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AN INTRODUCTION TO ROBOTICS: MECHANICAL ASPECTS Géradin, Michel ; Duysinx, Pierre Learning material (2004) Detailed reference viewed: 283 (12 ULg)A trust region algorithm for automatic identification of elasto-viscoplastic model parameters in metallurgical finite element model Jeunechamps, Pierre-Paul ; ; Duysinx, Pierre et al in Steel Grips 2 (2004), Supplement Metal Forming 2004 Simulation of manufacturing processes, here metal forming, has made major progresses during the last years. The virtual simulation of the manufacturing process being now quite well established, a natural ... [more ▼] Simulation of manufacturing processes, here metal forming, has made major progresses during the last years. The virtual simulation of the manufacturing process being now quite well established, a natural step ahead consists in trying to find automatic procedures to optimize it. Another perspective is also to take care of the influence of the manufacturing constraints upon the design, which is the long term objective of the present research project. It aims at optimizing the design subject to both service constraints (stiffness and strength) and manufacturing constraints. A preliminary stage is to be able to build high fidelity digital models. Complex models require more and more material parameters for behavior laws (e.g. material constitutive and friction laws), which have to be identified numerically from experimental data. In this material parameter identification process, three steps can be identified. At first, an experimental testing is carried out. The second step consists in building a simulation model of the experiment. Finally, the unknown model parameters are determined to match the experimental data. A standard identification procedure consists in minimizing a given norm (here the Euclidean norm) of the error between the model predictions and the experimental results. Even if the identification problem is generally quasi-unconstrained, it has the same complexity as structural optimization problems because of the highly nonlinear and implicit character of the functions, which is especially amplified by the large deformation simulation analysis. In this paper, we use an approach of elastoplastic calculation by finite elements combined with two optimization algorithms: a Levenberg-Marquardt algorithm, which is rather classical in the literature for solving identification problems (see [2]) and a trust-region one (see [1]), which is a rather novel approach at least for structural problems. The results obtained with these two methods are then compared and discussed on two test cases. The first application is an academic test case to validate the identification method. The second one, the compression of a cylinder, takes into account an actual experiment. In this application, the material is assumed to be elasto-viscoplastic and described by a Norton-Hoff behavior law and an isotropic strain hardening law. The parameters to be identified are the coefficients of the Norton-Hoff law. [less ▲] Detailed reference viewed: 54 (9 ULg)A model reduction method for the control of rigid mechanisms Bruls, Olivier ; Duysinx, Pierre ; Golinval, Jean-Claude in Proceedings of the ECCOMAS Conference on Advances in Computational Multibody Systems (2003, July) This paper proposes a control strategy for flexible mechanisms. Our starting-point is a classical collocated PID control of the joint actuators designed for the equivalent rigid mechanism. An additional ... [more ▼] This paper proposes a control strategy for flexible mechanisms. Our starting-point is a classical collocated PID control of the joint actuators designed for the equivalent rigid mechanism. An additional state feedback is implemented to control the flexible modes. On the basis of a few vibration measurements, it generates an additional command for the joint actuators. This non-collocated control scheme is designed according to the H procedure in order to have robust performances and stability with respect to configuration changes. In this paper, a new reduction methodology is presented to build a linear low-order and sufficiently accurate model of the mechanism with the PID feedback, which is suitable for the design of the H controller. First, a detailed Finite Element model of the mechanism is elaborated including the initial PID compensator. This set of nonlinear differential and algebraic equations is then linearized around a chosen reference configuration and a reduction technique is developed to extract a compact set of ordinaray differential equations. The retained degrees of freedom are the joint coordinates and a few modal coordinates representing the deformation of the whole mechanism. The kinematic description is thus decomposed into two parts, a rigid body motion described by the joint coordinates and a flexible motion for which shape functions have to be selected. For this selection, a modal analysis of the controlled mechanism is performed and the first few modes are kept, as in the Craig-Bampton or McNeal-Rubin reduction techniques. For robust performance specifications, the variations of the model with respect to the configuration changes should be estimated. Thus, the reduction procedure is realized for a few values of the joint coordinates, and the reduced models are compared. As the set of shape functions changes with the configuration, the physical meaning of the modal