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Abstract This work deals with the structural behaviour, ultimate strength and design of fixed-ended cold-formed steel (CFS) lipped channel columns experiencing various levels of local-distortional-global buckling mode interaction (more or less close critical local, distortional and global loads). First, a comparison between experimental results, obtained from three tests carried out at The University of Hong Kong (UHK), and the corresponding A baqus shell numerical simulations are presented and discussed – the UHK test campaign is reported in Part I of this two-part paper. The comparison (i) involves equilibrium paths, deformed configurations, failure loads and collapse mechanisms, and (ii) provides enough evidence to ensure that the numerical model developed may be deemed validated. Then, this numerical model is employed to perform a parametric study, aimed at obtaining numerical failure load data concerning lipped channel columns experiencing different levels of local-distortional-global interaction – 368 fixed-ended columns, exhibiting different geometries (cross-section dimensions and lengths) and various yield stresses, thus covering a wide slenderness range. Finally, the present (Part II) paper also assesses the quality of the failure load estimates provided by various design approaches, based on the Direct Strength Method (DSM), for CFS columns affected by the triple coupling phenomenon under consideration. This assessment is based on the comparison with both (i) experimental failure loads, namely those reported in Part I and others collected from the literature, and (ii) numerical failure loads, obtained from A baqus shell finite element analyses (SFEA) and either reported in this work or gathered from previous publications by the authors. [ABSTRACT FROM AUTHOR]

A major difficulty in finite element analysis is the preparation of an effective mesh leading to a good response solution. In engineering analyses of complex components, oftentimes, much more time is spent to arrive at an adequate mesh than to obtain the solution of the established finite element model. The difficulty in meshing is due to the fact that finite elements need to abut each other and cannot overlap. This can lead to highly distorted elements, e.g. sliver elements, reducing the accuracy of solution. In practice, to establish an effective mesh, frequently, significant expertise in building meshes is needed, because great care must be taken in cleaning up the CAD geometry and preparing an effective mesh. The objective in this paper is to present a new finite element solution scheme including meshing in which the elements can overlap. The property that finite elements can overlap removes many of the meshing difficulties, leads to an effective meshing procedure and an overall easy-to-use solution scheme for an analyst or a designer. We first present the meshing scheme that we propose, which combines the use of traditional finite elements and overlapping finite elements. A particular feature is that the meshing procedure can be directly embedded in CAD driven solutions. We then present the theory used for the formulation of the overlapping finite elements and the coupling with traditional finite elements. We consider spherical and brick-shaped overlapping finite elements for which the theory is largely based on the formulation of the method of finite spheres. Finally, we illustrate the complete solution scheme in the analysis of some two-dimensional problems using the CAD geometry as the starting point. While the paper presents a new paradigm for analysis in CAD environments, with much potential, we realize that much further study and research is needed on some of the important ingredients of the method to render the complete procedure effective for general practical engineering analyses of static and dynamic problems. [ABSTRACT FROM AUTHOR]

Highlights • We developed a numerical method for magneto-fluid-structure interaction problems. • A stabilization scheme and a conservative method have been introduced. • The analytical solution to a submerged cylinder in a magnetic field was established. • Correction and extension have been made to FSI benchmark solution by Chen et al. [26]. • We provided validating cases for future magneto-fluid-structure interaction solvers. Abstract To study the magneto-fluid-structure interaction (MFSI) problems for rigid bodies and conducting fluids, a numerical method and an analytical approach have been carried out. The numerical scheme is based on a partitioned arbitrary Lagrangian-Eulerian framework, and is suitable for viscous, incompressible magneto-fluid-structure interaction simulation. A displacement prediction-pressure stabilization scheme has been established to enhance the stability and efficiency. Meanwhile, a consistent and conservative scheme for deforming configurations has been developed. This method can numerically ensure the divergence-free condition of the current density, and can conserve the momentum from the Lorentz forces after grids update. The analytical approach has considered a vibrating cylinder surrounded by confined fluids in a magnetic field. By assuming a small amplitude and a low magnetic Reynolds number, the analytical solution can describe the temporal and spatial distribution of the fluid fields, the electromagnetic fields, and the solid motion. These solutions are also suitable for general fluid-structure interaction (FSI) problems. Comparative results suggest good agreement between the two methods developed in this paper. Nonlinear effects of the magnetic fields were presented and discussed based on the numerical results. These cases are based on careful validations, and can hopefully be used for future verification and validation work. [ABSTRACT FROM AUTHOR]

As is well-known to all, the conventional finite element method (FEM) is constrained by the “numerical dispersion error” issue for solving acoustic problems at high frequencies. In this paper, the gradient smoothing technique (GST) which is based on the edges of the elements is combined with the conventional FEM to construct a novel edge-based smoothed FEM (ES-FEM) for two dimensional exterior structural–acoustic problems. The smoothed gradient field is obtained by performing the GST over the obtained smoothing domains (SDs). The present ES-FEM is able to provide a relatively appropriate stiffness of the real system owing to the “softening effects” from the GST. Therefore, the accuracy of the numerical solutions can be significantly improved. To effectively handle the exterior Helmholtz equation in unbounded domains, a predefined artificial boundary B is employed to obtain a bounded computational domain and the well-known Dirichlet-to-Neumann (DtN) map is used to prevent the possible reflections from the far-field. Several supporting numerical examples indicated that the ES-FEM with DtN map was very effective for exterior structural–acoustic problems and could produce more accurate numerical results than the conventional FEM. [ABSTRACT FROM AUTHOR]

