本文对托卡马克的符号辅助计算特征值和线性求解程序(symbolic computation aided eigenvalue and linear code for Tokamaks,SCELT)进行了并行开发及功能拓展。具体为优化了非均匀网格加密的功能,提高了程序的收敛速度和收敛精度;增加...本文对托卡马克的符号辅助计算特征值和线性求解程序(symbolic computation aided eigenvalue and linear code for Tokamaks,SCELT)进行了并行开发及功能拓展。具体为优化了非均匀网格加密的功能,提高了程序的收敛速度和收敛精度;增加了程序对稀疏矩阵功能的支持,减少了程序对内存的消耗;使用并行思想和信息传递接口(message passing interface,MPI)技术对程序数值离散模块并行开发,通过多进程并行提高了程序数值离散的效率。同时,基于特征值问题计算的可扩展库(the scalable library for eigenvalue problem computations,SLEPc)特征值求解库为程序添加了大规模稀疏矩阵特征值并行求解功能,提高了程序研究问题的速度以及规模。通过计算内扭曲模(m=1,n=1)和电阻撕裂模(m=2,n=1)的线性增长率和模结构验证了并行及拓展后的程序的可靠性。此外,通过与初始版本的运行结果进行比较,展示了优化后的程序在运行速度、运行规模上的巨大优势,以及程序在研究复杂的磁流体动力学(magnetohydrodynamic,MHD)特征值问题的潜力。展开更多
The Dst index has been commonly used to measure the geomagnetic effectiveness of magnetic storm events for several decades.Based on Burton’s empirical Dst model and the global magneto-hydrodynamic(MHD)simulation of E...The Dst index has been commonly used to measure the geomagnetic effectiveness of magnetic storm events for several decades.Based on Burton’s empirical Dst model and the global magneto-hydrodynamic(MHD)simulation of Earth’s magnetosphere,here we proposed a semi-empirical model to forecast the Dst index during geomagnetic storms.In this model,the ring current contribution to the Dst index is derived from Burton’s model,while the contributions from other current systems are obtained from the global MHD simulation.In order to verify the model accuracy,a number of recent magnetic storm events are tested and the simulated Dst index is compared with the observation through the correlation coefficient(CC),prediction efficiency(PE),root mean square error(RMSE)and central root mean square error(CRMSE).The results indicate that,in the context of moderate and intense geomagnetic storm events,the semi-empirical model performs well in global MHD simulations,showing relatively higher CC and PE,and lower RMSE and CRMSE compared to those from the empirical model.Compared with the physics-based ring current models,this model inherits the advantage of fast processing from the empirical model,and easy implementation in a global MHD model of Earth’s magnetosphere.Therefore,it is suitable for the Dst estimation under a context of a global MHD simulation.展开更多
Solar flares are one of the strongest outbursts of solar activity,posing a serious threat to Earth’s critical infrastructure,such as communications,navigation,power,and aviation.Therefore,it is essential to accuratel...Solar flares are one of the strongest outbursts of solar activity,posing a serious threat to Earth’s critical infrastructure,such as communications,navigation,power,and aviation.Therefore,it is essential to accurately predict solar flares in order to ensure the safety of human activities.Currently,the research focuses on two directions:first,identifying predictors with more physical information and higher prediction accuracy,and second,building flare prediction models that can effectively handle complex observational data.In terms of flare observability and predictability,this paper analyses multiple dimensions of solar flare observability and evaluates the potential of observational parameters in prediction.In flare prediction models,the paper focuses on data-driven models and physical models,with an emphasis on the advantages of deep learning techniques in dealing with complex and high-dimensional data.By reviewing existing traditional machine learning,deep learning,and fusion methods,the key roles of these techniques in improving prediction accuracy and efficiency are revealed.Regarding prevailing challenges,this study discusses the main challenges currently faced in solar flare prediction,such as the complexity of flare samples,the multimodality of observational data,and the interpretability of models.The conclusion summarizes these findings and proposes future research directions and potential technology advancement.展开更多
