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This paper deals with a new explicit framework for numerical dynamic analysis that could be applied to any explicit-implicit time integration, i.e. predictor-corrector time integrations. For this purpose, Dynamic Relaxation method is combined with the explicit-implicit time integrations so that the proposed algorithm is performed by full vector operations. This subject helps to obtain an explicit algorithm, which does not involve solving simultaneous system of equations in each time increment, even linear one. Moreover, the number of corrections, which is the main concern in the explicit-implicit algorithms, is selected automatically in the suggested procedure. Afterwards, some numerical examples are solved to illustrate the validity and the robustness of the proposed algorithm. Results show that applying the proposed framework to the higher order explicit-implicit integrations exhibits excellent accuracy in comparison with the well-known implicit Newmark- β and Wilson- θ schemes. Simplicity, more stable integration, automated procedure and vector operations are some of the salient features of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper tests the hypothesis that the tessellation used in tessellated continuum mechanics can form a mesh in a continuous Galerkin finite element method. Although the tessellation is not unique, neither is it arbitrary, and its construction imposes constraints on any numerical analysis. A distinctive feature of the tessellation is that it can possess highly distorted elements yet—as a consequence of associated anisotropy in material properties—can still return accurate results. The numerical procedure is tested on classical fractal porous geometries to demonstrate the potential of the method, and also illustrate the capability for analysis of disparate porous materials on continua. [ABSTRACT FROM AUTHOR]

This paper proposes an uncertain analysis method named Polynomial Chaos Response Surface method (PCRSM) for uncertainty propagation in structural-acoustic system containing hybrid uncertainties. The polynomial chaos expansion method combined with the response surface methodology is employed to handle the random and interval uncertainty. The PCRSM does not require efforts to modify model equations due to its non-intrusive characteristic. The PCRSM is also able to predict the response of the system with only random or only interval uncertainty. The numerical results demonstrate that the PCRSM is effective and computationally efficient. [ABSTRACT FROM AUTHOR]

This paper presents a class of arc-length methods for the quasi-static analysis of problems involving material and geometric nonlinearities. A constraint equation accounting for geometric and dissipative requirements is adopted: the geometric part refers to the Riks and Crisfield equations, while the dissipative one refers to the dissipated energy. The approach allows for a continuous variation of the nature of the constraint, and a switch criterion is not needed to trace the elastic and the dissipative parts of the equilibrium paths. To illustrate the robustness and the efficiency of the methods, three examples involving geometric and material nonlinearities are discussed. [ABSTRACT FROM AUTHOR]

This paper presents the 2D and 3D numerical analysis of pullout tests on steel anchorages in concrete blocks using standard and mixed finite elements. A novel (stabilized) mixed formulation in the variables of total strain ε and displacements u is introduced to overcome the intrinsic deficiencies of the standard displacement-based one in the context of localization of strains, such as mesh dependency. The quasi-brittle behavior of concrete is described through an elastoplastic constitutive law with a local Rankine yielding criterion. The proposed formulation is shown to be a reliable and accurate tool, sensitive to the physical parameters of the pullout tests, but objective with respect to the adopted FE mesh. Furthermore, the mixed ε / u finite element is able to capture the correct failure mechanism with relatively coarse discretizations. At the same time, the spurious behavior of the standard formulation is not alleviated by mesh-refinement. [ABSTRACT FROM AUTHOR]

In this paper, the Hamiltonian approach developed for beam with solid cross-section is generalized to deal with beams consisting of thin-walled panels. The governing equations of plates and cylindrical shells for the panels are cast into Hamiltonian canonical equations and closed-form central and extremity solutions are found. Typically, the end-effect zones for thin-walled beams are much larger than those for beams with solid cross-sections. Consequently, extremity solutions affect the solution significantly. Correct boundary conditions based on the weak form formulation are derived. Numerical examples are presented to demonstrate the capabilities of the analysis. Predictions are found to be in good agreement with those of plate and shell FEM analysis. [ABSTRACT FROM AUTHOR]

