Coupled Field Model Research Articles

Study on the Formation of the Crater and Modified Layer in EDM Titanium Alloys Based on Fluid–Solid Coupled Temperature Field Model

Study on the Formation of the Crater and Modified Layer in EDM Titanium Alloys Based on Fluid–Solid Coupled Temperature Field Model

Partial-inductance retarded partial coefficients: Their exact computation based on the Cagniard–DeHoop technique

The Partial Element Equivalent Circuit (PEEC) method is a well recognized integral-equation (IE) technique to solve Maxwell’s equations. Similarly to the method of moments (MoM), the electromagnetic (EM) interactions between currents and between charges are described in terms of integrals. In contrast to the standard MoM, the PEEC method keeps the electric and magnetic coupling phenomena separate, which leads to different interaction integrals to be computed. These integrals admit simplified solutions for the case of the static free-space Green’s function and orthogonal geometries but their applicability is limited to electrically small problems only. When the full-wave free-space Green’s function is considered, the integrals are typically computed in the frequency domain (FD) by resorting to Gaussian quadrature schemes. The accuracy and efficiency of such schemes is a delicate issue. Therefore, recent works have investigated the possibility of applying the Cagniard–DeHoop (CdH) technique to calculate the interaction integrals for zero-thickness elementary domains. In this paper, we close the loop and shall apply the CdH technique to calculate the partial-inductance between two elementary bricks as prescribed by the PEEC technique exactly in the time domain (TD). The analytical approach is demonstrated on the interaction between two bricks as it occurs in the modeling of the magnetic field coupling between volumetric currents. The accuracy of the proposed approach is (successfully) tested for two representative cases.

Calculation and analysis the dynamic breakdown characteristic of SF6 discharge caused by GIS disconnector operation

In order to accurately calculate the very fast transient overvoltage(VFTO), it is very important and necessary to carry out the study on breakdown characteristic of SF6 gas discharge and get the expression of critical breakdown voltage during GIS disconnector operation. Therefore, a study of dynamic breakdown characteristic of SF6 discharge caused by GIS disconnector operation is conducted. For gas discharge modeling, considering the micro discharge process will lead to the problems of complex modeling and difficult solution. A new method which can avoid the problems of complex modeling and solution is proposed in this paper. Researches have revealed that there is a certain relationship between the critical electric field breakdown strength and the gas density. Thus, the solution of dielectric strength is transformed into the solution of gas density. Then a 3D multiple physical field coupling model of disconnector operation to solve the gas density is established. The dynamic meshing technology is applied to solve the problem of dynamic description contact moving. And then linear regression fitting method is used to obtain the expression of dynamic breakdown voltage of SF6 gas discharge. After checking the quality of fitting function by index F, P and R2, the SF6 gas breakdown voltage expression with the characteristic of dynamic variation under different operation conditions are obtained successfully.

Melting Distribution of Armature in Electromagnetic Rail Launcher

This article established a 3-D transient melting calculation model of the electromagnetic rail launcher (EMRL), considering the combined effects of electromagnetic fields, structural fields, heat transfer, and armature motion. To verify the accuracy of the multiphysics field coupling model, an experiment platform of EMRL that is capable of retrieving the launched armature is set up. Compared with the armature surface profiles obtained from the experiment, the simulation model describes the locations of deeper melting accurately but is not precise enough for the shallower melting. Through analyzing the evolution of the melting region, it is found that the deepest crater forms at the point where the armature begins to melt. Analysis of the heat sources shows that contact resistance heat and body heat are two critical factors in the process of armature melting. Despite the high power of the frictional heat, there is no melting in the region where it exists. It is proven that the proposed model can predict the melting performance of the armature.

Подходы к геомиграционному моделированию при оценке безопасности пункта захоронения РАО в расчетном комплексе GeRa

The study focuses on the safety assessment of near-surface radioactive waste disposal facilities (NSDF) based on the numerical simulation of radionuclide transport in the near field via groundwater flow and mass transport processes using the GeRa software. It also evaluates the methods that may provide near and far field model coupling seeking to arrange a sound safety assessment process. The study specifically focuses on the degradation of the underlying concrete safety barrier indicated through a reduced radionuclide absorption capacity. The study provides calculations for those radionuclides that are typically found in the radioactive waste subject to disposal in deep disposal facilities. The findings evidence some fundamental difference in the activity-yield curves associated with the sorption properties, changes in the barrier properties and the half-lifes of the modelled radionuclides.

