Coupled Numerical Simulation of Electromagnetic and Flow Fields in a Magnetohydrodynamic Induction Pump

Magnetohydrodynamic(MHD)induction pumps are contactless pumps able to withstand harsh environments.The rate of fluid flow through the pump directly affects the efficiency and stability of the device.To explore the influence of induction pump settings on the related delivery speed,in this study,a numerical model for coupled electromagnetic and flow field effects is introduced and used to simulate liquid metal lithium flow in the induction pump.The effects of current intensity,frequency,coil turns and coil winding size on the velocity of the working fluid are analyzed.It is shown that the first three parameters have a significant impact,while changes in the coil turns have a negligible influence.The maximum increase in working fluid velocity within the pump for the parameter combination investigated in this paper is approximately 618%.As the frequency is increased from 20 to 60 Hz,the maximum increase in the mean flow rate of the working fluid is approximately 241%.These research findings are intended to support the design and optimization of these devices.

An internal ballistic model of electromagnetic railgun based on PFN coupled with multi-physical field and experimental validation

To accelerate the practicality of electromagnetic railguns,it is necessary to use a combination of threedimensional numerical simulation and experiments to study the mechanism of bore damage.In this paper,a three-dimensional numerical model of the augmented railgun with four parallel unconventional rails is introduced to simulate the internal ballistic process and realize the multi-physics field coupling calculation of the rail gun,and a test experiment of a medium-caliber electromagnetic launcher powered by pulse formation network(PFN)is carried out.Various test methods such as spectrometer,fiber grating and high-speed camera are used to test several parameters such as muzzle initial velocity,transient magnetic field strength and stress-strain of rail.Combining the simulation results and experimental data,the damage condition of the contact surface is analyzed.

Research on heat dissipation characteristics of magnetic fluid bearings under multiple field coupling effects

This paper analyzes the sources of heat losses in magnetic fluid bearings,proposes various cou-pling relationships of physical fields,divides the coupled heat transfer surfaces while ensuring the continuity of heat flux density,and analyzes the overall heat dissipation pathways of the bearings.By changing parameters such as input current,rotor speed,and inlet oil flow rate,the study applies a multi-physics field coupling method to investigate the influence of different parameters on the temper-ature field and heat dissipation patterns of the bearings,which is then validated through experi-ments.This research provides a theoretical basis for the optimal design of magnetic fluid bearing sys-tems.

Transient multi-physics behavior of an insert high temperature superconducting no-insulation coil in hybrid superconducting magnets with inductive coupling

A transient multi-physics model incorporated with an electromagneto-thermomechanical coupling is developed to capture the multi-field behavior of a single-pancake(SP)insert no-insulation(NI)coil in a hybrid magnet during the charging and discharging processes.The coupled problem is resolved by means of the finite element method(FEM)for the magneto-thermo-elastic behaviors and the Runge-Kutta method for the transient responses of the electrical circuits of the hybrid superconducting magnet system.The results reveal that the transient multi-physics responses of the insert NI coil primarily depend on the charging/discharging procedure of the hybrid magnet.Moreover,a reverse azimuthal current and a compressive hoop stress are induced in the insert NI coil during the charging process,while a forward azimuthal current and a tensile hoop stress are observed during the discharging process.The induced voltages in the insert NI coil can drive the currents flowing across the radial turns where the contact resistance exists.Therefore,it brings forth significant Joule heat,causing a temperature rise and a uniform distribution of this heat in the coil turns.Accordingly,a thermally/mechanically unstable or quenching event may be encountered when a high operating current is flowing in the insert NI coil.It is numerically predicted that a quick charging will induce a compressive hoop stress which may bring a risk of buckling instability in the coil,while a discharging will not.The simulations provide an insight of hybrid superconducting magnets under transient start-up or shutdown phases which are inevitably encountered in practical applications.

Numerical simulation and experimental validation of multiphysics field coupling mechanisms for a high power ICP wind tunnel

We take the established inductively coupled plasma(ICP) wind tunnel as a research object to investigate the thermal protection system of re-entry vehicles. A 1.2-MW high power ICP wind tunnel is studied through numerical simulation and experimental validation. The distribution characteristics and interaction mechanism of the flow field and electromagnetic field of the ICP wind tunnel are investigated using the multi-field coupling method of flow, electromagnetic, chemical, and thermodynamic field. The accuracy of the numerical simulation is validated by comparing the experimental results with the simulation results. Thereafter, the wind tunnel pressure, air velocity, electron density, Joule heating rate, Lorentz force, and electric field intensity obtained using the simulation are analyzed and discussed. The results indicate that for the 1.2-MW ICP wind tunnel, the maximum values of temperature, pressure, electron number density, and other parameters are observed during coil heating. The influence of the radial Lorentz force on the momentum transfer is stronger than that of the axial Lorentz force. The electron number density at the central axis and the amplitude and position of the Joule heating rate are affected by the radial Lorentz force. Moreover, the plasma in the wind tunnel is constantly in the subsonic flow state, and a strong eddy flow is easily generated at the inlet of the wind tunnel.

