Multi-physical Field Coupling Research Articles

Multifield Coupling Mechanism of Unloading Deformation and Fracture of Composite Coal-Rock

The deformation and fracture evolution of coal and rock under unloading are prone to sudden instability or dynamic damage. To solve the problem, this paper combines interdisciplinary theories such as damage mechanics and electromagnetic field theory. The mathematical model of multiphysics coupling during loading and unloading of composite coal-rock is deduced. In addition, numerical simulations along with experimental verification are carried out to study multi-physical field variation and coupling mechanisms. The composite coal-rock deforms and ruptures under unloading, and the brittle failure of the rock body becomes more sudden when the confining pressure is unloaded. Macroscopically, many microcracks are generated and expanded during the loading and unloading of composite coal-rock. Microscopically, the internal old molecular chains are broken to form new molecular chains by the force. Simulation results show that, during the loading and unloading process, the three physical fields of the composite coal-rock all change regularly. During the unloading of coal and rock, there is a transition period in which the temperature increases sharply and reaches the maximum. Then, the temperature decreases due to the gradual decrease of its bearing capacity. Besides, the electromagnetic field is strongest on the surface of the coal body, and its propagation in the air decays exponentially. There are small fluctuations that appear at the junction of the coal body and the air. The experimental results show that the internal infrared radiation temperature of the composite coal-rock decreases during the initial stage of loading and unloading due to the discharge of internal gas. In the first stage of “loading and unloading,” it increases with the increase in stress, and the temperature suddenly increases in a short time after unloading. The electromagnetic radiation fluctuates in small amplitudes at the initial stage. When the stress is about to reach the peak, the electromagnetic radiation intensity increases and reaches the peak suddenly. Then, the coal-rock ruptures, the stress decreases, and the electromagnetic radiation weakens. The experiment and simulation results are consistent. The multiphysics coupling model is used to study the characteristics of coal and rock unloading under complex conditions, providing a theoretical basis and new method for the prediction and forecast of coal and rock mining dynamic disasters.

Nanofibrous membrane through multi-needle electrospinning with multi-physical field coupling

The mass electrospinning is the key way to promote the industrial application of nanofibrous membrane, in which the multi-parameter controlling is the challenge for the multi-needle electrospinning. A constant temperature and humidity environment was introduced to studied the effect of process parameters on the ejection process of multi-needle electrospinning process. This article focused on the nanofiber deposition behaviors of multi-needle electrospinning from two different polymer solution of aqueous solution of poly (ethylene oxide) and the non-aqueous solution of polyvinylidene fluoride. We found that the same humidity has opposite effects on the deposition morphology of the water-soluble material PEO and the non-water-soluble material PVDF electrospun fiber. At the same time, we explored the effects of solution conductivity, solvent volatility, temperature and viscosity on electrospinning on water-insoluble and water-soluble materials. What this paper aim is to provide a process debugging reference for the batch preparation of nanofibers of different materials by multi-needle electrospinning.

CO emission regularity and its influencing factors in a fully mechanized caving face

To explore the problem of CO concentration overrun in fully mechanized caving faces, a multiphysical field coupling model of CO emission regularity was established in this study based on the gas flow theory, gas concentration field theory, and heat transfer theory. Taking the 014N1−1 working face of the No. 1 coal seam in Ruian coal mine as the research object, the model was applied to simulate the CO concentration in the fully mechanized caving face. The simulation results were found to be consistent with the field detection results. Based on the simulation results, the effects of advancing speed and wind velocity on the CO emissions in the gob and the CO concentration distribution in the working face were analyzed. The results showed that, the lower the wind velocity, the greater the CO emissions. With increasing advancing speed, the CO emissions in the gob first increased, reached maximum, and then decreased. The production conditions were found to be most suitable when the advancing speed and wind velocity were 2 and 1.8 m/s, respectively. Moreover, the CO emission characteristics of the fully mechanized caving face under the conditions of periodic roof weighting, production process, and atmospheric pressure change were monitored and analyzed. We verified the presence of CO in the coal seam and its emission with the progress of coal seam mining. Our results will be useful in the research and analysis of CO emission source, emission regularity, and overrun warning in fully mechanized working faces.