coordinates should be reinterpreted in each model, which is one difficulty of the approach. To illustrate the method, the case of a two-link flexible manipulator is presented. Simulation of the complete nonlinear Finite-Element model with the global control scheme is performed in order to assess the final performances of the closed-loop system. [less ▲] Detailed reference viewed: 34 (2 ULg)Solution of topology optimization problems with sequential convex programming Duysinx, Pierre ; Bruyneel, Michaël ; Fleury, Claude Speech/Talk (2003) Introduction to efficient solution algorithms to large scale topology optimization problems. Detailed reference viewed: 65 (5 ULg)Identification of elastoplastic model in large deformation problems Jeunechamps, Pierre-Paul ; Walmag, Jérôme ; Delhez, Eric et al in Cinquini, Carlo (Ed.) Proceedings of the 5th World Congress of Structural and Multidisciplinary Optimization WCSMO5 (2003, May) This paper reports on preliminary results of parameter identification problems in finite element non-linear analyses such as metal forming simulations. Two approaches are compared. The first one is the ... [more ▼] This paper reports on preliminary results of parameter identification problems in finite element non-linear analyses such as metal forming simulations. Two approaches are compared. The first one is the classic Levenberg-Marquardt algorithm. The second one is a trust-region algorithm based on a quadratic model. The two algorithms are compared on two cases, one of them being an actual experiment. [less ▲] Detailed reference viewed: 85 (13 ULg)Contribution to the optimization of closed-loop multibody systems : application to parallel manipulators ; ; Duysinx, Pierre in Proceedings of the 5th World Congress of Structural and Multidisciplinary Optimization WCSMO5 (2003, May) This paper describes an original and robust method to optimize the design of closed-loop mechanisms, especially parallel manipulators. In other words, these mechanisms include assembling constraints we ... [more ▼] This paper describes an original and robust method to optimize the design of closed-loop mechanisms, especially parallel manipulators. In other words, these mechanisms include assembling constraints we solved using a Newton-Raphson algorithm which may fail when the Jacobian matrix of the constraints is ill-conditioned. Therefore, the technique we propose takes advantage of that conditioning to penalize properly the objective function. Applications are shown: on the one hand, a simple example about the design of a planar ejector and, on the other hand, more realistic examples about the kinematical properties of parallel robots, in particular Delta-type and HexaSlide-type manipulators. [less ▲] Detailed reference viewed: 17 (0 ULg)Computational environment for the design of flexible mechanisms with feedback control Bruls, Olivier ; Duysinx, Pierre ; Golinval, Jean-Claude in Proceeding of 6th National Congress on theorical and Applied Mechanics (2003, May) In this article, numerical methods are exploited for the design of mechatronic systems. A method is presented for the simulation of a flexible mechanism subject to the action of a digital control system ... [more ▼] In this article, numerical methods are exploited for the design of mechatronic systems. A method is presented for the simulation of a flexible mechanism subject to the action of a digital control system. In the context of model-based control, reduction techniques of mechanical models are also discussed. [less ▲] Detailed reference viewed: 14 (0 ULg)Identification of elastoplastic model parameters in large deformation problems using gamma methods Jeunechamps, Pierre-Paul ; ; et al in Proceedings of the 5th World Congress on Structural and Multidisciplinary Optimization (2003) This paper reports on preliminary results of parameter identification problems in finite element non-linear analyses such as metal forming simulations. Two approaches are compared. The first one is the ... [more ▼] This paper reports on preliminary results of parameter identification problems in finite element non-linear analyses such as metal forming simulations. Two approaches are compared. The first one is the classic Levenberg-Marquardt algorithm. The second one is a trust-region algorithm based on a quadratic model. The two algorithms are compared on two cases, one of them being an actuel experiment. [less ▲] Detailed reference viewed: 79 (17 ULg)Dual approach using a variant perimeter constraint and efficient sub-iteration scheme for topology optimization ; Duysinx, Pierre in Computers & Structures (2003), 81(22-23), 2173-2181 To prevent numerical instabilities associated with the mesh-dependence, checkerboards and grey regions in topology optimization, a variant perimeter-constrained version of the SIMP algorithm is proposed ... [more ▼] To prevent numerical instabilities associated with the mesh-dependence, checkerboards and grey regions in topology optimization, a variant perimeter-constrained version of the SIMP algorithm is proposed using a smooth and quadratic function. In order to have an efficient implementation and to make sure the strict satisfaction of such an upper-bound perimeter constraint, a diagonal quadratic approximation of the perimeter constraint is used in the construction of each explicit optimization subproblem. The latter is then solved by a dual sub-iteration scheme. Numerical results show that the incorporation of such