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When landing on the lunar surface, the astronauts need to wear the spacesuit and fly the lunar module in a standing posture. At this time, the astronauts bear the impact from the vertical and horizontal directions at the same time. In order to ensure the safety of the astronauts in bearing the impact load and experiencing the second collision, it is necessary to determine the impact load threshold and vulnerable parts of impact collision that the human body can bear. In this paper, the explicit finite element analysis software LSDYNA is used to simulate and analyze the modified Hybird III dummy model, and the responses of various parts of the human body are obtained. After analysis, the following conclusions are drawn:①Under the combined impact load, the longitudinal load has a great impact on the injury of human lower limbs, and the transverse load has a little impact.②Under the boundary conditions in this paper, it is recommended that the peak value of longitudinal load borne by the human body should not exceed 7g and the peak value of transverse load should not exceed 3G.③Under the action of transverse loads in different directions, the human head, chest and waist are prone to secondary collision with spacesuit, and the neck is the most vulnerable to damage, so it is necessary to fully protect the neck. [ABSTRACT FROM AUTHOR]

The emerging concept of mechanical meta-materials has gained increasing attention in recent years, partly due to advances in additive manufacturing techniques (additive manufacturing, 3D printing) that have allowed the fabrication of materials with arbitrarily complex micro / nanostructures. The designed geometry of these structures gives rise to unprecedented or rare mechanical properties that can used to create advanced elements with new, unprecedented functions. This paper presents the method of prototyping a vibro-isolator made of a material that has the properties of storing and disposing of mechanical vibration energy and that can freely be shaped by modern manufacturing techniques. An example of a vibration isolator of the proprietary concept analyzed, using the concept of stepped and adding elements. The method is based on the use of two main tools. Mechanical properties verified by analyzing the frequency and mode of free vibrations of the prototype using the finite element method. The same CAD model of the vibro-isolator prototype produced by 3D printing. The paper presents one of the production techniques, which is 3D printing in SLS (Selective Laser Sintering) technology, and the SolidWorks and Comsol Multhiphysics software used in the CAD / CAE prototyping method. [ABSTRACT FROM AUTHOR]

This paper introduces a model of sound energy harvesting that operates at a low frequency of less than 200 Hz. This investigation focuses on the produced outcomes when the vibrations of sound energy are converted into electricity. Sound vibrations are received from outside sources and pass through a piezoelectric barrier (wall) equipped with 4*3 array of energy harvesting elements of lead zirconate titanate (PZT-5H) cantilever plates which are constructed to harvest noise in the form of sound from passing trains and vehicles on roads. This paper covers how sound vibrations change into electrical energy at two sound pressure levels (85 dB and 100 dB for environmental noise of road vehicles and railways, respectively). Furthermore, the effects of changing the pressure level on the generated voltage for the intended model have been studied as well as the effects of increasing the piezoelectric plate number on the voltage generated for the 85 dB pressure level. The simulation is conducted numerically using the Finite Element Method FEM (COMSOL). An analytical model of a literature paper is used and simulated using MATLAB to be compared with the FEM results and found to be completely converged. Afterward, to figure out the relationship between voltage and sound pressure level, an equation is derived analytically. According to simulation results, 15 V and 18.2 V are produced for an incoming acoustic pressure level of 85 dB and 100 dB, respectively. Two models are compared, an array of beams with similar dimensions and a single beam with a volume that equals the dimensions of all array beams; it is observed that the array of beams produced 33.9 % more voltage than a single beam with the same volume. The comparison of the proposed model results with experimental literature results is conducted and exhibited an excellent convergence. [ABSTRACT FROM AUTHOR]

Bronchoscopy has a crucial role in the current treatment of lung diseases, and it is typical of interventional medical instruments led by manual intervention. The scientific study of bronchoscopy is now of primary importance in eliminating problems associated with manual intervention by scientific means. However, for its intervention environment, the trachea is often treated statically, without considering the effect of tracheal deformation on bronchoscopic intervention during respiratory motion. Therefore its findings can deviate from practical application. Thus, studying kinetic problems in respiratory motion is of great importance. This paper developed a mathematical model of mechanical properties of respiratory motion to express respiratory force from the perspective of dynamics of respiratory motion. The dynamical model was solved using MATLAB. Then, a finite element model of respiratory motion was built using Mimics, and the results of respiratory force solution were used as the load of model for dynamics simulation in ABAQUS. Then, a human–computer interaction platform was designed in MATLAB APP Designer to realize parametric calculation and fitting of respiratory force, and a personalized human respiratory motion dynamics simulation was completed in conjunction with ABAQUS. Finally, experimental validation of the interactive platform was performed using pulmonary function test data from three patients. Validation analysis by respiration striving solution, kinetic simulation and experiment found that Dynamical model and simulation results can be better adapted to the individualized study of human respiratory motion dynamics. [ABSTRACT FROM AUTHOR]

