Shock wave caused by a sudden release of high-energy,such as explosion and blast,usually affects a significant range of areas.The utilization of a uniform fine mesh to capture sharp shock wave and to obtain precise re...Shock wave caused by a sudden release of high-energy,such as explosion and blast,usually affects a significant range of areas.The utilization of a uniform fine mesh to capture sharp shock wave and to obtain precise results is inefficient in terms of computational resource.This is particularly evident when large-scale fluid field simulations are conducted with significant differences in computational domain size.In this work,a variable-domain-size adaptive mesh enlargement(vAME)method is developed based on the proposed adaptive mesh enlargement(AME)method for modeling multi-explosives explosion problems.The vAME method reduces the division of numerous empty areas or unnecessary computational domains by adaptively suspending enlargement operation in one or two directions,rather than in all directions as in AME method.A series of numerical tests via AME and vAME with varying nonintegral enlargement ratios and different mesh numbers are simulated to verify the efficiency and order of accuracy.An estimate of speedup ratio is analyzed for further efficiency comparison.Several large-scale near-ground explosion experiments with single/multiple explosives are performed to analyze the shock wave superposition formed by the incident wave,reflected wave,and Mach wave.Additionally,the vAME method is employed to validate the accuracy,as well as to investigate the performance of the fluid field and shock wave propagation,considering explosive quantities ranging from 1 to 5 while maintaining a constant total mass.The results show a satisfactory correlation between the overpressure versus time curves for experiments and numerical simulations.The vAME method yields a competitive efficiency,increasing the computational speed to 3.0 and approximately 120,000 times in comparison to AME and the fully fine mesh method,respectively.It indicates that the vAME method reduces the computational cost with minimal impact on the results for such large-scale high-energy release problems with significant differences in computational domain size.展开更多
The mechanical properties of Mg–Al–Ca alloys are significantly affected by their Laves phases,including the Al_(2)Ca phase.Laves phases are generally considered to be brittle and have a detrimental effect on the duc...The mechanical properties of Mg–Al–Ca alloys are significantly affected by their Laves phases,including the Al_(2)Ca phase.Laves phases are generally considered to be brittle and have a detrimental effect on the ductility of Mg.Recently,the Al_(2)Ca phase was shown to undergo plastic deformation in a dilute Mg-Al-Ca alloy to increase the ductility and work hardening of the alloy.In the present study,we investigated the extent to which the deformation of Al_(2)Ca is driven by dislocations in the Mg matrix by simulating the interactions between the basal edge dislocations and Al_(2)Ca particles.In particular,the effects of the interparticle spacing,particle orientation,and particle size were considered.Shearing of small particles and dislocation cross-slips near large particles were observed.Both events contribute to strengthening,and accommodate to plasticity.The shear resistance of the dislocation to bypass the particles increased as the particle size increased.The critical resolved shear stress(CRSS)for activating dislocations and stacking faults was easier to reach for small Al_(2)Ca particles owing to the higher local shear stress,which is consistent with the experimental observations.Overall,this work elucidates the driving force for Al_(2)Ca particles in Mg–Al–Ca alloys to undergo plastic deformation.展开更多
Porous materials are widely used in the field of protection because of their excellent energy absorption characteristics.In this work,a series of polyurethane microscopic models are established and the effect of poros...Porous materials are widely used in the field of protection because of their excellent energy absorption characteristics.In this work,a series of polyurethane microscopic models are established and the effect of porosity on the shock waves is studied with classical molecular dynamics simulations.Firstly,shock Hugoniot relations for different porosities are obtained,which compare well with the experimental data.The pores collapse and form local stress wave,which results in the complex multi-wave structure of the shock wave.The microstructure analysis shows that the local stress increases and the local velocity decreases gradually during the process of pore collapse to complete compaction.Finally,it leads to stress relaxation and velocity homogenization.The shock stress peaks can be fitted with two exponential functions,and the amplitude of attenuation coefficient decreases with the increase of density.Besides,the pore collapse under shock or non-shock are discussed by the entropy increase rate of the system.The energy is dissipated mainly through the multiple interactions of the waves under shock.The energy is dissipated mainly by the friction between atoms under non-shock.展开更多
MicroMagnetic.jl is an open-source Julia package for micromagnetic and atomistic simulations.Using the features of the Julia programming language,MicroMagnetic.jl supports CPU and various GPU platforms,including NVIDI...MicroMagnetic.jl is an open-source Julia package for micromagnetic and atomistic simulations.Using the features of the Julia programming language,MicroMagnetic.jl supports CPU and various GPU platforms,including NVIDIA,AMD,Intel,and Apple GPUs.Moreover,MicroMagnetic.jl supports Monte Carlo simulations for atomistic models and implements the nudged-elastic-band method for energy barrier computations.With built-in support for double and single precision modes and a design allowing easy extensibility to add new features,MicroMagnetic.jl provides a versatile toolset for researchers in micromagnetics and atomistic simulations.展开更多
