References of "Bruls, Olivier"
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See detailThermal model reduction using the super-face concept
Masset, Luc ULg; Bruls, Olivier ULg; Kerschen, Gaëtan ULg

Conference (2011)

The objective of this presentation is to carry out thermal model reduction in the context of the finite element method. The finite element model is decomposed in several sets of adjacent faces called ... [more ▼]

The objective of this presentation is to carry out thermal model reduction in the context of the finite element method. The finite element model is decomposed in several sets of adjacent faces called super-faces. Specialized algorithms such as the METIS partitioning algorithm are used to automatically generate the super-faces. Several constraints may be imposed, e.g., the size of the super-face, its aspect ratio or its aperture angle. Once the model is decomposed, view factors between super-faces are calculated with direct numerical integration or ray-tracing methods. This method offers a very substantial reduction of the computational burden compared to the full model, which is particularly interesting for pre-design studies or specific applications such as deployable structures. [less ▲]

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See detailProper Orthogonal Decomposition for Nonlinear Radiative Heat Transfer Problems
Hickey, D.; Masset, Luc ULg; Kerschen, Gaëtan ULg et al

in Proceedings of the ASME International Design Engineering Technical Conferences (2011)

Analysing large scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally very expensive ... [more ▼]

Analysing large scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally very expensive, especially if the number of degrees-of-freedom is high. This paper develops modal reduction techniques for such nonlinear multiphysical systems. The paper focuses on Proper Orthogonal Decomposition (POD), a multivariate statistical method that obtains a compact representation of a data set by reducing a large number of interdependent variables to a much smaller number of uncorrelated variables. A fully coupled, thermomechanical model consisting of a multilayered, cantilever beam is described and analysed. This linear benchmark is then extended by adding nonlinear radiative heat exchanges between the beam and an enclosing box. The radiative view factors, present in the equations governing the heat fluxes between beam and box elements, are obtained with a raytracing method. A reduction procedure is proposed for this fully coupled nonlinear, multiphysical, thermomechanical system. Two alternative approaches to the reduction are investigated, a monolithic approach incorporating a scaling factor to the equations, and a partitioned approach that treats the individual physical modes separately. The paper builds on previous work presented previously by the authors. The results are given for the RMS error between either approach and the original, full solution. [less ▲]

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See detailComputation of bounded feed-forward control for underactuated multibody systems using nonlinear optimization
Seifried, Robert; Guimaraes Bastos Junior, Guaraci ULg; Bruls, Olivier ULg

in Proceedings in Applied Mathematics and Mechanics, Volume 1, Special Issue: 82nd Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM) (2011)

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See detailInvestigating the performance of model order reduction techniques for nonlinear radiative heat transfer problems
Hickey, D.; Masset, Luc ULg; Kerschen, Gaëtan ULg et al

in Proceedings of the International Conference on Advanced Computational Methods in Engineering (2011)

The problem of nonlinear radiative heat transfer is one of great importance to the aerospace industry. However, analysing large-scale, nonlinear, multiphysical, dynamical structures, by using mathematical ... [more ▼]

The problem of nonlinear radiative heat transfer is one of great importance to the aerospace industry. However, analysing large-scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally expensive. This provides motivation for the development of Model-Order Reduction (MOR) techniques capable of reducing simulation times without the loss of important information. The objective is to demonstrate the method of Proper Orthogonal Decompostition (POD) as a technique for nonlinear MOR. The nonlinear radiative exchanges between a linear benchmark beam within an external box (Figure 1) are analysed and a reduction procedure for this fully coupled, nonlinear, multiphysical, thermomechanical system is established. The solution to the strongly coupled, thermomechanical equations of motion is found by making use of an extended version of the implicit generalized-alpha scheme. In the reduced model, the residual of the unreduced system of equations need to be evaluated at each Newton iteration of each time step. In order to optimise the efficiency of the reduction method it is shown that the internal forces can be split into their linear and nonlinear counterparts. Only the nonlinear terms change at each time step, thus only these terms need to remain in the iterative loop significantly reducing the number of parameters that are to be computed at each step. These efficiency improvements to the method are discussed and the results are given. [less ▲]

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See detailOptimization of multibody systems and their structural components
Bruls, Olivier ULg; Lemaire, Etienne ULg; Duysinx, Pierre ULg et al

in Blajer, W.; Arczewski, K.; Fraczek, J. (Eds.) et al Multibody Dynamics: Computational Methods and Applications (2011)

This work addresses the optimization of flexible multibody systems based on the dynamic response of the full system with large amplitude motions and elastic deflections. The simulation model involves a ... [more ▼]