A new proposal has been applied using Bridge Information Modeling associated to Terrestrial Laser Scanning TLS and photogrammetry to obtain the digital model of an existing bridge. For the laser scanning process. Thus, it was also possible to identify the pathologies and damages in the concrete of the bridge. Furthermore, it was shown how geo-information with remote sensing using the station Trimble SX 10 can be applied in area of bridge projects with less time and lower cost, in relationship to a conventional survey Asbuilt with manual survey in field. One of the innovations of this paper was to obtain the digital model of the bridge by integration of TLS and photogrammetry to obtain the 3D digital model. The new methodology consisted of acquisition of the bridge scenes through points previously implanted, making the polygonal contour of the entire bridge. Furthermore, the execution of the field survey from georeferenced points to capture the scenes during the sweep with TLS facilitated the refinement and, consequently, it was possible to obtain the digital model with the concrete damage. It was also possible to perform a complex nonlinear analysis with Finite Element with the digital model of the bridge. Therefore, it was applied a reverse analysis of the strength of the structure using the Concrete Damage Plasticity Model using ABAQUS software. Two numerical analyses were performed on the bridge; one considering only the static behavior of the bridge and another considering the dynamic behavior. In the static analysis, the behavior of the dapped-end beam of the bridge, was investigated. On the other hand, in the dynamic evaluation, the natural frequency and damping ratio for bridges with Dapped-end beams was obtained in ABAQUS through Rayleigh damping and compared with the technical literature, which presented satisfactory results. [ABSTRACT FROM AUTHOR]

Finite element (FE) analysis has emerged as the primary tool to investigate complex problems that are difficult to test clinically on living tissues, yielding valuable but not necessarily applicable information on orthodontic treatment modalities. Many studies are being published but the findings are difficult to interpret, lack in relevance, or cannot be critically appraised. In this paper, the FE modeling design and impact on the quality and outcome of research are discussed, with focus on how to narrow the gap between theory and clinical application. [ABSTRACT FROM AUTHOR]

[Display omitted] The mechanics of vascular tissue, particularly its fracture properties, are crucial in the onset and progression of vascular diseases. Vascular tissue properties are complex, and the identification of fracture mechanical properties relies on robust and efficient numerical tools. In this study, we propose a parameter identification pipeline to extract tissue properties from force-displacement and digital image correlation (DIC) data. The data has been acquired by symconCT testing porcine aorta wall specimens. Vascular tissue is modelled as a non-linear viscoelastic isotropic solid, and an isotropic cohesive zone model describes tissue fracture. The model closely replicated the experimental observations and identified the fracture energies of 1.57 ± 0.82 kJ m − 2 and 0.96 ± 0.34 kJ m − 2 for rupturing the porcine aortic media along the circumferential and axial directions, respectively. The identified strength was always below 350 kPa, a value significantly lower than identified through classical protocols, such as simple tension, and sheds new light on the resilience of the aorta. Further refinements to the model, such as considering rate effects in the fracture process zone and tissue anisotropy, could have improved the simulation results. This paper identified porcine aorta's biomechanical properties using data acquired through a previously developed experimental protocol, the symmetry-constraint compact tension test. An implicit finite element method model mimicked the test, and a two-step approach identified the material's elastic and fracture properties directly from force-displacement curves and digital image correlation-based strain measurements. Our findings show a lower strength of the abdominal aorta as compared to the literature, which may have significant implications for the clinical evaluation of the risk of aortic rupture. [ABSTRACT FROM AUTHOR]

• The non-uniform wrapping process is studied in theoretical analysis, numerical simulation and experiments. • A tape spring can be rolled around a hub, and localized folds are formed. • A theoretical model is presented to predict the shape of the tape spring during the non-uniform wrapping process. • The shape of a tape spring after non-uniform wrapped is a polygon or a continuous curve. • The shapes of four tape springs stay the same as that of single tape spring. A tape spring, which has a high ratio of retraction and deployment, is a type of basic deployable member that plays an important role in deployable structures. This paper is focused on the non-uniform wrapping process of a tape spring that the fixed end section preserves the initial shape. A theoretical method is presented to predict the non-uniform wrapping process of a metallic tape spring based on classical theories about the bending behavior of this type of tape spring. There are two possible shapes for a tape spring after the non-uniform wrapping process, namely a polygon or a continuous curve. The boundary lines of the two possible shapes are studied, and it is shown that the shape depends on the radius of the central cylindrical hub. A finite element model is built using the commercial software ABAQUS to verify the reliability of the theoretical model. Experimental measurement is also conducted to record the shape change process of a tape spring. The comparisons of the results of the three different methods show that they are in good agreement with each other, which means that the theoretical model can be used to predict the non-uniform wrapping behavior of the tape spring. Additionally, the behavior of four tape springs during the non-uniform wrapping process is studied, and the results show that the shapes of multiple tape springs in a coiled state correspond to that of a single tape spring. [ABSTRACT FROM AUTHOR]

Many stable and convergent numerical methods are not pressure robust for an incompressible flow problem, due to the relaxation of a discrete divergence constraint called poor mass conservation. As a result, the velocity error is polluted by the pressure error, particularly when the fluid viscosity is relatively small and pressure is comparably large. A grad-div stabilization is an efficient remedy in conforming finite element methods. In this paper, an analogue of the grad-div stabilization that the penalization of the jumps of the normal velocities over facets of the triangulation in discontinuous Galerkin (DG) methods is investigated for a coupled Stokes and Darcy problem, it can efficiently improve the accuracy of velocity and mass conservation. Firstly, we present the existence and uniqueness of a solution, unconditional stability and a priori estimates for the DG method. Then, by using the principle of superposition and orthogonal decomposition cleverly, we prove the limiting behavior that the DG method with an analogue of grad-div stabilization for a coupled Stokes and Darcy problem converge to the strongly conservative BDM DG method with a convergence rate of O (λ f − 1 + λ s − 1) , it allows for arbitrarily large stabilization parameters. Finally, some numerical tests are given to validate the optimal convergence rates and their effectiveness. [ABSTRACT FROM AUTHOR]