Thermal error prediction and reliability sensitivity analysis of motorized spindle based on Kriging model

A large amount of heat is generated by motorized spindles during the machining process of CNC machine tools, and it is the main factor restricting the further improvement of machining accuracy. Furthermore, physical properties and material parameters of the motorized spindle are uncertain in practical engineering. Therefore, it is necessary to evaluate the reliability and reliability sensitivity of the motorized spindle system. In this paper, a new thermal error estimation model of motorized spindle is established based on multi-physical field coupling theory. The Quasi-Monte Carlo (QMC) method is introduced to calculate the reliability of the motorized spindle system. An accurate and efficient surrogate model, called Kriging, is used to calculate the reliability and reliability sensitivity of the motorized spindle system to further improve computational efficiency. Moreover, the experimental platform for measuring the temperature and thermal error of the motorized spindle is built to verify the applicability of the proposed model. The analytical framework proposed in this paper provide a guidance for the reliability design and robustness evaluation of motorized spindle.

Research on the multi-physics field coupling simulation of aero-rotor blade electrochemical machining

Aimed at the problem that the quality of the formation of aero-rotor blades with complex shaped structures is difficult to predict due to the coupling of each physical field in the process of electrochemical machining, a mathematical model of electrochemical machining characterized by the conductivity of the multi-physics field is established firstly by studying the coupling action mechanism of the flow field and temperature field on electric field conductivity in the machining process. Then, utilizing the Runge–Kutta method, the relationship between the conductivity and the machine path is analysed; Finally, based on this relationship, the multi-physics field electrochemical machining erosion model is compared with the traditional single electric field electrochemical machining erosion model. The results show that the error of the multi-physical field coupling prediction model proposed in this study is in the range of 1.27–2.35%, while the accuracy of the single electric field prediction model is in the range of 4.35–5.88%. The theoretical value of the multi-physics field coupling simulation is closer to the measured value of the test and can accurately simulate the actual electrochemical machining process, which can provide a theoretical basis for the design of cathode tools and parameter optimization in the actual processing process and is of great significance to improve the quality and efficiency of the electrochemical machining of aero-rotor blades.

Transient numerical modelling of a thermoelectric generator system used for automotive exhaust waste heat recovery

The automotive thermoelectric generator system is a promising technology of exhaust waste heat recovery, but reasonable theoretical models to predict its dynamic performance are lacking. In this work, a transient fluid-thermal-electric multiphysics coupling field numerical model is proposed for the first time, and the model is used to evaluate the dynamic performance of a simplified automotive thermoelectric generator system under vehicle driving cycles. The transient numerical model, which takes into account the dynamic characteristics, fluid-thermal-electric multiphysics field coupling effects, and material temperature dependence, is thus far the most complete model ever. Numerical results reveal that there is a delay in output response with the change of exhaust temperature, and the change of output voltage and output power is often accompanied by the change of exhaust mass flow rate. The small and short-term fluctuation of exhaust gases has a slight influence on output performance. With the transient variation of exhaust characteristics, the output voltage and output power show more stable changes and slower responses, but the situation is the opposite for conversion efficiency. The output power predicted by steady-state numerical simulation is 12.6% higher than that of transient numerical simulation. Moreover, the proposed transient numerical model is recommended to investigate the dynamic performance of automotive thermoelectric generator systems.

Study on electromagnetic-fluid-temperature multiphysics field coupling model for drum of mine cable winding truck

Aiming at solving problems of low efficiency, low cable capacity in current 300m open-pit mine cable winding truck, a 900 m cable winding plan was proposed. In this paper, the mechanism of the thermal effect of the cable was described, and a two-dimensional axisymmetric electromagnetic-fluid-temperature multiphysics coupling model of the cable reel was established regarding the 900m cable reel as independent system. Considering the structure of the drum, the number of cable winding layers, the factors of heat conduction, heat radiation and convective heat transfer in the actual working process, the steady state analysis of the multi-physical field coupling was carried out. The sum of the losses of each part of the cable was obtained through the calculation of electromagnetic field, which was used as a heat source to calculate and analyze the temperature distribution of different layers of cable winding, as well as the temperature distribution and heat dissipation characteristics of different structures of the drum. The results show that three layers of cable winding is the best design. The lowest temperature of closed cylindrical drum is 70°C after heat dissipation, which has obvious advantages compared with the lowest temperature of 85° after heat dissipation of squirrel-cage cylindrical drum. The results provide a reliable theoretical basis for the research and development of a new type of mine cable winding truck with 900 m cable capacity.

Numerical simulation and experimental validation of multiphysics field coupling mechanisms for a high power ICP wind tunnel* *Project supported by the National Natural Science Foundation of China (Grant No. 11705143), the Open Foundation for Key Laboratories of National Defense Science and Technology of China (Grant No. 6142202031901), and the Foundation for Research and Development of Applied Technology in Beilin District

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.

