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The paper presents a fast online predictive method to solve the task-priority differential inverse kinematics of redundant manipulators under kinematic constraints. It implements a task-scaling technique to preserve the desired geometrical task, when the trajectory is infeasible for the robot capabilities. Simulation results demonstrate the effectiveness of the methodology. [ABSTRACT FROM AUTHOR]

In the field of service management plays a decisive role the location of the facilities to improve the quality of services. The maximal covering location problem allows locating a known number of facilities in order to maximize the demand covered. An important aspect to take into account is the varying of demand of the nodes with respect to the time (multi-period model). In addition, each facility could be of different types. A model that takes into account the existence of different types of facilities in order to cover the demand in multi-period environments has not been found in the literature. In this paper we propose a new generalization of the dynamic maximal covering location problem where different types of facilities (with different radius of coverage) could be open in each location. In this work we used the model on case study with the objective to locate the police patrol. [ABSTRACT FROM AUTHOR]

This paper proposes an affine scaling interior trust-region method in association with nonmonotone line search filter technique for solving nonlinear optimization problems subject to linear inequality constraints. Based on a Newton step which is derived from the complementarity conditions of linear inequality constrained optimization, a trust-region subproblem subject only to an ellipsoidal constraint is defined by minimizing a quadratic model with an appropriate quadratic function and scaling matrix. The nonmonotone schemes combining with trust-region strategy and line search filter technique can bring about speeding up the convergence progress in the case of high nonlinear. A new backtracking relevance condition is given which assures global convergence without using the switching condition used in the traditional line search filter technique. The fast local convergence rate of the proposed algorithm is achieved which is not depending on any external restoration procedure. The preliminary numerical experiments are reported to show effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper deals with shape optimization for elastic materials under stochastic loads. It transfers the paradigm of stochastic dominance, which allows for flexible risk aversion via comparison with benchmark random variables, from finite-dimensional stochastic programming to shape optimization. Rather than handling risk aversion in the objective, this enables risk aversion by including dominance constraints that single out subsets of nonanticipative shapes which compare favorably to a chosen stochastic benchmark. This new class of stochastic shape optimization problems arises by optimizing over such feasible sets. The analytical description is built on risk-averse cost measures. The actual optimized cost functional measures the volume and perimeter of the structure. In the implementation, shapes are represented by a phase field which permits an easy estimate of a regularized perimeter. The analytical description and the numerical implementation of dominance constraints are built on risk-averse measures for the cost functional. A suitable numerical discretization is obtained using finite elements both for the displacement and the phase field function. Different numerical experiments demonstrate the potential of the proposed stochastic shape optimization model and in particular the impact of high variability of forces or probabilities in the different realizations. [ABSTRACT FROM AUTHOR]

This study present an original approach of wood durability by proposing a coupling between different genetic families of Douglas and the structures durability using as 'marker', the hygroscopic behavior of materials. This approach appears as a statistical study which has the ambition to highlight some markers linked with a low diffusion coefficient and of low equilibrium moisture. This paper present a preliminary study that concerns the development of a numerical tool for performing a finite elements modeling of moisture transfers in the wood material. The purpose of modeling is to simulate the experimental tests that characterize the diffusion processes in controlled humidity and temperature. The hygroexpansion behavior will also be studied. The aim of this paper is to optimize dimensions of samples with time necessary to obtain the equilibuim hygroscopic for each climatic condition defined. [ABSTRACT FROM AUTHOR]

In this paper we consider a finite one-dimensional lattice with N=2n+1 sites such that one of them is empty and the others have a black or white token. There are two players (one for each color), such that step by step alternately they move one of their tokens to the empty site trying to obtain a connected configuration. This game is related with the Schelling’s social segregation model, where colors represent two different populations such that each one tries to take up a position with more neighbors as itself (same color). In this work we study strategies to play the game as well as their relation with the associated Schelling’s one-dimensional case (line and cycle graphs). [ABSTRACT FROM AUTHOR]

We present new results where free parameters in spurious oscillations at layers diminishing (SOLD) method are adaptively chosen. Provided numerical results are for conforming piecewise linear finite element space with free parameters from piecewise constant finite element space. We focus on a higher order convergence we discovered in previous paper by Lukáš (2015). [ABSTRACT FROM AUTHOR]