The present paper is concerned with numerical simulation of two-dimensional (2-D) cracks and material interfaces by an effective computational approach. A local mesh refinement in terms of extended finite element method is thus described. The new approach combines a posteriori error estimation algorithm, a local non-conformal mesh connection strategy, and local enrichment. An error estimator based on recovery strain for adaptivity is used; allowing the mesh where it is needed is subsequently refined. Unlike preceding local refined methods, variable-node elements are integrated into the present formulation instead, which aims to treat mismatching problem induced by different scale-meshes in an effective way. The discontinuity and singularity of cracks or material interfaces are captured by local enrichments in terms of partition of unity. Due to existence of different types of elements in the model, a special technique is thus proposed for appropriately and accurately treating numerical integration. We address the developed methodology, assessing its numerical properties and performance through several numerical examples. In particular, discontinuity problems with material interfaces, multiple inclusions, single and multiple cracks are analyzed. The obtained results indicate a high accuracy, low cost and good performance of the proposed method in simulation of 2-D cracks and material interfaces. [ABSTRACT FROM AUTHOR]

In this paper an efficient numerical tool is proposed to investigate delamination type failure in multi-layered composite shells. In the current contribution the extended finite element method (XFEM), the mixed-mode cohesive zone model, the contact formulation, and the damage criterion are incorporated into a new algorithm to study the interfacial delamination initiation and growth with less computational effort. A flat-shell formulation is developed in the geometrically non-linear regime to study the response of shells in small strains and moderate rotations. In addition, the equivalent single layer theory (ESLT) is applied to simulate the multi-layered laminates. This formulation is enhanced through the XFEM topology to be able to model discontinuous domains and a mixed-mode bilinear cohesive formulation to track the delamination growth. In the current study, the simulation can be initiated in an intact laminate. Thus, unlike formulations in existing finite element models, incorporating cohesive zone model at all available interfaces is not necessary. The interlaminar stresses are calculated during post-processing and they are being used in the delamination onset criterion. As soon as the criterion is satisfied at a specific layer and location, the formulation of that corresponding element is locally changed to XFEM and the cohesive behaviour. Consequently, the possibility to track delamination growth is locally provided; and hence, the computational cost is reduced. [ABSTRACT FROM AUTHOR]

Local fatigue strength assessment based on threshold values obtained by linear-elastic notch stress calculation is commonly utilized due to its applicability to complex geometries with an acceptable effort. As the result of a finite element computation is affected by the element type and mesh refinement, this paper investigates the numerical influence on the notch stress based fatigue strength assessment of non-welded and welded components. Based on extensive finite element studies employing the software package Abaqus it is concluded that quadratic shape functions with a number of sixteen for non-welded parts and twelve elements over a semicircle for welded joints should be at least applied to minimize the numerical impact. [ABSTRACT FROM AUTHOR]

A comparative study of three composite implicit schemes including the Bathe scheme (Bathe and Baig, 2005), the TTBDF scheme (Chandra et al., 2015) and the Wen scheme (Wen et al., 2017) is conducted in this paper. The stability and accuracy characteristics of these schemes are studied and compared by analytical and numerical simulation analysis. In the solution of wave propagation problems, a demonstrative dispersion analysis is given and problems are solved to illustrate the capabilities of the schemes for the solution of wave propagation problems as well as the numerical dissipation characteristics of the schemes. The nonlinear dynamic behavior of the Wen scheme is studied by considering commonly used nonlinear dynamic problems where the nonlinear performance of the scheme is exclusively compared with the Bathe and TTBDF schemes. The priority ranks of three presented composite schemes for different types of dynamic problems are obtained by theoretical and numerical analysis. [ABSTRACT FROM AUTHOR]

• An extended bond-based peridynamic (PD) model is used to investigate interfacial and subinterfacial fracture behaviors in bimaterial structures. • The extended peridynamic model overcomes the limitations of Poisson's ratio and thus can simulate realistic material properties. • The PD/FEM coupling strategy can eliminate the influence of the "boundary effects" and improve computational efficiency. • Crack propagation characteristics predicted by PD are compared qualitatively and quantitatively with the experimental results. The interaction between crack propagation and interfaces is one of the critical problems in bimaterial systems. In this paper, interfacial and subinterfacial fracture behaviors are simulated to investigate this interaction. The modeling approach for bimaterial structures is first introduced, where the extended bond-based peridynamic model is adopted. Then a convergence study is carried out with a bimaterial plate containing two asymmetric inclusions under tensile load. The comparison with the finite element solution validates the proposed modeling approach. Subsequently, several interfacial and subinterfacial fracture cases are considered to pinpoint the influence of interfaces on crack propagation. The numerical results show that the proposed method can satisfactorily capture the interplay between interfaces and crack propagation. Furthermore, in the subinterfacial fracture case, an equilibrium state of mode-I crack growth is successfully obtained, implying that a specific loading condition can counteract the effect of the interface. [ABSTRACT FROM AUTHOR]

