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The aim of this discussion is to establish a connection between the model for sandwich beams presented in Schöftner (Acta Mech 234:2543–2560, 2023) and the so-called Krajcinovic model. Although the two models turn out to be quite similar, Krajcinovic model displays a richer kinematics and has been developed in the literature by following slightly different methodologies with respect to that adopted by Schöftner, the latter having the merit of providing equilibrium equations that allow the computation of the interfacial stresses. We also offer some remarks on the capabilities and accuracies of the models discussed. [ABSTRACT FROM AUTHOR]

This work deals with fracture mechanisms in quasi-brittle materials, focusing on the characterization of the Fracture Process Zone (FPZ) of specimens under tensile load. Particularly, paper was used as model material. Experiments were conducted on notched and unnotched specimens. Based on an image analysis of these observations, a stochastic finite element model was developed, using both a nonlocal stress-based approach and a discretized random field modeling of the Young's modulus. The proposed methodology allowed characterizing the damage zone and the size of the FPZ, analyzing the influence of the mesostructure, composed of flocs (fiber aggregates where the basis weight is larger than the average one) and antiflocs (complement of flocs). The area of the active FPZ and the normalized stress drop were linked using a surface energy dissipated in the active FPZ. The stress drop, until limiting value, increased with the width of the active FPZ. Finally, a relationship between the surface energy and the nonlocal internal length was established. [ABSTRACT FROM AUTHOR]

It is pointed out that the Levinson-Reddy beam theory should not be used as a higher-order model for the core, although it considers cross-sectional warping: this beam model is applicable for zero shear stress conditions at the core-skin-interfaces only, which is usually not the case for sandwich structures. The resulting sandwich beam model in [[2]] is a special solution from the Krajcinovic-Bardella derivation, which allows for richer kinematics because it considers zig-zag kinematics. Author's response to "Discussion on the paper by Schoeftner, J., "A verified analytical sandwich beam model for soft and hard cores: comparison to existing analytical models and finite element calculations", Acta Mech, 234, 2543-2560 (2023)" by Lorenzo Bardella. [Extracted from the article]

The thermal response in paper has been studied by thermography. It was observed that an inhomogeneous deformation pattern arose in the paper samples during tensile testing. In the plastic regime a pattern of warmer streaks could be observed in the samples. On the same samples digital image correlation (DIC) was used to study local strain fields. It was concluded that the heat patterns observed by thermography coincided with the deformation patterns observed by DIC. Because of its fibrous network structure, paper has an inhomogeneous micro-structure, which is called formation. It could be shown that the formation was the cause of the inhomogeneous deformations in paper. Finite element simulations was used to show how papers with different degrees of heterogeneity would deform. Creped papers, where the strain at break has been increased, were analysed. For these paper it was seen that an overlaid compaction of the paper was created during the creping process. During tensile testing this was recovered as the paper network structure was strained. [ABSTRACT FROM AUTHOR]

Twinning is an important deformation mechanism for magnesium alloys, which has a significant impact on the texture evolution and mechanical properties. Pre-twinning deformation has been considered as an effective method for texture regulation. For each twinning mode, there are six crystallographically equivalent variants. Properly identifying the activated twin and understanding its variant selection criteria are essential for the development of high-performance magnesium alloys. As summarized in this paper, the observed twin variant by the commonly employed electron backscatter diffraction technique can be identified by several approaches, including misorientation analysis, trace analysis and matrix method. Schmid factor analysis was commonly performed to explain the selection of twin variants. To broaden the application scope under complex stress state, a generalized Schmid factor was derived by introducing a stress tensor. The efficiency of Schmid criteria to assess twin variant selection was confirmed to be influenced by the type of the applied stress. To consider the local effect on twin activation, in particular twin-twin transfer and slip-induced twinning, displacement gradient tensor calculation and geometrical compatibility factor analysis have been employed. It was demonstrated that local strain accommodation played a critical role in selecting the variants of cross-boundary twins in magnesium alloys. Assisted with crystal plasticity finite element modeling, the resolved shear stress on twinning and a composite Schmid factor combining the global Schmid factor and geometrical compatibility factor were obtained to better explain the activated twin variants in magnesium alloys. All the above-mentioned Schmid law based criteria and some energy based criteria as well are summarized in this paper. Their applications in evaluating twin variant selection in magnesium alloys are critically reviewed and discussed. [ABSTRACT FROM AUTHOR]

This paper offers a concise critical review of finite element studies of the jetting phenomenon in cold spray (CS). CS is a deposition technique wherein solid particles impact a substrate at high velocities, inducing severe plastic deformation and material deposition. These high-velocity particle impacts lead to the ejection of material in a jet-like shape at the periphery of the particle/substrate interface, a phenomenon known as "jetting". Jetting has been the subject of numerous studies over recent decades and remains a point of debate. Two main mechanisms, Adiabatic Shear Instability (ASI) and Hydrodynamic Pressure-Release (HPR), have been proposed to explain the jetting phenomenon. These mechanisms are mainly elucidated through finite element method (FEM) simulations, a numerical technique rooted in continuum mechanics. However, it is important to emphasize that FEM is limited by the equations established for analysis, and as such, its predictive capabilities are confined to those principles clearly defined within these equations. The choice of employed equations and approaches significantly influence the outcomes and predictions in FEM. While recognizing FEM's capabilities, this study reviews the ASI and HPR mechanisms within the context of CS. Additionally, this paper reviews FEM's algorithms and the core principles that govern FEM in calculating plastic deformation, which can lead to the formation of jetting. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose an experimental procedure for determining the characteristic length of a strain gradient model. The identification problem is studied through a virtual pull-out test of a rigid bar along the symmetry axis of a cylindrical strain gradient elastic domain. To allow an accurate parameter identification based on measured data, we investigate the effect of the characteristic length on the mechanical fields for this problem. We see a significant sensitivity of the inflection point of the displacement profile evaluated on the cross section of the cylinder, with respect to the characteristic length. By adjusting the characteristic length of the strain gradient such that the theoretical models match best with experimental measurements of the surface displacement fields, the characteristic length of the strain gradient can be estimated. In order to allow for more efficient analysis and an almost real-time parameter identification, the initial three-dimensional (3D) problem is reduced to a one-dimensional (1D) problem by exploiting the cylindrical symmetry of the problem. As will be shown, an accurate 1D finite element method (FEM) strain gradient solution can be obtained for this simplified problem. Since the cylindrical symmetry is only true in an infinitely long cylinder, specific boundary conditions are constructed on a cylinder of finite length, which is then used for the comparison of the 1D and 3D problems. Results show, however, that the structural response at the inflection point is insensitive to whether the specific boundary conditions are considered or not, which is why the 1D model can be used for parameter identification. Since the proposed approach is methodological, it can be applied to any material. As a prototype problem in this paper, we consider the case of a bar embedded in Portland cement concrete. [ABSTRACT FROM AUTHOR]