This paper presents the numerical results of a shape optimisation problem with regard to delaying the transition of a Navier-Stokes flow field from laminar to turbulent by using the theory developed by Nakazawa and Azegami. The theory was reviewed within the framework of functional analysis and updated with another expression of the shape derivative with respect to the objective function. A computer program was developed with the FreeFEM++. Numerical analyses were performed for two types of problems: a two-dimensional Poiseuille flow field with a sudden expansion and a two-dimensional uniform flow field around an isolated body. From the first example, two local minimum points of symmetric and asymmetric flow fields were determined, and the asymmetric flow field was found to be more stable. With regard to the second example, we reached the local minimum point of an elliptical shape, and infrequently determined a solution converging to an elliptical shape with the bluff in the leeward direction. By comparison, the superiority of the elliptical shape was obvious. [ABSTRACT FROM AUTHOR]

Computer experiments often have inputs that are proportions/fractions of components in a mixture. In these mixture computer experiments, it can be of interest to perform robust and tolerance design on the mixture proportions since the proportions are subjected to noise variations. Traditionally, manufacturing of mixture products is controlled via interval tolerances for mixture amounts. In this paper, an optimal tolerance region for proportions, which gives optimal quality cost among all possible tolerance regions for mixture proportions with the same acceptance probability, is proposed for integrated parameter and tolerance design in mixture computer experiments. Real examples are given to demonstrate the improvements that can be achieved with the optimal tolerance region. [ABSTRACT FROM AUTHOR]

Diffusion modeling is essential in understanding many physical phenomena such as heat transfer, moisture concentration, and electrical conductivity. In the presence of material and geometric discontinuities and nonlocal effects, a nonlocal continuum approach, named peridynamics (PD), can be advantageous over the traditional local approaches. PD is based on integro-differential equations without including any spatial derivatives. In general, these equations are solved numerically by employing meshless discretization techniques. Although fundamentally different, commercial finite-element software can be a suitable platform for PD simulations that may result in several computational benefits. Hence, this paper presents the PD diffusion modeling and implementation procedure in a widely used commercial finite-element analysis software, ANSYS. The accuracy and capability of this approach is demonstrated by considering several benchmark problems. [ABSTRACT FROM AUTHOR]

Nowadays, the widespread use of resistance spot welding (RSW) in various industries is evidence for the importance of this manufacturing process. In this paper, the finite element method (FEM) is utilized to model the weld nugget geometry and tensile-shear strength in RSW process of the galvanized interstitial free (IF) and bake hardenable (BH) steel sheets. Computational results have good agreement with experimental data. The investigation of input parameters influence, namely welding current, welding time, and electrode force on nugget size variations reveals that welding current is the most influential parameter. The examination of input parameters interaction on joint strength indicates that increase in welding current and time and also reduction in electrode force result in larger nugget size and bigger joint strength. Although by increasing the nugget size, at first, the joint strength is raised, after reaching the maximum strength, increase in nugget size results in decreasing the joint strength, and it may lead to expulsion phenomenon. The analysis of variance (ANOVA) results of response surface methodology (RSM) modeling demonstrate that beside the welding parameters, their interactions have significant effect on nugget geometry and tensile-shear strength. The relative error between RSM predicted and FEM calculated maximum strength is attained about 3% that specifies the efficiency of RSM. [ABSTRACT FROM AUTHOR]

Abstract: Shape optimization in connection with numerical modelling is used to reduce bending and associated flexural stresses in buried concrete arches. Modelling of the arch is carried out via a nonlinear finite element model that accounts for soil constitutive relations, soil–structure interactions, sequential construction stages and soil compaction. Centre line of the arch is parameterized by Bézier curve with three degrees of freedom that are subjected to optimization by genetic and Levenberg–Marquardt algorithm. The paper presents a parametric study which aims to determine the optimal shapes for buried arches of various span/rise ratios, backfill depths and foundation soil types. In the second part of the paper it shows a theoretical reduction in tensile stresses obtained by shape optimization of concrete arch culvert with a 9.4m span tested at the University of Massachusetts at Amherst. [Copyright &y& Elsevier]

Abstract: Upper and lower bound theorems of limit analyses have been presented in part I of the paper. Part II starts with the finite element discretization of these theorems and demonstrates how both can be combined in a primal–dual optimization problem. This recently proposed numerical method is used to guide the development of a new class of closed-form limit loads for circumferential defects, which show that only large defects contribute to plastic collapse with a rapid loss of strength with increasing crack sizes. The formulae are compared with primal–dual FEM limit analyses and with burst tests. Even closer predictions are obtained with iterative limit load solutions for the von Mises yield function and for the Tresca yield function. Pressure loading of the faces of interior cracks in thick pipes reduces the collapse load of circumferential defects more than for axial flaws. Axial defects have been treated in part I of the paper. [Copyright &y& Elsevier]

