Multi-physical Field Coupling Research Articles

Multi-physical field coupling for vibration feed electrochemical machining of diamond-shaped hole in titanium alloy

Titanium alloy is widely used in manufacturing because of its high heat resistance, excellent corrosion resistance, high specific strength, and low thermal conductivity. This study led to the development of a multi-physics field-coupling model of vibrating feed electrolysis processing of diamond-shaped hole in titanium alloy TC4. The model is based on the coupling relationships among the electric, flow, and temperature fields of electrolytic processing. The distributions of the electric field, flow field, temperature field, and bubble rate were obtained via vibration feed electrolysis processing of three kinds of flutes for the cathode tool. Compared with the diamond-shaped and circular liquid channels, no liquid vacancy arises at the acute angle of the rhombic hole, and the stability of the flow field is good when the cathode tool has a short circular arc liquid channel. In addition, the test results show that a channel with this form allows sufficient fluid at the acute angle of the diamond-shaped hole, and the quality of the sidewall and the bottom surface are uniform. The coupling of the electric, flow, and temperature fields increases the forming accuracy of the short circular arc liquid channel. This is consistent with the results of the multi-physics field coupling calculation of the titanium alloy vibration feed electrolysis processing. The reciprocating motion of the cathode tool at the time of vibration feed also facilitates the discharge of insoluble matter on the surface of the titanium alloy in the processing area.

Effects of electromagnetic compound field on the escape behavior of pores in molten pool during laser cladding

In order to improve the escape ability of the pores in the laser cladding molten pool, an electromagnetic compound field (ECF) is coupled in the laser cladding system to generate the directional Lorentz force in the molten pool. Based on the multi-physical field coupling theory, a laser cladding molten pool model is proposed, considering the heat transfer, fluid flow, morphology, buoyancy, surface tension, Lorentz force and pore movement of the molten pool. The simulation results reveal that the fluid flow status and geometry of the molten pool are changed significantly due to addition of the directional Lorentz force. The pore escape velocity in the molten pool can be improved effectively with the downward Lorentz force generated by a current of 500 A and a steady magnetic flux density of 1.2 T. On the contrary, more pores are trapped inside the molten pool when the direction of Lorentz force is changed to upward. The experimental observations and data confirm the model results that with the electromagnetic compound field applied, and the escape state of pores in laser cladding molten pool can be effectively controlled. Attributed to the downward Lorentz force, dense cladding layers with low porosity can be achieved successfully.

Study on Permeability Anisotropy of Bedded Coal Under True Triaxial Stress and Its Application

Anisotropy is a very typical observation in the intrinsic bedding structure of coal. To study the influence of anisotropy of coal structure and stress state on the evolution of permeability, a newly developed multifunctional true triaxial geophysical apparatus was used to carry out mechanical and seepage experiments on bedded coal. The permeability and deformation of three orthogonal directions in cubic coal samples were collected under true triaxial stress. It has detected the significant permeability anisotropy, and the anisotropy is firmly determined by the bedding direction and stress state of coal. Based on the true triaxial mechanical and seepage test results, the coal with bedding was simplified to be represented by a cubic model, and the dynamic anisotropic (D-A) permeability model was derived by considering the influence of bedding and stress state. The rationality of the permeability model was verified by the experimental data. Comparing the permeability model with Wang and Zang (W–Z) model, Cui and Bustin (C–B) model and Shi and Durucan (S–D) model, it is found that the theoretical calculated values of the D-A permeability model are in better agreement with the experimental measured values, reflecting the superiority of the D-A permeability model. Based on incorporating the model of D-A permeability under the concept of multiphysics field coupling, the numerical simulation experiments of coal seam gas extraction with different initial permeability anisotropic ratios were carried out by using COMSOL multiphysics simulator. The influence of initial permeability anisotropy ratio on gas pressure distribution in coal seam during gas extraction was explored, which provides theoretical guidance for the optimization of borehole layout for gas extraction in coal mine.

