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• An attempt to characterize thin, low impedance paper at various high strain-rates. • The creation of a digital twin of the physical Split Hopkinson Test bench. • To demonstrate that there can be distortions of the transmitted measuring signal. This work deals with the high strain-rate characterization of paper under uniaxial tension using a Split Hopkinson test bench. An aluminum bar system featuring a highly sensitive hollow transmission bar was used. Paper tests were performed in a strain-rate range between approximately 60 s−1 and 210 s−1. The experimental tests showed that the breaking strength appears to decrease with increasing strain-rate. To verify these results, a digital twin of both the paper specimen and the entire test rig was created in an explicit Finite Element method environment. The numerical model was then used to perform a parameter study with different types of transmission bars. It was shown that the system is quite sensitive to additional masses caused by the specimen fixtures, as well as to drastic reductions in the cross section of the transmission bar. As a result, the transmitted measuring signal can be distorted and may need to be corrected using the digital twin. [ABSTRACT FROM AUTHOR]

Stacking REBCO tapes is an effective way to increase the current-carrying capacity of the cable. Various loading conditions, including combined tension-bend, are applied to these tapes during fabrication and operation of the magnets. This paper investigates the degradation behaviors of critical current (I c) in stacked rare earth–barium–copper–oxide (REBCO) coated conductor (CC) tapes under tension loading through experimental. Uniaxial tension experiments are conducted on single tapes and 4-tape cables with different stacking at 77 K. The critical current degrades rapidly when strain exceeds an irreversible threshold around 0.4-0.5%. A 3D finite element model analyzes the non-uniform stress distribution in the cable cross-section under tension, causing different degradation behaviors. An empirical model combining the Ekin law and Weibull distribution is proposed to relate I c and axial strain. By fitting experimental data, the key parameters are determined. The I c of a single tape reduces 20% at 0.4% strain. Face-to-face stacking decays at 0.45% irreversible strain, while back-to-back decays at 0.38%. The model provides an effective way to optimize the electromechanical performance of stacked REBCO cables. • This study focuses on the electromechanical behavior of REBCO cables under axial loads. • This study used 3D simulations to understand stress distributions in the cables. • This study conducted fitting of experimental results using a combination of Ekin law and Weibull distribution. [ABSTRACT FROM AUTHOR]

The paper considers quadrature-cubic interpolation in problems of restoration of functions of two arguments. The properties of the most common finite elements Q12 (Lagrange version) and Q10 (Serendipity version) are investigated as finite elements. For more than fifty years, researchers of the finite element method have known the procedure of converting the Lagrangian model to the serendipity model. But, as is known, not all results when using this procedure satisfy users, especially proponents of physical interpretation. We are talking about the magnitude of the nodal loads of the uniform mass force of the serendipity finite element. Thus, if we consider the finite element Q10, it receives the physical inadequacy of the "spectrum" as an inheritance from the "parent" pair of Lagrangian finite elements Q8 and Q12. In Pascal's scheme, there is also a hidden connection between the finite element Q10 and the finite element Lagrangian Q12. The analysis of the inherited properties suggests that it is fundamentally possible for a Q10 substitute-base to exist in nature with the same local and integral characteristics. It turns out that the search for such a base goes beyond the capabilities of traditional modeling methods. An alternative substitute-basis Q10 was found by nonmatrix condensation of the prototype of element Q10, i.e., by using the Lagrangian model Q12. The universal nature of the non-matrix transformation of Q12 into Q10 opens up the possibility of designing a model series of mixed finite elements with physically adequate spectra of nodal loads. [ABSTRACT FROM AUTHOR]

The characteristics of the piezo-stack and the flexible mechanism are both influenced by temperature, which induces the performance change of piezoelectric actuators in low-temperature. This study investigates how temperature affects the dynamics model's stiffness, damping, driving force, and friction. An axial heat conduction model based on Fourier's heat conduction law was established, and finite element analysis was carried out to study the temperature distribution of the piezo-stack. Moreover, finite element analysis was carried out at various temperatures to investigate the impact of temperature on the flexible mechanism's deformation. Based on the aforementioned study, a dynamics model with variable stiffness and damping is proposed in this paper, and the simulation results are verified. In the experiment, the effects of temperature, voltage, and frequency on the output performance of the piezoelectric actuator were investigated separately using impedance and amplitude-frequency characteristic curves to determine the resonant frequency and damping ratio of the flexible mechanism at low temperatures. Theory and experiment show that high stiffness and low piezoelectric constants at low temperatures reduce the piezoelectric actuator's output displacement, friction reduction will enhance the driving displacement of the piezoelectric actuator, and the effect of damping on output displacement is insignificant. This study offers significant theoretical value and guidance for the use of piezoelectric actuators in low-temperature situations. • Temperature distribution across a piezo stack via mechanical series and electrical parallel connections. • Calculate stiffness, damping, and piezo constants at low temperatures, integrate them with a dynamics model for simulation. • Assess the influence of dynamics model parameters on piezo actuators through theoretical simulations and experiments. • Clarify the effect of each parameter of the dynamics model on the performance of piezoelectric actuators by means of experimental and theoretical simulations. [ABSTRACT FROM AUTHOR]

In this paper, we consider the linearized backward Euler finite element scheme for the Navier-Stokes-Poisson-Nernst-Planck (NSPNP) equations. We aim to derive the unconditional error estimates of all variables in l ∞ (L 2) and l ∞ (H 1) norms. Compared with some previous results, we remove the mesh restriction. In addition, we derive two important physical properties for the proposed numerical scheme. Finally, three numerical examples are implemented to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