This paper proposes a robust optimization algorithm, enabling global optimum tracking and manufacturing uncertainty factors handling, for high-speed permanent magnet motor design. A new robustness criterion is introduced, considering effectively the impact of the construction tooling uncertainties on the design variables in all objectives. An adaptive-network-based fuzzy inference system is adopted acting as a surrogate for the time-consuming finite-element (FE) analyses and results in computationally fast robust electric machine design procedure. The procedure has been validated through FE high-speed motor design. [ABSTRACT FROM AUTHOR]

This paper combines thermal-structure coupling technique and pattern search optimization algorithm to establish an optimization system for the start-up process of a turbine unit. Firstly, a finite element model for thermal-structure coupling calculation is established to accurately analyze the transient temperature field and thermal stress field, which can obtain the thermal stress distribution during start-up process. Afterwards, a program of optimization on rotor start-up process is exploited to improve the time allocation in each operating stage of start-up process, which minimizes the maximum equivalent stress of rotor. The maximum equivalent stress has reduced 25.7% after the optimization, which reveals obvious effect. [ABSTRACT FROM AUTHOR]

Abstract: This paper shows how advanced numerical methods can help to improve the thermal efficiency of walls made up of multi-holed bricks with large recesses. In order to get this objective, a new methodology based on different numerical simulations is presented here. With the help of the finite element analysis (FEA), we present an optimization procedure in order to determine the best candidate brick with large recesses from the thermal point of view. With respect to the ecological design and the energy saving for housing and industrial structures, there is also a great interest in light building materials with good physical and thermal behaviours, which fulfils all thermal requirements of the new CTE Spanish rule for further energy savings. On one hand, we want to validate the numerical analysis procedure, based on the simulation of three-dimensional walls by the finite element method (FEM). On the other hand, we have analyzed the material conductivity for different compositions of the light concrete. The FEM technique is used for finding accurate solutions of the heat transfer equation in walls made up of light concrete multi-holed bricks with large recesses. Mathematically, the non-linearity is due to the radiation boundary condition inside the inner recesses of the bricks. Next, the thermal optimization of the walls is carried out from the FEM technique of several hollow brick geometries using the average mass overall thermal efficiency and the equivalent thermal conductivity. In order to select the appropriate wall satisfying the CTE requirements, detailed instructions are obtained and indicated to the readers. Finally, conclusions of this paper are exposed. [Copyright &y& Elsevier]

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]

Abstract: A temporal finite element discretization of a boundary value problem has several advantages compared to a time-integrating evolution form for optimized target movement simulations. The paper gives some basic aspects on how such a finite element form can be stated, with both displacements and controls discretized and seen as unknowns. Aspects on the resulting formulations are discussed. Important issues are the order, continuity and fineness of the discretizations. When the formulation is seen in an optimization context, minimizing the effort for a prescribed movement, the discretization affects the results obtained in several manners, where some aspects of results are artifacts. The paper discusses these effects from basic principles, but also verifies them in numerical simulations. [Copyright &y& Elsevier]

The goal of the paper is to present an outline of different modeling approach at determining of backward extrusion force on AlCu5PbBi material and to compare them with experimental obtained results. Stochastic modeling in the paper is based on the statistic processing of central composite experimental design i.e. in this investigations central composite circumscribed (CCC) design. The numerical modeling is based on the finite element method (FEM) using ABAQUS 6.4.1. Explicit software. [ABSTRACT FROM AUTHOR]

This paper discusses mathematical properties of preconditioned finite-element matrices based on vector potential formulation (A method) and vector and scalar potential formulation (A-V method) for eddy-current problems. Numerical results show that A-V method with preconditioning is stable at all frequencies in contrast to A method. In this paper, this property is mathematically discussed by considering the diagonal scaling which is one of the simple preconditioning methods. In addition, regularization of A method is discussed. [ABSTRACT FROM AUTHOR]

