In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the re...In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the relationship between the experimental and simulation results were explored.Our computational findings on the secondary structure of SEB showed that at room temperature,the CD spectroscopic results were highly consistent with the MD results.Moreover,under heating conditions,the changing trends of helix,sheet and random coil obtained by CD spectral fitting were highly consistent with those obtained by MD.In order to gain a deeper understanding of the thermal stability mechanism of SEB,the MD trajectories were analyzed in terms of root mean square deviation(RMSD),secondary structure assignment(SSA),radius of gyration(R_(g)),free energy surfaces(FES),solvent-accessible surface area(SASA),hydrogen bonds and salt bridges.The results showed that at low heating temperature,domain Ⅰ without loops(omitting the mobile loop region)mainly relied on hydrophobic interaction to maintain its thermal stability,whereas the thermal stability of domain Ⅱ was mainly controlled by salt bridges and hydrogen bonds.Under high heating temperature conditions,the hydrophobic interactions in domain Ⅰ without loops were destroyed and the secondary structure was almost completely lost,while domain Ⅱ could still rely on salt bridges as molecular staples to barely maintain the stability of the secondary structure.These results help us to understand the thermodynamic and kinetic mechanisms that maintain the thermal stability of SEB at the molecular level,and provide a direction for establishing safer and more effective food sterilization processes.展开更多
To investigate the effect of void defects on the shock response of hexanitrohexaazaisowurtzitane(CL-20)co-crystals,shock responses of CL-20 co-crystals with energetic materials ligands trinitrotoluene(TNT),1,3-dinitro...To investigate the effect of void defects on the shock response of hexanitrohexaazaisowurtzitane(CL-20)co-crystals,shock responses of CL-20 co-crystals with energetic materials ligands trinitrotoluene(TNT),1,3-dinitrobenzene(DNB),solvents ligands dimethyl carbonate(DMC) and gamma-butyrolactone(GBL)with void were simulated,using molecular dynamics method and reactive force field.It is found that the CL-20 co-crystals with void defects will form hot spots when impacted,significantly affecting the decomposition of molecules around the void.The degree of molecular fragmentation is relatively low under the reflection velocity of 2 km/s,and the main reactions are the formation of dimer and the shedding of nitro groups.The existence of voids reduces the safety of CL-20 co-crystals,which induced the sensitivity of energetic co-crystals CL-20/TNT and CL-20/DNB to increase more significantly.Detonation has occurred under the reflection velocity of 4 km/s,energetic co-crystals are easier to polymerize than solvent co-crystals,and are not obviously affected by voids.The results show that the energy of the wave decreases after sweeping over the void,which reduces the chemical reaction frequency downstream of the void and affects the detonation performance,especially the solvent co-crystals.展开更多
A deep understanding of explosive sensitivities and their factors is important for safe and reliable applications.However,quantitative prediction of the sensitivities is difficult.Here,reactive molecular dynamics simu...A deep understanding of explosive sensitivities and their factors is important for safe and reliable applications.However,quantitative prediction of the sensitivities is difficult.Here,reactive molecular dynamics simulation models for high-speed piston impacts on explosive supercells were established.Simulations were also performed to investigate shock-induced reactions of various high-energy explosives.The fraction of reacted explosive molecules in an initial supercell changed linearly with the propagation distance of the shock-wave front.The corresponding slope could be used as a reaction rate for a specific shock-loading velocity.Reaction rates that varied with the shock-loading pressure exhibited two-stage linearities with different slopes.The two inflection points corresponded to the initial and accelerated reactions,which respectively correlated to the thresholds of shock-induced ignition and detonation.Therefore,the ignition and detonation critical pressures could be determined.The sensitivity could then be a quantitative prediction of the critical pressure.The accuracies of the quantitative shock sensitivity predictions were verified by comparing the impact and shock sensitivities of common explosives and the characteristics of anisotropic shock-induced reactions.Molecular dynamics simulations quantitatively predict and rank shock sensitivities by using only crystal structures of the explosives.Overall,this method will enable the design and safe use of explosives.展开更多
