References of "Bruls, Olivier"
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See detailAdvanced Aeroservoelastic Modeling for Horizontal axis Wind Turbines
Prasad, Chandra Shekhar ULg; Chen, Qiong-zhong; Dimitriadis, Grigorios ULg et al

in Cunha, A.; Caetano, E.; Riberio, P. (Eds.) et al Proceedings of the 9th International Conference on Structural Dynamics, EURODYN 2014 (2014, July)

This paper describes the development of a complete methodology for the unsteady aeroelastic and aeroservoelastic modeling of horizontal axis wind turbines at the design stage. The methodology is based on ... [more ▼]

This paper describes the development of a complete methodology for the unsteady aeroelastic and aeroservoelastic modeling of horizontal axis wind turbines at the design stage. The methodology is based on the implementation of unsteady aerodynamic modeling, advanced control strategies and nonlinear finite element calculations in the S4WT wind turbine design package. The aerodynamic modeling is carried out by means of the unsteady Vortex Lattice Method, including a free wake model. The complete model also includes a description of a doubly fed induction generator and its control system for variable speed operation and enhanced power output. The S4WT software features a non-linear finite element solver with multi-body dynamics capability. The complete methodology is used to perform complete aeroservoelastic simulations of a 2MW wind turbine prototype model. The interaction between the three components of the approach is carefully analyzed and presented here. [less ▲]

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See detailOrder reduction in time integration caused by velocity projection
Arnold, Martin; Cardona, Alberto; Bruls, Olivier ULg

in Proceedings of the 3rd Joint International Conference on Multibody System Dynamics and the 7th Asian Conference on Multibody Dynamics (2014, July)

Holonomic constraints restrict the configuration of a multibody system to a subset of the configuration space. They imply so called hidden constraints at the level of velocity coordinates that may ... [more ▼]

Holonomic constraints restrict the configuration of a multibody system to a subset of the configuration space. They imply so called hidden constraints at the level of velocity coordinates that may formally be obtained from time derivatives of the original holonomic constraints. A numerical solution that satisfies hidden constraints as well as the original constraint equations may be obtained considering both types of constraints simultaneously in each time step (stabilized index-2 formulation) or using projection techniques. Both approaches are well established in the time integration of differential-algebraic equations. Recently, we have introduced a generalized- alpha Lie group time integration method for the stabilized index-2 formulation that achieves second order convergence for all solution components. In the present paper, we show that a separate velocity projection would be less favourable since it may result in an order reduction and in large transient errors after each projection step. This undesired numerical behaviour is analysed by a one-step error recursion that considers the coupled error propagation in differential and algebraic solution components. This one-step error recursion has been used before to prove second order convergence for the application of generalized-alpha methods to constrained systems. As a technical detail, we discuss the extension of these results from symmetric, positive definite mass matrices to the rank deficient case. [less ▲]

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See detailGeometric interpretation of a non-linear beam finite element on the Lie group SE(3)
Sonneville, Valentin ULg; Cardona, Alberto; Bruls, Olivier ULg

in Archive of Mechanical Engineering (2014), 61(2), 305-329

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See detailRecent progresses in the nonsmooth contact dynamics method for flexible multibody systems
Bruls, Olivier ULg

Scientific conference (2014, January 10)

This talk will start with a brief overview of the current research activities undertaken at the Multibody & Mechatronic Systems Laboratory with a number of applications in the fields of wind turbines ... [more ▼]

This talk will start with a brief overview of the current research activities undertaken at the Multibody & Mechatronic Systems Laboratory with a number of applications in the fields of wind turbines, deployable space structures, robotics and human motion analysis. Then, the presentation will focus on some recent results related with the modelling of dynamic contact conditions in multibody systems. Typical applications include the modelling of non-ideal joints with backlash and friction, the analysis of mechanical transmission systems and gearboxes, the modelling of grasping tasks or the description of the foot-ground contact in gait analysis. The proposed formalism relies on the nonsmooth contact dynamics method. Accordingly, the condition of impenetrability of the bodies in contact is expressed as a unilateral constraint, with the consequence that impacts and/or instantaneous changes in the velocities may arise in the dynamic response. Also, the resulting set of equations is solved in the time domain using a time-stepping strategy, which is known its robustness and its ability to deal with a large number of events in an efficient way. After a review of the time-stepping method originally proposed by Moreau and Jean, a number of improvements are addressed during the talk. Firstly, a splitting method is introduced to isolate the contributions of impacts, which can only be integrated with first-order accuracy, from smooth contributions, which can be integrated using a higher order scheme. Secondly, following the idea of Gear, Gupta and Leimkuhler, the equation of motion is reformulated so that the bilateral and unilateral constraints appear both at position and velocity levels. This strategy leads to an algorithm which exactly satisfies the constraints at both levels, i.e., no penetration is allowed in the numerical response. After time discretization, the equation of motion involves two complementarity conditions and it can be solved at each time step using a monolithic semi-smooth Newton method. The numerical behaviour of the proposed scheme is studied and compared to other approaches for a number of numerical examples. It is shown that the formulation offers a unified and valid approach for the description of contact conditions between rigid bodies as well as between flexible bodies. [less ▲]

