Multi-physics Coupling Model Research Articles

Theoretical investigation of multipulse femtosecond laser processing on silicon carbide: ablation, shielding effect, and recast formation

In this study, we propose a transient multi-physics coupling model for ultrafast laser ablation based on the material point method (MPM). By employing the continuum assumption for material, heat transfer equation and particle phase change, as well as spatial discretization of the model, we achieve simulations of various coupled physical phenomena such as material temperature, phase change, stress, and recast layer formation. In terms of time, we simulate laser processing processes with up to 1000 pulses. The model is validated by comparing with experimental results on ablation morphology, recast layer formation from melted particles, and surface oxidation. The proposed model accurately captures the multi-physics aspects of ultrafast laser ablation processes in SiC ceramics. The experimental validation confirms the model’s reliability and offers valuable insights into the underlying physical phenomena.

Research Progress of Three-dimensional Geological Modeling and Multi-field Coupling of Fractured Oil and Gas Reservoirs

Fractured oil and gas reservoirs play an important role in oil and gas exploration and development due to their complex fracture network structure. As the main fluid channel in the reservoir, fractures have a significant impact on the migration, accumulation and exploitation efficiency of oil and gas. This paper summarizes the key geological characteristics of fractured reservoirs, including fracture types, distribution rules and main controlling factors of fracture development, and discusses the influence of fractures on reservoir physical properties. Furthermore, the deterministic and stochastic modeling methods of three-dimensional geological modeling of fractured reservoirs and the latest progress of discrete fracture network modeling technology are introduced in detail. In addition, this paper also discusses in detail the application of multi-field coupling model in the numerical simulation of fluid flow in fractured reservoirs, including continuous medium model and discrete medium model, and their advantages and disadvantages in simulating fluid flow in fractured reservoirs. Finally, this paper summarizes the research progress of multi-physics coupling model of fractured reservoirs, and points out the direction and challenges of future research. Through these studies, it can provide theoretical support and technical guidance for oil and gas exploration and development, in order to achieve more effective development and management of fractured reservoirs.

Study on the effect of Lorentz force on the nuclear reactor core melt stratification in electromagnetic cold crucible

To understand the effect of the Lorentz force on core melt stratification during experiments, a multi-physical field coupling model of electromagnetic induction, non-isothermal flow, and two-phase flow is established in this paper. The evolution of the layered core melt in the electromagnetic cold crucible is studied for different relative densities and phase volume fraction ratios between metal and oxide. The calculation results show that the coupling model can accurately describe the structural evolution of core melt. The Lorentz force cannot change the relative positions of the metal and oxide, but it can significantly affect the morphology of the core melt. If the density of the metal is less than that of the oxide, the Lorentz force causes the light metal with a small phase volume fraction to form a hemispherical shape in the top center of the crucible. As the phase volume fraction increases, the Lorentz force become weaker than those of gravity and buoyancy. The light metal is then flat. When the metal density is greater than the oxide density, the Lorentz force causes the heavy metal with a small phase volume fraction to appear as a hemisphere, but causes the heavy metal with a large phase volume fraction to appear as an ellipsoid in the lower part of the crucible.

Establishment of Multi-Physics coupling model and analysis on thermal stress and crack risk in directional growth of TiAl alloys under electromagnetic confinement

The electromagnetic confinement directional solidification (EMCDS) technique is an optimal method for preparing large-size and non-contamination directional TiAl alloy crystals. Despite its advantages, the high temperature gradient inherent to this process induces thermal stress within the ingot, which increases the risk of cracking. To address this challenge, an innovative Integrated Multi-Physics Coupling Model was established to map and study the thermal stress field during EMCDS in this study. It synchronized the computation of the electromagnetic field, temperature field, solute field, flow field, and stress field during the crystal growth of TiAl alloy, and its high accuracy was proved by the micro-indentation experiment. Our analysis reveals that transverse temperature differences are crucial in inducing thermal stresses, and identifies that hot cracks and cold cracks are prone to occur respectively at the area of radial 23R along the sample (X = 23R) and on the sample surface, which aligns with experimental observations impressively. This model can more accurately and efficiently optimize the process parameters of the EMCDS process to avoid cracks and promote its industrial application.

