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Finite element modelling and optimization of flexible multibody systems Bruls, Olivier Scientific conference (2010, June) Detailed reference viewed: 31 (4 ULg)Multibody Dynamics Analysis of Differentials in Vehicle Drivetrains Virlez, Geoffrey ; Bruls, Olivier ; 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 ▲] Detailed reference viewed: 158 (38 ULg)Trajectory Optimization of Flexible Robots Using an Optimal Control Approach Guimaraes Bastos Junior, Guaraci ; Bruls, Olivier 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 ▲] Detailed reference viewed: 150 (26 ULg)Modular mechatronic modelling for wind turbine generating systems based on an integrated finite element approach Chen, Qiongzhong ; ; Bruls, Olivier 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 ▲] Detailed reference viewed: 124 (32 ULg)Numerical solution of DAEs in flexible multibody dynamics using Lie group time integrators Bruls, Olivier ; ; 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 ▲] Detailed reference viewed: 160 (8 ULg)Time integration of finite rotations in flexible multibody dynamics using Lie group integrators Bruls, Olivier ; Conference (2010, May) Detailed reference viewed: 14 (2 ULg)Recent developments in optimization of flexible components of multibody systems Duysinx, Pierre ; ; Virlez, Geoffrey 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 ▲] Detailed reference viewed: 142 (17 ULg)De la dynamique des structures aux systèmes non-linéaires : enjeux et perspectives pour la réduction de modèle Bruls, Olivier Conference given outside the academic context (2010) Detailed reference viewed: 15 (1 ULg)Recent developments in simulation, optimization and control of flexible multibody systems Bruls, Olivier 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 ▲] Detailed reference viewed: 63 (4 ULg)Toward robust parameterized reduced-order models of non-linear structures using POD Hoffait, Sébastien ; Kerschen, Gaëtan ; Bruls, Olivier in IV European Conference on Computational Mechanics, Paris, 2010 (2010) Detailed reference viewed: 43 (12 ULg)Finite element analysis of strongly nonlinear phenomena in deployable flexible systems Bruls, Olivier ; Hoffait, Sébastien ; et al in 1st ESA Multibody Dynamics Workshop on Multibody Dynamics for Space Applications, Noordwijk, 2010 (2010) Detailed reference viewed: 31 (4 ULg)Dynamic analysis of the self-locking phenomenon in tape spring hinges Hoffait, Sébastien ; Bruls, Olivier ; et al in Acta Astronautica (2010), 66(7-8), 1125-1132 This paper investigates the dynamic behaviour of tape-spring hinges that are commonly used in space deployable structures. During the deployment of an appendice (e.g. a solar panel or a beam), a tape ... [more ▼] This paper investigates the dynamic behaviour of tape-spring hinges that are commonly used in space deployable structures. During the deployment of an appendice (e.g. a solar panel or a beam), a tape-spring hinge allows the simultaneous achievement of the actuating, guiding and self-locking functions without friction elements. The proposed finite element model is able to capture buckling and hysteresis phenomena, which have a strong influence on the 3D motion of the system. A detailed analysis of those effects is developed, leading to a physical explanation of the crucial self-locking phenomenon. [less ▲] Detailed reference viewed: 138 (20 ULg)USING INERTIA MEASUREMENT UNIT (IMU) FOR EXERCISE ANALYSIS Jidovtseff, Boris ; Bruls, Olivier ; Tubez, François et al in 7th International conference on strength training - abstract book (2010) Detailed reference viewed: 81 (8 ULg)Conception et réalisation du système de déploiement des antennes du nanosatellite OUFTI-1 Wertz, Jérôme ; ; Bruls, Olivier et al in Coudyser, A. (Ed.) Revue Scientifique des Instituts Supérieurs Industriels Libres Francophones, volume 24 (2010) The OUFTI-1 satellite is a CubeSat (a standard cubic satellite of 10cm edge and 1 kg mass maximum) developed at University of Liège. The subject of the master thesis is the design and realization of its ... [more ▼] The OUFTI-1 satellite is a CubeSat (a standard cubic satellite of 10cm edge and 1 kg mass maximum) developed at University of Liège. The subject of the master thesis is the design and realization of its antennas, and also of their deployment system. The thesis result is a prototype including all the system functions and which has been vacuum-tested. [less ▲] Detailed reference viewed: 177 (23 ULg)On the use of Lie group time integrators in multibody dynamics Bruls, Olivier ; in Journal of Computational and Nonlinear Dynamics (2010), 5(3), 031002 This paper proposes 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. As an ... [more ▼] This paper proposes 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. As an extension of the classical generalized-alpha method for dynamic systems, it can deal with constrained equations of motion. Second-order accuracy is demonstrated in the unconstrained case. The performance is illustrated on several critical benchmarks of rigid body systems with high rotation speeds and second order accuracy is evidenced in all of them, even for constrained cases. The remarkable simplicity of the new algorithms opens some interesting perspectives for real-time applications, model-based control and optimization of multibody systems. [less ▲] Detailed reference viewed: 156 (11 ULg)Integrating structural and input design of a 2-DOF high-speed parallel manipulator: A flexible model-based approach ; ; Bruls, Olivier et al in Mechanism & Machine Theory (2010), 45 This paper discusses the integrated design of parallel manipulators, which exhibit varying dynamics. This characteristic affects the machine stability and performance. The design methodology consists of ... [more ▼] This paper discusses the integrated design of parallel manipulators, which exhibit varying dynamics. This characteristic affects the machine stability and performance. The design methodology consists of four main steps: (i) the system modeling using flexible multibody technique, (ii) the synthesis of reduced-order models suitable for control design, (iii) the systematic flexible model-based input signal design, and (iv) the evaluation of some possible machine designs. The novelty in this methodology is to take structural flexibilities into consideration during the input signal design; therefore, enhancing the standard design process which mainly considers rigid bodies dynamics. The potential of the proposed strategy is exploited for the design evaluation of a two degree-of-freedom high-speed parallel manipulator. The results are experimentally validated. [less ▲] Detailed reference viewed: 32 (0 ULg)Fully coupled