Abstract: The topic of this paper is the estimation of modal parameters from nonstationary ambient vibration data by applying the random decrement algorithm. If the ambient excitation can be modeled as a nonstationary white noise in the form of a product model, then the nonstationary cross randomdec signatures of structural response evaluated at any fixed time instant are shown theoretically to be proportional to the nonstationary cross-correlation functions, which is of the same form as the free-vibration decay or impulse response of the original system. The practical problem of insufficient data samples available for evaluating nonstationary randomdec signatures can be approximately resolved by first extracting the amplitude-modulating function from the response and then transforming the nonstationary responses into stationary ones. However, the error involved in the approximate free-decay response would generally lead to a distortion in the modal identification. In the present paper, we also further propose that, if the ambient excitation can be modeled as a zero-mean nonstationary process, without any additional treatment of transforming the original nonstationary responses, the nonstationary cross randomdec signatures of structural response are shown in the same mathematical form as that of free vibration of a structure, from which modal parameters of the original system can thus be identified. Numerical simulations, including one example of using the practical excitation data, confirm the validity of the proposed method for identification of modal parameters from nonstationary ambient response data only. [Copyright &y& Elsevier]

In this paper, a novel sub-step composite implicit time integration scheme is presented for solving the problems in structural dynamics. The proposed scheme possesses desirable stability and accuracy. With appropriate algorithmic parameter value, the scheme can attain controllable amplitude decay and period elongation. Effectiveness of the proposed scheme is tested in some example solutions by comparing with other well-known implicit schemes. Theoretical analysis and numerical simulations demonstrate that the proposed scheme possesses high computation efficiency as well as desirable numerical dissipation characteristics. [ABSTRACT FROM AUTHOR]

Concrete is an heterogeneous structural material whose constitutive behaviour is strictly depending on the mechanical properties of the aggregates and the cement paste. A large number of methods have been devoted to the prediction of the mechanical properties of this material by means of meso-scale analysis. The paper concerns a new meso-scale model of concrete, that considers the composite as a multi-phase material. The numerical description of the meso-scale structure is attained using a random method that allocates at each Gauss point of the finite element discretisation of the Representative Volume Element (RVE) a specific phase of the mixture: aggregate, cement paste, void. Each phase is characterised by a specific non linear constitutive model, whose parameters have been determined by means of experimental tests on the components. More experimental tests have been performed on concrete samples, and they have been numerically reproduced by means of the proposed procedure. Numerical simulations of cyclic uniaxial compression tests have shown the ability of the meso-model to correctly predict the peak strength, the tangent and secant elastic stiffness of the mixture for strains above the peak strain, even adopting a relatively coarse finite element discretisation of the RVE. [ABSTRACT FROM AUTHOR]

Abstract: This work deals with the numerical evaluation of the structural response of simply supported (transversally loaded at mid-span) and cantilever (subjected to tip point loads) beams built from a commercial pultruded I-section GFRP profile. In particular, the paper addresses the beam (i) geometrically linear behaviour in service conditions, (ii) local and lateral-torsional buckling behaviour, and (iii) lateral-torsional post-buckling behaviour, including the effect of the load point of application location. The numerical results are obtained by means of (i) novel Generalised Beam Theory (GBT) beam finite element formulations, able to capture the influence of the load point of application, and (ii) shell finite element analyses carried out in the code Abaqus. These numerical results are compared with (i) the experimental values reported and discussed in the companion paper (Part 1) and (ii) values provided by analytical formulae available in the literature. [Copyright &y& Elsevier]

Abstract: A critical parameter for evaluating the resistance of concrete against chloride diffusion is effective diffusivity. While it can be obtained experimentally, this paper concerns computer simulations to estimate diffusivity of mortars as influenced by paste, aggregate, and interfacial effects. However, when performing such simulations, the size of the mortar sample modeled must be large enough to reliably characterize these randomly distributed effects, while remaining small enough for computational efficiency. The purpose of this paper is to report the influence of sample size on computed results and to recommend the smallest specimen size needed to obtain reliable estimates of diffusivity. [Copyright &y& Elsevier]

The objective in this paper is to improve the performance of the 4-node MITC quadrilateral shell finite element, referred to as the MITC4 element (Dvorkin and Bathe, 1984). We propose a new MITC4 shell element, the MITC4+ element, in which the mid-surface membrane strain components are assumed using the concept of the MITC method. The tying membrane strains are obtained from four triangular domains which subdivide the mid-surface of the 4-node quadrilateral shell element. This approach alleviates locking that can happen when the MITC4 shell elements are geometrically distorted in curved geometries. Several basic tests including the isotropy, zero energy mode, and patch tests are performed. Through the solution of various shell problems, the convergence behavior of the MITC4+ shell element is studied to show the improvements reached. [ABSTRACT FROM AUTHOR]