a sub-iteration scheme leads to a convergent solution without needs of move-limits or artificial control parameters. In addition to this, it is found that successive relaxations of the perimeter constraint by increasing the upper-bound tend to regularize the topology solution and result in a checkerboard free and satisfactory design solution without grey regions. [less ▲] Detailed reference viewed: 31 (0 ULg)Modeling of the influence of electric forces on mechanical structures Rochus, Véronique ; Duysinx, Pierre ; Golinval, Jean-Claude Conference (2003) This paper is a summary concerning the modeling of the strong electro-mechanical coupling appearing in micro-electro-mechanical systems (MEMS). These systems are very small devices (typical size of a few ... [more ▼] This paper is a summary concerning the modeling of the strong electro-mechanical coupling appearing in micro-electro-mechanical systems (MEMS). These systems are very small devices (typical size of a few microns), in which electric phenomena as well as mechanical and dynamical phenomena exist. The finite element method is used to discretize simultaneously the electrostatic and mechanical fields. The formulation is consistently derived from variational principles based on the electro-mechanical free energy. In classical weakly coupled formulations staggered iteration is used between the electrostatic and the mechanical domain. Therefore, in those approaches, linear stiffness is evaluated by finite differences and equilibrium is reached typically by relaxation techniques. The strong coupling formulation presented here allows to derive exact tangent matrices of the electro-mechanical system. Thus it allows to compute non-linear equilibrium positions using Newton- Raphson type iterations combined with adaptive meshing in case of large displacements. Furthermore, the tangent matrix obtained in the method considered in this paper greatly simplifies the computation of vibration modes and frequencies of the coupled system around equilibrium configurations. The non-linear variation of frequencies with respect to voltage and stiffness can then be investigated until pull-in appears. In order to illustrate the effectiveness of the proposed formulation numerical results are shown first for the reference problem of a simple flexible cap acitor, then for the model of a micro-bridge. [less ▲] Detailed reference viewed: 35 (3 ULg)A family of MMA approximations for structural optimization Bruyneel, Michaël ; Duysinx, Pierre ; Fleury, Claude in Structural and Multidisciplinary Optimization (2002), 24(4), 263-276 This paper proposes a new first-order approximation scheme used for solving structural optimization problems. It is based on approximations of the MMA family (MMA and GCMMA), but it utilizes the gradients ... [more ▼] This paper proposes a new first-order approximation scheme used for solving structural optimization problems. It is based on approximations of the MMA family (MMA and GCMMA), but it utilizes the gradients and/or the function values at two successive design points to improve the quality of the approximation. In addition, this scheme can consider simultaneously monotonous and nonmonotonous structural behaviour. According to the characteristics of the treated problem, one of the approximations or a mix of them is automatically selected. Based on this approach, the accuracy of the approximated subproblems is improved and the solution process can be sped up. Numerical results compare the effectiveness of the method with previously derived approximations of the MMA family for shape optimization of trusses and for composite design problems. The benefit of using mixed approximations is also discussed. [less ▲] Detailed reference viewed: 143 (23 ULg)An Adaptation of the Newmark Scheme for the Integrated Simulation of Mechatronic Systems Bruls, Olivier ; Duysinx, Pierre ; Golinval, Jean-Claude in Proceeding of 6th Int. Conf. on Motion and Vibration Control (MOVIC) (2002, August) A methodology is developed to simulate flexible multibody systems subject to the action of a digital control system. The mechanical model is built in the formalism of flexible multibody dynamics using the ... [more ▼] A methodology is developed to simulate flexible multibody systems subject to the action of a digital control system. The mechanical model is built in the formalism of flexible multibody dynamics using the Finite Element Method. At the begining of each sampling period, the model of the control system is used to compute the control forces and torques applied to the mechanism. A second-order system with a direct velocity feedback controller is considered to study the performances of the method. A modification of the classical Newmark algorithm yields outstanding improvements in the results quality. [less ▲] Detailed reference viewed: 35 (5 ULg)Selection of approximation schemes in topology optimization Bruyneel, Michaël ; Duysinx, Pierre in Hogge, Michel (Ed.) Proceedinsg of the ACOMEN 2002, 2nd International Conference on Advanced Computational Methods in Engineering (2002, May) Detailed reference viewed: 36 (1 ULg)Finite Element Analysis of the Electro-Mechanical Coupling in MEMS Rochus, Véronique ; Duysinx, Pierre ; Golinval, Jean-Claude Conference given outside the academic context (2002) This paper concerns the modelling of the strong electro-mechanical coupling appearing in micro-electro-mechanical systems (MEMS). These systems are very