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Improved stability and transient behaviour of generalized-alpha time integrators for constrained flexible systems ; Bruls, Olivier ; Conference (2011, November) Detailed reference viewed: 26 (0 ULg)Two optimal control methods for the inverse dynamics of underactuated multibody systems Guimaraes Bastos Junior, Guaraci ; ; Bruls, Olivier Conference (2011, November) The inverse dynamics analysis of underactuated multibody systems aims at determining the control inputs in order to track a prescribed trajectory. This work studies the inverse dynamics of non-minimum ... [more ▼] The inverse dynamics analysis of underactuated multibody systems aims at determining the control inputs in order to track a prescribed trajectory. This work studies the inverse dynamics of non-minimum phase underactuated multibody systems, e.g. for end-effector control of flexible manipulators or manipulators with passive joints. Unlike for minimum phase systems, the inverse dynamics of non-minimum phase systems cannot be solved by adding trajectory constraints to the equations of motion and by applying a forward time integration. Indeed, the inverse dynamics of a non-minimum phase system is known to be non-causal, which means that the control forces and torques should start before the beginning of the trajectory (pre-actuation phase) and continue after the end-point is reached (post-actuation phase). The existing stable inversion method proposed for general nonlinear non-minimum phase systems requires to derive explicitly the equations of the internal dynamics and to solve a boundary value problem. In this work, an alternative solution strategy is proposed which is based on an optimal control approach. More precisely, the direct collocation method and the multiple shooting are considered to solve the resulting optimization problem. The method is illustrated for the inverse dynamics of rigid and flexible underactuated mechanisms. An important advantage of the proposed approach is that it can be applied directly to the standard equations of motion of multibody systems either in ODE or in DAE form. Therefore, it is easier to implement this method in a general purpose simulation software. [less ▲] Detailed reference viewed: 64 (14 ULg)Simulation of differentials in four-wheel drive vehicles using multibody dynamics Virlez, Geoffrey ; Bruls, Olivier ; et al in Proceedings of the ASME 2011 International Design Engineering Technical Conference & Computers and Information in Engineering Conference IDETC/CIE 2011 (2011, August 31) The dynamic performance of vehicle drivetrains is significantly influenced by differentials which are subjected to complex phenomena. In this paper, detailed models of TORSEN differentials are presented ... [more ▼] The dynamic performance of vehicle drivetrains is significantly influenced by differentials which are subjected to complex phenomena. In this paper, detailed models of TORSEN differentials are presented using a flexible multibody simulation approach, based on the nonlinear finite element method. A central and a front TORSEN differential have been studied and the numerical results have been compared with experimental data obtained on test bench. The models are composed of several rigid and flexible bodies mainly constrainted by flexible gear pair joints and contact conditions. The three differentials of a four wheel drive vehicle have been assembled in a full drivetrain in a simplified vehicle model with modeling of driveshafts and tires. These simulations enable to observe the four working modes of the differentials with a good accuracy. [less ▲] Detailed reference viewed: 97 (28 ULg)Integrated power control analysis of DFIG wind turbines considering structural flexibility Chen, Qiongzhong ; Bruls, Olivier in Proceedings of the ASME 2011 International Design Engineering Technical Conference & Computers and Information in Engineering Conference IDETC/CIE 2011 (2011, August) Doubly-fed induction generators (DFIGs) are commonly used in variable-speed wind turbines for more power extraction. Unlike previous research on DFIG wind turbines, which typically uses an equivalent ... [more ▼] Doubly-fed induction generators (DFIGs) are commonly used in variable-speed wind turbines for more power extraction. Unlike previous research on DFIG wind turbines, which typically uses an equivalent lumped mass model of the drive train dynamics, but does not include detailed aerodynamic/mechanical representations, this paper investigates on the modelling and control of DFIG wind turbines by following a systematic approach based on a flexible multibody simulation software. The wind turbine structure, generator and control subsystem models are modularly developed for the S4WT package (Samcef for Wind Turbines), which is a user interface for the analysis of wind turbines. An extension of the finite element method is available in the flexible multibody dynamics solver, for the