This paper proposes a novel metaheuristic optimizer, named crow search algorithm (CSA), based on the intelligent behavior of crows. CSA is a population-based technique which works based on this idea that crows store their excess food in hiding places and retrieve it when the food is needed. CSA is applied to optimize six constrained engineering design problems which have different natures of objective functions, constraints and decision variables. The results obtained by CSA are compared with the results of various algorithms. Simulation results reveal that using CSA may lead to finding promising results compared to the other algorithms. [ABSTRACT FROM AUTHOR]

The extended scaled boundary finite element method (X-SBFEM) based on the level set method (LSM) is proposed in this paper to combine the advantages of the scaled boundary finite element method (SBFEM) and the extended finite element method (XFEM). The level set method (LSM) algorithm is applied to further develop the X-SBFEM, especially for the crack propagation problem. The Heaviside enrichment function is used to represent a jump across a discontinuity surface in a split element, and the non-smooth behavior around the crack tip is described using the semi-analytical SBFEM. The stiffness of the region containing the crack tip is computed directly, and the generalized stress intensity factors of many types of singularities are obtained directly from their definitions using consistent formulas. In the numerical simulations, a square plate with an edge crack under tension, a three-point bending beam, a four-point shear beam and a dam (the Koyna dam) with a single propagating crack are modeled. The results show that the proposed X-SBFEM is capable of calculating the stress intensity factors of cracks and predicting crack trajectories and load–displacement relations accurately. An analysis of the sensitivity of the parameters is employed to demonstrate that various mesh densities and crack propagation step lengths led to consistent results. [ABSTRACT FROM AUTHOR]

This paper describes a generative methodology for optimum design of truss structures. The novelty of the proposed method is its combination of generative design synthesis methods with conventional gradient-based optimization and simulation models. This combination is able to achieve optimal topologies and shapes for cable trusses under various constraints: stress, displacement, stability. Furthermore, manufacturing issues properly limit the generated solutions. A graph grammar is used to define different topologies for a given load problem. The effectiveness of the method is checked by solving a variety of available test problems found in the literature as well as several new three-dimensional solutions. [ABSTRACT FROM AUTHOR]

The design of an offshore structure is highly dependent on the operating environmental parameters, where a realistic statistical model of the latter is essential to produce a representative estimate of the performance and failure probability. Establishing an accurate model of the offshore environment can be a challenging task. The use of simple probabilistic models may lead to biased results in the stochastic structural analysis since the environmental impact to an existing offshore structure is associated with a wide range of inter-dependent factors. In this paper, the specification of long-term design loads for offshore structures considering multiple environmental factors is investigated where the dependency between several commonly used sea state parameters are instituted through a copula-based multivariate probabilistic model. Several copula functions, capable of modeling both linear and non-linear dependence structures, are considered. The developed multivariate model based on copula concept is compared with the available approaches in the literature using actual environmental data. The modeled sea state parameters are then utilized to characterize the sea load for the reliability analysis of a real jacket structure where the prediction of the long term load is derived in a discretized form. The applicability of this approach in a high dimensional multivariate problem is also discussed. [ABSTRACT FROM AUTHOR]

The paper focuses on numerical simulation of the 3D phase-field (PF) equations for modeling cubic-to-tetragonal martensitic transformations in shape memory alloys (SMAs), their complex microstructures and thermo-mechanical behavior. The straightforward solution to the fourth-order diffuse interface 3D PF equations, based on the Landau–Ginzburg potential, is numerically solved using an isogeometric analysis. We present microstructure evolution in different geometries of SMA nanostructures under temperature-induced phase transformations to illustrate the geometrical flexibility, accuracy and robustness of our approach. The simulations successfully capture the dynamic thermo-mechanical behavior of SMAs observed experimentally. [ABSTRACT FROM AUTHOR]

In the present paper, a linear complementarity method for a vehicle-bridge dynamic system considering separation and random roughness is established. By introducing the linear complementarity relationship between the relative displacement of the wheels and the bridge at the contact points, the dynamic interaction problem of the vehicle-bridge coupled system is transformed into a standard linear complementarity problem, and two models with different connection relations between the wheels and the bridge are proposed. The presented models characterize the system with one unified formulation whether the wheels separate from the bridge or not, and the conventional trial-and-error iterative process in numerical simulation is avoided. In the numerical examples, the proposed method is verified by comparing it with the conventional method, and it is found that the velocity, the vehicle to bridge mass ratio and the road roughness have a significant influence on separation. By considering a vehicle model of three rigid bodies with four wheels and the randomness of the rail roughness in train–track–bridge system, the possibility of separation and the expectation of the maximum separation distance at different velocities are studied. The results show that it is very useful to carry out a stochastic analysis of the system and consider the influence of separation in vehicle and bridge design. [ABSTRACT FROM AUTHOR]

