401)the National Natural Science Foundation of China(No.51779236)the National Natural Science Foundation of China-Shandong Joint Fund(No.U1706226).
文摘As a common and extensive datum to analyze wind,wind rose is one of the most important components of the meteorological elements.In this study,a model is proposed to establish the joint probability distribution of wind speed and direction using grouped data of wind rose.On the basis of the model,an algorithm is presented to generate pseudorandom numbers of wind speed and paired direction data.Afterward,the proposed model and algorithm are applied to two weather stations located in the Liaodong Gulf.With the models built for the two cases,a novel graph representing the continuous joint probability distribution of wind speed and direction is plotted,showing a strong correlation to the corresponding wind rose.Moreover,the joint probability distributions are utilized to evaluate wind energy potential successfully.In cooperation with Monte Carlo simulation,the model can approximately predict annual directional extreme wind speed under different return periods under the condition that the wind rose can represent the meteorological characters of the wind field well.The model is beneficial to design and install wind turbines.
基金supported by the National Natural Science Foundation of China (Grant No. 52041601)Hebei Natural Science Foundation (Grant No. E202203156)+1 种基金Chinese Scholarship Council (Grant No. 202106120167)partly funded the research activities—Enabling cooperation of the Harbin Institute of Technology with the Technical University of Denmark。
文摘In this study, a novel model of photothermal conversion in a direct absorption solar collector based on the Monte Carlo and finite volume methods was built and validated and the temperatures of the novel and traditional solar collectors were compared. The sensitivity of the parameters to the radiative heat loss was investigated. Finally, the radiative heat transfer characteristics were discussed using the radiative exchange factor. The results of this study validated the advantages of the novel solar collector at both the surface and fluid temperatures. Under the conditions used in this study, the maximum temperature difference of the novel solar collector was 30 K, compared with 193 K for the traditional solar collector. Furthermore, the collector was divided into several units along the flow direction. The radiative exchange factor indicated that with an increase in the attenuation coefficient, the percentage of radiation intensity in the total solar radiation absorbed by the corresponding unit increased.Simultaneously, it decreased with an increase in the incident angle and scattering albedo. These results provide a reference for addressing the low efficiency and thermal damage caused by traditional solar collectors at high temperatures.
基金NASA for financial support of this work,through grant NNX08AD02A.
文摘A new criterion is presented to detect global convergence to steady state,and to identify local transient characteristics,during rarefied gas flow simulations performed using the direct simulation Monte Carlo(DSMC)method.Unlike deterministic computational fluid dynamics(CFD)schemes,DSMC is generally subject to large statistical scatter in instantaneous flow property evaluations,which prevents the use of residual tracking procedures as are often employed in CFD simulations.However,reliable prediction of the time to reach steady state is necessary for initialization of DSMC sampling operations.Techniques currently used in DSMC to identify steady state convergence are usually insensitive to weak transient behavior in small regions of relatively low density or recirculating flow.The proposed convergence criterion is developed with the goal of properly identifying such weak transient behavior,while adding negligible computational expense and allowing simple implementation in any existing DSMC code.Benefits of the proposed technique over existing convergence detection methods are demonstrated for representative nozzle/plume expansion flow,hypersonic blunt body flow and driven cavity flow 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.
