Multi-field Coupling Analysis Research Articles

A thermodynamic theory coupling photo-chemo-mechano interactions for light-responsive hydrogel

Light-responsive hydrogel, as a typical functional hydrogel, is composed of crosslinked hydrophilic polymer chains, photosensitive molecules and water. Under illumination, the photosensitive molecules exhibit a transition in hydrophilic/ hydrophobic properties, leading to migration of water molecules and deformation of the hydrogel based on the temporal and spatial distribution of light. In this study, we propose a nonequilibrium thermodynamic framework to study the photo-chemo-mechano behaviors of light-responsive hydrogel. We firstly describe the light propagation in the hydrogel and the photochemical reaction kinetics. New free energy functions to expound the relationship between the photochemical reaction and thermodynamic process are established, and the constitutive equations are derived. Subsequently, we implant the model into a multi-field coupling analysis software, COMSOL, to conduct a spatio-temporal analysis of the hydrogel's response under uniform light exposure. Finally, we simulate the inhomogeneous deformation of light-responsive hydrogel strips under different illumination conditions and compare the results with experiments. The results highlight the importance of the photochemical reaction rate and the redistribution of light field caused by deformation. The present research holds potential for the precise manipulation and optimal design of light-responsive hydrogel in prospective applications, and offers insights for the synthesis of similar materials as well as the design of pertinent devices.

Prediction of Grain Porosity Based on WOA–BPNN and Grain Compression Experiment

The multi-field coupling of grain piles in grain silos is a focal point of research in the field of grain storage. The porosity of grain piles is a critical parameter that affects the heat and moisture transfer in grain piles. To investigate the distribution law of the bulk grain pile porosity in grain silos, machine learning algorithms were incorporated into the prediction model for grain porosity. Firstly, this study acquired the database by conducting compression experiments on grain specimens and collecting data from the literature. The back propagation neural network (BPNN) algorithm was optimized using three metaheuristic algorithms (genetic algorithm (GA), particle swarm optimization (PSO), and whale optimization algorithm (WOA)). Five machine learning models (GA–BPNN, PSO–BPNN, WOA–BPNN, BPNN, and random forest (RF)) were developed to predict the grain porosity using three input parameters (vertical pressure, grain type, and moisture content). The five models were assessed using four evaluation metrics: coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE), and mean absolute percentage error (MAPE), to determine the best porosity prediction model. Finally, the generalization ability of the best prediction model was verified using the results of the grain cell box experiment on wheat piles. The results indicated that the WOA–BPNN model was the best prediction model with an R2 value of 0.9542, an RMSE value of 0.0079, an MAE value of 0.0044, and an MAPE value of 1.1467%. The WOA–BPNN model demonstrated strong generalization ability, confirming the feasibility of using this model to predict grain porosity. It also established an expression for the relationship between wheat porosity and the vertical pressure of the grain pile. This study presents a machine learning prediction method for determining the porosity of grain piles. The obtained porosity distribution law serves as a crucial basis for conducting comprehensive multi-field coupling analysis of grain piles and offers theoretical support for safe grain storage.

Numerical simulation of bulk superconductor during pulsed field magnetization based on multi-field coupled analysis

High-temperature bulk superconductors are widely used in various superconducting devices due to their high critical current density, which enables them to trap high magnetic fields. However, the critical current density of bulk superconductors is influenced by magnetic field, temperature and stress, and both increase of stress and temperature can lead to a decrease in the critical current density. And the influence of magnetic field, current, stress are interactional. In this paper, the multi-field coupled analysis is employed to investigate the electromagnetic and mechanical behavior on bulk superconductor during pulsed field magnetization. The simulation results were compared with the present experimental results. The results showed a good agreement between the simulation and experimental results, further validating the reliability of the numerical simulation method. The magnetic field, current, temperature, and stress distribution and variation within the bulk sample during the pulsed magnetization process were calculated and analyzed. Additionally, the influence of the central crack and edge crack in the bulk superconductor was investigated. The results indicate that the region near the crack experiences a variation in current flow direction, resulting in local temperature rise and significant electromagnetic forces. The tip of the crack exhibits stress concentration, leading to a decrease in critical current density. Bulk supercondutor with edge crack case exhibits greater stress concentration compared to those with central crack case. The impact of crack length on maximum stress was analyzed, revealing that as the crack length increases, both the maximum hoop stress and radial stress within the bulk sample rise.