We present an application of stable finite element (FE) approximations of convection-diffusion initial boundary value problems (IBVPs) using a weighted least squares FE method, the automatic variationally stable finite element (AVS-FE) method [1]. The transient convection-diffusion problem leads to issues in classical FE methods as the differential operator can be considered a singular perturbation in both space and time. The stability property of the AVS-FE method, allows us significant flexibility in the construction of FE approximations in both space and time. Thus, in this paper, we take two distinct approaches to the FE discretization of the convection-diffusion problem: i) considering a space-time approach in which the temporal discretization is established using finite elements, and i i) a method of lines approach in which we employ the AVS-FE method in space whereas the temporal domain is discretized using the generalized- α method. We also consider another space-time technique in which the temporal direction is partitioned, thereby leading to finite space-time "slices" in an attempt to reduce the computational cost of the space-time discretizations. We present numerical verifications for these approaches, including numerical asymptotic convergence studies highlighting optimal convergence properties. Furthermore, in the spirit of the discontinuous Petrov-Galerkin (DPG) method by Demkowicz and Gopalakrishnan [2–6] , the AVS-FE method also leads to readily available a posteriori error estimates through a Riesz representer of the residual of the AVS-FE approximations. Hence, the norm of the resulting local restrictions of these estimates serves as error indicators in both space and time for which we present multiple numerical verifications in mesh adaptive strategies. [ABSTRACT FROM AUTHOR]

In this paper, we present a new error analysis of a class of charge-conservative finite element methods for stationary inductionless magnetohydrodynamics (MHD) equations. The methods use the standard inf-sup stable Mini/Taylor–Hood pairs to discretize the velocity and pressure, and the Raviart–Thomas face element for solving the current density. Due to the strong coupling of the system and the pollution of the lower-order Raviart–Thomas face approximation in analysis, the existing analysis is not optimal. In terms of a mixed Poisson projection and the corresponding estimate in negative norms, we establish new and optimal error estimates. In particular, we prove that the method with the lowest-order Raviart–Thomas face element and Mini element provides the optimal accuracy for the velocity in L 2 -norm, and the method with the lowest-order Raviart–Thomas face element and P 2 − P 1 Taylor-Hood element supplies the optimal accuracy for the velocity in H 1 -norm and the pressure in L 2 -norm. Furthermore, we propose a simple recovery technique to obtain a new numerical current density of one order higher accuracy by re-solving a mixed Poisson equation. Numerical results are provided to verify the theoretical analysis. • New and optimal error analysis of charge-conservative finite element methods are established. • A simple recovery technique is proposed to obtain a new current density with higher accuracy. • Numerical examples are provided to verify the theoretical findings. [ABSTRACT FROM AUTHOR]

This paper is concerned with a class of nonlinear multi-term time fractional wave equations. Based on the Galerkin finite element method (FEM) in space and the L 2- 1 σ formula in time, combined with the corresponding fast algorithm, an efficient fully discrete scheme is constructed. The unconditional optimal convergence property in H 1 -norm of the proposed scheme is discussed by utilizing the time-space splitting technique. Furthermore, the optimal L 2 -norm convergence and the H 1 -norm superconvergence results of the method are obtained. Finally, several illustrative numerical experiments are performed to verify the theoretical results. Compared with the existing works, studying the convergence of FEMs for the nonlinear fractional wave equation is a great challenging task, and there are significant differences in research approaches. [ABSTRACT FROM AUTHOR]

• Dynamic modelling of soft tissue deformation based on the dynamic model decomposition. • No prior knowledge of the system governing equation is required. • Construct a reduced-order model by extracting the essential features of the full model. This paper studies a new approach to dynamic modelling of soft tissue nonlinear deformation behavior based on dynamic model decomposition. This approach derives the deformation relationship between two continuous time points from correlated system snapshots. Subsequently, it constructs a reduced-order system by extracting most relevant information via thin-singular value decomposition to capture dynamic characteristics of the full-order deformation system. Unlike the existing methods which mainly rely on the establishment of complex constitutive equations for governing soft tissue deformation, the proposed method conducts tissue deformation directly from measured samples without involving constitutive governing equations. Simulation results show that the proposed method not only achieves real-time performance, but also sustains similar accuracy as the nonlinear finite element method. [ABSTRACT FROM AUTHOR]

The scaled boundary finite element method (SBFEM) is a semi-analytical numerical approach based on the scaled boundary coordinates. Recently, the method which uses interpolations in both the circumferential and radial directions has also been developed based on the scaled boundary representation. However, the stress fields are always discontinuous within the S-elements by both the original SBFEM and the latter method. In this paper, a new class of quadrilateral elements with interior smoothness is constructed by extending the B-net method based on the area coordinates into the S-net method based on the scaled boundary coordinates. In the S-net method, the Bernstein bases are separately applied to discretize both circumferential and radial directions in each sub-triangle of an S-element (or quadrilateral element), and the smoothness conditions between adjacent triangles can be simply represented in the form of linear equations. Then, by using the S-net method, we obtain a new class of quadrilateral elements with interior smoothness and high-order completeness. The shape functions or interpolation bases can be obtained explicitly and determined by the same interpolation nodes of the S-element as the original SBFEM. Some numerical tests also show that the proposed elements can obtain good results. • A new class of quadrilateral FEM elements is constructed in the scaled boundary coordinates with interior C 1 continuity. • The B-net method based on the area coordinates is extended into the S-net method based on the scaled boundary coordinates. • The new elements overcome the stress singularity at the scaling centre and stress discontinuity inside the S-element. • The high-order completeness of the new elements is proved theoretically and thus the convergence is guaranteed. • The extended S-net method can construct new polygonal elements with high-order continuity. [ABSTRACT FROM AUTHOR]

This paper proposes an extended virtual element method based on the combination of the extended finite element method and the virtual element method on interface-unfitted meshes for solving elliptic interface problems. The well-posedness of the discrete problem is shown and the optimal error estimate is derived, which is independent of the location of the interface relative to the mesh and the contrast between the diffusion coefficients. Numerical experiments verify the theoretical results. [ABSTRACT FROM AUTHOR]