representation of the non-mechanical components, i.e., the generator and the control system, so that the coupled mechatronic system is simulated in a strongly coupled way. This integrated approach is less intricate and more robust than approaches based on an external DLL or co-simulation methods. The objective of this work is to analyze the control-generator-structure interactions in a wind turbine system. The power optimization control is elaborated in detail. A 2MW DFIG wind turbine prototype model is presented for validation. Dynamic analysis including the control effects and the influence of the structural flexibility is provided in an overall range. [less ▲] Detailed reference viewed: 54 (9 ULg)Two Lie Group Formulations for Dynamic Multibody Systems with Large Rotations Bruls, Olivier ; ; in Proceedings of the ASME 2011 International Design Engineering Technical Conferences (2011, August) This paper studies the formulation of the dynamics of multibody systems with large rotation variables and kinematic constraints as differential-algebraic equations on a matrix Lie group. Those equations ... [more ▼] This paper studies the formulation of the dynamics of multibody systems with large rotation variables and kinematic constraints as differential-algebraic equations on a matrix Lie group. Those equations can then be solved using a Lie group time integration method proposed in a previous work. The general structure of the equations of motion are derived from Hamilton principle in a general and unifying framework. Then, in the case of rigid body dynamics, two particular formulations are developed and compared from the viewpoint of the structure of the equations of motion, of the accuracy of the numerical solution obtained by time integration, and of the computational cost of the iteration matrix involved in the Newton iterations at each time step. In the first formulation, the equations of motion are described on a Lie group defined as the Cartesian product of the group of translations R^3 (the Euclidean space) and the group of rotations SO(3) (the special group of 3 by 3 proper orthogonal transformations). In the second formulation, the equations of motion are described on the group of Euclidean transformations SE(3) (the group of 4 by 4 homogeneous transformations). Both formulations lead to a second-order accurate numerical solution. For an academic example, we show that the formulation on SE(3) offers the advantage of an almost constant iteration matrix. [less ▲] Detailed reference viewed: 68 (11 ULg)Modeling of contact between stiff bodies in automotive transmission systems Virlez, Geoffrey ; Bruls, Olivier ; Duysinx, Pierre in Samin, Jean-Claude; Fisette, Paul (Eds.) Proceedings of MULTIBODY DYNAMICS 2011, ECCOMAS Thematic Conference (2011, July 05) Many transmission components contain moving parts which can enter in contact. The TORSEN differentials are mainly composed of gear pairs and thrust washers. The friction involved by contacts between these ... [more ▼] Many transmission components contain moving parts which can enter in contact. The TORSEN differentials are mainly composed of gear pairs and thrust washers. The friction involved by contacts between these two kind of parts is essential in the working principle of such differentials. In this paper, two different contact model are presented. The former uses an augmented Lagrangian technique and is defined between a rigid body and a flexible structure. The second contact formulation is a continuous impact modeling based on a restitution coefficient. [less ▲] Detailed reference viewed: 42 (5 ULg)Optimization of flexible components in reciprocating engines with cyclic dynamic loading Tromme, Emmanuel ; Bruls, Olivier ; Duysinx, Pierre in Samin, Jean-Claude; Fisette, Paul (Eds.) Proceedings of Multibody Dynamics 2011, Eccomas Thematic Conference: Brussels (Belgium), 4-7 juillet 2011 (2011, July 05) This work considers the optimization of flexible components of mechanical systems modeled as multibody systems. This approach permits to better capture the effects of dynamic loading under service ... [more ▼] This work considers the optimization of flexible components of mechanical systems modeled as multibody systems. This approach permits to better capture the effects of dynamic loading under service conditions. This process is challenging because most state-of-the-art studies in structural optimization have been conducted under static or quasi-static conditions. The formulation of the optimization problem for dynamic systems is fundamental; it is not a simple extension of static optimization. Naive implementation leads to fragile and unstable results. The present paper addresses the optimization of a connecting rod of a reciprocating engine with cyclic dynamic loading. Gradient-based methods are adopted for their convergence speed. Different formulations are investigated and compared. A first numerical application considers the optimization of