The next generation fusion device listed on ENN’s fusion roadmap,named as(ENN He-Long)EHL-2,is under both physics and engineering designs.The instabilities of ideal magnetohydrodynamics(MHD)mode and neoclassical tear...The next generation fusion device listed on ENN’s fusion roadmap,named as(ENN He-Long)EHL-2,is under both physics and engineering designs.The instabilities of ideal magnetohydrodynamics(MHD)mode and neoclassical tearing mode(NTM)stabilized by electron cyclotron current drive(ECCD)for EHL-2’s two typical operation scenarios are analyzed.For high-ion-temperature operating(HITO)scenario,the vertical displacement event(VDE)could be a big challenge to the device safety.For the steady-state operating(SSO)scenario,the limitation may rise from the ideal MHD mode,NTM,etc.This suggests that the MHD analysis of both operation scenarios should be done with different focusing.Preliminary analysis based on the current physics and engineering design of both two scenarios is given in this paper.Based on the analysis result of above,the future assessments might target at active control method and the effect of boron on MHD activities.展开更多
In this paper,we consider the plasma-vacuum interface problem in a cylindrical tube region impressed by a special background magnetic field.The interior region is occupied with plasma,which is governed by the incompre...In this paper,we consider the plasma-vacuum interface problem in a cylindrical tube region impressed by a special background magnetic field.The interior region is occupied with plasma,which is governed by the incompressible inviscid and resistive MHD system without damping term.The exterior vacuum region is governed by the so-called the“pre-Maxwell equations”.And on the free interface,additionally,the effect of surface tension is taken into account.The original region can be transformed into a horizontally periodic slab through the cylindrical coordinate transformation,which will be impressed by a uniform nonhorizontal magnetic field.Appending with the appropriate physical boundary conditions,the global well-posedness of the problem is established by the energy method.展开更多
Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds nu...Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds number is Re=6299,and the inlet Hartmann number is Ha=2900,with the magnetic field strength decreasing along the flow direction.The results indicate that the dynamic reversal of the three-dimensional(3D)Lorentz force direction near the inflection point of the magnetic field dominates the flow reconstruction,driving the wall jet acceleration and forming an M-type velocity distribution.Moreover,the high-speed shear layer of the jet triggers Kelvin-Helmholtz instability,resulting in the generation of secondary vortex structures near the parallel layer in the non-uniform magnetic field region.In the cross-section perpendicular to the flow direction,the secondary flow gradually evolves into a four-vortex structure,while the velocity fluctuations and turbulent kinetic energy reach the peak.Based on the characteristics of the vortex rotation direction near the shear layer,the intrinsic mechanism behind the unique bimodal distribution of the root-mean-square of velocity fluctuations in the parallel layers is revealed.Furthermore,by comparing the evolution of turbulence under different magnetic field gradients,it is revealed that the distributions of shear stress,Reynolds stress,and turbulent kinetic energy exhibit significant parameter dependence.The strong 3D magnetohydrodynamic effects at the magnetic field gradientγ=0.6 have an immediate impact on the pressure distribution.The transverse Lorentz force LFz further promotes the fluid to accumulate at the wall,leading to a significant increase in the pressure drop and transverse pressure difference in the flow.展开更多
