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The effect of grading direction on the natural frequencies of heterogeneous isotropic beams is investigated and the artificial neural network approach is conducted to estimate the free vibration characteristics. The two-dimensional beam is graded in axial or transverse direction according to the power-law form. An artificial neural network model has been developed to estimate relationship between material properties and model, grading direction, slenderness ratio as an input layer and natural frequencies obtained by Finite-Element method as an output layer. The Levenberg–Marquardt back-propagation method is used as a training algorithm. The novelty of this study is that it deals with the estimation of free vibration characteristics of beams made of functionally-graded material using aforementioned input layer for the first time. The proposed artificial neural network model can predict the natural frequencies without the need for a solution of any differential equation or time-consuming experimental processes. The results show that artificial intelligence techniques can be efficiently adopted to free vibration problems of functionally graded beams. The influence of grading direction on the natural frequency is also demonstrated.

In this paper, we derive the weak form for clamped plates composed of incompressible neo-Hookean material from the uniformly valid asymptotic plate theory. By using the finite-element software COMSOL, we study the numerical solutions of the weak form. We show the accuracy and the efficiency of the weak form by comparing the numerical results for the two-dimensional weak form and a three-dimensional model. As a basis for comparison we choose numerical values of the displacement, the second Piola–Kirchhoff stress, and the Green–Lagrange strain at the bottom. The numerical simulations are performed for three different cases of thickness–span ratios, including (1) very thin plate, (2) thin plate, and (3) moderately thick plate. The results show that the uniformly valid plate theory is a reliable and implementable plate theory for even moderately thick plates with large deformations.

A research subject in structural engineering is the problem of vibration under a loading object. The two-dimensional (2D) model of a structure under loading is an example. In general, this case uses an object that is given a random frequency, which then causes various changes in shape depending on the frequency model. To determine the difference in performance by looking at the different forms of each mode, modal analysis with ANSYS was used. The samples to be simulated were metal plates with three variations of the model, namely, a virgin metal plate without any holes or stiffness, plates with given holes, and metal plates with stiffness on one side. The model was simulated with modal analysis, so that 20 natural frequencies were recorded. The sample also used different materials: low-carbon steel materials (AISI 304), marine materials (AISI 1090), and ice-class materials (AR 235). Several random-frequency models proved the deformation of different objects. Variations of sheet-metal designs were applied, such as pure sheet metal, giving holes to the sides, and stiffening the simulated metal sheet.

Ultrasound provides a way to clean fouled pipes in industrial settings without interrupting the production. Ultrasonic clamp-on cleaners are used to clean pipes, but they typically cannot focus the cleaning power. This leads to insufficient cleaning results in cases where the fouling is localized to certain parts of the pipe. To solve this issue, we propose a finite-element method -based time-reversal (FEM-TR) technique for controlling the acoustic field produced by an ultrasonic clamp-on cleaner. We demonstrate by simulations and experimental validation that FEM-TR can be used to control the acoustic field in clamp-on cleaners featuring relatively few narrow-band and high-power transducers. The proposed method allows us to focus sound to arbitrary pre-selected locations inside the structure. © 2022 The Authors 8868/31/2017 We thank Mr. Joni Mäkinen for his valuable input regarding the implementation of the simulation model. This work was supported by Altum Technologies Oy and Business Finland (project no. 8868/31/2017).

The aim of this paper is to present a novel model-order reduction (MOR) technique for the efficient frequency-domain finite-element method (FEM) simulation of microwave components. It is based on the standard reduced-basis method, but the subsequent expansion frequency points are selected following the so-called sparsified greedy strategy. This feature makes it especially useful to perform a fast-frequency sweep of problems that lead to systems of equations exhibiting a nonaffine frequency dependence. This property appears, for example, when the excitation of the problem is characterized by a frequency-dependent waveguide mode pattern, or when the computational domain includes materials with frequency-dependent permittivity or permeability tensors. Moreover, the new MOR scheme can be also used to accelerate the frequency sweep of problems with many excitations, for which the standard reduction algorithms tend to be time-consuming. Its effectiveness and accuracy is verified through analysis of three microwave structures: planar microstrip branch-line coupler, three-port waveguide junction with ferrite post, and an eighth-order dual-mode waveguide filter.

The objective of this study is to compare the performance for welded beam-column joints in aluminum structures using moment-rotation diagrams and to evaluate the influence of welding on joint rigidity. A nonlinear numerical calculation of welded beam–column joints is performed using the finite element method. Material and geometric nonlinearities were included in the model. The connection was analyzed for two cases: variants with and without welded stiffener plates. Two material models were used. The first was derived from the applicable standard for aluminum structures, while the other was based on the results of a previous material study and calibrated using a separate numerical calculation. From the results of the calculations, moment-rotation diagrams for different geometries and material properties of joints were constructed and compared. The obtained moment-rotation diagrams for the stiffened and unstiffened joints demonstrate that stiffening of the joints in aluminum structures improves the properties of the joint in terms of higher rigidity, resistance, and ductility, regardless of the existence of the heat affected zone.

This letter proposes the application of a hybrid numerical technique to two cases of interest in the space business: the reallocation of radiators and scatters on satellite platforms; and the analysis of antennas for mobile communications. It is based on the analytical manipulation of the generalized scattering matrix obtained from the finite-element method, when concave and convex spherical surfaces are defined as ports. The technique combines: the power of full-wave resolution, the flexibility and speed of the direct domain decomposition techniques and the application of analytical rotations and translations from the addition theorems for spherical vector waves, while keeping the same accuracy as a complete full-wave method since no model simplifications are considered.