Hydrogen storage vessels in hydrogen refueling stations are densely arranged, so high-speed fragments generated by explosion accidents may endanger adjacent vessels. It is of great significance to explore the dynamic responses and damage modes of hydrogen storage vessels under impact loads to promote the intrinsic safety development of hydrogen storage vessels. In this paper, a finite element analysis model is developed for simulating the dynamic responses of vessels under the impact of fragments. The influences of the number of winding layers, impact velocity, fragment mass, and fragment shape are investigated. The results show that fragment impact is a kind of local damage behavior with two typical stages of hitting and rebounding. The impact resistance of vessels increases with the number of winding layers. Impact velocity and fragment mass are positively related to deformation and damage. Conical fragments have stronger damage abilities, while spherical fragments cause greater deformation. [Display omitted] • The dynamic response and damage modes of vessels under impact were investigated. • The impact resistance of vessels increases with the number of winding layers. • Different factors have different effects on the damage and deformation of vessels. • System energy is mainly converted into internal energy. [ABSTRACT FROM AUTHOR]

In simulations involving fluid-structure interactions, the partitioned coupling approach allows calculating the fluid flow and the structural displacement using different solvers, which are coupled by a structure-to-fluid algorithm. This partitioned scheme can result in non-conforming meshes at the solid-fluid interface, especially when the fluid and the structure meshes contain elements of different characteristic sizes. In this context, a mesh-interpolation technique is required to transmit the nodal information from one mesh to the other. This paper focuses on comparing radial basis functions and k-nearest neighbours interpolations on fluid-structure interaction test cases. Indeed, those are fast and flexible techniques requiring no topological information other than relative distances between nodes, allowing a straightforward transfer of nodal data between non-conforming meshes. This feature is particularly favourable in the Particle Finite Element Method (PFEM), where remeshing procedures result in significant changes of the finite element discretisation at the fluid-structure interface. Accordingly, our contribution compares the interpolations in a PFEM/FEM partitioned scheme, using 2D and 3D benchmark problems. [ABSTRACT FROM AUTHOR]

In this paper, one non-iterative two-grid parallel stabilized finite element method based on overlapping domain decomposition is developed and investigated for the Stokes problem. The lowest-order finite element pairs P 1 − P 1 are utilized to approximate the velocity and pressure, respectively. The difference between a consistent and an under-integrated mass matrices is chosen as the stabilized term to circumvent the so-called inf-sup condition. Algorithm distributes legitimately residuals into local domains with a partition of unity. Error estimates are rigorously established. Theoretical results indicate that patches of diameter H | l n H | (| l n H | − l n | l n H |) or H | l n H | are sufficient to preserve optimal convergence rates with a proper configuration between the coarse mesh size H and the fine mesh size h in 2-D or 3-D case, respectively. Finally, some numerical experiments are reported to support our theoretical results. [ABSTRACT FROM AUTHOR]

In this paper, we report an innovative approach of using spark plasma sintering (SPS) combining with finite element modeling (FEM) to investigate the transient behavior of nuclear fuels. The temperature ramping rates of the SPS with special tooling can be controlled from 5 to 10 °C/s up to 500 °C/s, mimicking prototypical thermal profiles of the loss-of-coolant-accident (LOCA) and reactivity-induced-accident (RIA) events, respectively. The fresh UO 2 pellets with micron grain size are synthesized by SPS. Their fracture and fragmentation behaviors are investigated under transient thermal testing, and temperature-gradient and thermal-stress are calculated by FEM. The micron-sized fresh UO 2 displays good thermal shock stability and anti-cracking performance under the LOCA thermal test. Under simulated RIA conditions, the UO 2 fuels crack due to the stress induced by the large thermal gradient. The unique capability of SPS with controlled temperature ramping enables a cost-effective approach for rapid screening and high throughput evaluation of nuclear fuels under power transients. [ABSTRACT FROM AUTHOR]

The primary objective of this paper is to investigate the error analysis for the damped Boussinesq equation with the Ciarlet-Raviart mixed finite element method, focusing on achieving superconvergence. By employing a skillful mean technique and a high precision estimate of the bilinear element, as well as combining with projection and interpolation technique, we first obtain a superclose error estimate between interpolation of the exact solution and numerical solution. Subsequently, by applying an interpolation post-processing approach, we efficiently derive a global superconvergence result. Finally, several numerical results are presented to support our theoretical analysis. [ABSTRACT FROM AUTHOR]

INCONEL® machining poses great challenges in predicting its behaviour, and exhaustive experimental evaluation of its machinability is expensive and unsustainable. Design of Experiments (DOE) can be performed without destroying components via Finite Element Analysis (FEA). However, it is paramount to establish if numerical modelling and the constitutive models can cope with an accurate predictability of INCONEL® machining. Hence, a broad review of FEA strategies will be given to systematically summarise and analyse the progress taken on INCONEL® machining predictability through FEA from 2013 to 2023 and present the most recent researchers' digital solutions, prospects, and limitations. Thanks to articles and books, this paper was conceived. The main keywords used in searching information were: "INCONEL® 718", "INCONEL® 625", "FEA", "Traditional Machining Modelling", "Johnson-Cook criteria", "ABAQUS™", "ANSYS®" and "DEFORM®". Combining these keywords was crucial to filter the current information about the evolution of INCONEL® alloy machining predictability through FEA. INCONEL® alloys FEA machining can nowadays effectively provide good quality and accurate results regarding the counterpart experiments. [ABSTRACT FROM AUTHOR]