Multiphysics field coupling simulation for shell-and-tube heat exchangers with different baffles

Baffles are important components to control shell-side flow distribution and enhance heat transfer for shell-and-tube heat exchangers (STHXs). Based on multiphysics field coupling simulation, thermal–structural performance was studied for three types of STHXs with different baffles including segmental baffles, plain helical baffles and fold helical baffles. The results show that zigzag flow appears in STHXs with segmental baffles, and flow behavior is helical pattern in STHXs with helical baffles. Especially, much vortex and high velocity are generated in STHXs with fold helical baffles, where the shell-side pressure drop and Nussult number are the highest, and thermal enhancement factor (TEF) to evaluate thermal–hydraulic performance is also the largest. Although higher von-Mises stress distributes on the tube bundle, results of stress linearization at dangerous location in elastic stage show that membrane stress and sum of primary stress and secondary stress are both within range of corresponding stress intensity. Therefore, the comprehensive thermal–structural performance of STHXs with fold helical baffles is the best. The research can have a degree of theoretical guidance for design and choice of heat exchangers.

Performance study of a novel multi-functional Trombe wall with air purification, photovoltaic, heating and ventilation

A novel multi-functional passive solar wall, i.e., photocatalytic-photovoltaic-Trombe wall (PC-PV-Trombe wall), which can obtain heat, electricity and fresh air simultaneously was proposed firstly. Then a multi-physical fields (velocity, temperature and concentration fields) coupling model was established to study the performance of PC-PV-Trombe wall. The effects of channel height and width on the thermal, electrical and degradation performance of PC-PV-Trombe wall were analyzed. Finally, the performance of PC-PV-Trombe wall, built-in PV-Trombe wall and PC-Trombe wall were compared under different solar radiation intensities and ambient temperatures. The results show that the ventilation volume, thermal efficiency, heat output, electrical efficiency and the clean air delivery rate of PC-PV-Trombe wall present different trends of increase or decrease with the change of channel height and width. As opposed to the effect on the electrical efficiency, the lower ambient temperature has a negative influence on the ventilation volume, thermal performance and air purification performance, especially for the condition of lower solar radiation intensity. PC-PV-Trombe wall can realize the comprehensive utilization for air purification, photovoltaic, heating and ventilation of solar energy and the total efficiency can reach a maximum of 0.67.

Research on Temperature Rise Calculation of the Large Synchronous Compensator in UHVDC System

In order to study the temperature distribution characteristics of stator and stator winding of large dual-water internal cooling synchronous compensator. According to the fluid-solid multi-physical field coupling method, a three-dimensional calculation model of large-scale dual-water internal cooling synchronous compensator is established. Considering the complexity of the stator slot structure and the high requirement for computer performance, the simplified equivalent treatment of the stator slot structure is made. Then, based on the fluid-temperature coupled heat transfer theory, the temperature distribution is solved by finite element method with the loss of stator core and stator coil as heat source. Finally, the accuracy of temperature distribution and simplified equivalent model is verified by steady-state temperature field analysis method.

Study on laser-stricken damage to alumina ceramic layer of different surface roughness

This study examines the laser-stricken damage to different alumina ceramic surfaces of different roughness through multi-physical field coupling simulations and laser-striking experiments. The surfaces of different morphologies can be described by waves of different frequencies and amplitudes, and the waves which are discretized can be described by rectangular microstructures of different heights. In this paper, we found that the reaction of roughness surfaces to gauss lasers stricken on them could be simulated by the reaction of rectangular microstructures of different heights to laser strike. The simulation was carried out through the multi-physical field coupling method. The distribution of temperature and stress on rectangular microstructure were examined after being treated by high energy laser. It was found that overhigh temperature and stress were the main causes of laser-stricken damage, but there existed a critical rectangular column height value. The microstructure became increasingly prone to damage and fall-off with the increase of the rectangular column’s height, but it became decreasingly prone to damage after the rectangular column reached the critical value. In the experiments, seven roughness zones of alumina ceramic layer were chosen as sample surfaces for laser-striking experiment. The results showed that there was a critical roughness value at a fixed laser energy density. As a result, the amount of particles falling off the surfaces caused by laser strike was rising when the roughness was increasing. However, the amount of particles falling off the surfaces was decreasing after roughness reached the critical value. The critical rectangular column height value in the simulation corresponded to the critical roughness value in the experiment. Therefore, an appropriate selection of roughness is an important factor for obtaining high laser-stricken damage threshold.