Historically, seepage failure has always been the primary cause of failures and accidents of earth dams after overtopping. However, research on the reliability of earth dams against seepage failure remains scarce. Meanwhile, the influence of the uncertainty of the soil–water characteristic curve (SWCC) on the reliability of dams against seepage failure is still unclear. In this study, the van Genuchten–Mualem model is used to describe SWCC, and its uncertainty is characterized by discretizing SWCC fitting parameters a and n into cross-correlation lognormal random fields. Based on the random finite element method, this paper systematically studies the influence of the heterogeneity, autocorrelation, and cross-correlation of hydraulic parameters Ks, a, and n on the reliability of a dam against seepage failure. Sensitivity analysis indicates that Ks and autocorrelation distance crucially affect the reliability of the dam against seepage failure. Additionally, this paper also emphasizes and proves that considering the correlation between the hydraulic conductivity field and the critical hydraulic gradient field has a significant impact on evaluating the reliability of earth dams against seepage failure. However, this subtle but important potential characteristic has not been paid attention to in previous studies. [ABSTRACT FROM AUTHOR]

The space debris in Earth's orbit has increased drastically due to the failure of spacecraft, rocket bodies, and mission-related objects. These objects in orbit increase the space waste and challenge other flying objects such as spacecraft. A hypervelocity impact of space debris on spacecraft structures can have a range of effects (mechanical damage and functional failure), raising significant concerns about spacecraft safety. This paper reviews the different studies on the performance and development of the Whipple shield against the hypervelocity impact of space debris. The study focuses on the impact mechanism, dynamic Fragmentation of materials, strength models, Equation of state, characteristics, and model of the debris cloud. The strength models (Steinberg–Guinan and Johnson–Cook) and Mie–Gruneisen equation of state, primarily used for hypervelocity impact applications, are thoroughly covered in this study. The study also reported the various experimental and numerical techniques for high and hypervelocity impact. The study concluded that mesh-based, mesh-free, and hybrid finite element methods are reliable for analyzing Whipple shield targets to resist hypervelocity impact. The study also observed that the two-stage light gas gun technique investigates most experimental analyses of hypervelocity impact on the Whipple shield. Alongside reviewing the abovementioned aspects, this paper also underlines the future scope of study in this paradigm. The authors strongly believe that this study provides more insights into the fundamentals and perceptions of the Whipple shield to protect the spacecraft against the hypervelocity impact of space debris. [ABSTRACT FROM AUTHOR]

In the tunneling driven by large diameter slurry shield (SS), the working face is at risk of passive failure when the overburden is insufficient or the support pressure is excessive. This paper examines the partial progressive failure of the tunnel face by developing a hybrid mechanism which incorporates the failure zone into the complex movement. The failure blocks include a translational and a rotational one, and a spatial discretization technique is used to construct the velocity discontinuity between the blocks to ensure compatibility. To identify the failure extent of the face, the incipient failure origination is introduced. A kinematic approach is utilized to determine the upper bound solution for support pressure. By optimizing, the minimum support pressure is searched and the failure mechanism is gained in response. Additionally, this study performs the parametric analysis to discuss the influences of the factors such as frictional angle, cohesion, overburden depth, ground surface surcharge, and slurry weight on incipient failure origination as well as support pressure. The numerical analysis included in the framework of finite element limit analysis is carried out for verification. This paper ends with the validation of the current solution by re-examining the previous case. [ABSTRACT FROM AUTHOR]

Numerical simulation of radon migration in fractured rock masses is crucial for environmental radon pollution protection, radon tracing technology and the co-exploitation of coal and uranium resources. This paper proposed a novel model based on a fractal discrete fracture network (DFN) to simulate radon migration in fractured rock masses. The paper provided a detailed method for determining the locations of three-dimensional fractures using the multiplicative cascade process. The governing equations for radon migration in fractures and the rock matrix were established and numerically solved using the finite element method. The study developed open-source software DFNRn (Discrete Fracture Network model for Radon migration), which was publicly available on GitHub. The software simulated radon migration in a fractured rock mass with a domain size of 100 m. The results demonstrate that fluid convection in fractures drives radon migration, which is dominant compared to the diffusion process. The accuracy of our proposed model was verified by comparing it with the measured data of the fractured rock. Furthermore, the study investigated the relationship between the percolation threshold of the fracture density P 32 ′ and the key parameters of the DFN. The results show that P 32 ′ decreased with the fractal dimension Df (1.4 ≤ Df ≤ 1.9) and normalization constant α (1.4 ≤ α ≤ 1.8) and is not correlated with the length exponent a (1.2 ≤ a ≤ 2.8). P 32 ′ decreased with the mean orientation angle and has no correlation with the Fisher constant. The radon source term of the rock matrix has the greatest impact on radon migration in fractured rock masses compared to the radon diffusion coefficient and permeability. Highlights: A new approach is proposed to model radon migration in fractured rock masses. An open-source software DFNRn was developed and is publicly available on GitHub. The procedure of the multiplicative cascade method in 3D space is given in detail. [ABSTRACT FROM AUTHOR]

Reliability analysis can be particularly challenging when performance functions require time-consuming simulations. Such simulations often involve multiple fidelity sources. This paper aims to enhance the efficiency of reliability analysis by leveraging multiple sample datasets with varying sources of fidelity. Firstly, this paper extends the GP model to integrate multiple low fidelity data into high fidelity predictions. In order to consider the correlations among data from different fidelity sources, the latent space representation from LMGP is introduced into the correlation matrix of different fidelity data. This multi-fidelity GP model is referred to as a latent map multi-fidelity Kriging (LMmfK). The effectiveness of LMmfK is validated through 1-dimensional analytical test and 8-dimensional Borehole test. Secondly, based on LMmfK, this paper proposes an active learning point-selected strategy suitable for scenarios with multiple fidelity sources, referred to as mfUEFF. The mfUEFF strategy intelligently selects the best data points from multiple fidelity sources, leveraging the benefits of both global improvement and local uncertainty. This integration enhances the efficiency and accuracy of reliability analysis. Two classic cases demonstrate that the proposed reliability method demonstrates superior computational accuracy and efficiency compared to other reliability methods. Finally, this paper applies the proposed method to the static reliability analysis of gears, involving time-consuming finite element models. Engineering application demonstrates that this method significantly improves efficiency, especially in scenarios with multiple fidelity sources. [ABSTRACT FROM AUTHOR]

The wear of backup rolls will have a great impact on the quality of the shape of hot rolled strip sheet. In order to overcome the limitations of the finite element method (FEM) in calculating backup roll wear in terms of efficiency and accuracy, this paper proposes a tandem FEM + ML hybrid model to optimise the predictive effect of the finite element method (FEM) on backup roll wear. Firstly, a backup roll wear model based on FEM is established. Secondly, in order to select the optimal machine learning (ML) algorithm as the finite element error compensation model, three types of finite element error compensation models were established based on the random forest (RF) algorithm, the radial basis function (RBF) neural network algorithm, and the particle swarm optimisation support vector machine (PSO-SVM) algorithm. Finally, the three types of finite element error compensation models were connected in series with the FEM model to compare the prediction performance of the three types of FEM + ML models on backup roll wear. The numerical experimental results show that the FEM + PSO-SVM model can better predict the wear of the backup roll, and the PSO-SVM algorithm is the most suitable for building the finite element error compensation model. It is proved that the FEM + ML model proposed in this paper can effectively improve the accuracy and computational efficiency of the FEM model for predicting backup roll wear without adding microelements. In addition, among the hot rolling parameters, the rolling force has the greatest influence on the backup roll wear, and excessive rolling force for a single pass should be avoided to slow down the backup roll wear. [ABSTRACT FROM AUTHOR]