Morphological evolution mechanism of microstructures involved in shaping micro-pillar arrays into microlens arrays on fused silica surfaces by CO2 laser polishing

The periodic micro-pillars on the hard-brittle fused silica surface can be shaped into the smooth and defect-free microlens arrays (MLA) by CO2 laser polishing, which can be applied in imaging and beam-shaping. However, the morphology evolution mechanism of the micro-pillars is not clear during polishing, which seriously affects the rapid preparation of high-quality MLAs. Herein, a multi-physics coupling model is established to investigate the interaction between CO2 lasers and micro-pillars on the fused silica surface, and is verified from the perspectives of temporal and spatial temperature. The steady surface temperature evolution law with laser power and spot radius is explored, based on which, the parameter ‘Window’ for polishing is determined to make the material melt and flow without ablation removal. The morphology evolution of micro-pillars is investigated as well as laser-material interaction. It is found that under laser irradiation, the micro-pillar height first increases and then decreases, and its top curvature radius increases. The surface tension makes the dominant contributions to the melting and flow of the micro-pillar materials, while the Marangoni effect and the gravity have little effect. Furthermore, to fabricate the target MLAs with the specific dimensions, the influence of micro-pillar aspect ratio (φ) on microlens surface morphology is investigated. It is found that there are two critical φ for the target MLAs. For the required MLA with the target period of 200 μm and the target height of 40 μm, when the φ is larger than 5.1, the micro-pillar array fails to be shaped into the target MLA by CO2 laser polishing. As the φ decreases, the junction of micro-pillar and the substrate sags downwards significantly, and the deviation between the shaped- and the ideal spherical contours increases. To successfully prepared the target MLA and guarantee the geometry accuracy, the minimum φ is selected to be 0.71. This work has important theoretical significance for obtaining the smooth and defect-free target fused silica MLAs with the specific dimensions by CO2 laser non-evaporative polishing.

Numerical Investigation of coupling hazard zone of coal spontaneous combustion and gas in gob for high-gas mines

As coal mining operations continue to deepen, the frequency of coal spontaneous combustion (CSC) and gas explosion disasters in high-gas mines is increasing. Understanding the distribution patterns of CSC and gas compound disaster zones in the gob during the extraction process is crucial for reducing the risks of combustion and explosion. This study focuses on the 201 working face of the Shuanglong Coal Mine, where a multi-physical field coupling model of pressure, temperature, gas seepage, and diffusion was established to investigate the evolution characteristics of compound disaster zones and propose corresponding prevention and control measures. The results demonstrate that the area with the most severe composite hazard is mainly located at the return roadway side, extending to the middle of the gob. With increased ventilation volume and advance rate, the area of the CSC and gas coupling hazard zone expands continuously. By implementing measures such as brattice cloth and nitrogen injection, the areas of spontaneous combustion and CH4 explosion zones were reduced by 53.6 % and 49.5 %, respectively, effectively controlling the extent of the compound disaster zone and eliminating the risk of gas explosions.

Structural simulation and performance evaluation of self-priming electrostatic diesel vehicle emission particle sensor

Here is reported a self-priming electrostatic particulate matter (PM) sensor for real-time monitoring of diesel exhaust under different operating conditions. Initially, a multi-physics coupling model for the sensor was established. By varying the exhaust flow and temperature, the emissions of diesel vehicles were simulated to evaluate the sensor. The results showed that within the typical velocities (5 to 60 m/s) and temperature ranges (100 to 500 °C) of diesel exhaust, the sensor outlet pressure was consistently below the inlet pressure, with a maximum differential pressure of 259 Pa, indicating the capability for self-priming sampling of exhaust under different operating conditions. Additionally, the calibration platform was constructed using a miniature inverted soot generator which produced a series of samples to calibrate the relationship between current and mass concentration with a correlation coefficient of 0.99. From 0 to 100 mg/m3, the PM sensor exhibited a relative error between −6.00% and 6.00% with good stability and consistency for samples of different sizes and concentrations, with correlation coefficients exceeding 0.98. The results between the self-developed sensor and a commercial instrument revealed that the former provided high-precision real-time measurement of diesel exhaust.

