The magneto-plastic instability of a ferromagnetic beam-type plate with simple supports and small initial imperfection is analytically investigated in this paper for that the plastic deformation of the plate with a ...The magneto-plastic instability of a ferromagnetic beam-type plate with simple supports and small initial imperfection is analytically investigated in this paper for that the plastic deformation of the plate with a linear-strain hardening relation is considered when the plate is located in a strong uniformly distributed magnetic ?eld. After the distribution of magnetic ?elds related to the de?ected con?guration of plate is imaginably divided into two parts, i.e., one is related to the ?at plate and the other dependent on the perturbation of magnetic ?elds for which the plate con?guration changes from the ?at into the deformed state, the perturbation technique is employed to analyze the distribution of the perturbation magnetic ?elds in and out-of the magnetic medium of the ferromagnetic structure in a transverse magnetic ?eld, which leads to some analytical formulae/solutions for the magnetic ?elds and the resulting magnetic force exerted on the plate. Based on them, the magneto-plastic buckling and snapping of the plate in a transverse magnetic ?eld is discussed, and the critical magnetic ?eld is analytically formulated in terms of the parameters of geometry and material of the plate employed by solving the governing equation of the magneto-plastic plate in the applied magnetic ?eld. Further, the sensitivity of the initial imperfection on the magneto-plastic instability, expressed by an ampli?cation function, is obtained by solving the dynamic equation of de?ection of the plate after the inertial force in the transverse direction is taken into account. The results obtained show that the critical magnetic ?eld is sensitive to the plastic characteristic, e.g., hardening coe?cient, and the instability mode and de?ection of the plate are dependent on the geometrical imperfection as well.展开更多
Global Existence of Smooth Solutions for the Diffusion Approximation Model of General Gas in Radiation Hydrodynamics Hyejong KIM Hakho HONG Jongsung KIM Abstract In this paper,we consider the 3-D Cauchy problem for th...Global Existence of Smooth Solutions for the Diffusion Approximation Model of General Gas in Radiation Hydrodynamics Hyejong KIM Hakho HONG Jongsung KIM Abstract In this paper,we consider the 3-D Cauchy problem for the diffusion approximation model in radiation hydrodynamics.The existence and uniqueness of global solutions is proved in perturbation framework,for more general gases including ideal polytropic gas.Moreover,the optimal time decay rates are obtained for higher-order spatial derivatives of density,velocity,temperature,and radiation field.展开更多
In this paper, the mechanical responses of a thick-walled functionally graded hollow cylinder subject to a uniform magnetic field and inner-pressurized loads are studied. Rather than directly assume the material const...In this paper, the mechanical responses of a thick-walled functionally graded hollow cylinder subject to a uniform magnetic field and inner-pressurized loads are studied. Rather than directly assume the material constants as some specific function forms displayed in pre-studies, we firstly give the volume fractions of different constituents of the functionally graded material(FGM) cylinder and then determine the expressions of the material constants. With the use of the Voigt method, the corresponding analytical solutions of displacements in the radial direction, the strain and stress components, and the perturbation magnetic field vector are derived. In the numerical part, the effects of the volume fraction on the displacement, strain and stress components, and the magnetic perturbation field vector are investigated. Moreover, by some appropriate choices of the material constants, we find that the obtained results in this paper can reduce to some special cases given in the previous studies.展开更多
In the RD of the CSNS Drift Tube Linac（DTL）, the first unit tank with 28 drift tubes has been developed. The axial accelerating field is ramped from 2.2 MV/m to 3.1 MV/m in this tank. The required field flatness is ...In the RD of the CSNS Drift Tube Linac（DTL）, the first unit tank with 28 drift tubes has been developed. The axial accelerating field is ramped from 2.2 MV/m to 3.1 MV/m in this tank. The required field flatness is less than±2% with the standard deviation of 1% for the beam dynamics; the field stability should be less than 1% for machine stable operation. After successful alignment, RF tuning was carried out focusing on the field profile measurement. Four slug tuners and eleven post couplers were applied in this procedure. The ramped field and required stability had been achieved by fine adjustment of the slug tuners and post couplers. In this paper, the preliminary tuning results are presented and discussed.展开更多