Soil environments are heterogeneous in their nature. This heterogeneity creates significant difficulties both in terms of construction practice and in terms of the mathematical modeling and computer simulation of the physical-chemical processes in these heterogeneous soil arrays. From the standpoint of mathematical modeling, the issue is the discontinuity of functions, which characterize the examined processes, on such inclusions. Moreover, the characteristics of such inclusions may depend on the defining functions of the processes studied (head, temperature, humidity, the concentration of chemicals, and their gradients). And this requires the modification of conjugation conditions and leads to the nonlinear boundary-value problems in heterogeneous areas. That is why this work has examined the impact of the existence of thin inclusions on the conjugation conditions for the defining functions of the filtration and geomigration processes on them. The conjugation condition for heads has also been modified while the mathematical model of an elastic filtration mode in a heterogeneous array of soil, which contains thin weakly permeable inclusions, has been improved. The improvement implies the modification of conjugation conditions for heads on thin inclusions when the filtering factor of the inclusion itself is nonlinearly dependent on the head gradient. The numerical solution to the corresponding nonlinear boundary-value problem has been found using a finite-element method. A series of numerical experiments were conducted and their analysis was carried out. The possibility of a significant impact on the head jump has been shown taking into consideration the dependence of filtration characteristics of an inclusion on head gradients. In particular, the relative difference of head jumps lies between 26% and 99% relative to the problem with a stable filtration factor for an inclusion. In other words, when conducting forecast calculations, the influence of such dependences cannot be neglected

Modelling soft robots is a non-trivial task since their behaviours rely on their morphology, materials and surrounding elements.These robots are very useful to safely interact with their environment and because of their inherent exibility and adaptability skills. However, they are usually very hard to model because of their intrinsic non-linearities. This fact presents a unique challenge in the computer graphics and simulation scopes. Current trends in these elds tend to narrow the gap between virtual and real environments. This work will explain a challenging modelling process for a cable-driven soft robot called Kyma. For this purpose, the real-time Finite Element Method (FEM) is applied using the Simulation Open Framework Architecture. And two methods are implemented and compared to optimize the model efciency: a heuristic one and the Model Order Reduction. Both models are also validated with the real robot using a precise motion tracking system. Moreover, an analysis of robot–object interactions is proposed to test the compliance of the presented soft manipulator. As a result, the real-time FEM emerges as a good solution to accurately and efciently model the presented robot while also allowing to study the interactions with its environment, This research has been supported by RoboCity2030-DIH-CM, Madrid Robotics Digital Innovation Hub, S2018/NMT-4331, funded by “Programas de Actividades I+D en la Comunidad de Madrid” and co-funded by Structural Funds of the EU. And also by the Program project VJIDOCUPM18JCG from Universidad Politécnica de Madrid.

Highly sensitive characterization of surface plasmon resonance (SPR) modes lays the solid foundation for wide SPR-related applications. Herein, we discover that these SPR modes based on all-metal nanostructures without any probed molecule can be characterized with ultrahigh sensitivities at both excitation and emission wavelengths by utilizing plasmon-enhanced sum frequency generation (PESFG) spectroscopy. The theory of PESFG for sensitively characterizing SPR modes is first validated experimentally. Moreover, we have elaborately demonstrated that PESFG strongly depends on both the resonant wavelengths of SPR modes and spatial mode distributions when azimuthal angles of excitations are varied. Our study not only enhances the understanding of the mechanism that governs PESFG, but also offers a potentially new method for exploring new-style SPR modes (e.g. plasmon-induced magnetic resonance and bound states in the continuum) by PESFG.

In this paper, a finite-element method with unstructured mesh is used to numerically simulate the line source model of three-dimensional borehole-to-surface electrical potential method. A new total field potential is synthesized using the calculated anomalous field potential and the analytic solution of the background field. In solving for the original total field potential and background potential, this method can guarantee a small near-field error in the new total field potential without the need to densely mesh the region with the source. By comparing the synthesized total field and analytic solution, the high accuracy of the numerical solution is verified. The results of model calculation show that the detection effectiveness of the borehole-to-surface electrical method depends on the length of the line source. The detection effectiveness increases substantially with increasing length of the line source within a certain range. However, when the line source is excessively long, the increase in detection effectiveness for anomalies is insignificant. For a low-resistance anomaly of a given volume, the borehole-to-surface electrical method is more sensitive to changes in the lateral area than to changes in the thickness. When the gob contains only a small amount of water (e.g., Model IV containing 5% of water by volume), it will appear as a low-resistance anomaly. In addition, the detection of a water-logged gob by the borehole-to-surface electrical method depends on the depth and size of the gob. The borehole-to-surface method can accurately delineate the profile boundary of an anomaly, even though the side closer to the source is susceptible to the effect of source current. These results are significant for guiding the field exploration of the borehole-to-surface electrical method, improving result interpretation, and assisting the application.

In the present work we study the static response of functionally graded (FG) porous nanocomposite beams, with a uniform or non-uniform layer-wise distribution of the internal pores and graphene platelets (GPLs) reinforcing phase in the matrix, according to three different patterns. The finite-element approach is developed here together with a non-local strain gradient theory and a novel trigonometric two-variable shear deformation beam theory, to study the combined effects of the non-local stress and strain gradient on the FG structure. The governing equations of the problem are solved introducing a three-node beam element. A comprehensive parametric study is carried out on the bending behavior of nanocomposite beams, with a particular focus on their sensitivity to the weight fraction and distribution pattern of GPLs reinforcement, as well as to the non-local scale parameters, geometrical properties, and boundary conditions. Based on the results, it seems that the porosity distribution and GPLs pattern have a meaningful effect on the structural behavior of nanocomposite beams, where the optimal response is reached for a non-uniform and symmetric porosity distribution and GPLs dispersion pattern within the material.

We consider a mathematical model for skin contraction, which is based on solving a momentum balance under the assumptions of isotropy, homogeneity, Hooke’s Law, infinitesimal strain theory and point forces exerted by cells. However, point forces, described by Dirac Delta distributions lead to a singular solution, which in many cases may cause trouble to finite element methods due to a low degree of regularity. Hence, we consider several alternatives to address point forces, that is, whether to treat the region covered by the cells that exert forces as part of the computational domain or as ‘holes’ in the computational domain. The formalisms develop into the immersed boundary approach and the ‘hole’ approach, respectively. Consistency between these approaches is verified in a theoretical setting, but also confirmed computationally. However, the ‘hole’ approach is much more expensive and complicated for its need of mesh adaptation in the case of migrating cells while it increases the numerical accuracy, which makes it hard to adapt to the multi-cell model. Therefore, for multiple cells, we consider the polygon that is used to approximate the boundary of cells that exert contractile forces. It is found that a low degree of polygons, in particular triangular or square shaped cell boundaries, already give acceptable results in engineering precision, so that it is suitable for the situation with a large amount of cells in the computational domain.