Comparison and parametric study of two theoretical modeling approaches based on an air-to-water thermoelectric generator system

Numerical model and thermal resistance model are two commonly used modeling approaches to analyze the performance of thermoelectric devices. However, a great number of assumptions and simplifications are made in previous researches. This work presents a steady state and fluid-thermal-electric multi-physical numerical model and improves the conventional thermal resistance model to investigate the performance of an air-to-water thermoelectric generator system. In considering the multi-physical field coupling effects and temperature dependent thermoelectric material properties, the comparison of these two theoretical models and parametric investigation on the thermoelectric generator system are conducted. The results indicate that the thermal resistance model can be used to preliminarily evaluate the performance of thermoelectric generator system with acceptable accuracy at appropriate working conditions, but more precisely, the numerical model should be adopted. Besides, the heat losses should not be omitted in the theoretical analysis, and an optimal load resistance must be chosen between the maximum power one and the maximum conversion efficiency one. The findings of this work can guide the future theoretical analysis of the thermoelectric generator system by numerical model or thermal resistance model.

PSpice-COMSOL-Based 3-D Electrothermal–Mechanical Modeling of IGBT Power Module

The behavior of the insulated gate bipolar transistor (IGBT) module results in the electric field, temperature field, and stress field, and there are strong coupling effects among its electrical, temperature, and mechanical characteristics. Meanwhile, the packaging failure of IGBT module is also the interaction results of multi-physical fields coupling. In this article, a multi-physical fields transient modeling method based on PSpice and COMSOL is proposed. This method synthesizes the advantages of the physical model and the finite-element model. According to the time constants of different physical fields, continuous simulation analysis is carried out on different timescales. Through flexible multispeed simulation strategy, the dynamic characteristics of IGBT devices at different timescales can be accurately characterized. First, the electric-thermal–mechanical coupling mechanism of IGBT is described. Then, the electrical model and thermomechanical coupling model of IGBT are constructed in PSpice and COMSOL, respectively, and the multi-physical fields simulation in multi-timescale is realized through the control file of MATLAB script. The proposed modeling approach is verified by a short-circuit test of Starpower 1200-V/50-A IGBT module. Finally, an example of multi-time-scale simulation analysis under short-circuit condition is given, and the reasons for module failure under multi-field coupling effect are studied.

Investigation by numerical modeling of the mechano-electrochemical interaction of circumferentially aligned corrosion defects on pipelines

In this work, a finite element based multi-physics field coupling model was developed to investigate the mechano-electrochemical (M-E) interaction between adjacent, circumferentially aligned corrosion defects on an X46 steel pipeline. The M-E effect existing between the defects results in a high local stress concentration, a negative corrosion potential and a large anodic current density at the defect adjacency, contributing to an increased corrosion of the pipeline steel in service environments. At increased internal pressures, local stress concentration and plasticity occur primarily at the corrosion defects, while the effect on the adjacent area between the defects is slight. With the increase of the defect spacing, the interaction between the defects disappear, and the defects can be treated separately. The increased internal pressure caused a shift of corrosion potential more negatively and a more rapid increase of the anodic current density at the corrosion defects than the adjacent area. The ratio of the anodic current density at the middle of the defect adjacency to that of the uncorroded region is used as to define the separation of adjacent corrosion defects which can be considered as non-interacting. The critical ratio depends on the defect geometry under a given internal pressure.