According to the recently developed single-trough floating machine with the world's largest volume(inflatable mechanical agitation flotation machine with volume of 320 m3) in China, the gas-fluid two-phase flow in...According to the recently developed single-trough floating machine with the world's largest volume(inflatable mechanical agitation flotation machine with volume of 320 m3) in China, the gas-fluid two-phase flow in flotation cell was simulated using computational fluid dynamics method. It is shown that hexahedral mesh scheme is more suitable for the complex structure of the flotation cell than tetrahedral mesh scheme, and a mesh quality ranging from 0.7 to 1.0 is obtained. Comparative studies of the standard k-ε, k-ω and realizable k-ε turbulence models were carried out. It is indicated that the standard k-ε turbulence model could give a result relatively close to the practice and the liquid phase flow field is well characterized. In addition, two obvious recirculation zones are formed in the mixing zones, and the pressure on the rotor and stator is well characterized. Furthermore, the simulation results using improved standard k-ε turbulence model show that surface tension coefficient of 0.072, drag model of Grace and coefficient of 4, and lift coefficient of 0.001 can be achieved. The research results suggest that gas-fluid two-phase flow in large flotation cell can be well simulated using computational fluid dynamics method.展开更多
This paper presents a time-efficient numerical approach to modelling high explosive(HE)blastwave propagation using Computational Fluid Dynamics(CFD).One of the main issues of using conventional CFD modelling in high e...This paper presents a time-efficient numerical approach to modelling high explosive(HE)blastwave propagation using Computational Fluid Dynamics(CFD).One of the main issues of using conventional CFD modelling in high explosive simulations is the ability to accurately define the initial blastwave properties that arise from the ignition and consequent explosion.Specialised codes often employ Jones-Wilkins-Lee(JWL)or similar equation of state(EOS)to simulate blasts.However,most available CFD codes are limited in terms of EOS modelling.They are restrictive to the Ideal Gas Law(IGL)for compressible flows,which is generally unsuitable for blast simulations.To this end,this paper presents a numerical approach to simulate blastwave propagation for any generic CFD code using the IGL EOS.A new method known as the Input Cavity Method(ICM)is defined where input conditions of the high explosives are given in the form of pressure,velocity and temperature time-history curves.These time history curves are input at a certain distance from the centre of the charge.It is shown that the ICM numerical method can accurately predict over-pressure and impulse time history at measured locations for the incident,reflective and complex multiple reflection scenarios with high numerical accuracy compared to experimental measurements.The ICM is compared to the Pressure Bubble Method(PBM),a common approach to replicating initial conditions for a high explosive in Finite Volume modelling.It is shown that the ICM outperforms the PBM on multiple fronts,such as peak values and overall overpressure curve shape.Finally,the paper also presents the importance of choosing an appropriate solver between the Pressure Based Solver(PBS)and Density-Based Solver(DBS)and provides the advantages and disadvantages of either choice.In general,it is shown that the PBS can resolve and capture the interactions of blastwaves to a higher degree of resolution than the DBS.This is achieved at a much higher computational cost,showing that the DBS is much preferred for quick turnarounds.展开更多