the connecting rod regarding its mass and its elongation. After, another numerical application is carried on considering the stresses in the connecting rod. A conclusion on the influence of the optimization problem formulation is realized. [less ▲] Detailed reference viewed: 92 (13 ULg)INVERSE DYNAMICS OF UNDERACTUATED MULTIBODY SYSTEMS USING A DAE OPTIMAL CONTROL APPROACH Guimaraes Bastos Junior, Guaraci ; ; Bruls, Olivier in Proceedings of the ECCOMAS Thematic Conference (MULTIBODY DYNAMICS) 2011 (2011, July) The inverse dynamics analysis of underactuated multibody systems aims at determining the control inputs in order to track a prescribed trajectory. This paper studies the inverse dynamics of non-minimum ... [more ▼] The inverse dynamics analysis of underactuated multibody systems aims at determining the control inputs in order to track a prescribed trajectory. This paper studies the inverse dynamics of non-minimum phase underactuated multibody systems, e.g. for end-effector control of flexible manipulators or manipulators with passive joints. Unlike for minimum phase systems, the inverse dynamics of non-minimum phase systems cannot be solved by adding trajectory constraints to the equations of motion and by applying a forward time integration. Indeed, the inverse dynamics of a non-minimum phase system is known to be non-causal, which means that the control forces and torques should start before the beginning of the trajectory (pre-actuation phase) and continue after the end-point is reached (post-actuation phase). The existing stable inversion method proposed for general nonlinear non-minimum phase systems requires to derive explicitly the equations of the internal dynamics and to solve a boundary value problem. This paper proposes an alternative solution strategy which is based on an optimal control approach. The method is illustrated for the inverse dynamics of a planar underactuated manipulator with rigid links and four degrees-of-freedom. An important advantage of the proposed approach is that it can be applied directly to the standard equations of motion of multibody systems either in ODE or in DAE form. Therefore, it is easier to implement this method in a general purpose simulation software. [less ▲] Detailed reference viewed: 137 (25 ULg)Analysis of Control-Generator-Structure Interactions in Wind Turbines using an Integrated Simulation Approach Bruls, Olivier ; ; et al in Proceedings of Multibody Dynamics ECCOMAS Conference (2011, July) This paper addresses the modelling of the interactions between the generator, the controller and the structural components in wind turbines. Those interactions have a direct influence on the mechanical ... [more ▼] This paper addresses the modelling of the interactions between the generator, the controller and the structural components in wind turbines. Those interactions have a direct influence on the mechanical loads, which need to be evaluated for the design of the machine. Using the sofware Samcef For Wind Turbines, a model is developed which includes a description of the aeroelastic behaviour of the blades, the gearbox dynamics, the tower flexibility, as well as the electrical and control parts. Electrical and control subsystems can be modelled either by linking an external DLL, by a co-simulation approach or by using an integrated and monolithic model. This paper shows that the monolithic approach can be exploited for the reliable analysis of electrical-control-structure interactions in wind turbines. Non-mechanical elements are represented in a modular way using a newly developed library of block diagram elements. The coupled equations of motion are established by numerical assembly and they include a finite element description of the mechanical components and a block diagram description of the generator and its control system. A fully implicit, stable and reliable solver is then exploited to solve the coupled equations of motion. Simulation results are presented for a 2 MW wind turbine with a doubly-fed induction generator and they illustrate the coupling between the power control system and the dynamic structural response. [less ▲] Detailed reference viewed: 97 (15 ULg)Convergence analysis of generalized-alpha Lie group integrators for constrained systems ; Bruls, Olivier ; in Proceedings of Multibody Dynamics ECCOMAS Conference (2011, July) Detailed reference viewed: 39 (0 ULg)Reproducibility and repeatability of upper limb landmarks palpation for junior operators Schwartz, Cédric ; Fedrigo, Tatiana ; Bruls, Olivier et al Poster (2011, July) In human motion analysis, bone motions are usually expressed relatively to anatomical reference frames. The anatomical reference frames are constructed thanks to the localization of bony landmarks during ... [more ▼] In human motion analysis, bone motions are usually expressed relatively to anatomical reference frames. The anatomical reference frames are constructed thanks to the localization of bony landmarks