Abstract: According to the characteristic of modern product and optimization design, the conception and content of parameterized finite element analysis (PFEA) are introduced in this paper. Based on the request of PFEA, the conception of parameterized meshing is presented. The approach of establishing finite element models by parameterized meshing is elaborated. The content and realization method of parameterized meshing are researched in this thesis. Simultaneously, the process to realize parameterized meshing on Unigraphics (UG) software is proposed. And by programming, ParaMesh system—the parameterized meshing system based on history is developed for the first time in this paper, and the parameterized meshing for the surface is realized. At last, several examples on parameterized meshing are provided. [Copyright &y& Elsevier]

The aim of this paper is to describe a software tool for conception and optimisation of permanent magnet synchronous machines associated to their converters, using a coupled model for magnetic field and electrical circuit equations. In this paper, the emphasis is on the specifications of the tool: modularity, adaptability and evolutive capacity. [ABSTRACT FROM AUTHOR]

In this paper, we consider an inverse problem of identifying a space-dependent source in the parabolic equation which is a classical ill-posed problem. The inverse source problem is formulated into a regularized optimization problem. Then, a non-iterative algorithm based on a sequence well-posed direct problems solved by the finite element method is proposed for solving the optimization problem. In order to obtain a reasonable regularization solution, we utilize the damped Morozov discrepancy principle together with the linear model function method for choosing regularization parameters. Numerical results for one- and two-dimensional examples show that the proposed method is efficient and robust with respect to data noise, especially for reconstructing the discontinuous source functions. Furthermore, the proposed method is successfully used to solve a real example of identifying the magnitude of groundwater pollution source. [ABSTRACT FROM AUTHOR]

The paper is devoted to the Galerkin method and Finite Element Method for a stationary variational–hemivariational inequality modelling unilateral adhesive and frictionless contact of an elastic body with a foundation. Adhesion is modelled by a simplified Winkler-type law. An abstract theorem on the convergence of the Galerkin method for a class of nonlinear and pseudomonotone elasticity operators is proved. The theorem generalizes the result of Haslinger et al. (1999, Finite Element Method for Hemivariational Inequalities, Theory, Methods and Applications. Boston: Kluwer Academic Publishers). The problem is solved numerically on a mesh of linear triangles, by minimization of an associated energy functional for the linear, coercive and symmetric case. For nonsmooth optimization the Proximal Bundle Method (PBM) is used. For the benchmark problem of 2D linear elasticity, the numerical assessment of the method convergence rate is done. Moreover, tests are performed to establish the speed of PBM convergence. [ABSTRACT FROM AUTHOR]

In this paper, based on the previous research experiences in the lumped parameter modeling and study of active control mounts (ACM) model, an analytical model of active ACM in powertrain is developed and implemented in MATLAB. In order to validate this newly developed model in this work, a finite element analysis (FEA) method is conducted in ANSYS and the results of FEA is compared with analytical model for validation. After the validation, the control strategy is integrated into the analytical model by using the linear quadratic regulator (LQR) method. Numerical results show a good control performance. Furthermore, this work examines the application of genetic algorithms (GA) in optimizing the weight matrices of LQR. An optimal configuration is obtained and thus this approach could help the practical design of ACM systems. [ABSTRACT FROM AUTHOR]

In this paper, a rectangular plenum internally equipped with two crossed baffles within a fixed space is assessed. To simplify the optimization process, a simplified objective function (OBJ) is constructed using the finite element model (FEM) in conjunction with the polynomial neural network model (ANNM). To assess an optimal plenum, the best OBJ will be numerically searched using a genetic algorithm (GA). Before the GA operation is performed, the accuracy of the FEM is verified using the analytical data. In addition, a case study of shape optimization on a space-constrained plenum at three targeted tones (1950 Hz, 2450 Hz, and 2850 Hz) has been introduced and carried out. The results reveal that the maximum value of the sound transmission loss (STL) can be accurately obtained at the desired frequencies. Consequently, the algorithm proposed in this study provides an efficient way to develop optimal rectangular plenums internally equipped with two crossed baffles. [ABSTRACT FROM AUTHOR]

Abstract: Various kinds of finite elements are proposed and employed for one-dimensional wave-field simulations, each of which has their own capabilities and disadvantages. This paper deals with structural similarities and differences that arise at the element level, by the use of reduced forms of mass and stiffness matrices. General parameterized forms are then developed for mass and stiffness matrices of n-noded elements (elements with n nodes with arbitrary arrangement). Optimization for the free parameters will deliver elements with better performance and less numerical dispersion error. Two of such elements are developed and compared for their ability in dispersion-error remission. [Copyright &y& Elsevier]