This paper has proposed an efficient analysis method to calculate interface stress intensity factors (SIFs) based on a proportional stress field of a reference problem whose exact solution is available. In the previous proportional methods, the same crack length and the same element size were applied to both reference and unknown problems so that the same FEM error can be produced. Therefore, when analyzing many unknown problems, the conventional method needs to analyze many reference problems at the same time. Since this approach is time-consuming, this paper considers how to calculate many crack lengths efficiently by using only one single reference solution modeling. For this purpose, several general relations of SIFs are derived for the unknown and the reference problems when both crack length and element size are different. To analyze many unknown problems accurately by using a single reference solution modeling, how to choose the most suitable element dimension of the reference model is clarified. The proposed method is especially useful for crack propagation analysis. [ABSTRACT FROM AUTHOR]

The finite element limit analysis solution presented in this paper offers novel approaches for estimating the ultimate bearing capacity of annular foundations on Hoek–Brown criterion. The study examines the effects of five of dimensionless parameters, including the ratio of internal to external radii, the depth ratio, the adhesive factor, the yield parameter, and the geological strength index, on the findings of bearing capacity as well as the processes of collapse. Furthermore, one of the soft-computing regression methodologies, the multi-objective evolutionary polynomial regression analysis (MOGA-EPR) method, is utilized along with the requirement of the FELA outcomes as input data. This paper provides accurate limit-state predictions for annular footings on diverse rock masses using the MOGA-EPR model. By using the MOGA-EPR approach, the findings are highly precise and trustworthy, empowering designers to choose the best annular foundation design for various Hoek–Brown material varieties. Moreover, this study extends its scope by encompassing the application of multiple linear regression, multiple nonlinear regression, and artificial neural network models for an extensive comparative analysis. The amalgamation of these models widens the evaluative framework, fostering a more comprehensive exploration of predictive capabilities and insights into the stability assessment of annular footings across rock mass conditions. Through this multifaceted approach, a holistic comprehension emerges, thereby enhancing the decision-making process pertaining to the design of annular foundations within diverse Hoek–Brown material contexts. [ABSTRACT FROM AUTHOR]

Shale anisotropy characteristics have great effects on the mechanical behaviour of the rock. Understanding shale anisotropic behaviour is one of the key interests to several geo-engineering fields, including tunnel, nuclear waste disposal and hydraulic fracturing. This research adopted the finite discrete element method (FDEM) to create anisotropic shale models in ABAQUS. The FDEM models were calibrated using the mechanical values obtained from published laboratory tests on Longmaxi shale. The results show that the anisotropic features of shale significantly affect the brittleness and fracturing mechanism at the micro-crack level. The total fracture number in shale under the Uniaxial Compressive Strength (UCS) test is not only related to the brittleness of shale. It is also strongly dependent on the structure of the shale, which is sensitive to shale anisotropy. Two new brittleness indices, BIf and BICD, have been proposed in this paper. The expression for BIf directly incorporates the number of fractures formed inside of the rock, which provides a more accurate frac-ability using this brittleness index. It can be used to calculate the frac-ability of rocks in projects where there are concerns about fractures after excavation. Meanwhile, BICD links brittleness to the CD/UCS ratio in shale for the first time. BICD is easy to obtain in comparison to other brittleness indices because it is based on the Uniaxial Compressive Strength test only. In addition, it has been shown there is a relationship between tensile strength and the crack damage strength in shale. Based on this, an empirical relationship has been proposed to predict the tensile strength based on the Uniaxial Compressive Strength test. Highlights: Through the use of FDEM simulations, the fracturing mechanics of shale, fracturing behaviour, and brittleness of shale have been investigated from a micro-scopic viewpoint taking shale anisotropy into account. Two new brittleness indices are proposed. One relies on the number of fractures in the shale to reflect the shale's frac-ability, and the other uses strength parameters that can be easily obtained from UCS tests. This paper proposes an empirical relationship to predict the tensile strength of rocks based on UCS tests. [ABSTRACT FROM AUTHOR]

This paper presents a forced vibration analysis of open doubly curved sandwich panels subjected to a moving constant force. In this paper, the effect of softness of the core is considered by implementing a semi-layerwise theory. To this aim, the first-order shear deformation theory is adopted for the face sheets and a higher-order theory which was obtained based on 3D elasticity theory is considered for the core. The presented formulation is general and as the deepness parameter is accounted in the strain–displacement relations, the formulation can be used for a wide range of deep as well as shallow doubly curved shells. To obtain the dynamic response of the system, the finite element method (FEM) along with the Newmark method is used. The proposed element is a higher-order one with nine nodes and each node has fifteen degrees of freedom. The effect of various parameters such as length-to-thickness ratio, in-plane aspect ratio, boundary conditions, lamination scheme, and fiber orientation angles on the dynamic response of the structure is examined. Additionally, the critical velocity of the force at which the structure experiences maximum dynamic deflection is obtained in each case. The results show that as the length-to-thickness ratio of the structure increases, the dynamic magnification factor curve increases with respect to non-dimensional velocity. This study provides insights into the dynamic behavior of doubly curved sandwich panels with soft cores and can aid in the design of such structures for specific applications. The results of this study can also serve as a benchmark for future studies on the forced vibration behavior of doubly curved sandwich panels. [ABSTRACT FROM AUTHOR]

This paper introduces a novel index for static eccentricity (SE) fault diagnosis in synchronous reluctance motors (SynRMs). Although SynRMs with rotor barriers under SE have been modeled in a few papers, any indices for the fault detection have not yet been reported. The proposed index is a specific frequency pattern in the motor current, which can also determine the fault severity. A novel analytical magnetic field investigation is applied to ascertain the proposed index. An accurate nonlinear numerical method is proposed for the motor inductances calculation. The model considers the rotor flux barriers, magnetic saturation, and the stator slots effect. The air gap flux density and the motor current are then achieved. The fast Fourier transform is exploited as a signal-processing tool to calculate motor current spectra. Then, a two-dimension time-stepping finite element method is used to attest of the proposed numerical model. Effectiveness of the proposed index is verified by simulation and experimental tests. [ABSTRACT FROM AUTHOR]