Multi-field coupling analysis of mechanical responses in methane hydrate exploitation with a practical numerical approach combining T + H with DEM

The methane hydrate (MH) is widely distributed in deep-sea sedimentary layers, considered as the most promising clean energy to replace conventional oil and gas in the 21st century. Large-scale exploitation of MH may lead to a series of geotechnical engineering problems. To numerically estimate the seabed stability during MH exploitation which should involve multi-field coupling simulation of complex mechanical behaviors of methane hydrate bearing sediment (MHBS), a new practical hybrid numerical method is proposed, which combines the TOUGH + HYDRATE (T + H) code, targeting multiphase flow analysis of hydrate-bearing geologic systems, with the improved Distinct Element Method (DEM). Porosity, temperature, pressure, salinity fields are exchanged between DEM and T + H to realize the thermal-hydro-mechanical-chemical (THMC) coupling and to reproduce the progressive discontinuous failure process. The results of verification show obvious uniformity between numerical and analytical results for one-dimensional (1D) consolidation and 1D heat conduction tests on soils. The paper tries to analyze evolutions of THMC fields, gas production, hydrate bond breakage and other mechanical behaviors of actual depressurization production by using this method, focusing on geotechnical risks of exploitation. In addition, study observes significant changes within certain range from the wellbore for gas production and mechanical responses in the early stage.

Exact solution of magneto-elastoplastic problem of functionally graded cylinder subjected to internal pressure

With the development of composite material technology, the multi-field coupling analysis of functionally graded (FG) structures has attracted extensive attention. For FG cylindrical pressure vessels, due to the non-uniform distribution of stresses filed in the structure, plastic deformation occurs irreversibly under external load, and Lorentz's force under static magnetic field is also one of the key factors affecting the elastoplastic state. Assuming that the elastic modulus of FG cylinder changes as a power function along the thickness and Poisson's ratio is constant, the hollow cylinder under the combined action of applied magnetic field and internal pressure may have four deformation states containing pure elastic deformation, partial plastic deformation yielding from the inner surface, partial plastic deformation yielding from the outer surface, and full plasticity. In this paper, analytical solutions of stress and displacement fields of the FG cylinder under these four different elastoplastic states are given, and the critical load conditions corresponding to the transition between these four different states are proposed. The correctness of the present analytical solution in this paper is verified by comparing it with the existing results of related simplified problems. In addition, the analytical solution of residual stress distribution caused by unloading internal pressure is discussed for self-reinforcing processing. Based on the analytical solution in this paper, the influence of FG parameter, applied magnetic field and internal pressure on the elastoplastic state, plastic zone size, stresses and displacements distribution of FG cylinder is analyzed in detail. This study shows that for this magneto-elastoplastic problem of FG cylinder, plastic deformation may appear from the inner surface or outer surfaces. With the increase of FG parameter, the first yielding position of FG cylinder changes from the inner surface to the outer surface. In addition, the existence of an applied magnetic field reduces the critical internal pressure required for FG cylinders to yield, making the FG hollow cylinder more prone to plastic deformation.

Cast-rolling force model of multi-roll solid–liquid cast-rolling bonding process for fabricating metal cladding materials

Based on twin-roll casting technology and multi-roll groove rolling technology, a Multi-Roll Solid-Liquid Cast-Rolling Bonding (MRSLCRB) process was proposed to fabricate Cu/steel cladding bars, which processes the advantages of short flow and high-efficiency. However, it is a typical 3-D thermal-fluid-mechanics coupled problem, and determining cast-rolling force is difficult during the equipment design. Therefore, the geometrical evolution of the cast-rolling area was studied, laying the foundation to establish contact boundary equations and analyze mechanical schematics and metal flow. Then, a 3-D steady-state thermal-fluid coupled simulation model, including casting roll, substrate bar, and cladding metal, was established. The Kissing Point (KP) height, average outlet temperature, and process window were predicted, and simulation results of the three-roll layout indicate that the KP distribution along the circumferential direction can be considered uniform. Hence, the engineering cast-rolling force model was derived based on the differential element method and plane deformation hypothesis. The accuracy was verified by the 3-D finite element model, and the influences of process layouts and technological parameters on the cast-rolling force were analyzed. Through the indirect multi-field coupled analysis method, the temperature–pressure evolution and reasonable process window can be predicted, which provides a significant basis for guiding equipment design and improving product quality.

