References of "Bruls, Olivier"
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See detailNormalizing shoulder EMG: an optimal set of maximum isometric voluntary contraction tests considering reproducibility
Schwartz, Cédric ULiege; Tubez, François ULiege; WANG, François-Charles ULiege et al

in Journal of Electromyography and Kinesiology (in press)

Normalization of the electromyography (EMG) signal is often performed relatively to maximal voluntary activations (MVA) obtained during maximum isometric voluntary contraction (MVIC). The first aim was to ... [more ▼]

Normalization of the electromyography (EMG) signal is often performed relatively to maximal voluntary activations (MVA) obtained during maximum isometric voluntary contraction (MVIC). The first aim was to provide an inter-session reproducible protocol to normalize the signal of eight shoulder muscles. The protocol should also lead to a level of activation >90% of MVA for >90% of the volunteers. The second aim was to evaluate the influence of the method used to extract the MVA from the EMG envelope on the normalized EMG signal. Thirteen volunteers performed 12 MVICs twice (one-week interval). Several time constants (100 ms to 2 s) were compared when extracting the MVA from the EMG envelope. The EMG activity was also acquired during an arm elevation. Our results show that a combination of nine MVIC tests was required to meet our requirements including reproducibility. Both the number of MVIC tests and the size of the time constant influence the normalized EMG signal during the dynamic activity (variations up to 15%). A time constant of 1 s was a good compromise to extract the MVA. These findings are valuable to improve the reproducibility of EMG signal normalization. [less ▲]

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See detailSystem-based approaches for structural optimization of flexible mechanisms
Tromme, Emmanuel; Held, Alexander; Duysinx, Pierre ULiege et al

in Archives of Computational Methods in Engineering (in press)

This paper reviews the state-of-the-art methods to perform structural optimization of flexible mechanisms. These methods are based on a system-based approach, i.e. the formulation of the design problem ... [more ▼]

This paper reviews the state-of-the-art methods to perform structural optimization of flexible mechanisms. These methods are based on a system-based approach, i.e. the formulation of the design problem incorporates the time response of the mechanism that is obtained from a dynamic simulation of the flexible multibody system. The system-based approach aims at considering as precisely as possible the effects of nonlinear dynamic loading under various operating conditions. Also, the optimization process enhances most existing studies which are limited to (quasi-) static or frequency domain loading conditions. This paper briefly introduces flexible multibody system dynamics and structural optimization techniques. Afterwards, the two main methods, named the weakly and the fully coupled methods, that couple both disciplines are presented in details and the influence of the multibody system formalism is analyzed. The advantages and drawbacks of both methods are discussed and future possible research areas are mentioned. [less ▲]

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See detailInterpolation schemes for geometrically exact beams: A motion approach
Sonneville, Valentin; Bruls, Olivier ULiege; Bauchau, Olivier A.

in International Journal for Numerical Methods in Engineering (in press)

This paper focuses on the interpolation of the kinematic fields describing the configuration of geometrically exact beams, namely, the position and rotation fields. Two kinematic representations are ... [more ▼]

This paper focuses on the interpolation of the kinematic fields describing the configuration of geometrically exact beams, namely, the position and rotation fields. Two kinematic representations are investigated: the classical approach that treats the displacement and rotation fields separately and the motion approach that treats those two fields as a unit. The latter approach is found to be more consistent with the kinematic description of beams. Then, two finite element interpolation strategies are presented and contrasted. The first interpolates the displacement and rotation fields separately, whereas the second interpolates both fields as a unit, in a manner consistent with the motion approach. The performance of both strategies is evaluated in light of the fundamental requirements for the convergence of the finite element method: the ability to represent rigid-body motions and constant strain states. It is shown that the traditional uncoupled interpolation scheme for the position field approximates that based on the motion approach and that the coupling induced by the interpolation of motion yields superior convergence rates for the representation of constant strain states. This property is known to lead to finite elements that are less prone to the locking phenomenon. [less ▲]

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See detailModel Order Reduction of Nonlinear Eddy Current Problems Using Missing Point Estimation
Paquay, Yannick ULiege; Bruls, Olivier ULiege; Geuzaine, Christophe ULiege

in Model Reduction of Parametrized Systems (2017)

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See detailReliability of unipodal and bipodal counter movement jump landings in a recreational male population
Schwartz, Cédric ULiege; Forthomme, Bénédicte ULiege; Paulus, Julien ULiege et al

in European Journal of Sport Science (2017), 17(9), 1143-1152

Movement patterns during landing have been suggested to be related to injury risk. The purpose of this study was to determine the inter-session reliability of kinematic variables and ground reaction ... [more ▼]