Accurate evaluation of nearly singular integrals plays an important role in the overall accuracy of the boundary element analysis. The paper presented here reviews some numerical techniques used currently to calculate such integrals in the boundary element method (BEM). Some incorrect algorithms published before are discussed and a new numerical technique to calculate nearly singular integrals with hyper-singularities is developed. The accuracy and efficiency of the method are demonstrated through several examples that are commonly encountered in the applications of the BEM. Comparison of this method with some of the existing methods is also presented. It is shown that, for the evaluation of nearly hyper-singular integrals, several orders of magnitude improvement in relative error can be obtained using the current method compared to most of existing methods. [ABSTRACT FROM AUTHOR]

In this paper, we simplify the error estimation technique developed for the Craig–Bampton (CB) method (Kim et al., 2014). The original formulation is simplified by neglecting insignificant terms, a new error estimator is obtained, and thus computational cost is significantly reduced with negligible accuracy loss. In addition, the contribution of a specific substructure to a relative eigenvalue error can be estimated using the new formulation, in which the estimated relative eigenvalue error is represented by a simple summation of the substructural errors estimated. Therefore, the new formulation can be employed for error control by using the detailed errors estimated for a certain substructure. Through various numerical examples, we verify the accuracy and computational efficiency of the new formulation, and demonstrate an error control strategy. [ABSTRACT FROM AUTHOR]

This paper reports the parallel implementation of a hybrid-mixed stress finite element model for the analysis of three-dimensional structures. The stress and the displacement fields in the domain and the displacement fields on the static boundary are independently approximated. All field equations are imposed in a weighted residual form and Legendre polynomials are used to define the approximation bases. The parallel implementation of the model uses a message passing scheme based on the MPI standard. For the parallel solution of the governing system, two distinct approaches are tested. The first corresponds to the use of a third-party parallel direct solver code, named MUMPS. The second uses an in-house developed hybrid solver inspired by the FETI method and designed to deal with the typical pattern of the hybrid-mixed stress model governing system. Some numerical examples are discussed to illustrate the effectiveness and performance of the adopted parallel approach. [ABSTRACT FROM AUTHOR]

This paper introduces a metamodeling strategy able to account for the uncertainties in simulating nonlinear, dynamically evolving engineering systems. Polynomial Chaos (PC) expansion is implemented for the development of stochastic metamodels capable of representing the response of numerical models with uncertain input variables. The models employed are of the Nonlinear AutoRegressive with eXogenous (NARX) input form, comprising parameters that are random variables themselves. By expanding these parameters onto an appropriately selected PC basis, the resulting PC-NARX metamodel achieves vast reduction in computational time with sufficient accuracy, yielding a suitable tool for implementations where replacement of computationally costly models is sought. [ABSTRACT FROM AUTHOR]

This paper presents a study on topology optimization of continuum structures under buckling constraints. New algorithms are developed for minimization of structural compliance considering constraints on volume and buckling load factors. The SIMP (Solid Isotropic Material with Penalization) material model is employed and nodal relative densities are used as topology design variables. A new approach based on the eigenvalue shift and pseudo mode identification is proposed for eliminating the effect of pseudo buckling modes. Two-phase optimization algorithms are also proposed for achieving better optimized designs. Numerical examples are presented to illustrate the effectiveness of the new methods. [ABSTRACT FROM AUTHOR]

This paper presents the development of a new concept, the Embedded Unit Cell (EUC) approach, to calculate local responses in elastic media. The EUC approach is based on a multi-scale formulation of non-periodic domains to evaluate the local/micro response where stress concentrations are expected. The formulation is based on alternative boundary conditions which is not restricted to periodic assumptions of the unit cell response that is required in the classical theory. This approach provides a reduced computational cost model of the macroscopic/global problem while preserving the accuracy at the microscale problem. We conclude with a numerical verification study. [ABSTRACT FROM AUTHOR]