small devices (typical size of a few microns), in ... [more ▼] This paper concerns the modelling of the strong electro-mechanical coupling appearing in micro-electro-mechanical systems (MEMS). These systems are very small devices (typical size of a few microns), in which electric phenomena as well as mechanical and dynamical phenomena exist. The coupling between the electric and mechanical fields induce non-linear terms in the dynamic equilibrium equations of these microscopic structures so that instability may occur. In this paper, the finite element method (FEM) is used to perform modal analysis around non-linear equilibrium positions, taking into account large displacements. [less ▲] Detailed reference viewed: 52 (7 ULg)Integrated simulation of mechanical structures and their control system Bruls, Olivier ; ; Duysinx, Pierre et al in Proc. of the 2nd Int. Conf. on Advanced Computational Methods in Engineering (ACOMEN) (2002, May) This paper concerns the modeling and the integrated numerical simulation of flexible mechanisms subject to the action of a digital control system. A general method is proposed, based on the formalism of ... [more ▼] This paper concerns the modeling and the integrated numerical simulation of flexible mechanisms subject to the action of a digital control system. A general method is proposed, based on the formalism of flexible multibody systems (MBS) using the Finite Element Method (FEM). Nonlinear e ects in the mechanical structure or in the control system can be taken into account. The numerical simulation tool is applied to design an active control system in a hot-dip galvanizing line, which aims at reducing the vibrations of the steel strip. [less ▲] Detailed reference viewed: 16 (2 ULg)Recent Progress In Preliminary Design Of Mechanical Components With Topology Optimization Duysinx, Pierre ; Bruyneel, Michaël in Chedmail, Patrick; Cognet, Gérard; Fortin, Clément (Eds.) et al Integrated Design and Manufacturing in Mechanical Engineering (2002) Since 10 years topology optimisation has been trying to bring an efficient answer to the problem of automatic choice of morphology of mechanical components. This choice is one of the main questions to be ... [more ▼] Since 10 years topology optimisation has been trying to bring an efficient answer to the problem of automatic choice of morphology of mechanical components. This choice is one of the main questions to be addressed during the preliminary design phase of mechanical and structural components. By topology or morphology of a mechanical or structural component one means here all the basic data that touch the layout. So topology covers for example the number and the relative positions of the wholes in the structural domains, the number and the nature of the structural members, their connectivity and the character of the connecting joints. Before having topology optimisation tool, the selection of the mechanical morphology had been let to engineers’ experience or (even worse sometimes) to their intuition. For example it was a common use in industry to take the topology of an existing product and to use it as it is for the new design. With topology optimisation the choice of morphology can now rely on rational arguments and can be made in order to fit to the product characteristics. Furthermore mathematical tools, because of the optimisation formulation of the design problem, drive the determination of the structural layout. This has two advantages. At first topology optimisation can facilitate the automation of preliminary design steps. Then it can improve substantially the performance of new mechanical products. This means that topology optimisation can propose original and innovative solutions to engineering problems. Some authors suggested that in some problems topology could lead to a gain of performance that could grow up to 50 percents. This paper reports some novel contributions to topology optimisation techniques. Two areas will be addressed. The first one is concerned with recent progress related to the perimeter method of topology optimisation. The perimeter method, which was originally introduced by Haber et al (1996) in topology optimisation, consists in bounding the perimeter of the material distribution in addition to its area. At first recent research focussed on extending the method to 3-D structures. Then other work was made to new quasi-isotropic measures of the perimeter that are nearly insensitive to the mesh. The second axis of our work has been devoted to the treatment of stress constraints. We have continued along the initial work of Duysinx and Bendsøe (1998). The new developments were made to consider stress constraints in practical (industrial) design problems. Firstly we investigated the formulation of the problem in terms of global (i.e. integrated) stress constraints instead of the local stress constraints which can be very cumbersome for practical applications. A second research was devoted to extend the classic von Mises equivalent stress criterion to other kinds of criteria. Indeed in many cases such as in structures made of a material with unequal stress limits, the von Mises criterion is unable to predict a correct topology design. In order to include the effect of different behaviours in tension and compression, we are going to show that Raghava and Ishai quadratic criteria can be used. Finally in the final stage of the paper we will discuss the position of topology optimisation