The widespread utilisation of tunnel boring machines(TBMs)in underground construction engineering requires a detailed investigation of the cutter-rock interaction.In this paper,we conduct a series of largescale standi...The widespread utilisation of tunnel boring machines(TBMs)in underground construction engineering requires a detailed investigation of the cutter-rock interaction.In this paper,we conduct a series of largescale standing rotary cutting tests on granite in conjunction with high-fidelity numerical simulations based on a particle-type discrete element method(DEM)to explore the effects of key cutting parameters on the TBM cutter performance and the distribution of cutter-rock contact stresses.The assessment results of cutter performance obtained from the cutting tests and numerical simulations reveal similar dependencies on the key cutting parameters.More specifically,the normal and rolling forces exhibit a positive correlation with penetration but are slightly influenced by the cutting radius.In contrast,the side force decreases as the cutting radius increases.Additionally,the side force shows a positive relationship with the penetration for smaller cutting radii but tends to become negative as the cutting radius increases.The cutter's relative effectiveness in rock breaking is significantly impacted by the penetration but shows little dependency on the cutting radius.Consequently,an optimal penetration is identified,leading to a low boreability index and specific energy.A combined Hertz-Weibull function is developed to fit the cutter-rock contact stress distribution obtained in DEM simulations,whereby an improved CSM(Colorado School of Mines)model is proposed by replacing the original monotonic cutting force distribution with this combined Hertz-Weibull model.The proposed model outperforms the original CSM model as demonstrated by a comparison of the estimated cutting forces with those from the tests/simulations.The findings from this work that advance our understanding of TBM cutter performance have important implications for improving the efficiency and reliability of TBM tunnelling in granite.展开更多
Molecular dynamics （MD） simulations of monocrystalline copper （100） surface during nanomachining process were performed based on a new 3D simulation model. The material removal mechanism and system temperature dis...Molecular dynamics （MD） simulations of monocrystalline copper （100） surface during nanomachining process were performed based on a new 3D simulation model. The material removal mechanism and system temperature distribution were discussed. The simulation results indicate that the system temperature distribution presents a roughly concentric shape, a steep temperature gradient is observed in diamond cutting tool, and the highest temperature is located in chip. Centrosymmetry parameter method was used to monitor defect structures. Dislocations and vacancies are the two principal types of defect structures. Residual defect structures impose a major change on the workpiece physical properties and machined surface quality. The defect structures in workpiece are temperature dependent. As the temperature increases, the dislocations are mainly mediated from the workpiece surface, while the others are dissociated into point defects. The relatively high cutting speed used in nanomachining results in less defect structures, beneficial to obtain highly machined surface quality.展开更多
We analyze a large-scale molecular dynamics simulation of work hardening in a model system of a ductile solid. With tensile loading, we observe emission of thousands of dislocations from two sharp cracks. The dislocat...We analyze a large-scale molecular dynamics simulation of work hardening in a model system of a ductile solid. With tensile loading, we observe emission of thousands of dislocations from two sharp cracks. The dislocations interact in a complex way, revealing three fundamental mechanisms of work-hardening in this ductile material. These are (1) dislocation cutting processes, jog formation and generation of trails of point defects; (2) activation of secondary slip systems by Frank-Read and cross-slip mechanisms; and (3) formation of sessile dislocations such as Lomer-Cottrell locks. We report the discovery of a new class of point defects referred to as trail of partial point defects, which could play an important role in situations when partial dislocations dominate plasticity. Another important result of the present work is the rediscovery of the Fleischer-mechanism of cross-slip of partial dislocations that was theoretically proposed more than 50 years ago, and is now, for the first time, confirmed by atomistic simulation. On the typical time scale of molecular dynamics simulations, the dislocations self-organize into a complex sessile defect topology. Our analysis illustrates numerous mechanisms formerly only conjectured in textbooks and observed indirectly in experiments. It is the first time that such a rich set of fundamental phenomena have been revealed in a single computer simulation, and its dynamical evolution has been studied. The present study exemplifies the simulation and analysis of the complex nonlinear dynamics of a many-particle system during failure using ultra-large scale computing.展开更多
Grain boundary(GB)segregation substantially influences the mechanical properties and performance of magnesium(Mg).Atomic-scale modeling,typically using ab-initio or semi-empirical approaches,has mainly focused on GB s...Grain boundary(GB)segregation substantially influences the mechanical properties and performance of magnesium(Mg).Atomic-scale modeling,typically using ab-initio or semi-empirical approaches,has mainly focused on GB segregation at highly symmetric GBs in Mg alloys,often failing to capture the diversity of local atomic environments and segregation energies,resulting in inaccurate structure-property predictions.This study employs atomistic simulations and machine learning models to systematically investigate the segregation behavior of common solute elements in polycrystalline Mg at both 0 K and finite temperatures.The machine learning models accurately predict segregation thermodynamics by incorporating energetic and structural descriptors.We found that segregation energy and vibrational free energy follow skew-normal distributions,with hydrostatic stress,an indicator of excess free volume,emerging as an important factor influencing segregation tendency.The local atomic environment's flexibility,quantified by flexibility volume,is also crucial in predicting GB segregation.Comparing the grain boundary solute concentrations calculated via the Langmuir-Mc Lean isotherm with experimental data,we identified a pronounced segregation tendency for Nd,highlighting its potential for GB engineering in Mg alloys.This work demonstrates the powerful synergy of atomistic simulations and machine learning,paving the way for designing advanced lightweight Mg alloys with tailored properties.展开更多
