Multiphysics Finite Element Model Research Articles

Equivalent circuit model of eddy current damping regarding frequency-dependence with test validation

This study proposes an equivalent circuit model to simulate the mechanical behavior and frequency-dependent characteristic of eddy current (EC) damping, with the validations from multi-physics finite element (FE) modeling and dynamic testing. The equivalent circuit model is first presented with a theoretical expression of the EC damping force. Then, the transient analysis with an ANSYS-based FE model of an EC damper is performed. The time-history forces from the FE model are compared with that from the proposed equivalent circuit model. The favorable agreement indicates that the proposed model can simulate the nonlinear behavior of EC damping under different excitation scenarios. A noncontact and friction-free planar EC damper is designed, and its dynamic behavior is measured by employing shake table testing. The experimental observations can be reproduced by the proposed equivalent circuit model with reasonable accuracy and reliability. The proposed equivalent circuit model is compared with the classical viscous model and the higher-order fractional model using a complex EC damper simulated in ANSYS to show the advantages of the proposed model regarding model simplicity and prediction accuracy. A single-degree-of-freedom (SDOF) structure with different EC damping models is further analyzed to illustrate the need for accurate EC damping modeling.

System-Level Modelling and Simulation of a Multiphysical Kick and Catch Actuator System

This paper presents a system-level model of a microsystem architecture deploying cooperating microactuators. An assembly of a piezoelectric kick-actuator and an electromagnetic catch-actuator manipulates a structurally unconnected, magnetized micromirror. The absence of mechanical connections allows for large deflections and multistability. Closed-loop feedback control allows this setup to achieve high accuracy, but requires fast and precise system-level models of each component. Such models can be generated directly from large-scale finite element (FE) models via mathematical methods of model order reduction (MOR). A special challenge lies in reducing a nonlinear multiphysical FE model of a piezoelectric kick-actuator and its mechanical contact to a micromirror, which is modeled as a rigid body. We propose to separate the actuator–micromirror system into two single-body systems. This step allows us to apply the contact-induced forces as inputs to each sub-system and, thus, avoid the nonlinear FE model. Rather, we have the linear model with nonlinear input, to which established linear MOR methods can be applied. Comparisons between the reference FE model and the reduced order model demonstrate the feasibility of the proposed methodology. Finally, a system-level simulation of the whole assembly, including two actuators, a micromirror and a simple control circuitry, is presented.

Machine learning approaches for predicting geometric and mechanical characteristics for single P420 laser beads clad onto an AISI 1018 substrate

The final mechanical and physical properties should be predicted in tandem with the bead geometry characteristics for effective additive manufacturing (AM) solutions for processes such as directed energy deposition. Experimental approaches to investigate the final geometry and the mechanical properties are costly, and simulation solutions are time-consuming. Alternative artificial intelligent (AI) systems are explored as they are a powerful approach to predict such properties. In the present study, the geometrical properties as well as the mechanical properties (residual stress and hardness) for single bead clads are investigated. Experimental data is used to calibrate multi-physics finite element models, and both data sets are used to seed the AI models. The adaptive neuro-fuzzy inference system (ANFIS) and a feed-forward back-propagation artificial neural network (ANN) system are utilized to explore their effectiveness in the 1D (discrete values), 2D (bead cross-sections), and 3D (complete bead) domains. The prediction results are evaluated using the mean relative error measure. The ANFIS predictions are more precise than those from the ANN for the 1D and 2D domains, but the ANN had less error for the 3D scenario. These models are capable of predicting the geometrical and the mechanical properties values very well, including capturing the mechanical properties in transient regions; however, this research should be extended for multi-bead scenarios before a conclusive “best approach” strategy can be determined.

Validated Multi-Physical Finite Element Modelling of the Spot Welding Process of the Advanced High Strength Steel DP1200HD.

