Observations indicate that Ellerman bombs （EBs） and chromospheric microflares both occur in the lower solar atmosphere,and share many common features,such as temperature enhancements,accompanying jet-like mass motio...Observations indicate that Ellerman bombs （EBs） and chromospheric microflares both occur in the lower solar atmosphere,and share many common features,such as temperature enhancements,accompanying jet-like mass motions,short life-time,and so on.These strongly suggest that EBs and chromospheric microflares could both probably be induced by magnetic reconnection in the lower solar atmosphere.With gravity,ionization and radiation considered,we perform two-dimensional numerical simulations of magnetic reconnection in the lower solar atmosphere.The influence of different parameters,such as intensity of the magnetic field and anomalous resistivity,on the results are investigated.Our result demonstrates that the temperature increases are mainly due to the joule dissipation caused by magnetic reconnection.The spectral profiles of EBs and chromospheric microflares are calculated with the non-LTE radiative transfer theory and compared with observations.It is found that the typical features of the two phenomena can be qualitatively reproduced.展开更多
Calculation of magnetic pressure is the basis of application of electromagnetic forming (EMF). This paper carries out a numerical simulation of magnetic pressure under the influence of die by means of finite element m...Calculation of magnetic pressure is the basis of application of electromagnetic forming (EMF). This paper carries out a numerical simulation of magnetic pressure under the influence of die by means of finite element method. The analysis model of electromagnetic bulging with die is created by using ANSYS, and the distribution of magnetic pressure acting on the tube and the die is obtained. The differences between EMF and other technologies and the effect of die on tube formability are analyzed. The die has important influence upon the calculation accuracy. The simulating conclusions with different discharge energy and current frequency are verified through the technologic tests. The distribution of magnetic pressure acting on the tube agrees well with the measurements of the deformed tube.展开更多
The casing damage has been a big problem in oilfield production. The current detection methods mostly are used after casing damage, which is not very effective. With the rapid development of China's offshore oil i...The casing damage has been a big problem in oilfield production. The current detection methods mostly are used after casing damage, which is not very effective. With the rapid development of China's offshore oil industry, the number of offshore oil wells is becoming larger and larger. Because the cost of offshore oil well is very high, the casing damage will cause huge economic losses. What's more, it can also bring serious pollution to marine environment. So the effective methods of detecting casing damage are required badly. The accumulation of stress is the main reason for the casing damage. Magnetic anisotropy technique based on counter magnetostriction effect can detect the stress of casing in real time and help us to find out the hidden dangers in time. It is essential for us to prevent the casing damage from occurring. However, such technique is still in the development stage. Previous studies mostly got the relationship between stress and magnetic signals by physical experiment, and the study of physical mechanism in relative magnetic permeability connecting the stress and magnetic signals is rarely reported. The present paper uses the ANSYS to do the three-dimensional finite element numerical simulation to study how the relative magnetic permeability works for the oil casing model. We find that the quantitative relationship between the stress' s variation and magnetic induction intensity's variation is: Δδ =K* ΔB, K = 8.04×109, which is proved correct by physical experiment.展开更多
A new numerical scheme of 3rd order Weighted Essentially Non-Oscillatory (WENO) type for 2.5D mixed GLM-MHD in Cartesian coordinates is proposed. The MHD equations are modified by combining the arguments as by Dellar ...A new numerical scheme of 3rd order Weighted Essentially Non-Oscillatory (WENO) type for 2.5D mixed GLM-MHD in Cartesian coordinates is proposed. The MHD equations are modified by combining the arguments as by Dellar and Dedner et al to couple the divergence constraint with the evolution equations using a Generalized Lagrange Multiplier (GLM). Moreover, the magnetohydrodynamic part of the GLM-MHD system is still in conservation form. Meanwhile, this method is very easy to add to an existing code since the underlying MHD solver does not have to be modified. To show the validation and capacity of its application to MHD problem modelling, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems are used to verify this new MHD code. The numerical tests for 2D Orszag and Tang's MHD vortex, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems show that the third order WENO MHD solvers are robust and yield reliable results by the new mixed GLM or the mixed EGLM correction here even if it can not be shown that how the divergence errors are transported as well as damped as done for one dimensional ideal MHD by Dedner et al.展开更多
The third order accurate upwind compact difference scheme has been applied to the numerical study of the magnetic reconnection process possibly occurring near the interplanetary current sheet, under the framework of t...The third order accurate upwind compact difference scheme has been applied to the numerical study of the magnetic reconnection process possibly occurring near the interplanetary current sheet, under the framework of the two-dimensional compressible magnetohydrodynamics (MHD). Our results here show that the driven reconnection near the current sheet can occur within 10-30 min for the interplanetary high magnetic Reynolds number, RM =2 000-10 000, the stable magnetic reconnection structure can be formed in hour-order of magnitude, and there are some basic properties such as the multiple X-line reconnections, vortical velocity structures, filament current systems, splitting and collapse of the high-density plasma bulk. These results are helpful in understanding and identifying the magnetic reconnection phenomena near the interplanetary current sheets.展开更多