Improving the accuracy of the evaluation of the performance of wind farms in large wind power bases located in complex terrain under the actual atmosphere is crucial to the sustainable development of wind power.To thi...Improving the accuracy of the evaluation of the performance of wind farms in large wind power bases located in complex terrain under the actual atmosphere is crucial to the sustainable development of wind power.To this end,this study combined the Weather Research and Forecasting(WRF)model with the Wind Farm Parameterization(WFP)method to investigate the wake characteristics and operational performance of large onshore wind farms in the complex terrain of Jiuquan City,Gansu Province,China.The research results showed that after verification,the systematic error of the WRF simulations was less than 3%.The WRF model and the WFP scheme simulated a significant warming phenomenon within the wind power base area,while a cooling effect was observed outside.The analysis of the wake effects indicated that the impact of PhaseⅠconstruction on PhaseⅡconstruction of the wind power base was minimal.During the operation of the entire wind power base,the wind speed within the wind farm decreased by approximately 10%,and the influence range of the predominant wind direction extended over a hundred kilometers downwind.The research conclusions provide a powerful scientific basis for optimizing design and operation,improving efficiency,minimizing the negative impacts on adjacent wind turbines,and ensuring the sustainable development of wind energy through dynamic planning and scientific assessment.展开更多
Deformation twinning, i.e., twin nucleation and twin growth （or twin boundary migration, TBM） activated by impinged basal slip at a symmetrical tilt grain boundary in HCP Mg, was examined with molecular dynamics （M...Deformation twinning, i.e., twin nucleation and twin growth （or twin boundary migration, TBM） activated by impinged basal slip at a symmetrical tilt grain boundary in HCP Mg, was examined with molecular dynamics （MD） simulations. The results show that the {1^-1^-21}-type twinning acts as the most preferential mode of twinning. Once such twins are formed, they are almost ready to grow. The TBM of such twins is led by pure atomic shuffling events. A secondary mode of twinning can also occur in our simulations. The {112^-2} twinning is observed at 10 K as the secondary twin. This secondary mode of twinning shows different energy barriers for nucleation as well as for growth compared with the {1^-1^-21}-type twining. In particular, TBMs in this case is triggered intrinsically by pyramidal slip at its twin boundary.展开更多
Coupled atomistic/dislocation/continuum simulation of interfacial fracture is performed in this paper.The model consists of a nanoscopic core made by atomistic assembly and a surrounding elastic continuum with discret...Coupled atomistic/dislocation/continuum simulation of interfacial fracture is performed in this paper.The model consists of a nanoscopic core made by atomistic assembly and a surrounding elastic continuum with discrete dislocations. Atomistic dislocations nucleate from the crack tip and move to the continuum layer where they glide according to the dislocation dynamics curve.An atoms/continuum overlapping belt is devised to facilitate the transition between the two scales.The continuum constraint on the atomic assembly is imposed through the mechanics at- mosphere along the overlapping belt.Transmissions of mechanics parameters such as displacements,stresses,masses and momenta across the belt are realized.The present model allows us to explore interfacial fracture processes under different mode mixity.The effect of atomistic zigzag interface on the fracture process is revealed:it hinders dislocation emission from the crack tip,especially under high mode mixity.展开更多
The phenomenon of interfacial fracture, as manifested by atom- istic cleavage, debonding and dislocation emission, provides a challenge for combined atomistic-continuum analysis. As a precursor for fully coupled atomi...The phenomenon of interfacial fracture, as manifested by atom- istic cleavage, debonding and dislocation emission, provides a challenge for combined atomistic-continuum analysis. As a precursor for fully coupled atomistic-continuum simulation of interfacial fracture, we focus here on the atomistic behavior within a nanoscopic core surrounding the crack tip. The inter-atomic potential under Em- bedded Atom Method is recapitulated to form an essential framework of atomistic simulation. The calculations are performed for a side-cracked disc configuration un- der a remote K field loading. It is revealed that a critical loading rate defines the brittle-to-ductile transition of homogeneous materials. We further observe that the near tip mode mixity dictates the nanoscopic profile near an interfacial crack tip. A zigzag interface structure is simulated which plays a significant role in the dislocation emission from an interfacial crack tip, as will be explored in the second part of this investigation.展开更多
How to correctly extract Cauchy stress from the atomistic simulations is a crucial issue in studying the mechanical behaviours of atomic systems, but is still in controversy. In this paper, three typical atomistic sim...How to correctly extract Cauchy stress from the atomistic simulations is a crucial issue in studying the mechanical behaviours of atomic systems, but is still in controversy. In this paper, three typical atomistic simulation examples are used to validate various existing stress definitions. It is found that the classical virial stress fails in predicting the stresses in these examples, because the velocity depends on the choice of the local average volume or the reference frame velocity and other factors. In contrast, the Lagrangian cross-section stress and Lagrangian virial stress are validated by these examples, and the instantaneous Lagrangian atomic stress definition is also proposed for dynamical problems.展开更多