International audience; Plant-based concrete is a construction material which, in addition to having a very low environmental impact, exhibits excellent hygrothermal comfort properties. It is a material which is, as yet, relatively unknown to engineers in the field. Therefore, an important step is to implement reliable mass-transfer simulation methods. This will make the material easy to model, and facilitate project design to deliver suitable climatic conditions. In recent decades, numerous studies have been carried out to develop models of the coupled transfers of heat, air and moisture in porous building envelopes. Most previous models are based on Luikov’s theory, considering mass accumulation, air and total pressure gradient. This theory considers the porous medium to be homogeneous, and therefore allows for hygrothermal transfer equations on the basis of the fundamental principles of thermodynamics. This study presents a methodology for solving the classical 1D (one-dimensional) HAM (heat, air, and moisture) hygrothermal transfer model with an implementation in MATLAB. The resolution uses a discretization of the problem according to the finite-element method. The detailed solution has been tested on a plant-based concrete. The energy and mass balances are expressed using measurable transfer quantities (temperature, water content, vapor pressure, etc.) and coefficients expressly related to the macroscopic properties of the plant-based concrete (thermal conductivity, specific heat, water vapor permeability, etc.), determined experimentally. To ensure this approach is effective, the methodology is validated on a test case. The results show that the methodology is robust in handling a rationalization of the model whose parameters are not ranked and not studied by their degree of importance

A major cause of bone mass loss worldwide is osteoporosis. X-ray is considered to be the gold-standard technique to diagnose this disease. However, there is currently a need for an alternative modality due to the ionizing radiations used in X-rays. In this vein, we conducted a numerical study herein to investigate the feasibility of using microwave tomography (MWT) to detect bone density variations that are correlated to variations in the complex relative permittivity within the reconstructed images. This study was performed using an in-house finite-element method contrast source inversion algorithm (FEM-CSI). Three anatomically-realistic human leg models based on magnetic resonance imaging reconstructions were created. Each model represents a leg with a distinct fat layer thickness, thus, the three models are for legs with thin, medium, and thick fat layers. In addition to using conventional matching media in the numerical study, the use of commercially available and cheap ultrasound gel was evaluated prior to bone image analysis. The inversion algorithm successfully localized bones in the thin and medium fat scenarios. In addition, bone volume variations were found to be inversely proportional to their relative permittivity in the reconstructed images with the root mean square error as low as 2.54. The observations found in this study suggest MWT as a promising bone imaging modality owing to its safe and non-ionizing radiations used in imaging objects with high quality.

A modified micromechanics failure criterion (MMF3) based multi-scale analysis strategy was proposed in this article to analyze the failure behaviors of the plain-woven fabric composites. The finite-element (FE) representative unit cell (RUC) models of different scales were first established, and the RUC based stress transformation methods were developed. The micro-scale strengths of the constituents in the unidirectional laminate were achieved based on the tested macro-scale strengths. Under the micro-scale strength invariance hypothesis, the meso-scale strengths of the fiber tows from the plain-woven fabric composites were back-calculated first and were then validated and corrected with the assistance of tested strengths of the fabric laminates. With the micro-scale RUC and the calculated meso-scale strengths of the fiber tows, the micro-scale strengths of the constituents suitable for the plain-woven fabric composites were determined. The multi-scale analysis procedure for the plain-woven fabric composites was then established in providing a more direct failure observation at the constituent level. Open-hole compression specimens were tested according to the ASTM standard D6484, and the failure of the open-hole fabric laminate was simulated with the proposed multi-scale strategy. The numerical predictions were in good agreement with the experimental results, and the feasibility of the multi-scale strategy was validated.

The paper compares the performance of different design methods for power magnetics. The Finite element method solvers provided by ANSYS Electronics are compared to the theoretical magnetic models. The performance of the modelling tools is quantified by comparing simulations against impedance measurements for 2 different inductor types both for 2D approximations and 3D geometry models. The key goal is to evaluate when a more complex design procedure is required to achieve certain design goals, such as accurate parasitic and be aware of the limitations in different methods.

The finite-element analysis is a powerful method to obtain detailed insight into the operation of any electromagnetic equipment. However, the required computational power to solve a finite-element modeled power equipment is so heavy that most Newton-Raphson-method-based algorithms can barely achieve real-time simulation. The low latency and hardware parallelism of the field-programmable gate array (FPGA) provides a path forward. In this paper, a parallel and deeply pipelined adaptive transmission-line modeling method with preconditioned conjugate gradient solver is designed in hardware and implemented on two Xilinx® XCVU37P FPGAs for the finite-element modeling of a three-phase transformer. The accuracy of the transformer solver under both current-excited and voltage-excited conditions of the transformer was validated against the commercial FE simulation tool.

For predicting the sliding wear in Pin-on-Disc (PoD) tribometer contact, a numerical wear simulation technique is presented in this paper. It is based on the Finite element method (FEM) which incorporates the Archard's wear law and the UMESHMOTION subroutine for calculating the wear depth for a 3-D PoD tribometer contact. FEM is utilized in solving the 3-D contact problem. The geometry is updated using the UMESHMOTION subroutine coupled with the Augmented Lagrangian-Eulerian (ALE) remeshing technique of ABAQUS. But, a significant disadvantage of FEM wear prediction is the enormous computational time required for performing 3-D analysis. Hence, to minimize the computational time, an approximation technique is introduced which accounts for the contact pressure evolution at the contact region. It decreased the simulation time and also preserved the accuracy of 3-D wear prediction. Finally, the results obtained from the simulations are compared with the experiments for brass-on-bearing steel PoD contact. An accuracy of 98.81% was obtained for the 10N and 83.10% for the 30N load.