in the design chain. Usual answers in accordance with the current state of the art consider this topology tool as a preliminary design tool. However our experience lead us to a more complicated answer. In a similar way to stress constraints, the ‘optimal’ topology can be dependent on all the design constraints and not only stiffness performance. These constraints can come from the structural (or functional) behaviour, but they can also be related to the manufacturing aspects. Our experience showed that perimeter constraint is quite efficient to limit the design complexity in same cases, especially for planar structures. However this perimeter constraint can lead designs that are totally impossible to manufacture especially in 3-D. For example, perimeter constraint never prevents included wholes that would be impossible to carve out with some fabrication techniques. Thus we come to the conclusion that new progress in topology optimisation should be oriented towards a simultaneous approach of the design problem including most of the functional requirements as well as of the manufacturing restrictions. [less ▲] Detailed reference viewed: 88 (9 ULg)Modeling of Electro-mechanical coupling in MEMS Rochus, Véronique ; Duysinx, Pierre ; Golinval, Jean-Claude Scientific conference (2002) Detailed reference viewed: 27 (7 ULg)Topology optimization with self-weight loading: (un-expected) problems and solutions Bruyneel, Michaël ; Duysinx, Pierre in Bendsoe, M. P.; Olhoff, Niels; Rassmussen, John (Eds.) Proceedings of the 2nd Max Planck Workshop on Engineering Design Optimization (2001, October) Detailed reference viewed: 56 (0 ULg)A family of MMA approximations for structural optimization Bruyneel, Michaël ; Duysinx, Pierre ; Fleury, Claude Conference (2001, July) This paper deals with the approximation concepts approach applied to structural optimization. In 1987, Svanberg proposed the method of moving asymptotes for solving structural optimization problems. This ... [more ▼] This paper deals with the approximation concepts approach applied to structural optimization. In 1987, Svanberg proposed the method of moving asymptotes for solving structural optimization problems. This approximation is monotonous and can efficiently treat problems characterized by such a behavior. Svanberg (1995) proposed a modification of the MMA approximation by making it non monotonous. This property is based on an heuristically updated parameter. The resulting approximation is called GCMMA. In Bruyneel et al. (1999), it is shown that it is possible to generate non monotonous GCMMA based approximations, called GBMMA, by using the gradient and/or the function values from previous iteration. It was shown that such approximations improve the convergence speed of the optimization process. In many optimization problems (for example composite structures optimization or simultaneous sizing and optimal configuration of truss structures), the structural responses present both monotonous and non monotonous behaviors. A mixed monotonous/non monotonous approximation scheme has to be used for approximating in the best way the optimization problem (Zhang et al., 1998 and Bruyneel and Fleury, 2000). In this paper, we propose to show that it is possible to derive a very general approximation of the MMA family based on gradients and/or functions values at two successive design step, that present a mixed monotonous/non monotonous behavior. This approximation scheme is based on the GMMA approximation of Dusyinx et al. (1995) and on the non monotonous GBMMA approximations of Bruyneel and Fleury (1999). As the approximation scheme proposed in this paper is general, it contains all the approximations of the MMA family described above, that is MMA, GCMMA, GBMMA and GMMA. According to the characteristics of the problem under consideration, one of those approximations or of a mix of them is used to solve the optimization problem. This selection can be automatic or based on the designer’s knowledge. Numerical applications will show that the derived GMMA/GBMMA approximation scheme is efficient for solving structural optimization problems. Results will be compared with the ones obtained with the other approximations of the MMA family. [less ▲] Detailed reference viewed: 158 (3 ULg)Estimating diagonal second order terms in structural approximations with quasi-Cauchy techniques Duysinx, Pierre ; ; Bruyneel, Michaël et al in CHENG, Gen Dong (Ed.) Proceedings of the 4th World Congress of Structural and Multidisciplinary Optimization WCSMO4 (2001, June) This paper reports preliminary results obtained when estimating diagonal second order terms to be used in structural approximations with the quasi-Cauchy updates which was recently proposed by Zhu ... [more ▼] This paper reports preliminary results obtained when estimating diagonal second order terms to be used in structural approximations with the quasi-Cauchy updates which was recently proposed by Zhu, Nazareth, and Wolkowicz (SIAM J. of Optimization, 9 (4), 1192-1204, 1999). At first, the theory of quasi-Cauchy updates is presented. Main characteristics of the developments that were necessary to use quasi-Cauchy updates in the context of structural optimization are drawn. The available numerical results allow comparing quasi-Cauchy second order term estimations with other estimation procedures. [less ▲] Detailed reference viewed: 41 (0 ULg) |
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