References of "Duysinx, Pierre"
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See detailNote on topology optimization of continuum structures including self-weight
Bruyneel, Michaël ULg; Duysinx, Pierre ULg

in Structural and Multidisciplinary Optimization (2005), 29

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See detailNote on topology optimization of continuum structures including self-weight
Bruyneel, Michael; Duysinx, Pierre ULg

in Structural and Multidisciplinary Optimization (2005), 29(4), 245-256

This paper proposes to investigate topology optimization with density-dependent body forces and especially self-weight loading. Surprisingly the solution of such problems cannot be based on a direct ... [more ▼]

This paper proposes to investigate topology optimization with density-dependent body forces and especially self-weight loading. Surprisingly the solution of such problems cannot be based on a direct extension of the solution procedure used for minimum-compliance topology optimization with fixed external loads. At first the particular difficulties arising in the considered topology problems are pointed out: non-monotonous behaviour of the compliance, possible unconstrained character of the optimum and the parasitic effect for low densities when using the power model (SIMP). To get rid of the last problem requires the modification of the power law model for low densities. The other problems require that the solution procedure and the selection of appropriate structural approximations be revisited. Numerical applications compare the efficiency of different approximation schemes of the MMA family. It is shown that important improvements are achieved when the solution is carried out using the gradient-based method of moving asymptotes (GBMMA) approximations. Criteria for selecting the approximations are suggested. In addition, the applications also provide the opportunity to illustrate the strong influence of the ratio between the applied loads and the structural weight on the optimal structural topology. [less ▲]

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See detailContribution to the optimization of closed-loop multibody systems: Application to parallel manipulators
Collard, Jean-François; Fisette, Paul; Duysinx, Pierre ULg

in Multibody System Dynamics (2005), 13(1), 69-84

This paper describes an original and robust method to optimize the design of closed-loop mechanisms, especially parallel manipulators. These mechanisms involve non linear assembling constraints. During ... [more ▼]

This paper describes an original and robust method to optimize the design of closed-loop mechanisms, especially parallel manipulators. These mechanisms involve non linear assembling constraints. During optimization, the Newton-Raphson algorithm we use to solve these constraints may fail when the Jacobian matrix of the constraints is ill-conditioned and stops the redesign process. To circumvent the difficulty, the technique we propose takes advantage of numerical conditioning to penalize the objective function. Applications to an academic example and parallel robots demonstrate the capabilities of the methodology. [less ▲]

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See detailGeneration of closed-form models for the control of flexible mechanisms: a numerical approach
Bruls, Olivier ULg; Duysinx, Pierre ULg; Golinval, Jean-Claude ULg

in Proc. of the 7th Int. Conf. on Motion and Vibration Control (MOVIC) (2004, August)

In robotics, most high performances control strategies require a closed-form representation of the mechanical dynamic behaviour. This is even more critical when significant flexible effects are to be ... [more ▼]

In robotics, most high performances control strategies require a closed-form representation of the mechanical dynamic behaviour. This is even more critical when significant flexible effects are to be considered in the control algorithm. This paper presents a method to build closed-form dynamic equations for flexible multibody systems in terms of minimal coordinates. Relying on the Finite Element (FE) formulation, the method is able to tackle complex topologies with closed-loops in a systematic way. The method is based on an interpolation strategy. For a number of selected points in the configuration space, a full Finite Element model is built and reduced according to a component mode synthesis. Then, a piecewise polynomial model is adjusted to match the collected data. In order to guarantee the continuity of the model, a mode tracking strategy is implemented. After the presentation of the reduction procedure and of the interpolation strategy, a four-bar mechanism is analyzed as an illustrative example. [less ▲]

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See detailA systematic model reduction method for the control of flexible multibody systems
Bruls, Olivier ULg; Duysinx, Pierre ULg; Golinval, Jean-Claude ULg

in Proc. of the 21st Int. Congress of Theoretical and Applied Mechanics (ICTAM) (2004, August)

This paper presents a method to build closed-form dynamic equations for flexible multibody systems with a minimal kinematic description. Relying on the Finite Element formalism, the method is able to ... [more ▼]

This paper presents a method to build closed-form dynamic equations for flexible multibody systems with a minimal kinematic description. Relying on the Finite Element formalism, the method is able to tackle complex topologies with closed-loops in a systematic way. Thus, it will be of great use in the framework of model based control of flexible mechanisms. The reduction procedure is based on an interpolation strategy: a Finite Element model is built and reduced for a number of selected points in the configuration space, and then, a piecewise polynomial model is adjusted to match the collected data. A few applications of the reduction method are considered: a serial pick-and-place machine, a flexible four bar mechanism, and a parallel kinematic manipulator. [less ▲]