In electron optics, calculation of the electric field plays a major role in all computations and simulations. Accurate field calculation methods such as the finite element method (FEM), boundary element method and finite difference method, have been used for years. However, such methods are computationally very expensive and make the computer simulation challenging or even infeasible when trying to apply automated design of electrostatic lens systems with many free parameters. Hence, for years, electron optics scientists have been searching for a fast and accurate method of field calculation to tackle the aforementioned problem in the design and optimization of electrostatic electron lens systems. This paper presents a novel method for fast electric field calculation in electrostatic electron lens systems with reasonably high accuracy to enable the electron-optical designers to design and optimize an electrostatic lens system with many free parameters in a reasonably short time. The essence of the method is to express the off-axis potential in an axially symmetrical coordinate system in terms of derivatives of the axial potential up to the fourth order, and equate this to the potential of the electrode at that axial position. Doing this for a limited number of axial positions, we get a set of equations that can be solved to obtain the axial potential, necessary for calculating the lens properties. We name this method the fourth-order electrode method because we take the axial derivatives up to the fourth order. To solve the equations, a quintic spline approximation of the axial potential is calculated by solving three sets of linear equations simultaneously. The sets of equations are extracted from the Laplace equation and the fundamental equations that describe a quintic spline. The accuracy and speed of this method is compared with other field calculation methods, such as the FEM and second order electrode method (SOEM). The new field calculation method is implemented in design/optimization of electrostatic lens systems by using a genetic algorithm based optimization program for electrostatic lens systems developed by the authors. The effectiveness of this new field calculation method in optimizing optical parameters of electrostatic lens systems is compared with FEM and SOEM and the results are presented. It should be noted that the formulation is derived for general axis symmetrical electrostatic electron lens systems, however the examples shown in this paper are with cylindrical electrodes due to the simplicity of the implementation in the software. [ABSTRACT FROM AUTHOR]

This paper presents a computer-based methodology to support the design for additive manufacturing of metal components. Metal additive manufacturing, and in particular powder bed fusion systems, are playing a prominent role in the industry 4.0 scenario. The state of the art concerning design methods and tools to support design for additive manufacturing is reviewed by the authors. The key phases of product design and process design to achieve lightweight functional designs and reliable processes are deepened, and the computer-aided technologies to support the approaches implementation are described. Indeed, the state of the art design for additive manufacturing general workflow can be enriched by holistic approaches, use of numerical simulation, and integration and automation between the required tasks. The paper provides a methodology based on the systematic use of numerical simulation to achieve the optimization of both products and associated processes. To take advantage of the holistic perspective, the approach relies on the use of integrated product-process design platforms, allowing to streamline the digital process chain. Product design is based on the systematic integration of topology optimization and automatized tools for concept development and selection and subsequent product simulation driven design refinement. Process design is based on a systematic use of process simulation to prevent manufacturing flaws related to the high thermal gradients of metal processes and minimize residual stress and deformations. This is achieved by working on both the build cycles layouts and the 3D models' distortion compensation. An automotive use case of product and process design performed through the proposed simulation-driven integrated approach is provided to assess the actual method suitability for effective re-designs of additive manufacturing high-performance metal products. The bridged gaps are systematically outlined, and further developments are discussed. [ABSTRACT FROM AUTHOR]

This review paper addresses the development of numerical modeling of electromagnetic fields in geophysics with a focus on recent finite element simulation. It discusses ways of estimating errors of our solutions for a perfectly matched modeling domain and the problems that arise from its insufficient representation. After a brief outline of early methods and modeling approaches, the paper mainly discusses the capabilities of the finite element method formulated on unstructured grids and the advantages of local h-refinement allowing for both a flexible and largely accurate representation of the geometries of the multi-scale geomaterial and an accurate evaluation of the underlying functions representing the physical fields. In summary, the accuracy of the solution depends on the geometric mapping, the choice of the mathematical model, and the spatial discretization. Although the available error estimators do not necessarily provide reliable error bounds for our complex geomodels, they are still useful to guide grid refinement. Therefore, an overview of the most common a posteriori error estimators is given. It will be shown that the sensitivity is the most important function in both guiding the geometric mapping and the local refinement. [ABSTRACT FROM AUTHOR]

Nowadays, finite element tyre models are often used to perform vehicle NVH (noise, vibration, harshness) simulations. To account for the specific operating conditions, a road surface must be properly included in the model. This paper deals with a methodology to experimentally evaluate and process road irregularity measurements, so as to generate a road surface input. These surfaces are used to simulate the tyre/road interaction at the footprint, which is modelled as a contact surface in finite element tyre models. For this reason, a linear profile of the road surface is not suitable for these simulations and the whole surface must be considered. Starting from the measurements taken through a test equipment specifically designed to carry laser sensors and scan road profiles, the Power Spectral Density (PSD) of a specific track is estimated and then interpolated considering piecewise functions. Finally, a model to generate a road surface starting from the measured PSD is developed, discussed and validated. [ABSTRACT FROM AUTHOR]

Accelerated bridge construction (ABC) is prevalent all over the world attributable to its technical advantages including the higher construction efficiency, less traffic disruption, and higher construction quality. Grouting sleeves (GS) and grouting corrugated pipes (GCP) are the traditional connection methods of ABC in high seismic regions, with the disadvantages of uncompacted grouting and high requirement of construction accuracy. To this end, this paper developed a new type of prefabricated concrete bridge pier connected with ultra-high performance concrete (PCBP–UHPC) jacketing to solve the problems. To validate the seismic performance of the proposed innovative bridge pier, quasi-static tests on three full-scale specimens PCBP–UHPC, PCBP–GS, and PCBP–GCP were carried out. The results indicated that the failure mode of specimen PCBP–UHPC was similar to that of specimens PCBP–GS and PCBP–GCP with the characteristics of longitudinal steel yielding and concrete crushing at the base of the hollow pier. The obvious plastic hinge outward shifting could be observed during the loading for specimen PCBP–UHPC. The positive ultimate load of specimen PCBP–UHPC was 636.33 kN, which was 14.8% and 13.3% higher than those of specimens PCBP–GS and PCBP–GCP, respectively. In addition, a refined finite element model (FEM) was established by ABAQUS to provide an in-depth understanding on the failure mechanism of the proposed PCBP–UHPC. The parametric analyses were conducted to reveal the influence of the socket depth and axial compression ratio on seismic performance of the proposed PCBP–UHPC. The results indicated that the socket depth had little effect on seismic performance of the prefabricated pier, while the ultimate load bearing capacity of specimen PCBP–UHPC increased to some extent as the increase of the axial compression ratio. The present research work provides an innovative prefabricated bridge pier and a comprehensive experimental–numerical understanding on its seismic performance, which is beneficial for its engineering application. [ABSTRACT FROM AUTHOR]

Elastic deformation in thin-walled parts during machining is affected by the coupling of force and flexibility. Obtaining flexibility information along machining tool paths is crucial for online monitoring of this deformation. However, the current finite element method (FEM) is limited by mesh nodes, hampering its ability to accurately determine flexibility along tool paths. To overcome this limitation, this paper proposes a method that combines FEM with the surrogate model to predict flexibility accurately at any position on thin-walled parts' surfaces. The surrogate model is the hybrid model K-K-CNN based on two K-nearest neighbor (KNN-KNN) algorithms and a convolutional neural network (CNN) model. Initially, an initial dataset containing positions and flexibility of mesh nodes is generated automatically through secondary development of ABAQUS. Then, the K-K-CNN hybrid model is introduced and trained on this dataset to calculate flexibility accurately at any position on the surface of thin-walled parts. The hybrid model employs a CNN to address the nonlinear spatial correlation issue in flexibility prediction. Moreover, the hybrid model incorporates two KNN algorithms to alleviate the overfitting challenge stemming from the straightforward input features and extensive dataset size. In comparison to traditional deep learning models, the K-K-CNN hybrid model presents notable benefits in predicting flexibility for complex thin-walled parts at any given position, which affirms its robustness and accuracy. The proposed prediction method for flexibility can provide high-quality data-driven information for monitoring the elastic deformation of thin-walled parts. [ABSTRACT FROM AUTHOR]

