Search

Abstract A Boolean Finite Synchronous Dynamical System (BFDS, for short) consists of a finite number of objects that each maintains a boolean state, where after individually receiving state assignments, the objects update their state with respect to object-specific time-independent boolean functions synchronously in discrete time steps. The present paper studies the computational complexity of determining, given a boolean finite synchronous dynamical system, a configuration, which is a boolean vector representing the states of the objects, and a positive integer t , whether there exists another configuration from which the given configuration can be reached in t steps. It was previously shown that this problem, which we call the t -Predecessor Problem, is NP-complete even for t = 1 if the update function of an object is either the conjunction of arbitrary fan-in or the disjunction of arbitrary fan-in. This paper studies the computational complexity of the t -Predecessor Problem for a variety of sets of permissible update functions as well as for polynomially bounded t. It also studies the t -Garden-Of-Eden Problem, a variant of the t -Predecessor Problem that asks whether a configuration has a t -predecessor, which itself has no predecessor. The paper obtains complexity theoretical characterizations of all but one of these problems. [ABSTRACT FROM AUTHOR]

Avionics and air traffic management (ATM) systems are evolving with the introduction of progressively higher levels of automation, toward attaining the ambitious operational, technical, and safety enhancements required to sustain the present growth of global air traffic. This paper presents novel 4-Dimensional Trajectory (4DT) functionalities that are being developed for integration in ATM and avionics systems to support trajectory based operations (TBO). The 4DT planning process, which is the main focus of the paper, is supported by a custom multiobjective variant of state-of-the-art optimal control algorithms, incorporating various operational, economic, and environmental factors. Capitalizing on the higher theoretical accuracy offered by optimal control algorithms compared to other methods, a key feature of the proposed approach is the introduction of a postprocessing stage to ensure that the mathematically optimal trajectories are translated into a set of standardized 4DT descriptors, which can be flown by state-of-the-art automatic flight control systems. Additionally, to support air-ground 4DT intent negotiation and validation in the TBO context, the 4DT postprocessing ensures that optimal trajectories are synthetically described by a limited number of parameters, minimizing the bandwidth requirements imposed on airborne data links. Simulation-based verification activities addressing operational efficiency improvements and computational performance in the terminal area ATM context support the viability of the proposed 4DT planning functionality for online tactical TBO. [ABSTRACT FROM AUTHOR]

Highlights • The mathematical model of corrugated shells with special shapes is presented. • Effect of corrugation parameters on critical load is investigated. • Linear and nonlinear buckling analyses are conducted. • Critical load of corrugated shells is compared to smooth ones. • Specific range of corrugation parameters significantly increase the value of relative critical load. Abstract The problem of elastic stability of the shells with special shapes with corrugated middle surfaces under external pressure is debated in the presented paper. Solution of the problem is based on FEM study. Corrugated barrelled, pseudo-barrelled, and cylindrical shells of constant mass are considered. Geometrical modification of the middle surface geometry is based on sine wave along principal directions. Middle surface of the corrugated shells are described referring to differential geometry of surfaces by parametric functions in three-dimensional Euclidean space. Linear and nonlinear buckling analyses are conducted. Examples of buckling modes are presented, which differ significantly from those typical for shells of revolution with positive or zero Gaussian curvature. It is proven that corrugation may lead to serious increase or decrease of critical load for all types of presented shells. [ABSTRACT FROM AUTHOR]

In this paper, we study, from the numerical point of view, a dynamic problem involving a mixture of two viscoelastic solids. The mechanical problem is written as a system of two coupled partial differential equations. Its variational formulation is derived and an existence and uniqueness result, and an energy decay property, are recalled. Then, fully discrete approximations are introduced by using the classical finite element method and the implicit Euler scheme. A discrete stability property and a priori error estimates are shown, from which we deduce the linear convergence of the algorithm. Finally, some numerical simulations, including examples in one and two dimensions, are presented to show the accuracy of the approximation and the behaviour of the solution. [ABSTRACT FROM AUTHOR]

Damping through friction tends to be one of the most efficient methods to suppress damage to structures from earthquakes. Realizing robust structures is therefore highly dependent on designing for the dynamic forces of friction- damped structures and exploring their reliability against natural disasters. This paper presents a simplified matrix analysis algorithm for multi-storey friction- damped buildings. We have analyzed the behavior of friction- damped systems more accurately by modeling the master-slave degree of freedom of the joints. First, the formulation of the problem is discussed, and a condensed general equation is derived. Then, an end- to- end solution is proposed to find the responses of structures. The displacement response of each storey has been carried out in both condensed and non-condensed general equations, and the results clearly show the accuracy of the proposed method. The numerical analysis and the results of the simulation of various friction- damped structures depicts the proposed approach consists with the commercial finite element method and is applicable for the analysis various types of structures. It is noted that the acceleration and displacement responses of the structures investigated under the proposed method and the traditional finite element method are so consistent that only a 1.5% difference is observed. Moreover, as a result of the proper allocation of degrees of freedom during the analysis, this method yields a reduction in computational costs especially in large buildings. [ABSTRACT FROM AUTHOR]

In this paper, a combined numerical and experimental method, called Extended Load Confluence Algorithm, is presented to accurately predict the dynamic response of non-periodic structures when little or no information about the applied loads is available. This approach, which falls into the category of Shape Sensing methods, inputs limited experimental information acquired from sensors to a mapping algorithm that predicts the response at unmeasured locations. The proposed algorithm consists of three major cores: an experimental core for data acquisition, a numerical core based on Finite Element Method for modeling the structure, and a mapping algorithm that improves the numerical model based on a modal approach in the frequency domain. The robustness and precision of the proposed algorithm are verified through numerical and experimental examples. The results of this paper demonstrate that without a precise knowledge of the loads acting on the structure, the dynamic behavior of the system can be predicted in an effective and precise manner after just a few iterations. [ABSTRACT FROM AUTHOR]

Blade is one of the core components of turbine machinery. The reliability of blade is directly related to the normal operation of plant unit. However, with the increase of blade length and flow rate, non-linear effects such as finite deformation must be considered in strength computation to guarantee enough accuracy. Parallel computation is adopted to improve the efficiency of classical nonlinear finite element method and shorten the blade design period. So it is of extraordinary importance for engineering practice. In this paper, the dynamic partial differential equations and the finite element method forms for turbine blades under centrifugal load and flow load are given firstly. Then, according to the characteristics of turbine blade model, the classical method is optimized based on central processing unit + graphics processing unit heterogeneous parallel computation. Finally, the numerical experiment validations are performed. The computation speed of the algorithm proposed in this paper is compared with the speed of ANSYS. For the rectangle plate model with mesh number of 10 k to 4000 k, a maximum speed-up of 4.31 can be obtained. For the real blade-rim model with mesh number of 500 k, the speed-up of 4.54 times can be obtained. [ABSTRACT FROM AUTHOR]