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See detailSensitivity analysis for multibody systems formulated on a Lie group
Sonneville, Valentin ULg; Bruls, Olivier ULg

in Multibody System Dynamics (2014), 31

A direct differentiation method and an adjoint variable method are proposed for the efficient semi-analytical evaluation of the sensitivities of multibody systems formulated in a matrix Lie group ... [more ▼]

A direct differentiation method and an adjoint variable method are proposed for the efficient semi-analytical evaluation of the sensitivities of multibody systems formulated in a matrix Lie group framework. These methods rely on the linearization of the equations of motion and/or of the time integration procedure. The simpler structure of the equations of motion in the Lie group formalism appears as an advantage for that purpose. Lie bracket contributions and the non-linearity of the exponential map need to be taken into account in the sensitivity algorithms. Nevertheless, essential characteristics of formulations of the direct differentiation method and the adjoint variable method on linear spaces are recovered. Some implementation issues are discussed and two relevant examples illustrate the properties of these methods. [less ▲]

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See detailA stable inversion method for feedforward control of constrained flexible multibody systems
Bruls, Olivier ULg; Bastos, Guaraci Jr.; Seifried, Robert

in Journal of Computational and Nonlinear Dynamics (2014), 9(1), 011014

The inverse dynamics of flexible multibody systems is formulated as a two-point boundary value problem for an index-3 differential-algebraic equation (DAE). This DAE represents the equation of motion with ... [more ▼]

The inverse dynamics of flexible multibody systems is formulated as a two-point boundary value problem for an index-3 differential-algebraic equation (DAE). This DAE represents the equation of motion with kinematic and trajectory constraints. For so-called nonminimum phase systems, the remaining dynamics of the inverse model is unstable. Therefore, boundary conditions are imposed not only at the initial time but also at the final time in order to obtain a bounded solution of the inverse model. The numerical solution strategy is based on a reformulation of the DAE in index-2 form and a multiple shooting algorithm, which is known for its robustness and its ability to solve unstable problems. The paper also describes the time integration and sensitivity analysis methods that are used in each shooting phase. The proposed approach does not require a reformulation of the problem in input-output normal form known from nonlinear control theory. It can deal with serial and parallel kinematic topology, minimum phase and nonminimum phase systems, and rigid and flexible mechanisms. [less ▲]

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See detailGeometrically exact beam finite element formulated on the special Euclidean group SE(3)
Sonneville, Valentin ULg; Cardona, Alberto; Bruls, Olivier ULg

in Computer Methods in Applied Mechanics & Engineering (2014), 268

This paper describes a dynamic formulation of a straight beam finite element in the setting of the special Euclidean group SE(3). First, the static and dynamic equilibrium equations are derived in this ... [more ▼]

This paper describes a dynamic formulation of a straight beam finite element in the setting of the special Euclidean group SE(3). First, the static and dynamic equilibrium equations are derived in this framework from variational principles. Then, a non-linear interpolation formula using the exponential map is introduced. It is shown that this framework leads to a natural coupling in the interpolation of the position and rotation variables. Next, the discretized internal and inertia forces are developed. The semi-discrete equations of motion take the form of a second-order ordinary differential equation on a Lie group, which is solved using a Lie group time integration scheme. It is remarkable that no parameterization of the nodal variables needs to be introduced and that the proposed Lie group framework leads to a compact and easy-to-implement formulation. Some important numerical and theoretical aspects leading to a computationally efficient strategy are highlighted and discussed. For instance, the formulation leads to invariant tangent stiffness and mass matrices under rigid body motions and a locking free element. The proposed formulation is successfully tested in several numerical static and dynamic examples. [less ▲]

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See detailSimultaneous enforcement of constraints at position and velocity levels in the nonsmooth generalized-alpha scheme
Bruls, Olivier ULg; Acary, Vincent; Cardona, Alberto

in Computer Methods in Applied Mechanics & Engineering (2014), 281

This paper presents a formalism for the transient simulation of nonsmooth dynamic mechanical systems composed of rigid and flexible bodies, kinematic joints and frictionless contact conditions. The ... [more ▼]