A solution scheme is proposed in this paper for an existing RTDHT system to simulate large-scale finite element （FE） numerical substructures. The analysis of the FE numerical substructure is split into response anal...A solution scheme is proposed in this paper for an existing RTDHT system to simulate large-scale finite element （FE） numerical substructures. The analysis of the FE numerical substructure is split into response analysis and signal generation tasks, and executed in two different target computers in real-time. One target computer implements the response analysis task, wherein a large time-step is used to solve the FE substructure, and another target computer implements the signal generation task, wherein an interpolation program is used to generate control signals in a small time-step to meet the input demand of the controller. By using this strategy, the scale of the FE numerical substructure simulation may be increased significantly. The proposed scheme is initially verified by two FE numerical substructure models with 98 and 1240 degrees of freedom （DOFs）. Thereafter, RTDHTs of a single frame-foundation structure are implemented where the foundation, considered as the numerical substructure, is simulated by the FE model with 1240 DOFs. Good agreements between the results of the RTDHT and those from the FE analysis in ABAQUS are obtained.展开更多
The deformation behavior in magnesium single crystal under c-axis tension is investigated in a temperature range between 250 K and 570 K by molecular dynamics simulations. At a low temperature, twinning and shear band...The deformation behavior in magnesium single crystal under c-axis tension is investigated in a temperature range between 250 K and 570 K by molecular dynamics simulations. At a low temperature, twinning and shear bands are found to be the main deformation mechanisms. In particular, the {102} tension twins with the reorientation angle of about 90 °are observed in the simulations. The mechanisms of {102} twinning are illustrated by the simulated motion of atoms. Moreover, grain nucleation and growth are found to be accompanied with the {102} twinning. At temperatures above 450 K, the twin frequency decreases with increasing temperature. The {102} extension twin almost disappears at the temperature of 570 K. The non-basal slip plays an important role on the tensile deformation in magnesium single crystal at high temperatures.展开更多
Free transverse vibration of monolayer graphene, boron nitride (BN), and silicon carbide (SiC) sheets is investigated by using molecular dynamics finite element method. Eigenfrequencies and eigenmodes of these three s...Free transverse vibration of monolayer graphene, boron nitride (BN), and silicon carbide (SiC) sheets is investigated by using molecular dynamics finite element method. Eigenfrequencies and eigenmodes of these three sheets in rectangular shape are studied with different aspect ratios with respect to various boundary conditions. It is found that aspect ratios and boundary conditions affect in a similar way on natural frequencies of graphene, BN, and SiC sheets. Natural frequencies in all modes decrease with an increase of the sheet’s size. Graphene exhibits the highest natural frequencies, and SiC sheet possesses the lowest ones. Missing atoms have minor effects on natural frequencies in this study.展开更多
We investigate the mechanical and microstructural changes of the densified silica glass under uniaxial loading-unloading via atomistic simulations with a modified BKS potential. The stress–strain relationship is foun...We investigate the mechanical and microstructural changes of the densified silica glass under uniaxial loading-unloading via atomistic simulations with a modified BKS potential. The stress–strain relationship is found to include three respective stages: elastic, plastic and hardening regions. The bulk modulus increases with the initial densification and will undergo a rapid increase after complete densification. The yield pressure varies from 5 to 12 GPa for different densified samples. In addition, the Si–O–Si bond angle reduces during elastic deformation under compression, and 5-fold Si will increase linearly in the plastic deformation. In the hardening region, the peak splitting and the new peak are both found on the Si–Si and O–O pair radial distribution functions, where the 6-fold Si is increased. Instead, the lateral displacement of the atoms always varies linearly with strain, without evident periodic characteristic. As is expected, the samples are permanently densified after release from the plastic region, and the maximum density of recovered samples is about 2.64 g/cm^3, which contains 15 % 5-fold Si, and the Si–O–Si bond angle is less than the ordinary silica glass. All these findings are of great significance for understanding the deformation process of densified silica glass.展开更多
With the purpose of making calculation more efficient in practical hydraulic simulations, an improved algorithm was proposed and was applied in the practical water distribution field. This methodology was developed by...With the purpose of making calculation more efficient in practical hydraulic simulations, an improved algorithm was proposed and was applied in the practical water distribution field. This methodology was developed by expanding the traditional loop-equation theory through utilization of the advantages of the graph theory in efficiency. The utilization of the spanning tree technique from graph theory makes the proposed algorithm efficient in calculation and simple to use for computer coding. The algorithms for topological generation and practical implementations are presented in detail in this paper. Through the application to a practical urban system, the consumption of the CPU time and computation memory were decreased while the accuracy was greatly enhanced compared with the present existing methods.展开更多
The embedded atom type potentials and static relaxation method combined with a steepest decent computational technique have been used to simulate the interaction between the grain boundary (GB) and dislocations in Ni_...The embedded atom type potentials and static relaxation method combined with a steepest decent computational technique have been used to simulate the interaction between the grain boundary (GB) and dislocations in Ni_3Al alloys.The focus has been placed on the energy feature of the interaction,the distortion of GB structural units,and the dislocation core structure near the GB.Im- plication has also been made on the results for the understanding of the mechanism responsible for B-enhanced ductility.展开更多