Mechano-electrochemical interaction for pipeline corrosion: A review

Engineering structures such as pipelines usually operate under stressing conditions. When corrosion occurs on the structures in service environments, the stress and corrosion reactions synergistically result in a so-called mechano-electrochemical (M-E) interaction, adversely affecting the structural integrity. This work reviewed the fundamentals of the M-E interaction for pipeline corrosion, where both corrosion thermodynamics and kinetics were derived by incorporating the effect of stress and strain applied on the pipelines. Under an elastic deformation, the M-E interaction for pipeline corrosion is usually negligible, while a dynamic elastic stress can degrade the integrity of corrosion scale on the steel and slightly accelerates the steel corrosion. However, plastic deformation results in an appreciable M-E interaction, remarkably changing both corrosion potential and corrosion rate of pipeline steels. Based on the M-E interaction theory, a multi-physics field coupling model with finite element analysis was developed to assess corrosion defects on pipelines for failure prediction. Perspectives of the M-E interaction in pipeline corrosion research and preventive management were analyzed.

Calculation and analysis of thermal flow field in hydrodynamic torque converter with a new developed stress-blended eddy simulation

Purpose The flow phenomenon of particle image velocimetry has revealed the transition process of the complex multi-scale vortex between the boundary layer and mainstream region. Nonetheless, present computational fluid dynamics methods inadequately distinguish the discernable flows in detail. A multi-physical field coupling model, which was applied in rotor-stator fluid machinery (Umavathi, 2015; Syawitri et al., 2020), was put forward to ensure the identification of multi-scale vortexes and the improvement of performance prediction in torque converter. Design/methodology/approach A newly-developed multi-physical field simulation framework that coupled the scale-resolving simulation method with a dynamic modified viscosity coefficient was proposed to comparatively investigate the influence of energy exchange on thermal and flow characteristics and the description of the flow field in detail. Findings Regardless of whether quantitative or qualitative, its description ability on turbulence statistics, pressure-streamline, vortex structure and eddy viscosity ratio were visually experimentally and numerically analyzed. The results revealed that the modification of transmission medium viscous can identify flows more exactly between the viscous sublayer and outer boundary layer. Compared with RANS and large eddy simulation, a stress-blended eddy simulation model with a dynamic modified viscosity coefficient, which was further used to achieve blending on the stress level, can effectively solve the calculating problem of the transition region between the near-wall boundary layer and mainstream region. Research limitations/implications This indeed provides an excellent description of the transient flow field and vortex structure in different physical flow states. Furthermore, the experimental data has proven that the maximum error of the external performance prediction was less than 4%. Originality/value An improved model was applied to simulate and analyze the flow mechanism through the evolution of vortex structures in a working chamber, to deepen the designer with a fundamental understanding on how to reduce flow losses and flow non-uniformity in manufacturing.

Numerical Simulation Analysis and Experimental Research on Damping Performance of a Novel Magnetic Fluid Damper

Considering the low-frequency and large-amplitude vibration characteristics of the high-rise structure, a tuned magnetic fluid rolling-ball damper is proposed to suppress the vibration of the structure. By adjusting the external magnetic field to control the natural rolling frequency of the ball, the purpose of tuning vibration reduction is achieved. Firstly, the working principle of the damper is theoretically analysed, a three-dimensional (3D) magnetic-fluid-solid multiphysical field coupling mathematical model of the damper is established and the governing equations of multiphysical field coupling are derived. Secondly, the magnetic field distribution and operating characteristics of the damper are simulated and analysed. Finally, the effectiveness of the model is verified by experiments, and the damping performance of the damper with two kinds of magnetic fluid is tested and compared. The results show that the magnetic-fluid-solid multiphysical field coupling model can accurately simulate the working characteristics of the damper. The maximum damping force of the damper is about 12% of the elastic force of the structure, which can increase the damping ratio of the structure by about two times, effectively reduce the vibration response time, and suppress the vibration of the high-rise structure.

Multiphysics Coupling Simulation and Parameter Study of Planar Solid Oxide Fuel Cell.

In this paper, a numerical model of gas flow, heat transfer, mass transfer and electrochemical reaction multi-physics field coupling of a planar SOFC is established and solved. According to the calculation results, the distribution of velocity, temperature and concentration inside the SOFC cell is analyzed. The influence of cathode inlet flow rate, porosity, rib width and other parameters on the performance of SOFC is also discussed. The results show that within a certain range, increasing the cathode inlet flow rate can significantly increase the average current density of the cell. Increasing the porosity of the electrode can improve the gas diffusion of the porous electrode, thereby increasing the rate of the electrochemical reaction. Increasing the width of the ribs will result in a significant decrease in cell performance. Therefore, the rib width should be reduced as much as possible within the allowable range to optimize the working performance of the cell.