Analysis of Multi-Physics Coupling Field of Multi-Degree-of-Freedom Permanent Magnet Spherical Motor

Motors are usually operated in electromagnetic, thermal, fluid, solid, and other multi-physical field coupling environments. Considering the influence of electromagnetic heat and fluid-structure interaction on the actual deformation of multi-degree-of-freedom permanent magnet spherical motor, with multi-physics finite-element multi-physical field simulation software, the coupling simulation calculation of electromagnetic heat, fluid dynamics analysis, and structural mechanics of the motor is realized, and the temperature rise and displacement distribution of the motor are obtained. The oil film pressure distribution is obtained by programming, which is compared with the results obtained by finite-element simulation. The results are generally consistent and mutually verified. The experimental platform of oil film pressure at different rotational speeds of the spherical rotor is built, and the measured experimental data are in good agreement with the numerical results. In the practical application of the motor, appropriate parameters should be selected, which is helpful to improve the working condition of spherical bearings, ensure the stable operation of bearings, and prolong their service life.

Assessment of the Nonlinear Flow Characteristic of Water Inrush Based on the Brinkman and Forchheimer Seepage Model

Underground fault water inrush is a hydrogeological disaster that frequently occurs in underground mining and tunnel construction projects. Groundwater may pour from an aquifer when disasters occur, and aquifers are typically associated with fractured rock formations. Water inrush accidents are likely to occur when fractured rock masses are encountered during excavation. In this study, Comsol Multiphysics, cross-platform multiphysics field coupling software, was used to simulate the evolution characteristics of water flow in different flow fields of faults and aquifers when water inrush from underground faults occurs. First, the Darcy and Brinkman flow field nonlinear seepage models were used to model the seepage law of water flow in aquifers and faults. Second, the Forchheimer flow field was used to modify the seepage of fluid in fault-broken rocks in the Brinkman flow field. In general, this phenomenon does not meet the applicable conditions of Darcy’s formula. Therefore, the Darcy and Forchheimer flow models were coupled in this study. Simulation results show that flow behavior in an aquifer varies depending on fault permeability. An aquifer near a fault is likely to be affected by non-Darcy flow. That is, the non-Darcy effect zone will either increase or decrease as fault permeability increases or decreases. The fault rupture zone that connects the aquifer and upper roadway of the fault leads to fault water inrush due to the considerably improved permeability of the fractured rock mass.

Constructal studies on hexagonal microchannel heat sinks based on multi-physics field coupling calculations

The design prototypes of four kinds of channel structures for three fluid recirculation ways, i.e. without reverting microchannels, with rim reverting microchannels and with central reverting microchannels, respectively, for the hexagonal heat sink are put forward. The influences of the fluid recirculation way, the microchannel branch number and the microchannel distribution on the maximum thermal resistance and the equivalent thermal resistance based on entransy dissipation of the hexagonal heat sink are studied based on thermo-fluid-stress-deformation multi-physics field coupling calculations and the thermal stress and strain analyses are carried out. The results of numerical calculations show that the fluid recirculation way with central reverting microchannels is the best among the three fluid recirculation ways with the objectives of minimizing the maximum thermal resistance and the equivalent thermal resistance. The construct of the hexagonal heat sink with six branch microchannels and central reverting microchannels, in which the upper microchannels distribute along the radius of the hexagonal inscribed circle and the lower microchannels distribute along the hexagonal circumscribed circle, is optimal, and its heat transfer performance is the best. Its maximal thermal strain is 0.28 GPa, and is an order of magnitude smaller than the yield strength of silicon. Its maximal deformation is 1.4 μm. The results can provide some theoretical supports for multidisciplinary design of practical microchannel heat sinks.

Numerical simulation and experimental study on the evolution of multi-field coupling in laser cladding process by disk lasers

Laser cladding exhibits highly complex heat transfer and thermo-elastic-plastic-flow changes. The multi-physics field coupling changes affect heat transfer, mass transfer, solidification, and phase transformation behavior. The quick cooling and rapid heating of the laser cladding process cause complex residual stress and deformation, which ultimately affect the quality of the cladding layer. It is notably difficult to reveal the mechanism of multi-physical field coupling in laser cladding by experiments. In this paper, the material’s temperature-dependent physical parameters by the CALPHAD method were obtained and a multi-field coupling model for laser cladding process by disk lasers was established. In the mathematical model, the interactions between the laser beam and the powder flow, the influence of the surface tension and buoyancy on the liquid metal flow in the melt pool, and the instantaneous change in the shape of the cladding layer were considered. Finally, the laws for the temperature, flow, and stress fields in the cladding process were obtained. The microstructure of the cladding layer was observed by Zeiss-IGMA HD FESEM. The accuracy of the model was verified by comparing the growth morphology of the grain and the size of the cladding layer. The study provides an effective way to reduce and eliminate residual stresses.