A set of potential parameters for modeling zircon was obtained by atomistic simulation techniques and a reasonable structural model of zircon was established by fitting some important properties of zircon.Based on the...A set of potential parameters for modeling zircon was obtained by atomistic simulation techniques and a reasonable structural model of zircon was established by fitting some important properties of zircon.Based on the equilibrium configuration of zircon, authors calculated the formation energies of basic point defects and intrinsic disorders. The heats of solution of substituting Pu for Zr showed that there was an immiscible gap at the composition of (Pu75%-Zr25%, in mole fraction), which suggests that the amount of Pu substituting for Zr in zircon be≤50%.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12302435 and 12221002)。
文摘Shock wave caused by a sudden release of high-energy,such as explosion and blast,usually affects a significant range of areas.The utilization of a uniform fine mesh to capture sharp shock wave and to obtain precise results is inefficient in terms of computational resource.This is particularly evident when large-scale fluid field simulations are conducted with significant differences in computational domain size.In this work,a variable-domain-size adaptive mesh enlargement(vAME)method is developed based on the proposed adaptive mesh enlargement(AME)method for modeling multi-explosives explosion problems.The vAME method reduces the division of numerous empty areas or unnecessary computational domains by adaptively suspending enlargement operation in one or two directions,rather than in all directions as in AME method.A series of numerical tests via AME and vAME with varying nonintegral enlargement ratios and different mesh numbers are simulated to verify the efficiency and order of accuracy.An estimate of speedup ratio is analyzed for further efficiency comparison.Several large-scale near-ground explosion experiments with single/multiple explosives are performed to analyze the shock wave superposition formed by the incident wave,reflected wave,and Mach wave.Additionally,the vAME method is employed to validate the accuracy,as well as to investigate the performance of the fluid field and shock wave propagation,considering explosive quantities ranging from 1 to 5 while maintaining a constant total mass.The results show a satisfactory correlation between the overpressure versus time curves for experiments and numerical simulations.The vAME method yields a competitive efficiency,increasing the computational speed to 3.0 and approximately 120,000 times in comparison to AME and the fully fine mesh method,respectively.It indicates that the vAME method reduces the computational cost with minimal impact on the results for such large-scale high-energy release problems with significant differences in computational domain size.
基金funded by the National Natural Science Foundation of China(nos.51631006 and 51825101)。
文摘The mechanical properties of Mg–Al–Ca alloys are significantly affected by their Laves phases,including the Al_(2)Ca phase.Laves phases are generally considered to be brittle and have a detrimental effect on the ductility of Mg.Recently,the Al_(2)Ca phase was shown to undergo plastic deformation in a dilute Mg-Al-Ca alloy to increase the ductility and work hardening of the alloy.In the present study,we investigated the extent to which the deformation of Al_(2)Ca is driven by dislocations in the Mg matrix by simulating the interactions between the basal edge dislocations and Al_(2)Ca particles.In particular,the effects of the interparticle spacing,particle orientation,and particle size were considered.Shearing of small particles and dislocation cross-slips near large particles were observed.Both events contribute to strengthening,and accommodate to plasticity.The shear resistance of the dislocation to bypass the particles increased as the particle size increased.The critical resolved shear stress(CRSS)for activating dislocations and stacking faults was easier to reach for small Al_(2)Ca particles owing to the higher local shear stress,which is consistent with the experimental observations.Overall,this work elucidates the driving force for Al_(2)Ca particles in Mg–Al–Ca alloys to undergo plastic deformation.
基金financial support from National Natural Science Foundation of China(Grant No.12172325)。
文摘Porous materials are widely used in the field of protection because of their excellent energy absorption characteristics.In this work,a series of polyurethane microscopic models are established and the effect of porosity on the shock waves is studied with classical molecular dynamics simulations.Firstly,shock Hugoniot relations for different porosities are obtained,which compare well with the experimental data.The pores collapse and form local stress wave,which results in the complex multi-wave structure of the shock wave.The microstructure analysis shows that the local stress increases and the local velocity decreases gradually during the process of pore collapse to complete compaction.Finally,it leads to stress relaxation and velocity homogenization.The shock stress peaks can be fitted with two exponential functions,and the amplitude of attenuation coefficient decreases with the increase of density.Besides,the pore collapse under shock or non-shock are discussed by the entropy increase rate of the system.The energy is dissipated mainly through the multiple interactions of the waves under shock.The energy is dissipated mainly by the friction between atoms under non-shock.
基金supported by the National Key R&D Program of China(Grant No.2022YFA1403603)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB33030100)+2 种基金the National Natural Science Fund for Distinguished Young Scholar(Grant No.52325105)the National Natural Science Foundation of China(Grant Nos.12374098,11974021,and 12241406)the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-084).
文摘MicroMagnetic.jl is an open-source Julia package for micromagnetic and atomistic simulations.Using the features of the Julia programming language,MicroMagnetic.jl supports CPU and various GPU platforms,including NVIDIA,AMD,Intel,and Apple GPUs.Moreover,MicroMagnetic.jl supports Monte Carlo simulations for atomistic models and implements the nudged-elastic-band method for energy barrier computations.With built-in support for double and single precision modes and a design allowing easy extensibility to add new features,MicroMagnetic.jl provides a versatile toolset for researchers in micromagnetics and atomistic simulations.
基金supported by the National Natural Science Foundation of China(Grant Nos.52278407 and 52378407)the China Postdoctoral Science Foundation(Grant No.2023M732670)the support by the Postdoctoral Fellowship Program of China Postdoctoral Science Foundation.