An investigation on improving the homogeneity of plasma generated by linear microwave plasma source with a length of 1550 mm

To develop a larger in-line plasma enhanced chemical vapor deposition (PECVD) device, the length of the linear microwave plasma source needs to be increased to 1550 mm. This paper proposes a solution to the problem of plasma inhomogeneity caused by increasing device length. Based on the COMSOL Multiphysics, a multi-physics field coupling model for in-line PECVD device is developed and validated. The effects of microwave power, chamber pressure, and magnetic flux density on the plasma distribution are investigated, respectively, and their corresponding optimized values are obtained. This paper also presents a new strategy to optimize the wafer position to achieve the balance between deposition rate and film quality. Numerical results have indicated that increasing microwave power and magnetic flux density or decreasing chamber pressure all play positive roles in improving plasma homogeneity, and among them, the microwave power is the most decisive influencing factor. It is found that the plasma homogeneity is optimal under the condition of microwave power at 2000 W, chamber pressure at 15 Pa, and magnetic field strength at 45 mT. The relative deviation is within −3.7% to 3.9%, which fully satisfies the process requirements of the equipment. The best position for the wafer is 88 mm from the copper antenna. The results are very valuable for improving the quality of the in-line PECVD device.

Method of building transformer acoustic diagnosis database based on multi physical field coupling modeling

In this paper, a method of building dynamic acoustic diagnosis database of dry-type transformer is proposed. The method is mainly combined with collecting the basic noise of transformer and simulating the acoustic signals of transformer under different working conditions to improve the fault database of transformer. Due to the incomplete working conditions on site, the simulated working conditions are relatively complete, and the marked acoustic signal file is generated, and then form the composition of the database. This paper focuses on the finite element simulation analysis of transformer vibration and noise radiation based on COMSOL, and the idea of establishing transformer biological diagnosis database. Improve the efficiency of transformer fault design and research, and provide reliable and convenient data services for researchers.

Modeling of mechano-electrochemical interaction at a corrosion defect on a suspended gas pipeline and the failure pressure prediction

Suspension effect poses a big threat to the integrity and safety of corroded pipelines. In this work, a finite element (FE) based multi-physics field coupling model was developed to determine the mechano-electrochemical (M-E) interaction at an external corrosion defect on a suspended X100 steel pipe and predict its failure pressure. Theoretical calculations were used for model validation. Parameter effects including the defect location on the pipe, geometry of the defect, suspension length and pipe burial depth were determined. Results demonstared that, generally, the M-E effect at corrosion defect caused an increased stress concentration and anodic current density (i.e., corrosion rate), decreasing the failure pressure of the pipeline. The effect became more apparent when the pipe was in suspension. Both the stress and the anodic current density at the corrosion defect were dependent on the defect geometry, especially the defect depth. When the depth was up to 40% of pipe wall thickness, the von Mises stress exceeded the yield stress of the steel, causing local plastic deformation. A critical defect length of 20Dt (D is the outer diameter of the pipe and t is pipe wall thickness) existed, below which the von Mises stress and the anodic current density at the corrosion defect increased with increased defect length. When the defect length exceeded the critical value, the effect was not obvious. An increased suspension length of the pipe would elevate the local stress and anodic current density at the corrosion defect, reducing the failure pressure of the pipe. A critical pipe burial depth of 2.5 m was identified, exceeding which the failure pressure of the pipe decreased rapidly with the increased burial depth. When the burial depth was smaller than 2.5 m, the effect was marginal. The location of the corrosion defect on the pipe did not affect the local stress, anodic current density and failure pressure at an appreciable level, and could be ignored in defect assessment on suspended pipelines.

Research on multi-physical field coupling of solid electrothermal storage unit

In recent years, the solid-state electro-thermal storage device has been connected to the power supply side of the power system for peak regulation by virtue of its high voltage and large capacity characteristics, which plays a positive role in the consumption of wind power, photovoltaic and other new energy. Based on the coupling effects of heat, current, electricity, magnetism, force and other physical fields in the equipment, this paper studies the optimal design of thermal storage structure. A multi-physical field and multi-criteria collaborative optimization design method was proposed to design the surface load of heating power, heat transfer channel of heat storage body, and porosity of body. Through the multi-field coupling numerical simulation and experiment verification, the thermal field, flow field, stress field, electric field and other changes are analyzed, and it is verified that the design method can effectively overcome the malpractice of low heat transfer rate temperature imbalance of thermal storage materials. The experimental results provide theoretical guidance for device design and engineering application.