A critical challenge of any blast simulation facility is in producing the widest possible pressure-impulse range for matching against equivalent high-explosive events.Shock tubes and blast simulators are often constra...A critical challenge of any blast simulation facility is in producing the widest possible pressure-impulse range for matching against equivalent high-explosive events.Shock tubes and blast simulators are often constrained with the lack of effective ways to control blast wave profiles and as a result have a limited performance range.Some wave shaping techniques employed in some facilities are reviewed but often necessitate extensive geometric modifications,inadvertently cause flow anomalies,and/or are only applicable under very specific configurations.This paper investigates controlled venting as an expedient way for waveforms to be tuned without requiring extensive modifications to the driver or existing geometry and could be widely applied by existing and future blast simulation and shock tube facilities.The use of controlled venting is demonstrated experimentally using the Advanced Blast Simulator(shock tube)at the Australian National Facility of Physical Blast Simulation and via numerical flow simulations with Computational Fluid Dynamics.Controlled venting is determined as an effective method for mitigating the impact of re-reflected waves within the blast simulator.This control method also allows for the adjustment of parameters such as tuning the peak overpressure,the positive phase duration,and modifying the magnitude of the negative phase and the secondary shock of the blast waves.This paper is concluded with an illustration of the potential expanded performance range of the Australian blast simulation facility when controlled venting for blast waveform tailoring as presented in this paper is applied.展开更多
The effects of tensile temperatures ranging from 100 K to 900 K on the phase transition of hexagonal close-packed(HCP)zirconium were investigated by molecular dynamics simulations,which were combined with experimental...The effects of tensile temperatures ranging from 100 K to 900 K on the phase transition of hexagonal close-packed(HCP)zirconium were investigated by molecular dynamics simulations,which were combined with experimental observation under high resolution transmission electron microscopy.The results show that externally applied loading first induced the HCP to body-centered cubic(BCC)phase transition in the Pitsch-Schrader(PS)orientation relationship(OR).Then,the face-centered cubic(FCC)structure transformed from the BCC phase in the Bain path.However,the HCP-to-BCC transition was incomplete at 100 K and 300 K,resulting in a prismatic-type OR between the FCC and original HCP phase.Additionally,at the temperature ranging from 100 K to 600 K,the inverse BCC-to-HCP transition occurred locally following other variants of the PS OR,resulting in a basal-type relation between the newly generated HCP and FCC phases.A higher tensile temperature promoted the amount of FCC phase transforming into the BCC phase when the strain exceeded 45%.Besides,the crystal stretched at lower temperatures exhibits relatively higher strength but by the compromise of plasticity.This study reveals the deformation mechanisms in HCP-Zr at different temperatures,which may provide a better understanding of the deformation mechanism of zirconium alloys under different application environments.展开更多
为提升低空风切变预报精度,本文综合运用欧洲中期天气预报中心第五代再分析资料[European Centre for Medium-Range Weather Forecasts(ECMWF)fifth-generation reanalysis data,ERA5]和美国国家环境预报中心(National Centers for Envi...为提升低空风切变预报精度,本文综合运用欧洲中期天气预报中心第五代再分析资料[European Centre for Medium-Range Weather Forecasts(ECMWF)fifth-generation reanalysis data,ERA5]和美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)的FNL全球再分析资料(Final Operational Global Analysis)、先进星载热发射和反射辐射仪全球数字高程模型以及兰州中川机场的实况观测资料,采用中尺度数值天气预报模式(Weather Research and Forecasting Model,WRF)、WRF结合计算流体动力学(Computational Fluid Dynamics,CFD)方法、长短期神经网络(Long Short-Term Memory,LSTM)方法,对2021年4月15-16日兰州中川机场的两次风切变过程进行模拟分析。结果表明:(1)在小于1 km的网格中使用大涡模拟,WRF模式在单个站点风速模拟任务中表现更好,但在近地面水平风场风速模拟效果上,不如WRF模式结合计算流体力学模型方案;(2)对于飞机降落过程中遭遇的两次低空风切变的模拟,WRF-LES和WRF-CFD两种模式都可以模拟出第一次低空风切变,而第二次受传入模式的WRF风速数据值较小的影响,两种模式风速差都没有达到阈值,需要在后续工作中进一步验证;(3)低风速条件(6 m·s^(-1))下,基于LSTM的单变量风速预测模型平均绝对误差基本维持在0.59 m·s^(-1),能较好地把握不同地形与环流背景条件下风速变化的非线性关系,虽然受到WRF误差和观测要素不全的限制,多变量风速预测能在保证平均绝对百分比误差小于6.60%的情况下,以更高的计算效率和泛化能力实现风速预测。本文不仅验证了WRF-CFD和WRF-LES耦合方案在风场和低空风切变预报中的差异,还探讨了基于LSTM的风速预测的可行性和准确性,期望为提高风场模拟精度,缩短精细风场模拟时间提供新的视角和方法。展开更多