Resistance spot welding (RSW) is a common joining technique in the production of car bodies in white for example, because of its high degree of automation, its short process time, and its reliability. While different steel grades and even dissimilar metals can be joined with this method, the current paper focuses on similar joints of galvanized advanced high strength steel (AHSS), namely dual phase steel with a yield strength of 1200 MPa and high ductility (DP1200HD). This material offers potential for light-weight design. The current work presents a multi-physical finite element (FE) model of the RSW process which gives insights into the local loading and material state, and which forms the basis for future investigations of the local risk of liquid metal assisted cracking and the effect of different process parameters on this risk. The model covers the evolution of the electrical, thermal, mechanical, and metallurgical fields during the complete spot welding process. Phase transformations like base material to austenite and further to steel melt during heating and all relevant transformations while cooling are considered. The model was fully parametrized based on lab scale material testing, accompanying model-based parameter determination, and literature data, and was validated against a large variety of optically inspected burst opened spot welds and micrographs of the welds.

Static and fatigue behavior of induction-welded single lap carbon fiber reinforced polyetherketoneketone thermoplastic composite joints

This paper presents details of the mechanical properties related to the static and fatigue strength of carbon fiber reinforced polyetherketoneketone (CF/PEKK) thermoplastic induction-welded composite joints. To better understand the process parameters, the finite element modeling (FEM) of the heat distribution was analyzed based on the generator power, coil coupling distance, coil moving speed, frequency, compaction force, and coil geometry while maintaining the optimal coil speed. The temperature behavior calculated using the simulation model exhibited good agreement with experimental results. A microscopic inspection, non-destructive test (NDT) was conducted to check the morphology characteristics of the welded joints. To check the mechanical performance of the induction-welded specimens, single-lap shear strength (SLSS) tests under static and cyclical fatigue loading conditions were conducted to check the weld qualities from a practical perspective. The mechanical testing results indicated that the static and cyclical fatigue specimens were dominated by a cohesive failure mode with a light fiber tear (LFT). These results suggested that using the optimal process parameters based on multi-physics FEM simulation could potentially improve mechanical performance.

Optimal design and analysis of airfoil radiator fins based on weakly compressible turbulence

In order to further improve the heat dissipation performance of the forced air-cooled radiator in the simplest and most efficient way, this paper firstly proposes an airfoil optimization design of radiator fin structure. Then, based on the weakly compressible turbulence theory, a multi-physics coupling finite element model (FEM) that can highly restore actual phenomena is constructed. The temperature field, velocity field, and pressure field in the radiator are analyzed and verified qualitatively and quantitatively by this FEM. Finally, a comprehensive comparative analysis of the cooling power, average pressure loss, and cooling power per unit volume of traditional radiators and airfoil radiators are carried out in terms of the number of fins and the airflow rate. The results show that the performance of the airfoil radiator is significantly better than the traditional radiator: the cooling power is increased by at least 8.14%, the average pressure loss is greatly reduced, at least 31.15%, and the cooling power per unit volume is steadily increased by 15.92%. It can be seen that the optimized design can take into account both efficiency and practicality. The analysis methods and conclusions presented in the article have not only direct guiding significance for solving practical problems, but also have universal reference value for future research.

Experimental Investigation of Thermal Actuation Crosstalk in Phase-Change RF Switches Using Transient Thermoreflectance Imaging

This article reports an experimental investigation of transient heat distribution and thermal actuation crosstalk in phase-change material (PCM) germanium telluride (GeTe)-based radio frequency (RF) switches. The RF switches are designed and optimized for efficient thermal energy transport from the embedded microheater to the PCM. Various multiport miniaturized monolithically integrated complex RF components require several switches to be integrated extremely close to each other. Thermal crosstalk is crucial in multiport complex devices to ensure that individual tuning elements actuate independently without influencing nearby switches’ performance. Thermal cross section simulations are performed using multiphysics finite-element modeling (FEM) to optimize the heat distribution within the PCM channel and are experimentally validated via transient thermoreflectance imaging technique with ultrafast temporal and spatial resolution. The devices are fabricated in-house using a custom eight-layer microfabrication process. The optimum device bias conditions, melt-quench sequence, and thermal actuation crosstalk limits are experimentally validated to develop miniaturized monolithic densely packed complex reconfigurable phase-change circuits. It is the first-ever demonstration of experimental transient thermal insights on phase-change RF switches.