This paper is devoted to create new exact and numerical solutions of the generalized Korteweg-de Vries (GKdV) equation with ansatz method and Galerkin finite element method based on cubic B-splines over finite elements. Propagation of single solitary wave is investigated to show the efficiency and applicability of the proposed methods. The performance of the numerical algorithm is proved by computing L2 and L1 error norms. Also, three invariants I1, I2, and I3 have been calculated to determine the conservation properties of the presented algorithm. The obtained numerical solutions are compared with some earlier studies for similar parameters. This comparison clearly shows that the obtained results are better than some earlier results and they are found to be in good agreement with exact solutions. Additionally, a linear stability analysis based on Von Neumann's theory is surveyed and indicated that our method is unconditionally stable. [ABSTRACT FROM AUTHOR]

This paper aims to obtain exact and numerical solutions of the nonlinear Benjamin Bona Mahony-Burgers (BBM-Burgers) equation. Here, we propose the modified Kudryashov method for getting the exact traveling wave solutions of BBM-Burgers equation and a septic B-spline collocation finite element method for numerical investigations. The numerical method is validated by studying solitary wave motion. Linear stability analysis of the numerical scheme is done with Fourier method based on von-Neumann theory. To show suitability and robustness of the new numerical algorithm, error norms L2, L∞ and three invariants I1, I2 and I3 are calculated and obtained results are given both numerically and graphically. The obtained results state that our exact and numerical schemes ensure evident and they are penetrative mathematical instruments for solving nonlinear evolution equation. [ABSTRACT FROM AUTHOR]

An earlier paper proved the convergence of a variable stepsize Bregman operator splitting algorithm (BOSVS) for minimizing ø(Bu) + H(u), where H and ø are convex functions, and ø is possibly nonsmooth. The algorithm was shown to be relatively efficient when applied to partially parallel magnetic resonance image reconstruction problems. In this paper, the convergence rate of BOSVS is analyzed. When H(u) = ‖Au - f ‖2, where A is a matrix, it is shown that for an ergodic approximation uk obtained by averaging k BOSVS iterates, the error in the objective value ø(Buk)+H(uk) is O(1/k). When the optimization problem has a unique solution u*, we obtain the estimate ‖uk-u*‖ = O(1/ √ k). The theoretical analysis is compared to observed convergence rates for partially parallel magnetic resonance image reconstruction problems where A is a large dense ill-conditioned matrix. [ABSTRACT FROM AUTHOR]

In this paper, we consider the effect of adding a coarse mesh correction to the two‐grid algorithm for the mixed Navier–Stokes/Darcy model. The method yields both L2 and H1 optimal velocity and piezometric head approximations and an L2 optimal pressure approximation. The method involves solving one small, coupled, nonlinear coarse mesh problem, two independent subproblems (linear Navier–Stokes equation and Darcy equation) on the fine mesh, and a correction problem on the coarse mesh. Theoretical analysis and numerical tests are done to indicate the significance of this method. [ABSTRACT FROM AUTHOR]

This paper presents a stable numerical algorithm for the Brinkman equations by using weak Galerkin (WG) finite element methods. The Brinkman equations can be viewed mathematically as a combination of the Stokes and Darcy equations which model fluid flow in a multi-physics environment, such as flow in complex porous media with a permeability coefficient highly varying in the simulation domain. In such applications, the flow is dominated by Darcy in some regions and by Stokes in others. It is well known that the usual Stokes stable elements do not work well for Darcy flow and vice versa. The challenge of this study is on the design of numerical schemes which are stable for both the Stokes and the Darcy equations. This paper shows that the WG finite element method is capable of meeting this challenge by providing a numerical scheme that is stable and accurate for both Darcy and the Stokes dominated flows. Error estimates of optimal order are established for the corresponding WG finite element solutions. The paper also presents some numerical experiments that demonstrate the robustness, reliability, flexibility and accuracy of the WG method for the Brinkman equations. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of Nanjing University of Aeronautics & Astronautics is the property of Editorial Department of Journal of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, an on-going research effort aimed at detecting and localising damage in plate-like structures by using mode shape curvature-based damage detection algorithms is described. Two alternative damage indexes are examined. The first one uses exclusively mode shape curvature data from the damaged structure. This method was originally developed for beam-like structures. In this paper, the method is generalised to plate-like structures that are characterised by two-dimensional mode shape curvature. To examine limitations of the method, several sets of simulated data are applied and damage detection results are compared to the damage identification method that requires mode shape information from both the undamaged and the damaged states of the structure. The modal frequencies and the corresponding mode shapes for the first 15 modes of a plate are obtained via finite element models. Simulated test cases include damage of various levels of severity. In order to ascertain the sensitivity of the proposed method to noisy experimental data, numerical mode shapes are corrupted with different levels of random noise. [ABSTRACT FROM AUTHOR]

Temperature and thermal stress responses of an improved TTSV structure under the impact of hotspots are numerically analyzed in this paper. A Fin structure is added to the circular TTSV to strengthen the effect of thermo-mechanical mitigation. The nonlinear finite element method (N-FEM) is presented to obtain the coupled thermal and mechanical fields. Running time of the N-FEM algorithm is compared with that of commercial software to indicate its e±ciency. The model of state-of-the-art 3D Dynamic Random Access Memory (DRAM) is adopted in our simulation. Besides the single-layer TTSV and TTSV array, the extended case of multi-layer TTSVs is also investigated. To take into consideration the nonlinear effects, the temperature dependent results for the issues of hotspot alignment and liner materials selection are provided, both of which are compared with the corresponding temperature independent results. This paper is aimed to provide some practical guidance to the design of TTSV for effective thermo-mechanical management. [ABSTRACT FROM AUTHOR]

Abstract: The system of equations arising in finite element simulations of components made of ferroelectroelastic materials is non-linear if the loading is sufficiently high. The Newton–Raphson method represents a widely used iterative technique to solve this system of non-linear equations. However, if the scalar potential formulation is utilised, convergence difficulties may occur. This circumstance can be primarily attributed to the specific form of the non-linear response of typical ferroelectroelastic materials being subjected to electrical loading. The present paper is devoted to modifications of the Newton–Raphson method, which are capable of improving the convergence behaviour experienced in the finite element iteration. We extend an existing modification to the fully coupled, ferroelectroelastic case. Additionally, a new modification of the Newton–Raphson method is proposed. This method applies an iteration algorithm, which is virtually equivalent to the iteration algorithm of the unmodified Newton–Raphson method combined with the vector potential formulation. An important feature of both modifications is that they are applied on the integration point level. Therefore, the global non-linear finite element iteration scheme remains unchanged. Finally, the practicability of the modifications discussed in the paper is shown in a numerical example. [Copyright &y& Elsevier]