Movement patterns during landing have been suggested to be related to injury risk. The purpose of this study was to determine the inter-session reliability of kinematic variables and ground reaction forces during landing in a population of male recreational athletes after a counter movement jump. Both unipodal and bipodal landings were evaluated. Furthermore, the possibility to improve landing reliability with a verbal instruction was also studied. Twenty- four male volunteers with no history of lower-extremity trauma were randomly assigned to two groups (with and without verbal landing instruction). An optoelectronic 3D system and force plates were used to measure the lower-limb joint angles and the ground reaction forces during landing. Intraclass correlation values show moderate to excellent inter-session reliability for the bipodal task (ICC average: 0.80, range: 0.46 to 0.97) and poor to excellent reliability for the unipodal task (ICC average: >0.75, range: 0.20 to 0.95). However, large standard errors of measurement values at the ankle joint at impact (27.6 ± 11.5°) and for the vertical ground reaction forces (394 ± 1091 N) show that some variables may not be usable in practice. The verbal instruction had a negative effect on the reliability of unipodal landing but improved the reliability of bipodal landing. These findings show that the reliability of a landing task is influenced by its motor complexity as well as the instruction given to the subject. [less ▲]

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See detailExperimental and numerical investigation of the nonlinear dynamics of compliant mechanisms for deployable structures
Dewalque, Florence ULiege; Schwartz, Cédric ULiege; Denoël, Vincent ULiege et al

in Mechanical Systems & Signal Processing (2017), 101

This paper studies the dynamics of tape springs which are characterised by a highly geometrical nonlinear behaviour including buckling, the formation of folds and hysteresis. An experimental set-up is ... [more ▼]

This paper studies the dynamics of tape springs which are characterised by a highly geometrical nonlinear behaviour including buckling, the formation of folds and hysteresis. An experimental set-up is designed to capture these complex nonlinear phenomena. The experimental data are acquired by the means of a 3D motion analysis system combined with a synchronised force plate. Deployment tests show that the motion can be divided into three phases characterised by different types of folds, frequencies of oscillation and damping behaviours. Furthermore, the reproducibility quality of the dynamic and quasi-static results is validated by performing a large number of tests. In parallel, a nonlinear finite element model is developed. The required model parameters are identified based on simple experimental tests such as static deformed configurations and small amplitude vibration tests. In the end, the model proves to be well correlated with the experimental results in opposite sense bending, while in equal sense, both the experimental set-up and the numerical model are particularly sensitive to the initial conditions. [less ▲]

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See detailA Novel Accelerometer-Based Method for Stride Length Estimation
Boutaayamou, Mohamed ULiege; Schwartz, Cédric ULiege; Denoël, Vincent ULiege et al

Poster (2017, July 14)

We demonstrate the feasibility of accurately and precisely estimating the left/right average stride length from measured heel/toe accelerations in the gait of healthy, old adults. Our approach relies on ... [more ▼]

We demonstrate the feasibility of accurately and precisely estimating the left/right average stride length from measured heel/toe accelerations in the gait of healthy, old adults. Our approach relies on (1) a novel method that uses only accelerometer data without the need of additional data from, e.g., gyroscopes and/or magnetometers, and on (2) the validation of the results using reference 3D optoelectronic system data. [less ▲]

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See detailMaximal voluntary isometric contraction tests for normalizing surface EMG of scapular stabilizers muscles
Schwartz, Cédric ULiege; Tubez, François ULiege; Soulier, Maxime et al

Conference (2017, July 04)

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See detailTrajectory planning of soft link robots with improved intrinsic safety
Lismonde, Arthur ULiege; Sonneville, Valentin; Bruls, Olivier ULiege

in Proceedings of the 20th World Congress of the International Federation of Automatic Control (2017, July)

For human-robot cooperation, intrinsic safety approaches aim at reducing the energy involved in the motion of the robotic system and at increasing the system compliance in order to reduce the risk of ... [more ▼]

For human-robot cooperation, intrinsic safety approaches aim at reducing the energy involved in the motion of the robotic system and at increasing the system compliance in order to reduce the risk of injury in case of an unexpected collision. Robots based on lightweight and inherently exible links exhibit attractive features in this context but the control of their motion then leads to a tremendous challenge. This paper presents a novel trajectory planning method for 3D robots which aims at improving the tracking accuracy despite the link exibility. [less ▲]