A new type of iteration method is proposed in this paper to solve the Steklov eigenvalue problem by the finite element method. In this scheme, solving the Steklov eigenvalue problem is transformed into a series of solutions of boundary value problems on multilevel meshes by the multigrid method and solutions of the Steklov eigenvalue problem on the coarsest mesh. Besides the multigrid scheme, all other efficient iteration methods can also serve as the linear algebraic solver for the associated boundary value problems. The computational work of this new scheme for the Steklov eigenvalue problem can reach the same optimal order as the solution of the corresponding boundary value problem. Therefore, an improvement of efficiency for the Steklov eigenvalue solving method can be achieved. Some numerical experiments are presented to validate the efficiency of the new method. [ABSTRACT FROM AUTHOR]

In this paper, the formulation of a lower-bound limit analysis for axisymmetric problems by means of finite elements leads to an optimization problem with a large number of variables and constraints. For the Mohr-Coulomb criterion, it is shown that these axisymmetric problems can be solved by second-order cone programming (SOCP). First, a brief introduction to SOCP is given and how axisymmetric lower-bound limit analysis can be formulated in this way is described. Through the use of an efficient toolbox ( MOSEK or SDPT3), large-scale SOCP problems can be solved in minutes on a desktop computer. The method is then applied to estimate the collapse load of circular footings and uplift capacity of single or multiplate circular anchors. By comparing the present analysis with the results reported in the literature, it is shown that the results obtained from the proposed method are accurate and computationally more efficient than the numerical lower-bound limit analysis incorporated with linear programming. [ABSTRACT FROM AUTHOR]

This paper is concerned with the investigation of mathematical and numerical methods to find the optimal shape of a nozzle by means of shape optimization. The nonviscous, incompressible potential field within the nozzle is assumed to satisfy the Laplace PDE with mixed boundary conditions. We try to track the geometry of the nozzle to match the resulting velocity field with a prescribed one in some given critical subdomain. The problem is reformulated as an output least-squares minimization problem with the nozzle boundary being the control variable. The shape gradient of the cost functional is derived by combining the adjoint method and the techniques in the Lie derivative framework proposed by Hiptmair and Li (2012). An arbitrary Lagrangian-Eulerian finite element method is proposed to numerically solve the problem in an efficient way. Numerical experiments are presented to demonstrate the applicability and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents an approach to shape/topology optimization of continuous structures. The proposed approach combines the design element technique and the level set function in order to obtain an efficient topology parameterization of the domain under consideration. The shape and the level set function are both parameterized by the control points and corresponding blending functions of the design elements. For the sake of generality, nonlinear finite elements are employed, which have to be adapted adequately in order to be able to describe full material, void, and any intermediate state. In this way the design element technique has not yet been used for topology optimization, partially because it requires that the domain geometry and finite element mesh have to be defined by utilizing control-point-based design elements. In spite of this drawback, the proposed approach offers several attractive benefits. Namely, in contrast to other level set methods, the proposed approach does not make any use of the Hamilton-Jacobi differential equation. Consequently, the boundary evolution stage of the process need not to be treated separately, but is integrated with the strain/stress analysis stage into a rather conventional optimization scheme. Furthermore, the proposed approach allows for any type of finite elements (linear/nonlinear) to be implemented into the procedure if adjusted adequately. The formulation of the optimization problem is also completely arbitrary. The properties of the proposed approach are illustrated by several numerical examples. [ABSTRACT FROM AUTHOR]

The concept of finite-time stability (FTS) has gained much attention from researchers in recent years, after the emergent utilization of linear matrix inequalities (LMIs) in the field of control systems. In this paper, FTS and finite-time boundedness (FTB) analysis and synthesis procedure for a ‘finite-time H∞ filter’ for discrete-time switching systems are presented. Assuming the external disturbance to be energy bounded, sufficient conditions for the designated H∞ filter-based system to be finite-time stable are proposed. Considering dwell-time switching, average and minimum dwell time in terms of ‘finite-time’ system parameters has been formulated. Furthermore, these results are extended to uncertain switching system, by assuming the switching system subject to norm-bounded parameter uncertainties. The intended filter design steps have been demonstrated for both certain and uncertain system models. A cost function is introduced and then a parametric optimization algorithm is devised to calculate optimal filter parameters and present the derived results in LMI form. Numerical design examples are presented at the end to demonstrate the results. [ABSTRACT FROM AUTHOR]