Percolation characteristics of pore fluid during hydrate depressurization dissociation from multi-phase multi-field coupling analysis

The recovery of gas from hydrate-bearing reservoirs is essentially controlled by pore fluid flow. Four numerical models with different multi-phase multi-field were established in this work based on the thermo-hydro-chemical model, considering ice phase, fluidized sand phase, depositing sand phase, and ice, fluidized sand and depositing sand phases, respectively. These above models were used to simulate the dissociation of hydrate-bearing cores by depressurization and to investigate the effects of freezing and melting behavior, sand production behavior, and their combined behavior on pore fluid migration. By comparing the simulations with and without the ice phase, it can be found that the permeability decreases sharply due to ice generation resulting in a decrease of 89.16% in pore-water velocity and of 99.95% in pore-gas velocity. This indicates an inhibition of pore fluid migration by freezing behavior. Meanwhile, it can be found that the ice melting behavior can temporarily promote pore-water migration but has no obvious promotion for pore-gas migration. It is difficult for the pore fluid to percolate in the regions prone to ice generation during hydrate dissociation. In addition, the permeability at 300 min with sand detachment is 16% higher than that without sand detachment. But at the same time, the pore water velocity is 28.44% smaller since sand detachment behavior does not directly power pore fluid migration. By comparing the simulations with and without the combined behavior, it can be concluded that the freezing behavior and the sand production behavior can jointly weaken the pore fluid mobility. Significantly, the former has a stronger negative effect on the pore fluid mobility than the latter during the depressurization dissociation of the hydrate-bearing sediment.

Multi-field Coupling Analysis of Electrolytic Machining of Magazine Mounts Based on COMSOL

In electrolytic processing, the flow field of the electrolyte, the applied voltage, and the magnetic effect of the current itself have a significant effect on the stability, efficiency, and surface quality of the process. In this paper, the effects of different inlet pressures on the flow rate and different treatment voltages on the current density and magnetic induction strength are investigated by coupling several fields, such as flow, electric and magnetic fields, using COMSOL software. The simulation results show that the flow rate increases with the increase of inlet pressure, and the flow rate increases by 1 m/s for every 0.1 MPa. The current density increases with the increase of processing voltage, but its uniformity decreases, and the magnetic effect of the current itself also influences the magnitude of the current density

Thermal stability model of power coupler niobium tube for accelerator based on multi-field coupling analysis

The power coupler is the key component of superconducting accelerator, and its thermal stability will seriously affect the stable operation of the superconducting cavity. The niobium (Nb) tube at the end of the power coupler directly connected to the superconducting cavity is taken as the research object, and a one-dimensional thermal stability model based on multi-field coupling analysis is established. The coupling relationship between the electromagnetic field, liquid helium boiling heat transfer and temperature field is considered. The finite difference method was used to discretize the control equations of the model, and the Newton-Raphson method was used to handle the influence of material parameters and internal heat sources nonlinearity on the accuracy and stability of the discrete equations. The results show that the thermal stability of the Nb tube can be improved by controlling the upstream heat leakage and maintaining the upstream temperature below 9.2 K. Under transient conditions, timely recovery of the upstream cooling capacity can stop the quench caused by the decrease of cooling capacity and restore the superconducting state. The maximum quench propagation speed caused by the increase of magnetic field is 0.188 m/s, which is higher than that caused by the decrease of cooling capacity. When the local region of the liquid helium contact enters the film boiling 0.0034 s, the entire region will enter the film boiling, and the maximum temperature will reach 11.3 K, which will cause the thermal quench of the superconducting cavity. The model can accurately analyze the factors affecting the thermal stability of Nb tube and provide a reliable theoretical basis for the thermal design and stable operation of this type of power coupler.