simulation of mechatronic and flexible multibody systems: An extended finite element approach Bruls, Olivier Scientific conference (2009, November) In this talk, I will discuss some extensions and refinements of classical finite element tools for the numerical simulation of complex mechatronic systems. The presentation will be divided into three main ... [more ▼] In this talk, I will discuss some extensions and refinements of classical finite element tools for the numerical simulation of complex mechatronic systems. The presentation will be divided into three main parts. In the first part, I will show how this approach allows the modeling of dynamic systems with large amplitude motions composed of rigid bodies, flexible bodies, kinematic joints, actuators, sensors and control units. A fully coupled model of a semi-active suspension will be used to illustrate the methodology. The second part 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 of the coupling between control state variables and mechanical generalized coordinates will be discussed in more detail. In the third part, the simulation tool will be exploited for the topology optimization of structural components embedded in multibody systems. 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. In order to illustrate the benefits of this integrated design approach, the optimization of a two degrees-of-freedom robot arm with flexible truss linkages will be analyzed. [less ▲] Detailed reference viewed: 37 (2 ULg)Lie group vs. classical time integrators in multibody dynamics: Formulations and numerical benchmarks Bruls, Olivier ; Conference (2009, September) The dynamics of flexible multibody systems with large rotations is often described using large sets of index-3 differential-algebraic equations. In this context, the Lie group structure of the dynamic ... [more ▼] The dynamics of flexible multibody systems with large rotations is often described using large sets of index-3 differential-algebraic equations. In this context, the Lie group structure of the dynamic system may be exploited in order to provide an elegant solution to the rotation parameterization problem. The talk discusses an original Lie-group extension of the classical generalized-alpha method, which can be used to solve index-3 differential-algebraic equations in multibody dynamics. Second-order accuracy is demonstrated at least in the unconstrained case and the performance is illustrated on several critical benchmarks with high rotational speeds. The remarkable simplicity of the new algorithms opens some interesting perspectives for real-time applications, model-based control and optimization of multibody systems. [less ▲] Detailed reference viewed: 52 (0 ULg)A system-level model reduction technique for efficient simulation of flexible multibody dynamics ; Bruls, Olivier ; in Proceedings of the Multibody Dynamics ECCOMAS Conference (2009, June) In flexible multibody dynamics, body-level model reduction is typically used to decrease the computational load of a simulation. Body-level model reduction is generally performed by means of Component ... [more ▼] In flexible multibody dynamics, body-level model reduction is typically used to decrease the computational load of a simulation. Body-level model reduction is generally performed by means of Component Mode Synthesis. This offers an acceptable solution for many applications, but does not result in significant model reduction for systems with moving connection points, e.g. due to a flexible sliding joint. In this research, Global Modal Parametrization, a model reduction technique initially proposed for real-time control of flexible mechanisms, is further developed to speed up simulation of multibody systems. The reduction is achieved by a system-level modal description, as opposed to the classic body-level modal description. As the dynamics is configuration-dependent, the system-level modal description is chosen configuration-dependent in such a way that the system dynamics are optimally described with a minimal number of degrees of freedom. Moving connection points do not pose a problem to the proposed model reduction methodology. The complexity of simulation of the reduced model equations is estimated. The applicability to systems with moving connection points is highlighted. In a numerical experiment, simulation results for the original model equations are compared with simulation results for the model equations obtained after model reduction, showing a good match. The approximation errors resulting from the model reduction techniques are investigated by comparing results for different mode sets. The mode set affects the approximation error similarly as it does in linear modal synthesis. [less ▲] Detailed reference viewed: 81 (5 ULg)A system-level modal description of flexible multibody dynamics ; Bruls, Olivier ; in Proceedings of the 9th National Congress on Theoretical and Applied Mechanics (2009, May) Current modelling techniques only allow realtime simulation of strongly simplified models of flexible mechanisms. Both the number of degrees of freedom needed to accurately describe flexibility as the DAE ... [more ▼] Current modelling techniques only allow realtime simulation of strongly simplified models of flexible mechanisms. Both the number of degrees of freedom needed to accurately describe flexibility as the DAE-character of the system equations limit the computational efficiency. Bodylevel model reduction such modal synthesis is typically used to decrease the computational load of a simulation, but this cannot fully meet the demands for real-time simulation of flexible mechanisms. In this research, Global Modal Parametrization, a model reduction technique initially proposed for controller design for flexible mechanisms, is further developed to speed up simulation of multibody systems. The reduction is achieved by a system-level modal description, as opposed to the classic body-level modal description. As the dynamics is configuration-dependent, the systemlevel modal description is chosen configuration-dependent in such a way that the system dynamics is optimally described with a minimal number of degrees of freedom. Another novelty is GMP-based simulation. In a numerical experiment, simulation results for the original model equations are compared with simulation results for the model equations obtained after model reduction, showing a good match. The approximation errors resulting from the model reduction techniques are investigated by comparing results for different mode sets. The mode set affects the approximation error similarly as it does in linear modal synthesis. [less ▲] Detailed reference viewed: 60 (2 ULg) |
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