Abstract: High strength thin-walled rectangular concrete-filled steel tubular (CFST) slender beam-columns under eccentric loading may undergo local and overall buckling. The modeling of the interaction between local and overall buckling is highly complicated. There is relatively little numerical study on the interaction buckling of high strength thin-walled rectangular CFST slender beam-columns. This paper presents a new numerical model for simulating the nonlinear inelastic behavior of uniaxially loaded high strength thin-walled rectangular CFST slender beam-columns with local buckling effects. The cross-section strengths of CFST beam-columns are modeled using the fiber element method. The progressive local and post-local buckling of thin steel tube walls under stress gradients is simulated by gradually redistributing normal stresses within the steel tube walls. New efficient Müller''s method algorithms are developed to iterate the neutral axis depth in the cross-sectional analysis and to adjust the curvature at the columns ends in the axial load–moment interaction strength analysis of a slender beam-column to satisfy equilibrium conditions. Analysis procedures for determining the load–deflection and axial load–moment interaction curves for high strength thin-walled rectangular CFST slender beam-columns incorporating progressive local bucking and initial geometric imperfections are presented. The new numerical model developed is shown to be efficient for predicting axial load–deflection and axial load–moment interaction curves for high strength thin-walled rectangular CFST slender beam-columns. The verification of the numerical model and parametric studies is given in a companion paper. [Copyright &y& Elsevier]

Abstract: This paper is the first in this series to develop a numerical homogenization method for heterogeneous media and integrate it with goal-oriented finite element mesh adaptivity. We describe the physical application, Step and Flash Imprint Lithography, in brief and present the mathematical ideas and numerical verification. The method requires the Moore–Penrose pseudoinverse of element stiffness matrices. Algorithms for efficiently computing the pseudoinverse of sparse matrices will be presented in the second paper. The purpose of numerical homogenization is to reduce the number of degrees of freedom, find locally optimal effective material properties, and perform goal-oriented mesh refinement. Traditionally, a finite element mesh is designed after obtaining material properties in different regions. The mesh has to resolve material discontinuities and rapid variations in the solution. In our approach, however, we generate a sequence of coarse meshes (possibly 1-irregular), and homogenize material properties on each coarse mesh element using a locally posed constrained convex quadratic optimization problem. This upscaling is done using the Moore–Penrose pseudoinverse of the linearized fine-scale element stiffness matrices, and a material-independent interpolation operator. Numerical verification is done using a two dimensional conductivity problem with known analytical limit. Finally, we present results for two and three dimensional geometries. The results show that this method uses orders of magnitude fewer degrees of freedom to give fast and approximate solutions of the original fine-scale problem. [Copyright &y& Elsevier]

A concave finite element-boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA) is presented for scattering by a large body with nonuniform deep cavities. Different from the conventional FE-BI-MLFMA, the boundary integral equation in this concave FE-BI-MLFMA is established on a concave surface to reduce the region of the finite element method (FEM), which can significantly reduce the dispersion error from the FEM and improve the efficiency of FE-BI-MLFMA especially for nonuniform cavities. To eliminate the problem of slow convergence caused by concave surface, an efficient preconditioner based on the sparse approximate inverse (SAI) is constructed in this paper. Numerical performance of the constructed preconditioner based on the SAI is investigated in detail. Numerical experiments demonstrate the accuracy and efficiency of this SAI preconditioned concave FE-BI-MLFMA for nonuniform deep and large cavites. This SAI preconditioned concave FE-BI-MLFMA is parallelized to further improve its capability in this paper. An extremely big and deep nonuniform cavity has been calculated, demonstrating the great capability of this parallel concave FE-BI-MLFMA. [ABSTRACT FROM PUBLISHER]

A hybrid h- and p-Type multiplicative Schwarz (h-p-MUS) preconditioned algorithm is proposed to improve efficiency of higher-order finite element-boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA) for 3D scattering in this paper. An h-p-MUS precondtioner is first constructed for the FEM matrix obtained by using vector higher-order hierarchical basis functions. Numerical experiments show that this preconditioner can offer a better efficiency both in CPU time and memory requirement than the h-MUS and the p-MUS preconditioners. Then this h-p-MUS preconditioner for the FEM matrix is applied to different algorithms of FE-BI-MLMFA. Analysis and Numerical results show that the h-p-MUS preconditioned conventional algorithm (h-p-MUS-CA) has a better efficiency over other h-p-MUS preconditioned algorithms. A variety of numerical experiments are performed for large objects in this paper, demonstrating that this h-p-MUS-CA exhibits superior efficiency in the CPU time and memory, and greatly improves the capability of the higher-order FE-BI-MLFMA. [ABSTRACT FROM PUBLISHER]

This paper which depended on the foundation of back strip method has established mathematic model to simulate stratum burial history, which considered the computation of stratum skeleton depth based on max depth and the equation-depth point on the procedure to recover stratum by stripping each layer, and put forward the enhanced restoration method taking layers group as studying object. Finally, the method has been applied to build the computer model and program automatic back strip algorithm successfully. Experiments have proved that the method is accurate, applicable, and extensible under the conditions of various complex strata. [ABSTRACT FROM AUTHOR]

The emerging of depth-camera technology is paving the way for a variety of new applications and it is believed that plane detection is one of them. In fact, planes are common in man-made living structures, thus their accurate detection can benefit many visual-based applications. The use of depth information allows detecting planes characterized by complex pattern and texture, where the texture-based plane detection algorithms usually fail. In this paper, we propose a robust depth-driven plane detection (DPD) algorithm which consists of two parts: the growing-based plane detection and a two-stage refinement. The proposed approach starts from the seed patch with the highest planarity and uses the estimated equation of the growing plane and a dynamic threshold function to steer the growing process. Aided with this mechanism, each seed patch can grow to its maximum extent, and then the next seed patch starts to grow. This process is iteratively repeated so as to detect all the planes. Moreover, the refinement is proposed to tackle two common problems suffered by growing-based approaches, the over-growing problem, and the under-growing problem. Validated by extensive experiments, the proposed DPD algorithm is able to accurately detect planes and robust to various testing conditions. In terms of applications, it can be used as the pre-processing step for a variety of applications, such as, planar object recognition, super-resolution of the time-of-flight depth images with intrinsically low resolution. [ABSTRACT FROM AUTHOR]

Frame rate up-conversion (FRUC) is a technology for generating a higher frame rate video from one with a lower frame rate. The multi-view plus depth map (MVD) system has been recently considered a promising solution for three-dimensional video systems. Accordingly, an FRUC efficient solution for the MVD system is greatly needed. In this paper, we thus propose an FRUC approach that considers the MVD system characteristics. It divides a frame into multiple layers using a depth map, and it reconstructs occluded regions using neighboring views and depth map information. With reconstructed information, it accurately performs motion estimation when a region occlusion occurs. Experimental results demonstrated that the proposed method significantly improved the quality of interpolated frames, and it can effectively complement other conventional FRUC approaches. [ABSTRACT FROM AUTHOR]