In this paper, a generalized parametric iterative method (GPIM) is proposed to solve the nonlinear discrete formulation of the magnetohydrodynamic (MHD) equations. We exploit the idea of decoupling to solve the strongly coupled MHD system, expecting to save storage space and to accelerate the convergence. The noticeable advantage of the proposed algorithm is that it is not necessary to solve the saddle point system for each iteration step and converge geometrically with the contract number. Numerical experiments are given to verify the validity and correctness of the theoretical results. [ABSTRACT FROM AUTHOR]

In this paper, we propose a marker and cell method (MAC) with a proper quadrature scheme over non-uniform cuboid grids by using a staggered finite volume element method (FVEM) for 3D Stokes equations. The stability of the proposed MAC scheme is proven under Petrov-Galerkin method. By establishing a connection between MAC and FVEM, we rigorously prove the superconvergence property and the optimal order L 2 error estimate. Finally, numerical results verify our theoretical findings. [ABSTRACT FROM AUTHOR]

In this paper we propose and analyze Banach spaces-based fully-mixed approaches yielding new finite element methods for numerically solving the coupled partial differential equations describing the pseudostress-assisted diffusion of a solute into an elastic material. Two mixed formulations employing the diffusive flux as an additional variable are introduced for the diffusion equation, and the concentration gradient is considered as an auxiliary unknown of the second one of them. The resulting coupled systems are rewritten as equivalent fixed point operator equations, so that the respective unique solvabilities are proved by applying the classical Banach theorem along with the Babuška-Brezzi theory. The nonlinear dependency on the elastic variables of the diffusion coefficient and its source term, as well as the nonlinear dependency on the concentration of the elastic source term, suggest, for appropriate continuous and discrete analyses, that the unknowns be sought in suitable Lebesgue spaces. The associated Galerkin schemes are addressed similarly, and the Brouwer theorem yields the existence of discrete solutions. A priori error estimates are derived for both approaches, and rates of convergence for specific finite element subspaces satisfying the required discrete inf-sup conditions, are established in 2D. Finally, several numerical examples illustrating the performance of the two methods and confirming the theoretical findings, are reported. [ABSTRACT FROM AUTHOR]

This paper considers a stabilized mixed finite element method (MFE) for a quasistatic Maxwell viscoelastic model based on the L 2 (Ω) × H 1 (Ω) variational framework. The spatial discretization uses arbitrary degree piecewise polynomials P l − P k (l ≥ 0 , k ≥ 1) to approximate stress and velocity. The temporal discretization in the fully discrete method adopts a backward Euler difference scheme. We give a unified analysis to show the stability of the semi-discrete and fully discrete solutions and derive the corresponding priori error estimates. Numerical examples are provided to support the theoretical analysis. [ABSTRACT FROM AUTHOR]

• A finite element method solves the nonlinear film force of SFD in real-time. • Development of the finite element model of the bevel gear system supported on SFD. • The damping characteristics of SFD are studied theoretically and experimentally. • SFD can effectively suppress the vibration of bevel gear systems at high speeds. A central drive bevel gear system of aero-engines extracts power from a high-pressure rotor. The high speed of the high-pressure rotor aggravates the gear system's vibration. This work adopts squeeze film dampers (SFD) as damping devices to suppress excessive vibration of the spiral bevel gear rotor system. This paper establishes the general Reynolds equation of SFD and calculates the nonlinear oil-film force of SFD in real-time based on the finite element method. Besides, the finite element method and Timoshenko beam element are employed to model the flexible gear shaft. Then, the dynamic model of the spiral bevel gear system supported by SFD s is established, including the nonlinear oil-film force of SFD and time-varying meshing stiffness of the gear system. The dynamic response of the spiral bevel gear system is analyzed theoretically and experimentally to study the vibration attenuation characteristics of SFD. The findings indicate that SFD can effectively suppress the vibration amplitude of the system at high speeds. The theoretical analysis and experimental amplitude are within an order of magnitude, and the changing trend is consistent. [ABSTRACT FROM AUTHOR]

In this paper, we propose new basis functions defined on curved sides or faces of curvilinear elements (polygons or polyhedrons with curved sides or faces) for the weak Galerkin finite element method. Those basis functions are constructed by collecting linearly independent traces of polynomials on the curved sides/faces. We then analyze the modified weak Galerkin method for the elliptic equation and the interface problem on curvilinear polytopal meshes with Lipschitz continuous edges or faces. The method is designed to deal with less smooth complex boundaries or interfaces. Optimal convergence rates for H 1 and L 2 errors are obtained, and arbitrary high orders can be achieved for sufficiently smooth solutions. The numerical algorithm is discussed and tests are provided to verify theoretical findings. • A high-order weak Galerkin method is proposed for second order PDEs with Lipschitz continuous curved boundaries/interfaces. • The definition of basis functions on curved sides/faces is presented. These functions are constructed by collecting linearly independent traces of polynomials. • The proposed method can attain arbitrarily high orders for sufficiently smooth solutions. The rate of convergence is independent of the geometry. • Implementation of the algorithm is discussed. Tests are presented to verify our theoretical findings. [ABSTRACT FROM AUTHOR]