This paper presents a formalism for the transient simulation of nonsmooth dynamic mechanical systems composed of rigid and flexible bodies, kinematic joints and frictionless contact conditions. The proposed algorithm guarantees the exact satisfaction of the bilateral and unilateral constraints both at position and velocity levels. Thus, it significantly differs from penalty techniques since no penetration is allowed. The numerical scheme is obtained in two main steps. Firstly, a splitting method is used to isolate the contributions of impacts, which shall be integrated with only first-order accuracy, from smooth contributions which can be integrated using a higher order scheme. Secondly, following the idea of Gear, Gupta and Leimkuhler, the equations of motion are reformulated so that the bilateral and unilateral constraints appear both at position and velocity levels. After time discretization, the equations of motion involve two complementarity conditions and it can be solved at each time step using a monolithic semi-smooth Newton method. The numerical behaviour of the proposed method is studied and compared to other approaches for a number of numerical examples. It is shown that the formulation offers a unified and valid approach for the description of contact conditions between rigid bodies as well as between flexible bodies. [less ▲]

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See detailDominance effect on scapula 3-dimensional posture and kinematics in healthy male and female populations
Schwartz, Cédric ULg; Croisier, Jean-Louis ULg; Rigaux, Elise et al

in Journal of Shoulder and Elbow Surgery (2014), 23(0), 873-881

Background: The contralateral shoulder is often used as a reference when evaluating a pathological shoulder. However literature provides contradictory results regarding the symmetry of the scapular ... [more ▼]

Background: The contralateral shoulder is often used as a reference when evaluating a pathological shoulder. However literature provides contradictory results regarding the symmetry of the scapular pattern in a healthy population. We assume that several factors including the gender and the type of motion may influence the scapula bilateral symmetry. Method: The dominant and non dominant shoulders of two populations of men and women composed of 11 subjects each were evaluated for three distinct motions: flexion in the sagittal plane, abduction in the frontal plane and gleno-humeral internal/external rotation with the arm abducted at 90°. Posture, kinematic and range of motion were studied separately. Results: Asymmetries are observed for motions performed in the frontal and sagittal plane but not for the internal/external rotation with the arm abducted at 90°. Multiplane asymmetries are observed for the male population, whereas asymmetries for the female one are mainly uniplanar. For both men and women, the scapula has a larger upward rotation on the dominant side. For men, a larger posterior tilt is also observed. The asymmetries mainly originate in the scapula kinematic and not in its original posture. Discussion: Even if the asymmetries are not large in terms of amplitude (inferior to 5°), one should be aware of their existence and the influence of the composition of the studied population when using the contralateral shoulder as a reference. [less ▲]

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See detailImportance of structural damping in the dynamic analysis of compliant deployable structures
Dewalque, Florence ULg; Rochus, Pierre ULg; Bruls, Olivier ULg

in Proceedings of the 65th International Astronautical Congress (IAC) (2014)

Compliant mechanisms such as tape springs are often used on satellites to deploy appendices, e.g. solar panels, antennas, telescopes and solar sails. Their main advantage comes from the fact that their ... [more ▼]

Compliant mechanisms such as tape springs are often used on satellites to deploy appendices, e.g. solar panels, antennas, telescopes and solar sails. Their main advantage comes from the fact that their motion results from the elastic deformation of structural components, unlike usual hinges or prismatic joints, the motion of which is dictated by contact surfaces. No actuators or external energy sources are required and the deployment is purely passive, which appears as a decisive feature for the design of low-cost missions with small satellites or cubesats. The mechanical behaviour of a tape spring is intrinsically complex and nonlinear involving buckling, hysteresis and self-locking phenomena. High-fidelity mechanical models are then needed to get a detailed understanding of the deployment process, improve the design and predict the actual behaviour in the space 0-g environment. In the majority of the previous works, dynamic simulations were performed without any physical representation of the structural damping. These simulations could be successfully achieved because of the presence of numerical damping in the transient solver. However, in this case, the dynamic response turns out to be quite sensitive to the amount of numerical dissipation, so that the predictive capabilities of the model are questionable. In this work based on numerical case studies, we show that the dynamic simulation of a tape spring can be made less sensitive to numerical parameters when the structural dissipation is taken into account. [less ▲]

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See detailExperimental Study of the Human Ability to Deliberately Excite a Flexible Floor
Schwartz, Cédric ULg; Berger, Alexis; Bruls, Olivier ULg et al

in Zingoni, Alphose (Ed.) Proceedings of the 5th International Conference on Structural Engineering, Mechanics and Computation (2014)

Human-structure interactions are not completely understood yet. This paper presents an experimental study focusing on the interaction between a human and a flexible support, with a major aim to better ... [more ▼]

