Multiphysics Numerical Model Research Articles

Mechanism and Effects of Cellular Creep in a Microfluidic Filter.

Biomicroparticles such as proteins, bacterium, and cells are known to be viscoelastic, which significantly affects their performance in microfluidic applications. However, the exact effects and the quantitative study of cellular viscoelastic creep within different applications remain unclear. In this study, the cellular-deforming evolution within a filter unit was studied using a multiphysics numerical model. A general cellular creep deformation process of viscoelastic particle trapping in pores was revealed. Two featured variables, namely, the maximum surface displacement and the volumetric strain, were identified and determined to quantitatively describe the evolution. The effects of flow conditions and physical characteristics of the microparticles were studied. Furthermore, a Giardia concentration experiment was conducted using an integrated hydraulic filtration system with a porous membrane. The experimental results agreed well with the numerical analysis, indicating that, compared to pure elastic particles, it is more difficult to release cellular material matters including cells, chemical synthetic particles, and microbes from trapping due to their time-accumulated creep deformation.

Comparison and Parametric Analysis of Thermoelectric Generator System for Industrial Waste Heat Recovery with Three Types of Heat Sinks: Numerical Study

In this study, a fluid–thermal–electrical multiphysics numerical model was developed for the thermal and electrical analyses of a heat sink-based thermoelectric generator (TEG) in a waste heat recovery system used for casting a bronze ingot mold. Moreover, the model was validated based on experimental data. Heat sinks were installed on the hot side of the TEG module to recover the waste heat from the flue gas generated in the casting process. The numerical results of the thermal and electrical characteristics of a plate fin (PF)-based TEG showed good agreement with the experimental findings. Numerical simulations of heat sinks with three different fin structures—PF, cylinder pin fin (CPF), and rectangular pin fin (RPF)—were conducted. The simulated system pressure drop, hot- and cold-side temperature difference in the TEG module, TEG power output, and TEG efficiency were compared for the differently designed fin structures. The results showed that for the same fin area, the CPF heat sink-based TEG system achieved a lower pressure drop, higher power output, and higher efficiency than the other two designs. This was particularly true when the velocity of the flue gas and the fin height exceed 5 m/s and 28.6 mm, respectively. Therefore, for low and high flue gas velocities, PF and CPF heat sinks are recommended as the best choices, respectively.

A 2D image-based multiphysics model for lifetime evaluation and failure scenario analysis of self-healing ceramic-matrix mini-composites under a tensile load

We propose a multi-physics numerical model for a self-healing ceramic matrix mini-composite under tensile load. Crack averaged PDEs are proposed for the transport of oxygen and of all the chemical species involved in the healing process and studied in the dimensionless form to perform the most appropriate discretization choices concerning time integration, and boundary conditions. Concerning the fibres’ degradation, a slow crack growth model explicitly dependent on the environmental parameters is calibrated using a particular exact solution and integrated numerically in the general case. The tow failure results from the statistical distribution of the fibres’ initial strength, the slow crack growth kinetics, and the load transfer following fibres breakage. The lifetime prediction capabilities of the model, as well as the effect of temperature, spatial variation of the statistical distribution of fibres strength, and applied load, are investigated highlighting the influence of the diffusion/reaction processes (healing) on the fibre breakage scenarios.

Feasibility of additive manufacturing processes for lunar soil simulants

Combination of In-situ Resource Utilization (ISRU) and on-site Additive Manufacturing (AM) is one of the “outer space applied technologies” candidates where free shape fabrication from micro (e.g., tools) to mega scale (e.g. lunar habitats) will allow in coming future to settle the Moon or potentially other celestial bodies. Within this research, Selected Laser Melting (SLM) of lunar soil (regolith) simulants (LHS-1 LMS-1 and JSC-2A) using a continuous wave 100 W 1090 nm fiber laser was applied. The resulting samples were mechanically and optically characterized. A numerical multiphysics model was developed to understand the heat transfer and optimize the SLM process. Results obtained are in good agreement with the numerical model. The physical and chemical characteristics of the various materials (granulometry, density, composition, and thermal properties) have a strong impact on the AM parameters.

