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See detailReproducibility of a tennis serve protocol
Tubez, François ULg; FORTHOMME, Bénédicte ULg; Croisier, Jean-Louis ULg et al

Conference (2016, July 08)

INTRODUCTION Serve in modern tennis game is a real offensive weapon for players. In kinematic analysis, it is the most studied stroke of this game because it is the only stroke played in a closed skill ... [more ▼]

INTRODUCTION Serve in modern tennis game is a real offensive weapon for players. In kinematic analysis, it is the most studied stroke of this game because it is the only stroke played in a closed skill. Players have a maximum of control on this stroke. It is unclear whether 3D kinematic tests are reproducible for the same player under identical conditions and if a familiarization session is necessary. In practice, with professional players, who have little time available to perform tests, familiarization sessions are difficult. The aim of our study is to measure the reproducibility of a 3D serve protocol test. METHODS Nine tennis players (righties, regional level, 20 ± 2 years) were asked to hit first flat serves in a 1 m² area placed on the "T" zone of deuce diagonal of the tennis court. Two identical tests are performed one week apart. For each test, we selected the three best serves of the 25 trials (with the highest speed and the highest accuracy). Kinetics measurements were performed using a 3D analysis system (Codamotion), a force platform (Kistler) and a radar gun. 28 markers were placed on the players’ bodies to measure kinematics of the movements: ankles, knees, hips, trunk, shoulder, elbow and wrist dominant side. We measured ball speed, leg drive, linear velocity of the racket and joints, joints range of motion and maximum angular velocities at different positions (armed, maximum external rotation and impact) (1). RESULTS All analyzed parameters (linear speeds of racket and joints, leg drive force, joint angles and angular velocities) are reproducible with exception of a small part of them. Our study shows that 5,7% (7 of 122 measurements) joint position parameters and 8,3% (4 of 48 measures) angular velocity parameters are not reproducible from a session to another. DISCUSSION Various errors sources encountered in 3D analysis can justify the presence of non-reproducible parameters (2-3). However, after this work, we can state that the established protocol provides reproducible results when analyzing the tennis serve. [less ▲]

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See detailApplications of the multiple timescale spectral analysis in wind engineering
Denoël, Vincent ULg

in Zingoni, Alphose (Ed.) Proceedings of the Sixth International Conference on Structural Engineering, Mechanics and Computation (2016, July)

The random response of civil engineering structures to the buffeting action of wind loads is typically composed of several components, usually referred to as the background component, in the low fre ... [more ▼]

The random response of civil engineering structures to the buffeting action of wind loads is typically composed of several components, usually referred to as the background component, in the low fre- quency zone and the resonant component(s) in the neighborhood of modal natural frequencies. It has become customary to study separately and add the contributions of these components to the total response, at least as far as the second order response (variance of structural responses) is concerned. Such a decomposition exists but is less usual for the computation of covariances of modal coordinates or of structural displacements, which are in turn necessary for the determination of internal stresses. The question of such a decomposition also holds for nonlinear systems, or even for the higher statistical moments of a linear structural system, should the response be non Gaussian. With very wide ranges of applicability, the Multiple Timescale Spectral Analysis summarizes under a unified framework recent works aiming at the development of such decompositions. This paper briefly pictures this particular theory based on perturbation methods, and provides illustrations of its applicability to the problems cited above. [less ▲]

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See detailEulerian Formulation of Elastic Rods
Huynen, Alexandre ULg; Detournay, Emmanuel; Denoël, Vincent ULg

in Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences (2016), 472(2190),

In numerous biological, medical and engineering applications, elastic rods are constrained to deform inside or around tube-like surfaces. To solve efficiently this class of problems, the equations ... [more ▼]

In numerous biological, medical and engineering applications, elastic rods are constrained to deform inside or around tube-like surfaces. To solve efficiently this class of problems, the equations governing the deflection of elastic rods are reformulated within the Eulerian framework of this generic tubular constraint defined as a perfectly stiff canal surface. This reformulation hinges on describing the rod deformed configuration by means of its relative position with respect to a reference curve, defined as the axis or spine curve of the constraint, and on restating the rod local equilibrium in terms of the curvilinear coordinate parameterizing this curve. Associated with a segmentation strategy, which partitions the global problem into a sequence of rod segments either in continuous contact with the constraint or free of contact (except for their extremities), this approach not only trivializes the detection of new contacts but also suppresses the isoperimetric constraints resulting from the self-feeding feature of these elementary problems and the imposition of the rod position at the extremities of each rod segments. [less ▲]