The paper presents numerical simulations of punching shear in a reinforced concrete slab-column configuration formerly tested in the laboratory. A brief description of the test program at the University of Waterloo is reported. For the simulation, a symmetric quarter of the test configuration is employed. Full three-dimensional finite element discretized geometry is considered together with elastic–plastic reinforcement embedded as truss elements in concrete. Two regularized numerical models of concrete, formulated within elastic–plastic-damage theories, are applied. The first one, called gradient damage, is refined by an additional averaging equation where gradient enhancement involves an internal length scale. In the second one, called rate-dependent damaged plasticity model, a viscoplastic strain rate is introduced. The results for the first model implemented in FEAP and the second model from ABAQUS are discussed in detail. Different issues of numerical simulation to properly predict punching shear behaviour in the slab-column configuration are presented. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of aggregate shape on the diffusivity of mortar in three dimensions by random packing models of ellipsoidal and convex polyhedral particles. From a digital mesostructure and by a lattice approach, the diffusivity of mortar can be predicted. Simulations are compared with experimental results from literature and are discussed for mono-sized and multi-sized particle packing with and without interfacial transition zones (ITZ). It was found that the shape of aggregate has a significant effect on the diffusivity of mortar, and for oblate ellipsoids, the shape effect is most pronounced comparing to prolate ellipsoids and polyhedrons. [ABSTRACT FROM AUTHOR]

In aeronautics, the issue of ice shedding prediction is of prime importance in the assessment of electro-thermal ice protection systems. In this paper, an ice shedding mechanism based on pressure redistribution in the water film formed at the ice/airfoil interface is proposed. This pressure distribution induces a stress concentration that leads to crack propagation in the ice. To determine whether this mechanism is relevant or not, two numerical experiments are performed. The results of these numerical experiments and the influence of a few material parameters are discussed, as well as their limitations and possible consequences arising from some of the hypotheses. The numerical modeling is based on recent works on damage/fracture mechanics which provide a general framework for fracture mechanics computation. The effects of numerical parameters and mesh size are discussed. A mixed mode test case based on experimental data is also performed. This test case had not been attempted before on this particular numerical method, which therefore serves as further validation. [ABSTRACT FROM AUTHOR]

• Design of adaptive structures through Total Energy Optimization (TEO) based on MINLP. • Minimization of whole-life energy (material embodied + operational energy during service). • Structural sizing, actuator layout and control commands are obtained simultaneously. • TEO-MINLP produces similar solutions to those obtained by the method TEO-Nested. • Structural adaptation is particularly beneficial for stiffness governed design. This paper presents a new All-In-One (AIO) implementation of an existing formulation to design adaptive structures through Total Energy Optimization (TEO). The method implemented in previous work is a nested optimization process, here named TEO-Nested. Numerical simulations and experimental testing have shown that the TEO-Nested method produces structures that embody and use significantly lower energy compared to passive designs. However, TEO-Nested does not guarantee solution optimality. The formulation presented in this paper is an AIO optimization based on Mixed Integer Nonlinear Programming (MINLP), here named TEO-MINLP. Element cross-section areas, internal forces, nodal displacements and control commands are treated as continuous variables while the actuator positions as binary variables. Stress and displacement limits are included in the optimization constraints. Case studies of reticular structures are employed to benchmark the solutions with those produced by the TEO-Nested method. Results have shown that both formulations produce similar solutions which are only marginally different in energy terms thus proving that the TEO-Nested method tends to converge to optimal (local) solutions. However, the computation time required by TEO-Nested is only a fraction of that required by TEO-MINLP, which makes the former more suitable for structures of complex layout that are made of many elements. [ABSTRACT FROM AUTHOR]

Highlights: [•] Response of reinforced concrete pile to a buried explosion is treated. [•] Fully coupled computer simulation techniques are used in the analysis. [•] Material models for air, soil, explosive, concrete and steel are incorporated. [•] Pile reinforcements have a significant effect on pile response to blast load. [•] Findings of this paper will serve as a reference for future analysis and design. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present thermo-plasticity model for dealing with localized failure with softening, which is capable of accounting for mechanical loading and heat transfer simultaneously. The main point concerns the localized failure of the structure which results with heterogeneity of stress and strain field for temperature dependent properties. We discuss how to employ structured mesh for such case, and construct the appropriate enhancements of the displacement and temperature fields by using the finite element method with embedded discontinuities (ED-FEM). For clarity, we first consider 1D case, and provide several illustrative numerical simulations. We then provide the corresponding generalization of the proposed model to 2D case and its numerical implementation based upon structured ED-FEM mesh. [Copyright &y& Elsevier]

• The node-scheme method is firstly introduced into the XFEM to solve the frictional contact crack problems. • The stress redistribution is considered in the local part of the crack surface in the proposed method. • The proposed method has the ability to solve locking problems in the numerical simulation of the frictional contact crack. In this paper, based on the nodal displacement of the crack surface element, a novel node-scheme method is proposed to model the frictional contact problem in the framework of extended finite element method (XFEM). The paper systematically illustrates the novel node-scheme including the fundamentals of the proposed method, the coupled Coulomb's friction model. The novelty of the proposed method is that the node-scheme method is first introduced into the XFEM, it can consider the stress redistribution in the local part of the crack surface, and it has the advantage of solving the locking phenomenon in the numerical simulation of the frictional contact problem. The numerical results show that the proposed method is accurate and applicable to efficiently solve the frictional contact crack problem. [ABSTRACT FROM AUTHOR]