• An automatic algorithm for generating polyhedral meshes was systematically developed. • Hexahedral elements near the given STL surface were categorized into polyhedral volume topologies based on the MC algorithm. • Topology ambiguities of the MC algorithm were effectively resolved to provide an appropriate mesh for complex geometry. • The effectiveness was demonstrated through numerical analysis using the smoothed finite element method. Hexahedral meshes that exhibit the superiority in terms of solution accuracy and convergence rate are preferred to other types of meshes in the finite element analysis. However, the construction of the hexahedral meshes for complex geometries is still considered troublesome due to their poor geometric adaptability. This paper presents an efficient grid-based scheme to automatically generate polyhedral meshes including the hexahedral elements, and thus to provide hexahedral-dominant meshes for three-dimensional geometry with complex shapes. On the basis of the marching cube algorithm with a background grid composed of a regular arrangement of cubes, surface topologies for the background cubes are defined to represent the three-dimensional boundaries of a given domain. Then, in order to generate a three-dimensional finite element mesh, the surface topologies of the marching cube algorithm are systematically expanded to polyhedral volume topologies. Meanwhile, a topology ambiguity problem inherent in the marching cube algorithm is effectively resolved to generate an appropriate polyhedral mesh even for an arbitrary complex geometry. Several examples including biostructure modeling demonstrate that the proposed mesh generation scheme can easily discretize complex three-dimensional domains with hexahedral-dominant meshes, which are composed of the polyhedral elements near the domain boundaries and the hexahedral elements that come from the background cubes inside the domains. Furthermore, to show the applicability and effectiveness of polyhedral meshes in the finite element analysis, some structural analyses are performed using the smoothed finite element method that can be straightforwardly adapted to polyhedral elements of arbitrary shape. [ABSTRACT FROM AUTHOR]

This paper presents an efficient and accurate numerical technique based upon the scaled boundary finite element method for the analysis of two-dimensional, linear, second-order, boundary value problems with a domain completely described by a circular defining curve. The scaled boundary finite element formulation is established in a general framework allowing single-field and multi-field problems, bounded and unbounded bodies, distributed body source, and general boundary conditions to be treated in a unified fashion. The conventional polar coordinates together with a properly selected scaling center are utilized to achieve the exact description of the circular defining curve, exact geometry of the domain, and exact spatial differential operators. Standard finite element shape functions are employed in the discretization of both trial and test functions in the circumferential direction and the resulting eigenproblem is solved by a selected efficient algorithm. The computational performance of the implemented procedure is then fully investigated for various scenarios to demonstrate the accuracy in comparison with standard linear elements. [ABSTRACT FROM AUTHOR]

Highlights • Analytical and numerical study results of Y-type self-centering eccentrically braced frame (SCEBF-Y) are presented. • Post-gap opening stiffness of SCEBF-Y depend on PT cable properties. • Finite element model of the SCEBF-Y is verified with analytical and experimental test data. • Post-gap-opening stiffness and equivalent yield strength of SCEBF-Y is adjustable. Abstract This paper presents the results from both analytical and numerical study of a Y-type self-centering eccentrically braced frame (SCEBF-Y) subjected to earthquake loading. In this study, a three-story SCEBF-Y frame building has been designed along with a three-story conventional D-type eccentrically braced frame (EBF-D) for a site located in Los Angeles, California. The analytical results reveal that initial stiffness and post-gap opening stiffness of SCEBF-Y depend on brace section properties and PT strand properties respectively. The finite element model of the SCEBF-Y frame has been verified with analytical results as well as experimental test data from a similar one-story one-bay D-type self-centering eccentrically braced frame specimen. The study results demonstrate that SCEBF-Y frame can be designed to the same strength and stiffness as conventional EBFs while it can re-center itself after design basis earthquake (DBE). In the SCEBF-Y system, replaceable energy dissipation devices termed RHD devices are installed to dissipate seismic energy, and the primary structural members are intended to remain elastic under the DBE earthquakes. The nonlinear time history analysis results for the prototype SCEBF-Y buildings show that not only the SCEBF-Y building has negligible residual drift, but also it has its major damage confined to replaceable energy dissipation devices. In the parametric study, three different levels of PT strands' initial stress along with different PT cable length has been considered and the parametric study suggests that by properly choosing cable length and cable's initial post-tensioning stress level, key structural system properties such as the post-gap-opening stiffness and the equivalent yield strength of SCEBF-Y can be adjusted accordingly. [ABSTRACT FROM AUTHOR]

Highlights • Partially bonded (PB)-FREBs can retain the same advantages of unbonded-FREBs. • No relative slip occurs under low-rate lateral displacements in a PB-bearing. • The influence of static rotations on the hysteresis loops of PB-FREBs has been investigated. • A new copolymer employed in the bearings, and its response was examined experimentally. • The PB-application of FREBs as seismic isolators/bridge bearings is feasible. Abstract There are two classical types of application for fiber reinforced elastomeric bearings (FREB), namely, "bonded (B)" and "unbonded (UB)" applications. Although the UB-application results in improved seismic isolation efficiency due to rollover deformations, UB-FREB are not capable of transferring tensile forces, and may experience slip under certain loading conditions. As such, a new application type called Partially Bonded (PB) has been introduced to overcome these two limitations. A PB-FREB is achieved by partially bonding the top and bottom surfaces of the bearing to its contact supports. This paper presents the results of a comparative experimental study between UB-FREB and PB-FREB. Heat accelerated deterioration tests based on Arrhenius law was also conducted on the PB-FREB. Additionally, the low-temperature horizontal response of the PB-FREB was investigated. Results show that the displacement characteristics and damping values, long-term performance, and low-temperature response of the PB-FREB investigated in this study comply with current standard requirements. [ABSTRACT FROM AUTHOR]

Highlights • Formulation of random field theory for the elastic properties of old concrete dams. • Evaluation of the correlation length effect on the frequency response dispersion and inter-correlation among vibrational modes. • First-time analysis of six arch dams in the context of a "dam class". • Proposal of an experimental design using a dam frequency analytical model. • Proposal of an iterative random field-based system identification technique for arch dams. Abstract Determining vibration characteristics constitutes the first step in calibrating the finite element model in an old arch dam analysis. These characteristics provide the required information for a proper dynamic analysis of the coupled fluid-structure system used for risk assessment purposes. This paper investigates the detailed vibration characteristics of arch dams with heterogeneous material by applying random field theory. A group of six double-curvature arch dams are studied herein. The spatial material distribution using different correlation lengths is compared, and the response dispersion is quantified. An experimental meta-model design is developed for a specific class of dams, with an approximate analytical solution being derived. Ultimately, an iterative, random field-based system identification technique is proposed for old arch dams. [ABSTRACT FROM AUTHOR]