This paper applies the asymptotic homogenization method to predict effective properties of periodic heterogeneous beam structures. A improved FEM formulation and algorithm of the unit cell problems is developed. The effective properties are rewritten in terms of the nodal quantities of the FEM model of the unit cell. With this approach, periodic beam structure of complicated microstructure can be modeled by various elements and modeling techniques and solved by using the commercial software as a black box. Numerical examples illustrate the versatility and efficiency of the method. Finally, the size effect of basic cell in thickness direction is studied. [ABSTRACT FROM AUTHOR]

This paper presents an interior-point implementation method of the relaxed strain energy function to model the stress distribution in membranes in the presence of wrinkles. The relaxed strain energy function is reformulated using the interior-point method. This formulation is proven to be quasi-convex with respect to the deformation gradient. A set of governing equations for the membrane is developed in the standard finite element format. The solution to this set of equations is obtained using the interior-point method, and several numerical examples are presented for validation. The proposed method is shown to converge and to be robust and efficient. [ABSTRACT FROM AUTHOR]

The consistently linearized eigenproblem (CLE) plays an important role in stability analysis of structures. Solution of the CLE requires computation of the tangent stiffness matrix K ∼ T and of its first derivative with respect to a dimensionless load parameter λ , denoted as K ∼ ̇ T . In this paper, three approaches of computation of K ∼ ̇ T are discussed. They are based on (a) an analytical expression for the derivative of the element tangent stiffness matrix K ∼ T e , (b) a load-based finite difference approximation (LBFDA), and (c) a displacement-based finite difference approximation (DBFDA). The convergence rate, the accuracy, and the computing time of the LBFDA and the DBFDA are compared, using the analytical solution as the benchmark result. The numerical investigation consists of the analysis of a circular arch subjected to a vertical point load at the vertex, and of a thrust-line arch under a uniformly distributed load. The main conclusion drawn from this work is that the DBFDA is superior to the LBFDA. [ABSTRACT FROM AUTHOR]

This paper explores the adverse and beneficial effects of structure–soil–structure interaction (SSSI) under seismic excitation on a group of three buildings. A simple discrete formulation of the problem is employed that uses rotational interaction springs between buildings. A physical experimental shake-table test program is used to qualitatively validate the discrete theoretical model. Subsequently, a numerical study is performed which demonstrates that the central building in a three building case can act as a tuned mass damper for its adjacent buildings. Results indicated that this adverse effect can be more pronounced than the case where there are just two buildings interacting. [ABSTRACT FROM AUTHOR]

The stiffness of cable nets is conditioned by their states of prestress. The decrease of prestress due to creep of cables determines the serviceability and load bearing capacity of the cable net. In this paper, a modified force density method for a time-dependent non-linear static analysis of pre-stressed cable nets based on the application of creep theory is presented. Creep constitutive equations are directly used for the adjustment of cable lengths. The accuracy and efficiency of the formulation are assessed by comparison with available results obtained by other authors using different numerical approaches. The applicability of this method is demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents a unified Ritz-based method for the computation of modal properties of both thick and thin, circular and annular isotropic plates with different boundary conditions. The solution is based on an appropriate and simple formulation capable of handling in an unified way a large variety of two-dimensional higher-order plate theories. The formulation is also invariant with respect to the set of Ritz admissible functions. In this work, accurate upper-bound vibration solutions are presented by using kinematic models up to sixth order and products of Chebyshev polynomials and boundary-compliant functions. Considering the circumferential symmetry of annular plates and the 2-D nature of underlying theories, the present method is also computationally efficient since only single series of trial functions in the radial direction are required. [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]