Abstract: Coupled electro-mechanical problems are frequently encountered when dealing with micro electro-mechanical systems (MEMS) with capacitive actuation and/or readout systems; their numerical solution can be extremely time consuming, due to the nonlinearity of the coupling terms. Coupled electrostatic – structural dynamic simulations are carried out in this paper through an innovative numerical procedure, based on the combined use of a domain decomposition technique and of a proper orthogonal decomposition methodology. The approach is assessed through the analysis of the dynamic response of a doubly clamped beam and of a plane resonator subjected to an electrostatic actuation, showing computational gains up to 98%. [Copyright &y& Elsevier]

Abstract: In this paper, we present an immersed boundary (IB) method to simulate a 2 dimensional wet foam. Whereas most of the volume in a dry foam is attributed to its gas phase, a wet foam contains a considerable amount of liquid volume which comprises the Plateau borders as well as thin liquid boundaries separating cells. Wet foam dynamics involves the interaction between a surrounding gas, a liquid inside the Plateau borders, and a collection of thin liquid-film boundaries that partition a domain filled with gas and liquid into discrete cells and Plateau borders. The liquid-film boundaries are flexible, contract under the influence of surface tension. The boundary between cells is permeable to the gas, which moves across them by diffusion at a rate proportional to the local pressure difference across the boundary. The boundary between a cell and a Plateau border is impermeable to the gas, however. We here introduce an IB method that takes into account the non-equilibrium fluid mechanics of the fluid. To model gas diffusion across the internal boundaries between cells, we allow normal slip between the boundary and the gas at velocity proportional to the (normal) force generated by the boundary surface tension. We implement this method in the two-dimensional case, and test it by verifying the modified von-Neumann relation, which governs the coarsening of a two-dimensional wet foam. The method is further validated by a convergence study, which confirms its first-order accuracy. [Copyright &y& Elsevier]

Abstract: This paper treats the blast response of a pile foundation in saturated sand using explicit nonlinear finite element analysis, considering complex material behavior of soil and soil–pile interaction. Blast wave propagation in the soil is studied and the horizontal deformation of pile and effective stresses in the pile are presented. Results indicate that the upper part of the pile to be vulnerable and the pile response decays with distance from the explosive. The findings of this research provide valuable information on the effects of underground explosions on pile foundation and will guide future development, validation and application of computer models. [Copyright &y& Elsevier]

Abstract: This paper introduces an original model to simulate the bond failure between concrete and reinforcing steel bars. The model was developed to be used in threedimensional analyses within the framework of the Finite Element Method and for general loading cases. It was designed using a hierarchical approach by combining what is called the base model, which acts as the skeleton of the model and introduces the basic response under monotonic and reversed loading, and four independent and optional sub-models used to enhance the simulation when needed, by considering the cyclic resistance degradation, the peak stress slip evolution, the reload slip evolution and the radial stress effect. The model implementation within the framework of the Finite Element Method is described and its accuracy is assessed using a series of validation tests. At the end, the main conclusions extracted from this work are presented. [Copyright &y& Elsevier]

Abstract: This paper describes features of a fully coupled thermo-mechanical model for Friction Stir Welding (FSW) simulation. An apropos kinematic setting for different zones of the computational domain is introduced and an efficient coupling strategy is proposed. Heat generation via viscous dissipation as well as frictional heating is considered. The results of the simulation using the proposed model are compared with the experimental evidence. The effect of slip and stick condition on non-circular pin shapes is analyzed. Simulation of material stirring is also carried out via particle tracing, providing insight of the material flow pattern in the vicinity of the pin. [Copyright &y& Elsevier]

Abstract: The main objective of the paper is to present the computational model of a bi-cable aerial ropeway, which provides a scope for investigating the nonlinear interaction between the carrying cable motion and the swaying motion of traveling passenger carriers, depending on cable track inclination. To solve nonlinear equations of motion of two coupled sub-systems: multi-span cable and carriers idealized as physical pendulums, the special numerical method is developed, where initial vibrations of carriers (before entering a cable track) are used as a base for predicting further history of motion. Numerical analysis performed for different inclinations of a cable track led to the conclusion that nonlinear interaction effects are not significant and can be neglected to simplify the computational procedure in further research. [Copyright &y& Elsevier]

Abstract: This paper discusses the effect of the structure and packing conditions of centre displacement of the membrane in a circular piezoelectric actuator. A mathematical model was constructed using classical laminated plate theory (CLPT) to describe the transverse displacement of a circular actuator. In the applied loading simulation, the effect on static displacement from varying the thickness in each layer of the structure as well as the packaging boundary constraint methods was studied. Results show the radius and thickness of the thin film has little effect on the maximum displacement, however an increase in elastic modulus decreased the maximum transverse displacement. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses the computational modelling used to simulate the structural behaviour of the historic ship Cutty Sark and her response to different load and new support conditions, various treatments and interventions as part of a major conservation programme. A novel modelling approach suitable to analyse quickly and at a global level complex heritage structures with composite shell-like nature such as the Cutty Sark is presented. This modelling approach is validated and applied to understand and analyse a number of structural assessment problems relevant to the conservation programme including plank removal procedures and the design of a new support structure. [Copyright &y& Elsevier]