Abstract: In modern finite element analysis (FEA), a mesh is said to be ‘tangled’ if it contains one or more inverted elements. Tangling can occur, for example, during mesh optimization and mesh morphing. Modern finite element theory and commercial FEA packages are not designed to handle tangled meshes, i.e., they can lead to erroneous results. Researchers and practitioners therefore unanimously recommend untangling prior to analysis. In this paper, a new mathematical framework for FEA over tangled meshes is proposed. Specifically, by defining a cell decomposition of a tangled mesh, and an associated set of cell shape functions, it is shown that FEA can be successfully carried out over tangled meshes. The cell shape functions are constructed through an oriented linear combination of the classic element shape functions. Numerical examples illustrate the correctness of the proposed framework. Potential applications of the proposed framework are also illustrated. [Copyright &y& Elsevier]

This paper proposes a topology optimization method for a dielectric optical cloak that provides results that are perfectly free from intermediate materials, based on a level set boundary expression and the Finite Element Method. The finite element mesh is re-generated to fit the iso-surface of the level set function at every iterative step, to remove intermediate materials, so that the obtained optimal structure consists of only two materials, the dielectric material and air. First, the level set-based topology optimization is formulated and a topology optimization algorithm is proposed for the exact level set approach. Next, design requirements for the dielectric optimal cloak device are clarified and an objective functional for the design is formulated. The proposed method is then applied to a simple numerical problem to illustrate its effectiveness. [ABSTRACT FROM PUBLISHER]

Abstract: conforming finite element discretizations are a powerful tool for the numerical solution of the system of Maxwellʼs equations in electrodynamics. In this paper we construct a basis for conforming high-order finite element discretizations of the function space in 3 dimensions. We introduce a set of hierarchic basis functions on tetrahedra with the property that both the -inner product and the -inner product are sparse with respect to the polynomial degree. The construction relies on a tensor-product based structure with properly weighted Jacobi polynomials as well as an explicit splitting of the basis functions into gradient and non-gradient functions. The basis functions yield a sparse system matrix with nonzero entries per row. The proof of the sparsity result on general tetrahedra defined in terms of their barycentric coordinates is carried out by an algorithm that we implemented in Mathematica. A rewriting procedure is used to explicitly evaluate the inner products. The precomputed matrix entries in this general form for the cell-based basis functions are available online. [Copyright &y& Elsevier]

Abstract: Integrated design of the structure topology and involved component layout is a challenging design issue when compared with traditional topology optimization. In this paper, we propose an implicit modeling approach that works completely on an Eulerian finite element mesh throughout the whole optimization process. To this aim, implicit level-set functions and R-functions are employed to describe geometrical shapes of movable components. In particular, a modified arctan function is adopted to depict the material discontinuity along the interface between the structure domain and each component domain. They are then used for material interpolations and analytical sensitivity analysis w.r.t. both pseudo-density design variables and location design variables related to the host structure and components, respectively. Based on a variety of numerical tests, it is demonstrated that considered design problems with movable components can easily be solved by extending the SIMP material model based topology optimization approach using an Eulerian mesh and the gradient-based optimization algorithm. [Copyright &y& Elsevier]

Friction plays an important role in forming processes, in fact it influences the material flow and therefore it affects the process and part characteristics. In particular, friction is a very influencing factor in tube hydroforming (THF), where high die-part contact pressure and area make the material sliding very difficult. As a consequence, the material hardly flows to the expansion zones and the part formability can be compromised. To obtain sound parts, FEM models allow the study of the process and optimize its parameters, but they require the right definition of the friction at tube-die interface. For these reasons, friction represents a key-point in THF processes and its knowledge and prediction are very important even if, nowadays, a comprehensive friction test for THF is not available in literature. With this paper, the authors want to propose and evaluate a method to estimate friction for THF processes. In particular, a numerical inverse method allowing the estimation of the Coulombian friction coefficient combining experimental test and FE simulation results will be described. The method is based on the effects of friction on the tube final thickness distribution when it is pressurized and compressed by two punches under different lubrication conditions without expansion. In particular, how the use of few and fast FE simulations allows to estimate an analytical function that takes into account the process conditions and that can be used in combination with experimental results in order to estimate the friction coefficient in THF processes will be shown. [ABSTRACT FROM AUTHOR]