We present in this paper the development and use of a novel and promising numerical scheme, the method of finite spheres, for the analysis of wave propagations. The solution of two-dimensional linear elastic and visco-elastic waves is considered. The procedure does not require a mesh and hence avoids element distortions. We discuss the construction of the interpolations in which harmonic functions are included to make the method effective for the analysis of wave propagations. A simple and efficient numerical integration scheme is proposed and the solution effort is evaluated versus using the standard finite element method. Several numerical examples are used to demonstrate capabilities of the method. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the efficiency of a high-order nodal discontinuous Galerkin method for the numerical solution of Maxwell’s equations using hybrid meshes. An unstructured triangular or tetrahedral mesh is used near curved boundaries and a structured Cartesian mesh is used to fill the remainder of the domain. A quadrature-free implementation is employed for the regular quadrilateral and hexahedral elements which, together with the reduction in the number of internal faces, leads to a reduction in the cpu time requirements. Numerical examples in two and three dimensions are used to illustrate the benefits of using hybrid meshes. [Copyright &y& Elsevier]

Abstract: The hybrid test method is a relatively recently developed dynamic testing technique that uses numerical modelling combined with simultaneous physical testing. The concept of substructuring allows the critical or highly nonlinear part of the structure that is difficult to numerically model with accuracy to be physically tested whilst the remainder of the structure, that has a more predictable response, is numerically modelled. In this paper, a substructured soft-real time hybrid test is evaluated as an accurate means of performing seismic tests of complex structures. The structure analysed is a three-storey, two-by-one bay concentrically braced frame (CBF) steel structure subjected to seismic excitation. A ground storey braced frame substructure whose response is critical to the overall response of the structure is tested, whilst the remainder of the structure is numerically modelled. OpenSees is used for numerical modelling and OpenFresco is used for the communication between the test equipment and numerical model. A novel approach using OpenFresco to define the complex numerical substructure of an X-braced frame within a hybrid test is also presented. The results of the hybrid tests are compared to purely numerical models using OpenSees and a simulated test using a combination of OpenSees and OpenFresco. The comparative results indicate that the test method provides an accurate and cost effective procedure for performing full scale seismic tests of complex structural systems. [Copyright &y& Elsevier]

Abstract: Resonant vibrations of aircraft engine blades cause blade fatigue problems in engines, which can lead to thicker and aerodynamically lower performing blade designs, increasing engine weight, fuel burn, and maintenance costs. In order to mitigate undesirable blade vibration levels, active piezoelectric vibration control has been investigated, potentially enabling thinner blade designs for higher performing blades and minimizing blade fatigue problems. While the piezoelectric damping idea has been investigated by other researchers over the years, very little study has been done including rotational effects. The present study attempts to fill this void. The particular objectives of this study were to: (a) develop a methodology to analyze a multiphysics piezoelectric finite element composite blade model for harmonic forced vibration response analysis coupled with a tuned RLC circuit for rotating engine blade conditions, (b) validate a numerical model with experimental test data, and (c) achieve a cost-effective numerical modeling capability which enables simulation of rotating blades within the NASA GRC Dynamic Spin Rig Facility. A numerical and experimental study for rotating piezoelectric composite subscale fan blades was performed. It was proved that the proposed numerical method is feasible and effective when applied to the rotating blade base excitation model. The experimental test and multiphysics finite element modeling technique described in this paper show that piezoelectric vibration damping can significantly reduce vibrations of aircraft engine composite fan blades. [Copyright &y& Elsevier]

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]

Highlights: [•] This paper proposes a progressive damage detection approach. [•] The approach is based on multi-scale wavelet finite element model (WFEM). [•] Structural sub-element damage can be identified in a progressive manner. [•] The effectiveness of the proposed approach is validated by numerical examples. [•] Compared with traditional methods, the new method improves computation efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Copeland and Moon’s experimental results for a long pipe conveying fluid in the presence of a relatively large end-mass have displayed some truly fascinating dynamical behavior. Numerical studies, on the other hand, have all dealt with shorter pipes and smaller end-masses, mainly because the numerical convergence of the theoretical results for long pipes with large end-masses is problematic. In this paper, numerical results are presented for Copeland and Moon’s system parameters, reproducing some of the rich dynamics they obtained, including coupled planar and pendular oscillations, planar oscillations rotating through a finite angle, and planar motions rotating clockwise or counter-clockwise. [Copyright &y& Elsevier]