Human-structure interactions are not completely understood yet. This paper presents an experimental study focusing on the interaction between a human and a flexible support, with a major aim to better understand how the behavior of a human subject, bouncing on a flexible structure, adapts to the support motion. Exploratory experiments are undertaken with a 7m-span timber footbridge tested in the Human Motion Analysis Laboratory of the University of Liege. The movements of the coupled system composed of the subject and the footbridge are recorded by Motion Capture technology; the subject\textquoteright{}s 3-D body motion is defined by three important angles: ankle, knee and hip. The interaction between the subject and the footbridge is also quantified by means of force platform measurements. The experiments indicate an influence of the support amplitude and natural frequency on the phase shift between the oscillatory floor motion and the three angles characterizing the motion. [less ▲]

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See detailDiscussion on the optimization problem formulation of flexible components in multibody systems
Tromme, Emmanuel ULg; Bruls, Olivier ULg; Emonds-Alt, Jonathan et al

in Structural and Multidisciplinary Optimization (2013), 48(6), 1189-1206

This paper is dedicated to the structural optimization of flexible components in mechanical systems modeled as multibody systems. While most of the structural optimization developments have been conducted ... [more ▼]

This paper is dedicated to the structural optimization of flexible components in mechanical systems modeled as multibody systems. While most of the structural optimization developments have been conducted under (quasi-)static loadings or vibration design criteria, the proposed approach aims at considering as precisely as possible the effects of dynamic loading under service conditions. Solving this problem is quite challenging and naive implementations may lead to inaccurate and unstable results. To elaborate a robust and reliable approach, the optimization problem formulation is investigated because it turns out that it is a critical point. Different optimization algorithms are also tested. To explain the efficiency of the various solution approaches, the complex nature of the design space is analyzed. Numerical applications considering the optimization of a two-arm robot subject to a trajectory tracking constraint and the optimization of a slider-crank mechanism with a cyclic dynamic loading are presented to illustrate the different concepts. [less ▲]

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See detailIntroduction to model order reduction methods for linear and nonlinear multiphysics systems
Bruls, Olivier ULg

Scientific conference (2013, November 08)

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See detail3D analysis of gait using accelerometer measurements
Boutaayamou, Mohamed ULg; Schwartz, Cédric ULg; Stamatakis, Julien et al

Scientific conference (2013, November 07)

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See detailA nonsmooth generalized-alpha scheme for flexible multibody systems with unilateral constraints
Chen, Qiong-zhong; Acary, Vincent; Virlez, Geoffrey ULg et al

in International Journal for Numerical Methods in Engineering (2013), 96(8), 487-511

Mechanical systems are usually subjected not only to bilateral constraints but also to unilateral constraints. Inspired by the generalized-alpha time integration method for smooth flexible multibody ... [more ▼]

Mechanical systems are usually subjected not only to bilateral constraints but also to unilateral constraints. Inspired by the generalized-alpha time integration method for smooth flexible multibody dynamics, this paper presents a nonsmooth generalized-alpha method, which allows a consistent treatment of the nonsmooth phenomena induced by unilateral constraints and an accurate description of the structural vibrations during free motions. Both the algorithm and the implementation are illustrated in detail. Numerical example tests are given in the scope of both rigid and flexible body models, taking account for both linear and nonlinear systems, and comprising both unilateral and bilateral constraints. The extended nonsmooth generalized-alpha method is verified through comparison to the traditional Moreau-Jean method and the fully implicit Newmark method. Results show that the nonsmooth generalized-alpha method benefits from the accuracy and stability property of the classical generalized-alpha method with controllable numerical damping. In particular, when it comes to the analysis of flexible systems, the nonsmooth generalized-alpha method shows much better accuracy property than the other two methods. [less ▲]

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See detailLie group formalisms in flexible multibody dynamics
Bruls, Olivier ULg

Conference (2013, September)

This course presents a recently-developed Lie group approach for the analysis of flexible multibody systems with large rotations and kinematic constraints in a parameterization-free setting. More ... [more ▼]

This course presents a recently-developed Lie group approach for the analysis of flexible multibody systems with large rotations and kinematic constraints in a parameterization-free setting. More precisely, the equations of motion are formulated as differential-algebraic equations (DAE) on a matrix Lie group and are then solved using a Lie group time integration method. Based on a nonlinear finite element approach, the lecture shows how the kinematics of a flexible multibody system, including the description of nodal frames, velocity fields, constraints, and flexible bodies, are described in the Lie group framework. The general structure of the equations of motion are derived from the Hamilton principle in a general and unifying approach. A Lie group generalized-alpha time integration scheme is proposed for DAEs on a Lie group and practical implementation issues are discussed. Finally, semi-analytical algorithms for sensitivity analysis on a Lie group are proposed for optimization purpose. The theoretical concepts and the numerical properties of the algorithms are illustrated with a number of examples. [less ▲]

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