Numerical study on power battery thermal management system based on heat pipe technology

In the present work, a power battery pack and a novel thermal management system (TMS) based on the tubular heat pipe (THP) technology are designed according to the parameters of a pure electric light truck and battery. The TMS consists of THPs, power batteries, cooling plates, fins, and equivalent thermal conductivity is used to characterize the excellent thermal conductivity of THP. The heat generation rate of the battery at different discharge rates is obtained by establishing a multi-scale electrochemical–thermal coupling model, which accuracy is verified by the experiment. A multi-physics field coupling model is built to the thermal management system designed for the study. The results show that the battery temperature is higher when the battery is far from the THP in the cooling plate, and the maximum temperature reaches 35.6 °C at 1 C. Furthermore, the temperature difference between batteries is proportional to the discharge rate, and the maximum temperature difference reaches 7 °C at 2 C. The change in inlet temperature and wind speed can only restrain the temperature rise, while the temperature difference of the battery module is always 3.2 °C. When a fin spacing of 3 mm is chosen, the best temperature uniformity of the battery module is achieved at this time. The use of the multi-scale multi-physics field coupling analysis method in BTMS with heat pipes can be used as a reference for future numerical simulations of the same type.

A Prediction Model Based on Artificial Neural Network for E1 HEMP Coupling With Distribution Power Lines

Some electromagnetic pulses, such as the high-altitude electromagnetic pulse (HEMP), can couple with power lines in the range of thousands of kilometers. Conventional numerical methods cannot efficiently predict the voltage induced by the early-time (E1) HEMP on the power lines in a large area. This paper presents an efficient model based on an artificial neural network (ANN) which can predict the coupled voltage induced by the E1 HEMP on distribution power lines quickly. Based on Agrawal's model of the electromagnetic field coupling with transmission lines, the important parameters which affect the coupled voltages of distribution power lines are analyzed firstly. The Baum-Liu-Tesche equation and inverse Fourier transform is applied to compute the voltage magnitude when the elevation angle, azimuth angle, and the polarization angle of the E1 HEMP change and more than twenty thousand numerical results are obtained. Then an ANN is developed and trained by the numerical results. Once the ANN is trained, the prediction time is on the order of milliseconds. The results show that the proposed model based on the ANN can provide accurate prediction results for the E1 HEMP coupling with power lines at different observation points.

An Efficient Model of High-Frequency Electromagnetic Field Coupling to Multiconductor Transmission Lines With the Presence of the Lossy Ground

The modeling of the high-frequency electromagnetic field coupling to multiconductor transmission lines (MTLs) is the essential subject for the protection of power lines. When the wavelength of the electromagnetic wave is smaller than the cross sections between MTLs, the response of MTLs cannot be evaluated by the classical transmission line approximation. Even though the full-wave method can deal with this problem, it is time consuming to evaluate the response of long MTLs. This article presents a theory and an efficient method to solve the problem of the high-frequency electromagnetic field coupling to MTLs with the presence of the lossy ground. The asymptotic method, adopted for its high computational efficiency, is extended to obtain the solutions of MTLs above the lossy ground. The problem is solved semianalytically using the proposed method, which is much more computationally efficient in dealing with long MTLs. Several numerical examples are presented to validate the accuracy and efficiency of the proposed method.

Design and Performance Analysis of a Double-Outlet-Rod Magnetorheological Damper for Impact Load

In order to improve the performance of magnetorheological dampers under impact load, a double-rod magnetorheological damper is designed in this paper, and its multi-physical field coupling model is established. The performance of a double-rod magnetorheological damper under impact conditions is characterized from the aspects of viscosity, velocity, peak pressure, impact energy consumption and viscous damping force ratio. The research contents include: a comparison of dynamic characteristics such as the viscosity, velocity and pressure of the magnetorheological damper under impact conditions and low-speed vibration; the influence of temperature on the mechanical performance parameters of the magnetorheological damper, such as peak pressure, impact energy dissipation and viscous damping force ratio, under impact load; and the establishment of a peak sensitivity function to study the influence of three key structural parameters on the magnetic flux density and impact energy dissipation at the damper damping channel. On the basis of the above theoretical research, an impact test of the processed double-rod magnetorheological damper prototype under different excitation currents is carried out. The results show that the viscosity distribution of the damping channel activation region (i.e., the region where the magnetorheological effect occurs after energization) of the magnetorheological damper under impact is disordered, the region of the structural flow in the semi-solid state is small and the influence of the Coulomb damping force is greatly weakened. When the current is 0.5 A, the viscous damping force accounts for 91.2%, and the viscous damping force plays a major role in buffering energy absorption. With an increase in working temperature, the effect of the Coulomb damping force decreases, and the peak pressure and impact energy consumption of the MR damper decrease greatly. With increasing excitation current, this reduction is further increased. The influence of gap height, piston diameter and effective length on magnetic flux density and impact energy dissipation is determined via the peak sensitivity function. When the change in the structural parameters ∆α is 30%, the change in the piston diameter has the greatest influence on the peak sensitivity of the magnetic flux density, and the peak sensitivity index of the magnetic flux density reaches 25%. The change in clearance height has the greatest influence on the impact energy consumption, and the peak sensitivity index of the impact energy consumption reaches 115%. This shows that the magnetic flux density is most affected by the piston diameter, and the impact energy consumption is most affected by the clearance height. The test results show that the test pressure peak-change curve is consistent with the simulation pressure peak-change curve, and the pressure peak error between the two is within 10%.