COUPLED SIMULATION OF 3D ELECTRO-MAGNETO-FLOW FIELD IN HALL-HEROULT CELLS USING FINITE ELEMENT METHOD

Two full 3D steady mathematical models are developed by finite element method （FEM） to calcalate coupled physics fields. the electro-magnetic model is built and solved first and so is the fluid motion model with the acquired electromagnetic force as source body forces in Navier-Stokes equations. Effects caused by the ferromagnetic shell, busbar system around, and open boundary problem as well as inside induced current were considered in terms of the magnetic field. Furthermore, a new modeling method is found to set up solid models and then mesh them entirely with so-called structuralized grids, namely hex-mesh. Examples of 75kA prebaked cell with two kinds of busbar arrangements are presented. Results agree with those disclosed in the literature and confirm that the coupled simulation is valid. It is also concluded that the usage of these models facilitates the consistent analysis of the electric field to magnetic field and then flow motion to the greater extent, local distributions of current density and magnetic flux density are very much dependent on the cell structure, the steel shell is a shield to reduce the magnetic field and flow pattern is two dimensional in the main body of the metal pad.

Simulation study on electron heating characteristics in magnetic enhancement capacitively coupled plasmas with a longitudinal magnetic field

The electron heating characteristics of magnetic enhancement capacitively coupled argon plasmas in presence of both longitudinal and transverse uniform magnetic field have been explored through both theoretical and numerical calculations.It is found that the longitudinal magnetic field can affect the heating by changing the level of the pressure heating along the longitudinal direction and that of the Ohmic heating along the direction which is perpendicular to both driving electric field and the applied transverse magnetic field,and a continuously increased longitudinal magnetic field can induce pressure heating to become dominant.Moreover,the electron temperature as well as proportion of some low energy electrons will increase if a small longitudinal magnetic field is introduced,which is attributed to the increased average electron energy.We believe that the research will provide guidance for optimizing the magnetic field configuration of some discharge systems having both transverse and longitudinal magnetic field.

Research on Simulation Methods of Electric Field Intensity on Surface of 10 kV Cable Joint

The electric field intensity (EFI) is important characteristic quantity for evaluating the internal insulation state of cable joints. Based on finite element method, this paper proposes two EFI research methods, field-circuit coupling method and equivalent circuit method. The average EFI of the inner surface of the outer semi-conducting shield can be calculated from the current in the measuring circuit. The relative error between these two methods is about 15%, which roughly proves the consistency of the two methods. Further practical application research enables online monitoring of cable joints.

Numerical simulation of temperature distribution of deep field in temperature mine

In order to study the temperature distribution of deep field,mathematical mod- els of temperature field in field and surrounding rock were built based on heat transfer and seepage theory.Combined test data with mathematical model,the temperature distribution under heat-transfer and underground-water coupling was studied by using Golden Soft- ware Surfer and Matlab.The results show that distribution law of most isothermal lines is very similar in deep field,and temperature gradient is equal in general.At the same time, temperature distribution is influenced by underground-water and fault.In surrounding rock, seepage changes symmetrical distribution of temperature field and vector,and the tem- perature field may divide into inward-diffusion area and outward-diffusion area.Peripheral temperature of working will approach to the temperature of airflow.In inward diffusion area the distribution of temperature and temperature vector is symmetric,and the direction of temperature vector point to the center of working.The action of airflow is stronger than seepage in inward diffusion area,however,the case opposite is true in outward diffusion area.

NUMERICAL SIMULATION OF CASTING PROCESS

In this paper, the development status of casting numerical simulation technology is introduced. In additional, mathematical model, solution method, initial condition, boundary condition and defect predicting scheme of foundry process are also analyzed, which include the mold filling process, solidification process and the process coupling fluid flow with heat transfer. Finally, a practical casting is taken out to show how to predict defects and optimize foundry process with numerical simulation technology.

NUMERICAL SIMULATION OF MOLTEN POOL AND CONTROL STRATEGY OF KISS POINT IN A TWIN-ROLL STRIP CASTING PROCESS

Coupled turbulent flow, temperature fields of the twin-roll casting strip process were simulated by three-dimensional finite element method. Based on the heat balance calculation and using inverse methods between the simulations and real experiments, the relational models among casting speed, location, and coefficient of heat transfer between molten metal and rolls in different regions are given. In the simulation, the calculated surface temperatures are in good agreement with the measured values. An on-line model of kiss point is derived by simulations and the geometry of molten pool, corresponding control strategy is also proposed.