Highlights • Investigated seismic performance of seismically isolated and non-isolated buildings. • Buildings designed using the minimum ASCE 7 criteria and enhanced design criteria. • Calculated annual rate of exceeding drift, residual drift and floor acceleration. • Probabilities of exceeding response limits that relate to damage are computed. Abstract Recent studies have shown that seismically isolated buildings designed by the minimum criteria of ASCE/SEI 7 may have unacceptable probabilities of collapse in the MCE R. Acceptable probabilities of collapse in the MCE R are achieved when the isolation system displacement capacity and the strength of the superstructure are increased. The same studies have shown that conventional buildings designed by the minimum criteria of ASCE/SEI 7 have acceptable probabilities of collapse in the MCE R , and that the collapse probabilities may be much lower than those of minimally designed seismically isolated buildings and may even be lower than those of seismically isolated buildings designed by enhanced collapse performance criteria. This paper investigates what isolated buildings offer in terms of performance criteria other than collapse performance. Based on a probabilistic approach, mean annual frequencies of exceedance of story drift, residual story drift and floor acceleration are computed for a number of isolated and non-isolated buildings that meet the minimum criteria of ASCE/SEI 7 and other enhanced criteria. Based on the mean annual frequencies, probabilities of exceeding response limits that relate to damage are computed for a lifetime of 50 years. It is shown that seismically isolated buildings designed by the minimum or enhanced criteria generally have lower probabilities to develop damage or to be in need of demolishing in 50 years of lifetime than any minimally designed non-isolated building. [ABSTRACT FROM AUTHOR]

Highlights • For precast concrete bridge decks, HSS-formed shear pockets should be designed to ensure ductile behavior. • Concrete strength and shear pocket dimensions are key parameters in the design of shear pocket connections. • Using HSS in forming shear pockets is an efficient way for confining pocket concrete/grout and controlling splitting cracks. • FEA can be utilized in modeling the predicting the behavior of HSS-formed shear pockets. Abstract Current bridge design codes do not provide adequate criteria/procedures for designing full-depth precast concrete deck systems, especially those with shear pocket connections. Instead, these systems and their connections are designed on a case-by-case basis by either conducting necessary testing or adopting the design criteria/procedures developed primarily for cast-in-place concrete deck systems. Shear pocket connections formed using steel hollow structural sections (HSS) provide a promising solution to connecting precast concrete deck panels to the supporting girders due to their superior structural performance and simplicity of panel fabrication. The main objective of this paper is to develop criteria/procedures for designing HSS formed shear pocket connections in full-depth precast concrete deck systems. These procedures will assist bridge designers in selecting pocket dimensions, HSS thickness, pocket anchorage and reinforcement necessary to maximize the connection capacity while allowing adequate construction tolerance. Experimental investigation (push-off testing) and finite element analysis (FEA) were performed to validate the developed design criteria/procedures. Analysis and testing results indicated that the developed design criteria/procedures for HSS formed shear pocket connections are satisfactory. [ABSTRACT FROM AUTHOR]

Abstract Assuming specific behavior models, the variety of design codes currently used for the design of concrete beams inevitably results in different solutions, ensuring service during the whole expected lifetime with a maximum functional quality and safety. However, from a sustainable design perspective, such differences may have remarkable environmental impacts. This paper analyses if the approach of the newest design code, i.e., the Model Code, leads to a reduction in resource consumption and greenhouse gas emissions (GHG) over the life-cycle of concrete beams. To do so, a comparative analysis of the environmental impact of concrete beams was carried out depending on the reference code used for its design (i.e., EHE-08 or Model Code). The results show that the reduction of reinforcing steel is a basic objective to minimize the life cycle environmental impacts of concrete beams. Every country may have its own design codes and, thus, the reinforcing steel use can vary for structures subjected to the same loads and with equivalent structural reliability. Hence, regulations play a key role in the sustainability of construction assets. Conclusions depend on the beam length (L) and height (h) and characteristic compressive strength (f ck). For short beams (4 m), the greater the h , the greater the reinforcement difference between the two codes. With regard to beams of 8 m, these differences can lead to varying steel and GHG savings, e.g., up to 5.0% with MC-2010 (h = 0.6 m and f ck ≤ 35 MPa), almost 40% with EHE – 08 (h = 1.0 m and 35 MPa < f ck ≤ 50 MPa) and more than 30% with EHE–08 (h = 0.6 m and 35 MPa < f ck ≤ 50 MPa). For long beams (L = 12.0 m), steel consumption is 0.3–19% lower when the beam is designed with EHE-08, and this difference decreases as f ck increases. [ABSTRACT FROM AUTHOR]

Highlights • Developed a moment connection for a progressive collapse resistant precast frame. • Experimental destructive testing was performed to obtain moment-rotation behavior. • 2 configurations were tested: higher strength with lower ductility and vice versa. • Experimental results were input into a system-level computational model. • Models show that both tested connections prevent collapse for a column removal. Abstract This paper documents the experimental development of a new spandrel-to-column moment connection detail for progressive collapse resistance in precast concrete building frames. This study focuses on a 10-story prototype precast concrete frame building with perimeter special moment frames (SMF) that are subjected to a ground-floor column removal. The experimental subassembly represents a spandrel-to-column connection on the perimeter SMF near the middle of the building face (i.e. not at the corners). The connection is non-emulative and utilizes unbonded high-strength steel post-tensioning (PT) bars which pass through ducts in the column and are anchored to the spandrels via bearing plates. The proposed design strives for construction simplicity, avoids field welding and/or grouting, and maximizes ductility by allowing the high strength steel bars to act as structural "fuses" when yielding. A full-scale quasi-static pushdown test is performed on two variants of the proposed connection: one with higher moment-rotation capacity and limited ductility, and another with lower capacity and higher ductility. The results show that the connection can reliably achieve its design yield capacity, performs well under service level demands, and can achieve moderate-to-high ductility. The experimental results are then applied to a system-level computational model of the prototype building frame under a column removal scenario. The results of a nonlinear dynamic analysis demonstrate that the system can arrest progressive collapse in the event of a single column loss scenario when either variant of the proposed connection is considered. [ABSTRACT FROM AUTHOR]

Highlights • DMF for the vertical pseudo- and absolute-acceleration response spectra based on 3198 earthquake records. • Effects of earthquake magnitude, epicenter distance, hypocenter depth, site condition, and PGA on the vertical spectral DMF. • The probabilistic properties of the vertical spectral DMF simulated by the normal distribution model. • Highly accurate models for the mean and the standard deviation of the vertical spectral DMF. Abstract This paper aims to establish a regional (Japanese) damping modification model for scaling the 5%-damped vertical seismic response spectra to other damping ratios. In doing so, 3198 strong vertical ground motion (VGM) records are selected from the Japanese seismic database, and their linear elastic response spectra are computed by the Newmark- β algorithm. Taking the 5%-damped vertical response spectra as benchmarks, the vertical spectral damping modification factors (DMFV) for ζ (damping ratio) = 0.5%, 1%, 2%, 3%, 4%, 6%, 7%, 8%, 9%, 10%, 12.5%, 15%, 17.5%, 20%, 25%, 30%, 35% and 40% are calculated. For structural design purpose, the DMFV s of both the vertical pseudo acceleration response spectra and the vertical absolute acceleration response spectra are calculated. The DMFV spectra have their peaks (for ζ < 5%) or valleys (for ζ > 5%) at T = 0.12 s (here T indicates spectral period), and their values get farther away from unity as earthquake magnitude or VGM epicenter distance increases. The effect of earthquake hypocenter depth, local site condition (represented by Vs30) and peak ground acceleration on DMFV generally shows no pattern. For each ζ , the mean DMFV -lg T curves are simulated by highly accurate piecewise functions. Moreover, it is revealed that the normal distribution model is feasible for representing the probabilistic properties of DMFV , especially in the short-to-medium period region where the skewness of the DMFV distribution is not quite pronounced. The standard deviations of DMFV are modeled by piecewise functions as well, yet it is emphasized that the variation of a damping-scaled spectral ordinate is jointly controlled by the probabilistic properties of DMFV and the uncertainties of the 5%-damped spectral ordinates. [ABSTRACT FROM AUTHOR]

