Many recent laboratory experiments and numerical simulations support a non-equilibrium dissipation scaling in decaying turbulence before it reaches an equilibrium state.By analyzing a direct numerical simulation(DNS)d...Many recent laboratory experiments and numerical simulations support a non-equilibrium dissipation scaling in decaying turbulence before it reaches an equilibrium state.By analyzing a direct numerical simulation(DNS)database of a transitional boundary-layer flow,we show that the transition region and the non-equilibrium turbulence region,which are located in different streamwise zones,present different non-equilibrium scalings.Moreover,in the wall-normal direction,the viscous sublayer,log layer,and outer layer show different non-equilibrium phenomena which differ from those in grid-generated turbulence and transitional channel flows.These findings are expected to shed light on the modelling of various types of non-equilibrium turbulent flows.展开更多
Over the past half century,a variety of computational fluid dynamics(CFD)methods and the direct simulation Monte Carlo(DSMC)method have been widely and successfully applied to the simulation of gas flows for the conti...Over the past half century,a variety of computational fluid dynamics(CFD)methods and the direct simulation Monte Carlo(DSMC)method have been widely and successfully applied to the simulation of gas flows for the continuum and rarefied regime,respectively.However,they both encounter difficulties when dealing with multiscale gas flows in modern engineering problems,where the whole system is on the macroscopic scale but the nonequilibrium effects play an important role.In this paper,we review two particle-based strategies developed for the simulation of multiscale nonequilibrium gas flows,i.e.,DSMC-CFD hybrid methods and multiscale particle methods.The principles,advantages,disadvantages,and applications for each method are described.The latest progress in the modelling of multiscale gas flows including the unified multiscale particle method proposed by the authors is presented.展开更多
Heterostructure is an effective approach in modulating the physical and chemical behavior of materials. Here, the first-principles calculations were carried out to explore the structural, electronic, and carrier mobil...Heterostructure is an effective approach in modulating the physical and chemical behavior of materials. Here, the first-principles calculations were carried out to explore the structural, electronic, and carrier mobility properties of Janus MoSSe/GaN heterostructures. This heterostructure exhibits a superior high carrier mobility of 281.28 cm^(2)·V^(−1)·s^(−1) for electron carrier and 3951.2 cm^(2)·V^(−1)·s^(−1) for hole carrier. Particularly, the magnitude of the carrier mobility can be further tuned by Janus structure and stacking modes of the heterostructure. It is revealed that the equivalent mass and elastic moduli strongly affect the carrier mobility of the heterostructure, while the deformation potential contributes to the different carrier mobility for electron and hole of the heterostructure. These results suggest that the Janus MoSSe/GaN heterostructures have many potential applications for the unique carrier mobility.展开更多
Many macroscopic equations are proposed to describe the rarefied gas dynamics beyond the Navier-Stokes level,either from the mesoscopic Boltzmann equation or some physical arguments,including(i)Burnett,Woods,super-Bur...Many macroscopic equations are proposed to describe the rarefied gas dynamics beyond the Navier-Stokes level,either from the mesoscopic Boltzmann equation or some physical arguments,including(i)Burnett,Woods,super-Burnett,augmented Burnett equations derived from the Chapman-Enskog expansion of the Boltzmann equation,(ii)Grad 13,regularized 13/26 moment equations,rational extended thermodynamics equations,and generalized hydrodynamic equations,where the velocity distribution function is expressed in terms of low-order moments and Hermite polynomials,and(iii)bi-velocity equations and“thermo-mechanically consistent"Burnett equations based on the argument of“volume diffusion”.This paper is dedicated to assess the accuracy of these macroscopic equations.We first consider the RayleighBrillouin scattering,where light is scattered by the density fluctuation in gas.In this specific problem macroscopic equations can be linearized and solutions can always be obtained,no matter whether they are stable or not.Moreover,the accuracy assessment is not contaminated by the gas-wall boundary condition in this periodic problem.Rayleigh-Brillouin spectra of the scattered light are calculated by solving the linearized macroscopic equations and compared to those from the linearized Boltzmann equation.We find that(i)the accuracy of Chapman-Enskog expansion does not always increase with the order of expansion,(ii)for the moment method,the more moments are included,the more accurate the results are,and(iii)macroscopic equations based on“volume diffusion"do not work well even when the Knudsen number is very small.Therefore,among about a dozen tested equations,the regularized 26 moment equations are the most accurate.However,for moderate and highly rarefied gas flows,huge number of moments should be included,as the convergence to true solutions is rather slow.The same conclusion is drawn from the problem of sound propagation between the transducer and receiver.This slow convergence of moment equations is due to the incapability of Hermite polynomials in the capturing of large discontinuities and rapid variations of the velocity distribution function.This study sheds some light on how to choose/develop macroscopic equations for rarefied gas dynamics.展开更多