A diagonal finite element-projection-proximal gradient (DFE-P-PG) algorithm and its accelerated forms for elliptic optimal control problem with L 1 -control cost are proposed in this paper. Firstly, the elliptic optimal control problem is discretized by the diagonal finite element method (DFEM). Then the discrete problem is optimized by projection-proximal gradient (P-PG) algorithm. The global convergence of DFE-P-PG algorithm is proven. In addition, two accelerated methods are used to enhance the convergence rate of DFE-P-PG algorithm. Numerical examples are performed to illustrate the efficiency and effectiveness of DFE-P-PG algorithm. • A diagonal finite element-projection-proximal gradient algorithm for elliptic optimal control problem is proposed. • We use two accelerated schemes to improve the convergence rate of finite element-projection-proximal gradient algorithm. • The convergence properties of algorithms are proven theoretically. [ABSTRACT FROM AUTHOR]

This paper presents an efficient parallel computing strategy to solve large-scale structural vibration problems. The proposed approach utilises a novel direct method that operates using simplex-shaped space-time finite elements and allows for the direct decoupling of variables during the assembly of global matrices. The method uses consistent stiffness, inertia and damping matrices and deals with non-symmetric matrices. One significant advantage of this approach is that the computational cost remains unaffected by the bandwidth of the matrix in the traditional sense because only non-zero coefficients are retained. The speed of computations demonstrates a noticeable increase as the number of nodes and the problem's dimensionality grow. To demonstrate the effectiveness of the parallel space-time approach, a comparison with a sequentially executed code was conducted. The results indicate that the proposed method enables calculations at least 20 times faster than those achieved using the classical finite element method. Furthermore, the parallelisation algorithm was successfully implemented to solve a dynamics problem involving a large-scale, three-dimensional railway structure subjected to a moving load. Remarkably, the problem was solved in a reasonable amount of time using a relatively low-cost personal computer. • Strategy allows efficient parallel computing for large scale structural problems. • Direct method uses simplex-shaped space-time finite elements. • Variables are decoupled while assembling global matrices. • Computational cost is independent of the bandwidth. • Simulations of travelling load problems exhibit twenty times faster computations. [ABSTRACT FROM AUTHOR]

In this paper we present an immersed weak Galerkin method for solving second-order elliptic interface problems on polygonal meshes, where the meshes do not need to be aligned with the interface. The discrete space consists of constants on each edge and broken linear polynomials satisfying the interface conditions in each element. For triangular meshes, such broken linear polynomials coincide with the basis functions in immersed finite element methods [33]. We establish some approximation properties of the broken linear polynomials and the discrete weak gradient of a certain projection of the solution on polygonal meshes. We then prove an optimal error estimate of our scheme in the discrete H 1 -seminorm under some assumptions on the exact solution. Numerical experiments are provided to confirm our theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, we present an immersed finite element (IFE) method for solving the elastodynamics interface problems on interface-unfitted meshes. For spatial discretization, we use vector-valued P 1 and Q 1 IFE spaces. We establish some important properties of these IFE spaces, such as inverse inequalities, which will be crucial in the error analysis. For temporal discretization, both the semi-discrete and the fully discrete schemes are derived. The proposed schemes are proved to be unconditionally stable and enjoy optimal rates of convergence in the energy, L 2 and semi- H 1 norms. Numerical examples are designed to verify our theoretical analysis and to demonstrate the stability and robustness of our schemes. [ABSTRACT FROM AUTHOR]

Weak Galerkin finite element methods (WG-FEMs) for H (curl ; Ω) and H (curl , div ; Ω) -elliptic problems are investigated in this paper. The WG method as applied to curl-curl and grad-div problems uses two operators: discrete weak curl and discrete weak divergence, with appropriately defined stabilizations that enforce a weak continuity of the approximating functions. This WG method is highly flexible by allowing the use of discontinuous approximating functions on the arbitrary shape of polyhedra and, at the same time, is parameter-free. The optimal order of convergence is established for the WG approximations in discrete H 1 norm and L 2 norm. In fact, theoretical convergence analysis holds under low regularity requirements of the analytical solution. Results of numerical experiments that corroborate the theoretical results are also presented. [ABSTRACT FROM AUTHOR]

In this paper, we propose a two-level additive Schwarz preconditioner for the Nitsche extended finite element discretization of elliptic interface problems. The intergrid transfer operators between the coarse mesh and the fine mesh spaces are constructed and a stable space decomposition is given. It is proved that the condition number of the preconditioned system is bounded by C (1 + H δ + H h) , where H and h respectively stand for the coarse and fine mesh sizes, and δ measures the size of the overlaps between subdomains. The constant C does not depend on the contrast of the coefficients, how the interface intersects with the meshes. Numerical experiments are carried out to validate theoretical results. [ABSTRACT FROM AUTHOR]

In this paper, we present the virtual element approximation for the modified transmission eigenvalue problem. The eigenvalue problem arises in inverse scattering theory for artificial inhomogeneous media characterized as a metamaterial. By the shifting argument and spectral approximation theory of compact operators, we prove the correct spectral approximation of the virtual element scheme, and derive the optimal order error estimates for the eigenfunctions and the double order for the eigenvalues. Finally, we implement numerical experiments to illustrate behaviors of the standard and serendipity virtual element schemes, and the finite element scheme. [ABSTRACT FROM AUTHOR]