Highlights • The rotation required by structural elements to perform a plastic design is evaluated. • The proposed approach allows to the failure mode of the structure to be predicted. • Information on the more efficient configuration of additional bolts are provided. • Theoretical results are applied to rack joints tested in an experimental campaign. Abstract The structural behaviour of beam-column joints plays a critical role in the seismic response of frame structures. In the case of steel rack systems, uprights (columns) are usually 3rd or 4th class open thin-walled cold-formed steel members according to Eurocode 3, as such, local buckling occurs before the plastic moment resistance (in the case of the 3rd class) or yield stress (4th class) is achieved. Beams are usually 1st or 2nd class, so they can form a plastic hinge with the rotation capacity required from plastic analysis without reduction of the resistance (1st class) or with a limitation on the rotation capacity due to local buckling (2nd class). For this reason, only beams and connections, which can be easily equipped with additional bolts to increase their structural performance, can provide a post-elastic behaviour with energy dissipation. This paper presents and develops a method capable of evaluating the rotational capacity, or ductility, required by beams and connections to perform a plastic design. The proposed approach allows for the failure mode of the structure to be predicted starting from mechanical properties of structural members, and it is valid for both service and seismic loads. The analytical method could be applied to different structural systems and materials; in the present work it is presented with reference to industrial pallet racks. Theoretical assessment herein of the required plastic rotation for beams and connections provides useful information for bolted connection design to increase capacity of the racks with minimal additional cost. [ABSTRACT FROM AUTHOR]

Highlights • Descriptions of the experimental tests of two large-size RC containment specimens. • Descriptions of CSMM-based shell element for simulation of RC shell-type structures. • Nonlinear FE analysis of the RC containments using CSMM-based shell element. • Discussions and comparisons of experimental outcomes and analytical results. Abstract The nuclear containment structure is one of the most important infrastructure systems ensuring the safety of a nuclear power plant. The structural behavior of a cylindrical containment structure made of reinforced concrete (RC) with large dimensions and numerous rebars is complex and difficult to predict. The complex behavior of the RC containment structure has been investigated in an international collaboration project between the National Center for Research on Earthquake Engineering (NCREE) in Taipei, Taiwan and the University of Houston (UH), Houston, Texas. At NCREE two 1/13 scaled cylindrical RC containment specimens were tested under reversed cyclic loads [1]. At UH, a finite element simulation of the two tested specimens was developed using a finite element analysis (FEA) program SCS [2]. In the program, a new shell element, the so-called CSMM-based shell element, was developed based on the Cyclic Softened Membrane Model [3] and the formulation of an 8-node Serendipity curved shell element [4] with a multi-layer approach [5]. The UH simulated seismic behavior was close to the NCREE experimental results. This paper presents the theoretical development of the FEA program SCS and the comparisons of its predictions with the experimental structural behavior of the two RC containment specimens. This simulation model and the FEA program are excellent tools to develop effective performance-based design provisions. [ABSTRACT FROM AUTHOR]

Highlights • A new type of anti-tension equipment used in isolation building is proposed. • The equipment with double column and steel brace may be more convenient and practicable after analyzed by FEA in detail. • A scale model was tested, test results have good agreement with that of FEA. Abstract When the height-width ratio of high-rise isolation buildings is excessively large, elastomeric isolators may suffer from tension in severe earthquakes. Because of the tension limits of isolators, an anti-tension equipment must be added to such buildings for safety. In this paper, a new type of anti-tension equipment is proposed. It consists of two steel frames: one is shape "□", and the other shape "∏", which are perpendicularly connected together. There are diagonal braces and short columns made of rebars on the top of shape "□" steel frame. A small-scale model was first tested, and then a series of parametric study were performed using FEA. In the FEA, the nonlinearity of material and geometry were considered. The yielding and ultimate loads, as well as the stress distribution of the equipment, were investigated for the vertical tensile load condition, considering different shapes of structure, steel materials, and constraint conditions. FEA results match well with the test results. Furthermore, FEA results show that the anti-tension equipment with double column is more effective than that with single column, especially in the case of eccentric tension state. The containment of the bar by the concrete is effective in increasing the ultimate load in the condition of eccentric tension state. Stiffening strips added to the vertical steel arms can significantly increase the ultimate capacity of the equipment. Mostly, as the state of eccentricity increases, the ultimate capacity of the anti-tension equipment decreases. [ABSTRACT FROM AUTHOR]

Highlights • Eight slender RC columns were strengthened with steel tube and sandwiched concrete jackets. • The experimental results showed that the mechanical properties of the RC columns were enhanced. • An accurate FE model was developed to simulate the response of the retrofitted columns. • A modified load-bearing capacity prediction model was proposed. Abstract Steel tube and sandwiched concrete jacketing has been proved to be effective in improving the load-bearing capacity and ductility of deficient reinforced concrete (RC) stub columns. However, the effectiveness of this technique for slender RC columns remains to be validated due to instability problems. In this study, nine slender specimens, including one reference column and eight retrofitted columns, were tested under axial compression. The experimental results showed that the load-bearing capacity, stiffness and ductility of the slender RC square columns were significantly enhanced. The load enhancement was not only attributed to section enlargement, but also due to the confinement provided by the steel tube. Based on the experimental results, a finite element (FE) model was developed to simulate the structural response of the retrofitted slender columns under axial load. The FE results demonstrated that the sandwiched concrete shared a higher load than the steel tube for the cross-section of this paper, justifying the use of "steel tube and sandwiched concrete jacketing". Moreover, the confinement effects on the load-bearing capacity of the RC part and the sandwiched concrete part were quantitatively analyzed. A modified formula was subsequently proposed to predict the load-bearing capacity of the retrofitted columns, the results of which agreed well with the experimental and FE results. [ABSTRACT FROM AUTHOR]