The unique and unanticipated properties of multiple principal component alloys have reinvigorated the field of alloy design and drawn strong interest across scientific disciplines.The vast compositional parameter spac...The unique and unanticipated properties of multiple principal component alloys have reinvigorated the field of alloy design and drawn strong interest across scientific disciplines.The vast compositional parameter space makes these alloys a unique area of exploration by means of computational design.However,as of now a method to compute efficiently,yet with high accuracy the thermodynamic properties of such alloys has been missing.One of the underlying reasons is the lack of accurate and efficient approaches to compute vibrational free energies—including anharmonicity—for these chemically complex multicomponent alloys.In this work,a density-functional-theory based approach to overcome this issue is developed based on a combination of thermodynamic integration and a machine-learning potential.We demonstrate the performance of the approach by computing the anharmonic free energy of the prototypical five-component VNbMoTaW refractory high entropy alloy.展开更多
The UK Catalysis Hub(UKCH)is designing a virtual research environment to support data processing and analysis,the Catalysis Research Workbench(CRW).The development of this platform requires identifying the processing ...The UK Catalysis Hub(UKCH)is designing a virtual research environment to support data processing and analysis,the Catalysis Research Workbench(CRW).The development of this platform requires identifying the processing and analysis needs of the UKCH members and mapping them to potential solutions.This paper presents a proposal for a demonstrator to analyse the use of scientific workflows for large scale data processing.The demonstrator provides a concrete target to promote further discussion of the processing and analysis needs of the UKCH community.In this paper,we will discuss the main requirements for data processing elicited and the proposed adaptations that will be incorporated in the design of the CRW and how to integrate the proposed solutions with existing practices of the UKCH.The demonstrator has been used in discussion with researchers and in presentations to the UKCH community,generating increased interest and motivating furtherdevelopment.展开更多
Chemically complex multicomponent alloys possess exceptional properties derived from an inexhaustible compositional space.The complexity however makes interatomic potential development challenging.We explore two compl...Chemically complex multicomponent alloys possess exceptional properties derived from an inexhaustible compositional space.The complexity however makes interatomic potential development challenging.We explore two complementary machine-learned potentials—the moment tensor potential(MTP)and the Gaussian moment neural network(GM-NN)—in simultaneously describing configurational and vibrational degrees of freedom in the Ta-V-Cr-W alloy family.Both models are equally accurate with excellent performance evaluated against density-functional-theory.They achieve root-mean-square-errors(RMSEs)in energies of less than a few meV/atom across 0 K ordered and high-temperature disordered configurations included in the training.Even for compositions not in training,relative energy RMSEs at high temperatures are within a few meV/atom.High-temperature molecular dynamics forces have similarly small RMSEs of about 0.15 eV/Åfor the disordered quaternary included in,and ternaries not part of training.MTPs achieve faster convergence with training size;GM-NNs are faster in execution.Active learning is partially beneficial and should be complemented with conventional human-based training set generation.展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.12002318,11572025,11772032,and 51420105008)the Science Foundation of North University of China(No.XJJ201929)。
文摘Many recent laboratory experiments and numerical simulations support a non-equilibrium dissipation scaling in decaying turbulence before it reaches an equilibrium state.By analyzing a direct numerical simulation(DNS)database of a transitional boundary-layer flow,we show that the transition region and the non-equilibrium turbulence region,which are located in different streamwise zones,present different non-equilibrium scalings.Moreover,in the wall-normal direction,the viscous sublayer,log layer,and outer layer show different non-equilibrium phenomena which differ from those in grid-generated turbulence and transitional channel flows.These findings are expected to shed light on the modelling of various types of non-equilibrium turbulent flows.