The electrodynamics of rod-like microparticles based on optically induced dielectrophoresis.

Due to its characteristics of noncontact, non-damage, high flux, and easy-to-achieve flexible manipulation, optically induced dielectrophoresis (ODEP) technology has been employed to manipulate microspherical biological particles, including separation, enrichment, capture, arrangement, and fusion. However, in nature, biomolecules are morphologically diverse, and some of them are rodlike. In order to illustrate the electrodynamics of rodlike particles under the action of ODEP, a transient multi-physical field coupling model of ODEP chip under the hypothesis of electrical double layer thin layer was established in this paper. The arbitrary Lagrangian-Eulerian method is used to track single-rod particle in the strong coupled flow field and electric field simultaneously. The influence of several key factors, including the applied alternating current (AC) electric voltage, the width of optical bright area, and the initial position of particle, on the trajectory of particle center was analyzed in positive dielectrophoresis (DEP) action and negative DEP action, respectively. Especially, the planar motion process of rodlike particles was discussed together. The research results reveal the electrodynamics behavior of rodlike particles based on the action of ODEP, which may provide theoretical support for the further design of rodlike biological cells manipulation chip based on AC ODEP technology in the future.

Research on Multi-physics Field Coupling Dynamic Process in Forward Flow Electrochemical Trepanning Blades

In this work, a multi-physics field coupling model based on electric field, gas-liquid two-phase flow field and temperature field of the forward flow electrochemical trepanning (FFECT) blades was established, and the distribution law of hydrogen bubble volume fraction, electrolyte temperature and electrolyte conductivity in machining gap was obtained. Based on the simulation results, the time-varying process of electrolyte flow velocity distribution was divided into three stages according to the change in machining gap corresponding to different blade machining heights H, and the effects of the machining voltage U and the cathode feed rate v on the side gap Δ s and the end gap Δ e were investigated. The simulation analysis and experimental results show that both side gap and end gap increase as machining voltage increases while decrease with the increase in cathode feed rate. The model predictions are in good agreement with the experimental results, and the maximum errors of side gap and end gap are 10.6% and 17.7% respectively. In addition, the effects of machining voltage and cathode feed rate on the surface quality were studied experimentally. Results reveal that surface roughness can be reduced by appropriately decreasing the machining voltage and increasing the cathode feed rate.

Temperature damage regularity of granite based on micro-inhomogeneity

Enhanced geothermal system (EGS) is the primary means during Dry Hot Rock development. It is necessary to build an underground heat exchange area during its construction, and the temperature of underground rock will change significantly, thus, the mechanical properties of those rocks underground will be affected. In order to judge whether the mechanical properties under temperature are related to the crystal structure of granite, we firstly used the crystalline rock heterogeneity coefficient H to describe the crystal structure of granite. Then, the discrete element software was used to construct the GBM equivalent crystalline model and the thermal temperature field coupling model. Finally, the temperature effect test was carried out to explore the law of heterogeneity coefficient H and damage and fracture development. The results show that: 1) the variation of granite heterogeneity coefficient H and temperature will lead to the decline of mechanical properties of rock samples. 2) At the same temperature, the damage value D increases with the increase of the H value. This phenomenon is more apparent when the temperature is greater than 400°C. 3) The microcracks caused by temperature change are mainly tensile. The H value increases the number of microcracks in the crystal. 4) The damage phenomenon caused by temperature change will be affected by heterogeneity. When the temperature is high, the crystal will denature, and the stress concentration caused by heterogeneity is easier to be reflected.