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 study reports on energy efficiency optimization regarding bottom trawls. Efficient fishing gear uses up only a small amount of energy per fish caught. Drag and mouth area during trawling operations affect energy efficiency. Drag causes the energy consumption and the trawl mouth area impacts the quantity of fish caught, hence an energy efficient gear has a low ratio drag on the mouth area. A novel numerical optimization technique using spatial fish distribution is presented in this work. The tool is based on a FEM mechanical model for trawls which consist mostly of netting panels sewn together. This tool is adapted to minimize an objective function namely the drag-to-mouth area ratio. This technique consists in modifying the design of all the panels of the trawl. In this paper the modifications are constant and quantified in terms of mesh number. Moreover the trawl mouth area takes into account the presence of fish within a given depth with respect to sea bottom and the value of the depth is adapted to the fish species of interest. Trawl design optimization with two uniform fish distributions at a given depth (6m and 3m above the sea bed) and one linear distribution at 6m above the sea bed are compared. The application of this tool when designing a bottom trawl for research vessels leads to an energy economy ranging from 16% to 52% under certain assumptions. [Copyright &y& Elsevier]

Abstract: Two kinds of design variables, i.e., pseudo-density variables associated with the framework structure and location design variables associated with connected components are involved in the layout design of multi-component systems. Although sensitivities with respect to the first ones can easily be carried out as in topology optimization, the semi-analytical method (SAM) is often used for sensitivity analysis with respect to the location design variables. Due to the geometric perturbation of the finite element mesh, the latter can then be regarded as a geometric perturbation model (GPM). In this paper, we propose a material perturbation model (MPM) using fixed finite element (FE) mesh for sensitivity analysis with respect to location design variables. The material discontinuity across the boundary between each component and the framework structure is smoothed approximately by means of a modified Heaviside function. When a location design variable of a certain component is perturbed, attached finite elements to the component boundary are assumed to undertake only a shift of material properties while the finite element mesh itself remains geometrically unchanged. As a result, analytical sensitivities with respect to location design variables are achieved as easily as for pseudo-density variables. The computing efficiency is thus improved because the velocity field for the mesh perturbation in the semi-analytical scheme is no longer needed. The MPM is illustrated by means of numerical tests, especially the design optimization of 3D multi-component systems. [Copyright &y& Elsevier]

In this paper we investigate a space-time finite element approximation of parabolic optimal control problems. The first order optimality conditions are transformed into an elliptic equation of fourth order in space and second order in time involving only the state or the adjoint state in the space-time domain. We derive a priori and a posteriori error estimates for the time discretization of the state and the adjoint state. Furthermore, we also propose a space-time mixed finite element discretization scheme to approximate the space-time elliptic equations, and derive a priori error estimates for the state and the adjoint state. Numerical examples are presented to illustrate our theoretical findings and the performance of our approach. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a new numerical method for the design of multi-step stamping tools, in which the optimization approach is based on the Response Surface Method (RSM) with Kriging interpolation as well as the Sequential Quadratic Programming (SQP) algorithm. The present work attempts to provide a reliable methodology for the optimum design of the forming tools in order to produce a desired part by multi-step stamping within a severe tolerance (0.1mm). The numerical method has been proposed to reduce the number of forming steps and therefore increasing the process productivity. To reach this goal, an integrated optimization approach, using the commercial finite element code ABAQUS© together with an optimization algorithm was developed. The optimization algorithm consists in constructing an explicit form of the objective function according to the design variables. To search the global optimum of the objective function, the SQP algorithm has been used. A thin metallic part formed by manual press and without blank-holder has been considered, to demonstrate the effectiveness of the optimization approach to get the optimal tools shape in a few iterations. [Copyright &y& Elsevier]

Abstract: The paper presents a multiscale procedure for the linear analysis of components made of lattice materials. The method allows the analysis of both pin-jointed and rigid-jointed microtruss materials with arbitrary topology of the unit cell. At the macroscopic level, the procedure enables to determine the lattice stiffness, while at the microscopic level the internal forces in the lattice elements are expressed in terms of the macroscopic strain applied to the lattice component. A numeric validation of the method is described. The procedure is completely automated and can be easily used within an optimization framework to find the optimal geometric parameters of a given lattice material. [Copyright &y& Elsevier]