The Multi-field Coupled Vibration Analysis of AT-Cut Quartz Crystal Resonators with Parallelism Error

The Multi-field Coupled Vibration Analysis of AT-Cut Quartz Crystal Resonators with Parallelism Error

Ventilation and cooling of coal mining face based on CFD model optimization

To solve the problem of high temperatures at the coal mining workings site. The CFD model of the coal mining face was optimized by importing user-defined functions (UDF) in ANSYS-Fluent and simulating the gas-liquid two-phase flow. By analyzing different ventilation variables, an air volume of 36.81 m3/s and an air temperature of 298 K were determined as the optimum ventilation parameters. Based on dynamic multi-field coupling analysis, a spray cooling system was proposed. The influence of water temperature, height, different zones, and spray group spacing on the cooling effect is analyzed by numerical simulation. The results show that the best effect is achieved when the water temperature is 286 K and the group spacing is 10 m. At this point, the peak temperature of a single group on the pavement side is 0.5–1 ℃ lower than the conventional temperature. The maximum temperature was 27 ℃, and the minimum temperature was 24.4 ℃. The effect of the system on cooling is even more pronounced during summer ventilation.

Experimental and modeling investigation of freezing characteristic curve of silty clay using TDR

The soil freezing characteristic curve was investigated using TDR, and the freezing point model was established based on measured temperature-time curve. A modified model was established based on developed relationships between model parameters and total water content ωtotal. The freezing degree was defined to describe the freezing process. The freezing point increased hyperbolically with increasing ωtotal and decreased linearly with increasing dry density. A critical water content ωcr was proposed, the growth rate of unfrozen water content gradually decreased with increasing ωtotal when ωtotal < ωcr, and it was almost unaffected by ωtotal and dry density when ωtotal > ωcr. The three parameters that were related to initial phase transition position, residual unfrozen water content and phase transition intensity in the modified model changed with ωtotal rather than fixed constants, thereby overcoming the limitation that unfrozen water content continuously increases with increasing ωtotal in the original model, which is suitable and important for changing total water content in multi-field coupling analysis of freezing soil. Comparison between predicted and measured results showed a satisfactory agreement.

Design and test validation of a novel permanent magnet eddy current brake

Aiming at slippage and belt breakage of large mechanical conveyor belts, a new type of water-cooled permanent magnet brake (WPMB) is proposed. In order to determine the braking performance of WPMB, a multi-physics coupling model and analysis method of magneto-thermal-structure are built. The braking torque and temperature characteristics of WPMB under different working conditions are obtained. Based on the magnetic vector potential equation, an electromagnetic eddy current model is established, and the variation trend of braking torque with speed is predicted. The temperature field model is built based on the equivalent thermal network method. Using multi-field coupling analysis method and 3-D FEM, the influence factors of WPMB braking torque are analyzed. Two test prototypes with rated speed of 78 rpm, braking torque of 3000 N⋅m are designed and developed. Braking torque characteristic tests and magnetic shielding characteristic tests at different speeds and continuous braking characteristic test are carried out. Experiments show that the proposed method provides very practical results to ensure the continuous and stable operation of WPMB.

Formation mechanism of basin-like depression defect in electric upsetting process of Ni80A superalloy

A kind of surface instability, basin-like depression defect companied by mixed grain structure at the bottom of large-scale valve during electric upsetting process, would significantly influence the microstructures and mechanical properties of components. In order to analyze the forming process of the basin-like depression defect, a finite element model for the electric upsetting process of Ni80A superalloy was developed using multi-field and multi-scale coupling analysis method. Subsequently, a series of parameters loading path schemes for force and current were designed by varying the initial value, peak value and value level, and their effects on basin-like depression and mixed grain structure were simulated and uncovered. It is concluded that the changes of heating speed and pressurization speed result in the different flow velocities between the inner and outer layers of billet, thus exerting the basin-like depression. Simulation results also indicate that these defects can be optimized through the parameter coordination between force and current. Finally, the validity and reliability of the finite element model were verified by physical experiments in electric upsetting process.