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: Various types of partial differential equations have been playing increasingly important roles in the study of theoretical and numerical combustion. In this paper, we are particularly concerned with the numerical solution of certain premixed model problems in rectangular spatial domains. The two-dimensional reaction–diffusion equations involved are associated with an ignition type nonlinearity involving a mathematical degeneracy at a corner point. A Peaceman–Rachford–Strang splitting based adaptive method is proposed on exponentially evolving grids. Rigorous numerical analysis are given to ensure the satisfactory effectiveness, efficiency, and numerical stability of the algorithm developed. Simulation experiments are provided to illustrate our accomplishments. [Copyright &y& Elsevier]

Abstract: Computational vocal fold models are often used to study the physics of voice production. In this paper the sensitivity of predicted vocal fold flow-induced vibration and resulting airflow patterns to several modeling selections is explored. The location of contact lines used to prevent mesh collapse and assumptions of symmetry were found to influence airflow patterns. However, these variables had relatively little effect on the vibratory response of the vocal fold model itself. Model motion was very sensitive to Poisson’s ratio. The importance of these parameter sensitivities in the context of vocal fold modeling is discussed. [Copyright &y& Elsevier]

Abstract: This paper uses a multilayered shell element to compute the dynamic response of multilayered poroelastic structures such as car instrument panels, car floors, or car roofs. It is based on the P-order Shear deformation Theory with an added Zigzag function (ZPST). Biot’s theory is used to describe the poroelastic layer and standard couplings are realized between elastic and poroelastic layers. A method based on Padé approximants is also used in order to reduce the computation time. This acceleration technique enables to achieve fast frequency sweep computations compared to a standard direct method. Finally, numerical validations on plates and curved geometries are presented. [Copyright &y& Elsevier]

Abstract: This paper describes three analytical methods to calculate sensitivity and Hessian matrix of structural Power Spectral Density (PSD) functions for random seismic responses. The methods are derived based on Complete Quadratic Combination method (CQC), Square Root of the Sum of Squares method (SRSS) and Pseudo-Excitation Method (PEM) by direct differentiation. A planar frame and a building are demonstrated. The results indicate the first and second derivatives of PSD functions, achieved by CQC-based method, PEM-based method, are exactly same. The first and second derivatives achieved by SRSS-based method are almost the same as that obtained by other two methods. PEM-based method is the most efficient method. SRSS-based method is much more efficient than CQC-based method. [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: Three-dimensional (3D) cyclic analysis and constitutive material model are needed to better understand the behavior of unreinforced masonry (URM) buildings under earthquake excitations. So far, most of the existing constitutive material models applied to the field of masonry structures have focused on two-dimensional modeling and monotonic loading. In addition, most of the studies have used implicit dynamic procedures in the time domain. Based on the inherent features of implicit formulations for nonlinear problems, a number of iterations are required at each time step to achieve convergence, which leads to intensive computations and lack of convergence in some cases such as cyclic loadings. In this paper, a 3D cyclic constitutive material model implemented within an explicit analysis procedure is proposed, which can be used to model large deformation behavior of masonry walls. A rigorous constitutive material model is proposed and validated with available experimental data from previous researches, and for the attributes for which experimental data is not readily available; a number of new experimental tests has been conducted by the authors. The material model is implemented in a user-defined subroutine and compiled with ABAQUS (VUMAT). The subroutine is then tested by several numerical examples on a single element under cyclic normal and transverse deformations to examine the behavior of the material model. Moreover, several analyses are conducted and the numerical results are compared with experimental data to assess the robustness and predictive capabilities of the proposed material model and the numerical solution algorithms. [Copyright &y& Elsevier]

