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See detailGender effect on the scapular 3D posture and kinematic in healthy subjects
Schwartz, Cédric ULg; Croisier, Jean-Louis ULg; Rigaux, Elise et al

in Clinical Physiology and Functional Imaging (in press)

Populations considered for shoulder analysis are often composed of various ratios of men and women. It is consequently hypothesized that gender has no significant effect on the joint kinematic. However ... [more ▼]

Populations considered for shoulder analysis are often composed of various ratios of men and women. It is consequently hypothesized that gender has no significant effect on the joint kinematic. However the literature reports, for the shoulder, differences in the range of motion between genders. The specific influence of gender on the scapula-thoracic kinematics has not been studied yet. The dominant shoulder of two populations of men and women composed of 11 subjects each were evaluated in three dimensions 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, kinematics and range of motion were studied separately. For flexion and abduction and with regard to the scapular kinematic, external rotation were significantly larger for women than men. The differences were of at least 5° at 120° of humeral elevation. Upward rotations were identical. Women also showed larger average active humero-thoracic range of motion. The mean differences were of 13°, 7°, 12° and 5° for abduction, flexion, internal rotation and external rotation, respectively. No difference was observed between the scapular resting positions of both populations. The observed differences concerning both the scapular and humeral patterns would indicate that the shoulder behavior of men and women should not be expected to be similar. [less ▲]

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See detailBiomechanical Analysis of Abdominal Injury in Tennis Serves. A Case Report
Tubez, François ULg; Forthomme, Bénédicte ULg; Croisier, Jean-Louis ULg et al

in Journal of Sports Science & Medicine (2015), 14

The serve is an important stroke in any high level tennis game. A well-mastered serve is a substantial advantage for players. However, because of its repeatability and its intensity, this stroke is ... [more ▼]

The serve is an important stroke in any high level tennis game. A well-mastered serve is a substantial advantage for players. However, because of its repeatability and its intensity, this stroke is potentially deleterious for upper limbs, lower limbs and trunk. The trunk is a vital link in the production and transfer of energy from the lower limbs to the upper limbs; therefore, kin-ematic disorder could be a potential source of risk for trunk injury in tennis. This research studies the case of a professional tennis player who has suffered from a medical tear on the left rectus abdominis muscle after tennis serve. The goal of the study is to understand whether the injury could be explained by an inappropriate technique. For this purpose, we analyzed in three dimensions the kinematic and kinetic aspects of the serve. We also performed isokinetic tests of the player’s knees. We then compared the player to five other professional players as refer-ence. We observed a possible deficit of energy transfer because of an important anterior pelvis tilt. Some compensation made by the player during the serve could be a possible higher abdominal contraction and a larger shoulder external rotation. These partic-ularities could induce an abdominal overwork that could explain the first injury and may provoke further injuries. [less ▲]

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See detailHow bioméchanical analysis may help to identify abdominal injury causes in high level tennis
Tubez, François ULg; Forthomme, Bénédicte ULg; Croisier, Jean-Louis ULg et al

Conference (2015, July)

This research studies the case of a professional tennis player who has suffered from a medical tear on the left rectus abdominis muscle after a tennis serve. The goal of the study is to understand whether ... [more ▼]

This research studies the case of a professional tennis player who has suffered from a medical tear on the left rectus abdominis muscle after a tennis serve. The goal of the study is to understand whether the injury could be explained by an inappropriate technique. For this purpose, we analyzed the three dimensions kinematic and kinetic of the serve. We also performed isokinetic tests of the knees. We compared the player to five other professional players. We observed a possible deficit of energy transfer because of an important anterior pelvis tilt. Some compensations of the player during serve could be a possible higher abdominal contraction and a larger shoulder external rotation. These particularities could induce an abdominal overwork that would explain the first injury and may provoke a new injury. [less ▲]

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See detailTrajectory optimization for 3D robots with elastic links
Lismonde, Arthur ULg; Sonneville, Valentin ULg; Bruls, Olivier ULg

Scientific conference (2015, June 29)

