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Response of an oscillator to a random quadratic velocity-feedback loading Denoël, Vincent ; in Journal of Wind Engineering and Industrial Aerodynamics (2015), 147 Abstract The aerodynamic force acting on compact structures is often modeled as a quadratic function of the wind velocity, which fluctuates randomly due to the atmospheric turbulence. When a flexible ... [more ▼] Abstract The aerodynamic force acting on compact structures is often modeled as a quadratic function of the wind velocity, which fluctuates randomly due to the atmospheric turbulence. When a flexible structure is considered and the quasi-steady assumption is applied, the wind velocity is substituted by the wind-structure relative velocity and, even in case of linear structures, the composite aerodynamic-mechanical system is governed by a nonlinear differential equation characterized by a quadratic feedback term. This class of dynamical systems has been deeply investigated (with different levels of simplifications) applying several alternative mathematical approaches. In this paper we define a system approximation based on a 2nd-order Volterra series and obtain its statistical response in terms of cumulants. The response cumulants are calculated applying the Multiple Timescale Spectral Analysis leading to analytic or semi-analytic expressions. All the approximations are validated through Monte Carlo simulation within a wide parameter space. Then, the analytical structure of the obtained expressions is used to discuss, from a qualitative point of view, the behavior of the considered dynamical system. [less ▲] Detailed reference viewed: 13 (1 ULg)Numerical simulation of percussive drilling ; Denoël, Vincent ; in International Journal for Numerical and Analytical Methods in Geomechanics (2015), 39(8), 889-912 This paper presents a novel dynamical model to analyze the long-term response of a percussive drilling system. This departs from existing approaches that usually consider a single activation and bit/rock ... [more ▼] This paper presents a novel dynamical model to analyze the long-term response of a percussive drilling system. This departs from existing approaches that usually consider a single activation and bit/rock interaction cycle for the analysis of the process performance. The proposed model integrates the axial dynamics of an elastic piston and an elastic drill bit, a motion-dependent pressure law to drive the piston, and a generalized bit/rock interaction law representative of the dynamic indentation taking place at the bit/rock interface. It applies to down-the-hole percussive drilling as well as top-hole, with minor modifications. The model does not account for the angular motion or the hole cleaning, however. The model is first formulated mathematically; then, a finite-dimensional approximation is proposed for computations. Numerical analyses of the model response, for a low-size down-the-hole percussive system, follow. The period-1 stationary response for the reference configuration is studied in detail, and parametric analyses assessing the influence on the rate of penetration of the bit/rock interaction parameters, the feed force, and the percussive activation parameters are conducted. These analyses reveal that the multiscale nature of the process is well captured by the model and recover expected trends for the influence of the parameters. They also suggest that a significant increase of the penetration rate can be achieved by increasing the percussive frequency. Copyright © 2015 John Wiley & Sons, Ltd [less ▲] Detailed reference viewed: 13 (2 ULg)Segmentation of gait cycles using foot-mounted 3D accelerometers Boutaayamou, Mohamed ; Bruls, Olivier ; Denoël, Vincent et al in Proceedings of the IEEE International Conference on 3D Imaging 2015 (2015) We describe a new gait segmentation method based on the continuous wavelet transform to identify stride-by-stride gait cycles from measurements of foot-mounted three-dimensional (3D) accelerometers. The ... [more ▼] We describe a new gait segmentation method based on the continuous wavelet transform to identify stride-by-stride gait cycles from measurements of foot-mounted three-dimensional (3D) accelerometers. The detection of such gait cycles is indeed a crucial step for an accurate extraction of relevant gait events such as heel strike, toe strike, heel-off, and toe-off. We demonstrate the ability of this segmentation method, used in conjunction with a validated extraction algorithm, to calculate the following gait (duration) parameters for each gait cycle during the gait of a healthy young subject and of an elderly subject with Parkinson’s disease (PD) in OFF and ON states: