References of "Bruls, Olivier"
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See detailFinite element analysis of strongly nonlinear phenomena in deployable flexible systems
Bruls, Olivier ULg; Hoffait, Sébastien ULg; Cugnon, Frederic et al

in 1st ESA Multibody Dynamics Workshop on Multibody Dynamics for Space Applications, Noordwijk, 2010 (2010)

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See detailIntegrating structural and input design of a 2-DOF high-speed parallel manipulator: A flexible model-based approach
da Silva, M. M.; de Oliveira, L. P. R.; Bruls, Olivier ULg 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 ▲]

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See detailFully coupled simulation of mechatronic and flexible multibody systems: An extended finite element approach
Bruls, Olivier ULg

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 ▲]

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See detailLie group vs. classical time integrators in multibody dynamics: Formulations and numerical benchmarks
Bruls, Olivier ULg; Cardona, Alberto

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 ▲]

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See detailA system-level model reduction technique for efficient simulation of flexible multibody dynamics
Heirman, Gert H.K; Bruls, Olivier ULg; Desmet, Wim

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 ▲]

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See detailA system-level modal description of flexible multibody dynamics
Heirman, Gert H.K; Bruls, Olivier ULg; Desmet, Wim

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 ▲]

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See detailModelling of the squeeze film air damping in MEMS
Barroso, Juan José Gómez; Bruls, Olivier ULg; Berli, Claudio et al

in Proceedings of the ENIEF Conference (2009)

We propose a formulation for modeling the squeeze film air damping in micro-plates typical of micro-electromechanical devices for micro switch applications. A special finite element is developed, in which ... [more ▼]

We propose a formulation for modeling the squeeze film air damping in micro-plates typical of micro-electromechanical devices for micro switch applications. A special finite element is developed, in which the nonlinear Reynolds equation for compressible film is used to analyze the air pressure field, whereas a standard linear elastic model is used for the displacement field. The formulation is based on a finite element discretization of both the pressure and displacement fields. The coupled equations of motion are established and, for harmonic oscillations, we show that the resulting damping matrix depends on the frequency. The typical dimensions and properties of the MEMS device are in the order of hundred micrometers length and some micrometers (3-8 micrometers) thick, with a separation from the substrate of also some micrometers (e.g. 3-5 micrometers). For these dimensions, the influence of damping owing to the surrounding air cannot be neglected, having an important contribution to the quality factor of the device. The influence of plate holes, which are necessary because of the fabrication process, determines also the dynamic behavior of the plate. Examples are presented, with comparisons to results of the bibliography. [less ▲]

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See detailTopology Optimization of Structural Components: A Multibody Dynamics-Oriented Approach
Bruls, Olivier ULg; Lemaire, Etienne ULg; Duysinx, Pierre ULg et al

in Proceedings of the Multibody Dynamics ECCOMAS Conference (2009)

This work addresses the topology optimization of structural components embedded in multibody systems with large amplitude motions. Generally, topology optimization techniques consider that the structural ... [more ▼]

This work addresses the topology optimization of structural components embedded in multibody systems with large amplitude motions. 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, this paper proposes an optimization procedure based on the dynamic simulation of the full multibody system with large amplitude motions and elastic deflections. We show that the simulation model, which involves a nonlinear finite element formulation, a time integration scheme and a sensitivity analysis, can be efficiently exploited in an optimization loop. 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 detailComputer-aided integrated design for mechatronic systems with varying dynamics
da Silva, Maira M; Bruls, Olivier ULg; Paijmans, Bart et al

in Ulbrich, Heinz; Ginzinger, Lucas (Eds.) Motion and Vibration Control (Selected Papers from MOVIC 2008) (2009)

Some mechatronic systems have different spatial configurations or operation positions, and, as a consequence, their dynamic behavior, described by their most significant eigenfrequencies and mode-shapes ... [more ▼]

Some mechatronic systems have different spatial configurations or operation positions, and, as a consequence, their dynamic behavior, described by their most significant eigenfrequencies and mode-shapes, may vary in the configuration space. This inevitably affects the performance and the stability of the control system. Regarding the design of mechatronic systems with variable configuration, two main issues are treated in this paper: (i) the derivation of a parametric model able to capture the varying dynamics and the control actions, (ii) the integrated design of the structure and the controller. To cope with these issues, a parametric model is derived using a flexible multibody system technique based on the finite element method. A global modal parameterization is applied for model-order reduction, yielding a concise description of the flexible multibody model. A linear parameter varying controller is derived via interpolation of local controllers for the reduced models. This methodology is applied to a pick-and-place assembly robot with a gripper carried by a flexible beam. Eventually, design tradeoffs are evaluated considering the performance of the active system for different structural configurations. [less ▲]

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See detailComputer-aided integrated design for machines with varying dynamics
da Silva, Maira M; Bruls, Olivier ULg; Swevers, Jan et al

in Mechanism & Machine Theory (2009), 44(9), 1733-1745

This paper discusses the integrated design of mechatronic systems with varying dynamics, such as serial and parallel machine tools. This characteristic affects the machine stability and performance. A ... [more ▼]