Heating performance of a novel externally-heated geothermal bridge de-icing system: field tests and numerical simulations

An external geothermal bridge de-icing system deploys hydronic loops covered in insulation and attached to bridge decks to heat the bridge using geothermal energy. Several studies were performed on the laboratory system under controlled temperatures and showed promising results for field deployment. However, no field tests or investigations of its heating performance were conducted during snow events. In this study, the external geothermal bridge de-icing system was deployed on a mock-up bridge deck in the field and tested during several winter events, providing an opportunity to conduct non-heating, heating, and de-icing tests. A 3-dimensional multi-physics finite element model of the heated deck was developed in COMSOL and fully calibrated with the field tests in transient analyses. The simulated temperatures were verified with the measured thermocouple readings at the inlet and outlet of the bridge loops and different bridge deck depths. Based on the calibrated FEM model, a record snowfall event in the Spring of 2015 was simulated using the equivalent snow-melting heat flux loss on the deck surface. The heated bridge deck maintained a minimum temperature of 0.3 °C (32.6 °F) during the snow event with a supplied inlet temperature of 43.3 °C (110 °F), and the equivalent heat flux loss on the deck surface was around 220 W/m2. The developed FEM model provided satisfactory simulations of bridge heating in winter events. The external geothermal bridge de-icing system maintained a snow-free deck during the record snow event and is ready for implementation.

A thermo-mechanical terrestrial model of Arctic coastal erosion

Although the Arctic comprises one-third of the global coastline and has some of the fastest eroding coasts, current tools for quantifying permafrost erosion are unable to explain the episodic, storm-driven erosion events that occur in this region. In this paper, we present a novel multi-physics finite element model for the numerical simulation of Arctic coastal permafrost degradation: the terrestrial component of the Arctic Coastal Erosion (ACE) model. This model is comprised of two main ingredients: (1) a solid mechanics model that calculates the three-dimensional (3D) stress, strain and displacement fields of the underlying permafrost developing in response to a frozen water content dependent plasticity model, and (2) a novel thermal model governing the 3D heat conduction and solid–liquid phase change occurring within the permafrost. These two physics sets are coupled via a sequential thermo-mechanical coupling scheme developed within the AlbanyLCM open-source finite element code. Unlike prior approaches, our modeling methodology enables failure from any allowable deformation (block failure, thermo-denudation, thermo-abrasion); moreover, failure modes develop from constitutive (rather than empirical) relationships inherent in the underlying finite element model. Elements are dynamically removed from the underlying finite element mesh so as to simulate transient permafrost erosion events. Our thermo-mechanical terrestrial model is evaluated on a pseudo-realistic problem in which a slice of permafrost is exposed to realistic oceanic and atmospheric forcing boundary condition data occurring at Drew Point, Alaska in July 2018.

Impact of brain shift on neural pathways in deep brain stimulation: a preliminary analysis via multi-physics finite element models

Objective. The effectiveness of deep brain stimulation (DBS) depends on electrode placement accuracy, which can be compromised by brain shift during surgery. While there have been efforts in assessing the impact of electrode misplacement due to brain shift using preop- and postop-imaging data, such analysis using preop- and intraop-imaging data via biophysical modeling has not been conducted. This work presents a preliminary study that applies a multi-physics analysis framework using finite element biomechanical and bioelectric models to examine the impact of realistic intraoperative shift on neural pathways determined by tractography. Approach. The study examined six patients who had undergone interventional magnetic resonance-guided DBS surgery. The modeling framework utilized a biomechanical approach to update preoperative MR to reflect shift-induced anatomical changes. Using this anatomically deformed image and its undeformed counterpart, bioelectric effects from shifting electrode leads could be simulated and neural activation differences were approximated. Specifically, for each configuration, volume of tissue activation was computed and subsequently used for tractography estimation. Total tract volume and overlapping volume with motor regions as well as connectivity profile were compared. In addition, volumetric overlap between different fiber bundles among configurations was computed and correlated to estimated shift. Main results. The study found deformation-induced differences in tract volume, motor region overlap, and connectivity behavior, suggesting the impact of shift. There is a strong correlation (R = −0.83) between shift from intended target and intended neural pathway recruitment, where at threshold of ∼2.94 mm, intended recruitment completely degrades. The determined threshold is consistent with and provides quantitative support to prior observations and literature that deviations of 2–3 mm are detrimental. Significance. The findings support and advance prior studies and understanding to illustrate the need to account for shift in DBS and the potentiality of computational modeling for estimating influence of shift on neural activation.