Study on Welding Deformation and Optimization of Fixture Scheme for Thin-Walled Flame Cylinder.

In this paper, the best fixture scheme for the TIG welding torch of nickel-base solid solution superalloy GH3536 in the welding process is explored. First of all, to meet the extremely high-dimensional accuracy requirements of the flame cylinder, a multifield coupling analysis model based on the flame cylinder is established on SYSWELD software. By studying the stress and deformation of welded parts under different line constraint positions and applied pressure, the trend of welding deformation is obtained, and the relevant mathematical model is established based on this. Finally, the particle swarm optimization (PSO) algorithm is used to calculate the best fixture scheme to make the welding stress and deformation better. The simulation results show that the welding deformation is negatively related to the line constraint distance and positively related to the applied pressure. According to the optimized clamping scheme of PS0, through simulation calculation, the average axial deformation is reduced by 82.5%, the maximum radial shrinkage deformation is reduced by 60.6%, and the maximum residual stress is reduced by 60.3%. Finally, it is verified by the flame barrel experiment that it meets the acceptance requirements and successfully solves the problem of serious axial shrinkage during the TIG welding of the outer ring of the flame barrel.

Topology optimization design of deformable flexible thermoelectric devices for voltage enhancement

Flexible thermoelectric devices can generate electricity based on temperature differences and have great potential as an energy source for wearable devices and the Internet of Things. In this paper, an efficient topology optimization method is proposed for the design of deformable flexible thermoelectric devices, which facilitates an increase in the output voltage and a corresponding improvement in the power generation efficiency. The designed structures can produce out-of-plane displacement for an external load, which increases the temperature difference between the hot and cold ends, thus enhancing the power generation capacity. Using combined multi-field coupling analysis and experiments, the efficacy of the proposed method was evaluated for several scenarios based on different load cases and design domains. After optimization, the temperature difference of thermoelectric devices can be increased by more than 10 °C, and the output voltage can exhibit a three-fold increase compared to that of the in-plane configuration.

Influence of process layouts of multi-roll solid-liquid cast-rolling bonding process on circumferential performance uniformity during fabricating metal cladding materials

The twin-roll casting (TRC) process is typically used to fabricate laminated metal cladding strips with rectangular cross-sections, and it has the advantages of short flow, low energy consumption, green environmental protection, etc. Recently, a twin-roll solid-liquid cast-rolling bonding (TRSLCRB) process was proposed based on the TRC process to fabricate metal cladding materials with round cross-sections. However, the nonuniformity of heat transfer and mass transfer along the circumferential direction finally influences the performance uniformity. Therefore, a multi-roll solid-liquid cast-rolling bonding (MRSLCRB) process was proposed integrating cast-rolling bonding technology and multi-roll groove rolling technology. The steady-state thermal resistance network was established, and the influences of nominal roll radius, groove radius, and molten pool height on the heat transfer and mass transfer were studied systematically. 3-D steady-state thermal-fluid coupled simulation models of twin-roll, three-roll, and four-roll layouts were established. The results indicate that increasing casting roll number can improve the nominal cast-rolling velocity, service life of the casting roll, temperature uniformity, strain uniformity, and strain rate uniformity through regulating the heat transfer and mass transfer. Considering the manufacturing feasibility, the MRSLCRB equipment based on the three-roll layout was designed. Cu/steel cladding bars with uniform circumferential performance were fabricated, and the forming mechanism was revealed. The multi-field coupled analysis method provides a way to control heat and mass transfer uniformity, and the successful attempts of various typical metal cladding materials inspire exploring new forming processes.