Temperature distribution analysis of carbon fiber reinforced polymer composites during self-resistance electric heating process

Self-resistance electric (SRE) heating for carbon fiber reinforced plastics (CFRP) is an alternative out-of-autoclave curing methodology that has high efficiency and low energy consumption. However, thanks to the heating mechanism of inside-out conduction, which is significantly different from that of the traditional outside-in heating process, the temperature distribution and its homogenization strategy still need further investigation. This work focuses on analyzing the affecting factors of the temperature uniformity of CFRP laminates during the SRE curing process utilizing a multi-physical numerical computation model and experimental verification. It is found that mold sizes have the most significant impact due to the non-uniform center-to-edge heat absorption of the mold. The maximum temperature difference during the untreated process could be lower than 20 K if the excess size proportion of the mold is smaller than 10%. Thermal barriers made of aerogel homogenize the temperature distribution during the dwell stage, reducing the maximum temperature difference by 84.18%. Considering that the mold size is sometimes unchangeable, the existence of auxiliary heating elements compensates the heat dissipation from the self-heated laminate and reduces the maximum temperature difference by 79.81%. Based on analysis results, a temperature homogenization strategy is proposed, where the maximum temperature difference is reduced by 86.15%.

Study of the effect of mechanical uncertainties parameters on performance of PEMFC by coupling a 3D numerical multiphysics model and design of experiment

As the PEMFC is a complex multi-physics device whose reliability and durability depend on the thermal-mechanical-electrical and chemical parameters. In this paper, theoretical and numerical studies is proposed to optimize the fuel cell performance using multiphysics model and design of experiments. 3D finite element analysis including a fully coupling of thermal-electrical-mechanical model is proposed to predict the electrical resistance of fuel cell. As the mechanical parameters (bending radius of the bipolar plate, thickness of the GDL and clamping pressure) remain uncertain, the design of experiments procedure is used to optimize the fuel cell behavior under several conditions.

Internal mixing air-assisted spray nozzle for large droplets: Experimental measurements and numerical simulations

In the present study, detailed experimental measurements of a large-droplet spray nozzle under a wide range of operating conditions have been conducted at China Aerodynamics Research and Development Center (CARDC) low-speed vertical wind tunnel facility. The droplet size distributions obtained from these measurements have been modeled using the Rosin-Rammler distribution. A multi-physics multi-phase numerical model for the simulation of the complex spray dynamics associated with the large-droplet spray nozzle has been developed in order to support the performance characterization of this device. More specifically, the primary breakup of liquid (water) in the atomizer-produced spray is modeled using a volume of fluid (VOF) to discrete phase model (DPM) transition representation. The numerical model is validated using the experimental measurements. The small relative error between the numerical predictions and experimental measurements for the droplet size distribution and for a number of characteristic droplet diameters suggest that the numerical model provides accurate high-fidelity predictions of the spray dynamics of the large-droplet spray nozzle. Moreover, it is shown that a simple modification of the spray nozzle (increasing the length of the mixing chamber by 50%) has a significant effect on the performance of the nozzle. In particular, the droplet median volumetric diameter and the spray angle are increased as the air pressure is decreased. Furthermore, an increase in the nozzle mixing chamber length results in a much broader droplet size distribution. The validated VOF-to-DPM transition model developed in this study can be used for a future redesign (involving modifications of some key geometric parameters) of the original large-droplet spray nozzle to generate reliably and robustly larger droplets required to simulate various supercooled large droplet conditions of practical relevance.