The aim of this paper is to analyze from a mathematical and a numerical point of view a formulation of a transient eddy current problem in terms of a time-primitive of the electric field in a bounded domain with ferromagnetic conductors. To this aim, we introduce a Lagrange multiplier to impose the free-divergence condition in the isolated domain. Thus, we obtain a nonlinear degenerate parabolic problem in mixed form and prove its well-posedness. Then, we propose a fully-discrete scheme by using an implicit Euler scheme for time-discretization and a finite element method based on edge and nodal elements for the spatial discretization. We prove quasi-optimal error estimates for the approximation and include some numerical examples to confirm the obtained theoretical results. [ABSTRACT FROM AUTHOR]

Partial differential equations involving divergence or curl operators often introduce nonempty null-space components in their solutions, causing conventional numerical methods to produce inaccurate results. In this paper, we present a new algorithm that addresses this challenge by explicitly accounting for the null-space component. The dual system least squares method is used to identify this component and remove it from the approximation using negative-norm minimization. Our approach retains the use of H 1 -conforming basis functions, ensuring that the resulting approximation is orthogonal to the null space of the operator. The effectiveness of our algorithm is demonstrated through numerical experiments with various partial differential equations, showing improved accuracy compared to conventional methods. [ABSTRACT FROM AUTHOR]

In this paper, we describe weak Galerkin finite element methods for solving hyperbolic problems on polygonal meshes. We propose both semidiscrete and fully discrete schemes to numerically solve the second-order linear wave equation. For the time discretization, we have used implicit second order Newmark scheme. For sufficiently smooth solutions, optimal order error estimate in the L 2 norm is shown to hold as O (h k + 1 + τ 2) , where h is the mesh size and τ the time step. An extensive set of numerical experiments are conducted to demonstrate the robustness, reliability, flexibility, and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

Tether-nets are one of the most promising approaches for active removal of space debris. This paper investigated the collision dynamics of flexible nets with different configurations, the focus is on the selection of an optimal configuration with respect to collision dynamics. Firstly, the design method of net configuration is proposed based on undirected graph theory, and five flexible nets with different configurations are designed, including quadrilateral, pentagon, octagon, dodecagon and circle. Secondly, the collision dynamics model is presented and its effectiveness is verified via numerical simulations and ground experiments. Finally, collision dynamics of the five flexible nets are simulated based on the verified model and the differences of these nets are compared and analyzed. Comparison results show that the flexible net with octagon configuration has better collision dynamics than others according to the maximum deformation, stress, and energy dissipation during the collision process, which provided an optimal configuration of flexible nets for space debris removal. • A design method of net configuration based on undirected graph is proposed. • The collision dynamics model of flexible nets is proposed and verified. • The octagonal net has the best dynamic characteristics. [ABSTRACT FROM AUTHOR]

This paper proposes a robust finite element Kalman filter for the state estimation of flexible space tether systems, which are critical for space exploration and satellite missions. Due to the limited access to placing sensors along the flexible tether to measure them directly, the measurement of the state of these systems is challenging. To address this, a fully expandable, scalable, and robust approach is developed that fuses position/velocity sensors at tether ends, distributed fiber optic strain measurement along the tether, and a position/velocity estimation by a finite element-based Kalman filter to estimate the state of the tether system. The proposed estimator is mathematically proven to be observable, stable, and robust. The effectiveness of the estimator is demonstrated through numerical simulations of a space tether system in orbit, and the method can be extended to any flexible body system. The results of the simulations show that the proposed approach can accurately estimate the state of the tether system, even in the presence of disturbances and noise. • Expandable, scalable FE-Kalman state estimator for flexible space tether systems. • Data fusion with tether end position/velocity, distributed fiber optic strain measure, and estimated internal position/velocity. • Mathematically proven observability, stability, and robustness to noise of the estimator. [ABSTRACT FROM AUTHOR]

Due to the uncertainty of structure and material parameters, reliability analysis of hydrogen storage composite pressure vessel (CPV) is an important issue. In this paper, reliability analysis of hydrogen storage CPV is carried out based on kriging surrogate model with two types of random-interval uncertainties. First, progressive failure behavior is analyzed based on finite element model (FEM) of CPV. Second, the kriging model is built to surrogate the burst pressure. Then, global sensitivity analysis is conducted using Sobol method. Finally, uncertainty analysis and reliability analysis of CPV are carried out with two types of random-interval uncertainties. The results show that longitudinal tensile strength, thicknesses of the hoop layers and the helical layers are important factors of the CPV burst. Besides, the reliability of CPV is low (0.048) with random-interval uncertainties, which should be improved to increase the safety of CPV. The proposed method provides a general solution to the reliability analysis of CPV with two types of random-interval uncertainties, which would co-exist in the hydrogen storage CPV. [Display omitted] • The kriging model of hydrogen storage vessel burst is established and verified. • The global sensitivity analysis of burst is carried out by Sobol method. • Longitudinal tensile strength and layer thickness are important influencing factors. • Reliability analysis is carried out with random-interval uncertainties. • Reliability is smaller with hybrid uncertainties than with only random uncertainty. [ABSTRACT FROM AUTHOR]

In this paper, we present a convergence analysis of a weak Galerkin finite element method (WG-FEM) using polygonal meshes for the semilinear singularly perturbed time-dependent convection-diffusion-reaction equations. Piecewise polynomials of degree k ≥ 1 are used in the interior of each element, and polynomials of degree k ≥ 0 are employed on the edge of each element in this finite element technique. The convergence analysis is explored in two phases: first in space and later in time. The proposed method employs a Crank-Nicolson scheme for temporal discretization and a WG-FEM for spatial discretization. The key finding shows that the error bound of the weak Galerkin solution is O (τ 2 + h k) in the energy-like norm and O (τ 2 + h k + 1) in the L 2 norm. Several numerical experiments are carried out to validate the theoretical results. [ABSTRACT FROM AUTHOR]