基金National Numerical Windtunnel Project(Grant 2018-ZT3A05)National Natural Science Foundation of China(Grant No.11772034)Engineering and Physical Sciences Research Council(EPSRC,Grant No.EP/N016602/1).
文摘Over the past half century,a variety of computational fluid dynamics(CFD)methods and the direct simulation Monte Carlo(DSMC)method have been widely and successfully applied to the simulation of gas flows for the continuum and rarefied regime,respectively.However,they both encounter difficulties when dealing with multiscale gas flows in modern engineering problems,where the whole system is on the macroscopic scale but the nonequilibrium effects play an important role.In this paper,we review two particle-based strategies developed for the simulation of multiscale nonequilibrium gas flows,i.e.,DSMC-CFD hybrid methods and multiscale particle methods.The principles,advantages,disadvantages,and applications for each method are described.The latest progress in the modelling of multiscale gas flows including the unified multiscale particle method proposed by the authors is presented.
基金the Science Challenge Project(Grant No.TZ2018004)the National Natural Science Foundation of China(Grant Nos.51572016,U1530401,11747167,11804090,51472209,11774298,U1401241,and 21503012)+2 种基金the Natural Science Foundation of Hunan Province,China(Grant Nos.17C0626 and 2019JJ50148)a Tianhe-2JK computing time award at the Beijing Computational Science Research Center(CSRC)L.M.L.and G.T.acknowledge also support by the Royal Society Newton Advanced Fellowship scheme(Grant No.NAF\R1\0242).
文摘Heterostructure is an effective approach in modulating the physical and chemical behavior of materials. Here, the first-principles calculations were carried out to explore the structural, electronic, and carrier mobility properties of Janus MoSSe/GaN heterostructures. This heterostructure exhibits a superior high carrier mobility of 281.28 cm^(2)·V^(−1)·s^(−1) for electron carrier and 3951.2 cm^(2)·V^(−1)·s^(−1) for hole carrier. Particularly, the magnitude of the carrier mobility can be further tuned by Janus structure and stacking modes of the heterostructure. It is revealed that the equivalent mass and elastic moduli strongly affect the carrier mobility of the heterostructure, while the deformation potential contributes to the different carrier mobility for electron and hole of the heterostructure. These results suggest that the Janus MoSSe/GaN heterostructures have many potential applications for the unique carrier mobility.
文摘Many macroscopic equations are proposed to describe the rarefied gas dynamics beyond the Navier-Stokes level,either from the mesoscopic Boltzmann equation or some physical arguments,including(i)Burnett,Woods,super-Burnett,augmented Burnett equations derived from the Chapman-Enskog expansion of the Boltzmann equation,(ii)Grad 13,regularized 13/26 moment equations,rational extended thermodynamics equations,and generalized hydrodynamic equations,where the velocity distribution function is expressed in terms of low-order moments and Hermite polynomials,and(iii)bi-velocity equations and“thermo-mechanically consistent"Burnett equations based on the argument of“volume diffusion”.This paper is dedicated to assess the accuracy of these macroscopic equations.We first consider the RayleighBrillouin scattering,where light is scattered by the density fluctuation in gas.In this specific problem macroscopic equations can be linearized and solutions can always be obtained,no matter whether they are stable or not.Moreover,the accuracy assessment is not contaminated by the gas-wall boundary condition in this periodic problem.Rayleigh-Brillouin spectra of the scattered light are calculated by solving the linearized macroscopic equations and compared to those from the linearized Boltzmann equation.We find that(i)the accuracy of Chapman-Enskog expansion does not always increase with the order of expansion,(ii)for the moment method,the more moments are included,the more accurate the results are,and(iii)macroscopic equations based on“volume diffusion"do not work well even when the Knudsen number is very small.Therefore,among about a dozen tested equations,the regularized 26 moment equations are the most accurate.However,for moderate and highly rarefied gas flows,huge number of moments should be included,as the convergence to true solutions is rather slow.The same conclusion is drawn from the problem of sound propagation between the transducer and receiver.This slow convergence of moment equations is due to the incapability of Hermite polynomials in the capturing of large discontinuities and rapid variations of the velocity distribution function.This study sheds some light on how to choose/develop macroscopic equations for rarefied gas dynamics.