during a static phase prior to the acquisitions. These landmarks are identified by means of palpation. Accurate comparison between subjects and studies implies good reproducibility and repeatability of the palpation process. However, all investigators don’t have a long experience in palpation. In this paper, the reproducibility and repeatability of palpation for junior investigators were measured. Results show worse reproducibility and repeatability than what is usually expected. These errors have particularly an influence on the definition of the reference frames of the arm. This study therefore emphasizes on the need of a specific training of operators working in a motion lab. [less ▲] Detailed reference viewed: 90 (29 ULg)Improving 3D measurements accuracy with camera information redundancy Schwartz, Cédric ; Fringuellini, Anthony ; Bruls, Olivier et al Conference (2011, July) The accuracy of the Codamotion system for 3D measurement depends mainly on the signal level of the sensors and the resolution of the system at the marker localization. When using several units to cover a ... [more ▼] The accuracy of the Codamotion system for 3D measurement depends mainly on the signal level of the sensors and the resolution of the system at the marker localization. When using several units to cover a large field of view, the estimated position of the different units might differ. We propose a method taking both resolution and signal level in to account, instead of only the signal level as in the built-in weighting process. This new method offers improved accuracy. [less ▲] Detailed reference viewed: 117 (32 ULg)Utilisation de la biomécanique pour l’analyse de la performance Schwartz, Cédric ; Forthomme, Bénédicte ; Denoël, Vincent et al Learning material (2011) Detailed reference viewed: 353 (104 ULg)Control and simulation of doubly fed induction generator for variable speed wind turbine systems based on an integrated finite element approach Chen, Qiongzhong ; ; Bruls, Olivier in Proceedings of the European Wind Energy Conference and Exhibition 2011 (EWEA 2011) (2011, March) Regarding renewable energy and environment- friendly issues, wind energy nowadays has become the fastest-growing energy source in the world, and thus attracts a lot of research interest in the wind ... [more ▼] Regarding renewable energy and environment- friendly issues, wind energy nowadays has become the fastest-growing energy source in the world, and thus attracts a lot of research interest in the wind turbine generation system. A doubly fed induction generator (DFIG) is used for variable speed operation in a wind turbine system to extract more power. Following a systematic approach, this paper investigates on the modelling and simulation of wind turbine generating systems using the flexible multibody simulation software SAMCEF/MECANO [1]. The objective of this work is to analyze the control-generator-structure interactions in a wind turbine system. Firstly, an extension of the finite element method is integrated into the flexible multibody dynamics solver, and thus extends the solver to represent mechatronic systems in a strongly-coupled way. Secondly, DFIG and the control systems are modularly modeled for the wind turbine package. Control of DFIG for grid synchronization and power optimization are elaborated in detail, and the methods are validated through a 2MW DFIG wind turbine prototype model. At the end, a systematic system model of wind turbine structure connected with the DFIG generating system is presented, which provides the dynamic analysis for the whole system in an overall range. [less ▲] Detailed reference viewed: 267 (13 ULg)Convergence analysis for a generalized-alpha Lie group time integrator ; Bruls, Olivier ; Conference (2011, January) Detailed reference viewed: 11 (2 ULg)Thermal model reduction using the super-face concept Masset, Luc ; Bruls, Olivier ; Kerschen, Gaëtan 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 ▲] Detailed reference viewed: 41 (14 ULg)Proper Orthogonal Decomposition for Nonlinear Radiative Heat Transfer Problems ; Masset, Luc ; Kerschen, Gaëtan 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 ▲] Detailed reference viewed: 27 (7 ULg)Computation of bounded feed-forward control for underactuated multibody systems using nonlinear optimization ; Guimaraes Bastos Junior, Guaraci ; Bruls, Olivier 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) Detailed reference viewed: 15 (4 ULg)Investigating the performance of model order reduction techniques for nonlinear radiative heat transfer problems ; Masset, Luc ; Kerschen, Gaëtan 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 ▲] Detailed reference viewed: 48 (6 ULg)Optimization of multibody systems and their structural components Bruls, Olivier ; Lemaire, Etienne ; Duysinx, Pierre 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 ▲] Detailed reference viewed: 92 (15 ULg) |
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