This work addresses the optimization of flexible multibody systems based on the dynamic response of the full system with large amplitude motions and elastic deflections. The simulation model involves a nonlinear finite element formulation, a time integration scheme and a sensitivity analysis and it can be efficiently exploited in an optimization loop. In particular, the paper focuses on the topology optimization of structural components embedded in multibody systems. Generally, topology optimization techniques consider that the structural component is isolated from the rest of the mechanism and use simplified quasi-static load cases to mimic the complex loadings in service. In contrast, we show that an optimization directly based on the dynamic response of the flexible multibody system leads to a more integrated approach. The method is applied to truss structural components. Each truss is represented by a separate structural universe of beams with a topology design variable attached to each one. A SIMP model (or a variant of the power law) is used to penalize intermediate densities. The optimization formulation is stated as the minimization of the mean compliance over a time period or as the minimization of the mean tip deflection during a given trajectory, subject to a volume constraint. In order to illustrate the benefits of the integrated design approach, the case of a two degrees-of-freedom robot arm is developed. [less ▲]

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See detailUsing 3D to understand human motion
Schwartz, Cédric ULg; Forthomme, Bénédicte ULg; Bruls, Olivier ULg et al

Poster (2010, December)

The understanding and tracking of human motion has been a subject of interest in the scientific community for more than one century. The long history of human motion analysis comes from the large scope of ... [more ▼]

The understanding and tracking of human motion has been a subject of interest in the scientific community for more than one century. The long history of human motion analysis comes from the large scope of applications of such measurement that can be found in medicine, biomechanics, sport, ergonomics, and even civil engineering. More recently, those technologies have also been widely exploited for the development of animation movies and games. Needless to say, the techniques used one century ago significantly differ from those used today. This paper describes in a first part the evolution of the technological capabilities for motion analysis and the actual limitations. From this analysis and in a second part, we describe the experience related to the creation of a motion analysis laboratory at the University of Liège and show how such a platform could be the center of a multidisciplinary research and provide valuable information to various communities. [less ▲]

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See detailLie group integrators for the numerical solution of DAE’s in flexible multibody dynamics
Cardona, Alberto; Bruls, Olivier ULg; Arnold, Martin

Conference (2010, November)

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See detailNumerical solution of DAEs in flexible multibody dynamics with applications in control and mechatronics
Bruls, Olivier ULg

Scientific conference (2010, October 21)

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See detailModel order reduction techniques for thermomechanical systems with nonlinear radiative heat transfer using proper orthogonal decomposition
Hickey, Daryl ULg; Hoffait, Sébastien ULg; Rothkegel Ide, José Ignacio ULg et al

in Proceedings of ISMA 2010 (2010, September)

Analysing large scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally very expensive ... [more ▼]

Analysing large scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally very expensive, especially if the number of degrees-of-freedom is high. This paper develops modal reduction techniques for such nonlinear multiphysical systems. The paper focuses on Proper Orthogonal Decomposition (POD), a multivariate statistical method that obtains a compact representation of a data set by reducing a large number of interdependent variables to a much smaller number of uncorrelated variables. A fully coupled, thermomechanical model consisting of a multilayered, cantilever beam is described and analysed. This linear benchmark beam is then extended to incorporate an external box. The nonlinear radiative exchanges between the beam and the external box are analysed and a reduction procedure is proposed for this fully coupled, nonlinear, multiphysical, thermomechanical system. Two alternative approaches to the reduction are investigated, a monolithic scaled approach and a partitioned approach that treats the individual physical modes separately. [less ▲]

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See detailAdvances in optimization of flexible components in mutlibody systems: Application to robot-arms design
Duysinx, Pierre ULg; Emonts-Alt, Jonhatan; Virlez, Geoffrey ULg et al

in Proceedings of the 5th Asian Conference on Multibody Dynamics (2010, August)

The paper considers the optimization of the flexible components of mechanical systems modeled as multibody systems. This approach aims at considering as precisely as possible the dynamic loading of the ... [more ▼]

The paper considers the optimization of the flexible components of mechanical systems modeled as multibody systems. This approach aims at considering as precisely as possible the dynamic loading of the structural components under service conditions in their mechanical systems. While most of the structural optimization developments have been conducted under static or quasi static conditions, the approach is clearly a challenge. Naïve applications of this approach generally lead to fragile and unstable results. To elaborate a robust and reliable approach, we investigate and compare several formulations of the optimization problem. Different optimization algorithms are also tested. To explain the efficiency of the various solution approaches, the complex nature of the design space is investigated. The developments are illustrated using the test-case of the structural design of the links of a two-arm robot subject to a trajectory tracking constraint. [less ▲]

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See detailFinite element modelling and optimization of flexible multibody systems
Bruls, Olivier ULg

Scientific conference (2010, June)