There exist typically two kinds of low-level col fields over the middle and lower reaches of the Yangtze River of China during summer. ＇One is associated with the mesoscale vortex embedded in the Meiyu front; the oth...There exist typically two kinds of low-level col fields over the middle and lower reaches of the Yangtze River of China during summer. ＇One is associated with the mesoscale vortex embedded in the Meiyu front; the other is related to tropical cyclones making landfall over eastern or southern China. The first one is the focus of this study. The meso scale vortex （MβV） causing heavy rainfall usually forms in a col field or within a shear line associated with the mesoscale low-level jet （mLLJ）. The MβV, triggered by mesoscale wind perturbation in a col field, is simulated by using a three-dimensional q-coordinate mesoscale model. This col field represents the circumstance of the 98.7 heavy rainfall event over eastern Hubei Province. The results show that the MβV triggered by wind perturbation was weak and maintained only several hours if the latent heat feedback was switched off. The wind perturbation also weakened rapidly. However, when the latent heat feedback was included, precipitation became more intense and the mLLJ and MβV quickly developed. The MβV maintained quasi-stationary during its life cycle under the stable col field. The MβV triggered by the southwesterly perturbation was located closely to that by the northeasterly perturbation. They were both located in the weak wind region near the col point. The stronger the perturbation was, the more intense and longer the dynamic MβV lived. The 24-h accumulated precipitation in different experiments showed a similar pattern, which indicates that the relatively stable intensity and range of precipitation were the intrinsic characters of the stable col field. Furthermore, it is found that mesoscale perturbations had some impacts on the location and intensity of the rainfall. The fluctuation of large-scale LLJ to the south of the col field might produce a perturbation, causing instable stratification and rainfall within the low-level col field or shear line. The mLLJ near the rainfall was enhanced due to the latent heat feedback and then caused fo展开更多
An exact and a numerical solutions to the problem of a steady mixed convective MHD flow of an incompressible viscous electrically conducting fluid past an infinite vertical porous plate with combined heat and mass tra...An exact and a numerical solutions to the problem of a steady mixed convective MHD flow of an incompressible viscous electrically conducting fluid past an infinite vertical porous plate with combined heat and mass transfer are presented.A uniform magnetic field is assumed to be applied transversely to the direction of the flow with the consideration of the induced magnetic field with viscous and magnetic dissipations of energy.The porous plate is subjected to a constant suction velocity as well as a uniform mixed stream velocity.The governing equations are solved by the perturbation technique and a numerical method.The analytical expressions for the velocity field,the temperature field,the induced magnetic field,the skin-friction,and the rate of heat transfer at the plate are obtained.The numerical results are demonstrated graphically for various values of the parameters involved in the problem.The effects of the Hartmann number,the chemical reaction parameter,the magnetic Prandtl number,and the other parameters involved in the velocity field,the temperature field,the concentration field,and the induced magnetic field from the plate to the fluid are discussed.An increase in the heat source/sink or the Eckert number is found to strongly enhance the fluid velocity values.The induced magnetic field along the x-direction increases with the increase in the Hartmann number,the magnetic Prandtl number,the heat source/sink,and the viscous dissipation.It is found that the flow velocity,the fluid temperature,and the induced magnetic field decrease with the increase in the destructive chemical reaction.Applications of the study arise in the thermal plasma reactor modelling,the electromagnetic induction,the magnetohydrodynamic transport phenomena in chromatographic systems,and the magnetic field control of materials processing.展开更多
This paper studies singular optimal control problems for systems described by nonlinear-controlled stochastic differential equations of mean-field type(MFSDEs in short),in which the coefficients depend on the state of...This paper studies singular optimal control problems for systems described by nonlinear-controlled stochastic differential equations of mean-field type(MFSDEs in short),in which the coefficients depend on the state of the solution process as well as of its expected value.Moreover,the cost functional is also of mean-field type.The control variable has two components,the first being absolutely continuous and the second singular.We establish necessary as well as sufficient conditions for optimal singular stochastic control where the system evolves according to MFSDEs.These conditions of optimality differs from the classical one in the sense that here the adjoint equation turns out to be a linear mean-field backward stochastic differential equation.The proof of our result is based on convex perturbation method of a given optimal control.The control domain is assumed to be convex.A linear quadratic stochastic optimal control problem of mean-field type is discussed as an illustrated example.展开更多