Study on the microscopic damage of porous asphalt mixture under the combined action of hydrodynamic pressure and ice crystal frost heave

Hydrodynamic pressure and frost heaving damage of ice crystals are the main reasons for the damage of porous asphalt mixture pavement in winter. Therefore, the author takes the open graded friction course (OGFC) asphalt mixture as an example, uses ANSYS finite element software to conduct multi-field coupling analysis of fluid and temperature for OGFC-13 asphalt mixtures with different porosities, pore structures, and different temperatures. Results show that the phenomena of “washing” and “pumping” of dynamic water exist in the connected pores at the same time. Under low-temperature conditions, low speed and heavy load are the most disadvantageous to the pores of the pavement surface. The maximum positive and negative pressures were 1.162 and −0.616 MPa, respectively. The wall shear stress distributed at the entrance and exit of the pores also reached peaks of 33.40, 25.77, and 20.07 kPa at the load duration T/2. In the early stage of ice crystal development, the temperature was lower, the temperature difference was greater, and the freezing rate was faster. In the later stage, the temperature difference decreased, the freezing rate decreased, and the same temperature value as the asphalt mixture matrix was finally reached. In addition, under the combined influence of temperature and air voids contents, the maximum stress value in the bonding surface near the connected pores was 2.89 MPa, which was 1.5 times the maximum stress value in the asphalt mortar. Under the interaction of hydrodynamic pressure and frost heave force, the upper layer of porous asphalt concrete pavement in contact with the wheels is destroyed earlier than the internal structure of the pavement. This article provides a quantitative expression for the hydrodynamic pressure and frost heave damage of porous asphalt pavement. Also, it reveals the influence of ice and snow melt on the macro performance of asphalt pavement from a meso-level perspective.

Transient modeling of quench and recovery of LNG-HTS hybrid energy transmission system based on multi-field coupled analysis

• LNG cold energy is utilized for the operation of HTS cable. • A 1-D model with electromagnetic, thermal and flow analysis is originally proposed. • The complete quench and recovery characteristics can be obtained. • Under a specific condition, the quench of the system can be recovered by itself. • The recovery time has a power law relation with the velocity of liquid nitrogen. In a novel high temperature superconducting (HTS) hybrid energy transmission system, the liquefied natural gas (LNG) and electricity are transported together along the energy pipeline to attain very high energy transmission efficiency. The liquid nitrogen (LN 2 ) is used to provide a low temperature environment and can also restrain the quench phenomenon as a protective medium. As the safety of the system is the biggest concern, a one-dimensional model with the quasi static state method is originally proposed in this paper to analyze the quench and recovery behavior. The model firstly introduces the electromagnetic analysis into the thermal and flow analysis, combining intricate interaction of phase change, fluid flow, heat transfer and current sharing. In this paper, the complete quench and recovery characteristics can be obtained when the system is subjected to the default current or thermal disturbance. The results indicate that under a specific condition, the quench of the system can be recovered by itself including different stages, going through the cooling process of film boiling, nucleate boiling, transient boiling and forced convection in turn. The recovery time caused by the default current is much longer than that caused by thermal disturbance and it has a power law relation with the velocity of LN 2 . For the quench process caused by the default current, the maximum temperature of the system decreases with the increase of LN 2 velocity. For the thermal disturbance, the maximum temperature almost keeps constant. The proposed model can predict the quench and recovery behavior in advance, which is significant for the stable operation and design of the hybrid energy transmission system.

Analysis of Induction Heating Temperature Field of Plain Weave CFRP Based on Finite Element Meso Model

Electromagnetic induction can achieve rapid internal heating of the carbon fiber reinforced polymer composite (CFRP) materials, to achieve its low energy consumption and efficient curing molding. Still, the CFRP structure, heat transfer anisotropy, and the electro-magnetic-eddy current coupling during heating directly affect the curing temperature of the composite material’s field distribution and its forming quality. In this study, the mechanism of induction heating of plain weave CFRP is analyzed. Based on the finite element mesoscopic model, the induction electricity-magnetic-eddy current–temperature multi-field coupling analysis model of plain weave CFRP is established. The coupling and distribution rules of the electro-magnetic-eddy current field during induction heating were studied; the heating history and temperature distribution of carbon fiber composite materials during heating were analyzed, and the correctness of the finite element mesoscopic model was verified through experiments. An analysis model and method are provided for heating plain weave CFRP to achieve its curing and molding.