Supercritical water oxidation (SCWO) is well known as a promising end-of-pipe technology for treatment of hazardous wastes. Safety is undoubtedly the first concern as the SCWO should be operated under a harsh chemical and physical environment, including high temperature, high pressure, and high corrosive medium and plugging risk. This paper is the first report about a tube explosion incident that encountered during continuous SCWO treatment of industrial sludge. 3D imaging, Scanning Electron Microscope - Energy Dispersive Spectroscopy (SEM-EDS) and 3D finite element analysis are used to analyze the incident tube comprehensively. The results indicate that the incident tube was working at a hash corrosive environment of subcritical water and chloride, which leads to all of general, pitting and intergranular corrosions. Of which, the pitting is the most severe one that finally results to perforation. Then, leakage took place. Soon afterwards, the hard inorganic particle from sludge plugged the leaking pore for a second, but immediately split it as a big hole due to the local high pressure around the leaking pore. Finally, explosion occurred. Three lessons are drawn for the future safe design and operation of SCWO, i.e., selecting suitable pressure bearing material, checking regularly, and executing safety regulations. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, a combined scheme of edge/node-based smoothed finite element method (ENS-FEM) and the mixed interpolation of the tensorial components for the three-node triangular element (MITC3) named a ENS-MITC3 is developed to investigate the static and free vibration for functionally graded (FG) porous shells. The effective material properties of FG porous shells are estimated using the rule of mixture, which incorporates an additional term for porosity in the through-thickness direction. The improved first-order shear deformation theory (FSDT) is used to accurately describe the shear stress distributing evenly throughout the thickness and is zero on the top and bottom surfaces of the doubly curved shell. Using Hamilton's principle, the governing equation of FG porous shells is established. The obtained numerical results of a ENS-MITC3 are compared with other existing methods in the literature to show the effectiveness of the present method. Then, the effect of geometric parameters, porosity coefficients and power law indexes on the displacements and natural frequencies of FG porous curved shells are examined. [ABSTRACT FROM AUTHOR]

• A semi-analytical solution to incipient sliding contact on viscoelastic layered solids is proposed. • The spring-like interface between the coating and substrate is considered. • A two-step procedure is performed to verify the validity of the solution. • The influences of variation in parameters on the contact behaviors are analyzed. This paper presents a semi-analytical solution to the incipient sliding contact between a rigid sphere and a viscoelastic layer-elastic substrate with spring-like interface. In this solution, Papkovich–Neuber potentials in frequency domain are applied to calculate the influence coefficients (ICs) based on the surface and interface conditions; the elastic constant in the elastic solution is replaced by the creep function to cover the time-dependent characteristics of the viscoelastic layer; discrete convolution-fast Fourier transform (DC-FFT) is used to obtain the displacements and stresses caused by the external load; conjugate gradient method (CGM) is employed to compute the pressure on the top surface of the viscoelastic layer. The validity of the solution is verified by a previous method and the finite element method (FEM), where the relaxation and creep functions of the viscoelastic layer are expressed as Prony series. Influences of variations in parameters on the surface pressure, normal displacement and von Mises stress are analyzed by a parametric study of the time, relaxation time, relaxation modulus, stiffness coefficients, coating thickness and friction coefficient. The results indicate that this solution can predict the contact behaviors of viscoelastic layered half-space and may serve as a numerical experiment in research of coating materials. [ABSTRACT FROM AUTHOR]

Magnesium alloy is one of the lightest metal structural materials. The weight is further reduced through the hollow structure. However, the hollow structure is easily damaged during processing. In order to maintain the hollow structure and to transfer the stresses during the high temperature deformation, the sand mandrel is proposed. In this paper, the hollow AZ31 magnesium alloy three-channel joint is studied by hot extrusion forming. Sand as one of solid granule medium is used to fill the hollow magnesium alloy. The extrusion temperatures are 230 °C and 300 °C, respectively. The process parameters (die angle, temperature, bottom thickness, sidewall thickness, edge-to-middle ratio in bottom, bottom shape) of the hollow magnesium alloy are analyzed based on the results of experiments and the finite element method. The results are shown that the formability of the hollow magnesium alloy will be much better when the ratio of sidewall thickness to the bottom thickness is 1:1.5. Also when edge-to-middle ratio in bottom is about 1:1.5, a better forming product can be received. The best bottom shape in these experiments will be convex based on the forming results. The grain will be refined obviously after the extrusion. Also the microstructures will be shown as streamlines. And these lines will be well agreement with the mold in the corner. [ABSTRACT FROM AUTHOR]

In this paper the authors discuss optimal control problems of a new ecological model governed by nonlinear reaction–diffusion equations. There are four major ingredients. The first is the proof of the well posedness of the solution to the state equations. The second is to prove the existence of the optimal control by using functional analysis techniques. The third ingredient is the establishment of first order necessary optimality conditions satisfied by the optimal control. The fourth ingredient is an example of optimal control problem and its numerical results that confirm the theoretical results obtained in this paper. • The optimal control problem of a new ecological mode is studied. • By using fully discrete finite element methods, we offer a numerical example. • The model considered in this paper is of more general form. [ABSTRACT FROM AUTHOR]

This paper presents our researching results regarding numerical calculus by Finite Element Method (FEM) of the Functionally Graded Plates (FGP). Two approching ways were used: the concept of multilayered plate and the concept of equivalent plate. By using of the multilayer plate concept, the continuous variation of the material law is replaced by a step variation; the layers have homogeneous and isotropic properties, with values established according to the methodology presented in this paper. When the equivalent plate concept is used, the FGP is replaced by a completely homogeneous and isotropic plate, but with fictitious properties that lead to a behavior similar to the real plate. The significance of the study consists in the elaboration and presentation of the FGPs calculus models, which can be approached with the existing current means, available to any researcher. The aim of this study is to enrich the knowledge regarding the numerical calculus, with the finite element method, of the FGP, using the current general knowledge and software products. The objectives of our study were to develop models and methodologies for calculus by FEM, available immediately. The results of the numerical simulations were validated by comparison with the adopted analytical solution. The use of the Ansys program, with the general options, available in many professional program by FEM, is still a reliable element in the numerical results and the validation of the results of our study. The methodologies, observations and conclusions are valid for any of these material laws presented in this paper. [ABSTRACT FROM AUTHOR]