Abstract: This paper proposes an interval uncertain multi-objective optimisation (IUMOO) method for structures with uncertain-but-bounded parameters. An adaptive Kriging model is established to improve the computational efficiency and numerical accuracy in the approximation of design functions. Latin Hypercube Design (LHD) is applied to achieve a set of sampling points both in the design and uncertain spaces for calibrating the Kriging surrogate model. The interval number programming method is used to transform the uncertain optimisation into a corresponding deterministic multi-objective optimisation. Typical numerical examples are used to demonstrate the effectiveness of the proposed methodology. [Copyright &y& Elsevier]

Abstract: This paper proposes and validates a three degrees of freedom element formulation that accounts for torsion and transverse bending of three-dimensional curved elements in explicit numerical analyses methods such as Dynamic Relaxation. Using finite difference modeling, in-plane distortions and moments, the increment of twist (and hence torsion) and out-of-plane bending deformations are determined. Numerical stability and convergence limits of the element are discussed. Two sets of circular arc test cases validate the accuracy of the element against theoretical and six degrees of freedom finite-element results. This element is widely applicable and found in strained grid shells and spline stressed membranes. [Copyright &y& Elsevier]

Abstract: This paper proposes a transient strain model of concrete with a transient modulus under the biaxial stress state and a failure criterion for determining the fire resistance of two-way reinforced concrete slabs. A program was developed to calculate the three-stage response mode and fire resistance of such slabs. Unlike tests and past studies, this program verified the developed constitutive model of concrete and the necessity of including transient strain in the model. The parametric study included in this research further specified the influence of concrete’s thermal strain and steel’s creep strain on the behavior of the slab during fires. [Copyright &y& Elsevier]

Abstract: In this paper, two numerically robust algorithms based on Lagrangian velocity constraint and regularised penalty method are proposed for frictionless dynamic contact analysis utilising the standard Newmark method. It is shown that the Lagrangian velocity constraint method achieves energy conservation and a zero gap constraint approximately, where the errors can be reduced by temporal refinement. In addition to this, a regularised penalty force is devised to ensure exact energy conservation for frictionless contact analysis using the trapezoidal rule. Therefore, unlike the conventional penalty method, the proposed method achieves better accuracy in the impenetrability constraint whilst maintaining the energy stability with no need for extra refinement of the temporal discretisation. [Copyright &y& Elsevier]

Abstract: In this paper a novel approach based on evolutionary polynomial regression (EPR) is presented to develop constitutive models of materials. Stress–strain data are used to train EPR and develop EPR-based material models. It is shown that it is possible to construct the material stiffness (Jacobian) matrix using partial derivatives of the developed EPR models. The EPR-based Jacobian matrix is implemented in finite element (FE) model and two boundary value problems are used to verify the proposed EPR-based FE methodology. It is shown that the EPR-FE model can be successfully employed to analyse structural problems with both linear and non-linear material behaviour. [Copyright &y& Elsevier]