Abstract: The growing interest in sheet metal stamping processes, particularly in the automotive industry has led to three main issues in this field: [•] request of very complex shapes; [•] growing interest in springback control; [•] solution of multi-objective problems. These issues make a sheet metal stamping processes design very difficult and proper design methodologies to reduce times and costs are highly required. In this paper, a computer aided approach aiming to satisfy the mentioned issues is proposed. In particular, a progressive design approach based on the integration between numerical simulations, Response Surface Methodology (RSM) and Pareto optimal solutions search techniques was applied in order to design a complex 3D automotive stamping operation. An explicit/forming-implicit/springback approach was utilized to develop the numerical simulations. The proposed design approach is able to verify the necessity of a spatially differentiated restraining forces approach and to design the best policy for them. Pareto optimal solutions search techniques were applied in two different phases: the former Pareto frontier was built using an uniform restraining forces policy while the latter, which is the final process design tool, was based on a differentiated restraining forces strategy. Two different restraining force policies were applied: the former focused on drawbeads utilization, the latter utilized a segmented blankholder. As the optimization objective functions are concerned, indicators related both to thinning distribution and to springback amount were taken into account. The obtained Pareto curves can be used in order to discriminate which conditions have to be expected once a desired value of one of the objective functions is fixed. A new and flexible design methodology is proposed, able to: [•] deal with complex sheet metal stamping processes; [•] investigate many possible technological scenarios; [•] carry out a set of reliable solutions able to satisfy different design requirements. [Copyright &y& Elsevier]

Abstract: Damage detection procedures based on measured natural frequencies and building structure mode shapes are discussed in this paper. Modal curvature and structural flexibility approaches are tested. Attention is paid to the modal identification errors that influence damage detection. This problem is studied using a computer simulation of a simple supported beam. For practical cases, the peak picking method and its statistical errors are considered. In order to distinguish between true and false damage detection results, the Absolute Damage Index is proposed. Finally, the complexity of the problem in the case of a real building structure is presented. [Copyright &y& Elsevier]

Abstract: Mid-frequency response analysis often faces computational difficulties when a conventional modal approach is used for a finite element linear system. In this paper, the computational burden is relieved by frequency sweep algorithm or mode acceleration method for a reduced-order system constructed by algebraic substructuring, a variant of model order reduction. The two methods are compared with the help of numerical experiments and their computational complexity. As demonstrated by the finite element simulations, in which proportional damping is assumed, of a turbo-prop aircraft and a ring resonator, the frequency sweep algorithm for reduced-order systems shows the best performance among all considered numerical solutions, including the conventional approach. [Copyright &y& Elsevier]

Abstract: This paper addresses accuracy issues of nodal stresses in both finite elements and finite volumes. Strategies to evaluate nodal stresses for finite elements are also briefly discussed. Emphasis is placed on the application of finite volumes to solid mechanics and an overview of recent advancements is presented. Numerical simulation of test problems shows that accuracy of nodal stresses evaluated using finite elements is strongly dependent on the recovery strategy. In all cases, stress recovery at boundary nodal points renders large errors for all non-patch schemes. Contrastingly, finite volumes provide an accurate computation of nodal stresses, including at domain boundaries. [Copyright &y& Elsevier]

Abstract: This paper deals with the understanding and the numerical simulation of complex dissipative phenomena involved in composite absorbers for two main degradation modes: the fragmentation and the delamination modes. Fragmentation is the last step of degradation in pure compression leading to total failure of a laminate and for CFRP it is mainly initiated by a microbuckling mechanism, which is dependant on the microstructural imperfections. The dissipated energies associated to the fragment creation are evaluated through micromodelling approaches and contrary to expectations, these energies seem to be insensitive to microscopic parameters. A Weibull density knowledge on peak load and dissipated energy is also proposed. On the other hand, computation control on the delamination process has been investigated. Numerical sensitivities are justified, thanks to analytical approaches and physical-based mesh criteria are proposed for classical propagation tests. Some quasi-static experiments have been performed and good accuracy is obtained with the model. All these results give perspectives to implement delamination and fragmentation interactions at mesoscale within an absorber-like configuration. [Copyright &y& Elsevier]

Abstract: This paper reports development of a two-dimensional solver for compressible viscous flow using spectral difference (SD) method and its applications on simulating laminar flow past two side-by-side cylinders at various spacings. The high-order spectral difference solver is based on unstructured quadrilateral grids. High-order curved wall boundary representation is developed for cylinders. Nine different spacings (center-to-center distance/diameter s =1.1, 1.4, 1.5, 1.7, 2, 2.5, 3, 3.4 and 4) are investigated. The simulation results are compared to experimental results and other numerical results. As s increases, single bluff-body, flip-flopping, anti-symmetric and symmetric wake patterns are predicted. [Copyright &y& Elsevier]

Abstract: Stretching computation strategies, including the hyperbolic exponential fittings along the lens interface, stretching transformations in z- and r-directions are discussed in this paper. The resulted adapted finite difference schemes are not only simple in structure, but also highly effective and efficient in the solution of paraxial Helmholtz equations for light beam propagation simulations and high performance lens designs. Cylindrically symmetric lens domains are assumed. Simulation results are given to illustrate the aforementioned numerical strategies with laboratory applications. Detailed algorithmic structures are given for immediate programming implementations and for similar lightwave propagation computation issues. [Copyright &y& Elsevier]