The microstructures and thermodynamic properties of mixed systems comprising pyridinium ionic liquid[HPy][BF_(4)]and acetonitrile at different mole fractions were studied using molecular dynamics simulation in this wo...The microstructures and thermodynamic properties of mixed systems comprising pyridinium ionic liquid[HPy][BF_(4)]and acetonitrile at different mole fractions were studied using molecular dynamics simulation in this work.The following properties were determined:density,self-diffusion coefficient,excess molar volume,and radial distribution function.The results show that with an increase in the mole fraction of[HPy][BF_(4)],the self-diffusion coefficient decreases.Additionally,the excess molar volume initially decreases,reaches a minimum,and then increases.The rules of radial distribution functions(RDFs)of characteristic atoms are different.With increasing the mole fraction of[HPy][BF_(4)],the first peak of the RDFs of HA1-F decreases,while that of CT6-CT6 rises at first and then decreases.This indicates that the solvent molecules affect the polar and non-polar regions of[HPy][BF_(4)]differently.展开更多
Molecular dynamics simulations are performed to observe the evolutions of 512 and 51262 cage-like water clusters filled with or without a methane molecule immersed in bulk liquid water at 250 K and 230 K. The lifetime...Molecular dynamics simulations are performed to observe the evolutions of 512 and 51262 cage-like water clusters filled with or without a methane molecule immersed in bulk liquid water at 250 K and 230 K. The lifetimes of these clusters are calculated according to their Lindemann index δ (t) using the criteria of δ≥0.07. For both the filled and empty clusters, we find the dynamics of bulk water determines the lifetimes of cage-like water clusters, and that the lifetime of 512 62 cage-like cluster is the same as that of 512 cage-like cluster. Although the methane molecule indeed makes the filled cage-like cluster more stable than the empty one, the empty cage-like cluster still has chance to be long-lived compared with the filled clusters. These observations support the labile cluster hypothesis on the formation mechanisms of gas hydrates.展开更多
The application of a novel Automatic Dynamic Simulator of Fouling (ADSF) to evaluate the effectiveness of ion-rod water treater is reported.The effects of some parameters of the water treater were studied with an ADSF...The application of a novel Automatic Dynamic Simulator of Fouling (ADSF) to evaluate the effectiveness of ion-rod water treater is reported.The effects of some parameters of the water treater were studied with an ADSF made according to patented technology, and orthogonal experimental design was adopted with the use of artificial hard water.Experimental results validated that the ion-rod water treater could mitigate fouling,and the anti-fouling efficiency varies with the test conditions.The anti-fouling efficiency of treater increased with the increase of flow velocity in the range of 0.8—1.2 m·s -1 and output voltage in the range of 7500—15000 V.The efficiency weat up initially, and then went down with the increase in hardness.The rough surface of ion-rod was superior to the smooth one.The order of influence on treater performance with respect to these factors was as follows: water hardness, roughness of surface, flow velocity and output voltage.The research also provided a guide to improving the performance of ion-rod water treater.展开更多
文摘In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the relationship between the experimental and simulation results were explored.Our computational findings on the secondary structure of SEB showed that at room temperature,the CD spectroscopic results were highly consistent with the MD results.Moreover,under heating conditions,the changing trends of helix,sheet and random coil obtained by CD spectral fitting were highly consistent with those obtained by MD.In order to gain a deeper understanding of the thermal stability mechanism of SEB,the MD trajectories were analyzed in terms of root mean square deviation(RMSD),secondary structure assignment(SSA),radius of gyration(R_(g)),free energy surfaces(FES),solvent-accessible surface area(SASA),hydrogen bonds and salt bridges.The results showed that at low heating temperature,domain Ⅰ without loops(omitting the mobile loop region)mainly relied on hydrophobic interaction to maintain its thermal stability,whereas the thermal stability of domain Ⅱ was mainly controlled by salt bridges and hydrogen bonds.Under high heating temperature conditions,the hydrophobic interactions in domain Ⅰ without loops were destroyed and the secondary structure was almost completely lost,while domain Ⅱ could still rely on salt bridges as molecular staples to barely maintain the stability of the secondary structure.These results help us to understand the thermodynamic and kinetic mechanisms that maintain the thermal stability of SEB at the molecular level,and provide a direction for establishing safer and more effective food sterilization processes.