Numerical Simulation of CO2-ECBM Based on Multi-Physical Field Coupling Model

In this paper, heat injection and CO2 injection are combined, and the influence of coal seam parameters on CO2-ECBM is analyzed to improve the production of CH4 and CO2 reserves and the effective control of both greenhouse gases. A multi-physical field coupling model of CO2-ECBM was established based on Darcy’s law, Fick’s law of diffusion, the extended Langmuir model for adsorption, and the equation of state. Numerical simulation of CO2-ECBM under different coal seam parameters was carried out by COMSOL Multiphysics. The results show that increasing the injection pressure of the CO2 injection well and the initial pressure of the coal seam can effectively increase the gas pressure and concentration gradient, which has a positive effect on improving the extraction concentration of CH4 and the sequestration concentration of CO2 in the coal seam. The increase of the initial temperature of the coal seam will promote the desorption and diffusion of the binary elemental gas, resulting in a decrease in the concentration of coalbed methane and a decrease in the displacement effect. In the process of displacement, the greater the initial permeability, the greater the fracture opening of the coal seam, which is more conducive to the seepage transport of the gas. The closer to the position of the injection well, the better the displacement effect and the lower the permeability rate ratio.

Flow mechanism of Gaussian light-induced vortex motion inside a nanofluid droplet

PurposeThe purpose of this study is to use a weak light source with spatial distribution to realize light-driven fluid by adding high-absorbing nanoparticles to the droplets, thereby replacing a highly focused strong linear light source acting on pure droplets.Design/methodology/approachFirst, Fe3O4 nanoparticles with high light response characteristics were added to the droplets to prepare nanofluid droplets, and through the Gaussian light-driven flow experiment, the Marangoni effect inside a nanofluid droplet was studied, which can produce the surface tension gradient on the air/liquid interface and induce the vortex motion inside a droplet. Then, the numerical simulation method of multiphysics field coupling was used to study the effects of droplet height and Gaussian light distribution on the flow characteristics inside a droplet.FindingsNanoparticles can significantly enhance the light absorption, so that the Gaussian light is enough to drive the flow, and the formation of vortex can be regulated by light distribution. The multiphysics field coupling model can accurately describe this problem.Originality/valueThis study is helpful to understand the flow behavior and heat transfer phenomenon in optical microfluidic systems, and provides a feasible way to construct the rapid flow inside a tiny droplet by light.

A new magneto-acousto-electrical detection method for defects in high conductivity non-ferromagnetic materials

In order to further enrich the non-destructive detection methods for defects in high conductivity non-ferromagnetic materials, a new method of magneto-acousto-electrical (MAE) defect detection is proposed. First, a mathematical model of MAE multi-physical field coupling with coil induction was established. Subsequently, a geometric model of the object to be tested was constructed, and the simulation software COMSOL was used to solve the physical process of MAE defect detection. Two-dimensional distributions of mass point vibration velocity, current density of the coil’s cross-section, and one-dimensional curves of material vibration velocity surface integral, local current, and induced voltage as a function of time were obtained for various defect widths, defect shapes, and materials. The simulation result shows that the induction coil voltage pulse contains abundant information about the defect boundary information and the detection accuracy reaches 0.1 mm. Finally, experiments on MAE defect detection were conducted to prove the feasibility of the method. The research demonstrates a reliable method for the detection of internal defects in non-ferromagnetic materials with high electrical conductivity, such as aerospace and railways.

Numerical simulation of DC casting of large-size rare earth magnesium alloy ingot under low-frequency electromagnetic field

For studying the changes of macro-physical field in the casting process of large-scale rare earth magnesium alloy, through the numerical simulation method, a two-dimensional axisymmetric multi-physical field coupling model was established by using the multi-physical simulation software COMSOL Multiphysics. The changes of temperature field, flow field, Lorentz force, and liquid fraction of large-size rare earth magnesium alloy with diameter of 750 mm under different electromagnetic parameters (magnetic field frequency and current intensity) in steady state of direct-chill (DC) casting were studied. The results reveal that using a magnetic field can reduce the temperature gradient and greatly accelerate the melt flow, the depth of the sump is reduced by about 50 mm. As the current intensity rises, the flow rate in the melt becomes accelerated, the sump depth becomes shallower, while the melt area with a liquid fraction of 0.5 to 0.63 increases. The Lorentz force rises as the magnetic field frequency increases, but the skin depth of the magnetic field decreases from 64.9 to 36.4 mm.