Evaluation and validation of a multiphysics finite element model for a piezoelectric energy harvester

This study explores the applicability of the multiphysics finite element method to model a piezoelectric energy harvester. The piezoelectric energy harvester under consideration consists of a stainless-steel cantilever beam attached to a piezoelectric ceramic patch. Two configurations were considered: one without a proof mass and one with a proof mass. COMSOL Multiphysics software is used to simultaneously model three physics: solid mechanics, electrostatics, and electrical circuit physics. Several key relationships were investigated to predict the behaviour of the piezoelectric energy harvester. The effects of the electrical load resistance and proof mass on the performance of a piezoelectric energy harvester were evaluated. Experimental testing was conducted to validate the results obtained using the finite element model. Overall, the results from the finite element model closely matched those from the experimental testing. It was found that increasing the load resistance of the piezoelectric energy harvester caused an increase in voltage across the load resistor, and matching the impedance yielded the maximum power output. Increasing the proof mass reduces the fundamental frequency, which results in an increase in the displacement transmissibility and impedance-matched resistance. The study shows that the multiphysics finite element method is effective for modelling piezoelectric energy harvesters.

Modeling the effects of individual layer thickness and orientation on the tribocorrosion behavior of Al/Cu nanostructured metallic multilayers

Nanostructured metallic multilayers (NMMs) are emerging materials with excellent mechanical, tribological, and corrosion properties, making them ideal candidates to be used under extremely conditions. The high wear and corrosion resistance lead to enhanced tribocorrosion resistance of NMMs compared to many traditional metals and alloys. In this work, a multiphysics finite element model was developed to study the material deformation and degradation during tribocorrosion from wear, corrosion, as well as their synergy. Specifically, this model accounts for elastic-plastic mechanical deformation during wear and galvanic corrosion between exposed inner layers after wear. The effects of individual layer thickness (from 10 to 100 nm) and layer orientation (horizontally and vertically aligned) on the tribocorrosion behavior of Al/Cu NMMs was studied. Both factors were found to affect the subsurface stress and plastic strain distribution and localized surface corrosion kinetics, hence affecting the overall tribocorrosion rate. This model and the obtained understanding could shed light on future design and optimization strategies of NMMs against tribocorrosion.

Research on Steady‐State Thermal Behavior of SF6/N2 and CF3I/N2 Mixtures in High Voltage Gas‐Insulated Lines (GIL)

Gas‐insulated lines (GIL) are widely used due to their many advantages in power plants and substations. The security and reliability of GIL is achieved by continues testing and monitoring. The main fault in the GIL compartments is overheating, which is rarely to occur, nonetheless, it cannot be ignored. In the present study, GIL steady‐state thermal behavior was investigated. For this reason, a multiphysics finite element model (FEM) was built to analyze the magneto‐hydro‐thermal characteristics of the GIL insulation gas. The simulation coupling includes the electromagnetic field, flow field and thermal heat transfer field. SF6/N2 and CF3I/N2 mixtures were studied and the influence of different gas properties on the magnetic flux density, heat distribution and flow velocity had been investigated. The results were compared to an experimental setup to validate the model calculations. Temperature rise tests have been conducted on the GIL inner and outer shell. The measurements were in good agreement with the simulation results. Finally, the presented work is also to serve as a good reference in future design and optimization of GIL structure. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Modeling and simulation of 3D geometry prediction and dynamic solidification behavior of Fe-based coatings by laser cladding

To accurately predict the three-dimensional (3D) characteristics of the coating and dynamic solidification process during coaxial powder-fed laser cladding, an improved 3D multi-physics finite element model including heat transfer, fluid flow, shielding gas pressure, powder temperature-rise, surface tension, and free surface movement is proposed. The input parameters of the model only depend on the thermophysical properties of the deposited material and the process parameters. Therefore, the model has good universality, and can be flexibly applied in other laser cladding systems or deposited materials. The average width and height error for the experimental and simulated is 6.05% and 4.15%, respectively. The numerical model has good abilities to predict the 3D geometry of the coating. The accuracy of the model can be indeed improved by considering the powder temperature-rise and shielding gas pressure during the modeling process. The dynamic growth process of the coating, spatiotemporal variations of the temperature and temperature gradient were discussed in detail to reveal the solidification mechanism. Finally, the relationship between the crystal characteristic (planar, cellular, columnar, and equiaxed grains) and thermal parameters (the temperature, the temperature gradient, and the solidification rate) was established. The results show that the temperature gradient and undercooling at the solidification interface are significantly responsible for the crystal characteristic, while the grain size is mainly governed by the solidification rate.