Research on performance optimization of electrolytic cell: Non-parameter topology and parameter optimization

The technology of water electrolysis for hydrogen production converts renewable energy into hydrogen, enabling efficient storage and utilization of clean energy. The key to enabling the large-scale development of water electrolysis technology lies in enhancing the performance of electrolytic cells and minimizing energy consumption. The mastoid process structure obviously influences the electrolytic cell's flow and electrochemical performance. Therefore, this paper studied the sensitivity of the mastoid process structure to the optimization target, designed the shape topology and the parameter optimization structure, and further analyzed the influence of the two optimization methods on the flow and electrochemical performance of the electrolytic cell based on the multi-physics coupling model. The results show that under the same deformation area, the pressure drop of the topology and the parameter optimization structure is reduced by 17.17 % and 11.89 % compared with that of the original structure. The electrochemical properties were almost unaffected, and the change value was less than 0.1 %. Topology optimization design can achieve optimal performance within limited deformation constraints, and parameter optimization design is more conducive to industrial processing.

Research on the high-performance computing method for the neutron diffusion spatiotemporal kinetics equation based on the convolutional neural network

Due to the uncertainty of computational results and the lack of interpretability of models in solving physical field equations in current deep learning, this paper designs a convolutional neural network that can be used to solve the neutron diffusion spatiotemporal kinetics equation in polar and cylindrical coordinate systems. This algorithm directly utilizes the macroscopic cross-section of the material without using the lattice homogenization method, replaces the finite volume method with the extended matrices, and solves the extended matrices using the convolutional kernels instead of the iterative algorithms. Taking the simplified Tsinghua High Flux Reactor (THFR) as an example, the feasibility of the algorithm is verified on the PyTorch platform and compared with the calculation results of the source iteration method running on the GPU. The calculation results show that when the number of grids in the radial and axial sections of the simplified THFR model is 804,600 and 3,576,000, respectively, and the algorithm is iterated 3000 times, the normalized power of the convolutional neural network and the source iteration method converges to 10−10, and the maximum point by point error of the neutron flux density of the above two algorithms converges to 10−5. The computational time consumed by the convolutional neural network is approximately 880.64 s and 3729.62 s, which reduces the computational time by 4.66% and 5.05% compared to the GPU parallel accelerated source iteration method, and the former consumes 43.75% less memory compared to the latter. The convolutional neural network is mainly used as the virtual physics engine for the THFR digital twin system, in addition to solving the neutron diffusion spatiotemporal kinetics equation and further improving computational speed. The algorithm directly utilizes the neutron macroscopic cross-section of the material to calculate the neutron flux density distribution without using the lattice homogenization, providing theoretical guidance and algorithm support for developing the high-precision multi-physical field coupling model.

Study on heat and mass transfer behavior of coupled electrochemical reaction in porous structure of proton exchange membrane fuel cell

Proton exchange membrane fuel cell (PEMFC) is widely used in transportation, aviation and energy storage due to its unique advantages. Improving the performance of fuel cells depends largely on effective hydrothermal management. In this work, a multi-physical field coupling model based on the lattice Boltzmann method (LBM) is established to analyze the oxygen transport, liquid water transport, heat transfer and electrochemical reaction, mainly considering the difference between the overpotential of the cell and the surface wettability of the structure. The results show that the overpotential is closely related to the reaction process. The rate of water production is significantly accelerated by increasing the overpotential, and the breakage and merging of water clusters are observed. The increase of overpotential will lead to more energy loss in the form of heat, thus increasing the heat production. Enhancing the hydrophobicity of the structure has a positive effect on the performance of the fuel cell, and the possibility of local hot spots in the low-hydrophobic structure is greater. It is feasible to improve water management and fuel cell performance through wettability design.