This paper discusses the integrated design of mechatronic systems with varying dynamics, such as serial and parallel machine tools. This characteristic affects the machine stability and performance. A computer-aided integrated design methodology is proposed and validated on a pick-and-place robot. It consists of two main steps: (i) the derivation of reduced models from a flexible multibody model and (ii) the systematic robust control design. Eventually, the integrated design of the system, considering both structural and control parameters, can be performed. [less ▲]

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See detailIntegrated structure and control design for mechatronic systems with configuration-dependent dynamics
Da Silva, Maíra Martins; Bruls, Olivier ULg; Desmet, Wim et al

in Mechatronics (2009), 44(9), 10161025

This paper considers the optimal design of mechatronic systems with configuration-dependent dynamics. An optimal mechatronic design requires that, among the structural and control parameters, an optimal ... [more ▼]

This paper considers the optimal design of mechatronic systems with configuration-dependent dynamics. An optimal mechatronic design requires that, among the structural and control parameters, an optimal choice has to be made with respect to design specifications in the different domains. Two main challenges are treated in this paper: the non-convex nature of the optimization problem and the difficulty in modeling serial machines with flexible components and their embedded controllers. The optimization problem is treated using the direct design strategy which considers simultaneously structural and control parameters as variables and adopts non-convex optimization algorithms. Linear time-invariant and gain-scheduling PID controllers are addressed. This methodology is exploited for the multi-objective optimization of a pick-and-place assembly robot with a gripper carried by a variable-length flexible beam. The resulting design tradeoffs between system accuracy and control efforts demonstrate the advantage of an integrated design approach for mechatronic systems with configuration-dependent dynamics. 2009 Elsevier Ltd. All rights reserved. [less ▲]

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See detailAnalyse dynamique du phénomène d'auto-blocage dans les charnières de type Carpentier
Hoffait, Sébastien ULg; Bruls, Olivier ULg; Granville, D. et al

in Colloque National en Calcul des Structures, Giens, 2009 (2009)

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See detailTopology and generalized shape optimisation: why stress constraints are so important?
Duysinx, Pierre ULg; Van Miegroet, Laurent ULg; Lemaire, Etienne ULg et al

in International Journal of Simulation & Multidisciplinary Design Optimization (2008), 2(4), 253-258

The paper continues along the work initiated by the authors in taking into account stress constraints in topology optimization of continuum structures. Revisiting some of their last developments in this ... [more ▼]

The paper continues along the work initiated by the authors in taking into account stress constraints in topology optimization of continuum structures. Revisiting some of their last developments in this field, the authors point out the importance of considering stress constraints as soon as the preliminary design phase, that is, to include stress constraints in the topology optimization problem in order to get the most appropriate structural lay-out. Numerical applications that can be solved using these new developments make possible to exhibit interesting results related to the specific nature of strength based structural lay out for maximum strength compared to maximum stiffness. This particular character of stress design is clearly demonstrated in two kinds of situations: once several load cases are considered and when unequal stress limits in tension and compression are involved. [less ▲]

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See detailCoordinate transformation techniques for efficient model reduction in flexible multibody dynamics
Heirman, Gert H.K; Bruls, Olivier ULg; Sas, Paul et al

in Proceedings of ISMA 2008 (2008, September)

Computational efficiency is important for all numerical simulation tools. For real-time and faster-than-realtime applications, which rely on a strong interaction between simulation results and other ... [more ▼]

Computational efficiency is important for all numerical simulation tools. For real-time and faster-than-realtime applications, which rely on a strong interaction between simulation results and other subsystems, it is vital. This paper proposes a theoretical framework for coordinate transformations to recast the differential-algebraic system equations of a flexible mechanism into a simpler set of equations, which is cheaper to solve. Desirable properties of the coordinate transformation to minimize the computational burden of the simulation are discussed, as well as some assumptions that can be made for further simplification. A methodology to make practical use of coordinate transformation techniques to speed up simulation speed for real-time and faster- than-real-time applications is presented. [less ▲]

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See detailDesign of mechatronic systems with variable mechanical configuration
Da Silva, Maira; Bruls, Olivier ULg; Desmet, Wim et al

in Proceedings of the 9th International Conference on Motion and Vibration Control (MOVIC) (2008, September)

Some mechatronic systems have different spatial configurations or operation positions, and, as a consequence, their dynamic behavior, described by their most significant eigenfrequencies and mode-shapes ... [more ▼]

Some mechatronic systems have different spatial configurations or operation positions, and, as a consequence, their dynamic behavior, described by their most significant eigenfrequencies and mode-shapes, may vary in the configuration space. This inevitably affects the performance and the stability of the control system. Regarding the design of mechatronic systems with variable configuration, two main issues are treated in this paper: (i) the derivation of a parametric model able to capture the varying dynamics and the control actions, (ii) the integrated design of the structure and the controller. To cope with these issues, a parametric model is derived using a flexible multibody system technique based on the finite element method. A global modal parameterization is applied for model-order reduction, yielding a concise description of the flexible multibody model. A linear parameter varying controller is derived via interpolation of local controllers for the reduced models. This methodology is applied to a pick-and-place assembly robot with a gripper carried by a flexible beam. Eventually, design tradeoffs are evaluated considering the performance of the active system for different structural configurations. [less ▲]