基金supported by the National Natural Science Foundation of China (22275018)the Project of State Key Laboratory of Explosion Science and Technology (Beijing Institute of Technology)(Grant No.QNKT20-04)。
文摘To investigate the effect of void defects on the shock response of hexanitrohexaazaisowurtzitane(CL-20)co-crystals,shock responses of CL-20 co-crystals with energetic materials ligands trinitrotoluene(TNT),1,3-dinitrobenzene(DNB),solvents ligands dimethyl carbonate(DMC) and gamma-butyrolactone(GBL)with void were simulated,using molecular dynamics method and reactive force field.It is found that the CL-20 co-crystals with void defects will form hot spots when impacted,significantly affecting the decomposition of molecules around the void.The degree of molecular fragmentation is relatively low under the reflection velocity of 2 km/s,and the main reactions are the formation of dimer and the shedding of nitro groups.The existence of voids reduces the safety of CL-20 co-crystals,which induced the sensitivity of energetic co-crystals CL-20/TNT and CL-20/DNB to increase more significantly.Detonation has occurred under the reflection velocity of 4 km/s,energetic co-crystals are easier to polymerize than solvent co-crystals,and are not obviously affected by voids.The results show that the energy of the wave decreases after sweeping over the void,which reduces the chemical reaction frequency downstream of the void and affects the detonation performance,especially the solvent co-crystals.
基金supported by the National Natural Science Foundation of China(Grant No.11832006).
文摘A deep understanding of explosive sensitivities and their factors is important for safe and reliable applications.However,quantitative prediction of the sensitivities is difficult.Here,reactive molecular dynamics simulation models for high-speed piston impacts on explosive supercells were established.Simulations were also performed to investigate shock-induced reactions of various high-energy explosives.The fraction of reacted explosive molecules in an initial supercell changed linearly with the propagation distance of the shock-wave front.The corresponding slope could be used as a reaction rate for a specific shock-loading velocity.Reaction rates that varied with the shock-loading pressure exhibited two-stage linearities with different slopes.The two inflection points corresponded to the initial and accelerated reactions,which respectively correlated to the thresholds of shock-induced ignition and detonation.Therefore,the ignition and detonation critical pressures could be determined.The sensitivity could then be a quantitative prediction of the critical pressure.The accuracies of the quantitative shock sensitivity predictions were verified by comparing the impact and shock sensitivities of common explosives and the characteristics of anisotropic shock-induced reactions.Molecular dynamics simulations quantitatively predict and rank shock sensitivities by using only crystal structures of the explosives.Overall,this method will enable the design and safe use of explosives.
基金Project(51074027)supported by the National Natural Science Foundation of China
文摘According to the recently developed single-trough floating machine with the world's largest volume(inflatable mechanical agitation flotation machine with volume of 320 m3) in China, the gas-fluid two-phase flow in flotation cell was simulated using computational fluid dynamics method. It is shown that hexahedral mesh scheme is more suitable for the complex structure of the flotation cell than tetrahedral mesh scheme, and a mesh quality ranging from 0.7 to 1.0 is obtained. Comparative studies of the standard k-ε, k-ω and realizable k-ε turbulence models were carried out. It is indicated that the standard k-ε turbulence model could give a result relatively close to the practice and the liquid phase flow field is well characterized. In addition, two obvious recirculation zones are formed in the mixing zones, and the pressure on the rotor and stator is well characterized. Furthermore, the simulation results using improved standard k-ε turbulence model show that surface tension coefficient of 0.072, drag model of Grace and coefficient of 4, and lift coefficient of 0.001 can be achieved. The research results suggest that gas-fluid two-phase flow in large flotation cell can be well simulated using computational fluid dynamics method.