In rural areas, landslides can bury houses and result in major disasters in affected areas, which can greatly hinder local economic development and construction. When landslides occur, sliding debris can result in large impact forces, causing varying degrees of damage to building structures. Given the great harm caused by landslides, this paper studies the prediction of dynamic response characteristics of building structures under the impact of the Zhengjiamo landslide. The engineering geological background of the Zhengjiamo landslide is analyzed in detail via field investigations. Then, a numerical method is presented to simulate the runout process of the sliding debris, and the runout process and final deposition area are studied. A node-to-surface contact algorithm is adopted to transfer the displacements and contact forces between the sliding debris and the building. The building structure is simulated via the finite element method (FEM). The sliding debris is simulated via the smoothed particle hydrodynamics (SPH) method. An element erosion algorithm is adopted to simulate the destruction process. The SPH-FEM fluid–structure coupling method is implemented to simulate the landslide dynamic disaster process (the impact behavior for the building). The destruction process is considered in the interactions between the sliding debris and the building on the three-dimensional terrain. The landslide motion during each stage is analyzed, including the sliding, energy dissipation, impact, and damage to the building structure. The maximum runout of the landslide is about 280 m. The maximum stress of the impact on the building is 2 × 106 Pa. The impact speed of the sliding body is generally 16.5–24.07 m/s. On the basis of this, the disaster background, disaster status, and prediction of the landslide disaster effect are studied to provide new insights into landslide disaster prevention and reduction. [ABSTRACT FROM AUTHOR]

This paper investigates the space-time residual-based a posteriori error bounds of the mixed finite element method for the optimal control problem governed by the parabolic equation in a bounded convex domain. For the spatial discretization of the state and co-state variables, the lowest-order Raviart-Thomas spaces are utilized, although for the control variable, variational discretization technique is used. The backward-Euler implicit method is applied for temporal discretization. To provide a posteriori error estimates for the state and control variables in the L ∞ (L 2) -norm, an elliptic reconstruction approach paired with an energy strategy is utilized. The reliability and efficiency of the a posteriori error estimators are discussed. The effectiveness of the estimators is finally confirmed through the numerical tests. [ABSTRACT FROM AUTHOR]

This paper considers the iterative solution of finite element discretizations of second-order elliptic boundary value problems. Mesh independent estimations are given for the rate of superlinear convergence of preconditioned Krylov methods, involving the connection between the convergence rate and the Lebesgue exponent of the data. Numerical examples demonstrate the theoretical results. [ABSTRACT FROM AUTHOR]

In this paper, 3D braided composites are considered for high-performance piezoelectric energy harvester designing, and a 3D braided composite piezoelectric energy harvester (3D BCPEH) is proposed. The advantage of 3D BCPEH is that the natural frequency of the device can be adjusted by adjusting the stiffness of the spring, making the natural frequency of the device close to the vibration frequency of the environment, thereby achieving the best harvesting effect of the energy harvester. During the vibration process, spring support can cushion the impact and stress on the piezoelectric energy harvester, thereby protecting the device from damage and helping to improve the stability and performance of the system. Finite element analysis is used to obtain the elastic modulus, shear modulus, and Poisson's ratio of 3D braided composites with varying braiding angles. Based on Hamilton's variational principle, the vibration control equation of the spring supported 3D BCPEH is derived. The effects of spring rate, braiding angle, external excitation acceleration, external load resistance, and structure size on the output response of 3D BCPEH are simulated and analyzed. The validity of the proposed 3D BCPEH with spring support is confirmed by the simulation results. [ABSTRACT FROM AUTHOR]

Aluminum honeycomb sandwich structure with panels made of carbon fiber reinforced polymer (CFRP) are widely used in aerospace and other fields. Simulation of the eddy current (EC) testing of the sandwich structure using the finite element (FE) method is challenging as the traditional FE method has difficulties in mesh division and the solution of the algebraic equations. This paper proposes to use the domain decomposition FE method to solve such problems. The top CFRP panel, the aluminum honeycomb core, and the bottom CFRP panel of the sandwich structure and the ferrite core of the coil are placed in different subdomains and the subdomains are meshed independently. This method simplifies the mesh generation and does not require regenerating the meshes when simulating the scanning testing with the ferrite-core coil. In this way, the efficiency of simulation is greatly improved. The EC distributions in the sandwich structure are computed and the influence of defect on EC distribution is analyzed. The C scans of the sandwich structures are simulated. The images of the EC responses to the defects, such as wall fracture, node disconnection, and core wrinkle, are obtained. The simulation results are validated by experiments. [ABSTRACT FROM AUTHOR]

The fractures network generated during the excavation of underground research facilities can induce stress redistribution and alteration of flow and transport properties, becoming preferential paths for releasing radionuclides into the host rock. Nevertheless, in the long term, the fracture can be sealed through the resaturation of water coming from the rock as a function of its self-sealing potential. Despite the large number of experimental studies that have proven the self-sealing capacity of clay rocks, very few attempts have been made to describe and predict the phenomenon numerically. This may be due to the difficulty of measuring the initial hydro-mechanical conditions. Besides, samples artificially fractured in the laboratory can be disturbed by the preparation process itself, which can alter the hydro-mechanical state. This paper addresses that issue by bridging the gap between experiments and numerical modeling. Representative experimental tests performed on Callovo–Oxfordian Claystone (COx) are used to offer a hydro-mechanical fracture law taking into account the self-sealing capacity of the material. Implementing such a model in a finite element code allows its validation through comparison with laboratory tests. Furthermore, the role of the initial fracture size and the evolution of water permeability during the wetting/drying process is investigated. Due to its transmissivity, injected water can penetrate the rock, initially reaching the damaged zone around the fracture before spreading through the entire sample. This progression is accounted in the constitutive equation and represented numerically. Nevertheless, a larger initial crack leads to reduced recovery rates. These results match the experiments, offering a valuable perspective in the modeling of self-sealing in in situ conditions. [ABSTRACT FROM AUTHOR]

This paper presents a new finite element method (FEM) model to simulate the thermo-hydro-mechanical (THM) responses of water-saturated clay soils. The model can account for the effects of temperature variation on bound water dehydration and the corresponding thermo-poromechanical strains. The governing equations, including mass balance, momentum balance, and energy balance, are derived based on the principles of continuum mechanics for porous media. The impact of bound water dehydration on THM behavior is incorporated into the coupled THM equations. The model is equipped with an unconventional plasticity for more accurate description of elastoplastic behavior. To solve the nonlinear system of equations, a modified Newton–Raphson method is employed. The model is validated using laboratory tests on various clay soils with different geological origins, and reasonable agreement is achieved. The thermally induced contraction behavior of clay soils at a low overconsolidation ratio and thermally induced expansion behavior at a high overconsolidation ratio are well simulated. During heating, the effect of bound water dehydration on the generation of excess pore pressure in clay soils is highlighted in our numerical results. [ABSTRACT FROM AUTHOR]