基金We thank Jan Janssen and Konstantin Gubaev for fruitful discussions.Funding by the Deutsche Forschungsgemeinschaft(SPP 2006)the European Research Council(ERC)under the EU’s Horizon 2020 Research and Innovation Programme(Grant no.639211)is gratefully acknowledged+1 种基金F.K.acknowledges NWO/STW(VIDI grant 15707)A.S.was supported by the Russian Science Foundation(Grant no.18-13-00479)。
文摘The unique and unanticipated properties of multiple principal component alloys have reinvigorated the field of alloy design and drawn strong interest across scientific disciplines.The vast compositional parameter space makes these alloys a unique area of exploration by means of computational design.However,as of now a method to compute efficiently,yet with high accuracy the thermodynamic properties of such alloys has been missing.One of the underlying reasons is the lack of accurate and efficient approaches to compute vibrational free energies—including anharmonicity—for these chemically complex multicomponent alloys.In this work,a density-functional-theory based approach to overcome this issue is developed based on a combination of thermodynamic integration and a machine-learning potential.We demonstrate the performance of the approach by computing the anharmonic free energy of the prototypical five-component VNbMoTaW refractory high entropy alloy.
基金funded by EPSRC grant:EP/R026939/1,EP/R026815/1,EP/R026645/1,EP/R027129/1 or EP/M013219/1(biocatalysis)part-funded by the European Regional Development Fund(ERDF)via Welsh Government.
文摘The UK Catalysis Hub(UKCH)is designing a virtual research environment to support data processing and analysis,the Catalysis Research Workbench(CRW).The development of this platform requires identifying the processing and analysis needs of the UKCH members and mapping them to potential solutions.This paper presents a proposal for a demonstrator to analyse the use of scientific workflows for large scale data processing.The demonstrator provides a concrete target to promote further discussion of the processing and analysis needs of the UKCH community.In this paper,we will discuss the main requirements for data processing elicited and the proposed adaptations that will be incorporated in the design of the CRW and how to integrate the proposed solutions with existing practices of the UKCH.The demonstrator has been used in discussion with researchers and in presentations to the UKCH community,generating increased interest and motivating furtherdevelopment.
基金This project has received funding from the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation programme(grant agreement No.865855)The authors acknowledge support by the state of Baden-Württemberg through bwHPC and the German Research Foundation(DFG)through grant No.INST 40/575-1 FUGG(JUSTUS 2 cluster)+5 种基金We thank the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)for supporting this work by funding-EXC2075-390740016 under Germany’s Excellence StrategyWe acknowledge the support by the Stuttgart Center for Simulation Science(SimTech)K.G.and B.G.acknowledge support from the collaborative DFG-RFBR Grant(Grants No.DFG KO 5080/3-1,DFG GR 3716/6-1)K.G.also acknowledges the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-Project-ID 358283783-SFB 1333/22022V.Z.acknowledges financial support received in the form of a PhD scholarship from the Studienstiftung des Deutschen Volkes(German National Academic Foundation)P.S.would like to thank the Alexander von Humboldt Foundation for their support through the Alexander von Humboldt Postdoctoral Fellowship Program.A.D.acknowledges support through EPSRC grant EP/S032835/1.
文摘Chemically complex multicomponent alloys possess exceptional properties derived from an inexhaustible compositional space.The complexity however makes interatomic potential development challenging.We explore two complementary machine-learned potentials—the moment tensor potential(MTP)and the Gaussian moment neural network(GM-NN)—in simultaneously describing configurational and vibrational degrees of freedom in the Ta-V-Cr-W alloy family.Both models are equally accurate with excellent performance evaluated against density-functional-theory.They achieve root-mean-square-errors(RMSEs)in energies of less than a few meV/atom across 0 K ordered and high-temperature disordered configurations included in the training.Even for compositions not in training,relative energy RMSEs at high temperatures are within a few meV/atom.High-temperature molecular dynamics forces have similarly small RMSEs of about 0.15 eV/Åfor the disordered quaternary included in,and ternaries not part of training.MTPs achieve faster convergence with training size;GM-NNs are faster in execution.Active learning is partially beneficial and should be complemented with conventional human-based training set generation.