The work comparing the Yamada-Ota and Xue models for nanoparticle flow across a stretching surface has benefits in nanotechnology,medicinal treatments,environmental engineering,renewable energy,and heat exchangers.Mos...The work comparing the Yamada-Ota and Xue models for nanoparticle flow across a stretching surface has benefits in nanotechnology,medicinal treatments,environmental engineering,renewable energy,and heat exchangers.Most published nanofluid flow models assumed constant thermal conductivity and viscosity.With such great physiognomies in mind,the novelty of this work focuses on comparing the performance of the nanofluid models,Xue,and Yamada-Ota models on a stretched sheet with variable thickness under the influence of a magnetic field and quadratic thermal radiation.The altered boundary layer equations for momentum and temperature,subject to adequate boundary conditions,are numerically solved using an optimized,efficient,and extensive bvp-4c approach.The effects of non-dimensional constraints such as magnetic field,power index of velocity,wall thickness parameter,and quadratic radiation parameter on momentum and temperature profile in the boundary layer area are analyzed thoroughly and outcomes were illustrated graphically.Additionally,the consequences of certain distinctive parameters over engineering factors are also examined and results were presented in tabular form.From the outcomes,it is seen that fluid velocity slows down in the presence of a magnetic field but the opposite nature is observed in the case of temperature profile.With a higher index of velocity,the velocity profile decreases and the temperature field elevates.It has been found that the presence of quadratic convection improves the temperature field.The outcomes of the two models are compared.The Yamada-Ota model performed far better than the Xue model in the heat transfer analysis.展开更多
Tearing modes may play an important role in the density limit disruption.The Magnetohydrodynamic(MHD)code CLT with impurity modules is used to study the tearing mode excited and driven by impurity radiation.The impuri...Tearing modes may play an important role in the density limit disruption.The Magnetohydrodynamic(MHD)code CLT with impurity modules is used to study the tearing mode excited and driven by impurity radiation.The impurity radiation can lead to plasma contraction and local enhancement of the current density.When the locally enhanced region of the current density approaches to the resonance surface,the tearing mode can be excited,even if the tearing mode is stable in the initial equilibrium.Through a scan of the initial atomic number(Z)and impurity concentrations,it is found that impurities with different Z values exhibit similar behaviors in the radiation-driven tearing mode.The impurity radiation can drive tearing mode growth through temperature cooling near the resonance surface,and there exists a linear relationship between the temperature perturbation caused by impurity radiation and the linear growth rate of the tearing mode.Additionally,the impurity can promote the growth of magnetic islands through the radiation cooling inside the magnetic island,and there exists a correlation between the initial parameters of impurity and the width of the saturated magnetic island.展开更多
文摘本文对托卡马克的符号辅助计算特征值和线性求解程序(symbolic computation aided eigenvalue and linear code for Tokamaks,SCELT)进行了并行开发及功能拓展。具体为优化了非均匀网格加密的功能,提高了程序的收敛速度和收敛精度;增加了程序对稀疏矩阵功能的支持,减少了程序对内存的消耗;使用并行思想和信息传递接口(message passing interface,MPI)技术对程序数值离散模块并行开发,通过多进程并行提高了程序数值离散的效率。同时,基于特征值问题计算的可扩展库(the scalable library for eigenvalue problem computations,SLEPc)特征值求解库为程序添加了大规模稀疏矩阵特征值并行求解功能,提高了程序研究问题的速度以及规模。通过计算内扭曲模(m=1,n=1)和电阻撕裂模(m=2,n=1)的线性增长率和模结构验证了并行及拓展后的程序的可靠性。此外,通过与初始版本的运行结果进行比较,展示了优化后的程序在运行速度、运行规模上的巨大优势,以及程序在研究复杂的磁流体动力学(magnetohydrodynamic,MHD)特征值问题的潜力。
基金supported by NNSFC grants 42150101,42188105,42304189National Key R&D program of China No.2021YFA-0718600the Pandeng Program of National Space Science Center,Chinese Academy of Sciences.