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See detailA level set approach for the structural optimization of flexible mechanisms
Tromme, Emmanuel ULg; Tortorelli, Daniel; Bruls, Olivier ULg et al

Conference (2015, June 08)

With the evolution of virtual prototyping, mechanical systems are commonly analyzed using a multibody system (MBS) approach to study the behavior of the entire system and notably the dynamic interactions ... [more ▼]

With the evolution of virtual prototyping, mechanical systems are commonly analyzed using a multibody system (MBS) approach to study the behavior of the entire system and notably the dynamic interactions between the components. Modern structural optimization of mechanical systems considers the dynamic loading exerted on the individual flexible components. The consideration is an essential feature and can be implemented in two ways. Firstly, one can consider a strong coupling wherein the component’s optimization is performed using the time dependent loading conditions coming directly from the MBS simulation. Secondly, one can consider a weak coupling wherein the component’s optimization is performed using a series of static load cases that do not fully account for the interactions between the components of the MBS. Rather this approach performs a MBS simulation to evaluate the loads for the initial design and then optimizes the component assuming the loads do not change. The process of evaluating the loads and then performing the optimization is repeated until suitable convergence criteria is satisfied, assuming convergence is possible. The present paper focuses on the strong coupling method wherein the flexible MBS dynamic analysis is based on a nonlinear finite element formalism [1]. A level set (LS) description of the component geometry is used to enable a generalized shape optimization. The LS approach combines the advantages of shape and topology optimizations. Moreover, since the component boundaries are defined by CAD features, the manufacturing process is facilitated as no post-processing step of a rasterized design is required. The design sensitivity analysis for MBS is revisited in order to facilitate its implementation. The optimization of a slider-crank mechanism and a 2-dof robot is provided to exemplify the procedure. [1] Géradin M., Cardona A. (2001) Flexible Multibody Dynamics: A Finite Element Approach. John Wiley & Sons, New York. [less ▲]

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See detailNonlinear Interpolation on Manifold of Reduced Order Models in Magnetodynamic Problems
Paquay, Yannick ULg; Bruls, Olivier ULg; Geuzaine, Christophe ULg

Poster (2015, June)

Proper Orthogonal Decomposition (POD) is an efficient model order reduction technique for linear problems in computational sciences, recently gaining popularity in electromagnetics. However, its ... [more ▼]

Proper Orthogonal Decomposition (POD) is an efficient model order reduction technique for linear problems in computational sciences, recently gaining popularity in electromagnetics. However, its efficiency has been shown to considerably degrade for nonlinear problems. In this paper, we propose a reduced order model for nonlinear magnetodynamic problems by combining POD with an interpolation on manifolds, which interpolates the reduced bases to efficiently construct the desired solution. [less ▲]

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See detailDevelopment and validation of an accelerometer-based method for quantifying gait events
Boutaayamou, Mohamed ULg; Schwartz, Cédric ULg; Stamatakis, Julien et al

in Medical Engineering & Physics (2015)

An original signal processing algorithm is presented to automatically extract, on a stride-by-stride basis, four consecutive fundamental events of walking, heel strike (HS), toe strike (TS), heel-off (HO ... [more ▼]

An original signal processing algorithm is presented to automatically extract, on a stride-by-stride basis, four consecutive fundamental events of walking, heel strike (HS), toe strike (TS), heel-off (HO), and toe-off (TO), from wireless accelerometers applied to the right and left foot. First, the signals recorded from heel and toe three-axis accelerometers are segmented providing heel and toe flat phases. Then, the four gait events are defined from these flat phases. The accelerometer-based event identification was validated in seven healthy volunteers and a total of 247 trials against reference data provided by a force plate, a kinematic 3D analysis system, and video camera. HS, TS, HO, and TO were detected with a temporal accuracy ± precision of 1.3 ms ± 7.2 ms, ‒4.2 ms ± 10.9 ms, ‒3.7 ms ± 14.5 ms, and ‒1.8 ms ± 11.8 ms, respectively, with the associated 95% confidence intervals ranging from ‒6.3 ms to 2.2 ms. It is concluded that the developed accelerometer-based method can accurately and precisely detect HS, TS, HO, and TO, and could thus be used for the ambulatory monitoring of gait features computed from these events when measured concurrently in both feet. [less ▲]