A class of pseudo-reconnections caused by a shifted mesh in magnetohydrodynamics(MHD) simulations is reported. In terms of this mesh system, some non-physical results may be obtained in certain circumstances, e.g. mag...A class of pseudo-reconnections caused by a shifted mesh in magnetohydrodynamics(MHD) simulations is reported. In terms of this mesh system, some non-physical results may be obtained in certain circumstances, e.g. magnetic reconnection occurs without resistivity. After comparison, another kind of mesh is strongly recommended.展开更多
The effects of geometrical characteristics of echelon coil on the magnetic pressure distribution and their contribution to the final shape of parts were focused and investigated through experiments and numerical simul...The effects of geometrical characteristics of echelon coil on the magnetic pressure distribution and their contribution to the final shape of parts were focused and investigated through experiments and numerical simulation using FEM software ANSYS. The results show that the geometrical characteristics of echelon coil play a key role in controlling the magnetic pressure acting on the tube. They show a hump-like distribution near the interface between bigger diameter region and transition region of echelon coil, and affect the final shape of tubular parts then. With the reduction of relative diameter, the magnetic pressure in smaller diameter region decreases and its distribution gradient in transition region increases. With the augment of relative length, the magnetic pressure increases in bigger diameter region, while it almost remains constant in smaller diameter region, and the gradient in transition region enhances sharply. The distribution of magnetic pressure in the axial direction of tube agrees well with the profile of specimen.展开更多
The process of magnetic reconnection in non_periodic three_layer current sheets is studied numerically by using two_dimensional magnetohydrodynamic simulation. The results show that unlike periodic current sheets, it ...The process of magnetic reconnection in non_periodic three_layer current sheets is studied numerically by using two_dimensional magnetohydrodynamic simulation. The results show that unlike periodic current sheets, it is complex unsteady magnetic reconnection. It may be important for solar flare and corona heating.展开更多
Explosive events have been observed to occur consecutively in bursts at intermittent locations along theboundary near the opposite polarity. The aim of the present paper is to explore a possible mechanism to interpret...Explosive events have been observed to occur consecutively in bursts at intermittent locations along theboundary near the opposite polarity. The aim of the present paper is to explore a possible mechanism to interpret thisburst-like characteristic of explosive events. The 2D magnetohydrodynamic (MHD) numerical simulations with resistivityhave been carried out to reproduce the intermittent spatial-temporal magnetic reconnection events taking place along thelong, compressible current sheet. The observed density enhancements in previously published results have been verifiedto be associated to magnetic reconnection sites. Late observational evidences, which support present attempts, have alsobeen found, at least in morphological evolution of the consecutive explosive events.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10221001,10333040,10403003,10620150099,10610099 and 10673004)by the Major State Basic Research Development Program (973 project 2006CB806302)
文摘Observations indicate that Ellerman bombs （EBs） and chromospheric microflares both occur in the lower solar atmosphere,and share many common features,such as temperature enhancements,accompanying jet-like mass motions,short life-time,and so on.These strongly suggest that EBs and chromospheric microflares could both probably be induced by magnetic reconnection in the lower solar atmosphere.With gravity,ionization and radiation considered,we perform two-dimensional numerical simulations of magnetic reconnection in the lower solar atmosphere.The influence of different parameters,such as intensity of the magnetic field and anomalous resistivity,on the results are investigated.Our result demonstrates that the temperature increases are mainly due to the joule dissipation caused by magnetic reconnection.The spectral profiles of EBs and chromospheric microflares are calculated with the non-LTE radiative transfer theory and compared with observations.It is found that the typical features of the two phenomena can be qualitatively reproduced.
文摘Calculation of magnetic pressure is the basis of application of electromagnetic forming (EMF). This paper carries out a numerical simulation of magnetic pressure under the influence of die by means of finite element method. The analysis model of electromagnetic bulging with die is created by using ANSYS, and the distribution of magnetic pressure acting on the tube and the die is obtained. The differences between EMF and other technologies and the effect of die on tube formability are analyzed. The die has important influence upon the calculation accuracy. The simulating conclusions with different discharge energy and current frequency are verified through the technologic tests. The distribution of magnetic pressure acting on the tube agrees well with the measurements of the deformed tube.