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See detailFast In-Plane Dynamics of a Beam with Unilateral Constraints
Liakou, Anna; Denoël, Vincent ULg; Detournay, Emmanuel

in Journal of Engineering Mechanics (2016), 0(0), 04016116

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See detailstochastic stability of a rotational oscillator under gusty winds
Vanvinckenroye, Hélène ULg; Denoël, Vincent ULg

in Proceedings of the XIV Conference of the Italian Association for Wind Engineering (2016)

This work studies the rotational stability of an oscillator in a random wind velocity field. Its susceptibility to autorotation is assessed by the time necessary to reach a given energy barrier departing ... [more ▼]

This work studies the rotational stability of an oscillator in a random wind velocity field. Its susceptibility to autorotation is assessed by the time necessary to reach a given energy barrier departing from an initial energy level. This first passage time problem is solved by replacing the actual power spectral density of the loading by an equivalent δ-correlated noise. [less ▲]

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See detailStochastic rotational stability of tower cranes under gusty winds
Vanvinckenroye, Hélène ULg; Denoël, Vincent ULg

in Proceedings of the Sixth International Conference on Structural Engineering, Mechanics and Computation (2016)

This work aims to study the rotational stability of a tower crane left free to rotate. Indeed, in case of important wind velocities, small oscillations can increase and build up into autorotations due to ... [more ▼]

This work aims to study the rotational stability of a tower crane left free to rotate. Indeed, in case of important wind velocities, small oscillations can increase and build up into autorotations due to autoparametric excitation of the structure. Many references in the literature describe the limit between oscillation and autorotation for simple cases like the deterministic pendulum and evidence the importance of the Hamiltonian of a system on its stability. In this context the susceptibility of the structure to this dynamical instability is characterized by the average time necessary to reach a given energy barrier departing from an initial energy level. This first passage time is the solution of the Pontryagin equation and is approached by an asymptotic expansion. First- and second-order terms are calculated as well as the boundary layer solution providing a correction when the initial energy is close to the barrier level. [less ▲]

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See detailConditional expected static wind loads
Blaise, Nicolas ULg; Andrianne, Thomas ULg; Denoël, Vincent ULg

in In Vento 2016 (2016)

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See detailExtraction of temporal gait parameters using a reduced number of wearable accelerometers
Boutaayamou, Mohamed ULg; Denoël, Vincent ULg; Bruls, Olivier ULg et al

in Proceedings of the 9th International Conference on Bio-inspired Systems and Signal Processing (2016)

Wearable inertial systems often require many sensing units in order to reach an accurate extraction of temporal gait parameters. Reconciling easy and fast handling in daily clinical use and accurate ... [more ▼]

Wearable inertial systems often require many sensing units in order to reach an accurate extraction of temporal gait parameters. Reconciling easy and fast handling in daily clinical use and accurate extraction of a substantial number of relevant gait parameters is a challenge. This paper describes the implementation of a new accelerometer-based method that accurately and precisely detects gait events/parameters from acceleration signals measured from only two accelerometers attached on the heels of the subject’s usual shoes. The first step of the proposed method uses a gait segmentation based on the continuous wavelet transform (CWT) that provides only a rough estimation of motionless periods defining relevant local acceleration signals. The second step uses the CWT and a novel piecewise-linear fitting technique to accurately extract, from these local acceleration signals, gait events, each labelled as heel strike (HS), toe strike (TS), heel-off (HO), toe-off (TO), or heel clearance (HC). A stride-by-stride validation of these extracted gait events was carried out by comparing the results with reference data provided by a kinematic 3D analysis system (used as gold standard) and a video camera. The temporal accuracy ± precision of the gait events were for HS: 7.2 ms ± 22.1 ms, TS: 0.7 ms ± 19.0 ms, HO: ‒3.4 ms ± 27.4 ms, TO: 2.2 ms ± 15.7 ms, and HC: 3.2 ms ± 17.9 ms. In addition, the occurrence times of right/left stance, swing, and stride phases were estimated with a mean error of ‒6 ms ± 15 ms, ‒5 ms ± 17 ms, and ‒6 ms ± 17 ms, respectively. The accuracy and precision achieved by the extraction algorithm for healthy subjects, the simplification of the hardware (through the reduction of the number of accelerometer units required), and the validation results obtained, convince us that the proposed accelerometer-based system could be extended for assessing pathological gait (e.g., for patients with Parkinson’s disease). [less ▲]

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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 (2016)

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 detailSurface Constrained Elastic Rods with Application to the Sphere
Huynen, Alexandre ULg; Detournay, Emmanuel; Denoël, Vincent ULg

in Journal of Elasticity (2016)

The unilateral contact between an elastic rod and a rigid surface is encountered in numerous biological and engineering applications. Along continuous contacts, the centerline of the rod reflects the ... [more ▼]