文摘The Dst index has been commonly used to measure the geomagnetic effectiveness of magnetic storm events for several decades.Based on Burton’s empirical Dst model and the global magneto-hydrodynamic(MHD)simulation of Earth’s magnetosphere,here we proposed a semi-empirical model to forecast the Dst index during geomagnetic storms.In this model,the ring current contribution to the Dst index is derived from Burton’s model,while the contributions from other current systems are obtained from the global MHD simulation.In order to verify the model accuracy,a number of recent magnetic storm events are tested and the simulated Dst index is compared with the observation through the correlation coefficient(CC),prediction efficiency(PE),root mean square error(RMSE)and central root mean square error(CRMSE).The results indicate that,in the context of moderate and intense geomagnetic storm events,the semi-empirical model performs well in global MHD simulations,showing relatively higher CC and PE,and lower RMSE and CRMSE compared to those from the empirical model.Compared with the physics-based ring current models,this model inherits the advantage of fast processing from the empirical model,and easy implementation in a global MHD model of Earth’s magnetosphere.Therefore,it is suitable for the Dst estimation under a context of a global MHD simulation.
基金supported by the National Key Research and Development Program of China(grant No.2022YFF0503600)the National Natural Science Foundation of China(NSFC,grant No.42130202).
文摘Solar flares are one of the strongest outbursts of solar activity,posing a serious threat to Earth’s critical infrastructure,such as communications,navigation,power,and aviation.Therefore,it is essential to accurately predict solar flares in order to ensure the safety of human activities.Currently,the research focuses on two directions:first,identifying predictors with more physical information and higher prediction accuracy,and second,building flare prediction models that can effectively handle complex observational data.In terms of flare observability and predictability,this paper analyses multiple dimensions of solar flare observability and evaluates the potential of observational parameters in prediction.In flare prediction models,the paper focuses on data-driven models and physical models,with an emphasis on the advantages of deep learning techniques in dealing with complex and high-dimensional data.By reviewing existing traditional machine learning,deep learning,and fusion methods,the key roles of these techniques in improving prediction accuracy and efficiency are revealed.Regarding prevailing challenges,this study discusses the main challenges currently faced in solar flare prediction,such as the complexity of flare samples,the multimodality of observational data,and the interpretability of models.The conclusion summarizes these findings and proposes future research directions and potential technology advancement.
文摘The next generation fusion device listed on ENN’s fusion roadmap,named as(ENN He-Long)EHL-2,is under both physics and engineering designs.The instabilities of ideal magnetohydrodynamics(MHD)mode and neoclassical tearing mode(NTM)stabilized by electron cyclotron current drive(ECCD)for EHL-2’s two typical operation scenarios are analyzed.For high-ion-temperature operating(HITO)scenario,the vertical displacement event(VDE)could be a big challenge to the device safety.For the steady-state operating(SSO)scenario,the limitation may rise from the ideal MHD mode,NTM,etc.This suggests that the MHD analysis of both operation scenarios should be done with different focusing.Preliminary analysis based on the current physics and engineering design of both two scenarios is given in this paper.Based on the analysis result of above,the future assessments might target at active control method and the effect of boron on MHD activities.
基金supported by the NSFC(11571177)the National Key Research and Development Program of China(2020YFA0713803).
文摘In this paper,we consider the plasma-vacuum interface problem in a cylindrical tube region impressed by a special background magnetic field.The interior region is occupied with plasma,which is governed by the incompressible inviscid and resistive MHD system without damping term.The exterior vacuum region is governed by the so-called the“pre-Maxwell equations”.And on the free interface,additionally,the effect of surface tension is taken into account.The original region can be transformed into a horizontally periodic slab through the cylindrical coordinate transformation,which will be impressed by a uniform nonhorizontal magnetic field.Appending with the appropriate physical boundary conditions,the global well-posedness of the problem is established by the energy method.