文摘This paper presents a time-efficient numerical approach to modelling high explosive(HE)blastwave propagation using Computational Fluid Dynamics(CFD).One of the main issues of using conventional CFD modelling in high explosive simulations is the ability to accurately define the initial blastwave properties that arise from the ignition and consequent explosion.Specialised codes often employ Jones-Wilkins-Lee(JWL)or similar equation of state(EOS)to simulate blasts.However,most available CFD codes are limited in terms of EOS modelling.They are restrictive to the Ideal Gas Law(IGL)for compressible flows,which is generally unsuitable for blast simulations.To this end,this paper presents a numerical approach to simulate blastwave propagation for any generic CFD code using the IGL EOS.A new method known as the Input Cavity Method(ICM)is defined where input conditions of the high explosives are given in the form of pressure,velocity and temperature time-history curves.These time history curves are input at a certain distance from the centre of the charge.It is shown that the ICM numerical method can accurately predict over-pressure and impulse time history at measured locations for the incident,reflective and complex multiple reflection scenarios with high numerical accuracy compared to experimental measurements.The ICM is compared to the Pressure Bubble Method(PBM),a common approach to replicating initial conditions for a high explosive in Finite Volume modelling.It is shown that the ICM outperforms the PBM on multiple fronts,such as peak values and overall overpressure curve shape.Finally,the paper also presents the importance of choosing an appropriate solver between the Pressure Based Solver(PBS)and Density-Based Solver(DBS)and provides the advantages and disadvantages of either choice.In general,it is shown that the PBS can resolve and capture the interactions of blastwaves to a higher degree of resolution than the DBS.This is achieved at a much higher computational cost,showing that the DBS is much preferred for quick turnarounds.
基金funded partially by the Australian Government through the Australian Research Council’s Linkage Infrastructure,Equipment and Facilities (LIEF)funding scheme (LE130100133)。
文摘A critical challenge of any blast simulation facility is in producing the widest possible pressure-impulse range for matching against equivalent high-explosive events.Shock tubes and blast simulators are often constrained with the lack of effective ways to control blast wave profiles and as a result have a limited performance range.Some wave shaping techniques employed in some facilities are reviewed but often necessitate extensive geometric modifications,inadvertently cause flow anomalies,and/or are only applicable under very specific configurations.This paper investigates controlled venting as an expedient way for waveforms to be tuned without requiring extensive modifications to the driver or existing geometry and could be widely applied by existing and future blast simulation and shock tube facilities.The use of controlled venting is demonstrated experimentally using the Advanced Blast Simulator(shock tube)at the Australian National Facility of Physical Blast Simulation and via numerical flow simulations with Computational Fluid Dynamics.Controlled venting is determined as an effective method for mitigating the impact of re-reflected waves within the blast simulator.This control method also allows for the adjustment of parameters such as tuning the peak overpressure,the positive phase duration,and modifying the magnitude of the negative phase and the secondary shock of the blast waves.This paper is concluded with an illustration of the potential expanded performance range of the Australian blast simulation facility when controlled venting for blast waveform tailoring as presented in this paper is applied.
基金Projects(51901248,51828102)supported by the National Natural Science Foundation of ChinaProject(2018JJ3649)supported by the Natural Science Foundation of Hunan Province,ChinaProject(2019CX026)supported by the Innovation-driven Plan in Central South University,China。
文摘The effects of tensile temperatures ranging from 100 K to 900 K on the phase transition of hexagonal close-packed(HCP)zirconium were investigated by molecular dynamics simulations,which were combined with experimental observation under high resolution transmission electron microscopy.The results show that externally applied loading first induced the HCP to body-centered cubic(BCC)phase transition in the Pitsch-Schrader(PS)orientation relationship(OR).Then,the face-centered cubic(FCC)structure transformed from the BCC phase in the Bain path.However,the HCP-to-BCC transition was incomplete at 100 K and 300 K,resulting in a prismatic-type OR between the FCC and original HCP phase.Additionally,at the temperature ranging from 100 K to 600 K,the inverse BCC-to-HCP transition occurred locally following other variants of the PS OR,resulting in a basal-type relation between the newly generated HCP and FCC phases.A higher tensile temperature promoted the amount of FCC phase transforming into the BCC phase when the strain exceeded 45%.Besides,the crystal stretched at lower temperatures exhibits relatively higher strength but by the compromise of plasticity.This study reveals the deformation mechanisms in HCP-Zr at different temperatures,which may provide a better understanding of the deformation mechanism of zirconium alloys under different application environments.