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See detailReliable simulation of mechatronic systems using Newmark algorithms
Bruls, Olivier ULg; Duysinx, Pierre ULg; Golinval, Jean-Claude ULg

Conference (2004, March)

In the framework of flexible multibody systems simulation, the stability and the accuracy of the time integration process can be guaranteed by a family of implicit integrators derived from the Newmark ... [more ▼]

In the framework of flexible multibody systems simulation, the stability and the accuracy of the time integration process can be guaranteed by a family of implicit integrators derived from the Newmark scheme (Hilber-Hughes-Taylor and Generalized- methods). This paper deals with the extension of those reliable integrators for the simulation of mechatronic systems. In order to account for the strong coupling between the mechanism and the control system, the coupled set of equations contains mechanical and control variables. The generation of those equations, their numerical treatment and their time integration may become unmanageable for realistic control systems. In many cases, it is however sufficient to consider a weak coupling, which means that the action of the control system is treated as an external force disturbing the dynamic equilibrium. The weak coupling assumption is fully justified when a digital controller is present in the control loop. Then, the control actions exhibit discontinuous transitions at each sampling instant. The standard form of the Newmark scheme assumes continuity of the acceleration variables, and is thus not appropriate for this situation. Therefore, we propose an adapted Newmark scheme which achieves an explicit treatment of the acceleration jumps throughout the integration process, so that the proper simulation of the mechatronic system is guaranteed. The paper describes the detailed modifications of the integration algorithm. Illustrative examples are used to point out the critical situations where they prevent from substantial integration errors. [less ▲]

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See detailAN INTRODUCTION TO ROBOTICS: MECHANICAL ASPECTS
Géradin, Michel ULg; Duysinx, Pierre ULg

Learning material (2004)

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See detailA trust region algorithm for automatic identification of elasto-viscoplastic model parameters in metallurgical finite element model
Jeunechamps, Pierre-Paul ULg; Walmag, Jérôme; Duysinx, Pierre ULg 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 ▲]

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See detailA model reduction method for the control of rigid mechanisms
Bruls, Olivier ULg; Duysinx, Pierre ULg; Golinval, Jean-Claude ULg

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 ▲]

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See detailSolution of topology optimization problems with sequential convex programming
Duysinx, Pierre ULg; Bruyneel, Michaël ULg; Fleury, Claude ULg

Speech/Talk (2003)

Introduction to efficient solution algorithms to large scale topology optimization problems.

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See detailIdentification of elastoplastic model in large deformation problems
Jeunechamps, Pierre-Paul ULg; Walmag, Jérôme ULg; Delhez, Eric ULg 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 ▲]

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See detailContribution to the optimization of closed-loop multibody systems : application to parallel manipulators
Collard, Jean-François; Fisette, Paul; Duysinx, Pierre ULg

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 ▲]

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See detailComputational environment for the design of flexible mechanisms with feedback control
Bruls, Olivier ULg; Duysinx, Pierre ULg; Golinval, Jean-Claude ULg

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 ▲]

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See detailIdentification of elastoplastic model parameters in large deformation problems using gamma methods
Jeunechamps, Pierre-Paul ULg; Walmag, J.; Mathonet, V. 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 ▲]

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See detailDual approach using a variant perimeter constraint and efficient sub-iteration scheme for topology optimization
Zhang, Weihong; Duysinx, Pierre ULg

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 ▲]

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See detailModeling of the influence of electric forces on mechanical structures
Rochus, Véronique ULg; Duysinx, Pierre ULg; Golinval, Jean-Claude ULg

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 ▲]

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See detailA family of MMA approximations for structural optimization
Bruyneel, Michaël ULg; Duysinx, Pierre ULg; Fleury, Claude ULg

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 ▲]

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See detailAn Adaptation of the Newmark Scheme for the Integrated Simulation of Mechatronic Systems
Bruls, Olivier ULg; Duysinx, Pierre ULg; Golinval, Jean-Claude ULg

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 ▲]

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See detailSelection of approximation schemes in topology optimization
Bruyneel, Michaël ULg; Duysinx, Pierre ULg

in Hogge, Michel (Ed.) Proceedinsg of the ACOMEN 2002, 2nd International Conference on Advanced Computational Methods in Engineering (2002, May)

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See detailFinite Element Analysis of the Electro-Mechanical Coupling in MEMS
Rochus, Véronique ULg; Duysinx, Pierre ULg; Golinval, Jean-Claude ULg

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 ▲]

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