文摘The widespread utilisation of tunnel boring machines(TBMs)in underground construction engineering requires a detailed investigation of the cutter-rock interaction.In this paper,we conduct a series of largescale standing rotary cutting tests on granite in conjunction with high-fidelity numerical simulations based on a particle-type discrete element method(DEM)to explore the effects of key cutting parameters on the TBM cutter performance and the distribution of cutter-rock contact stresses.The assessment results of cutter performance obtained from the cutting tests and numerical simulations reveal similar dependencies on the key cutting parameters.More specifically,the normal and rolling forces exhibit a positive correlation with penetration but are slightly influenced by the cutting radius.In contrast,the side force decreases as the cutting radius increases.Additionally,the side force shows a positive relationship with the penetration for smaller cutting radii but tends to become negative as the cutting radius increases.The cutter's relative effectiveness in rock breaking is significantly impacted by the penetration but shows little dependency on the cutting radius.Consequently,an optimal penetration is identified,leading to a low boreability index and specific energy.A combined Hertz-Weibull function is developed to fit the cutter-rock contact stress distribution obtained in DEM simulations,whereby an improved CSM(Colorado School of Mines)model is proposed by replacing the original monotonic cutting force distribution with this combined Hertz-Weibull model.The proposed model outperforms the original CSM model as demonstrated by a comparison of the estimated cutting forces with those from the tests/simulations.The findings from this work that advance our understanding of TBM cutter performance have important implications for improving the efficiency and reliability of TBM tunnelling in granite.
基金Project (50925521) supported by the National Natural Science Fund for Distinguished Young Scholars of China
文摘Molecular dynamics （MD） simulations of monocrystalline copper （100） surface during nanomachining process were performed based on a new 3D simulation model. The material removal mechanism and system temperature distribution were discussed. The simulation results indicate that the system temperature distribution presents a roughly concentric shape, a steep temperature gradient is observed in diamond cutting tool, and the highest temperature is located in chip. Centrosymmetry parameter method was used to monitor defect structures. Dislocations and vacancies are the two principal types of defect structures. Residual defect structures impose a major change on the workpiece physical properties and machined surface quality. The defect structures in workpiece are temperature dependent. As the temperature increases, the dislocations are mainly mediated from the workpiece surface, while the others are dissociated into point defects. The relatively high cutting speed used in nanomachining results in less defect structures, beneficial to obtain highly machined surface quality.
文摘We analyze a large-scale molecular dynamics simulation of work hardening in a model system of a ductile solid. With tensile loading, we observe emission of thousands of dislocations from two sharp cracks. The dislocations interact in a complex way, revealing three fundamental mechanisms of work-hardening in this ductile material. These are (1) dislocation cutting processes, jog formation and generation of trails of point defects; (2) activation of secondary slip systems by Frank-Read and cross-slip mechanisms; and (3) formation of sessile dislocations such as Lomer-Cottrell locks. We report the discovery of a new class of point defects referred to as trail of partial point defects, which could play an important role in situations when partial dislocations dominate plasticity. Another important result of the present work is the rediscovery of the Fleischer-mechanism of cross-slip of partial dislocations that was theoretically proposed more than 50 years ago, and is now, for the first time, confirmed by atomistic simulation. On the typical time scale of molecular dynamics simulations, the dislocations self-organize into a complex sessile defect topology. Our analysis illustrates numerous mechanisms formerly only conjectured in textbooks and observed indirectly in experiments. It is the first time that such a rich set of fundamental phenomena have been revealed in a single computer simulation, and its dynamical evolution has been studied. The present study exemplifies the simulation and analysis of the complex nonlinear dynamics of a many-particle system during failure using ultra-large scale computing.
基金Z.X.and T.A.S.acknowledge the financial support by the German Research Foundation(DFG)(Grant Nr.505716422)T.A.S.are grateful for the financial support from the DFG(Grant Nr.AL1343/7-1,AL1343/8-1 and Yi 103/3-1)+4 种基金Z.X.,S.K.K.and U.K.acknowledge financial support by the DFG through the projects A05,A07 and C02 of the SFB1394 StructuralChemical Atomic Complexity-From Defect Phase Diagrams to Material Properties,project ID 409476157Additionally,Z.X.and S.K.K.are grateful for funding from the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation program(grant agreement No.852096 FunBlocks)J.G.acknowledges funding from the French National Research Agency(ANR),Grant ANR-21-CE08-0001(ATOUUM)and ANR-22-CE92-0058-01(SILA)The authors gratefully acknowledge the computing time provided to them at the NHR Center NHR4CES at RWTH Aachen University(project number p0020431 and p0020267)。
文摘Grain boundary(GB)segregation substantially influences the mechanical properties and performance of magnesium(Mg).Atomic-scale modeling,typically using ab-initio or semi-empirical approaches,has mainly focused on GB segregation at highly symmetric GBs in Mg alloys,often failing to capture the diversity of local atomic environments and segregation energies,resulting in inaccurate structure-property predictions.This study employs atomistic simulations and machine learning models to systematically investigate the segregation behavior of common solute elements in polycrystalline Mg at both 0 K and finite temperatures.The machine learning models accurately predict segregation thermodynamics by incorporating energetic and structural descriptors.We found that segregation energy and vibrational free energy follow skew-normal distributions,with hydrostatic stress,an indicator of excess free volume,emerging as an important factor influencing segregation tendency.The local atomic environment's flexibility,quantified by flexibility volume,is also crucial in predicting GB segregation.Comparing the grain boundary solute concentrations calculated via the Langmuir-Mc Lean isotherm with experimental data,we identified a pronounced segregation tendency for Nd,highlighting its potential for GB engineering in Mg alloys.This work demonstrates the powerful synergy of atomistic simulations and machine learning,paving the way for designing advanced lightweight Mg alloys with tailored properties.