A procedure has been devised for modeling the dynamic pro-cesses in the proposed structure of an electromechanical shock absorber. Such shock absorbers can recuperate a part of the energy of oscillations into electrical energy allowing the subsequent possibility to use it by rolling stock. The procedure is based on solving the Lagrange equation for the electromechanical system. The model’s features are as follows. The model takes the form of a Cauchy problem, thereby making it possible to use it when simulating the processes of shock absorber operation. Two generalized coordinates have been selected (the charge and displacement of the armature). The components of the Lagrange equation have been identified. Based on the results from magnetic field calculation and subsequent regression analysis, we have derived polynomial dependences of flux linkage derivatives for the current and linear displacement of an armature, which make it possible to identify a generalized mathematical model of the electromechanical shock absorber. The magnetic field calculations, performed by using a finite-element method, have allowed us to derive a digital model of the magnetic field of an electromechanical shock absorber. To obtain its continuous model, a regression analysis of discrete field models has been conducted. When choosing a structure for the approximating model, a possibility to analytically differentiate partial derivatives for all coordinates has been retained. Based on the results from modeling free oscillations, it was established that the maximum module value of current is 0.234 A, voltage – 52.9 V. The process of full damping of oscillations takes about 3 seconds over 4 cycles. Compared to the basic design, the amplitude of armature oscillations and its velocity dropped from 13 to 85 % over the first three cycles, indicating a greater efficiency of electromechanical shock absorber operation in comparison with a hydraulic one. The recuperated energy amounted to 3.3 J, and the scattered energy – 11.5 J. Для запропонованої конструкції електромеханічного амортизатору розроблено методику моделювання динамічних процесів. Такі амортизатори мають можливість рекуперувати частину енергії коливань в електричну енергію з подальшою можливістю її використання на рухомому складі. Методика основана на вирішенні рівняння Лагранжу для електромеханічної системи. Особливості моделі є наступними. Модель має вигляд задачі Коши, який спритний до вживання при моделювання процесів роботи амортизатору. Обрані дві узагальнені координати (заряд та переміщення якорю). Ідентифіковані складові частини рівняння Лагранжу. За результатами розрахунку магнітного поля і подальшого регресійного аналізу отримано поліноміальні залежності похідних потокозчеплення потоку і лінійному переміщенню якоря, які дають можливість ідентифікувати узагальнену математичну модель електромеханічного амортизатору. Проведені розрахунки магнітного поля методом скінчених елементів дозволили отримати цифрову модель магнітного поля електромеханічного амортизатору. Для отримання її безперервної моделі проведено регресійний аналізу дискретні моделі поля. Про виборі структури апроксимуючої моделі дотримана можливість аналітичного диференціювання часткових похідних по всіх координатах. За результатами моделювання вільних коливань встановлено, що максимальне по модулю значення струму складає 0,234 А, а напруги – 52,9 В. За близько 3 с. проходить процес повного погашення коливань за 4 періоду. Порівняно з базовою конструкцією амплітуда коливань ходу якоря та його швидкості знизилась від 13 до 85 % за перші три періоди, що свідчить про більшу ефективність роботи електромеханічного амортизатору в порівнянні з гідравлічним. Енергія, що рекуперовано, склала 3,3 Дж, а, що розсіяно – 11,5 Дж.

Full-film hydrodynamic lubrication of marine propulsion shafting journal bearings in running condition is discussed. Considerable computational difficulties in non-linear determining the quasi-static equilibrium of the shafting are highlighted. To overcome this problem the approach using two optimization methods (the particle swarm method and the interior point method) in combination with the specially developed relaxation technique is proposed. The developed algorithm allows to calculate marine propulsion shafting bending with taking into account lubrication in all journal bearings and exact form of journal inside bearings, compared to results of most of the publications which consider lubrication only in the aft most stern tube bearing and assume rest of bearings to be represented by points. The calculation results of typical shafting design with four bearings are provided. The significance of taking into account lubrication in all bearings is shown, specifically more exact values of bearings’ reactions, shafting deflections, minimum film thickness and maximum hydrodynamic pressure in the stern tube bearing in case of considering lubrication in all bearings.

Footing is an important part of a structure, because its repair is extremely difficult and cumbersome. Therefore, all structural parameters should be carefully considered when designing a footing. An isolated footing needs sufficient depth, when considering the fixed base assumption. Extensive research has previously been conducted to define and formalize the depth of a rigid footing, i.e., the depth required, such that footing behaves as a rigid. Alternatively, working stress method (WSM) and limit state method (LSM) provide a lower depth for low subgrades and a higher depth for high subgrades than that required by rigid condition if a unit width footing is considered for the design. This paper presents a simple approach for calculating the depth to meet the rigid condition under static loading. The proposed calculation method produced a better rigidity than the existing approaches and it correlated well to the finite-element method (FEM) for low subgrades. The reinforcement distribution is function of the bending moment (BM). Steel is uniformly embedded throughout the length or width of conventional footing methods, but this is inappropriate, because the bending moment is not uniform along the length or width of the footing. This paper proposes solutions to this by redefining the placement of steel in the central zone of the footing. The effective zone for reinforcement was based on the FEM results. This simple procedure was developed for calculating the maximum moment using the Diagonal Strip Method (DSM). DSM is a substitute for FEM, and it has been shown to correlate well. The BM at central zone as well as at the edges can be calculated to define the spacing of the reinforcements.

The phenomenological model for cell shape deformation and cell migration Chen (BMM 17:1429–1450, 2018), Vermolen and Gefen (BMM 12:301–323, 2012), is extended with the incorporation of cell traction forces and the evolution of cell equilibrium shapes as a result of cell differentiation. Plastic deformations of the extracellular matrix are modelled using morphoelasticity theory. The resulting partial differential differential equations are solved by the use of the finite element method. The paper treats various biological scenarios that entail cell migration and cell shape evolution. The experimental observations in Mak et al. (LC 13:340–348, 2013), where transmigration of cancer cells through narrow apertures is studied, are reproduced using a Monte Carlo framework.