durations of (1) loading response, (2) mid-stance, (3) push-off, (4) stance, (5) swing, (6) stride, (7) step, and (8) double support phases. The experimental results show that the proposed method can extract relevant refined gait parameters to quantify subtle gait disturbances in subjects with PD. [less ▲] Detailed reference viewed: 44 (6 ULg)Ambulatory system using wearable accelerometers for gait analysis in Parkinson’s disease Boutaayamou, Mohamed ; Demonceau, Marie ; Schwartz, Cédric et al in Proceedings of the 14th Belgian Day on Biomedical Engineering (2015) We describe a signal-processing algorithm for gait analysis in Parkinson’s disease (PD) using an ambulatory system with wearable accelerometers. This algorithm is versatile enough to detect, on a stride ... [more ▼] We describe a signal-processing algorithm for gait analysis in Parkinson’s disease (PD) using an ambulatory system with wearable accelerometers. This algorithm is versatile enough to detect, on a stride-by-stride basis, refined gait parameters that quantify subtle gait disturbances in PD in a rater-independent way. [less ▲] Detailed reference viewed: 56 (10 ULg)Stabilité des Constructions Denoël, Vincent ; Franssen, Jean-Marc Learning material (2015) Detailed reference viewed: 152 (9 ULg)Multiple timescale spectral analysis Denoël, Vincent in Probabilistic Engineering Mechanics (2015), 39(0), 69--86 Abstract Spectral analysis is a classical tool for the structural analysis of structures subjected to random excitations. The most common application of spectral analysis is the determination of the ... [more ▼] Abstract Spectral analysis is a classical tool for the structural analysis of structures subjected to random excitations. The most common application of spectral analysis is the determination of the steady-state second order cumulant of a linear oscillator, under the action of a stationary loading prescribed by means of its power spectral density. There exists however a broad variety of such similar problems, extending the concept to multi degree-of-freedom systems, non Gaussian excitation, slightly nonlinear oscillators or even transient excitations. In this wide class of problems, the cumulants of the response are obtained as the result of the integral of corresponding spectra over the frequency space, which is possibly multidimensional. Application of standard numerical integration techniques may be prohibitive, a reason why the spectral approach is often left aside. Besides, many engineering problems involve a clear timescale separation, usually of those pertaining to the loading and to the mechanical behavior of the system. In these problems, a proper consideration of the timescale separation results in dropping the order of integration by one, at least. This offers the possibility to derive analytical solutions, whenever the order of integration drops to zero, or to make numerical integration competitive. The paper presents this general method, together with some applications in wind and marine engineering. [less ▲] Detailed reference viewed: 23 (7 ULg)Monte Carlo Simulations of Autorotative Dynamics of a Simple Tower Crane Model Vanvinckenroye, Hélène ; Denoël, Vincent in Proceedings of the 14th International Conference on Wind Engineering (2015) The increasing number of crane accidents recorded over the last years might be understood as a need for progress on crane modeling. The induced risk of self-excited vibrations has already been ... [more ▼] The increasing number of crane accidents recorded over the last years might be understood as a need for progress on crane modeling. The induced risk of self-excited vibrations has already been investigated through numerous experiments. This work presents a simple numerical model of a crane in a turbulent wind field, in order to support the available experimental approaches. First, the problem is defined with the necessary assumptions of the model. Second, the equation of motion is developed and wind characteristics are detailed. This equation presents several specificities requiring dedicated resolution methods. In a first analysis, the crane model is simplified in order to approach the behavior of the parametric pendulum and enable a general comparison of both responses. Indeed, the parametric pendulum is a well-known problem that is already widely described in the literature. In a second step, the response of the crane is studied under a realistic stochastic wind load with the full model. [less ▲] Detailed reference viewed: 39 (10 ULg)Application of random eigenvalue analysis to assess bridge flutter probability ; ; Denoël, Vincent in Journal of Wind Engineering and Industrial Aerodynamics (2015), 140(0), 79--86 Abstract This