基金supported by the National Natural Science Foundation of China(No.41174157)
文摘The casing damage has been a big problem in oilfield production. The current detection methods mostly are used after casing damage, which is not very effective. With the rapid development of China's offshore oil industry, the number of offshore oil wells is becoming larger and larger. Because the cost of offshore oil well is very high, the casing damage will cause huge economic losses. What's more, it can also bring serious pollution to marine environment. So the effective methods of detecting casing damage are required badly. The accumulation of stress is the main reason for the casing damage. Magnetic anisotropy technique based on counter magnetostriction effect can detect the stress of casing in real time and help us to find out the hidden dangers in time. It is essential for us to prevent the casing damage from occurring. However, such technique is still in the development stage. Previous studies mostly got the relationship between stress and magnetic signals by physical experiment, and the study of physical mechanism in relative magnetic permeability connecting the stress and magnetic signals is rarely reported. The present paper uses the ANSYS to do the three-dimensional finite element numerical simulation to study how the relative magnetic permeability works for the oil casing model. We find that the quantitative relationship between the stress' s variation and magnetic induction intensity's variation is: Δδ =K* ΔB, K = 8.04×109, which is proved correct by physical experiment.
基金Supported by the National Natural Science Foundation of China (40374056, 40536029, 40574068)the International Collaboration Research Team Program of the Chinese Academy of Sciences
文摘A new numerical scheme of 3rd order Weighted Essentially Non-Oscillatory (WENO) type for 2.5D mixed GLM-MHD in Cartesian coordinates is proposed. The MHD equations are modified by combining the arguments as by Dellar and Dedner et al to couple the divergence constraint with the evolution equations using a Generalized Lagrange Multiplier (GLM). Moreover, the magnetohydrodynamic part of the GLM-MHD system is still in conservation form. Meanwhile, this method is very easy to add to an existing code since the underlying MHD solver does not have to be modified. To show the validation and capacity of its application to MHD problem modelling, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems are used to verify this new MHD code. The numerical tests for 2D Orszag and Tang's MHD vortex, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems show that the third order WENO MHD solvers are robust and yield reliable results by the new mixed GLM or the mixed EGLM correction here even if it can not be shown that how the divergence errors are transported as well as damped as done for one dimensional ideal MHD by Dedner et al.
基金the National Natural Foundation of China (Grant Nos. 49674243 and 49874040).
文摘The third order accurate upwind compact difference scheme has been applied to the numerical study of the magnetic reconnection process possibly occurring near the interplanetary current sheet, under the framework of the two-dimensional compressible magnetohydrodynamics (MHD). Our results here show that the driven reconnection near the current sheet can occur within 10-30 min for the interplanetary high magnetic Reynolds number, RM =2 000-10 000, the stable magnetic reconnection structure can be formed in hour-order of magnitude, and there are some basic properties such as the multiple X-line reconnections, vortical velocity structures, filament current systems, splitting and collapse of the high-density plasma bulk. These results are helpful in understanding and identifying the magnetic reconnection phenomena near the interplanetary current sheets.
文摘A class of pseudo-reconnections caused by a shifted mesh in magnetohydrodynamics(MHD) simulations is reported. In terms of this mesh system, some non-physical results may be obtained in certain circumstances, e.g. magnetic reconnection occurs without resistivity. After comparison, another kind of mesh is strongly recommended.
基金Sponsored by the Scientific Research Foundation of Harbin Institute of Technology (Grant No. HIT.2003.10)
文摘The effects of geometrical characteristics of echelon coil on the magnetic pressure distribution and their contribution to the final shape of parts were focused and investigated through experiments and numerical simulation using FEM software ANSYS. The results show that the geometrical characteristics of echelon coil play a key role in controlling the magnetic pressure acting on the tube. They show a hump-like distribution near the interface between bigger diameter region and transition region of echelon coil, and affect the final shape of tubular parts then. With the reduction of relative diameter, the magnetic pressure in smaller diameter region decreases and its distribution gradient in transition region increases. With the augment of relative length, the magnetic pressure increases in bigger diameter region, while it almost remains constant in smaller diameter region, and the gradient in transition region enhances sharply. The distribution of magnetic pressure in the axial direction of tube agrees well with the profile of specimen.
文摘The process of magnetic reconnection in non_periodic three_layer current sheets is studied numerically by using two_dimensional magnetohydrodynamic simulation. The results show that unlike periodic current sheets, it is complex unsteady magnetic reconnection. It may be important for solar flare and corona heating.
基金The project supported by National Natural Science Foundation of China under Grant Nos.40104006,40204010,40374056,and 40336053
文摘Explosive events have been observed to occur consecutively in bursts at intermittent locations along theboundary near the opposite polarity. The aim of the present paper is to explore a possible mechanism to interpret thisburst-like characteristic of explosive events. The 2D magnetohydrodynamic (MHD) numerical simulations with resistivityhave been carried out to reproduce the intermittent spatial-temporal magnetic reconnection events taking place along thelong, compressible current sheet. The observed density enhancements in previously published results have been verifiedto be associated to magnetic reconnection sites. Late observational evidences, which support present attempts, have alsobeen found, at least in morphological evolution of the consecutive explosive events.