The unilateral contact between an elastic rod and a rigid surface is encountered in numerous biological and engineering applications. Along continuous contacts, the centerline of the rod reflects the geometry of the constraining surface. This restriction of the rod axis to surface bound configurations enters its local equilibrium through a reaction pressure which ensures the compatibility between the deformation and the restraint geometry. The classic equations governing the static equilibrium of elastic rods are particularized to surface bound configurations by (i) specifying the location of the rod axis in terms of its coordinates in the parameter space associated with the constraining surface parameterization, and (ii) characterizing the orientation of its material frame through its rotation with respect to the surface normal. This formulation, which emphasizes the relations between the rod configuration and the geometry of the constraint, also leads to an expression for the reaction pressure. This approach is then validated on a spherical surface by comparing with known solutions for elastic curves, i.e., inextensible and twist free rods. [less ▲]

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See detailPerturbation Methods
Denoël, Vincent ULg

Learning material (2016)

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See detailReconstruction of the envelope of non-Gaussian structural responses with principal static wind loads
Blaise, Nicolas ULg; Canor, Thomas; Denoël, Vincent ULg

in Journal of Wind Engineering & Industrial Aerodynamics (2015), 149

In current practice, structural engineers commonly focus on the wind-resistant design by means of static wind loads. In case of non-Gaussianities, there is room for improvement to properly derive these ... [more ▼]

In current practice, structural engineers commonly focus on the wind-resistant design by means of static wind loads. In case of non-Gaussianities, there is room for improvement to properly derive these static loads. First, this paper extends in a non-Gaussian context the concept of the load-response correlation (LRC) method establishing equivalent static wind loads (ESWLs). This is done by a proper recourse to the new concept of conditional expected static wind load and a proposed bicubic model for the joint and conditional distribution functions. Second, this paper investigates the envelope reconstruction problem targeting the efficient reconstruction of the envelope values of a set of non-Gaussian structural responses by means of principal static wind loads (PSWLs). They have been introduced in a Gaussian context and are obtained by a singular value decomposition of ESWLs. This paper addresses the extension of PSWLs to non-Gaussian structural responses, as well. The developments apply to structures with a linear behavior and subjected to an aerodynamic pressure field exhibiting mildly to strongly non-Gaussian features. In this context, the well-known load-response correlation and conditional sampling methods are used for comparisons. This study is undertaken for quasi-static analysis of structures and is illustrated on a low-rise building. [less ▲]

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See detailPressure-impulse diagram of a beam developing non-linear membrane action under blast loading
Hamra, Lotfi ULg; Demonceau, Jean-François ULg; Denoël, Vincent ULg

in International Journal of Impact Engineering (2015), 86

The p–I diagram of a frame beam subjected to blast loading is established, including the elastic lateral restraint and inertia offered by the rest of the structure, the development of nonlinear membrane ... [more ▼]

The p–I diagram of a frame beam subjected to blast loading is established, including the elastic lateral restraint and inertia offered by the rest of the structure, the development of nonlinear membrane action and also, the bending-tension (M−N) interaction that develops in the plastic hinges. The analytical procedures to compute the asymptotes in the p–I diagram as well as a parametric study on the p–I diagram are provided. A dimensional analysis of the problem reveals that, under the considered assumptions, four dimensionless parameters mainly influence the required ductility of the beam. Two of them are related to the behavior of the indirectly affected part (the lateral restraint and mass). Another one is related to the mechanical properties of the investigated beam (i.e. the ratio of the bending to axial resistance). The last parameter incorporates scales of the geometry and of the deformed configuration at the onset of the plastic mechanism. [less ▲]

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See detailEssentials of actions
Cerfontaine, Benjamin ULg; Collin, Frédéric ULg; Denoël, Vincent ULg et al

Learning material (2015)

This document deals with the philosophy of safety in civil engineering structures, including loads and load combinations to be applied when designing a structure. It contains general concepts that are ... [more ▼]

This document deals with the philosophy of safety in civil engineering structures, including loads and load combinations to be applied when designing a structure. It contains general concepts that are presented and discussed as well as values for some important input data that can be used as order of magnitude in the initial phase of a project. [less ▲]

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See detailProgramme d'étirement appliqué à l'épaule raide : conséquences fonctionnelles
Forthomme, Bénédicte ULg; Croisier, Jean-Louis ULg; COLLIGNON, Pierre ULg et al

Conference (2015, October 09)

Les athlètes de lancer présentent une mobilité passive gléno-humérale de l’épaule dominante spécifique avec une majoration de la rotation externe et une limitation de la rotation interne. La limitation ... [more ▼]