Influence of Deep Cryogenic Treatment on Microstructural Evolution and Transformation Kinetics Simulation by Finite Element Method of Low‐Carbon High‐Alloy Martensitic‐Bearing Steel

Nowadays, deep cryogenic treatment (DCT) is taken as a promising technique for improving the performance of steel. This article is focused on the influence of different heat treatment processes involving DCT on the microstructural evolution of a high Cr–Co–Mo high‐temperature‐bearing steel. Moreover, a multiphysical field coupling numerical model is built to investigate the martensitic transformation kinetics during DCT. The results show that DCT significantly improves the hardness and promotes the transformation of retained austenite to martensite at low temperatures. DCT not only refines the retained austenite as thin‐film morphology but also increases the precipitation of carbides and induces the carbides more homogenous distribution. This indicates that DCT promoted the segregation of carbon atoms and reduced the carbon content of martensite. The finite element model simulation shows that the retained austenite transformation is still incomplete, and the simulation results agree well with the experimental data by X‐Ray diffraction and transmission electron microscope analysis. This implies that the finite element simulation can better reflect and verify the experimental results.

Multi-physical modelling of alloy element transportation in wire arc additive manufacturing of a [formula omitted]-TiAl alloy

How to obtain homogeneous element distribution is a challenging research in wire arc additive manufacturing (WAAM) of γ-TiAl alloys, and the wire transfer has a great influence on it. A multi-physical numerical model considering the dissimilar wire feeding and melting, and element mixing is developed, and a high-speed video camera is adopted to investigate the wire transfer behaviors in WAAM of a γ-TiAl alloy. The Ti and Al elements can be transferred to the molten pool through a liquid TiAl bridge. However, the liquid TiAl bridge is not very stable, and the breakup between the Al wire and liquid TiAl bridge can be observed. The wetting ability (wetting angle) of the liquid TiAl metal on the Ti wire surface can be used to predict the possibility of the liquid TiAl bridge breakup. The surface tension causes backward flow and growth of a liquid TiAl droplet, and thus suppresses the droplet transfer.

Anti-interfering method for environmental foreign bodies for the microstrip antenna sensor

As a result of the rapid development of intelligent equipment, the importance of intelligent sensing technology for use in structural health monitoring applications is increasing. Among the emerging intelligent structure monitoring methods, microstrip antenna sensing technology is attracting considerable attention. The working environments for mechanical equipment are often harsh and highly differentiated. Multiple environmental jamming factors, including water, dust, ice, and other foreign bodies, will reduce the parameter monitoring reliability of microstrip antenna sensors. In this paper, an anti-interfering method for these environmental foreign bodies based on antenna cladding technology is presented. First, a multi-physical numerical model is established to study the mechanism by which the environmental foreign bodies affect the resonant frequency of the antenna sensor. The effects of the foreign bodies on the sensor’s resonant frequency are analyzed via simulations. The anti-interfering cladding design method for environmental bodies is then studied. The structure,a shape, and size of the environmental anti-interfering cladding are designed using an FR4 epoxy plate with good heat and moisture resistance, largely causing the fluctuation level of the sensor’s resonant frequency with changes in the environment to be reduced by more than 95%. The simulation and experimental results show that the proposed anti-interfering method for environmental foreign bodies using antenna cladding technology greatly improves the reliability of the microstrip antenna sensor and has considerable engineering application value.

Comparison of state-of-the-art machine learning algorithms and data-driven optimization methods for mitigating nitrogen crossover in PEM fuel cells

Nitrogen gas crossover (NGC) and nitrogen accumulation at the anode of proton exchange membrane (PEM) fuel cells are ineluctable and it would lead to inferior performance and even irreversible damage to functional components. To mitigate this issue, multiphysics numerical models (MNMs) are established to describe NGC behaviors and further guide experimental studies. However, to obtain the optimized parameters that would suppress NGC and retain high performance, grid search conducted on MSMs would cost unaffordable computational resources and time. Therefore, we innovatively introduced a machine learning-assisted MNM (MSM-ML) as a surrogate model, in which 9 state-of-the-art machine learning algorithms were compared, to greatly boost the resolution of this engineering problem. Through the proposed MSM-ML workflow performed on an experimentally validated MSM, the cost for obtaining the best parameter combination is greatly reduced. Moreover, the impact of each parameter in this complex system is directly revealed through the application of black-box interpretation methods afterwards. As a result, a new approach was pioneered to solve engineering problems which was demonstrated to be more efficient and intelligent than traditional methods. The NGC coefficient is reduced by 49.5%, while the power density is improved by 20% through the multivariable optimization of the developed MSM-ML.