Abstract: The reconstruction of the equilibrium of a plasma in a Tokamak is a free boundary problem described by the Grad–Shafranov equation in axisymmetric configuration. The right-hand side of this equation is a nonlinear source, which represents the toroidal component of the plasma current density. This paper deals with the identification of this nonlinearity source from experimental measurements in real time. The proposed method is based on a fixed point algorithm, a finite element resolution, a reduced basis method and a least-square optimization formulation. This is implemented in a software called Equinox with which several numerical experiments are conducted to explore the identification problem. It is shown that the identification of the profile of the averaged current density and of the safety factor as a function of the poloidal flux is very robust. [Copyright &y& Elsevier]

Abstract: Modelling the scattering of guided waves by defects in three dimensions (3D) can be challenging. The most popular way to achieve this is the finite element (FE) method, at the cost of high computational load, which generally leads to a compromise between the accuracy of the results and the computational time, even when the geometry of the scatterer is simple. In this paper, we describe a procedure aimed at calculating the scattering matrix of an irregular defect in the most efficient way. The use of a frequency domain hybrid model which combines the flexibility of FE modelling and the efficiency of an integral representation of the acoustic fields allows very accurate results to be obtained with low computational load. The modelling procedure that we propose includes optimization of the size of the absorbing region and that of the mesh elements, minimization of number of incident directions, and the study of a spatial filter to smooth the geometry of the defect prior to meshing. Finally, the scattering matrix of a representative example of an irregular corrosion patch is calculated using the optimized procedure. Energy balance criteria are implemented to check the accuracy of the results. [Copyright &y& Elsevier]

This paper studies a regularization approach for an inverse problem of estimating a spatially-and-temporally dependent Robin coefficient arising in the analysis of convective heat transfer. The parameter-to-state map is analyzed, especially a differentiability result is established. A regularization approach is proposed, and the properties, e.g., existence and optimality system, of the functional are investigated. A finite element method is adopted for discretizing the continuous optimization problem, and the convergence of the finite element approximations as the mesh size and temporal step size tend to zero is established. Numerical results by the conjugate gradient method for one- and two-dimensional problems are presented. [ABSTRACT FROM AUTHOR]

Abstract: Non-linear finite element analyses were carried out to evaluate and optimize the seismic characteristics of knee-braced cold formed steel shear walls using software ANSYS. Different structural characteristics including: material nonlinearity, geometric imperfection, residual stresses and perforations are taken into account. The numerical models were verified based on experimental tests. Agreement of the numerical simulations and the test results showed that finite element analysis can be used effectively to predict the ultimate capacity of knee-braced CFS shear panels. A total of 12 models with a various ranges of knee-elements'' lengths were investigated. Of particular interests were the specimens'' maximum lateral load capacity and deformation behavior in addition to a rational estimation of the seismic response modification factor. Preliminary conclusions presented in this paper, refer to the optimum seismic characteristics of knee-braced CFS shear walls and the corresponding dimensions and configuration. [Copyright &y& Elsevier]

The aim of this paper is to present an efficient numerical procedure for the theoretical study of bimolecular reactions. It is based on the R matrix variational formalism and the p-version of the finite element method (p-FEM) for expanding the wave function in a finite basis set, and facilitates the development of an efficient algorithm to invert matrices that significantly reduces the computational time in R matrix calculations. We also utilise the self-consistent finite element method to optimise the elements mesh and provide faster convergence of results. We apply our methodology to the study of the collinear H + H process and evaluate its efficiency by comparing our results with several results previously published in the literature. [ABSTRACT FROM AUTHOR]

Abstract: Stabilized finite element methods for convection-dominated problems require the choice of appropriate stabilization parameters. From numerical analysis, often only their asymptotic values are known. This paper presents a general framework for optimizing stabilization parameters with respect to the minimization of a target functional. Exemplarily, this framework is applied to the SUPG finite element method and the minimization of a residual-based error estimator, an error indicator, and a functional including the crosswind derivative of the computed solution. Benefits of the basic approach are demonstrated by means of numerical results. [Copyright &y& Elsevier]

Abstract: In this paper, single and bi-layered tube hydroforming processes were numerically simulated using the finite element method. It was found that the final bulges heights resulted from the models were in good agreement with the experimental results. Both types of modeling have been kept with the same geometry, tube material, and process parameters to compare between the obtained hydroformed products (branch height, thickness reduction, and wrinkling) using different loading path types. Results were discussed. [Copyright &y& Elsevier]