Evaluating the exceedance probability within a time period (EPT) of the runout distance of rainfall-induced landslides is important for the quantitative risk assessment (QRA) of rainfall-induced landslides. However, assessing the EPT of the runout distance of rainfall-induced landslides using a mechanics-based method remains a challenging problem since it requires considering uncertainties in both soil properties and rainfall. This paper proposes a novel mechanics-based method to assess the EPT of the runout distance of rainfall-induced landslides with explicit consideration of the above two types of uncertainties. A two-stage numerical approach, which combines the finite element method (FEM) and the material point method (MPM), is first developed for the large deformation analysis to obtain runout distances of landslides under given rainfalls. To further enhance the computational efficiency, a machine learning-based surrogate model is built to predict the exceedance of the runout distance, and the EPT of the runout distance is finally estimated via Monte Carlo simulation. The proposed method is applied to a sandy slope under rainfall. The results show that the EPT increases as the time period becomes longer, and the runout distance of the landslide is controlled by the first failure of the slope caused by rainfall. This study contributes to the development of a general and efficient tool to support the QRA of rainfall-induced landslides. [ABSTRACT FROM AUTHOR]

This paper presents a forensic numerical study on hydro-fracturing at three locations within an excavation in a clayey till underlain by an aquifer in Ontario, Canada. The pioneering forensic studies were based on continuum mechanics using finite element method (FEM) combined with an effective medium approach, which did not explicitly simulate the physical process of fracture propagation. This has overestimated the size of the venting holes (i.e., model aperture approximately 8 m, observed approximately 0.1 m), hindering accurate assessment of the venting locations at the excavation base. For this reason, a coupled hydro-mechanical XFEM analysis, which explicitly models fracture propagation, was performed in this study to revisit the case history from the perspective of fracture mechanics. Parametric study is also performed to investigate the influence of flow rate on the direction of the fracture propagation, and thus location of venting holes. It is shown that the coupled hydro-mechanical XFEM analysis offers better predictions than previous FEM analysis for both, locations and sizes of the three observed venting holes. The parametric study reveals that an increase in the flow rate from 5 to 10 L/min (which is within the reported range) leads to a wider and less curved fracture, altering the predictions of the venting locations at the excavation base by around 8 m. This is because an increasing flow rate causes wider aperture and higher shear stress near the fracture tip, which intensifies the re-orientation of maximum principle stress that facilitates the re-direction of the propagating fractures. [ABSTRACT FROM AUTHOR]

The research on the crack propagation mechanism of bone has important research significance and clinical medical value for the selection of cutting parameters and the development of new surgical tools. In this paper, an extended finite element method (X-FEM) model of ultrasonic bone cutting considering microstructure was developed to further study the ultrasonic bone cutting mechanism and to quantitatively analyze the effects of cutting direction, ultrasonic parameters, and cutting parameters on the mechanism of ultrasonic bone cutting crack propagation. The results show that ultrasonic bone cutting is essentially a controlled crack propagation process, in which brittle crack and fatigue crack are the main crack propagation mechanisms. In order to improve the efficiency of ultrasonic bone cutting, large amplitude and high-frequency ultrasonic vibration are preferred. Compared with the other two cutting directions, the crack propagation deflection angle in the transverse cutting direction is the largest, resulting in the worst cutting surface. Therefore, in the path planning of orthopedic surgical robots, the transverse cutting direction should be avoided as much as possible. Frequency only has a significant effect on the crack propagation rate and has a positive correlation. There is a positive correlation between the deflection angle, propagation length, propagation rate, and amplitude, which provides the possibility to control the direction and length of crack propagation by controlling the amplitude of ultrasonic. The feed speed is much lower than the ultrasonic vibration speed, which makes the influence of ultrasonic vibration speed on the crack propagation characteristics dominant. The X-FEM model of ultrasonic bone cutting provides an effective method for selecting reasonable machining parameters of orthopedic robot and optimize the design of ultrasonic osteotome. [ABSTRACT FROM AUTHOR]

Compared to the first-order shear deformation theory and other classical shell theories, the higher-order shear theory is deemed more accurate due to its superior ability to capture transverse shear effects, especially vital for precision in modeling thicker, doubly curved shell panels. Additionally, the third-order shear deformation theory (TSDT) is acknowledged for its computational efficiency compared to the 3D solution striking a balance between result precision and computational efficiency. This paper explores the static bending and free vibration analysis of a porous bi-directional functionally graded doubly curved sandwich shell. For the first time, a combination of TSDT theory with the p-version finite element method is applied, demonstrated for the analysis of bi-directional functionally graded doubly curved sandwich shell. In the initial phase, the mathematical formulation has been meticulously derived. Four models of sandwich FGM distributions, taking into account the porosity effect and comprising a blend of two ceramic materials and a metallic material, have been thoroughly explored. Subsequently, the study evaluates the effectiveness and accuracy of the formulation implemented in FORTRAN CODE through benchmark results, showcasing its adaptability for different shell panel geometries by adjusting the values of the radius of curvature. The latter part of the research delves into new findings related to bi-directional functionally graded porous sandwich FGM shell panels, investigating the effects of gradient indexes and porosity distribution on their behavior. [ABSTRACT FROM AUTHOR]

Micrometeoroids and Orbital Debris (MMOD) travelling at extremely high velocities in space are a threat to the structural integrity of spacecrafts in the Low Earth Orbit. Whipple shield, consisting of a Bumper and a Rear Wall, with a stand-off distance in between, is widely used to protect spacecrafts from hypervelocity MMOD impacts. In this paper, we present numerical simulations of a set of well-known hypervelocity impact (HVI) experiments on aluminium-based Whipple shields reported in the literature. These simulations are conducted using the three-dimensional Lagrangian Finite Element Method in ABAQUS/Explicit software. In six out of the seven tests reported in the literature, the Whipple shield failed due to a detached spall from the back surface of the Rear Wall, while in the seventh test, the spall was not detached. The present work successfully replicates and favourably compares the failure mechanisms observed in these Whipple shields to the corresponding experimental results. Various critical aspects of the Whipple shield's failure mechanics and mechanisms are investigated. These include impact pressure on the projectile, Bumper and Rear Wall, Bumper hole diameter, temperature rise, and residual velocity of debris particles and spalled fragments. The predicted ballistic limit of the Whipple shield falls between 2.54 mm and 3.18 mm of Rear Wall thickness in excellent agreement with the experimental results reported in the literature. The present work provides valuable insights into Whipple shield performance. The developed methodology could be employed to optimize shield design through predictive simulations, thereby improving spacecraft protection. [ABSTRACT FROM AUTHOR]