Heat generation depth and temperature distribution in solar receiver tubes subjected to induction

Induction heating is commonly used in laboratory-scale facilities to replicate the heating conditions of the receiver tubes of concentrated solar power plants. This work aims at shedding light at the induction heating characteristics for such applications through the development of a multiphysics numerical model capable of replicating the experimental conditions of a molten salt loop locally heated by an induction heater. In the experiments, a stainless steel pipe is heated on its external surface by the induction heater, which is switched on and off during the experimental data acquisition while molten salts are continuously circulating in its interior. These conditions are replicated, for the first time, in a two-dimensional numerical domain fully coupling the electromagnetic and thermal physics, including thermally dependent material properties of the heated pipe. Once validated against the experiments, the numerical results revealed that the volumetric nature of the induction heating shall be considered for an accurate representation of the temperature profile inside the tube. As a novelty, different equivalent surface boundary conditions are presented and, despite the Gaussian-like behavior of the induction heating on the surface of the tube, the results indicate that there exists no equivalent wall boundary condition to fully replicate the temperature profile obtained with the induction heater. The effect of independently varying experimental parameters such as the geometry of the pipe (i.e., diameter and thickness) and its distance to the induction heating system is also evaluated. Using large diameters of the tube reduces the difference between the angular temperature profile obtained using induction heating and a simplified wall boundary condition. For small wall thicknesses, the induction heating is capable of penetrating along the whole thickness of the tube, the total heat generated in the volume of the tube being exposed to the counteracting effects of the volumetric generation and the enhancement of the heat dissipation by the molten salt, as both of them increase for small thicknesses. The distance of the inductor to the pipe wall appears to maintain the volumetric characteristics of the heating and only affects the induction heating magnitude and efficiency. • Fully coupled model of induction heating of a molten salt pipe is presented. • Induction promotes a volumetric heat generation in the pipe. • No equivalent surface heating can replicate induction heating. • Effect of different pipe geometries on the induction heating was characterized. • Induction reaches the whole pipe thickness for sufficiently thin tubes.

Parametric analysis and new performance correlation of the surface conventional rigid pavement temperature

A statistical model for predicting pavement surface temperature has been developed for the first time in this study. The main objective of this work is to analyse the impact of the input factors (solar radiation, ambient temperature, wind speed, and albedo) most affecting the conventional rigid pavement surface temperature. A multi-physics numerical model combining radiative, conductive, and convective heat transfers with a response surface methodology (RSM) model was created as an innovative and integrated approach. The numerical model of two-dimensional heat transport based on volume finite techniques is performed using FORTRAN software. Moreover, the analysis of variance (ANOVA) is used to establish the polynomial model or new correlation (quadratic regression) and analyse each input factor's statistical importance. Heat transfer model findings were in good agreement with the experimental data. For pavement surface temperature, the results show that the adjusted Radj2and predicted determination coefficients R2 achieved are 0.9912 and 0.9604, respectively. A good agreement is obtained between the statistical model's prediction values and the heat transfer model's numerical data. Based on the four analysed input factors, a simple polynomial statistical model is developed to forecast and reduce the conventional rigid surface pavement temperature. A wind speed of 1.215 m/s, an air temperature of 293.634 K, solar radiation of 222.305 W/m2 and albedo of 0.782 were found to be the optimal operating conditions for obtaining the lowest possible temperature on the pavement's surface.