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See detailExperimental characterisation of tape spring nonlinear compliant mechanisms
Dewalque, Florence ULiege; Schwartz, Cédric ULiege; Denoël, Vincent ULiege et al

Conference (2017, June 29)

Tape springs are compliant mechanisms used as alternative to kinematic joints, for example, in deployable space structures. To reach a detailed understanding of their highly nonlinear behaviour, involving ... [more ▼]

Tape springs are compliant mechanisms used as alternative to kinematic joints, for example, in deployable space structures. To reach a detailed understanding of their highly nonlinear behaviour, involving buckling, the formation of folds, nonlinear vibrations and hysteresis, an experimental set-up is designed. Dynamic and quasi-static tests are performed, as well as small amplitude vibration tests and large amplitude deployments in order to collect data in a broad variety of cases. The acquisition equipment consists of a 3D motion analysis system which triangulates the position of active markers and a force plate. The reproducibility of the acquisitions is assessed and the parameters affecting the measurements are identified. In the end, a finite element model is developed and correlated with the experimental results. [less ▲]

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See detailRelevance of early stretching in overhead athletes
Schwartz, Cédric ULiege; Tubez, François ULiege; Croisier, Jean-Louis ULiege et al

Conference (2017, June 16)

Overhead athletes often develop, over time, a tightness of the posterior structures of the shoulder, which may be associated with injuries. Ten symptomatic (with pain) and ten asymptomatic players with a ... [more ▼]

Overhead athletes often develop, over time, a tightness of the posterior structures of the shoulder, which may be associated with injuries. Ten symptomatic (with pain) and ten asymptomatic players with a tight shoulder were compared and the effect of a self-applied stretching program was evaluated. Before and after the stretching program, pain and stiffness of the shoulder were evaluated. Our results demonstrate that risk factors for shoulder pain such as glenohumeral internal rotation deficit and total range of motion deficit may only be limited in symptomatic athletes. The mobility of the shoulder was significantly improved after the stretching program for both groups. Pain was reduced when present. Because of the limited differences between the symptomatic and asymptomatic athletes, clinicians may find it advantageous to initiate early prevention or rehabilitation programs. [less ▲]

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See detailInfluence of the laboratory context and the size of the markers set on the tennis serve evaluation
Tubez, François ULiege; Forthomme, Bénédicte ULiege; Croisier, Jean-Louis ULiege et al

Conference (2017, June 15)

The purpose of this study was to identify the influence on the tennis serve evaluation of 1/ the test environment and 2/ the number of the markers placed of the player. Two different studies were ... [more ▼]

The purpose of this study was to identify the influence on the tennis serve evaluation of 1/ the test environment and 2/ the number of the markers placed of the player. Two different studies were performed. The first compared a 4 vs. 28 marker set in a laboratory the same day. The second compared a 4 markers test in a laboratory with a 4 markers test on an official tennis court one week apart. We observed similar results between the different tests of both studies. [less ▲]

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See detailRobot control based on human motion analysis with IMU measurements
Pellois, Robin ULiege; Joris, Laura ULiege; Bruls, Olivier ULiege

Scientific conference (2017, June 06)

The measurement of the operator motions can lead to innovation in the field of human-robot collaboration. Motion capture data can be used for robot programming by demonstration as well as controlling and ... [more ▼]

The measurement of the operator motions can lead to innovation in the field of human-robot collaboration. Motion capture data can be used for robot programming by demonstration as well as controlling and adapting robot trajectories. To measure motion, IMUs represent an interesting alternative compared to other sensing technologies such as vision. In order to illustrate this strategy, a demonstrator has been created to command a robot by human motion. Two IMU sensor modules are set on the human arm and forearm. The orientation of the module with respect to the inertial frame is computed by the fusion of accelerometer, magnetometer and gyroscope data. This information coupled with a simple human arm kinematic model is used to compute the wrist trajectory. The accuracy of this measurement has to be quantified. For that purpose, the estimated trajectory based on the IMU measurement is compared to the trajectory measured using a reference 3D optoelectronic motion analysis system (Codamotion, Charnwood Dynamics Ltd) available in the Laboratory of Human Motion Analysis of the University of Li`ege. [less ▲]

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See detailAmbulatory System for Gait Analysis
Boutaayamou, Mohamed ULiege; Bruls, Olivier ULiege; Croisier, Jean-Louis ULiege et al

Conference (2017, April 29)

We describe the principle and use of a wireless, 3-axis accelerometer-based ambulatory system that records acceleration signals and automatically analyses them to characterize normal and pathological gait ... [more ▼]