In this paper we introduce and analyze a Banach spaces-based approach yielding a fully-mixed finite element method for numerically solving the stationary chemotaxis-Navier-Stokes problem. This is a nonlinear coupled model representing the biological process given by the cell movement, driven by either an internal or an external chemical signal, within an incompressible fluid. In addition to the velocity and pressure of the fluid, the velocity gradient and the Bernouilli-type stress tensor are introduced as further unknowns, which allows to eliminate the pressure from the equations and compute it afterwards via a postprocessing formula. In turn, besides the cell density and the chemical signal concentration, the pseudostress associated with the former and the gradient of the latter are introduced as auxiliary unknowns as well. The resulting continuous formulation, posed in suitable Banach spaces, consists of a coupled system of three saddle point-type problems, each one of them perturbed with trilinear forms that depend on data and the unknowns of the other two. The well-posedness of it is analyzed by means of a fixed-point strategy, so that the classical Banach theorem, along with the Babuška-Brezzi theory in Banach spaces, allow to conclude, under a smallness assumption on the data, the existence of a unique solution. Adopting an analogue approach for the associated Galerkin scheme, and under suitable hypotheses on arbitrary finite element subspaces employed, we apply the Brouwer and Banach theorems to show existence and then uniqueness of the discrete solution. General a priori error estimates, including those for the postprocessed pressure, are also derived. Next, a specific set of finite element subspaces satisfying the required stability conditions, and yielding approximate local conservation of momentum, is introduced, which, given an integer k ≥ 0 , is defined in terms of Raviart-Thomas spaces of order k and piecewise polynomials of degree ≤ k only. The respective rates of convergence of the resulting Galerkin method are then provided. Finally, several numerical experiments confirming the latter and illustrating the good performance of the method, are reported. [ABSTRACT FROM AUTHOR]

It is common practice in industry to deliver a Craig–Bampton reduced version of the spacecraft's finite element model to the launch authorities to perform the dynamic coupled load analyses. During the dynamic coupled load analyses, the finite element model of the spacecraft is coupled with the finite element model of the launcher to predict the responses caused by the vibration environment produced during the launch phases (e.g., lift-off, engine start-up, etc.). Before being Craig–Bampton-reduced, the finite element model needs to be correlated and validated against physical test results to guarantee its capability to reproduce the actual behaviour of the physical hardware, which is essential to perform a meaningful dynamic coupled load analyses. Given the complexity and size of the finite element model, the entire process can be very demanding. In this paper, an alternative to the mathematical models usually used in the dynamic coupled load analyses is investigated. The main idea is to synthesize a Craig–Bampton equivalent model directly from the response data of a vibration test experiment. The system identification problem is solved using a particle swarm optimization algorithm, tailored specifically for this type of application, the hybrid PSO and Local Search (hPSO-LS). A mutation operator from genetic algorithm is used to improve the solution and the local search method to refine the final result. The proposed method is numerically tested on a 5-degrees of freedom lumped mass system, with full stiffness and damping matrices. A sensitivity analysis of the search space size is also carried out to investigate its influence on the final results. The hPSO-LS is tested in both noise-free and noisy scenarios. • Hybrid variant of PSO with refined research is proposed to solve system identification problem. • Reconstruction of full stiffness and damping matrices of a lumped mass system from accelerations only. • Sensitivity analysis on the size of the search space is carried out. [ABSTRACT FROM AUTHOR]

• A method for complex band structure computation of phononic crystals is proposed. • Local optimization semi-Cartesian grid is proposed to improve the grid quality near the interface. • Floquet transform is applied to transform the elastic wave equation into quadratic eigenvalue equation. • Complex band structures of phononic crystals with sharp-edged scatterer shapes are computed and analyzed. In this paper, we propose a finite element method based on the Floquet transform and local optimization semi-Cartesian grid to compute the complex band structure of phononic crystals. Floquet transform is applied to transform the elastic wave equation into a quadratic eigenvalue equation. Value-periodic test function independent of the interface is defined to derive the weak formulation. The local optimization semi-Cartesian grid is proposed to improve the quality of triangular elements near the interface. Our results are in good agreement with ones obtained by other mature methods, and the purely propagative mode coincides with the traditional band diagram. In addition to simple scatterer shapes such as circle or square, the proposed method is able to calculate the complex band structures of phononic crystals with complicated scatterer shapes. Numerical experiments demonstrated the effectiveness of this method in the computation of anisotropic inhomogeneous medium. The complex band structures under different lattice types, scatterer shapes, material properties, rotation angle and modes are obtained, and their effects on the width and number of band gaps are analyzed. [ABSTRACT FROM AUTHOR]