In this short paper, we compare the deterministic model for the nuclear reactor dynamic (Hetrick, 1993) with the stochastic model (Kinard and Allen, 2004). Our numerical results show coincidences between the deterministic model and the mean of the stochastic paths, although, as already observed by other authors, there is alarge amount of dispersion between the individual paths. Notably, we always observe that the neutron density approaches zero within a short time. In this paper, we investigate this question; more concretely, we study the mean-extinction of the neutron density. The technique used here first builds the backward Kolmogorov differential equation and then solves it numerically using the finite-element method with FreeFem++. Our results confirm that in a very short time the neutrons disappear although later they recover probably due to the external source. This work was supported by Spanish Ministry of Sciences Innovation and Universities with the project PGC2018-094522-B-100 and by the Basque Government with the project IT1247-19.

We present a numerical approach to efficiently calculate spin-wave dispersions and spatial mode profiles in magnetic waveguides of arbitrarily shaped cross section with any non-collinear equilibrium magnetization which is translationally invariant along the waveguide. Our method is based on the propagating-wave dynamic-matrix approach by Henry et al. and extends it to arbitrary cross sections using a finite-element method. We solve the linearized equation of motion of the magnetization only in a single waveguide cross section which drastically reduces computational effort compared to common three-dimensional micromagnetic simulations. In order to numerically obtain the dipolar potential of individual spin-wave modes, we present a plane-wave version of the hybrid finite-element/boundary-element method by Frekdin and Koehler which, for the first time, we extend to a modified version of the Poisson equation. Our method is applied to several important examples of magnonic waveguides including systems with surface curvature, such as magnetic nanotubes, where the curvature leads to an asymmetric spin-wave dispersion. In all cases, the validity of our approach is confirmed by other methods. Our method is of particular interest for the study of curvature-induced or magnetochiral effects on spin-wave transport but also serves as an efficient tool to investigate standard magnonic problems.

A long-standing problem at the frontier of biomechanical studies is to develop fast methods capable of estimating material properties from clinical data. In this paper, we have studied three surrogate models based on machine learning (ML) methods for fast parameter estimation of left ventricular (LV) myocardium. We use three ML methods named K-nearest neighbour (KNN), XGBoost and multi-layer perceptron (MLP) to emulate the relationships between pressure and volume strains during the diastolic filling. Firstly, to train the surrogate models, a forward finite-element simulator of LV diastolic filling is used. Then the training data are projected in a low-dimensional parametrized space. Next, three ML models are trained to learn the relationships of pressure–volume and pressure–strain. Finally, an inverse parameter estimation problem is formulated by using those trained surrogate models. Our results show that the three ML models can learn the relationships of pressure–volume and pressure–strain very well, and the parameter inference using the surrogate models can be carried out in minutes. Estimated parameters from both the XGBoost and MLP models have much less uncertainties compared with the KNN model. Our results further suggest that the XGBoost model is better for predicting the LV diastolic dynamics and estimating passive parameters than other two surrogate models. Further studies are warranted to investigate how XGBoost can be used for emulating cardiac pump function in a multi-physics and multi-scale framework.

A potential transonic solver with an embedded wake is presented. The flow outside of attached boundary layers of streamlined bodies flying at high Reynold numbers can be assumed to be irrotational and isentropic. This assumption reduces the Navier-Stokes equations to a single scalar nonlinear partial differential equation, namely the full-potential equation (FPE). The FPE expresses the conservation of mass in terms of the velocity potential. In this work, the FPE is discretized using a standard Galerkin finite element method, and the nonlinear system of equations stemming from the discretization is solved using Newton's method. An artificial compressibility method is used to stabilize the problem in supersonic flow regions. This method prevents the Jacobian from becoming singular and allows capturing shock waves. To include the viscosity effects in the lift generation, a model for the trailing wake needs to be introduced. In the presented method, the wake is modeled as a straight surface in the free-stream direction. This assumption is relaxed allowing mass flux across the wake. To capture the discontinuity in the velocity potential across the wake, a multivalued element method is employed. This implicit description of the wake within the mesh presents an effective approach to perform fluid-structure interaction computations and apply aeroelastic optimization methods, where the position of the wake changes during consecutive iterations. The solver is implemented in Kratos Multi-Physics and verified for different angles of attack and free-stream conditions. Since the pressure does not change in the transverse direction of the boundary layer, the FPE yields accurate lift, induced drag, and moment computations.

Under conditions where a product is subjected to extreme mechanical loading over a very short time period, the strain rate has considerable influence on the behaviour of the product&rsquo, s material. To simulate the behaviour of the material accurately under these loading conditions, the appropriate strain-rate parameters for the selected material model should be used. The aim of this paper is to present a quick method for easily determining the appropriate strain-rate-dependent parameter values of the selected material model. The optimisation procedure described in the article combines the design-of-experiment (DoE) technique, finite-element simulations, modelling a response surface and an evolutionary algorithm. First, a non-standard dynamic experiment was designed to study the behaviour of thin, flat, metal sheets during an impact. The experimental data from this dynamic and the conventional tensile experiments for mild steel were the basis for the determination of the Johnson-Cook material model parameters. The paper provides a comparison of two optimisation processes with different DoE techniques and with three different optimisation algorithms (one traditional and two metaheuristic). The performances of the presented method are compared, and the engineering applicability of the results is discussed. The identified parameter values, which were estimated with the presented procedure, are very similar to those from the literature. The paper shows how the application of a properly designed plan of simulations can significantly reduce the simulation time, with only a minor influence on the estimated parameters. Furthermore, it can be concluded that in some cases the traditional optimisation method is as good as the two metaheuristic methods. Finally, it was proven that experiments with different strain rates must be carried out when estimating the corresponding material parameters.