Influence of Immersion Orientation on Microstructural Evolution and Deformation Behavior of 40Cr Steel Automobile Front Axle during Oil Quenching.

This study employs the finite element method to investigate the microstructural evolution and deformation behavior of a 40Cr steel automobile front axle during the quenching process. By establishing a multi-physics field coupling model, the study elucidates the variation patterns of the microstructure field in the quenching process of the front axle under different immersion orientations. It is found that along the length direction, the bainite and martensite structures decrease from the center to the edge region, while the ferrite structure shows an increasing trend. Additionally, the influence of immersion orientation on the hardness of the front axle's microstructure and deformation behavior is thoroughly discussed. The results indicate that, firstly, when quenched horizontally, the hardness difference among different regions of the front axle is approximately 8.2 HRC, whereas it reaches 10.3 HRC when quenched vertically. Considering the uniformity of the microstructure, the horizontal immersion method is preferable. Secondly, due to the different immersion sequences in different regions of the front axle leading to varying heat transfer rates, as well as the different amounts of martensite structures obtained in different regions, the deformation decreases along the length direction from the center to the edge region. Horizontal immersion quenching, compared to vertical immersion, results in a reduction of approximately 56.2% and 48.9% in deformation on the representative central cross-section (A-A) and the total length of the front axle, respectively. Therefore, considering aspects such as microstructure uniformity and deformation, the horizontal immersion quenching orientation is more favorable.

Optimization method for geometric shape of DC GIL insulators based on electric thermal multi-physics field coupling model

Optimization method for geometric shape of DC GIL insulators based on electric thermal multi-physics field coupling model

First- and second-order unconditionally stable and decoupled schemes for the closed-loop geothermal system based on the coupled multiphysics model

First- and second-order unconditionally stable and decoupled schemes for the closed-loop geothermal system based on the coupled multiphysics model

Mechanistic definition and prediction of the mass exchange coefficient between rivers and hyporheic zones: The [formula omitted] of two [formula omitted]s

Solute transport in interconnected rivers and hyporheic zones is typically modeled through dual-domain models where first-order solute mass transfer between the two domains, ΩR and ΩHZ, is represented by a coefficient α. The transient storage model (TSM) is an example of such an approach. In practice, α is determined by fitting the tails of solute tracer breakthrough curves using a TSM. This approach has led to ambiguity regarding α’s physical meaning and transferability. Here, we investigated the physical basis for α and tested it with virtual experiments through the fully coupled multiphysics model hyporheicFoam for the ΩR−ΩHZ system. hyporheicFoam explicitly simulated coupled flow and solute transport over a kilometer with centimeter-scale resolution. Model results were analyzed to calculate α following its theoretical definition directly. Using the determined α within a TSM enables accurate reproduction of solute transport, underscoring α’s physical relevance and precision.

Research on charging monitoring method for lithium-ion batteries based on magnetic field sensing

With the rapid and continuous development of new energy vehicles, safety issues during charging have become increasingly prominent. Thus, there is an urgent need to strengthen charging safety management. However, current charging detection methods have limitations, such as difficulty in monitoring local battery pack currents, and indirect monitoring through temperature and gas sensors lead to lag. To address these limitations, this article proposes a safety monitoring method based on an improved lithium-ion battery magnetic field sensing model that covers the entire charging process. Specifically, thermal field analysis was introduced to the existing electric magnetic coupling model, resulting in an electric thermal magnetic multi-physical field coupling model. By conducting experiments, the study verified that the accuracy of the improved model has increased by 15.5 %. Based on this model, the study proposed a method for predicting and warning of abnormal currents using BP neural network and mathematical statistical laws. The results showed that the current prediction accuracy of this method reached 96.4 %. Such high accuracy ensures real-time comprehensive monitoring of the current information of lithium-ion battery packs, thereby eliminating the hidden dangers of charging safety accidents caused by the lack of local current detection.