Terahertz waveguides and resonators have brought numerous applications from biomedical to modern communications. In this paper, we have demonstrated numerically a straight semiconductor-insulator-semiconductor(SIS) waveguide attached to a split ring resonator, which acts as a terahertz frequency filter and can be used for refractive index sensing. The device's transmission properties have been studied using the finite element method. To fix the third dimension of the device, that is the depth of the waveguide the effective mode index and power density calculations are done for the propagating mode. The frequency tuning of the filter is achieved by changing the geometric parameters of the waveguide and resonator system such as ring radii and split width. Both the symmetric and antisymmetric modes of the split ring show almost the same rate of change of resonance frequency with the change in geometric parameters. To demonstrate the importance of the split position, the transmittance is studied by placing the split at different positions on the ring. We obtained the same transmittance for the split at left and right positions, whereas the split at the top and bottom shows different transmittance similar to the transmittance of a ring resonator. The symmetric and antisymmetric modes of the split ring are calculated for refractive index sensing and the highest sensitivity of 0.741 THz/ refractive index unit (RIU) for the symmetric mode as expected. [ABSTRACT FROM AUTHOR]

This paper presents a dual-core two-parameter optical fiber sensor based on the surface plasmonic resonance (SPR) effect. It is analyzed by the finite element method. The proposed sensor is a dual-channel structure designed with photonic crystal fiber (PCF) as the base material: one channel is coated with a gold film to measure the refractive index (RI) of the solution to be measured, and the other channel is coated with a gold film and polydimethylsiloxane to measure the temperature of the solution to be measured. The exposed microslot structure on both sides reduces the complexity of sensing measurements. The results show that the maximum RI sensitivity of the sensor is 19,900 nm/RIU, and the maximum sensitivity to temperature is 8.7 nm/℃. This work is conducive to realizing a PCF sensor with high sensitivity, large measurement range, real-time monitoring, and easy preparation. As a result, the sensor is expected to be widely used in fields such as biology and chemicals. [ABSTRACT FROM AUTHOR]

This paper presents a shape optimization for the three-dimensional cooling channel with high Reynolds number flow and strong convection heat transfer based on isogeometric analysis (IGA). Meanwhile, the applicability conditions of Darcy's potential flow, which is an approximate liner flow, are introduced to solve the heat-flow coupling problem. We call this method Darcy reduced-order isogeometric analysis (DRIGA). The volume parametric model is constructed by using the segmentation–mapping–merging mechanism of design features, and the model can be directly analyzed by IGA without data conversion and to eliminate discrete errors. The calculation formulas for DRIGA are derived. Then, a DRIGA-based shape optimization is achieved by applying the sensitivity analysis method with the average temperature as the objective function, the location coordinates of the fluid–solid boundary control points as the design variables, and the percentage of fluid volume and the pressure drop as the constraints. Several examples of approximate water-cooling devices show that our method can accurately describe the heat-flow coupling problem in the case of a narrow channel with a high flow velocity. The analytical results are in general agreement with those of the finite element convection–diffusion analysis, and the shape optimization results show that the average temperature is reduced, which proves the correctness of the method. [ABSTRACT FROM AUTHOR]

The permanent magnet claw pole machine (PMCPM) with soft magnetic composite (SMC) cores has shown better performance than the traditional transverse flux machine, and its performance can be improved by developing its stator with hybrid silicon sheet and SMC cores, and this kind of PMCPM is named as HPMCPM. Due to its complex 3D magnetic structure, analyzing its performance by using the traditional finite element method (FEM) is time-consuming. To overcome this constraint, this paper proposes a magneto-electric-thermal coupling network (METCN) model with bidirectional data transmission to calculate the electromagnetic performance and temperature distribution and the calculation results are verified by the FEM method and experimental measurement results. Compared with the 3D FEM, the proposed METCN method has the advantage of fast calculation speed and similar accuracy. [ABSTRACT FROM AUTHOR]

This paper proposes a design scheme for a wireless power transfer (WPT) system based on multi-relay coils to solve the power supply demand of 500 kV transmission line online monitoring equipment. The relationship between the operating frequency and the coil loss is established to analyze the influence of the number of relay coils and the coil distance on the transmission performance. The particle swarm optimization model is established with transmission efficiency as the optimization objective. The distribution spacing between coils, the working frequency, and the number of coils are optimized. Based on the equidistant arrangement of relay coils, an optimization scheme of non-equidistant arrangement is proposed. Under the condition of the same number of relay coils, the transmission efficiency of the system is increased by 20.56% and has been verified by experiments. In addition, finite element analysis software has simulated the surrounding high-voltage field strength of the WPT system added to the insulators. The results show that the insulators still meet the insulation standards. The simulation and experimental results show that the proposed scheme can effectively meet the power demand of high-voltage line monitoring equipment. [ABSTRACT FROM AUTHOR]

This paper proposes a new design for line-start operation of synchronous reluctance motors. In the past years, synchronous reluctance motors have been studied by many researchers. Due to high efficiency, they have gained increasing interest because in the synchronous operation, there is limited losses in the rotor. On the other hand, line-start operation of the synchronous reluctance motors is an important challenge that can make this type of the motors popular in many applications. However, line-start operation techniques should not considerably affect the steady-state characteristics of the motor. In the proposed design, the arrangement, size and shape of the rotor conductor bars are designed based on the rotor magnetic circuit difference between induction and reluctance synchronous motors. Complete assessment of the motor parameters are examined using finite element analysis. The proposed structure improves the starting characteristics of the motor. Moreover, power factor of the proposed motor is slightly increased in comparison to that of conventional line-start synchronous reluctance motors. The results obviously show effectiveness of the proposed line-start operation strategy for the synchronous reluctance motors. Finally, experimental verification are also included to confirm the finite element analysis results. [ABSTRACT FROM AUTHOR]

In this paper, three typical permanent magnet machines for All-Electric aircraft propulsion are designed, optimized and compared. Firstly, the necessary performances are determined based on the requirements of high power/torque density and an aircraft with a maximum takeoff weight of 1500 kg. The initial structures of interior permanent magnet (IPM) synchronous machine, vernier permanent magnet (VPM) machine and flux-switching permanent magnet (FSPM) machine are designed with identical stator outer radius and rotor shaft length. Then, parametric sensitivity analysis and multi-objective particle swarm are combined as an optimization methodology to optimize these machines. Based on the finite element analysis, the electromagnetic performances such as no-load airgap flux density harmonic spectrum, cogging torque, average output torque, losses, efficiency and power factor, etc., are generally compared and analyzed. Subsequently, the discussions are carried out, where the strength and weakness of these three machines are concluded and the future prospects are suggested. Finally, it is concluded that if effective measures are implemented to reduce the permanent magnet eddy current loss and improve the power factor, the VPM machine would be the most suitable choice among these machines for All-Electric aircraft propulsion. [ABSTRACT FROM AUTHOR]