Multi-physical field coupling simulation of TCVI process for preparing carbon/carbon composites

To prepare Carbon/Carbon (C/C) composites with advanced performance, the thermal gradient chemical vapor infiltration (TCVI) process has been optimized by simulation. A 2D axisymmetric unstable model was built, which included convection, conduction, diffusion, densification reactions in the pores and the evolution of the porous medium. The multi-physical field coupling model was solved by finite element method (FEM) and iterative calculation. The time evolution of the fluid, temperature and preform density field were obtained by the calculation. It is indicated that convection strongly affects the temperature field. For the preform of carbon/carbon composites infiltrated for 100 h by TCVI, the radial average densities from simulation agrees well with those from experiment. The model is validated to be reliable and the simulation has capability of forecasting the process.

FEM Simulation on Artificial Freezing of Seepage Ground

The coupling mechanism in freezing process of seepage ground was studied and a simplified coupling math model was proposed. The nonlinear and coupling problems of PDEs were well solved using the exponential function, error function and normal distribution function, and a series of FEM equations of coupled fields of temperature and seepage were deduced and put forward. With the example of shaft ground freezing, the formation of freezing wall in seepage ground was simulated.

Simulation Monitoring for Rainfall Infiltration in Soil Based on High Density Electrical Method

Rainfall infiltration is a porous medium flow problem with variable saturation. Based on the theoretical analysis of the flow field, electrical conductivity of rocks, the electrical field, the paper simulates the coupling relationship between the water saturation in soil and the apparent resistivity distribution. It combines the Richards equation, the Archie formula and the Laplace equation. The experiment simulates the potential field data by the Wenner setting in electrical exploration on a two-layer geologic model with continuous rainfall during 5 days, which shows that the effective saturation in soil is increasing with the rainfall time, while the apparent resistivity is decreasing. This can provide a theoretical basis for the analyzing the rainfall infiltration and porosity of the soil by using high-density electrical method in the future.

Numerical analysis for permafrost temperature field in the short term of permafrost subgrade filling

Purpose-It is of great significance to study the influence of subgrade filling on permafrost temperature field in permafrost area for the smooth construction and safe operation of railway.Design/methodology/approach-The paper builds up the model for the hydrothermal coupling calculation of permafrost using finite element software COMSOL to study how permafrost temperature field changes in the short term after subgrade filling,on which basis it proposes the method of calculation for the concave distortion of freezing front in the subgrade-covered area.Findings-The results show that the freezing front below the subgrade center sinks due to the thermal effect of subgrade filling,which will trigger hydrothermal erosion in case of sufficient moisture inflows,leading to the thawing settlement or the cracking of the subgrade,etc.The heat output of soil will be hindered the most in case of July filling,in which case the sinking and the distortion of the freezing front is found to be the most severe,which the recovery of the permafrost temperature field,the slowest,constituting the most unfavorable working condition.The concave distortion of the freezing front in the subgrade area increases with the increase in temperature difference between the filler and ground surface,the subgrade height,the subgrade width and the volumetric thermal capacity of filler,while decreases with the increase of the thermal conductivity of filler.Therefore,the filler chose for engineering project shall be of small volumetric thermal capacity,low initial temperature and high thermal conductivity whenever possible.Originality/value-The concave distortion of the freezing front under different working conditions at different times after filling can be calculated using the method proposed.

基于自抗扰的永磁同步电机附加谐波损耗抑制方法

针对永磁同步电机在变频器供电时,由时间电流谐波所引起的附加谐波损耗过大及难以在电机初始设计时被考虑到的问题,采用场路耦合联合仿真模型来计算电机的附加谐波损耗,并以4台现有的表贴式永磁同步电机为例,通过实验验证了场路耦合联合仿真模型的有效性,为电机设计之初附加谐波损耗的选取,以及后续温升的计算提供了前期计算的方法。同时提出一种基于自抗扰技术的附加谐波损耗抑制方法,设计一种适用于永磁同步电机矢量控制的自抗扰控制器,并从理论上验证了自抗扰控制器对于时间电流谐波的抑制作用,以及针对自抗扰控制器参数众多调参困难的问题,给出一种参数整定方案。最后通过引入所设计的自抗扰控制器,对电机的时间电流谐波进行计算和分析,使电机的附加谐波损耗降低了68.1%,为同类型电机的附加谐波损耗抑制提供了一种有效的方法。