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See detailMultibody Dynamics Analysis of Differentials in Vehicle Drivetrains
Virlez, Geoffrey ULg; Bruls, Olivier ULg; Poulet, Nicolas et al

in Proceedings of the First Joint International Conference on Multibody System Dynamics (2010, May 26)

Differentials are critical components whose behaviour influences the dynamics of vehicles. They often include complex phenomena whose modeling is not always easy. In this paper, a model has been developed ... [more ▼]

Differentials are critical components whose behaviour influences the dynamics of vehicles. They often include complex phenomena whose modeling is not always easy. In this paper, a model has been developed for a limited slip differential (type C Torsen) which is mainly composed of an epicyclic gear train. In order to take into account flexibility, the nonlinear finite element method based on the absolute nodal coordinates has been chosen. The differential is modeled as a multibody system with various gear pairs and contact conditions. The model has been validated qualitatively and future work will address the identification of the various parameters and comparisons with experimental data. [less ▲]

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See detailModular mechatronic modelling for wind turbine generating systems based on an integrated finite element approach
Chen, Qiongzhong ULg; Jetteur, Philippe; Bruls, Olivier ULg

in Proceedings of the First Joint International Conference on Multibody System Dynamics (2010, May)

Wind energy is nowadays the fastest-growing energy source in the world, which has been attracting a lot of research interest in wind turbine generator systems. This paper concerns the modelling and ... [more ▼]

Wind energy is nowadays the fastest-growing energy source in the world, which has been attracting a lot of research interest in wind turbine generator systems. This paper concerns the modelling and simulation of wind turbine generating systems using the flexible multibody simulation software SAMCEF/MECANO. Firstly, it introduces the formulation of an extension of the generalized-alpha method, which is integrated into the flexible multibody dynamics solver for strongly-coupled simulation of mechatronic systems, and then emphasizes on the doubly-fed induction generator (DFIG) and the controller models, which are developed as modular components of the wind turbine package. The mechatronic systems are simulated upon this strongly-coupled approach and simulation results show the validity of the newly-developed solver and the models. The interest of this work is to analyze the control-generator-structure interactions in a wind turbine. The general aim is to develop a computer-aided tool for customization, fast-prototyping and optimal design of wind turbine systems based on the dynamic simulation of the overall system. [less ▲]

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See detailTrajectory Optimization of Flexible Robots Using an Optimal Control Approach
Guimaraes Bastos Junior, Guaraci ULg; Bruls, Olivier ULg

in Proceedings of the First Joint International Conference on Multibody System Dynamics (2010, May)

In the context of the mechatronic design of lightweight machines and robots, this paper studies optimal control problems in flexible multibody dynamics. Based on a direct transcription of the initial ... [more ▼]

In the context of the mechatronic design of lightweight machines and robots, this paper studies optimal control problems in flexible multibody dynamics. Based on a direct transcription of the initial problem, a direct collocation method is used. This method leads to a large but sparse nonlinear programming problem for which standard solvers are available. The implemention of this method based on a finite element simulation tool for flexible multibody systems is described. The connections between the generalized-alpha time integration scheme, which is commonly used for this kind of applications, and the formulation of the optimization problem are highlighted. The methodology is illustrated for two academic examples of rigid and flexible robotic systems. [less ▲]

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See detailNumerical solution of DAEs in flexible multibody dynamics using Lie group time integrators
Bruls, Olivier ULg; Cardona, Alberto; Arnold, Martin

in Proceedings of the First Joint International Conference on Multibody System Dynamics (2010, May)

This paper studies a family of Lie group time integrators for the simulation of flexible multibody systems. The method provides an elegant solution to the rotation parameterization problem and, as an ... [more ▼]

This paper studies a family of Lie group time integrators for the simulation of flexible multibody systems. The method provides an elegant solution to the rotation parameterization problem and, as an extension of the classical generalized-alpha method for dynamic systems, it can deal with constrained equations of motion. Here, second-order accuracy of the Lie group method is demonstrated for constrained problems. The convergence analysis explicitly accounts for the nonlinear geometric structure of the Lie group. The performance is illustrated on two critical benchmarks of rigid and flexible systems with large rotation amplitudes. Second-order accuracy is evidenced in both of them. The remarkable simplicity of the new algorithms opens some interesting perspectives for real-time applications, model-based control and optimization of multibody systems. [less ▲]

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See detailTime integration of finite rotations in flexible multibody dynamics using Lie group integrators
Bruls, Olivier ULg; Cardona, Alberto

Conference (2010, May)

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See detailRecent developments in optimization of flexible components of multibody systems
Duysinx, Pierre ULg; Emonds-Alt, Jonathan; Virlez, Geoffrey ULg et al

Conference (2010, May)

Recently mechanical engineering has extended from a component to a system oriented approach. The structural analysis of components is now completed by the whole mechanical system simulation using ... [more ▼]