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See detailExperimental Validation of Structural Damping Models for Tape Springs
Dewalque, Florence ULg; Bruls, Olivier ULg

in Proceedings of the 6th European Conference for Aerospace Sciences (EUCASS) (2015)

The objective of this paper is to study the effect of structural dissipation on the dynamic response of tape springs using experimentally-validated finite element models. In order to reach this goal, an ... [more ▼]

The objective of this paper is to study the effect of structural dissipation on the dynamic response of tape springs using experimentally-validated finite element models. In order to reach this goal, an experimental set-up is built. It consists of two tape springs connected to a fixation support and a dummy panel. The data are collected through a force plate and a 3D motion analysis system. The post-treatment of the experimental results and a comparison with a finite element model show that the Kelvin-Voigt model gives a fair approximation of the structural damping for small oscillations, however, more advanced model should be considered in future works for a better understanding in case of large displacements. [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 Acta Astronautica (2015), 111

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 detailError analysis of generalized-alpha Lie group time integration methods for constrained mechanical systems
Arnold, Martin; Bruls, Olivier ULg; Cardona, Alberto

in Numerische Mathematik (2015), 129(1), 149-179

Generalized-alpha methods are very popular in structural dynamics. They are methods of Newmark type and combine favourable stability properties with second order convergence for unconstrained second order ... [more ▼]

Generalized-alpha methods are very popular in structural dynamics. They are methods of Newmark type and combine favourable stability properties with second order convergence for unconstrained second order systems in linear spaces. Recently, they were extended to constrained systems in flexible multibody dynamics that have a configuration space with Lie group structure. In the present paper, the convergence of these Lie group methods is analysed by a coupled one-step error recursion for differential and algebraic solution components. It is shown that spurious oscillations in the transient phase result from order reduction that may be avoided by a perturbation of starting values or by index reduction. Numerical tests for a benchmark problem from the literature illustrate the results of the theoretical investigations. [less ▲]

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See detailMerging multi-camera data to reduce motion analysis instrumental errors using Kalman filters
Schwartz, Cédric ULg; Denoël, Vincent ULg; Forthomme, Bénédicte ULg et al

in Computer Methods in Biomechanics and Biomedical Engineering (2015), 18(9), 952-960

In motion capture systems, markers are often seen by multiple cameras. All cameras do not measure the position of the markers with the same reliability because of environmental factors such as the ... [more ▼]

In motion capture systems, markers are often seen by multiple cameras. All cameras do not measure the position of the markers with the same reliability because of environmental factors such as the position of the marker in the field of view or the light intensity received by the cameras. Kalman filters offer a general framework to take the reliability of the various cameras into account and consequently improve the estimation of the marker position. The proposed process can be applied to both passive and active systems. Several reliability models of the cameras are compared for the Codamotion active system, which is considered as a specific illustration. The proposed method significantly reduces the noise in the signal, especially at long range distances. Therefore, it improves the confidence of the positions at the limits of the field of view. [less ▲]

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See detailA mortar method combined with an augmented Lagrangian approach for treatment of mechanical contact problems
Cavalieri, Federico J.; Bruls, Olivier ULg; Cardona, Alberto

in Terze, Zdravko (Ed.) Multibody Dynamics: Computational Methods and Applications (2015)

This work presents a mixed penalty-duality formulation from an augmented Lagrangian approach for treating the contact inequality constraints. The augmented Lagrangian approach allows to regularize the non ... [more ▼]

This work presents a mixed penalty-duality formulation from an augmented Lagrangian approach for treating the contact inequality constraints. The augmented Lagrangian approach allows to regularize the non differentiable contact terms and gives a C1 differentiable saddle-point functional. The relative displacement of two contacting bodies is described in the framework of the Finite Element Method (FEM) using the mortar method, which gives a smooth representation of the contact forces across the bodies interface. To study the robustness and performance of the proposed algorithm, validation numerical examples with finite deformations and large slip motion are presented. [less ▲]