In this paper, the stability and convergence results of finite volume method for the time-dependent incompressible magnetohydrodynamics equations are developed based on triangulation. The linear polynomials are used to approximate the velocity, magnetic fields and pressure. In order to overcome the restriction of the discrete inf-sup condition, the local pressure projection method is employed. Firstly, two self-adjoint linear mappings are introduced to establish the equivalences of temporal terms and bilinear terms in finite element method and finite volume method. Secondly, the existence and uniqueness of numerical solutions are presented by using the Oseen iteration and mathematical induction method. Thirdly, H 2 -stability and optimal error estimates are provided by introducing the Galerkin projection of generalized bilinear terms in finite volume method, using the energy method and constructing the corresponding dual problem. The main theoretical findings of this paper are as follows: ‖ (u h (t) , H h (t)) ‖ 0 2 + ∫ 0 t (min ⁡ { ν , γ σ − 1 } ‖ (u h , H h) ‖ 1 2 + G (p h , p h)) d s ≤ C , min ⁡ { ν , γ σ − 1 } ‖ (u h (t) , H h (t)) ‖ 1 2 + G (p h (t) , p h (t)) + ∫ 0 t ‖ (u h t , H h t) ‖ 0 2 d s ≤ C , ‖ ∇ (u h , H h) ‖ 0 2 + ∫ 0 t min ⁡ { ν , γ σ − 1 } ‖ (A 1 h u h , A 2 h H h) ‖ 0 2 d s ≤ C , τ 1 2 (t) ‖ (u (t) − u h (t) , H (t) − H h (t)) ‖ 0 + h (‖ (u (t) − u h (t) , H (t) − H h (t)) ‖ 1 + τ 1 2 (t) ‖ p (t) − p h (t) ‖ 0) ≤ C h 2 , where τ (t) = min ⁡ { 1 , t } , the letters ν , σ are the physical parameters, C and γ are two positive constants independent of the mesh size h , (u , H , p) and (u h , H h , p h) are the solutions of problems (2.1) and (4.1). Finally, some numerical results are presented to verify the established theoretical findings and show the performances of the considered numerical method. [ABSTRACT FROM AUTHOR]

Linear transverse flux permanent magnet machines (LTFPMs) are categorized as high force density topologies, which are suitable candidates for direct drive and low-speed applications. This paper introduces a novel LTFPM topology, which also proposes advantages of the flux-switching machines. This proposed linear transverse flux switching PM machine (LTFSPM) has two long passive translators located at the armature's top and bottom sides. The topology offers a high value of force density, and also, it is a cost-effective topology due to its double-sided passive translator. Furthermore, the PMs are fully utilized in the magnetic circuit, the end winding length is negligible, and the iron cores can be laminated easily. In this paper, the operation principle of the topology is explained and its magnetic circuit is discussed. To reduce the computational time of optimization procedure, a double-layer method is adopted, which provides high robustness, low computational time, and high precision. Results of the finite element method indicate that the proposed machine can be considered a potential candidate for linear motion applications especially direct drive wave energy conversion systems, which require high force density values. [ABSTRACT FROM AUTHOR]

• This paper firstly presented the coupled modeling of a spinning assembled cylindrical shell-plate structure. • Considering the displacement continuity condition, governing equations are derived by employing the Lagrange's equation. • The presented theoretical model and vibration analysis are verified by the finite element method. • Special attention is paid to the effects of structural parameters on the traveling wave frequencies. • The findings can shed an important light on the assembled structure design to achieve better mechanical performance. Hub-blade rotor structures are widely applied in many spinning machines, such as aero-engine, gas-turbine and so on. In theory, the hub and blade can be modeled by elastic cylindrical shell and plate, respectively. This paper firstly presented an investigation on the coupled modeling and vibration behaviors of a spinning assembled cylindrical shell-plate structure. According to the Donnell shell theory and the Kirchhoff plate theory, the coupled governing equations of the assembled cylindrical shell-plate structure are derived by employing the Lagrange's equation and considering the displacement continuity condition. Then, the method of hypothesis modes is adopted to obtain the free vibration results of the assembled cylindrical shell-plate structure. Moreover, the modeling and vibration analysis in this paper are verified by the finite element method. Special attention is paid to the effects of structural parameters, including plate length-to-thickness ratio, plate width-to-thickness ratio, plate position, cylindrical shell length-to-thickness ratio and cylindrical shell radius-to-thickness ratio on the traveling wave frequencies of the assembled cylindrical shell-plate structure. [ABSTRACT FROM AUTHOR]

Considering the interaction between concrete and steel reinforcement in numerical simulations of reinforced concrete structures is crucial for accurately capturing the concrete cracking process. This is particularly interesting when studying structures fulfilling functions that go beyond their simple mechanical resistance, such as waterproofing functions. While three-dimensional (3D) volumetric finite element modeling offers detailed insights into structural behavior, its computational intensity becomes prohibitive for large-scale structures. In such contexts, adopting beam and plate elements formulations proves computationally more efficient, due to their reduced number of degrees of freedom. This paper presents a kinematic enhancement technique designed to integrate steel-concrete interface behavior into beam and plate finite element formulations. The approach combines classical beam or plate elements representing concrete behavior, conventional beam or truss elements modeling steel reinforcement, and the incorporation of bond stresses at the interface. The paper provides comprehensive explanations of this enhancement technique along with a curated selection of numerical validation and application examples. These examples are supplemented by a comparison with experimental data, illustrating the efficiency of the proposed enhancement approach. • This work deals with a novel way to describe the steel-concrete interface. • A kinematic enhancement technique is proposed using additional degrees of freedom. • The proposed methodology can be based on existing beam and plate elements. • Experimental/numerical comparisons are shown. • The numerical results match with the experimental evidence. [ABSTRACT FROM AUTHOR]