• Derive new closed-form solution for multi contact responses from a six-DOF vehicle model. • Identify track modulus from the first "plus" frequency of the dual-beam with a simple formula. • Detect rail damage from the instantaneous amplitude squared generated from the driving component of the contact response. • Contact-point spectrum performs better since it is free of the vehicle frequencies. • Parametric study for factors affecting the technique. The vibration data recorded for the test vehicle cannot be directly used to detect the rail and bridge frequencies due to the overshadowing effect of vehicle's frequencies. To overcome this problem, the vehicle-rail contact response may be used instead. However, current techniques on this are available only for simple test vehicles with single or two degrees of freedom (DOFs). Normally, a train car contains a car body and two bogies (each of two wheelsets), and should be modeled by a multi- DOF system. The objective of this paper is first to solve the four wheelset-rail contact responses from the six measured vehicle responses. Then the contact responses are employed to retrieve the track modulus , while detecting the rail damages, for their salient feature of being free of the vehicle's frequencies. The railway track is modeled by a dual-beam system, with the upper (rail) and lower (bridge) beams connected by a spring-dashpot layer. The track modulus is retrieved through identification of the first "plus" frequency of the dual-beam, and the rail damage is detected from the instantaneous amplitude squared (IAS) generated from the driving component of the contact response. Through comparison with results by the finite element method (FEM), it is confirmed that: (1) the proposed procedure for computing the multi contact responses from the multi-DOF vehicle responses is reliable; (2) track irregularity presents a limited influence even for high disturbance; (3) to trade-off between efficiency and accuracy, a medium vehicle speed is suggested for the field measurement; (4) for the dual-beam with sufficient length, the use of simply supported condition is acceptable for rails; and (5) the effect of track damping is small and can be ignored. [ABSTRACT FROM AUTHOR]

This paper studies a class of nonlinear elliptic PDEs, arising for stationary reaction-diffusion models. The non-smooth nonlinearity gives rise to dead cores, that is, subdomains where the solution of the PDE vanishes. The paper gives a solid foundation for the numerical solution of the problem, including proper extensions of known maximum–minimum principles, Céa lemma, and convergence estimation of the FEM for locally Hölder continuous operators. Based on these, we finally detect dead cores numerically in various typical situations. [ABSTRACT FROM AUTHOR]

This paper investigates comprehensively the resonance and cancellation conditions for the free vibration of elastically-supported (ES) beams subjected to successive moving loads. Focus is placed on application of the cancellation condition to minimize bridge vibrations, considering particularly the effect of elastic supports. In terms of the modal amplitude R of free vibration of the ES beam, both resonance and cancellation conditions are identified. This paper is featured by the fact that the cancellations are classified into two types as the external (load-related) and internal (structure-related) ones. Through the (internal) cancellation function, the criterion for selecting the optimal support stiffness ratio (SSR) is derived for the first time for suppressing the resonance of short to medium-span railway bridges. It depends solely on the bridge/vehicle length ratio L / d , and can be utilized to achieve near-perfect cancellation. The theoretical findings are validated by the finite element method (FEM) for various parameters. The results reveal that for beams with lengths in the ranges of (0.5 d , d ] and (1.5 d , 2 d ], an SSR closer to the lower bound of the acceptable range should be selected to achieve the best effect. And for beams with lengths in the range of (d , 1.5 d ], the SSR should be selected as close to the optimal value as possible. Besides, it was found that damping in the beam and supports contributes to further suppression of vibration for bridges designed with optimal SSR. • Derive new resonance and cancellation conditions for elastically supported beams. • Classify cancellations as external (load-related) and internal (structure-related) ones. • Optimal support stiffness ratio (SSR) for near-perfect cancellation of resonance. • Optimal SSR relies solely on the bridge/vehicle length ratio and is easy to use. • Verify the effectiveness of SSR criterion for various factors. [ABSTRACT FROM AUTHOR]

Currently, progressive collapse studies are mostly conducted based on an event-independent assumption. With studies employing an event-dependent premise mainly concerning explosion or fire events, the aftermath of impact loading is seldom reported. Meanwhile, interactions between reinforced concrete (RC) members and superstructures under impact loading need further evaluation. In this paper, finite element models of RC structures subjected to impact loading and progressive collapse are established and validated utilizing LS-DYNA. A valuing methodology of erosion parameters for the continuous surface cap model (CSCM) considering element size is proposed in this process. The influence of impact column removal (ICR) on the progressive collapse performance of RC frame structures is studied at sub-assemblage and structure levels. The parametric study indicates that the ICR process can be described by an impact loading stage and a gravity load stage. It is also found that structures experiencing ICR are exposed to a higher risk of progressive collapse, with the downward force exerted by the impacted columns being a significant contributing factor. Dynamic analyses demonstrate that the acceleration of the column removal point (CRP) can be used to validate and quantify the downward force. The hybrid force-displacement boundary conditions of frame columns give rise to the development of downward force. Recommendations for resisting progressive collapse considering ICR are proposed based on the analytical results of the paper. • A new threat-dependent perspective to progressive collapse research is elucidated, focusing on impact column removal (ICR). • Interactions between impacted columns and superstructures are illuminated, emphasising the influence of downward force. • The boundary conditions of frame columns suggest a new research roadmap for impact response of structural members. • The study on the effects of ICR indicates higher progressive collapse risk due to downward forces and initial damage. • Recommendations of resisting progressive collapse considering ICR are proposed. [ABSTRACT FROM AUTHOR]