文摘为提升低空风切变预报精度,本文综合运用欧洲中期天气预报中心第五代再分析资料[European Centre for Medium-Range Weather Forecasts(ECMWF)fifth-generation reanalysis data,ERA5]和美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)的FNL全球再分析资料(Final Operational Global Analysis)、先进星载热发射和反射辐射仪全球数字高程模型以及兰州中川机场的实况观测资料,采用中尺度数值天气预报模式(Weather Research and Forecasting Model,WRF)、WRF结合计算流体动力学(Computational Fluid Dynamics,CFD)方法、长短期神经网络(Long Short-Term Memory,LSTM)方法,对2021年4月15-16日兰州中川机场的两次风切变过程进行模拟分析。结果表明:(1)在小于1 km的网格中使用大涡模拟,WRF模式在单个站点风速模拟任务中表现更好,但在近地面水平风场风速模拟效果上,不如WRF模式结合计算流体力学模型方案;(2)对于飞机降落过程中遭遇的两次低空风切变的模拟,WRF-LES和WRF-CFD两种模式都可以模拟出第一次低空风切变,而第二次受传入模式的WRF风速数据值较小的影响,两种模式风速差都没有达到阈值,需要在后续工作中进一步验证;(3)低风速条件(6 m·s^(-1))下,基于LSTM的单变量风速预测模型平均绝对误差基本维持在0.59 m·s^(-1),能较好地把握不同地形与环流背景条件下风速变化的非线性关系,虽然受到WRF误差和观测要素不全的限制,多变量风速预测能在保证平均绝对百分比误差小于6.60%的情况下,以更高的计算效率和泛化能力实现风速预测。本文不仅验证了WRF-CFD和WRF-LES耦合方案在风场和低空风切变预报中的差异,还探讨了基于LSTM的风速预测的可行性和准确性,期望为提高风场模拟精度,缩短精细风场模拟时间提供新的视角和方法。
文摘The microstructures and thermodynamic properties of mixed systems comprising pyridinium ionic liquid[HPy][BF_(4)]and acetonitrile at different mole fractions were studied using molecular dynamics simulation in this work.The following properties were determined:density,self-diffusion coefficient,excess molar volume,and radial distribution function.The results show that with an increase in the mole fraction of[HPy][BF_(4)],the self-diffusion coefficient decreases.Additionally,the excess molar volume initially decreases,reaches a minimum,and then increases.The rules of radial distribution functions(RDFs)of characteristic atoms are different.With increasing the mole fraction of[HPy][BF_(4)],the first peak of the RDFs of HA1-F decreases,while that of CT6-CT6 rises at first and then decreases.This indicates that the solvent molecules affect the polar and non-polar regions of[HPy][BF_(4)]differently.
基金supported by the National Natural Science Foundation of China(Grant No.40102005 and No.49725205).
文摘Molecular dynamics simulations are performed to observe the evolutions of 512 and 51262 cage-like water clusters filled with or without a methane molecule immersed in bulk liquid water at 250 K and 230 K. The lifetimes of these clusters are calculated according to their Lindemann index δ (t) using the criteria of δ≥0.07. For both the filled and empty clusters, we find the dynamics of bulk water determines the lifetimes of cage-like water clusters, and that the lifetime of 512 62 cage-like cluster is the same as that of 512 cage-like cluster. Although the methane molecule indeed makes the filled cage-like cluster more stable than the empty one, the empty cage-like cluster still has chance to be long-lived compared with the filled clusters. These observations support the labile cluster hypothesis on the formation mechanisms of gas hydrates.
基金supported by Jilin Distinguished YoungScholars Program (20040121).
文摘The application of a novel Automatic Dynamic Simulator of Fouling (ADSF) to evaluate the effectiveness of ion-rod water treater is reported.The effects of some parameters of the water treater were studied with an ADSF made according to patented technology, and orthogonal experimental design was adopted with the use of artificial hard water.Experimental results validated that the ion-rod water treater could mitigate fouling,and the anti-fouling efficiency varies with the test conditions.The anti-fouling efficiency of treater increased with the increase of flow velocity in the range of 0.8—1.2 m·s -1 and output voltage in the range of 7500—15000 V.The efficiency weat up initially, and then went down with the increase in hardness.The rough surface of ion-rod was superior to the smooth one.The order of influence on treater performance with respect to these factors was as follows: water hardness, roughness of surface, flow velocity and output voltage.The research also provided a guide to improving the performance of ion-rod water treater.