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See detailDesign of mechanism components using topology optimization and flexible multibody simulation
Bruls, Olivier ULg; Lemaire, Etienne ULg; Eberhard, Peter et al

in Proceedings of the 8th World Congress on Computational Mechanics (2008, July)

This work addresses the topology optimization of structural components embedded in multibody systems with large amplitude motions. For example, in deployable space structures, piston engines, automotive ... [more ▼]

This work addresses the topology optimization of structural components embedded in multibody systems with large amplitude motions. For example, in deployable space structures, piston engines, automotive suspensions, robots and high-speed machine-tools, the articulated components undergo large displacements and elastic deformations, and are subject to transient loads and nonlinear dynamic effects. The performance of such systems often depends on the mechanical design in a non-intuitive way. <br />Several researchers have addressed the optimization of the geometric parameters of mechanisms and also of the connectivity of mechanisms made of rigid members. In contrast, topology optimization techniques are often based on continuum mechanics assumptions, and usually aim at optimizing the layout of an isolated structural component under the assumption of small displacements and small deflections. In order to apply topology optimization to mechanism components, one may consider that each structural component is isolated from the rest of the mechanism and use simplified quasi-static load cases to mimic the complex loadings in service. However, two main drawbacks are associated with this approach. Firstly, defining the equivalent load cases is a rather difficult task, which is often based on trials and errors and which requires some expertise. Secondly, topology optimization is often sensitive to loading conditions, especially for multiple load cases and stress constraints, so that the optimal character of the resulting design becomes questionable if the loading is approximative. For these reasons, in order to obtain better optimal layouts, this paper proposes an optimization procedure based on dynamic simulations of the full flexible multibody system. <br />For this purpose, the nonlinear finite element approach is selected for the modelling and the simulation of the flexible multibody system. The present work is thus similar to the usual approach used in topology optimization in which the continuum domain is discretized into finite elements. The nonlinear finite element formalism accounts for both large rigid-body motions and elastic deflections of the structural components. 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). <br />The nonlinear equations of motion are solved using a generalized-alpha time integration scheme, and the sensitivity analysis of mechanical responses is based on a direct differentiation method. The efficient solution of the optimization problem relies on the sequential convex programming concept at the core of the CONLIN software. <br />In the present study, the method is applied to various types of mechanical systems. Firstly, planar mechanisms with truss structural components are considered. Each truss is represented by a structural universe of beams with a topology design variable attached to each one. Secondly, the discussion is extended to similar mechanisms with 3D motions. Finally, the topology optimization of spatial bodies represented by 3D finite element meshes is considered. [less ▲]

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See detailModel reduction techniques to speed up multibody dynamics simulations
Heirman, Gert; Bruls, Olivier ULg; Desmet, Wim et al

in 4th International Conference on Advanced Computational Methods in Engineering (ACOMEN) – Book of Abstracts (2008, May)

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See detailVariable step-size solvers for coupled DAEs in mechatronic applications
Bruls, Olivier ULg; Arnold, Martin

in 4th International Conference on Advanced Computational Methods in Engineering (ACOMEN) – Book of Abstracts (2008, May)

This work addresses a variable step-size formulation of the generalized- time integration scheme for mechanical and mechatronic systems represented by coupled differential-algebraic equations (DAEs). In ... [more ▼]

This work addresses a variable step-size formulation of the generalized- time integration scheme for mechanical and mechatronic systems represented by coupled differential-algebraic equations (DAEs). In previous publications, a variant of the generalized- alpha algorithm has been proposed, which is able to deal with a non-constant mass matrix, controller dynamics and kinematic constraints in a consistent way. We have shown that this fixed step-size method can be used to solve efficiently industrial problems. The present work focuses on variable step-size schemes. It is well-known that classical formulations of the generalized-alpha method are no more second-order accurate in this case. We argue that second-order accuracy can be recovered provided a modification of the coefficients of the method. Actually, the value of the coefficients should be modified at each time step according to a simple update formula. This approach can thus be implemented very easily in an existing code. We also report practical experience on the implementation of the method. A strategy for the selection of the step-size is described and the importance of a scaling of the equations and unknowns is highlighted. A number of examples and applications are presented in order to illustrate those results. [less ▲]

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See detailModelling of the squeeze film air damping in MEMS
Bruls, Olivier ULg

Report (2008)

This document proposes a formulation of the squeeze film air damping in micro-plates. The nonlinear Reynolds equation for compressible film is used to analyze the air pressure field, whereas a standard ... [more ▼]

This document proposes a formulation of the squeeze film air damping in micro-plates. The nonlinear Reynolds equation for compressible film is used to analyze the air pressure field, whereas a standard linear elastic model is used for the displacement field. The formulation is based on a finite element discretization of both the pressure and displacement fields. The coupled equations of motion are established and, for harmonic oscillations, we show that the resulting damping matrix depends on the frequency. [less ▲]

Detailed reference viewed: 31 (4 ULg)