Mechanical errors can not be avoided in fabrication. They will cause geometry errors and have impacts on the cavity performance. This paper systematically analyzes the impacts of mechanical errors on the RF performanc...Mechanical errors can not be avoided in fabrication. They will cause geometry errors and have impacts on the cavity performance. This paper systematically analyzes the impacts of mechanical errors on the RF performance of Peking University single spoke cavity. The various kinds of shape and size errors are considered, the influences on the resonation frequency and field flatness are studied by numerical simulation and the theoretical models are analyzed. The results show that the single spoke cavity is robust with respect to the mechanical tolerance. It also indicates the most essential factors for fabrication.展开更多
In this paper, with the application of the Delauney variables, according to the Hamilton equations, the influence on the perturbation of a satellite exerted by the gravitational force of the earth through canonical tr...In this paper, with the application of the Delauney variables, according to the Hamilton equations, the influence on the perturbation of a satellite exerted by the gravitational force of the earth through canonical transformation has been found out. As a result, the equation about how the position and velocity of the satellite vary with time is deduced.展开更多
Internal waves play a crucial role in ocean mixing, and density perturbation and energy flux are essential quantities to investigate the generation and propagation of internal waves. This paper presents a methodology ...Internal waves play a crucial role in ocean mixing, and density perturbation and energy flux are essential quantities to investigate the generation and propagation of internal waves. This paper presents a methodology for calculating density perturbation and energy flux of internal waves only using a velocity field that is based on linearized equations for internal waves. The method was tested by numerical simulations of internal waves generated by tidal flowing over a Gaussian topography in a stratified fluid. The density perturbations and energy fluxes determined using our method that only used velocity data agreed with density perturbations and energy fluxes determined by the equation of state based on temperature data. The mean relative error(MRE) and root mean square error(RMSE) between the two methods were lower than 5% and 10% respectively. In addition, an experiment was performed to exam our method using the velocity field measured by Particle Image Velocimetry(PIV), and the setup of the experiment is consistent with the numerical model. The results of the experiments calculated by the methods using PIV data were also generally equal to those of the numerical model.展开更多
基金Project supported by the National Key Basic Pre-Research Fund of the Ministry of Science and Technology of Chinathe Fund for Outstanding Young Researchers of the National Natural Sciences Foundation of China (No.10025208)+2 种基金 the KeyFund of the National Natural Science Foundation of China the Youth Fund of the National Natural Science Foundationof China (No.10302009) and the Youth Fund of Lanzhou University (Lzu200305).
文摘The magneto-plastic instability of a ferromagnetic beam-type plate with simple supports and small initial imperfection is analytically investigated in this paper for that the plastic deformation of the plate with a linear-strain hardening relation is considered when the plate is located in a strong uniformly distributed magnetic ?eld. After the distribution of magnetic ?elds related to the de?ected con?guration of plate is imaginably divided into two parts, i.e., one is related to the ?at plate and the other dependent on the perturbation of magnetic ?elds for which the plate con?guration changes from the ?at into the deformed state, the perturbation technique is employed to analyze the distribution of the perturbation magnetic ?elds in and out-of the magnetic medium of the ferromagnetic structure in a transverse magnetic ?eld, which leads to some analytical formulae/solutions for the magnetic ?elds and the resulting magnetic force exerted on the plate. Based on them, the magneto-plastic buckling and snapping of the plate in a transverse magnetic ?eld is discussed, and the critical magnetic ?eld is analytically formulated in terms of the parameters of geometry and material of the plate employed by solving the governing equation of the magneto-plastic plate in the applied magnetic ?eld. Further, the sensitivity of the initial imperfection on the magneto-plastic instability, expressed by an ampli?cation function, is obtained by solving the dynamic equation of de?ection of the plate after the inertial force in the transverse direction is taken into account. The results obtained show that the critical magnetic ?eld is sensitive to the plastic characteristic, e.g., hardening coe?cient, and the instability mode and de?ection of the plate are dependent on the geometrical imperfection as well.