Trans-scale multi-physics coupling finite element model of concrete during freezing and thawing

This paper presents a trans-scale finite element model based on hydraulic-thermal-mechanical coupling equations of porous medium to simulate the behavior of concrete during freezing and thawing. Unlike previous models that regard concrete as homogeneous material, this paper aims to establish a macro-size concrete model with detailed micro-structure, the aggregates (mm) and air voids (μm) are randomly generated by the Monte Carlo method, and the interfacial transition zones (μm) with random thickness are built around the aggregates. The capillary pores (nm) of concrete is expressed by the relationship between the percentage of frozen ice and the radius of capillary pore. The simulation results reveal the mechanism of air voids protecting the concrete from freezing and thawing damage, and the mechanical field shows the freezing and thawing damage occurs preferentially at the interfacial transition zone, because the stress concentration due to the irregular distribution of aggregates and water resistance of aggregates. The temperature boundary conditions were also varied to study the influence of the temperature change rate on hydrostatic pressure and volume stress. The effect of the cement paste's pore structure, including the spacing of air voids, on the ability of concrete to resist freezing and thawing is presented.

Electromechanical response of multilayered piezoelectric BaTiO3/PZT-7A composites with wavy architecture

Electromechanical laminated composites with piezoelectric phases are increasingly being explored as multifunctional materials providing energy conversion between electric and mechanical energies. The current work explores thus-far undocumented combined microstructural effects of amplitude-to-wavelength ratio, volume fraction, poling direction of piezoelectric phases on both the homogenized properties and localized stress/electric field distributions in multilayered configurations under fully coupled electro-mechanical loading. In particular, the Multiphysics Finite-Volume Direct Averaging Micromechanics (FVDAM) and its counterpart, an in-house micromechanical multiphysics finite-element model, are utilized to investigate the homogenized and localized responses of wavy multilayered piezoelectric BaTiO3/PZT-7A architectures. These two methods generate highly agreeable results. Moreover, we critically examine the convergence of the finite-volume and finite element-based approaches via the Average Stress Theorem and Average Electric Displacement Theorem. The comparison shows the finite volume-based approach possesses a better numerical convergence. This study illustrates the FVDAM’s ability toward the analysis and design of engineered multilayered piezoelectric materials with wavy architecture.

Microstructure and surface texture driven improvement in in-vitro response of laser surface processed AZ31B magnesium alloy

The present work explored effects of laser surface melting on microstructure and surface topography evolution in AZ31B magnesium alloy. Thermokinetic effects experienced by the material during laser surface melting were simulated using a multiphysics finite element model. Microstructure and phase evolution were examined using scanning electron microscopy, X-ray diffraction, and electron back scatter diffraction. Surface topography was evaluated using white light interferometry. The interaction of surface melted samples with simulated body fluid was monitored by contact angle measurements and immersion studies up to 7 days. Laser surface melting led to formation of a refined microstructure with predominantly basal crystallographic texture. Concurrently, the amount of β phase (Mg17Al12) increased with an increase in the laser fluence. β phase preferentially decorated the cell boundaries. In terms of topography, the surface became progressively rougher with an increase in laser fluence. As a result, upon immersion in simulated body fluid, the laser surface melted samples showed an improved wettability, corrosion resistance, and precipitation of mineral having composition closer to the hydroxyapatite bone mineral compared to the untreated sample.