Numerical Simulation Study on the Multi-Physical Field Response to Underground Coal and Gas Outburst under High Geo-Stress Conditions

Based on thermal–fluid–solid coupling law in coal and gas outburst, a multi-physical field numerical analysis model is built for the whole outburst process. The response laws of stress, gas pressure, temperature, and seepage in different areas and different time nodes around coal and rock mass in the coal and gas outburst under high stress condition are discussed. Research results show: Firstly, the stress response law of the coal and rock mass around the burst hole is initial vibration–sudden attenuation–late stability. Secondly, the gas pressure response law in different areas is that the gas pressure response rate decreases gradually with the increase of the distance from the outburst. Thirdly, the adsorbed gas contained in the broken coal near the outburst port is desorbed rapidly and expands to do work, and the temperature changes dramatically after outburst occurs. In contrast, with the increase of stress, the proportion of elastic potential in total coal and gas outburst energy increases, and the proportion of elastic potential is positively correlated with stress. The critical gas pressure under the energy condition of coal and gas outburst decreases with the increase of stress. It illustrates that the lower gas pressure can also meet the energy condition of coal and gas outburst under high stress.

Passive Intermodulation on Coaxial Connector Under Electro-Thermal-Mechanical Multiphysics

This work proposes and demonstrates a multiphysics model for the passive intermodulation (PIM) effect on coaxial connectors with complex electro-thermal-mechanical coupling. The PIM effect under multiphysics is numerically modeled and solved from the basis of contact components and parameters. In the experimental demonstration, to get rid of the random test error, the design of experiment method is utilized to build an empirical model for verification. The comparison shows the max prediction differences with comparison among the proposed numerical multiphysics model, empirical model, and experiment are within ±3 dB; the good match between the experiment and predictions proves the theory.

Study on the transition behavior of the bulging effect during deep penetration laser beam welding

The present work is devoted to the study of the transition behavior of the recently confirmed widening of the weld pool, known as the bulging effect, during high-power deep penetration laser beam welding of thick unalloyed steel sheets. A three-dimensional transient multi-physics numerical model is developed, allowing for the prediction of the bulge formation and the study of its temporal behavior. The model is generalized to account automatically for the transition from partial to complete penetration. Several experimental measurements and observations, such as drilling period, weld pool length, temperature, efficiency, and metallographic cross-sections are used to verify the model and assure the plausibility of the numerical results. The analysis of the calculated temperature and velocity distributions, as well as the evolution of the keyhole geometry, shows that the formation of a bulging region strongly depends on the penetration depth of the weld. Based on the numerical results, the bulge is found to occur transiently, having its transition from a slight bulge to a fully developed bulging between penetration depths of 6 mm and 9 mm, respectively.

Multiphysics Optimization for First Wall Design Enhancement in Water-Cooled Breeding Blankets

The commercial feasibility of the first fusion power plant generation adopting D-T plasma is strongly dependent upon the self-sustainability in terms of tritium fuelling. Within such a kind of reactor, the component selected to house the tritium breeding reactions is the breeding blanket, which is further assigned to heat power removal and radiation shielding functions. As a consequence of both its role and position, the breeding blanket is heavily exposed to both surface and volumetric heat loads and, hence, its design requires a typical multiphysics approach, from the neutronics to the thermo-mechanics. During last years, a great deal of effort has been put in the optimization of the breeding blanket design, with the aim of maximizing the tritium breeding and heat removal performances without undermining its structural integrity. In this paper, a derivative-free optimization method named “Complex method” is applied for the design optimization of the European DEMO Water-Cooled Lithium Lead breeding blanket concept. To this purpose, a potential performances-based objective function, focusing on the maximization of the tritium breeding, is defined and a multiphysics numerical model of the blanket is developed in order to solve the coupled thermo-mechanical problem, while the optimization algorithm leads the design towards a minimum optimum point compliant with the prescribed requirements. Once the optimized design is obtained, its nuclear and thermo-structural performances are assessed by means of specific neutron transport and multiphysics simulations, respectively. Finally, the structural integrity is verified by means of the application of the RCC-MRx design criteria. • A tool for First Wall optimization in water-cooled breeding blankets is developed. • The optimization is performed using the gradient-free method named “Complex method”. • An objective function aiming at tritium breeding maximization is defined. • A FE model is used to check the compliance with the thermo-structural requirements. • The optimized design is finally assessed by proper, more detailed numerical analyses.