Les athlètes de lancer présentent une mobilité passive gléno-humérale de l’épaule dominante spécifique avec une majoration de la rotation externe et une limitation de la rotation interne. La limitation interne semble liée à une raideur capsulo-musculaire postérieure, favorisant les pathologies de l’épaule sportive. Matériel et méthodes Vingt hommes, sportifs d’armer / lancer (volley-ball, handball) et pratiquant au moins 6 heures d’entraînement depuis plus de 5 années ont participé à cette étude. Ils présentaient tous une raideur des structures postérieures évaluée en clinique. Lors de l’inclusion dans l’étude, 10 athlètes (22,5 ± 4 ans) étaient asymptomatiques, 10 (24,8 ± 4 ans) présentaient une épaule dominante symptomatique (≥ 3/10 sur l’EVA). Les athlètes ont étiré chaque jour leur épaule dominante (sleeper stretch et cross body arm) pendant 4 semaines (5 x 30’'). Avant et après le programme d’étirement des structures postérieures, ils ont subi un test isocinétique de force maximale des rotateurs internes et externes ainsi qu’une analyse tridimensionnelle définissant la cinématique scapulaire. Résultats Après 4 semaines d’étirement des structures postérieures, tous les athlètes ont montré un gain significatif de mobilité en rotation interne passive. Nous n’observons aucune modification de la cinétique scapulaire lors de l’analyse 3D après les étirements chez les athlètes asymptomatiques ; les athlètes symptomatiques présentent une diminution du tilt antérieur scapulaire au repos après les 4 semaines. L’évaluation isocinétique des rotateurs d’épaules après les étirements montrent uniquement une légère réduction (- 4% ; p < 0,05) de la force des rotateurs internes à 60°/s en concentrique chez les athlètes asymptomatiques. Les sportifs qui décrivaient des douleurs avant les étirements sont significativement améliorés après le programme de 4 semaines ; cette diminution de la douleur est corrélée au gain en rotation interne passive. Discussion L’étirement pendant 4 semaines des structures postérieures de l’épaule raide sportive permet une augmentation de la mobilité passive. Ce gain de mobilité est corrélé à la diminution de la douleur chez les athlètes symptomatiques. [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 detailEffect of a stretching program on overhead athletes with a stiff and painful shoulder
Schwartz, Cédric ULg; Croisier, Jean-Louis ULg; Bruls, Olivier ULg et al

Conference (2015, July 01)

Overhead athletes are more at risk of suffering shoulder injuries or/and developing shoulder pain. Stretching programs have been shown to successfully reduce pain for this population. However no study has ... [more ▼]

Overhead athletes are more at risk of suffering shoulder injuries or/and developing shoulder pain. Stretching programs have been shown to successfully reduce pain for this population. However no study has provided a global overview of the effects of stretching. The present study evaluated the evolution of the pain, the strength of the shoulder muscles, potential instabilities or lesion of the shoulder as well as the 3D scapular kinematics of 10 overhead athletes having a painful and stiff dominant shoulder. Our results show a significant decrease of the pain and of the positive impingement syndrome tests. The kinematics of the scapula reveals a more upward rotation of the scapula after the stretching, which may reduce the risk of sub-acromial conflicts. The strength of the internal and external rotators of the shoulder is not modified by the program. [less ▲]

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See detailHow biomechanical 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 detailComparison of experimental results and numerical modelling of unreinforced load-bearing masonry structures subjected to earthquake loading
Mordant, Christophe ULg; Denoël, Vincent ULg; Degée, Hervé

in Proceedings of the SECED 2015 Conference: Earthquake Risk and Engineering towards a Resilient World (2015, July)

This paper presents a comparison of experimental tests results on unreinforced load-bearing masonry structures subjected to earthquake loading with numerical predictions. First, simple walls are submitted ... [more ▼]

This paper presents a comparison of experimental tests results on unreinforced load-bearing masonry structures subjected to earthquake loading with numerical predictions. First, simple walls are submitted to cyclic and shaking table tests. Some of them include soundproofing devices in order to investigate their influence on the general behaviour in static and dynamic conditions. Additional walls with an opening and T-shaped walls are then tested under cyclic loading. The study is focused on the frame effect, the contribution of the perpendicular wall to the global strength and the efficiency of the connection. These aspects are also studied through shaking table tests on two masonry frames with T- or L-shaped piers. The main information is expressed in terms of force-displacement curves, mechanical properties and energy dissipation for the cyclic tests. The shaking table tests provide results in terms of dynamic and mechanical properties. Comparison of the results with numerical predictions is finally performed thanks to the software TREMURI. [less ▲]

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