基金supported by the Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-087)and the National Key R&D Program of China(Grant No.2022YFA1204100)。
文摘Direct numerical simulations have been conducted to investigate the evolution process of liquid metal laminar to turbulent flow in a rectangular duct under the influence of a non-uniform magnetic field.The Reynolds number is Re=6299,and the inlet Hartmann number is Ha=2900,with the magnetic field strength decreasing along the flow direction.The results indicate that the dynamic reversal of the three-dimensional(3D)Lorentz force direction near the inflection point of the magnetic field dominates the flow reconstruction,driving the wall jet acceleration and forming an M-type velocity distribution.Moreover,the high-speed shear layer of the jet triggers Kelvin-Helmholtz instability,resulting in the generation of secondary vortex structures near the parallel layer in the non-uniform magnetic field region.In the cross-section perpendicular to the flow direction,the secondary flow gradually evolves into a four-vortex structure,while the velocity fluctuations and turbulent kinetic energy reach the peak.Based on the characteristics of the vortex rotation direction near the shear layer,the intrinsic mechanism behind the unique bimodal distribution of the root-mean-square of velocity fluctuations in the parallel layers is revealed.Furthermore,by comparing the evolution of turbulence under different magnetic field gradients,it is revealed that the distributions of shear stress,Reynolds stress,and turbulent kinetic energy exhibit significant parameter dependence.The strong 3D magnetohydrodynamic effects at the magnetic field gradientγ=0.6 have an immediate impact on the pressure distribution.The transverse Lorentz force LFz further promotes the fluid to accumulate at the wall,leading to a significant increase in the pressure drop and transverse pressure difference in the flow.
基金supported by the National Research Foundation,Korea(Grant No.NRF2022-R1A2C2002799)support provided by the German Jordanian University,Amman,Jordan,is greatly acknowledged by the authors.Ulavathi Shettar Mahabaleshwar wishes to thank Sang Woo Joo,School of Mechanical Engineering,Yeungnam University,Gyeongsan,Korea,for his hospitality.
文摘The work comparing the Yamada-Ota and Xue models for nanoparticle flow across a stretching surface has benefits in nanotechnology,medicinal treatments,environmental engineering,renewable energy,and heat exchangers.Most published nanofluid flow models assumed constant thermal conductivity and viscosity.With such great physiognomies in mind,the novelty of this work focuses on comparing the performance of the nanofluid models,Xue,and Yamada-Ota models on a stretched sheet with variable thickness under the influence of a magnetic field and quadratic thermal radiation.The altered boundary layer equations for momentum and temperature,subject to adequate boundary conditions,are numerically solved using an optimized,efficient,and extensive bvp-4c approach.The effects of non-dimensional constraints such as magnetic field,power index of velocity,wall thickness parameter,and quadratic radiation parameter on momentum and temperature profile in the boundary layer area are analyzed thoroughly and outcomes were illustrated graphically.Additionally,the consequences of certain distinctive parameters over engineering factors are also examined and results were presented in tabular form.From the outcomes,it is seen that fluid velocity slows down in the presence of a magnetic field but the opposite nature is observed in the case of temperature profile.With a higher index of velocity,the velocity profile decreases and the temperature field elevates.It has been found that the presence of quadratic convection improves the temperature field.The outcomes of the two models are compared.The Yamada-Ota model performed far better than the Xue model in the heat transfer analysis.
基金supported by the National Magnetic Confinement Fusion Energy R&D Program of China (Nos.2019YFE03030004 and 2022YFE03100001)。
文摘Tearing modes may play an important role in the density limit disruption.The Magnetohydrodynamic(MHD)code CLT with impurity modules is used to study the tearing mode excited and driven by impurity radiation.The impurity radiation can lead to plasma contraction and local enhancement of the current density.When the locally enhanced region of the current density approaches to the resonance surface,the tearing mode can be excited,even if the tearing mode is stable in the initial equilibrium.Through a scan of the initial atomic number(Z)and impurity concentrations,it is found that impurities with different Z values exhibit similar behaviors in the radiation-driven tearing mode.The impurity radiation can drive tearing mode growth through temperature cooling near the resonance surface,and there exists a linear relationship between the temperature perturbation caused by impurity radiation and the linear growth rate of the tearing mode.Additionally,the impurity can promote the growth of magnetic islands through the radiation cooling inside the magnetic island,and there exists a correlation between the initial parameters of impurity and the width of the saturated magnetic island.