渗流作用下粗粒土冻结壁交圈规律及预测模型探索

由于渗流作用下的冻结壁发育规律不明等原因,部分冻结法施工工程依靠人工经验,缺乏科学的预测模型,与精准化设计和控制还有很长的距离。为探索渗流作用下冻结法施工中粗粒土层冻结壁的演化规律,本文首先建立冻结法施工数值模型,并通过室内模型试验反演验证所建立模型的有效性和适用性。之后,考虑渗流速度、冻结管间距、环境温度、含水率和导热系数等五个因素,开展冻结壁形成正交数值试验,确定冻结壁交圈时间和厚度的主控因素。最后,通过数值模拟研究主控因素作用下冻结壁的发育和演化规律。基于结果建立临界流速、冻结壁厚度、冻结壁交圈时间的预测模型,给出冻结法施工参数的选择方案。结果表明,建立的冻土水热相变耦合模型可有效模拟渗流条件下土体冻结过程,能够满足冻结壁发育过程计算分析的需要。基于正交数值试验结果发现,渗流速度对冻结壁厚度和交圈时间的贡献百分比分别为78%和52%,是影响冻结壁能否交圈和最终厚度的主控因素。当渗流速度超过一定阈值时,冻结壁无法交圈。本文将这一阈值定义为冻结法施工中的临界流速。当冻结壁能够交圈,其最终形成的冻结壁厚度也主要由渗流速度决定,二者呈负指数函数关系。冻结管间距对冻结壁最终厚度影响不大,但是对冻结壁交圈时间影响较大,它们之间存在负指数函数关系。本文给出了0~6 m·d^(-1)条件下的临界流速、冻结壁厚度、冻结壁交圈时间计算模型,它们可为粗粒土地层的冻结法施工参数选择和施工工艺设计提供理论指导。

高压陶瓷电容特性及在配网柱上开关的应用研究

电压传感器是深度融合型柱上开关的关键器件,其自身直接承受电压载荷,是深度融合柱上开关产品开发成败的关键。以无机物介质为载体的高压陶瓷电容器,具有体积小、容量大、寿命长的特点,尤其契合深度融合型固封极柱的结构特点和应用场景。文中首先分析了陶瓷电容器件特性,再结合深度融合柱上开关产品的具体应用场景,开发了基于高压陶瓷电容器的一二次融合柱上开关产品;相关研究表明,高压陶瓷电容器在配网领域应用具有相当潜力。

超深层裂缝性致密砂岩气藏多尺度耦合流动数值模拟

塔里木盆地克拉苏气田白垩系气藏是罕见的超深层裂缝性致密砂岩气藏,该类气藏的储渗空间具有显著的多尺度特征,基质与多尺度裂缝、断层介质的渗透率级差相差5~6个数量级,常规渗流理论难以准确描述其流动规律和开发机理。为此,基于单裂缝流动物理实验结果及流体力学理论,结合多尺度裂缝几何信息,应用均化理论和体积平均尺度升级方法,将多尺度介质划分为5个流动系统,建立了考虑介质间的非稳态窜流多尺度耦合流动数学模型,并应用有限体积法对耦合流动模型进行了数值求解和数值试井分析。研究结果表明:(1)不同尺度裂缝中具有不同的流动特征,随缝宽增加流速加快,流动模态发生变化;(2)多尺度耦合流动模型与双重介质模型结果存在较大差异,导数曲线具有不同趋势特征;(3)应用所建立的多尺度耦合流动模型成功解释了气藏实际试井数据,模型能够反映实际地层中的流动过程。结论认为,超深层裂缝性致密砂岩气藏多尺度耦合流动模型揭示了多尺度裂缝以及致密基质间逐级动用、协同供气的开发机理,可为类似气藏制订合理开发技术政策及气藏提高采收率提供理论和技术支撑。

断块油藏注采耦合提高采收率机理及矿场实践

针对渤海湾盆地济阳坳陷东营凹陷古近系断块油藏水驱开发后期流线固定导致注入水无效循环的问题,基于渗流力学和油藏工程原理,通过室内物模模拟和油藏数值模拟,提出了“细分开发层系、轮注轮采”的注采耦合开发调整技术,并验证了该技术可提高采收率的原理。研究结果表明:(1)利用注采耦合开发技术建立的“注入期间的高渗通道与低渗通道吸水量比模型”和“采油期间主流线和非主流线产油量比模型”均揭示了“改变压力场促进渗流场调整,实现均匀注入和均匀采出,扩大水驱波及系数和增加驱油效率”的注采耦合渗流力学机制。(2)注采耦合技术可以实现“扩大波及系数、增加驱油效率”,起到类似“调剖”的作用,高含水期通过此项技术可将低渗透岩心的分流率由1.0%提到18.6%,模型驱替更均衡;经过2个轮次的注采耦合调整,高、低渗透岩心的原油采收率分别提高了10.3%和16.1%。(3)研究区D断块古近系沙河街组沙二段Es236含油小层油藏注采耦合开发数值模拟结果显示,主流线和非主流线驱替更均匀,两者压力梯度极差由2.3下降至1.4。经过3个轮次注采耦合开发调整,沙二段3—6砂层组油藏平均综合含水率下降了3.2%,累计增油1 760 t,提高原油采收率2.1%,增油降水效果显著。