A theoretical and experimental study on the design-to-performance characteristics of a compression-mode Pb(Zr,Ti)O3-based piezoelectric accelerometer is presented. Using the metamodeling to approximate the relationship between the design variables and the performances, the constituent components were optimized so that the generated electric voltage, representing sensitivity, could be maximized at different set values of the resonant frequency (25–40 kHz). Four kinds of optimized designs were created and fabricated into the accelerometer modules for empirical validation. The accelerometer modules fabricated according to the optimized designs were highly reliable with a broad range of resonant frequency as well as sufficiently high values of charge sensitivity. The fixed (or mounted) resonant frequency was between 16.1–30.1 kHz based on the impedance measurement. The charge sensitivity decreased from 296.8 to 79.4 pC/g with an increase of the resonant frequency, showing an inverse relation with respect to the resonant frequency. The design-dependent behaviors of the sensitivity and resonant frequency were almost identical in both numerical analysis and experimental investigation. This work shows that the piezoelectric accelerometer can be selectively prepared with best outcomes according to the requirements for the sensitivity and resonant frequency, fundamentally associated with trade-off relation.

Nondestructive ultrasound-based methods have been applied to evaluate the elastic properties of concrete materials. Although the wave modulus of elasticity of concrete frequently is reported to be higher than the static counterpart, the microstructural and physical mechanisms are not well understood. This study conducted a computational micromechanics to investigate the effects of aggregates and voids on both the effective wave modulus of elasticity and the static modulus of elasticity, based on concrete microstructures resolved with X-ray microtomography. It was demonstrated that the existence of void defects plays a significant role in the elastic properties of concrete compared with the aggregates. It was shown that the wave modulus of elasticity of concrete is higher than the static modulus of elasticity because of the existence of crack-like voids with small aspect ratios.

In this paper, we extend the model of wound healing by Boon et al. (J Biomech 49(8):1388–1401, 2016). In addition to explaining the model explicitly regarding every component, namely cells, signalling molecules and tissue bundles, we categorized fibroblasts as regular fibroblasts and myofibroblasts. We do so since it is widely documented that myofibroblasts play a significant role during wound healing and skin contraction and that they are the main phenotype of cells that is responsible for the permanent deformations. Furthermore, we carried out some sensitivity tests of the model by modifying certain parameter values, and we observe that the model shows some consistency with several biological phenomena. Using Monte Carlo simulations, we found that there is a significant strong positive correlation between the final wound area and the minimal wound area. The high correlation between the wound area after 4 days and the final/minimal wound area makes it possible for physicians to predict the most probable time evolution of the wound of the patient. However, the collagen density ratio at the time when the wound area reaches its equilibrium and minimum, cannot indicate the degree of wound contractions, whereas at the 4th day post-wounding, when the collagen is accumulating from null, there is a strong negative correlation between the area and the collagen density ratio. Further, under the circumstances that we modelled, the probability that patients will end up with 5% contraction is about 0.627.

International audience; In this work a 3D geometrically non-linear micropolar finite element formulation based on Biot-like tensor representation of stresses, couple stresses, strains and curvature is presented. The discrete approximation is based on hexahedral finite elements with Lagrange interpolation for displacements and rotational spins. The complete residual derivation, linearisation and update are presented in detail. The elements are tested against a non-linear generalisation of the linear micropolar pure-bending problem, derived in this work, and it is shown that the elements converge to the derived solution. The elements are additionally tested on a combined bending and torsion problem and a well-known 45 • bend as a genuine problem involving large 3D rotations, both also analysed in the framework of micropolar elasticity. It is observed that the derived finite elements are reliable and robust in modelling finite deformation problems in micropolar elasticity, exhibiting large displacements and large rotations and converge to reference geometrically non-linear classical elasticity solutions for small micropolar effects. With increasing micropolar effects the response becomes stiffer and the presented numerical examples may serve as benchmark problems to test geometrically non-linear micropolar finite elements including those involving large 3D rotations.

A method of topology optimization based on the convex linearization approach is proposed. The problem formulation implies minimization of the strain energy of a structure subject to volume constraint. The solution is based on explicit, convex and separable Lagrangian approximation with the involvement of the duality theory. A non-linear model is used to relate design variables (density) and elastic properties of the material (modulus of elasticity). The sensitivity of the gain function and the constraint function is analyzed. The basic design formulae for the iteration algorithm of topology optimization are obtained. A number of test problems that correspond to the basic load states: tension, shear and torsion are considered. For all cases the load-carrying factor is calculated: both analytically and with the use of finite-element models. The resulting topologies are shown to be in full compliance with engineering concepts of theoretically optimal structures.

This paper deals with the tire dynamic characteristics, which enable to forecast the trend of vibration signals, obtained from the tire-road system. Theory of the long-range dependence and the finite-element method were employed in this paper. To forecast the resonance effects, we use different frequency modes to avoid the appearance of undesirable inherent frequencies. The vibration intensity of the tire is related to the attrition rate with long-range dependence, which is distinguished by the Hurst effect. The model data can be obtained by the tire vibration sequence from a common pavement. Consequently, we used the fractional auto-regressive integrated moving average approach to forecast the vibration trend and the tire spectrum characteristics simultaneously. The proposed method can be useful for the monitoring of driving performance, tire design, and driving comfort improvement.

This paper presents the capabilities of ABAQUS finite-element program [1] in modelling sandwich beams and plates resting on deformable foundations. Specific systems of sandwich beams and plates separated by an elastic core layer were subjected to the action of point and distributed moving loads. A few theoretical examples are provided to present different techniques of modelling the foundations and the moving loads. The effects of the boundary conditions and of the foundation parameters on the deflections of the analysed structures are also presented.

This article presents a novel computational model to study the selective filtering of biological hydrogels due to the surface charge and size of diffusing particles. It is the first model that includes the random three-dimensional fibre orientation and connectivity of the biopolymer network and that accounts for elastic deformations of the fibres by means of beam theory. As a key component of the model, novel formulations are proposed both for the electrostatic and repulsive steric interactions between a spherical particle and a beam. In addition to providing a thorough validation of the model, the presented computational studies yield new insights into the underlying mechanisms of hindered particle mobility, especially regarding the influence of the aforementioned aspects that are unique to this model. It is found that the precise distribution of fibre and thus charge agglomerations in the network have a crucial influence on the mobility of oppositely charged particles and gives rise to distinct motion patterns. Considering the high practical significance for instance with respect to targeted drug release or infection defence, the provided proof of concept motivates further advances of the model towards a truly predictive computational tool that allows a case- and patient-specific assessment for real (biological) systems.