Abstract: This paper presents an adaptive density point refinement approach for continuum topology optimization on the basis of an analysis-mesh separated material density field description based on nodal design variables. The Shepard interpolants are used to construct a strictly range-restricted density field over the design domain with the density design variables defined on a density point grid. Since the density points are defined independent of the finite element mesh, it is easy to refine the density point grid without remeshing the finite element model. A refinement criterion is given to identify the gray transitional regions to be adaptively refined in the subsequent optimization iterations. With such a refinement scheme, the topology optimization can start from a relatively coarse density point grid but still yields a desired higher resolution of the structural boundaries in the final design. Because refinements are only performed when and where necessary, this method is able to improve the boundary description quality of the optimal result with much less design variables as compared with the case of global refinement, and therefore can greatly reduce the computational burden involved in the sensitivity analysis and optimization process. Moreover, the percentage of transitional regions in the final solutions can also be reduced. Compared with using a uniformly globally-dense density point arrangement, this approach can achieve similar optimal designs but with much less computational cost. Numerical examples are given to demonstrate the effectiveness and efficiency of the present approach. [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: This paper prepares new features for applying the Dynamic Relaxation (DR) method in buckling and post-buckling structural analyses. Here, controlling the displacement’s increment is the main concept so that the minimum residual displacement and the minimum kinetic energy criteria are designed for updating the load factor in DR iterations. These new formulations do not affect the DR’s stability and they are successfully applied to both viscous and kinetic DR algorithms. Numerical analyses of structures with snap-through and snap-back behaviors show that the accuracy and the convergence rate of the suggested methods are higher than the well-known existing approaches such as the arc-length technique, especially, if they are combined with the kinetic DR algorithm. Calculating the buckling load is another interesting application of the proposed methods, performed here. In this manner, the suggested DR algorithms could numerically present the accurate buckling load of structures. [Copyright &y& Elsevier]

Abstract: In this paper, the static non-linear behavior of masonry bridges is numerically analyzed by means of a 3D FE numerical code. In particular, the three dimensional behavior of the structures when subjected to eccentric loads, the actual 3D geometry of the bridges (particularly important when skew arches are analyzed) and the strengthening effect induced by the backfill are considered. The code is non-commercial and is applied here for the first time in presence of a very large number of elements and different materials. It relies in a FE discretization of the structure by means of rigid infinitely resistant eight-noded parallelepiped elements and non-linear interfaces, exhibiting deterioration of the mechanical properties. Each material of the bridge (arch, buttresses, piers, and fill) is suitably modeled using interfaces having different constitutive behavior and mechanical properties. Two real scale masonry bridges are analyzed, namely a skew single span structure experimentally tested up to failure at the Bolton Institute, UK and a straight multi span bridge constituted by five circular arches and loaded with an eccentric load. Both 2D and 3D limit analyses are also performed to have full insight into the actual capabilities of the 3D approach to reproduce peak loads and deformed shapes at failure and, at the same time, to investigate limitations of 2D hypotheses when transversal effects induced by geometry and load eccentricity are not considered. [Copyright &y& Elsevier]

Abstract: The crack band approach has been used in many engineering computations as a simple technique eliminating or reducing the sensitivity of numerical results to the size of finite elements in simulations that involve strain localization due to softening. In the present paper, this traditional technique is carefully analyzed and potential sources of errors are identified. The role of various components of the modeling strategy is elucidated by simple examples dealing with a one-dimensional tensile test and a two-dimensional model of a notched beam subjected to bending. The influence of the specific choice of finite elements, integration scheme and formula for estimation of the crack band width is analyzed. Particular attention is devoted to the differences among band width estimation methods based on element area or volume, on element projection, and on the idea proposed by Oliver . The results are summarized in the form of recommendations which can contribute to reduction of errors in practical simulations. [Copyright &y& Elsevier]

Abstract: In this paper a numerical method is proposed based on single vector iterations for finding a few natural frequencies and mode shapes of the modified regular systems. The proposed method utilizes the information obtained from a decomposable model, called the base model, to transform the eigenproblem associated with the free vibration of the modified system into a simpler problem which can be handled more efficiently through vector iterations such as shifted inverse iteration method. The efficiency of the proposed method is demonstrated through examples in terms of the number of iterations required, speed and storage requirements. Comparison is made with standard vector iteration method applied to the entire structural model. [Copyright &y& Elsevier]