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See detailDevelopment and validation of a 3D kinematic-based method for determining gait events during overground walking
Boutaayamou, Mohamed ULg; Schwartz, Cédric ULg; Denoël, Vincent ULg et al

in IEEE International Conference on 3D Imaging (IC3D) (2014, December 09)

A new signal processing algorithm is developed for quantifying heel strike (HS) and toe-off (TO) event times solely from measured heel and toe coordinates during overground walking. It is based on a rough ... [more ▼]

A new signal processing algorithm is developed for quantifying heel strike (HS) and toe-off (TO) event times solely from measured heel and toe coordinates during overground walking. It is based on a rough estimation of relevant local 3D position signals. An original piecewise linear fitting method is applied to these local signals to accurately identify HS and TO times without the need of using arbitrary experimental coefficients. We validated the proposed method with nine healthy subjects and a total of 322 trials. The extracted temporal gait events were compared to reference data obtained from a force plate. HS and TO times were identified with a temporal accuracy ± precision of 0.3 ms ± 7.1 ms, and –2.8 ms ± 7.2 ms in comparison with reference data defined with a force threshold of 10 N. This algorithm improves the accuracy of the HS and TO detection. Furthermore, it can be used to perform stride-by-stride analysis during overground walking with only recorded heel and toe coordinates. [less ▲]

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See detailValidation des paramètres de marche par un système accélérométrique (Locométrix*) à l'aide d'un système opto-électronique 3D (Coda Motion )
GILLAIN, Sophie ULg; Schwartz, Cédric ULg; Boutaayamou, Mohamed ULg et al

in Gériatrie et Psychologie Neuropsychiatrie du Vieillissement (2014), 12(supplément 3),

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See detailA formulation on the special Euclidean group for dynamic analysis of multibody systems
Sonneville, Valentin ULg; Bruls, Olivier ULg

in Journal of Computational and Nonlinear Dynamics (2014), 9(4), 041002

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See detailInfluence of players' level on racket speed and ball accuracy in the tennis serve
Tubez, François ULg; Croisier, Jean-Louis ULg; Cordonnier, Caroline ULg et al

Conference (2014, July 06)

INTRODUCTION Serve in modern tennis game is an important offensive weapon for players (1-2). In kinematic analysis, serve is the most studied stroke of this game. The aim of our study was to compare the ... [more ▼]

INTRODUCTION Serve in modern tennis game is an important offensive weapon for players (1-2). In kinematic analysis, serve is the most studied stroke of this game. The aim of our study was to compare the performance of two specific populations: international players versus national players. In particular, racket speed at impact and accuracy of ball were assessed. METHODS A tennis court was reconstructed in a motion analysis laboratory. The position of the racket was evaluated in 3D at a frequency rate of 200 Hz. Tests were performed on 6 professional players (international level) and 9 non-professional players (national level). Each of them served 25 trials in direction of the “T” area of deuce diagonal. Two squares of 1m² and 2 m² respectively were delimited on the corner of the serve square. The instruction for both groups was to serve in the “T” area with the highest ball speed and minimal ball rotation (flat serve). RESULTS Although the forward speed of the racket at impact was identical between the two groups of players (International 36.35 ± 2.37 m/s and national 36.37 ± 2.90 m/s, p-value 0,991), the accuracy and consistency of serves on the target area is better for international players group (1m² area: International 33% ± 7% and national 14% ± 12%, p-value 0.0053; 2m² area (including 1m² area): International 71% ± 8% and national 54% ± 12%, p-value 0.0096; Out of zone: International 29% ± 8% and national 46% ± 12%, p-value 0.014). DISCUSSION High-velocity ball seems to be a key factor for serve performance (3). It is known that there is a relationship between racket speed and ball velocity (4). Both groups have high racket speed. However, international players serve with better accuracy and consistency than national players. We hypothesize that these differences are due to capacity of international players to adapt to a particular environment. Moreover, international players could give priority to consistency over velocity. We conclude that high-velocity serve is not a sufficient criterion to perform at international level; consistency and accuracy are two important factors to reach this level. [less ▲]

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