The aim of the paper is to assess the applicability of a multi-objective biogeography-based optimisation algorithm in MEMS synthesis. In order to test the performances of the proposed method in this research field, the optimal shape design of an electrostatic micromotor, and two different electro-thermo-elastic microactuators are considered as the case studies.

A promising development of the last decade in the numerical modelling of geophysical fluids has been the compatible finite‐element framework. Indeed, this will form the basis for the next‐generation dynamical core of the Met Office. For this framework to be useful for numerical weather prediction models, it must be able to handle descriptions of unresolved and diabatic processes. These processes offer a challenging test for any numerical discretisation, and have not yet been described within the compatible finite‐element framework. The main contribution of this article is to extend a discretisation using this new framework to include moist thermodynamics. Our results demonstrate that discretisations within the compatible finite‐element framework can be robust enough also to describe moist atmospheric processes. We describe our discretisation strategy, including treatment of moist processes, and present two configurations of the model using different sets of function spaces with different degrees of finite element. The performance of the model is demonstrated through several test cases. Two of these test cases are new cloudy‐atmosphere variants of existing test cases: inertia–gravity waves in a two‐dimensional vertical slice and a three‐dimensional rising thermal.

The introduction of metallic nanostructures in optical fibers has revolutionized the field of plasmonic sensors since they produce sharper and fine-tuned resonances resulting in higher sensitivities and resolutions. This article evaluates the performance of three different plasmonic optical fiber sensors based on D-type and suspended core fibers with metallic nanowires. It addresses how their different materials, geometry of the components, and their relative position can influence the coupling between the localized plasmonic modes and the guided optical mode. It also evaluates how that affects the spatial distributions of optical power of the different modes and consequently their overlap and coupling, which ultimately impacts the sensor performance. In this work, we use numerical simulations based on finite element methods to validate the importance of tailoring the features of the guided optical mode to promote an enhanced coupling with the localized modes. The results in terms of sensitivity and resolution demonstrate the advantages of using suspended core fibers with metallic nanowires.

While seeking to achieve high performances of a bulk piezoelectric acceleration sensor, we investigated the behavior of the design variables of the sensor components and optimized the sensor design using a numerical simulation based on piezoelectric analysis and metamodeling. The optimized results demonstrated that there was an exponential dependency in the trade-off relation between two performance indicators, the electric voltage and the resonant frequency, as induced by the design characteristics of the sensor. Among the design variables, a decrease in the base height and epoxy thickness and an increase in the piezo element&rsquo, s inner diameter had a positive effect on two performances, while the head dimensions (diameter and height) exhibited the opposite effect on them. The optimal sensor designs are proposed within the valid range of resonant frequency (25&ndash, 47.5 kHz). Our redesign of a commercial reference sensor improved the resonant frequency by 13.2% and the electric voltage by 46.1%.

Origami in engineering is gaining interest for its potential as deployable or shape-adaptive structures. Practical systems could employ a network of actuators distributed across the structure to induce these deformations. Selecting the actuator locations requires an understanding of how the effect of a single actuator propagates spatially in an origami structure. We combine experimental results, finite element analysis, and reduced-order bar-and-hinge models to show how a localized static actuation decays elastically in Miura-ori tubes and sheets. We observe a strain reversal, before the origami structure springs back to the initial configuration further away from the point of actuation. The strain reversal is the result of bending of the facets, while the spring back requires in-plane facet deformations.

A new interface element constitutive model is proposed in this study for analyzing masonry using the simplified micromodeling (SMM) approach, in which mortar and two unit-mortar interfaces are lumped into a zero-thickness joint (modeled using an interface element) between expanded masonry units. The new model is capable of simulating tension cracking, shear slipping, and compression failure, and is defined by a convex composite failure surface consisting of a tension-shear and a compression cap failure criterion. It removes the singularity in the tension-shear region but not in the compression-shear region. In addition, the proposed model is based on the hypothesis of strain hardening. The robustness and computational cost of the proposed model were compared with different constitutive models (which are based on three, two, and one failure criteria) that have been widely used in the literature to describe masonry behavior through a series of one-element tests and through the comparison of finite-element (FE) response simulation of an unreinforced masonry shear wall. The FE response results indicate that the proposed constitutive model is more efficient than and at least as accurate as the other constitutive models for analyzing masonry using the SMM approach.

The surface integral equation (SIE) method, discretized with the method of moments, is a well-established methodology for the scattering analysis of subwavelength plasmonic nanoparticles. SIEs are usually discretized with low-order basis functions that preserve the normal continuity of the surface currents across the edges arising in the meshed boundary, such as Rao-Wilton-Glisson (RWG) functions. However, the plasmonic enhancement modeling on sharp-edged particles is an extremely challenging task, especially due to the singular fields exerted at sharp corners, exposing a slow (or no) convergence in the computation of the scattering and absorption spectra. In this paper, we propose an alternative discretization strategy based on a discontinuous basis function set in conjunction with a volumetric-tetrahedral testing scheme. We demonstrate the potential of the proposed discretization scheme by studying scattering and absorption spectra of three canonical plasmonic polyhedra, i.e., a hexahedral, an octahedral, and a tetrahedral silver inclusion. The results expose an improved accuracy and faster convergence in both far-field and near-field regions when compared to the standard RWG implementation. The proposed discretization scheme can offer faster and more accurate routes towards the exploration and design of the plasmonic resonant spectrum of sharp-edged nanoparticles and nanoantennas.