The Material Point Method (MPM) is an established and powerful numerical method particularly useful for simulating large-scale, rapid soil deformations. Therefore, it is often used for the numerical investigation of mass movement hazards such as landslides, debris flows, or avalanches. It combines the benefits of both mesh-free and mesh-based continuum-based discretization techniques by discretizing the physical domain with Lagrangian moving particles carrying the history-dependent variables while the governing equations are solved at the Eulerian background grid, which brings many similarities with commonly used finite element methods. However, due to this hybrid nature, the material boundaries do not usually coincide with the nodes of the computational grid, which complicates the imposition of boundary conditions. Furthermore, the position of the boundary may change at each time step and, moreover, may be defined at arbitrary locations within the computational grid that do not necessarily coincide with the body contour, leading to different interactions between the material and the boundary. To cope with these challenges, this paper presents a novel element-wise formulation to weakly impose non-conforming Dirichlet conditions using Lagrange multipliers. The proposed formulation introduces a constant Lagrange multiplier approximation within the constrained elements in combination with a methodology to eliminate superfluous constraints. Therefore, in combination with simple element-wise interpolation functions classically utilized in MPM (and FEM) to approximate the unknown field, a suitable Lagrange multiplier discretization is obtained. In this way, we obtain a robust, efficient, and user-friendly boundary imposition method for immersed methods specified herein for implicit MPM. Furthermore, the extension to frictionless slip conditions is derived. The proposed methodologies are assessed by comparing the numerical results with both analytical and experimental data to demonstrate their accuracy and wide range of applications. [ABSTRACT FROM AUTHOR]

Accurate estimation of rotational frequency response functions (FRFs) is an essential element of successful structural coupling. It is well known that the experimental estimation of structural excitations is very difficult with current technology. This paper proposes a scheme to improve the performance of the frequency-based substructuring (FBS) method by estimating unmeasured FRFs, including those corresponding to rotational degrees of freedom, from a set of experimentally determined translational FRFs. More specifically, the modal parameters extracted by modal analysis (EMA) from the experimentally determined FRFs are used for model updating, modal expansion and FRF synthesis. For this purpose, an approximate modelling approach is proposed, where a simplified and approximate finite element model (ASFE) is developed and updated to accurately reproduce the experimental responses. A modal expansion basis is then constructed from the ASFE to expand the mode shapes using the system equivalent reduction and expansion process (SEREP). FRF synthesis is then used to derive unmeasured translational and rotational FRFs. The synthesised FRFs within the frequency range of interest agree well with the experimental FRFs. The synthesised full FRF matrix is then used with the FBS method to derive the response model for the coupled structure in a bottom-up modelling approach. [ABSTRACT FROM AUTHOR]

This paper deals with the determination of numerical and experimental buckling loads for circular plates. In the study, plates made of isotropic material and laminated composites were taken into consideration. For the experimental part of the study, a buckling apparatus for circular plates (BACIP) was designed and manufactured to apply radial compression on plates simply supported along the outer edge, which was the most important aspect of the study. Experimental buckling loads were determined by connecting this apparatus to a tension machine. ANSYS software based on the Finite Element Method (FEM) and the analytical buckling load formula found in textbooks were also used for the determination of the numerical and analytical buckling loads. The effects of parameters such as plate thickness, number of layers, cutout sizes, and so on on critical buckling loads were investigated within the scope of the work. Comparisons of analytical, theoretical and experimental buckling loads were presented in both graphical and tabular form. The results of the experimental and theoretical buckling were found to be comparatively compatible. [ABSTRACT FROM AUTHOR]

We propose three hollow-core anti-resonant fibers with different nested tube structures and numerically analyse their confinement loss, single-mode performance and bending loss by using the finite element method. The results show that the nested semi-elliptical structure FD#2 and the hybrid nested FD#3 structure have excellent transmission performance. The confinement loss of FD#2 and FD#3 at 1.55 µm is 0.00037 dB/km and 0.0004 dB/km respectively, and the high order mode extinction ratio is around 1700 for both FD#2 and FD#3. The bandwidths of FD#2 and FD#3 with losses less than 0.01 dB/km are within 1.36–1.73 μm and 1.42–1.8 μm, respectively. In addition, the bending resistance of FD#2 and FD#3 is excellent, with bending losses of 0.003 dB/km and 0.001 dB/km at a bending radius of 8 cm. We also evaluated the manufacturing tolerance range of these two structures in the actual manufacturing process. The structure proposed in this paper is expected to provide new ideas for the design of nested elements, and provide more possibilities for optical fiber design suitable for large-capacity data transmission and gas sensing applications. [ABSTRACT FROM AUTHOR]

In this paper, a new and simple structure of a photonic crystal fiber (PCF) surface plasmon resonance biosensor is designed for detecting aqueous solutions. The graphene and magnesium fluoride (MgF2) materials are used externally around the PCF to increase the sensitivity of the sensor. The performance of the sensor is analyzed using the finite element method. The numerical results show that the proposed PCF provides an average wavelength sensitivity (Sw) and amplitude sensitivity (SA) as high as 4000 nm/RIU−1 and 16,905.15 RIU−1, respectively, for analytes with refractive indices (RIs) ranging from 1.33 to 1.342. When the MgF2 layer is eliminated from the structure, the values of Sw and SA are decreased to 2500 nm/RIU−1 and 12,155.2 RIU−1, respectively. Therefore, it is concluded that adding an MgF2 layer externally on the graphene layer of the proposed PCF increases the Sw and SA parameters. It is also exhibited that by increasing the thickness of graphene layers, the confinement loss is enhanced, and the SA is decreased. In addition, by adding the thickness of the MgF2, both SA and confinement loss parameters are increased. The results also show a linear relationship between the parameters with a very high figure of merit (FOM) of 17,416.66RIU−1 and a resolution of 2.5 × 10–5. [ABSTRACT FROM AUTHOR]

From the literature it is known that orthogonal polynomials as the Jacobi polynomials can be expressed by hypergeometric series. In this paper, the authors derive several contiguous relations for terminating multivariate hypergeometric series. With these contiguous relations one can prove several recursion formulas of those series. This theoretical result allows to compute integrals over products of Jacobi polynomials in a very efficient recursive way. Moreover, the authors present an application to numerical analysis where it can be used in algorithms which compute the approximate solution of boundary value problem of partial differential equations by means of the finite elements method. With the aid of the contiguous relations, the approximate solution can be computed much faster than using numerical integration. A numerical example illustrates this effect. [ABSTRACT FROM AUTHOR]

Fractional Feynman–Kac equation governs the functional distribution of the trajectories of anomalous diffusion. The non-commutativity of the integral fractional Laplacian and time-space coupled fractional substantial derivative, i.e., A s 0 ∂ t 1 - α , x ≠ 0 ∂ t 1 - α , x A s , brings about huge challenges on the regularity and spatial error estimates for the forward fractional Feynman–Kac equation. In this paper, we first use the corresponding resolvent estimate obtained by the bootstrapping arguments and the generalized Hölder-type inequalities in Sobolev space to build the regularity of the solution, and then the fully discrete scheme constructed by convolution quadrature and finite element methods is developed. Also, the complete error analyses in time and space directions are respectively presented, which are consistent with the provided numerical experiments. [ABSTRACT FROM AUTHOR]