Simulation Analysis of Vibration and Noise Characteristics of High Voltage Shunt Reactor Based on Multi-physical Field Coupling

In order to study the vibration characteristics of the high-voltage shunt reactor, a finite element model of the single-phase reactor was established based on the analysis of the vibration mechanism of the reactor body, by using COMSOL multi-physical field coupling simulation software. The magnetic flux density distribution of reactor core, windings, stress distribution and vibration displacement of iron core were analysed by simulation. The sound pressure distribution of the iron core was analysed based on the pressure sound field model. The results indicate that the magnetostrictive effect of the iron core reactor, the electromagnetic attraction between the iron core cakes and the ampere force on the winding are the main factors for its vibration. In addition, the reactor vibration to be mainly concentrated at the core air gap. The results obtained by multi-physics simulation are basically consistent with the measured data, which verifies the effectiveness of the simulation method. The conclusions can provide theoretical basis for the analysis and monitoring of reactor vibration and noise.

Study on gain stability of Thick Gas Electron Multiplier

In this paper, we propose and analyze a Gain Transient Perturbation (GTP) model to study the transient stability of THick Gas Electron Multiplier (THGEM). This model can be used to explain the instability of Micro Pattern Gaseous Detectors (MPGDs). Furthermore, the transient gain stability of THGEM was analyzed using the method of multi-physical field coupling. Simulations were carried out to study the influence of internal factors, namely, the size of the insulation rim, the conductivity of substrate materials and the relative dielectric constant of filling gas on the transient gain stability of THGEM. Using an experimental setup the counting rate of the THGEM was measured and the results were found to be in good agreement with the simulation results.

Study on Transient Fuel Hydrodynamic Force Characteristics of High-Speed Solenoid Valve for Common Rail Injector

The working process of the high-speed solenoid valve (HSV) of high-pressure common rail (CR) injector has the characteristics of electro-magnetic-mechanical-hydrodynamic multi-physical field coupling. However, most of the research work in this field is carried out without considering hydrodynamic environment of the HSV. Furthermore, the dynamic response characteristics of the transient fuel hydrodynamic force (TFHF) of the HSV should not be neglected. In this study, a three-dimensional finite element method is used to simulate the TFHF between the injector electromagnet and the armature. The results show that cavitation phenomena appears on the lower surface of the armature during the HSV opening process. The faster the armature moves up, the greater the cavitation intensity. Damping holes on the armature can reduce the TFHF acting on the upper surface of the armature; however, the armature structure with straight grooves and damping holes reduces the TFHF more evidently during the HSV opening and the inhibition effect of this structure on cavitation is more evident. The TFHF on the armature decreases with an increase in the depth of the coil groove. However, the selection of the groove depth should be considered together with the optimization of the electromagnetic force characteristics of the HSV.

The Modelling of Freezing Process in Saturated Soil Based on the Thermal-Hydro-Mechanical Multi-Physics Field Coupling Theory

The freezing process of saturated soil is studied under the condition of water replenishment. The process of soil freezing was simulated based on the theory of the energy and mass conservation equations and the equation of mechanical equilibrium. The accuracy of the model was verified by comparison with the experimental results of soil freezing. One-side freezing of a saturated 10-cm-high soil column in an open system with different parameters was simulated, and the effects of the initial void ratio, hydraulic conductivity, and thermal conductivity of soil particles on soil frost heave, freezing depth, and ice lenses distribution during soil freezing were explored. During the freezing process, water migrates from the warm end to the frozen fringe under the actions of the temperature gradient and pore pressure. During the initial period of freezing, the frozen front quickly moves downward, the freezing depth is about 5 cm after freezing for 30 h, and the final freezing depth remains about 6 cm. The freezing depth of the soil column is affected by soil porosity and thermal conductivity, but the final freezing depth mainly depends on the temperatures of the top and lower surfaces. The frost heave is mainly related to the amount of water migration. The relationship between the amount of frost heave and the hydraulic conductivity is positively correlated, and the thickness of the stable ice lens is greatly affected by the hydraulic conductivity. With the increase of the hydraulic conductivity and initial void ratio, the formation of ice lenses in the soil become easier. With the increase of the initial void ratio and thermal conductivity of soil particles, the frost heave of the soil column also increases. With high-thermal-conductivity soil, the formation of ice lenses become difficult.