The aim of this paper is to implement a numerical model to reproduce the nonlinear behavior of cob walls under shear loading. Axial compression, pull-off, and diagonal compression tests were carried out to derive the mechanical parameters. In addition, the stress-strain relationships, the nonlinear behavior, and the failure modes were defined. The experimental results were then used to calibrate a finite-element model. The material behavior was simulated through a macromodeling approach adopting the total strain rotating crack model. A sensitivity analysis was conducted to assess the effects of varying the parameters with higher uncertainty on the structural behavior. The numerical model achieved good correspondence with the experimental results in terms of simulation of the shear stress-shear strain relationship and of damage pattern. (c) 2019 American Society of Civil Engineers., The authors wish to express their gratitude to Mr. Andre Gardei for his important support in the experimental program and to Mr. Andreas Barner and Ms. Manuela Peuschel for their support with photogrammetric analyses. This study was funded by the European Commission within the framework of the project NIKER (Grant No. 244123) dealing with improving immovable Cultural Heritage assets against the risk of earthquakes. The study was partly financed by FEDER funds through the Competitivity Factors Operational Programme (project POCI-01-0145-FEDER-007633) and by national funds through the Portuguese Foundation for Science and Technology (project PTDC/ECM-EST/2777/2014 and Grant No. SFRH/BPD/97082/2013).

The mechanical behaviour of zinc dialkyldithiophosphate (ZDDP) tribofilms on diamond-like carbon (DLC) coatings has been studied by combining the nano-indentation experimental data and finite-element modelling. Different constitutive models, whose analysis was performed using a global algorithm that consists of forward and inverse algorithms, were chosen to establish which of them more accurately predicts the actual mechanical behaviour of the ZDDP tribofilms. A non-homogeneous, dual structure, which was also verified by the local stiffness using the AFM force-modulation mode, was found. Based on the proposed algorithm, the mechanical properties of the ZDDP tribofilms were found, e.g. the elastic modulus E=26 GPa and the yield stress Y=1.55 GPa for the harder component and approximately E=1.65 GPa and Y=0.144 GPa for the softer component.

Engineering components operating at high temperature often fail due to the initiation and growth of cracks in the heat-affected zone adjacent to a weld. Understanding the effects of microstructural evolution in the heat-affected zone is important in order to predict and control the final properties of welded joints. This study presents a combined finite element method and phase field method for simulation of austenite grain growth in the heat-affected zone of a tempered martensite (P91) steel weld. The finite element method is used to determine the thermal history of the heat-affected zone during gas tungsten arc welding of a P91 steel plate. Then, the calculated thermal history is included in a phase field model to simulate grain growth at various positions in the heat-affected zone. The predicted mean grain size and grain distribution match well with experimental data for simulated welds from the literature. The work lays the foundation for optimising the process parameters in welding of P91 and other ferritic/martensitic steels in order to control the final heat-affected zone microstructure.

We have developed the open-source toolbox custEM (customizable electromagnetic modeling) for the simulation of complex 3D controlled-source electromagnetic (CSEM) problems. It is based on the open-source finite-element library FEniCS, which supports tetrahedral meshes, multiprocessing, higher order polynomials, and anisotropy. We use multiple finite-element approaches to solve the time-harmonic Maxwell equations, which are based on total or secondary electric field and gauged potential formulations. In addition, we develop a secondary magnetic field formulation, showing superior performance if only magnetic fields are required. Using Nédélec basis functions, we robustly incorporate the current density on the edges of the mesh for the total field formulations. The latter enable modeling of CSEM problems taking topography into account. We evaluate semianalytical 1D layered-earth solutions with the pyhed library, supporting arbitrary configurations of dipole or loop sources for secondary field calculations. All system matrices have been modified to be symmetric and solved in parallel with the direct solver MUMPS. Aside from the finite-element kernel, mesh generation, interpolation, and visualization modules have been implemented to simplify and automate the modeling workflow. We prove the capability of custEM, including validation against analytic-solutions, crossvalidation of all implemented approaches, and results for a model with 3D topography with four examples. The object-oriented implementation allows for customizable modifications and additions or to use only submodules designed for special tasks, such as mesh generation or matrix assembly. Therefore, the toolbox is suitable for crossvalidation with other codes and as the basis for developing 3D inversion routines.

The paper contributes a new fully nonlinear planar finite element formulation, taking into accouint large deformations as well as material nonlinearity, for helical structures where helical constancy can be exploited. the helical structures may consist of one or several helices that may be free or embedded in some matrix material. While diverse homogeneous deformation modes could be considered, the present paper focuses on axial elongation and axial torsion, being the dominant ones. The derivations are explained and the model predictions are verified by comparison with those of three-dimensional finite element models using commercial software. Suggested applications of the numerically efficient model include analysis of highly hierarchical helical structures found in tendons., Computers & Structures, 224, ISSN:0045-7949

Funding Information: Funding: The research has been supported by the Estonian Research Council under grant PSG453 “Digital twin for propulsion drive of an autonomous electric vehicle”. Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Copyright: Copyright 2021 Elsevier B.V., All rights reserved. This paper proposes a modified dynamic equivalent circuit model for a linear induction motor considering both longitudinal end effect and transverse edge effect. The dynamic end effect (speed-dependent end effect) is based on conventional Duncan’s approach. The transverse edge effect is investigated by using three correction factors applied to the secondary resistance and magnetizing inductance. Moreover, the iron saturation effect, the skin effect, and the air-gap leakage effect are incorporated into the proposed model by using the field-analysis method. A new topology of the steady-state and space-vector model of linear induction, regarding all mentioned phenomena, is presented. The parameters of this model are calculated using both field analysis and the finite-element method. The steady-state performance of the model is first validated using the finite-element method. Additionally, the dynamic performance of the proposed model is studied. The results prove that the proposed equivalent circuit model can precisely predict the dynamic and steady-state performances of the linear induction.

Graphical abstract, Different variants of the Uzawa algorithm are compared with one another. The comparison is performed for the case in which this algorithm is applied to large-scale systems of linear algebraic equations. These systems arise in the finite-element solution of the problems of elasticity theory for incompressible materials. A modification of the Uzawa algorithm is proposed. Computational experiments show that this modification improves the convergence of the Uzawa algorithm for the problems of solid mechanics. The results of computational experiments show that each variant of the Uzawa algorithm considered has its advantages and disadvantages and may be convenient in one case or another.