Bridge girders are subjected to repeated patch loading during incremental launching (i.e. travelling over supports). Plastic deformations are likely to occur in the girder already at the first patch loading. They influence the girder's structural response and bring about a decrease in the ultimate resistance at subsequent patch loadings. This problem is analysed in the present paper through the serviceability limit state (SLS) of incrementally launched bridge I-girders (ILBGs). The SLS of ILBGs is a current problem since only a few studies, with contrasting conclusions and certain limitations, have been recognised in the literature. Research is limited on plate girders without longitudinal stiffeners made of structural steel. Flat slide-type launching shoes are considered in this paper. The serviceability requirement (repeatable behaviour of ILBGs) and criterion (that effective membrane strains should remain in the elastic range) are adopted from the literature. So, the serviceability resistance is adopted as a load at the start of the effective membrane plastic strains in the girder. In order to propose a practical and simple SLS design procedure, the serviceability resistance is normalised against the ultimate resistance, so a serviceability correction factor (k sls) is defined. The paper presents a parametric numerical analysis of the factor (k sls). A finite element model previously developed and validated by the author is employed to simulate a nonlinear response of patch-loaded girders. The parametric study includes 599 girders. k sls is inversely proportional to the web thickness and directly proportional to the flange thickness and the yield strength of the steel material. The load length, web depth and flange width do not influence k sls. The influence of the spacing between transverse stiffeners on k sls is negligible. Finally, by regression analysis of the results of parametric study, an original and reliable serviceability correction factor is proposed as the main objective of the research. The range when the SLS of ILBGs should be checked is also defined. [Display omitted] • The serviceability correction factor (k sls) is the serviceability resistance normalised against the ultimate resistance. • A parametric numerical analysis of k sls is conducted. The numerical database contains 599 patch-loaded girders. • The load length, web depth and flange width do not influence k sls , while the influence of the spacing between transverse stiffeners is negligible. • k sls is inversely proportional to the web thickness and directly proportional to the flange thickness and steel grade. • A reliable, original and simple empirical expression for k sls is proposed. [ABSTRACT FROM AUTHOR]

The paper conducted 19 partially and 5 fully loaded tests on round-ended concrete-filled steel tubular (CFST) columns. These tests revealed that the ultimate strengths of round-ended CFST columns under partial load declined as the cross-sectional aspect ratio or partial compression area ratio increased. However, the use of a top plate effectively enhanced their ultimate strengths. In addition, a finite element model (FEM) was utilized to generate 487 large-size models to explore the confinement effect, stress distribution, and parametric effects. Since there are no specific design standards available for round-ended CFST columns, the paper has evaluated the applicability of design methods provided in Eurocode 4, AISC 360–16, and Chinese code GB50396 which are intended for circular, square, or elliptical CFST columns for round-ended CFST columns under partial load. However, these existing design techniques showed inaccurate and dispersed resistance predictions for round-ended CFST columns. Therefore, an effective simplified method for forecasting the resistance predictions of round-ended CFST columns under the partial load has been proposed based on the testing results and FEM analysis. • For the first time, partial compression tests of 19 round-ended CFST columns were conducted. • The top endplate can be used to effectively enhance its partial compression resistance. • As the cross-sectional aspect ratio increase, the load-carrying capacity falls. • Exiting design methods are not applicable to partially loaded round-ended CFST columns. • For the first time, a simplified model for their partial compression resistance was proposed. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tube (CFST) columns are widely used in structures where high bearing capacity and ductility are crucial. They offer several advantages over conventional steel or concrete columns, such as a high strength-weight ratio, better ductility, and increased resistance to buckling and compression. Also, seismic damage in CFST columns primarily occurs within the plastic hinge region at their base. Therefore, by improving the ductility specifically in this plastic hinge region, the seismic resilience of CFST columns can be significantly enhanced. In this paper, the use of steel-polypropylene hybrid fiber engineered cementitious composites (HECC) in the plastic hinge region of square CFST columns is proposed to improve their hysteretic performance. This paper presents an experimental study of the hysteretic behavior with three different local HECC-enhanced CFST (LHECFST) columns. Based on the test results, modeling was performed using ABAQUS, and the reliability of the FE model was verified. Following this, FE models with smaller HECC pouring height gradients were developed, and these CFST columns were parametrically analyzed. The results show that the seismic performance of CFST columns is improved by local enhancement with HECC. The pouring of HECC will reduce the slope of the peak load descending stage of the CFST column. In addition, the formulas for calculating the peak load of LHECFST columns with different axial compression ratios and HECC pouring heights were developed and the accuracy was verified by contrasting the data. • Hysteresis tests on concrete-filled steel tube (CFST) columns were performed. • The validation data were established by finite element analysis. • Engineered cementitious composites (ECC) reduce damage in plastic hinge region. • The deterioration of peak loads in CFST columns with ECC localized pouring is slow. • Methods are proposed for calculating the peak load of two-material CFST columns. [ABSTRACT FROM AUTHOR]

This paper studies the undrained face stability of dual circular tunnels with the use of three-dimensional lower bound finite element limit analysis (3D LB-FELA) method based on a node-stress-based mesh adaptive refinement strategy. The effectiveness and correctness of the proposed 3D adaptive LB-FELA are proven through extensive comparison. In this paper, the non-homogeneous feature of the shear strength increases linearly with depth for the undrained clay is considered, and the dimensionless coefficient N s is adopted to assess the face stability. Through extensive calculations, the influences of depth C / D , the distance between dual tunnels S / D , soil gravity parameter γD / c 0 , and the strength coefficient ρD / c 0 on the face stability coefficient N s are deeply discussed. The research results show that the proposed 3D adaptive LB-FELA method can effectively evaluate the undrained face stability, and the evolution characteristics of failure mechanisms of dual circular tunnels can be studied according to the proposed method. The research results can also provide data support for evaluation of the face stability and formulating the reinforcement scheme for the dual circular tunnels. [ABSTRACT FROM AUTHOR]

An accurate prediction of motion responses of a moored floating structure requires high-fidelity coupled analysis between the structure and its mooring system in waves, which involves both mooring line dynamics and fluid dynamics. In this paper, we develop a nonlinear finite element dynamic mooring analysis module that allows large axial stretching of mooring lines under the open source CFD framework OpenFOAM, and couple it with an Overset CFD solver to establish a fully coupled finite element mooring-CFD analysis model for floating structures. The coupled model is advantageous over existing models in that it is able to deal with large axial mooring stretching and complex mesh motions induced by significant structure responses under severe operating conditions. The developed dynamic mooring analysis method is firstly validated against publicly available data. In order to validate the coupled model, a series of experimental tests were carried out for a semi-submersible platform moored by eight catenary lines under different operating conditions, including free decay, regular and irregular wave tests. The dynamic responses of the floating structure and mooring tension are analyzed and compared with experimental data. Results show that numerically predicted structure responses and mooring tension are generally in good agreement with experimental measurements. Meanwhile, the strongly nonlinear large-amplitude resonant motions generated by the interaction of irregular waves with the moored floating structure are also investigated. Comparisons reveal that the coupled model can accurately predict the resonant spectral peaks of the structure responses, indicating that the it is capable of simulating large-amplitude motions of moored floating structures. The coupled model developed in this paper can be further applied to study the survivability of moored floating structures under harsh sea conditions. • A finite element mooring dynamics module was developed in OpenFOAM. • The developed mooring module was coupled with an Overset CFD solver in OpenFOAM. • The coupled model was validated against model tests of a moored platform. • The coupled model can accurately predict large-amplitude motion responses. [ABSTRACT FROM AUTHOR]