Quantitative failure analysis of lithium-ion batteries based on direct current internal resistance decomposition model

Accurate failure analysis plays a pivotal role in the optimization design and lifetime prediction of 4.45 V high-voltage LiCoO2/Graphite (LCO/Gr) batteries. Multiphysics coupling model brings great opportunities to conduct battery failure analysis quantitatively, although it is quite challenging because many model parameters need to be handled properly. Herein, we systematically elaborate the differences of ion and electron transport properties before and after cycling ageing of LCO/Gr batteries by constructing direct current internal resistance (DCR) decomposition model. The key parameters acquisition method is established, and the mechanism of DCR growth is elucidated. Furthermore, the aforementioned model parameters are refined by using a hybrid power pulse characteristics (HPPC) curve optimization algorithm based on DCR decomposition results obtained from the three-electrode battery system. Through analyzing the influence of single-factor parameter ageing on battery voltage output capacity and discharge temperature rise, the main factors affecting battery failure process are identified. For instance, the account of the positive electrochemical reaction resistance related to the kpos increased from the initial 22.9% of total DCR to 37.3% after ageing. This work provides a reliable quantitative analysis basis for the global optimization design of advanced LIBs.

The role of ionic concentration polarization on the behavior of nanofluidic membranes

Water, the elixir of life, faces a pressing challenge—salinity. As humanity's demand for freshwater intensifies, the significance of efficient desalination processes becomes paramount. The promising prospects of nanofluidic membranes and unique electrokinetic phenomena like ion concentration polarization (ICP) signal optimistic strides in enhancing salt removal processes. This study is dedicated to elucidating the transport mechanism of buffer ions at interfaces between micro and nanochannels. To achieve this, we introduce a multiphysics coupling model that incorporates a boundary condition for the fixed surface voltage, offering a comprehensive description of the impact of nanochannel arrays. In this context, it is important to note that the nanochannel array is characterized by a positive charge density, akin to a cation exchange membrane (CEM), seamlessly integrated into the microchannel wall to serve as a cationic half-cell. The analysis involved solving governing equations, including the Poisson-Nernst-Planck, continuity, and Navier-Stokes equations, numerically using the finite element method in an unsteady state. Employing cylindrical nanochannel array configurations—single, dual, and triple—we scrutinized their impact on salt species concentration and removal efficiency under specified conditions (c0=1mM, ρv=2C/m3, LN=10μm, VT=26mV, Vsurr=4VT, VL/VR=8,t≥0.5 and ζ=−60mV). The single nanochannel array configuration demonstrated a relatively uniform salt distribution, achieving a removal efficiency of approximately 58%. The introduction of two nanochannel arrays at distinct locations resulted in a notable increase in removal efficiency, reaching 72%, particularly in the "down first" configuration, emphasizing a synergistic effect. The presence of three nanochannel arrays, each with varying lengths, produced intricate patterns, with the highest removal efficiency observed at 91% in the "different length" condition. This study emphasizes the superior desalination capabilities achievable through multiple nanochannel arrays, advancing our understanding of nanofluidic membrane applications for efficient water desalination. In conclusion, emulating electrodialysis membrane procedures, particularly by integrating an anionic half-cell, holds promise for further advancing desalination processes, offering a potential avenue to enhance efficiency.