Recently mechanical engineering has extended from a component to a system oriented approach. The structural analysis of components is now completed by the whole mechanical system simulation using multibody system analysis. This evolution aims at capturing better the real loading conditions accounting for the component interaction and couplings in the system. Structural optimization is continuing along the same tracks. Recent works in structural optimization have tried to optimize components with respect to loadings conditions defined through dynamic loading coming from multibody system dynamic analysis. Generally, optimization techniques consider that the structural component is isolated from the rest of the mechanism and use simplified quasi-static load cases to mimic the complex loadings in service. In contrast, we have shown in previous works devoted to topology optimization that an optimization directly based on the dynamic response of the flexible multibody system leads to a more integrated approach. In order to overcome the limitations of some previous approaches, a more integrated optimization technique is proposed here, based on the nonlinear finite element approach for flexible multibody systems. The non linear finite element formalism accounts for both large rigid-body motions and elastic deflection of the structural components. In previous work, the optimal design of components was realized as an optimal truss / beam layout. The present communication investigates the optimal design of components considered as a continuum medium. We study first sizing optimal design of structural components and we later extend the method to optimal material distribution approach to address their lay out optimization. The continuum domain is discretized into finite elements. For sizing optimization, the design variables are wall-thickness and lumped element variables. For topology optimization the design variables are classically density-like parameters associated to a power law interpolation of effective material properties for intermediate densities, also known as Simply Isotropic Material with Penalization (SIMP). This study assesses the feasibility of this approach, which extends optimization techniques to continuum flexible bodies included in MBS. The numerical implementation is conducted in SAMCEF MECANO for the flexible MBS analysis and BOSS Quattro for the optimization shell. The nonlinear equations of motion are solved using a generalized-a time integration scheme while the sensitivity analysis of mechanical responses is based on a direct differentiation method or finite differences. For sizing and parametric optimization the paper investigates and compares several optimization approaches methods such as classical gradient-based methods (SQP, Augmented lagrangian), sequential convex programming methods (CONLIN, MMA), but also surrogate-based optimization method (with Neural Networks) combined with genetic algorithms. The formulation of the problem is also discussed, and its influence on the convergence history is illustrated. Optimal sizing, shape and topology optimization of a simple model of a robot are addressed. The optimization approach is illustrated on numerical applications of sizing optimization of robot arms during trajectory tracking and lightweight layout optimal design of automotive components. [less ▲]

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See detailDe la dynamique des structures aux systèmes non-linéaires : enjeux et perspectives pour la réduction de modèle
Bruls, Olivier ULg

Conference given outside the academic context (2010)

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See detailRecent developments in simulation, optimization and control of flexible multibody systems
Bruls, Olivier ULg

Scientific conference (2010, January)

This talk addresses some recent extensions of the finite element approach for the analysis, design and control of flexible mechanisms. A particular attention is devoted to modular simulation concepts ... [more ▼]

This talk addresses some recent extensions of the finite element approach for the analysis, design and control of flexible mechanisms. A particular attention is devoted to modular simulation concepts, advanced time integration methods, efficient sensitivity analysis and topology optimization problems. Practical applications of those techniques can be found in various fields of engineering, e.g. in automotive engineering (vehicle suspensions, powertrains), aerospace engineering (landing gears, flaps, deployable space structures), robotics, machine tools, biomechanics or biomedical instruments. Firstly, an integrated simulation approach will be presented for articulated systems composed of rigid bodies, flexible bodies, kinematic joints, actuators, sensors and control units. I will focus on some numerical aspects concerning the time integration of the equations of motion which have the structure of strongly coupled differential-algebraic equations on a Lie group. The treatment of large rotation variables and the coupling between control state variables and mechanical generalized coordinates will be discussed in more detail. Secondly, based on this simulation tool, a particular class of optimization problems in multibody dynamics will be considered, i.e. the topology optimization of structural components. Generally, topology optimization techniques use simplified quasi-static load cases to mimic the complex dynamic loadings in service. In contrast, I will present an optimization procedure which properly accounts for the actual dynamic interactions which occur during the motion of the flexible multibody system. The method relies on an efficient sensitivity analysis based on a semi-analytical direct differentiation approach. In order to illustrate the benefits of the proposed design approach, the optimization of a two degrees-of-freedom robot arm with flexible truss linkages will be analyzed. Finally, I will discuss some perspectives for the integrated control-structure optimization of multibody systems. [less ▲]

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See detailToward robust parameterized reduced-order models of non-linear structures using POD
Hoffait, Sébastien ULg; Kerschen, Gaëtan ULg; Bruls, Olivier ULg

in IV European Conference on Computational Mechanics, Paris, 2010 (2010)

Detailed reference viewed: 34 (9 ULg)