• Developed a theoretical model for the conformal analysis of circular islands and substrates. • Predicts conformal behavior on surfaces of any curvature and modulus. • Proposed a generic strategy for conformal electronics in various applications. This paper introduces a set of design criteria that aim to integrate flexible electronics onto three-dimensional surfaces in a mechanically adaptive manner. Previous studies have been limited to conformal integration on specific shapes (Such as spherical surfaces and corrugated surfaces) of rigid surfaces or soft substrates, there is a lack of a universal design strategy that takes into account the complexity of substrate shapes and varying hardness. To address this gap, the paper outlines a mechanical model that utilizes Hertzian contact theory to describe the interaction between the thin film and the substrate, and the conformal surface morphology and stress state were derived from minimizing the total energy of the island-substrate structure. The proposed formulations are verified through finite element methods and experiments, analyzing the effects of Young's modulus, in-plane size, and thickness of the "island" on its conformability. Therefore, this paper proposes a generic on-demand conformal design strategy that takes into account the complexity and hardness of the substrate. This study's findings will contribute to the development of conformal electronics that can be used in various fields, such as epidermal electronics, flexible robots, robot electronic skin, and aircraft smart skin. [Display omitted] [ABSTRACT FROM AUTHOR]

As the demand for low-frequency and ultra-low-frequency vibration isolation in aerospace inspection and ultra-precision manufacturing grows exponentially, traditional vibration isolation strategies have been unable to satisfy these escalating needs due to their drawbacks such as a loose appearance, substantial dead weight, and elevated mechanical friction. Metamaterials, as artificially constructed periodic materials, have provided a promising solution to these above issues. In this paper, a novel compact one-dimensional quasi-zero-stiffness metamaterial with a tunable bandgap is presented, composed of a single unit centered on a truncated conical shell with a unique quasi-zero-stiffness structure. The monolithic quasi-zero-stiffness configuration significantly reduces the weight and size compared to conventional vibration isolation structures, ensuring high reliability with a minimum number of units and a compact form factor. A combination of theoretical analysis, finite element method and experiment is employed to investigate the vibration isolation properties of metamaterials comprehensively. Notably, the metamaterials designed in this paper can achieve vibration isolation at a very low frequency. Through the strategic application of pre-displacement, the entire bandgap can be systematically shifted to lower frequency ranges, which results in a reduction of the starting frequency to 15.01 Hz, marking a remarkable decrease of 46.6%. The novel proposed metamaterial, as detailed in this paper, can provide a reference for researchers involved in this field. [Display omitted] • A generic method for the design of quasi-zero-stiffness truncated conical shells is established. • Quasi-zero stiffness can be achieved with only single unit. • A novel compact one-dimensional quasi-zero-stiffness metamaterial is obtained. • The band gap of the metamaterial can be shifted to 15 Hz by adjusting the initial displacement, a reduction of 46.6%. [ABSTRACT FROM AUTHOR]

Structural fractures in carbonate reservoirs contribute prominently to hydrocarbon migration and accumulation. In this paper, the accuracy of structural fracture prediction is improved by two aspects of numerical simulation of traditional tectonic stress field and fracture distribution prediction methods in carbonate reservoirs. (1) The grid generation of finite element models for geological models is prioritized. Next, uniaxial and triaxial compression tests, well logging data, and 3D seismic data volume inversion are used to create a 3D volume of heterogeneous rock mechanics data that accurately reflects the geological body. Then, using the data, attribute assignments are made in the finite element model to create the three-dimensional heterogeneous rock mechanics model. This enhancement significantly diminishes the error induced by attributing rock mechanics parameters to individuals. (2) The size and orientation of in-situ stress are measured using acoustic emission, paleomagnetic, and wave velocity anisotropy tests in combination with imaging logging data. By introducing an adaptive boundary condition method to precisely calculate the in-situ stress magnitude at the applied boundary, we simulate the paleo- and current tectonic stress fields within the study area. The fracture rates for tension and shearing are calculated using the Griffith and Coulomb-Mohr fracture criteria. Based on the statistical results of characteristic fracture parameters at the core and imaging logging scales in the study area, the proportion of tensile and shear fractures is determined, and then the comprehensive fracture coefficient of carbonate reservoirs is calculated. A model for quantitatively predicting the multiperiod linear density of fractures suitable for carbonate reservoirs is developed following a thorough analysis of the various effects of multiperiod tectonic stress on the formation and alteration of reservoir fractures. The utilization of this technique in quantitatively forecasting the linear density of multiperiod fractures in carbonate reservoirs in the Tahe Oilfield, Tarim Basin, exhibits favorable feasibility. This paper improves the traditional method of tectonic stress field simulation and innovatively proposes a new method of high-precision numerical simulation of tectonic stress field based on heterogeneous rock mechanics model and adaptive boundary condition optimization. A quantitative prediction model for multi-period fracture linear density in carbonate reservoirs was developed. [Display omitted] • Constructed a high-precision heterogeneous rock mechanics model. • Adaptive boundary conditions improve the accuracy of numerical simulation. • Reconstructed the tectonic stress field of the three periods. • Achieved superimposed prediction of three-period fracture line density. • A prediction model for multi-period fracture line density was constructed. [ABSTRACT FROM AUTHOR]