study examines the well-known issue of evaluating the flutter probability for a long-span bridge, necessary for assessing structural integrity and reliability. The motivation stems from the ... [more ▼] Abstract This study examines the well-known issue of evaluating the flutter probability for a long-span bridge, necessary for assessing structural integrity and reliability. The motivation stems from the need for critically reviewing and investigating a number of existing numerical approaches (e.g., random perturbation analysis, collocation methods, Galerkin approach) for the modeling and the solution of stochastic dynamic problems, by adapting them to the specific problem. The study proposes a generalized formulation for stochastic bridge flutter in terms of random eigenvalue analysis. A 1200 m suspension bridge model is used in the numerical simulations to compare the various methods and to provide indications on advantages and limitations of each method. Moreover, the link between the proposed formulation and existing studies on the propagation of uncertainty in aeroelastic systems, for example associated with measurement errors in wind tunnel, is examined. [less ▲] Detailed reference viewed: 29 (6 ULg)Merging multi-camera data to reduce motion analysis instrumental errors using Kalman filters Schwartz, Cédric ; Denoël, Vincent ; Forthomme, Bénédicte 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 ▲] Detailed reference viewed: 94 (32 ULg)Development and validation of a 3D kinematic-based method for determining gait events during overground walking Boutaayamou, Mohamed ; Schwartz, Cédric ; Denoël, Vincent 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 ▲] Detailed reference viewed: 71 (19 ULg)An asymptotic expansion-based method for a spectral approach in equivalent statistical linearization Canor, Thomas ; Blaise, Nicolas ; Denoël, Vincent in Probabilistic Engineering Mechanics (2014), 38 Equivalent linearization consists in replacing a nonlinear system with an equivalent linear one whose parameters are tuned with regard to the minimization of a suitable function. In particular, the ... [more ▼] Equivalent linearization consists in replacing a nonlinear system with an equivalent linear one whose parameters are tuned with regard to the minimization of a suitable function. In particular, the Gaussian equivalent linearization expresses the properties of an equivalent linear system in terms of the mean vector and the covariance matrix of the responses, which are the unknowns of the optimization problem in a spectral approach. Even though the system has been linearized, the resulting set of equations is nonlinear. The computational effort in this method pertains to the solution of a possibly large set of nonlinear algebraic equations involving integrals and inversions of full matrices. This work proposes to develop and apply an asymptotic expansion-based method to facilitate and to improve the statistical linearization for large nonlinear structures. The proposed developments demonstrate that for slightly to moderately coupled nonlinear systems, the equivalent linearization can be applied with an appropriate modal approach and eventually seen as a convergent series initiated with the stochastic response of a main decoupled linear system. With this method, the computational effort is attractively reduced, the conditioning of the set of nonlinear algebraic equations is improved and inversion of full transfer matrices and repeated integrations are avoided. The paper gives a formal description of the method and illustrates its implementation and performances with the computation of stationary responses of nonlinear structures subject to coherent random excitation fields. [less ▲] Detailed reference viewed: 96 (28 ULg)Pressure-impulse diagram of a beam under explosion - Influence of the indirectly affected part Hamra, Lotfi ; Demonceau, Jean-François ; Denoël, Vincent in Landolfo, Raffaele; Mazzolani, Frederico (Eds.) Proceeding of the 7th European conference on steel and composite structures (Eurosteel 2014) (2014, September 10) The paper studies the structural response of a beam subjected to a close-field local internal blast loading. In the literature, the pressure-impulse (p-I) diagram is commonly used to design elements or ... [more ▼] The paper studies the structural response of a beam subjected to a close-field local internal blast loading. In the literature, the pressure-impulse (p-I) diagram is commonly used to design elements or structures for a given blast loading. The p-I diagram is a spectrum representing the level sets of damage or required ductility for a given structural system, nonlinear beam in this paper. This representation is much