Abstract: Phenomenological models are employed into composite structural systems for simulating passive devices aimed at vibration mitigation and the Bouc-Wen one subsists as a significant example. In recent years, the control systems progress has moved toward a more efficient and adaptable semi-active technology. Therefore the existent numerical procedures, which proved effective for the passive implementation, are expected to comprise such features as well. This paper deals with a method of controlling in real time the hysteresis component in simulated semi-active control systems through the Bouc-Wen model. An introductive discussion on the theoretical formulation of the original settlement allows to focus on a way for tuning the parameters which can be managed for hysteresis regulation. Proper algorithms, embedded into the analytical formulation of the model, are subsequently selected for implementing the semi-active characteristic. Finally, straightforward dynamic applications on a plane oscillator system point out the general capability of the proposed approach by seismic response simulation and mitigation of the induced structural effects. [Copyright &y& Elsevier]

Abstract: Stability analysis is a crucial aspect of structural design, particularly for beam type structures. This paper addresses the development of a complementary-energy based (dual) stability criterion for the quasi-static analysis of three-dimensional framed structures modeled using the so-called geometrically exact (Reissner–Simo) beam theory. The criterion is derived from the well known primal stability criterion based on the condition of minimum total potential energy. This is accomplished by resorting to the Lagrangian multiplier method together with the Legendre transformation. Several numerical benchmark problems are analyzed. The analyses are carried out using two dual finite element models and their corresponding stability criteria, namely, the traditional two-node displacement/rotation-based model with the primal stability criterion, and a recently introduced equilibrium-based model with the proposed dual stability criterion. [Copyright &y& Elsevier]

Abstract: This paper introduces the numerical model analysis of evolutionary sections (AES) as a tool for the analysis of precast concrete sections constructed in several phases. Constitutive models including both concrete cracking and post-peak response of the materials were implemented. Likewise, the time-dependent behavior of the materials has been considered to model the sequential construction process. In order to validate the results obtained by the model, an experimental campaign (from the literature) was used. The comparison of the experimental results to those numerically obtained was satisfactory. The AES is already in use in several Spanish precast concrete factories for the optimization of bridges constructed with precast – prestressed concrete girders. [Copyright &y& Elsevier]

Abstract: In Reinforced Concrete structures, the concrete damage configuration as well as the crack pattern distribution depend directly on bonding, and its implementation for numerical analysis is still complicated. In this work, a new thermodynamical non linear bond model is introduced taking into account tangential bond deterioration and coupling between tangential slip and normal decohesion/penetration. For FEM implementation, the model (based on a stress–strain relationship) is supported by a non-width interface element. The calibrated material parameters are grouped in four sets: elastic behavior; tangential degradation; crack friction and confinement; and normal behavior. Finally, some numerical examples are presented in this paper. [Copyright &y& Elsevier]

Abstract: An element free Galerkin (EFG) based formulation for limit analysis of rigid-perfectly plastic plane strain problems is presented. In the paper it is demonstrated that volumetric locking and instability problems can be avoided by using a stabilized conforming nodal integration scheme. Furthermore, the stabilized EFG method described allows stable and accurate solutions to be obtained with minimal computational effort. The discrete kinematic formulation is cast in the form of a second-order cone problem, allowing efficient interior-point solvers to be used to obtain solutions. Finally, the performance of the stabilized EFG method is illustrated by considering several numerical examples. [Copyright &y& Elsevier]

Abstract: Gorman’s Superposition method is known as one of the most efficient methods to solve the eigenvalue problems of plates because of its excellent convergence rate. However, there are few published results available that provide sufficient information on its boundedness. Here we have considered the nature of convergence of the eigenvalues for rectangular plates with the following sets of boundary conditions, completely free, fully clamped and cantilever. This paper shows numerically, the boundedness of the Superposition method for undamped vibration problems of rectangular isotropic plates subjected to different boundary conditions. The Superposition method gives upper bound results for eigenvalues of plates if the building blocks used in the Superposition method are subjected to stiffer boundary conditions than those of the original system being modelled. In contrast, the Superposition method yields lower bound results if the boundary conditions of building blocks are more flexible than those of the original system. The results would be useful to estimate the maximum possible error if the other bound can be obtained by another method. [Copyright &y& Elsevier]