基金funded by“The Factors Affecting the Accuracy of Wind Resource Assessment and Comprehensive Post-Evaluation Techniques for Operating Wind Power Projects,”grant number YJ24.002“The Research and Application of Future Medium to Long Term Wind Resource Assessment for Wind Farms Based on Artificial Intelligence Project,”grant number 2023021。
文摘Improving the accuracy of the evaluation of the performance of wind farms in large wind power bases located in complex terrain under the actual atmosphere is crucial to the sustainable development of wind power.To this end,this study combined the Weather Research and Forecasting(WRF)model with the Wind Farm Parameterization(WFP)method to investigate the wake characteristics and operational performance of large onshore wind farms in the complex terrain of Jiuquan City,Gansu Province,China.The research results showed that after verification,the systematic error of the WRF simulations was less than 3%.The WRF model and the WFP scheme simulated a significant warming phenomenon within the wind power base area,while a cooling effect was observed outside.The analysis of the wake effects indicated that the impact of PhaseⅠconstruction on PhaseⅡconstruction of the wind power base was minimal.During the operation of the entire wind power base,the wind speed within the wind farm decreased by approximately 10%,and the influence range of the predominant wind direction extended over a hundred kilometers downwind.The research conclusions provide a powerful scientific basis for optimizing design and operation,improving efficiency,minimizing the negative impacts on adjacent wind turbines,and ensuring the sustainable development of wind energy through dynamic planning and scientific assessment.
基金Project(2012CB932202)supported by the National Basic Research Program of ChinaProjects(50890174,50971088)supported by the National Natural Science Foundation of China
文摘Deformation twinning, i.e., twin nucleation and twin growth （or twin boundary migration, TBM） activated by impinged basal slip at a symmetrical tilt grain boundary in HCP Mg, was examined with molecular dynamics （MD） simulations. The results show that the {1^-1^-21}-type twinning acts as the most preferential mode of twinning. Once such twins are formed, they are almost ready to grow. The TBM of such twins is led by pure atomic shuffling events. A secondary mode of twinning can also occur in our simulations. The {112^-2} twinning is observed at 10 K as the secondary twin. This secondary mode of twinning shows different energy barriers for nucleation as well as for growth compared with the {1^-1^-21}-type twining. In particular, TBMs in this case is triggered intrinsically by pyramidal slip at its twin boundary.
基金The project supported by the National Natural Science Foundation of China
文摘Coupled atomistic/dislocation/continuum simulation of interfacial fracture is performed in this paper.The model consists of a nanoscopic core made by atomistic assembly and a surrounding elastic continuum with discrete dislocations. Atomistic dislocations nucleate from the crack tip and move to the continuum layer where they glide according to the dislocation dynamics curve.An atoms/continuum overlapping belt is devised to facilitate the transition between the two scales.The continuum constraint on the atomic assembly is imposed through the mechanics at- mosphere along the overlapping belt.Transmissions of mechanics parameters such as displacements,stresses,masses and momenta across the belt are realized.The present model allows us to explore interfacial fracture processes under different mode mixity.The effect of atomistic zigzag interface on the fracture process is revealed:it hinders dislocation emission from the crack tip,especially under high mode mixity.
基金The project supported by the National Natural Science Foundation of China
文摘The phenomenon of interfacial fracture, as manifested by atom- istic cleavage, debonding and dislocation emission, provides a challenge for combined atomistic-continuum analysis. As a precursor for fully coupled atomistic-continuum simulation of interfacial fracture, we focus here on the atomistic behavior within a nanoscopic core surrounding the crack tip. The inter-atomic potential under Em- bedded Atom Method is recapitulated to form an essential framework of atomistic simulation. The calculations are performed for a side-cracked disc configuration un- der a remote K field loading. It is revealed that a critical loading rate defines the brittle-to-ductile transition of homogeneous materials. We further observe that the near tip mode mixity dictates the nanoscopic profile near an interfacial crack tip. A zigzag interface structure is simulated which plays a significant role in the dislocation emission from an interfacial crack tip, as will be explored in the second part of this investigation.
基金supported by the National Natural Science Foundation of China (Grant Nos10702034,10732050 and 90816006)the National Basic Research Program of China (973 Program 2007CB936803,2010CB832701)
文摘How to correctly extract Cauchy stress from the atomistic simulations is a crucial issue in studying the mechanical behaviours of atomic systems, but is still in controversy. In this paper, three typical atomistic simulation examples are used to validate various existing stress definitions. It is found that the classical virial stress fails in predicting the stresses in these examples, because the velocity depends on the choice of the local average volume or the reference frame velocity and other factors. In contrast, the Lagrangian cross-section stress and Lagrangian virial stress are validated by these examples, and the instantaneous Lagrangian atomic stress definition is also proposed for dynamical problems.