文摘Global Existence of Smooth Solutions for the Diffusion Approximation Model of General Gas in Radiation Hydrodynamics Hyejong KIM Hakho HONG Jongsung KIM Abstract In this paper,we consider the 3-D Cauchy problem for the diffusion approximation model in radiation hydrodynamics.The existence and uniqueness of global solutions is proved in perturbation framework,for more general gases including ideal polytropic gas.Moreover,the optimal time decay rates are obtained for higher-order spatial derivatives of density,velocity,temperature,and radiation field.
基金supported by the National Natural Science Foundation of China(No.11772041)
文摘In this paper, the mechanical responses of a thick-walled functionally graded hollow cylinder subject to a uniform magnetic field and inner-pressurized loads are studied. Rather than directly assume the material constants as some specific function forms displayed in pre-studies, we firstly give the volume fractions of different constituents of the functionally graded material(FGM) cylinder and then determine the expressions of the material constants. With the use of the Voigt method, the corresponding analytical solutions of displacements in the radial direction, the strain and stress components, and the perturbation magnetic field vector are derived. In the numerical part, the effects of the volume fraction on the displacement, strain and stress components, and the magnetic perturbation field vector are investigated. Moreover, by some appropriate choices of the material constants, we find that the obtained results in this paper can reduce to some special cases given in the previous studies.
文摘In the RD of the CSNS Drift Tube Linac（DTL）, the first unit tank with 28 drift tubes has been developed. The axial accelerating field is ramped from 2.2 MV/m to 3.1 MV/m in this tank. The required field flatness is less than±2% with the standard deviation of 1% for the beam dynamics; the field stability should be less than 1% for machine stable operation. After successful alignment, RF tuning was carried out focusing on the field profile measurement. Four slug tuners and eleven post couplers were applied in this procedure. The ramped field and required stability had been achieved by fine adjustment of the slug tuners and post couplers. In this paper, the preliminary tuning results are presented and discussed.
基金Supported by the China Meteorological Administration Special Public Welfare Research Fund (GYHY200906011)the National Natural Science Foundation of China (40921160382 and 40905021)
文摘There exist typically two kinds of low-level col fields over the middle and lower reaches of the Yangtze River of China during summer. ＇One is associated with the mesoscale vortex embedded in the Meiyu front; the other is related to tropical cyclones making landfall over eastern or southern China. The first one is the focus of this study. The meso scale vortex （MβV） causing heavy rainfall usually forms in a col field or within a shear line associated with the mesoscale low-level jet （mLLJ）. The MβV, triggered by mesoscale wind perturbation in a col field, is simulated by using a three-dimensional q-coordinate mesoscale model. This col field represents the circumstance of the 98.7 heavy rainfall event over eastern Hubei Province. The results show that the MβV triggered by wind perturbation was weak and maintained only several hours if the latent heat feedback was switched off. The wind perturbation also weakened rapidly. However, when the latent heat feedback was included, precipitation became more intense and the mLLJ and MβV quickly developed. The MβV maintained quasi-stationary during its life cycle under the stable col field. The MβV triggered by the southwesterly perturbation was located closely to that by the northeasterly perturbation. They were both located in the weak wind region near the col point. The stronger the perturbation was, the more intense and longer the dynamic MβV lived. The 24-h accumulated precipitation in different experiments showed a similar pattern, which indicates that the relatively stable intensity and range of precipitation were the intrinsic characters of the stable col field. Furthermore, it is found that mesoscale perturbations had some impacts on the location and intensity of the rainfall. The fluctuation of large-scale LLJ to the south of the col field might produce a perturbation, causing instable stratification and rainfall within the low-level col field or shear line. The mLLJ near the rainfall was enhanced due to the latent heat feedback and then caused fo