Human brain FE modeling including incompressible fluid dynamics of intraventricular cerebrospinal fluid

Elucidating the mechanisms of mild traumatic brain injuries (mild TBIs), including concussions, is important for developing brain injury criteria and designing head protection devices. Using a finite element (FE) model of the human brain to predict the deformation of the brain parenchyma during a head impact could provide mechanical insights on mild TBIs. However, most conventional brain FE models do not consider how fluid behavior and the perfusion pressure of the cerebrospinal fluid (CSF) will affect brain deformation. This study proposes a novel brain FE model that uses incompressible fluid dynamics (ICFD) to represent the fluid behavior of CSF in the ventricle. In the model with ICFD, the validation accuracy scores on the brain strain during a head impact with a rotational acceleration were significantly higher than those in the model without ICFD. Reconstruction simulations based on two reported mild TBI cases from a rear-end collision and an American football game were conducted using the model with and without ICFD. We found that the maximum principal strain values in the subcortical region and corpus callosum of the model with ICFD were higher and lasted longer than those of the model without ICFD, and this tendency was further enhanced when perfusion pressure was applied. These findings suggested that the fluid behavior and perfusion pressure of the intraventricular CSF could significantly affect the deformation of the brain parenchyma during head impacts. The proposed brain multiphysical FE model could enhance the understanding of mild TBI mechanisms. Statement of SignificanceMild TBIs or concussions can result from brain deformations caused by the rapid acceleration of the head in the situations such as falls, vehicular accidents, and collisions in sports-related activities. A FE analysis is an effective tool for simulating head impact scenarios associated with mild TBIs and estimating the brain strain. Accurate prediction of mild TBIs requires a brain FE model with high biofidelity. Here, we firstly revealed that the validation accuracy of the model on the brain strain can be improved by considering the fluid behavior of intraventricular CSF. By analyzing existing mild TBI cases using the proposed model, the fluid behavior and perfusion pressure of the CSF were found to significantly affect the brain strain history, resulting in an outcome similar to the clinical symptom. The proposed multiphysical brain model could potentially provide new mechanical insights and further understanding of mild TBIs. Additionally, these findings in this study could be useful in developing brain injury criteria and designing protective equipment.

Micromechanics modeling and homogenization of glass fiber reinforced polymer composites subject to synergistic deterioration

Composites have been successfully adopted in manufacturing and aerospace applications and are rapidly expanding into civil infrastructure. This paper develops an experimentally-validated 3D multi-physics finite element model for predicting the synergistic effects of combined physical/chemical degradation processes of UV radiation and water condensation at elevated temperatures in representative volume elements of glass fiber reinforced polymeric matrix composites subjected to environmental exposure and mechanical loading. Validation studies are conducted by comparing the results of multi-physics FEM simulations with accelerated exposure experiments. Sensitivity analyses are conducted to investigate the effect of mesh density on the accuracy of results. The effects of woven structure, diffusive parameters, and matter loss flux on the evolution of deterioration are analyzed on both a local and global scale.

Surface acoustic wave pressure sensor on ScAlN/3C-SiC/Si layer structure incorporating biomimetic microcantilever: modelling and performance enhancement

This paper presents a bio-inspired cantilever-type SAW pressure sensor based on Scandium-doped AlN (ScAlN)/3CSiC/Si layer structure. The proposed biomimetic microcantilever is configured with stress concentration region (SCR) comprising of a series of narrow slits. For a given depth, by properly setting the number and the width of those slits for a given depth, homogeneous stress/strain distribution in vicinity of SCR are achieved. Furthermore, multi-physics finite element modeling for evaluating the pressure coefficient of frequency (PCF) of a one-port SAW resonant sensor is performed and validated. Then the PCF for the proposed SAW pressure sensor with the optimized biomimetic microcantilever is analyzed. The dependence of ScAlN thin film thickness h ScAlN and scandium-doped concentration r of Sc r Al1-r N thin film on PCF for different SAW modes including Rayleigh mode and Sezawa mode are calculated. The investigation results show that the maximum PCF of −111 ppm bar−1 can be achieved for Rayleigh mode, which is 2.4 times larger than that of the previously reported ZnO/Si structure. In addition, its PCF has weak dependence on h ScAlN, which are quite favorable for manufacturing pressure sensors with good reproducibility. The conceived bio-inspired cantilever-type SAW devices based on ScAlN/3 CSiC/Si structure will open the door to develop pressure sensors with a stable and reliable performance and enhanced sensitivity.