We describe the principle and use of a wireless, 3-axis accelerometer-based ambulatory system that records acceleration signals and automatically analyses them to characterize normal and pathological gait. The associated algorithm is versatile enough to detect, on a stride-by-stride basis, refined gait parameters that quantify subtle gait disturbances in, e.g., in Parkinson’s disease in a rater-independent way. The experimental results show the potential of the developed accelerometer-based technique to be used in neurology (e.g., characterization of Parkinsonian gait: slowness, shuffling, short steps, freezing of gait, asymmetries in gait), rehabilitation, geriatrics (ex. monitoring activity parameters in the elderly), orthopedics and sport. [less ▲]

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See detailFactors to be considered to perform a kinematic evaluation of the tennis serve
Tubez, François ULiege; Forthomme, Bénédicte ULiege; Croisier, Jean-Louis ULiege et al

in Journal of Medecine and Science in Tennis (2017), 22

With the 2D video cameras and later the appearance of 3D measurement methods, the tennis serve has been increasingly studied. In order to improve the biomechanical evaluation of the tennis serve. Our goal ... [more ▼]

With the 2D video cameras and later the appearance of 3D measurement methods, the tennis serve has been increasingly studied. In order to improve the biomechanical evaluation of the tennis serve. Our goal is to provide a comprehensive view of the major factors of an evaluation protocol. [less ▲]

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See detailAnalysis of stable model inversion methods for constrained underactuated mechanical systems
Bastos, Guaraci J.; Seifried, Robert; Bruls, Olivier ULiege

in Mechanism & Machine Theory (2017), 111

Inverse dynamics methods are presented and analyzed in detail for the feedforward control of underactuated manipulators. Thereby, two different exact strategies are discussed: the standard stable ... [more ▼]

Inverse dynamics methods are presented and analyzed in detail for the feedforward control of underactuated manipulators. Thereby, two different exact strategies are discussed: the standard stable inversion method, which relies on the formulation of a two-point boundary value problem, and an alternative optimization problem formulation, which does not require any boundary conditions. This paper proves that the solution of the optimization problem converges to the solution of the boundary value problem in the limit case where the lengths of the pre- and post-actuation phases tend to infinity. It is also shown that both strategies can be directly based on the DAE form of the equations of motion, so that there is no need to explicitly derive the input-output normal form, and standard multibody modeling codes can be used. The developments are illustrated using examples of manipulators with passive and compliant joints. [less ▲]

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See detailAlgorithm for Temporal Gait Analysis Using Wireless Foot-Mounted Accelerometers
Boutaayamou, Mohamed ULiege; Denoël, Vincent ULiege; Bruls, Olivier ULiege et al

Book published by Springer (2017)

We present a new signal processing algorithm that extracts five gait events: heel strike, toe strike, heel-off, toe-off, and heel clearance from only two accelerometers attached on the heels of the ... [more ▼]

We present a new signal processing algorithm that extracts five gait events: heel strike, toe strike, heel-off, toe-off, and heel clearance from only two accelerometers attached on the heels of the subjects usual shoes. This algorithm first uses a continuous wavelet-based segmentation that parses the signal of consecutive strides into motionless periods defining relevant local acceleration signals. Then, the algorithm uses versatile techniques to accurately extract the five gait events from these local acceleration signals. We validated, on a stride-by-stride basis, the extraction of these gait events by comparing the results with reference data provided by a kinematic 3D analysis system and a video camera. The accuracy and precision achieved by the extraction algorithm for healthy subjects, the reduced number of accelerometer units required, and the validation results obtained, encourage us to further study this system in pathological conditions. [less ▲]

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See detailAeroservoelastic Simulations for Horizontal Axis Wind Turbines
Prasad, Chandra Shekhar ULiege; Chen, Qiong Zhong; Bruls, Olivier ULiege et al

in Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy (2017), 231(2), 103-117

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

This paper describes the development of a complete methodology for the aeroservoelastic modeling of horizontal axis wind turbines at the conceptual design stage. The methodology is based on the implementation of unsteady aerodynamic modeling, advanced description of the control system and nonlinear finite element calculations in the SWT wind turbine design package. The aerodynamic modeling is carried out by means of fast techniques, such as the Blade Element Method and 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. The SWT software features a non-linear finite element solver with multi-body dynamics capability. The full methodology is used to perform complete aeroservoelastic simulations of a realistic 2MW wind turbine model. The interaction between the three components of the approach is carefully analyzed and presented here. [less ▲]

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