Highlights • Efficient static and dynamic analysis of jointed Euler-Bernoulli beams. • Step changes in material and cross-section. • Internal rotational, internal translational and external translational springs. • Free and forced vibration of jointed Euler-Bernoulli damped beam. • Closed-form expressions of the four integration constants. Abstract Many engineering systems can be modelled as an assembly of beams with different material properties and cross-sections jointed at their edges. This paper presents an approach to analyse jointed Euler-Bernoulli (EB) beams with step changes in material and cross-section under static and dynamic loads. The standard approaches to tackle this type of problem are not completely satisfactory in terms of: (i) computational efficiency in dealing with step changes in material and cross-section, when the continuity conditions must be enforced with auxiliary equations (classic approach) or when a denser mesh has to be used at the discontinuity interfaces (Finite Element Method); (ii) taking into account efficiently internal and external springs at the discontinuity interfaces; (iii) numerical errors in the evaluation of high-order modes for jointed beams. An approach is proposed to overcome these limitations. This approach tackles an assembly of n piecewise homogenous EB beams jointed at their edges using the generalised functions to obtain a single expression of the solution which depends on the 4 integration constants associated with the boundary conditions. Closed-form expressions of the 4 constants are provided. Further, in the presence of internal or external springs, additional constants representing the discontinuities have to be taken into account. The latter are computed by considering one additional condition for each discontinuity. The proposed approach is particularized for the static and dynamic analysis (modal analysis and forced vibration analysis). The feasibility of the proposed approach is shown with two numerical applications. [ABSTRACT FROM AUTHOR]

Highlights • Influence of the earthquake duration on damping reduction factor (DRF). • The displacement spectrum is obtained in stochastic way by mean of peak theory. • New DRF formulation considering effective duration, soil type, damping ratio, natural period. Abstract Damping Reduction Factor plays a key role in scientific literature and Technical Codes, but till now existing formulations present differences and inconsistences probably because obtained by integration of real recorded events, thus sensible to specific used data. This paper investigates the relation between damping reduction factor and earthquake duration by means of random vibration theory. A stochastic process, that is non-stationary and filtered, is used to model a seismic event. The modulation function is suitably chosen to describe earthquakes characterized by different durations. The stochastic process peak theory allows to calculate damping reduction factor after the definition of the probabilistic response of a simple linear visco-elastic oscillator. The variability with seismic duration for different soil conditions and damping ratios is investigated. The study points out that damping reduction factor is more sensitive to seismic duration in the range of high period and on rigid soil with respect to other conditions. The results show that, if damping ratio or effective duration values are increased, the damping reduction factor value diminishes. [ABSTRACT FROM AUTHOR]

Highlights • Fast 1D nonlinear dynamic model is validated to predict façade response. • External cladding systems influence stiffness and strength of high-rise structures. • Sensitivity to the façade typology is explored. • Locally, façades decrease stresses in structural key members up to 66.94%. • Globally, façades attenuate top displacements up to 4.94%. Abstract The dynamic interaction between glazed curtain wall stick systems and modern high-rise mega-frame buildings is investigated. In the present paper, four moment resisting frames (MRFs), consisting of thirty- and sixty-storey steel-based prototypes, are designed according to European standards: internal concentrically braced frame (CBF) core, outriggers and belt trusses are adopted to limit inter-storey drift and second order effects. Force-displacement relationships are derived from available full-scale test data performed on non-structural aluminium façade units. Therefore, 3D finite element (FE) models are developed to interpret the physical phenomena involved in façade dynamics: as a result, equivalent 1D nonlinear links are calibrated to simulate these phenomena independently. Nonlinear time history analyses (NLTHAs) are executed to investigate the potential combination of stiffness and strength of such hybrid systems, i.e. achieved through the integration of glazed curtain walls on the MRF lateral force resisting system (LFRs). Local and global performance will be shown in terms of inter-storey drifts and displacement peak profiles, forces and percentage peak variations, highlighting static-to-seismic load ratios in critical members and the sensitivity to the structural height. Conclusions point out that, even if accurately designed according to current standards, the façade omission from the seismic analyses of high-rise structures may lead to a crucial underestimation in the dissipation capacity of the building. [ABSTRACT FROM AUTHOR]

Highlights • SPSW in RCF with proposed connections improves load carrying capacity of RCF. • Initial stiffness and ductility is significantly influenced by connection types. • Three of proposed connections can be used for rehabilitation of RC structures. • One connection (type 4) proposed for new structures. Abstract In the reinforced concrete (RC) structures with steel plate shear walls (SPSWs) as a lateral resisting system, to obtain maximum capacity of SPSW, implementing proper connections play an important role to transfer force from wall to the frame. In this paper, four connection types are proposed and numerically investigated to transfer the tension field forces between SPSW and RC frame (RCF). Three types of connections are applicable for rehabilitating of existing RC structures and one type can be used for new construction. The behavior of connections has been evaluated using non-linear finite element analysis (NLFEA). Results of the specimens with different types of connections demonstrated that the use of SPSW in RCF with appropriate connections could provide excellent ductility as well as high load carrying capacity and initial stiffness by distributing the yielding zone in SPSW along the wall height. [ABSTRACT FROM AUTHOR]

Highlights • An optimal design procedure for nonlinear fluid viscous dampers is developed. • Nonlinear power law behavior is incorporated a priori in the optimal design process. • An improved stochastic linearization technique is used in the optimal design. • The procedure identifies the optimal dampers from an energy-based perspective. • Comparison with other methods proves key aspects and effectiveness of the procedure. Abstract The earthquake protection of structures equipped with energy dissipation devices in the form of nonlinear fluid viscous dampers (FVDs) is investigated. Most of the optimal design strategies from the literature either address a simplified linear (Newtonian) idealization of the devices, or identify the characteristics of the nonlinear FVDs in a later stage, by invoking the concept of "energy-equivalent" dampers to compromise between the nonlinear power law force-velocity behavior and a simplified (equivalent, in terms of energy dissipation) linear modeling. In this paper, the nonlinear power law behavior of the devices is incorporated a priori in the optimal design process. The proposed strategy, based upon a numerical approach to a constrained optimization problem, invokes a performance criterion that is derived from the energy balance equation of the system, expressed in stochastic terms. To handle the nonlinear constitutive behavior of the FVDs, a novel equal-energy non-Gaussian stochastic linearization technique is integrated in the optimal design process. For a given power-spectral-density function of the seismic excitation, the most effective set of nonlinear FVDs that maximize the energy dissipation behavior can be identified. By stochastic dynamic analysis and by nonlinear response-history-analysis with an ensemble of ground motions, the proposed energy-based design philosophy is found to be better able to control the overall seismic response of the structure than alternative procedures that are not based on energy concepts and that minimize other performance indices. [ABSTRACT FROM AUTHOR]

Highlights • The blast performance of concrete increases with material heterogeneity. • A compact material dissipates less energy within its structure. • Controlled heterogeneity predetermines blast damage zones. • Layer delamination increases blast energy dissipation. Abstract Because of the current geopolitical situation, research on improving the resistance of the civil and transport infrastructure to blast or impact loads has gained considerable attention. This paper presents the results of full-scale blast experiments designed to characterize the resistance of concrete-based composite bridge decks subjected to close-in blast loading. Three composite decks with different degrees of heterogeneity were proposed and tested: a slab with basalt fiber meshes in multiple layers along the depth of the specimen, a slab with recycled textile sheets 100 mm in total thickness, and a typical hollow-core prestressed slab. The dependence of the extent of the blast damage on the material characteristics of the composite material was studied. A detailed study of the damage to the specimen caused by the close-in explosion found apparent delamination of all tested composite specimens. The heterogeneity of the layered composite material converts the blast damage due to internal rebounds into layer delamination. [ABSTRACT FROM AUTHOR]