Modelling of mechano-electrochemical interaction of multiple longitudinally aligned corrosion defects on oil/gas pipelines

Assessment of corrosion defects and their effect on integrity of oil/gas pipelines are critical to the burst strength capability and safe operation of pipeline systems. In this work, a 3-dimensional finite element-based model was developed to investigate the mechano-electrochemical (M-E) interaction of multiple, longitudinally aligned corrosion defects on an X46 steel pipeline in a soil solution. A multi-physics field coupling technique was employed to derive the distributions of stress, strain, corrosion potential and anodic current density at the defects. For multiple corrosion defects, a critical spacing exists, below which there is an interaction between them to enhance the local corrosion. From this work, this value is between 100 mm and 150 mm. The maximum interacting spacing increases as the defect length increases. As the defect spacing reduces, there is a strong interaction between them, resulting in a high plastic stress at the defects. Under the identical defect spacing, the hoop stress condition causes an enhanced E-C interaction between adjacent corrosion defects, while the effect due to the uniaxial stress is ignorable. The interaction between multiple corrosion defects exists not only in the mechanical stress field, but also in the electrochemical corrosion field. An increase of the defect length, while keeping its depth fixed, enhances the local stress at the defects, shifts the corrosion potential negatively, and increases the anodic current density at both the defect and the adjacent area.

Performances Analysis of a Novel Electromagnetic-Frictional Integrated Brake Based on Multi-Physical Fields Coupling

In this article, a novel electromagnetic-frictional integrated brake is proposed, and its structure and working principle are introduced. The geometric model and mathematical models of integrated brake were established, and the multi-field coupling mechanism of integrated brake were analyzed. With BYD Qin as a reference vehicle, the boundary conditions of thermal load and force load of integrated brake were determined according to its structure and performance parameters. Based on the COMSOL software, numerical coupling calculations of electric, magnetic, thermal, and solid fields of integrated brake were carried out respectively in the emergency and downhill braking at a constant speed. The axial, circumferential, and radial temperature distributions of integrated brake disc were analyzed respectively, and they were compared with those of the traditional friction brake disc. The analysis results show that the proposed integrated brake can effectively improve the heat fading resistance of automotive brake during emergency and continuous braking. Under the two braking conditions, the temperature rise of friction brake was faster than that of an electromagnetic brake, and the effect of the electromagnetic brake on temperature rise of integrated brake was small.

Analysis and experimental research on the characteristic of skid steering vehicle based on a dynamic analysis model

Skid steering vehicle is mainly used in complex terrains, such as gravel roads and muddy roads, which requires platform with ability to adapt three-dimensional unstructured terrains and good cross-country motor performance. In this paper, in order to analyze dynamic characteristics in the process of driving, the vehicle’s dynamic characteristics analysis model is raised. According to the slip and track slip properties of tyre and ground, a theoretical model of dynamic characteristic of Skid steering vehicle is established, and effects of ground parameters on vehicle performance are analyzed. In order to establish a dynamic analysis model of engineering, AMESim software platform and Motion software platform are used to construct a multi-physical field coupling analysis model for Skid steering vehicle so that accurate quantitative analysis on wheel contact characteristics is carried out. In order to verify the theoretical model and the accuracy of physical field coupling analysis model, a real Skid steering vehicle is used for tests. Through collecting the system pressures and flow characteristic, wheel contact characteristic of Skid steering wheel is analyzed. Simulation and experimental results show that compared with the test data, theoretical model, and physical field coupling analysis have high precision. Compared with test data, the error is within 10%, which can be used to Skid steering vehicle’s research and development and performance prediction.