基金National Natural Science Foundation under Grant Nos.51179093,91215301 and 41274106the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No.20130002110032Tsinghua University Initiative Scientific Research Program under Grant No.20131089285
文摘A solution scheme is proposed in this paper for an existing RTDHT system to simulate large-scale finite element （FE） numerical substructures. The analysis of the FE numerical substructure is split into response analysis and signal generation tasks, and executed in two different target computers in real-time. One target computer implements the response analysis task, wherein a large time-step is used to solve the FE substructure, and another target computer implements the signal generation task, wherein an interpolation program is used to generate control signals in a small time-step to meet the input demand of the controller. By using this strategy, the scale of the FE numerical substructure simulation may be increased significantly. The proposed scheme is initially verified by two FE numerical substructure models with 98 and 1240 degrees of freedom （DOFs）. Thereafter, RTDHTs of a single frame-foundation structure are implemented where the foundation, considered as the numerical substructure, is simulated by the FE model with 1240 DOFs. Good agreements between the results of the RTDHT and those from the FE analysis in ABAQUS are obtained.
基金supported by National Natural Science Foundation of China (GrantNos.11072026 and 10632020)the Fundamental Research Funds for the Central Universities, and finalized during a sabbatical leave of D.S. at the Graduate Institute of Ferrous Technology (G.I.F.T.) of POSTECHPohang, Korea as part of an International Outgoing Fellowship (Marie Curie Actions) of the 7th Programme of the European Commission
文摘The deformation behavior in magnesium single crystal under c-axis tension is investigated in a temperature range between 250 K and 570 K by molecular dynamics simulations. At a low temperature, twinning and shear bands are found to be the main deformation mechanisms. In particular, the {102} tension twins with the reorientation angle of about 90 °are observed in the simulations. The mechanisms of {102} twinning are illustrated by the simulated motion of atoms. Moreover, grain nucleation and growth are found to be accompanied with the {102} twinning. At temperatures above 450 K, the twin frequency decreases with increasing temperature. The {102} extension twin almost disappears at the temperature of 570 K. The non-basal slip plays an important role on the tensile deformation in magnesium single crystal at high temperatures.
文摘Free transverse vibration of monolayer graphene, boron nitride (BN), and silicon carbide (SiC) sheets is investigated by using molecular dynamics finite element method. Eigenfrequencies and eigenmodes of these three sheets in rectangular shape are studied with different aspect ratios with respect to various boundary conditions. It is found that aspect ratios and boundary conditions affect in a similar way on natural frequencies of graphene, BN, and SiC sheets. Natural frequencies in all modes decrease with an increase of the sheet’s size. Graphene exhibits the highest natural frequencies, and SiC sheet possesses the lowest ones. Missing atoms have minor effects on natural frequencies in this study.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51727807 and 11875318)Beijing Institute of Technology Research Fund Program for Young ScholarsYue Qi Young Scholar Project in CUMTB。
文摘We investigate the mechanical and microstructural changes of the densified silica glass under uniaxial loading-unloading via atomistic simulations with a modified BKS potential. The stress–strain relationship is found to include three respective stages: elastic, plastic and hardening regions. The bulk modulus increases with the initial densification and will undergo a rapid increase after complete densification. The yield pressure varies from 5 to 12 GPa for different densified samples. In addition, the Si–O–Si bond angle reduces during elastic deformation under compression, and 5-fold Si will increase linearly in the plastic deformation. In the hardening region, the peak splitting and the new peak are both found on the Si–Si and O–O pair radial distribution functions, where the 6-fold Si is increased. Instead, the lateral displacement of the atoms always varies linearly with strain, without evident periodic characteristic. As is expected, the samples are permanently densified after release from the plastic region, and the maximum density of recovered samples is about 2.64 g/cm^3, which contains 15 % 5-fold Si, and the Si–O–Si bond angle is less than the ordinary silica glass. All these findings are of great significance for understanding the deformation process of densified silica glass.
文摘With the purpose of making calculation more efficient in practical hydraulic simulations, an improved algorithm was proposed and was applied in the practical water distribution field. This methodology was developed by expanding the traditional loop-equation theory through utilization of the advantages of the graph theory in efficiency. The utilization of the spanning tree technique from graph theory makes the proposed algorithm efficient in calculation and simple to use for computer coding. The algorithms for topological generation and practical implementations are presented in detail in this paper. Through the application to a practical urban system, the consumption of the CPU time and computation memory were decreased while the accuracy was greatly enhanced compared with the present existing methods.
文摘The embedded atom type potentials and static relaxation method combined with a steepest decent computational technique have been used to simulate the interaction between the grain boundary (GB) and dislocations in Ni_3Al alloys.The focus has been placed on the energy feature of the interaction,the distortion of GB structural units,and the dislocation core structure near the GB.Im- plication has also been made on the results for the understanding of the mechanism responsible for B-enhanced ductility.
文摘A set of potential parameters for modeling zircon was obtained by atomistic simulation techniques and a reasonable structural model of zircon was established by fitting some important properties of zircon.Based on the equilibrium configuration of zircon, authors calculated the formation energies of basic point defects and intrinsic disorders. The heats of solution of substituting Pu for Zr showed that there was an immiscible gap at the composition of (Pu75%-Zr25%, in mole fraction), which suggests that the amount of Pu substituting for Zr in zircon be≤50%.