Abstract: In sheet metal forming most of the problems are multi-objective problems, generally characterised by conflicting objectives. A classical approach to investigate such kind of problems is focused on a combination of multiple objectives into a unique objective function to be optimised. Actually, in metal forming processes optimisation two main phases have to be developed in order to reach an optimal solution: the former is the modelling phase (definition of the design variables and objective function) and the latter concerns the computational aspect (numerical simulations or experiment to be developed). In this paper, an integration between numerical simulations, response surface methodology and Pareto optimal solution search techniques was applied in order to design a complex Y shaped tube hydroforming. In particular, the calibration of internal fluid pressure and counterpunch action was investigated with the aim to achieve three different quality objectives: minimization of thinning, reduction of underfilling and accuracy of the final fillet radius at the bulge zone corner. [Copyright &y& Elsevier]

Abstract: In this paper, sloshing waves have been analyzed for baffled and un-baffled tanks. Numerical simulations were carried out based on volume of fluid (VOF) techniques with arbitrary-Lagrangian–Eulerian (ALE) formulation which adopts the displacement of solid, the pressure and displacement in the fluid as variables to model the coupled system. The response of the coupled system is obtained by using the well-known software ADINA, which offers efficient fully coupled fluid–structure interaction capabilities by finite element method. The results obtained are compared with the available experimental data to demonstrate the reduction of sloshing effects in fluid model. [Copyright &y& Elsevier]

Abstract: This paper treats the dynamic response and energy absorption of aluminum foam-filled conical tubes under axial impact loading using non-linear finite element techniques. The influence of geometrical, material and loading parameters on the impact response is investigated using validated numerical models. Results are quantified in terms of important impact response parameters and indicate that the foam filler stabilizes the crushing process and thus improves the energy absorption capacity. The superior performance of foam-filled conical tubes as impact energy absorbers is evident from the results. The research information generated will be useful in developing guidance towards the design of these devices in impact applications. [Copyright &y& Elsevier]

Abstract: This paper presents a new simple and efficient two-dimensional frame finite element (FE) able to accurately estimate the load-carrying capacity of reinforced concrete (RC) beams flexurally strengthened with externally bonded fibre reinforced polymer (FRP) strips and plates. The proposed FE, denoted as FRP–FB-beam, considers distributed plasticity with layer-discretization of the cross-sections in the context of a force-based (FB) formulation. The FRP–FB-beam element is able to model collapse due to concrete crushing, reinforcing steel yielding, FRP rupture and FRP debonding. The FRP–FB-beam is used to predict the load-carrying capacity and the applied load-midspan deflection response of RC beams subjected to three- and four-point bending loading. Numerical simulations and experimental measurements are compared based on numerous tests available in the literature and published by different authors. The numerically simulated responses agree remarkably well with the corresponding experimental results. The major features of this frame FE are its simplicity, computational efficiency and weak requirements in terms of FE mesh refinement. These useful features are obtained together with accuracy in the response simulation comparable to more complex, advanced and computationally expensive FEs. Thus, the FRP–FB-beam is suitable for efficient and accurate modelling and analysis of flexural strengthening of RC frame structures with externally bonded FRP sheets/plates and for practical use in design-oriented parametric studies. [Copyright &y& Elsevier]

A reduced-order modelling to predictively simulate the dynamics of piezoelectric structures with geometric nonlinearities is proposed in this paper. A formulation of three-dimensional finite element models with global electric variables per piezoelectric patch, and suitable with any commercial finite element code equipped with geometrically nonlinear and piezoelectric capabilities, is proposed. A modal expansion leads to a reduced model where both nonlinear and electromechanical coupling effects are governed by modal coefficients, identified thanks to a non-intrusive procedure relying on the static application of prescribed displacements. Numerical simulations can be efficiently performed on the reduced modal model, thus defining a convenient procedure to study accurately the nonlinear dynamics of any piezoelectric structure. A particular focus is made on the parametric effect resulting from the combination of geometric nonlinearities and piezoelectricity. Reference results are provided in terms of coefficients of the reduced-order model as well as of dynamic responses, computed for different test cases including realistic structures. [ABSTRACT FROM AUTHOR]

This paper presents a Petrov–Galerkin natural element method for the nonlinear analysis of 2-D dynamic contact problems without friction. The frictionless dynamic contact problem is formulated according to the linearized total Lagrangian method incorporated with the linearized penalty method. The displacement increment is approximated with Laplace interpolation functions defined with the help of Voronoi polygons, while the admissible virtual displacement is expanded with constant strain functions which are supported on Delaunay triangles. The spatial numerical integration is carried out by applying the conventional Gauss quadrature rule to Delaunay triangles and the temporal time integration is performed by the implicit Newmark method. The validity of the proposed method is examined through the illustrating numerical experiments. [Copyright &y& Elsevier]

In the present paper, the process of the formulation of the stiffness and transfer matrices and of the load vectors of Timoshenko beams on Kerr-type three-parameter elastic foundation is presented. These matrices are developed on the basis of the exact solution of the governing differential equations for all potential solution cases. The reliability and precision of the modeling of beams resting on elastic foundation through the use of these matrices is assessed by means of two numerical examples. [Copyright &y& Elsevier]