Highlights • Nonlinear finite element model of built-up section were developed and verified. • A proposed design approach is presented using direct strength method (DSM) • The proposed approach is evaluated by comparing with the current existing method and FEA data. • A parametric study showing the influence of D1/B ratio on the stability and strength of the built-up columns. Abstract This paper, based on new proposed approaches, is a numerical investigation of the behavior of thin-walled cold-formed steel built-up columns under a uniform compression. Two types of cross sections have been studied, built-up closed and open sections formed by two channels connected by battens plates. First, a nonlinear finite element model has been developed and the results obtained show a good agreement against experimental results, such as the ultimate strength, the type of deformed shapes at failure and the lateral displacement. Second, a new proposed approach based on the DSM approach where the local, distortional or global buckling has been obtained numerically, using finite element method software, the thickness at the contact area in the web is taken as 1.0 times the thickness of the plate "t", instead of 1.5 or 2.0 times "t". In this case, the compound section is acting as one rigidly connected section. Comparisons with experimental data give a satisfactory degree of accuracy in the proposed design method (DSM-t) and the results are more conservative than those found by the DSM-1.5 and DSM-2. The results, for either closed or open sections, are also slightly conservative for columns failing in global modes than in local ones, if compared with the AISI and EC3 specifications. Some parameters, such as the spacing channels-web length ratio (B1/D) influence the stability and strength of the built-up columns. [ABSTRACT FROM AUTHOR]

In this paper, we propose to extend the notion of the topological sensitivity analysis for parabolic equations. It consists in deriving an asymptotic expansion of a shape function with respect to the presence of a small insulator with an adiabatic condition on its boundary in a homogeneous heat conductor. Based on the obtained theoretical results, we propose a fast and accurate one-step algorithm to demonstrate the efficiency of the suggested approach. Furthermore, in order to perform and deepen the theoretical results, one seeks to obtain the optimal design of a heat conductor. [ABSTRACT FROM AUTHOR]

This paper focuses on the optimization of a linear actuator by the “output space mapping (OSM)” method. The underlying objective of this work lies in the minimization of the time required for the achievement of this optimal design. Indeed, in addition to the sole costs of optimization processes strictly speaking, the time needed for the developpement of the models is taken into account. In the context of OSM, two different finite-element models of the same actuator are used. This paper presents these modeling solutions and considers their corresponding accuracy. Results of this multi-objective optimization method are presented and compared with those obtained by the sequential simplex (SS) method based solely on the fine model. Both approaches give similar results. However, the comparison of their performances clearly shows that the OSM algorithm is an effective technique for reducing the computation time of optimization studies, even in the case of relatively simple electromagnetic structures. Hence, this approach leads to an original and effective optimization methodology. [ABSTRACT FROM AUTHOR]

In this paper we derive a framework for multiscale approximation of elliptic problems on standard and mixed form. The method presented is based on a splitting into coarse and fine scales together with a systematic technique for approximation of the fine scale part, based on the solution of decoupled localized subgrid problems. The fine scale approximation is then used to modify the coarse scale equations. A key feature of the method is that symmetry in the bilinear form is preserved in the discrete system. Other key features are a posteriori error bounds and adaptive algorithms based on these bounds. The adaptive algorithms are used for automatic tuning of the method parameters. In the last part of the paper we present numerical examples where we apply the framework to a problem in oil reservoir simulation. [ABSTRACT FROM AUTHOR]

Abstract: In principle, two approaches are possible for resolving strong material micro-heterogeneity: one approach is to adopt homogenization with the underlying assumption of scale separation, whereas the other approach is to completely resolve the fine scale(s) in a single-scale computation. The point of departure for this paper is a recently proposed algorithm for scale-transition such that the two extreme approaches are bridged in a “seamless” fashion. Numerical homogenization is carried out locally, where needed, based on the relation of the macro-scale mesh diameter to the typical length scale of the subscale structure. Moreover, the macroscale mesh adaptivity is driven by an estimation of discretization errors. In the present paper, we generalize this procedure by introducing two-scale adaptivity, whereby subscale discretization errors are viewed as model errors from the macroscale perspective. Numerical examples, adopting elastic–plastic subscale material properties, illustrate the principle and the effectiveness of the adaptive procedure. [Copyright &y& Elsevier]

Purpose - The purpose of this paper is to develop a hybrid-Trefftz (HT) finite element model (FEM) for simulating heat conduction in nonlinear functionally graded materials (FGMs) which can effectively handle continuously varying properties within an element. Design/methodology/approach - In the proposed model, a T-complete set of homogeneous solutions is first derived and used to represent the intra-element temperature fields. As a result, the graded properties of the FGMs are naturally reflected by using the newly developed Trefftz functions (T-complete functions in some literature) to model the intra-element fields. The derivation of the Trefftz functions is carried out by means of the well-known Kirchhoff transformation in conjunction with various variable transformations. Findings - The study shows that, in contrast to the conventional FEM, the HT-FEM is an accurate numerical scheme for FGMs in terms of the number of unknowns and is insensitive to mesh distortion. The method also performs very well in terms of numerical accuracy and can converge to the analytical solution when the number of elements is increased. Originality/value - The value of this paper is twofold: a T-complete set of homogeneous solutions for nonlinear FMGs has been derived and used to represent the intra-element temperature; and the corresponding variational functional and the associated algorithm has been constructed. [ABSTRACT FROM AUTHOR]

Highlights • A hierarchical RVE-based continuum-atomistic multi-scale procedure is developed. • The inter-scale kinematic and energetic consistency principals are exploited. • The kinematic compatibility is applied by the atomistic periodic boundary conditions. • The energetic consistency is satisfied by the Hill-Mandel periodic boundary conditions. • Coarse-scale is modeled using the stress tensor and tangent modulus computed from atomistic RVE. Abstract In this paper, a hierarchical RVE-based continuum-atomistic multi-scale procedure is developed to model the nonlinear behavior of nano-materials. The atomistic RVE is accomplished in consonance with the underlying atomistic structure, and the inter-scale consistency principals, i.e. kinematic and energetic consistency principals, are exploited. To ensure the kinematic compatibility between the fine- and coarse-scales, the implementation of periodic boundary conditions is elucidated for the fully atomistic method. The material properties of coarse-scale are modeled with the nonlinear finite element method, in which the stress tensor and tangent modulus are computed using the Hill-Mandel principal through the atomistic RVE. In order to clearly represent the mechanical behavior of the fine-scale, the stress-strain curves of the atomistic RVE undergoing distinct type of deformation modes are delineated. These results are then assessed to obtain the proper fine-scale parameters for the multi-scale analysis. Finally, several numerical examples are solved to illustrate the capability of the proposed computational algorithm. Graphical abstract Schematically representation of the hierarchical atomistic-continuum multi-scale procedure. Image, graphical abstract [ABSTRACT FROM AUTHOR]