Engineered Cementitious Composites (ECC) utilize the bridging effect of high toughness fibers to improve the brittle failure of concrete materials, achieve the effective control of cracks in cementitious materials, and significantly improve the deformation capacity. In view of the multi-stage crack-blocking effect of different fibers incorporated in ECC materials, 91 ECC specimens of steel-polypropylene hybrid fiber by mixing steel fiber (SF) and polypropylene fiber (PPF) into cement-base are made in this paper. The specimens are tested in compression, tensile, bending and damping properties, respectively, which is of great significance to study the response of ECC structures under the earthquake action. The effects of the volume content of SF and PPF on the mechanical properties of ECC are studied in this paper. The results show that the cube specimen has better ductility than the prismatic specimen under monotonic compression, and there is no obvious brittle failure. With the increase of the volume content of SF to PPF, the compressive strength and elastic modulus of hybrid fiber ECC gradually increase, while the corresponding strain and axial compressive toughness gradually decrease; the tensile strength and tensile modulus increase, while the bending strength and damping ratio decrease. According to the test results, constitutive models of monotonic and repeated loading of hybrid fiber ECC suitable for finite element (FE) analysis are proposed. This investigation provides a theoretical basis and an experimental reference for further study of steel-polypropylene hybrid fiber ECC. • Steel fiber and polypropylene fiber are mixed as hybrid fiber of ECC. • The mechanical properties of ECC are investigate. • Volume content of steel-polypropylene hybrid fiber has influence on concrete material. • The hybrid fiber ECC cube has better ductility than that of prismatic. • Constitutive models of hybrid fiber ECC are suitable for finite element analysis. [ABSTRACT FROM AUTHOR]

• The influence of different design parameters on the uplift performance of L- & J-bolts and diffusion angle of anchorage concrete cone was studied. • Anchorage concrete crack initiation and propagation of L- & J-bolts under uplift load was studied. • Combined with the variation law of concrete cone diffusion angle, the spatial angle-variation elliptic concrete cone calculation model of L- & J-bolts was proposed. This paper studies the anchorage failure mechanism and bearing capacity characteristics of hooked (L- & J-) anchor bolts in plain concrete under uplift load. Static tests on L- & J- anchor bolts were carried out to study the influence of different parameters (such as bolt diameter, anchorage depth, and bolt hook length) on the failure mode of hooked anchor bolts. The test results show that the uplift bearing capacity of L- & J- anchor bolts is greatly improved compared with that of smooth bolts. Two typical failure modes, that is, concrete breakout and bolt failure. In specific, the concrete breakout occurred in the L- & J- anchor bolts with anchorage depth of 5 d , and the failure mode changed from concrete breakout to bolt failure as the anchorage depth increased. The finite element model was further established to investigate the stress development of the anchorage bolt and concrete and thus reveal the anchorage failure mechanism. Furthermore, a calculation method was proposed to accurately predict the uplift bearing capacity for the hooked anchor bolts with concrete breakout, where the change rule of the breakout cone diffusion angle θ i and concrete crack propagation were mainly discussed. It reveals that the anchorage depth greatly influenced the diffusion angle when the concrete breakout occurs, and the diffusion angle on both sides of L- & J- anchor bolts presented an asymmetric distribution. Compared with the code ACI318, the proposed formula considered the effect of breakout cone diffusion angle on bearing capacity, and the calculation results coincided well with the experimental and numerical results, implying that the proposed formula in this paper can be considered reliable to guide the practical engineering design. [ABSTRACT FROM AUTHOR]

As a new type of connection methodology, hybrid-bonded/bolted (HBB) connections exhibit potential advantages over mechanical or pure adhesive connections in construction, aerospace, shipbuilding, machinery, and other fields. The key to designing HBB joints is reasonable load sharing between bolts and adhesive layers. An accurate analytical model could effectively and quickly help engineers perform design iterations and arrive at reasonable load-sharing predictions. The existing models usually consider HBB joints as a simple superposition of adhesive and bolted joints. This paper found through experiments that when the HBB joint is subjected to tension, the bolt hole undergoes a certain deformation, resulting in a different bolt-hole contact state than pure bolt joints. Therefore, in the HBB joint, the load transferred by the bolt calculated using the existing model is usually higher than the actual situation. In response to this situation, this paper proposes a new calculation approach for bolt shear stiffness for this particular deformation and develops an analytical model for HBB joints. By comparing with the finite element method (FEM) results, it has been proven that this model can accurately calculate the load-displacement curves of HBB joints of different materials and sizes, as well as the load distribution between bolts and adhesive layers. This provides favorable references for the design of HBB joints. • HBB joints exhibit significant hole deformation under tension, which leads to the special component's contact mode; • The special contact mode leads to the lower load-sharing of bolts in HBB joints; • The new model was derived to account for the effect of the hole deformation; [ABSTRACT FROM AUTHOR]

This paper presents an analytical formula for the second-order normal stresses in flanges of the imperfect I beam-columns with sinusoidal web corrugation. To deduce the analytical expression, the beam is separated into three parts. The flanges are modelled as thin-walled beam-columns and the corrugated web is modelled as a thin equivalent orthotropic plate with uniform thickness. The indispensable elastic critical loads are derived from the total potential strain energy of the imperfect beam-column using an energy method. To assess the accuracy of the proposed analytical formula, full shell finite element models were created in Abaqus software. The result of the benchmark example showed that the derived expression is accurate and applicable for geometrically nonlinear analysis of beam-columns with sinusoidal web corrugation. Based on the proposed analytical expression, the Ayrton-Perry type solutions for corrugated web columns and beams are also presented in this paper. • The proposed analytical expression has a strong mechanical background. • It is applicable for GNIA of imperfect beam-columns with sinusoidal web corrugation. • The Ayrton-Perry type solutions for columns and beams are derived. • The accuracy of the EC3-based imperfection factors is examined. [ABSTRACT FROM AUTHOR]