Impact of Pressure and Temperature on Charge Accumulation Characteristics of Insulators in Direct-Current Gas-Insulated Switchgear

Direct-current gas-insulated switchgear (DC GIS) is an important device for promoting the lightweight and compact design of offshore wind power platforms. Gas pressure and temperature gradients are crucial factors that must be considered during the design process of the DC GIS. In this study, the multi-physics coupling model of basin insulators considering surface charge accumulation was established, and the corresponding real-sized insulator surface charge measurement platform was constructed. The effects of gas pressure and temperature gradient on the surface charge accumulation characteristics were investigated, respectively. The results show that the effect of gas pressure on the surface charge distribution characteristics depends on the dominant mode of surface charge. When volume conduction is dominant, the effect of gas pressure on the surface charge is negligible. However, when gas conduction is dominant, the accumulation of a uniform charge pattern on the insulator surface increases with the rise in gas pressure. Furthermore, due to gas convection, the temperature of the upper part of the DC GIS is significantly higher than that of the lower part, which leads to a temperature difference between the upper and lower surfaces of the insulator. The charge density on the insulator upper surface near the central conductor rises with the increase in load current.

To study the effect of geometric parameters on the performance of a typical cone-shaped tubular segmented-in-series solid oxide fuel cell stack

Long electric current transfer path has been a common problem with tubular series cells. Cone-shaped tubular segmented-in-series solid oxide fuel cells (SIS-SOFCs) have attracted much attention due to their special advantages, such as short electric current path, unsealed requirement, small thermal stress, low operating electric current, and so on. In this paper, the electrochemical and multiphysics coupling model of a typical SIS-SOFC is developed. Then, the relationship between the geometric structure and the working characteristics within the SIS-SOFC is investigated. The results show that the size of the active reaction region in the downstream cone-shaped cell depends on the length of the interconnectors. Thus, increasing the length of the interconnectors increases the active reaction area of the series cell while decreasing the current transmission path. The ratio between the interconnector length and total cell length equals 0.5 is found to be a proper geometric factor for the SIS-SOFC to achieve a good overall performance and reaction uniformity.

Research on the effect of water-cooling steel pipe on preventing spontaneous combustion of coal pile and its thermal migration behavior

During the storage and transportation process after mining, coal piles are placed in open environments, making them prone to self-heating and spontaneous combustion due to the nature of coal and factors like natural wind flow. In recent years, there have been frequent spontaneous combustion incidents involving coal piles, posing significant safety risks. To effectively prevent and control spontaneous combustion disasters in open-air coal storage piles, we propose a method involving the arrangement of water-cooling steel pipes within the coal piles. This method applies theories of coal spontaneous combustion mechanisms, porous media heat transfer, and non-isothermal pipeline heat transfer. The multi-physics coupling model of COMSOL numerical simulation software is used to analyze the spontaneous ignition process and prevention effect of open pit coal pile. In the model, the thin material transfer of porous media is taken as the oxygen concentration field, the heat transfer of porous media is taken as the temperature field, and the free and porous media flow is taken as the air seepage velocity field. The simulation results of the spontaneous combustion process in the coal pile indicate that the high-temperature zone of spontaneous combustion is situated within the range of 0.5 ~ 1.5 m inside the wind-facing surface and extends 0.5 m above the ground level. These findings serve as a basis for determining the optimal placement of water-cooling steel pipes within the coal pile. The simulation results of a single water-cooling steel pipe demonstrate a positive correlation between the cooling effect on the coal pile and the water cool flow, and a negative correlation with the water cool temperature. Additionally, the cooling radius of the water-cooling steel pipe is determined by the circumference of the pipe and remains unaffected by the water cool flow. Finally, simulations were conducted to evaluate the cooling effect of multiple rows of steel pipes, and optimal arrangement parameters were determined: a center distance between steel pipes of 1 m and a water cool flow rate of 1500 L/min. As a result, the onset of the self-heating period in the coal pile was delayed by 11 days, and the spontaneous combustion period was extended by 56 days. The arrangement of water-cooling steel pipes in the coal pile has demonstrated significant efficacy in preventing and controlling spontaneous combustion.