Optimization design of color mixing nozzle based on multi physical field coupling

Fused deposition modeling, as one of the most widely used types of 3D printing, is undoubtedly a good method when it comes to personalizing custom production and producing some complicated parts which cannot be machined by cutting tools. However, existing FDM printers are restricted to printing only monochrome objects due to the poor mixing quality and nozzle blockage caused by the irrational structure of nozzle. In this paper, the 3D model of the color mixing nozzle is designed by SolidWorks software at first. Second, the temperature field and the stress field are simulated by using ANSYS software. Comparing the simulation results, the main reason for the blockage at the notch of the throat pipe is revealed. Some other design flaws, including the position of the thermistor, the shape of the flow channel and the material selection of each component, are found out and optimally modified. Finally, the nozzle is optimized, and the rationality of the optimization design is verified by thermal-mechanical coupling field analysis. The problem of nozzle blockage in the printing process is settled, and the printing quality and stability are significantly improved.

Dynamic Variation Characteristics of Seawater Intrusion in Underground Water-Sealed Oil Storage Cavern under Island Tidal Environment

In the case of constructing underground water-sealed oil storage caverns in island environments, the groundwater seepage characteristics are more complicated under the influence of seawater and tidal fluctuations. It also faces problems such as seawater intrusion. This research is based on multi-physical field coupling theory and analyzed the influence of tidal fluctuation and water curtain systems on the temporal-spatial variations of seawater intrusion in an island oil storage cavern in China using the finite element method. The results show that the operation of an underground water-sealed oil storage cavern in an island environment has a risk of inducing seawater intrusion. The tidal fluctuation has a certain degree of influence on the seepage field of the island. The water curtain system can decrease seawater intrusion and reduce the influence of tidal fluctuation on the seepage field inside the island. The research results provide a theoretical basis for the study of seawater intrusion in underground oil storage caverns under island tidal environments.

Numerical investigation on interaction mechanisms between flow field and electromagnetic field for nonequilibrium inductively coupled plasma

In this paper, the inductively coupled plasma (ICP) wind tunnel, which is widely used in the development of thermal protection system for reentry vehicle in the aerospace field, is studied. The distribution properties and the interaction mechanism of the flow field and electromagnetic field are investigated by numerically solving the multi-physics fields coupling among the flow field, electromagnetic field, thermodynamic field and turbulent field. In the numerical simulation, the thermochemical non-equilibrium plasma magneto-hydrodynamic model is used to accurately simulate the high-frequency discharge, Joule heating, energy conversion, and internal energy exchange of air ICP. Finally, the distribution of electron temperature, particle number density, Lorentz force, Joule heating rate, velocity, pressure and electric field strength of air plasma are obtained through the multi-physics field coupling calculation. The results show that the plasma flow is in a thermodynamic non-equilibrium state near the torch wall in the induction coil region and that the Lorentz force plays an important role in controlling the momentum transfer. A strong eddy flow occurs between the inlet and the second turn of the inductive coil. The eddy flow has a close relationship with the negative pressure gradient and the electromagnetic heating phenomenon in the induction coil region. The radial Lorentz force is always negative. This indicates that the free electrons are generated near the wall due to the fact that the skin effect are always subjected to a force making them move to the central axis of the ICP torch. The maximum value of the radial Lorentz force is 3.95 times higher than that of the axial Lorentz. This indicates that the momentum transfer is predominantly radial. The Joule heating effect of the air particles is also affected by the radial Lorentz force. The maximum value of <i>E</i><sub>I</sub> is 2.9 times larger than the real part of electric field, <i>E</i><sub>R</sub>. The positive <i>E</i><sub>I</sub> is generated by the free electrons inside the plasma. The number density of free electrons reaches a maximum value at a distance of 5.5 mm far from the inner wall surface of the torch below the second induction coil. 91% of N<sub>2</sub> are dissociated into atomic N near the central axis. The maximum electron and translational temperature simulated in this paper are 9921 K and 8507 K, respectively.