Ultrafast synchrotron X-ray imaging and multiphysics modelling of liquid phase fatigue exfoliation of graphite under ultrasound

Ultrasound-assisted liquid phase exfoliation is a promising method for manufacturing of 2D materials in large scale and sustainable manner. A large number of studies using ex-situ nano/micro structural characterization techniques have been made to investigate the underlying mechanisms, aiming to understand the exfoliation dynamics. Due to the complex multiphysics and multi-length nature of the process, those ex-situ methods cannot provide the real-time and in-situ dynamic information for understanding how exactly layer exfoliation starts and grows under ultrasound. Here, we used the ultrafast synchrotron-X-ray phase-contrast imaging (a combined temporal resolution of 3.68 μs and a spatial resolution of 1.9 μm/pixel) to study the exfoliation dynamics in real time and operando condition. We revealed, for the first time, the fatigue exfoliation phenomenon at the graphite surface caused by the imploding ultrasonic bubbles occurring cyclically in line with the ultrasound frequency. A multiphysics numerical model was also developed to calculate the shock wave produced at bubble implosion and the resulting cyclic and impulsive tensile and shear stresses acting on the graphite surface. Our research reveals that the graphite layer exfoliation rate and efficiency are predominantly determined by the number of imploding bubbles inside the effective cavitation bubble zone. The findings are valuable for developing industrial upscaling strategies for ultrasound processing of 2D materials.

Lubrication and stability enhancement by attaching superconducting magnetic force on non-contacting mechanical seals for reusable rocket turbopump

The purpose of this paper is to investigate the lubrication performance and stability improvement of rocket turbopump mechanical seals by attaching superconducting magnetic force. A comprehensive multiphysics numerical model is presented including microscale clearance flow, magnetic field, as well as three degrees of freedom dynamic motion. The Maxwell equation and modified Reynolds equation considering mass-conserving boundary conditions and turbulence flow were solved simultaneously at each time step to obtain the transient response of sealing parameters. Results indicate that the mechanical seal attaching superconducting magnetic force could dramatically improve carrying capacity and lubrication characteristics under heavy loading conditions, and it also has an appreciable effect on dynamic stability. It is worth exploring the application of superconducting magnetic force in reusable rockets and cryogenic equipment combined with its unique advantages.

Thermal stresses and temperature distribution of granite under microwave treatment

Efficient breakage of high strength rocks is a challenging task where conventional drilling and blasting methods are not preferred or allowed, for example, rock excavation in long tunnels at a great depth and urban environment sensitive to noise and vibration. Microwave treatment is an efficient and environmentally friendly method, which is considered to be one of the most promising ways to increase the performance of mechanical excavators, such as roadheaders and impact hammers. However, the mechanisms of microwave fracturing of granitic rocks have not been well investigated. In this study, Chinese granite was used as the research material. Its mineral composition and grain size were first characterized using petrographic thin section observation. Cubic granite samples were then heated in a single-mode industrial microwave. The temperature was captured using a high resolution infrared thermal camera. Then a realistic 3-D rock model with the same mineralogical properties was established using Voronoi tessellation. The multi-physics numerical model was calibrated using data from microwave heating tests. The effect of microwave power intensity, heating time, and mineral grain size on the temporal and spatial temperature distribution, and thermal stresses in the granite matrix was investigated in a comprehensive manner. The temperature gradients and thermal stresses were calculated. The maximum temperature gradient and the maximum tensile stress appeared at the interface between quartz and biotite. As either power level or heating time increased, the thermal gradient and the maximum tensile stress increased, and with same microwave energy output, greater temperature gradient and thermal stress could be generated during microwave heating at higher power levels for shorter durations. Moreover, the greater the grain size, the bigger the maximum tensile stress. The finding of the paper contributes the understanding of the mechanisms of microwave fracturing of rocks.