Study on dynamic response of debris flow to pipeline with defect

Based on the Finite Element Method (FEM) and the Smooth Particle Hydrodynamics (SPH) coupling method, this paper established full-size multi-physical field coupling model of debris flow impacting pipeline. By simplifying mud into Bingham fluid, this paper studied the dynamic response law of pipeline with defect and intact pipeline (pipeline without defect) under the joint action of mud and block stone, established the displacement equations of the pipeline under impact, thus obtained the displacement, stress and strain characteristics of different pipeline positions at different impact moment. The results showed that numerical simulation of dispersing mud into SPH particles can well simulate the movement process of mud splashing and detour flow. The maximum displacement occurred in the middle part of the pipeline. For the intact pipeline, the main failure was caused by the instantaneous impact of the mud, however, for the pipeline with defect, the dominant failure factor changed from the mud impact to the stone impact. This study provided a new pathway and theoretical reference for disaster prevention and control of pipelines in debris flow section.

Solution and Analysis of Wellbore Temperature and Pressure Field Coupling Model under Lost Circulation.

The fluid in the annulus is in a variable mass flow state under the lost circulation condition, significantly affecting wellbore pressure distribution and the heat transfer efficiency between wellbore and formation. Therefore, based on the hydrodynamics and energy conservation law, a coupling model of transient wellbore temperature and pressure field under lost circulation conditions is established, which fully considers the casing program, bottom hole assembly, and heat source generated in drilling, as well as the influence of the temperature and pressure coupling in wellbore on the physical parameters of drilling fluid. The calculation results of the model in this paper are in good agreement with the field measured data and the previous research results, which verifies the rationality and accuracy of the model in this paper. The effects of the loss rate and the lost circulation zone location on the wellbore temperature and pressure distribution are analyzed, and the variation rule of the physical parameters of drilling fluid under the lost circulation condition is studied. The numerical simulation results show that the density and viscosity of drilling fluid in the annulus and bottom hole pressure increase with the increase in the circulation time; the annulus temperature decreases gradually with the increase in cycle time and tends to become stable after 8 h of the cycle. The annulus temperature and bottom hole pressure decrease with the increase in loss rate and closeness of the loss zone to the well bottom. When the loss zone is in the upper open-hole section, an inflection point consistent with the location of the loss zone appears on the annular temperature difference curve between the loss circulation and the nonloss circulation, and the position of the loss zone can be judged according to the inflection point.

Simulation of electric-thermal coupled field of power cable terminals and a failure case study

The electrical and temperature fields are important factors affecting the performance of insulation materials, which causes the aging of insulation materials. In this work, the electric-temperature coupled field model is established using ANSYS for highvoltage cable terminals. It is found that the temperature of the cable terminal increases with the operating current and the dielectric dissipation factor of insulating silicone oil. The maximum temperature of the cable terminal is 22.6°C during normal operation. When a short circuit fault occurred, the maximum temperature of the center conductor reached 45.3°C. When the impurity present is copper, the local temperature of the cable termination is highest. When the dielectric dissipation factor starts to grow from 3×10−3, the average temperature of the insulating silicone oil rises rapidly by up to 11°C. Based on a failure case, it is found that the abnormal high temperature of cable terminal is closely related to the dielectric loss of insulating silicone oil.

Theory and shape optimization of acoustic driven triboelectric nanogenerators

As a clean, sustainable, and wildly distributing energy source, acoustic waves are rarely available for energy conversion because of their high entropy and low energy density. Although the triboelectric nanogenerator (TENG) has been utilized for efficient acoustic energy harvesting, and most works are focusing on the design and geometry structures of TENG devices towards specific applications, a theoretical framework and models of the complex energy conversion system are still limited. Here, a multi-physical field coupling model of an acoustic driven TENG is presented that establishes the theoretical guidelines and optimal strategies for a typical acoustic energy system. This coupling model is composed of a basic acoustic transducer model, a TENG model, and an external circuit model coupling the acoustic field, mechanical field, and the quasi-electrostatic field. Using the finite element method (FEM), the energy conversion process including acoustic vibrations, wave propagation, and transducer reception are simulated systematically which allow us to reveal the dynamic power output behaviors of the acoustic driven TENG. The built multi-physical model and comprehensive analysis in this work provides a new research frame and platform for the design, optimization, and application of the TENG acoustic energy harvesting system.