Minimizing system size and weight without sacrificing the desired imaging performance is a crucial and challenging goal in the design of off-axis optical systems. In this paper, we propose a design concept that combines freeform mirror and freeform detector to achieve more compact off-axis optical systems. Initially, by applying nodal aberration theory, the optimal focal surface shape for off-axis systems is demonstrated to be an off-axis paraboloid or even a freeform surface, rather than the commonly assumed spherical shape. Subsequently, we show the ability of the design concept to reduce off-axis system volume through a design example of a fast and wide-field off-axis three-mirror system. Results indicate that, under the same design parameters and imaging quality, the design with a freeform detector is 80% smaller than that with a flat detector in terms of volume. Finally, the bending capability of the freeform detector presented in this paper is ensured through finite element analysis, and its surface accuracy is achievable based on the current precision level of curved detector fabrication. The proposed design concept holds promise for application in planetary science, where the imaging performance of the instrument is highly required and the size and weight are strictly limited. • The optimal focal surface shape for off-axis system is a freeform surface according to nodal aberration theory. • Combining freeform mirror and freeform detector allows off-axis reflective optical systems to achieve greater compactness. • The freeform detector presented can be manufactured using current detector curving techniques. [ABSTRACT FROM AUTHOR]

Currently available permafrost protection techniques do not pay enough attention to the properties of asphalt pavement, and the problem of strong heat-absorbing asphalt pavement and permafrost constraining each other is a global challenge that needs to be urgently addressed. Phase change materials (PCMs) can regulate the operating temperature of pavement structures by storing and releasing large amounts of heat during phase changes. In this paper, composite shaped phase change material (CSPCM) was applied to the permafrost region of Qinghai-Tibetan Plateau, and a new method of phase-change pavement structures with gradient low-thermal conductivity was proposed to reduce the heat absorption of the pavement and realize the active protection of permafrost. The structures were designed based on finite element software, and the heat flux and temperature distribution within the structure were analyzed and verified with indoor and outdoor thermal regulation tests. Results showed that the preferred gradient low-thermal conductivity structure reduced the annual net heat absorption at the top of the pavement by 8.18 %, the heat absorption in summer by 7.65 %, and the heat release in winter by 6.75 % compared with the control group. The heat flux and the temperature distribution within the pavement structures were significantly altered by the phase-change asphalt pavement structures with gradient low-thermal conductivity, and the simulation results of the finite element model agreed well with the results of the indoor and outdoor thermal regulation tests. The temperature regulation factor (RT) was proposed as an evaluation index to quantitatively analyze the temperature regulation performance of CSPCM on the pavement structure, and the results showed that the flexible base layer had the greatest influence on the temperature regulation performance of the pavement structure. The phase-change asphalt pavement structures with gradient low-thermal conductivity proposed in this paper is a structure that has an efficient cooling effect on the interior of the pavement, and provides a new idea for improving the stability of permafrost subgrade and the integrated design of materials and structures in permafrost regions. • CSPCM and thermal induction can be combined to protect permafrost in permafrost regions. • Finite element model is established, and the regulation ability of phase-change pavement structure is studied. • Finite element numerical simulation analysis agreed with the experimental test. [ABSTRACT FROM AUTHOR]

This work presents an introduction to popular damage and fracture models along with the major breakthroughs and the current state of the art. The theoretical and computational aspects of each model are discussed. While the damage models incorporate the microstructural effects, the fracture models consider the damage mainly at the macro level. The damage models such as Continuum damage mechanics, lattice models, nonlocal damage models, and fracture models such as Extended Finite Element method, Phase field and Peridynamics are presented. Both the discrete and diffused crack approaches along with the numerical solution techniques are presented. A special emphasis on the recently developed Peridynamic models and the different formulations associated with Phase field models is made. • The paper is a compilation of widely used computational damage models. • It introduces readers, in general, how to model damage/fracture using various existing computational damage models. • Beginning from computational damage mechanics approach, the recent peridynamic and phase field approaches are discussed. • It provides the basic mathematical formulations associated with every model that is presented. • The paper highlights all the major developments and the benchmark papers associated with each model. • The state of the art and the drawbacks each model has to overcome has been mentioned. [ABSTRACT FROM AUTHOR]

Assembled joints are widely recognized and applied because they are green and perfectly fit the current development trend of the construction industry. This paper proposes a composite wall-steel beam joint with crossed U-plate connection. In order to study the influence of the seismic performance of the joint, 2 experimental specimens and 13 finite element models are designed. The thickness of the U-plate, the strength of the steel of the U-plate, and the overlap length with the steel beam are changed so that the low circumferential reciprocating loading test and numerical analysis of the finite element are carried out to determine the main indexes of the seismic performances, such as hysteresis curves, skeleton curves, ductility, energy dissipation capacity, and stiffness degradation. The results show that the wall-beam joints connected with U-plate have satisfactory seismic performance. With the improvement of U-plate thickness and steel strength, the ultimate bearing capacity and ultimate displacement of the joint increase significantly, and the increase of lap length with steel connecting beams improves the ductility performance of the joint. Moreover, M U / M B ≥ 1.41 at the node domain during design can get excellent bearing capacity; the corner at the bending of the U-plate is a weak part, and it is recommended to reduce or eliminate the residual stress in the area in practice. • An experimental investigation and numerical simulations of the combined wall-steel beam joint with cross U-plate connection is presented in this paper. • The combined wall-steel beam joint with cross U-plate connection had different thickness of U-plate, steel strength of plates and lap length with steel beam, including a total of 2 experimental specimens and 13 simulation specimens. • The deformed shapes of the combined wall-steel beam joint with cross U-plate connection and the effects of different parameters on seismic performance have been observed in the tests and discussed in this paper. • Finally, comparing the test and numerical simulation results, and expanding the analysis of the effect of different parameters on the seismic performance, the problems that should be paid attention to when designing are proposed, and the recommendations on the strength and stiffness of the combined wall-steel beam joint with cross U-plate connection are given. [ABSTRACT FROM AUTHOR]