文摘An exact and a numerical solutions to the problem of a steady mixed convective MHD flow of an incompressible viscous electrically conducting fluid past an infinite vertical porous plate with combined heat and mass transfer are presented.A uniform magnetic field is assumed to be applied transversely to the direction of the flow with the consideration of the induced magnetic field with viscous and magnetic dissipations of energy.The porous plate is subjected to a constant suction velocity as well as a uniform mixed stream velocity.The governing equations are solved by the perturbation technique and a numerical method.The analytical expressions for the velocity field,the temperature field,the induced magnetic field,the skin-friction,and the rate of heat transfer at the plate are obtained.The numerical results are demonstrated graphically for various values of the parameters involved in the problem.The effects of the Hartmann number,the chemical reaction parameter,the magnetic Prandtl number,and the other parameters involved in the velocity field,the temperature field,the concentration field,and the induced magnetic field from the plate to the fluid are discussed.An increase in the heat source/sink or the Eckert number is found to strongly enhance the fluid velocity values.The induced magnetic field along the x-direction increases with the increase in the Hartmann number,the magnetic Prandtl number,the heat source/sink,and the viscous dissipation.It is found that the flow velocity,the fluid temperature,and the induced magnetic field decrease with the increase in the destructive chemical reaction.Applications of the study arise in the thermal plasma reactor modelling,the electromagnetic induction,the magnetohydrodynamic transport phenomena in chromatographic systems,and the magnetic field control of materials processing.
基金The authorwould like to thank the editor,the associate editor,and anonymous referees for their constructive corrections and valuable suggestions that improved the manuscript.The author was partially supported by Algerian PNR Project Grant 08/u07/857,ATRST-(ANDRU)2011-2013.
文摘This paper studies singular optimal control problems for systems described by nonlinear-controlled stochastic differential equations of mean-field type(MFSDEs in short),in which the coefficients depend on the state of the solution process as well as of its expected value.Moreover,the cost functional is also of mean-field type.The control variable has two components,the first being absolutely continuous and the second singular.We establish necessary as well as sufficient conditions for optimal singular stochastic control where the system evolves according to MFSDEs.These conditions of optimality differs from the classical one in the sense that here the adjoint equation turns out to be a linear mean-field backward stochastic differential equation.The proof of our result is based on convex perturbation method of a given optimal control.The control domain is assumed to be convex.A linear quadratic stochastic optimal control problem of mean-field type is discussed as an illustrated example.
文摘Mechanical errors can not be avoided in fabrication. They will cause geometry errors and have impacts on the cavity performance. This paper systematically analyzes the impacts of mechanical errors on the RF performance of Peking University single spoke cavity. The various kinds of shape and size errors are considered, the influences on the resonation frequency and field flatness are studied by numerical simulation and the theoretical models are analyzed. The results show that the single spoke cavity is robust with respect to the mechanical tolerance. It also indicates the most essential factors for fabrication.
文摘In this paper, with the application of the Delauney variables, according to the Hamilton equations, the influence on the perturbation of a satellite exerted by the gravitational force of the earth through canonical transformation has been found out. As a result, the equation about how the position and velocity of the satellite vary with time is deduced.
基金supported by the National Key Research and Development Program of China (No. 2017YFA0604103)the Natural Science Foundation of China (NSFC) (No. 41476001)
文摘Internal waves play a crucial role in ocean mixing, and density perturbation and energy flux are essential quantities to investigate the generation and propagation of internal waves. This paper presents a methodology for calculating density perturbation and energy flux of internal waves only using a velocity field that is based on linearized equations for internal waves. The method was tested by numerical simulations of internal waves generated by tidal flowing over a Gaussian topography in a stratified fluid. The density perturbations and energy fluxes determined using our method that only used velocity data agreed with density perturbations and energy fluxes determined by the equation of state based on temperature data. The mean relative error(MRE) and root mean square error(RMSE) between the two methods were lower than 5% and 10% respectively. In addition, an experiment was performed to exam our method using the velocity field measured by Particle Image Velocimetry(PIV), and the setup of the experiment is consistent with the numerical model. The results of the experiments calculated by the methods using PIV data were also generally equal to those of the numerical model.