appreciated because a simple reading for the actual pressure p and impulse I of the considered load indicates the ductility demand of the structural system. Recent works of quasi-static behaviour have indicated the crucial need to account for the membrane effects taking place in the extreme loading of frame beams. This paper will thus extend the state-of-art features, establishing thus the p-I diagram for a beam including the lateral restraints offered by the rest of the structure, the development of non-linear membrane action and also, the M-N interaction that develops in the plastic hinges. [less ▲] Detailed reference viewed: 146 (25 ULg)Statistical analysis of velocity measurements in anatmospheric boundary layer in wind tunnel Andrianne, Thomas ; Denoël, Vincent Poster (2014, September) Detailed reference viewed: 19 (3 ULg)Aspects of non-smooth dynamics in models of percussion ; ; Denoël, Vincent in Proceedings of the 8th European Nonlinear Dynamics Conference (2014, July 08) Detailed reference viewed: 11 (0 ULg)Influence of players' level on racket speed and ball accuracy in the tennis serve Tubez, François ; Croisier, Jean-Louis ; Cordonnier, Caroline 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 ▲] Detailed reference viewed: 165 (30 ULg)Comparison between first and second landing for different vertical drop jump tasks. Implication in injury risk prevention Cordonnier, Caroline ; Croisier, Jean-Louis ; Forthomme, Bénédicte et al Conference (2014, July 04) Detailed reference viewed: 84 (16 ULg)Importance of quantitative return-to-field criteria Schwartz, Cédric ; Cordonnier, Caroline ; Lehance, Cédric et al Conference (2014, July 04) Detailed reference viewed: 43 (6 ULg)Event-driven integration of linear structural dynamics models under unilateral elastic constraints Depouhon, Alexandre ; ; Denoël, Vincent in Computer Methods in Applied Mechanics & Engineering (2014), 276 This paper proposes an algorithm for the numerical simulation of linear structural dynamics problems under unilateral elastic constraints, i.e., constraints with a linear force/displacement characteristic ... [more ▼] This paper proposes an algorithm for the numerical simulation of linear structural dynamics problems under unilateral elastic constraints, i.e., constraints with a linear force/displacement characteristic whenever active. The presented procedure relies on an event-driven strategy for the handling of the contact constraints, in combination with one-step schemes dedicated to the time integration of the second-order equations of motion. Efficiency of the procedure follows from the use of cubic Hermite interpolation to continuously extend the normal gap functions that reflect the openings of the contact interfaces. Robustness follows from the proper handling of complex numerical situations, e.g., numerical grazing or discontinuity sticking, through appropriate algorithm structure and numerical implementation. And, integration stability is guaranteed by the very nature of the algorithm and that of the one-step integration scheme. Following a detailed coverage of the integration procedure and the countermeasures to the expected numerical difficulties, three application examples are treated for illustration purposes. A MATLAB implementation of the procedure is provided online; download and usage information are given in the Appendix. [less ▲] Detailed reference viewed: 89 (24 ULg)Calculation of third order joint acceptance function for line-like structures Blaise, Nicolas ; Canor, Thomas ; Denoël, Vincent in Proceedings of the XIII Conference of the Italian Association for Wind Engineering (2014, June 24) Detailed reference viewed: 41 (12 ULg)Vascular Endothelial Growth Factor-111 (VEGF-111) and tendon healing: preliminary results in a rat model of tendon injury Kaux, Jean-François ; Janssen, Lauriane ; Drion, Pierre et al in Muscles, Ligaments and Tendons Journal (2014), 4(1 (eCollection 2014 Jan)), 25-28 Tendon lesions are among the most frequent musculoskeletal pathologies. Vascular endothelial growth factor (VEGF) is known to regulate angiogenesis. VEGF-111, a biologically active and proteolysis ... [more ▼] Tendon lesions are among the most frequent musculoskeletal pathologies. Vascular endothelial growth factor (VEGF) is known to regulate angiogenesis. VEGF-111, a biologically active and proteolysis-resistant splice variant of this family, was recently identified. This study aimed at evaluating whether VEGF-111 could have a therapeutic interest in tendon pathologies. Surgical section of one Achilles tendon of rats was performed before a local injection of either saline or VEGF-111. After 5, 15 and 30 days, the Achilles tendons of 10 rats of both groups were sampled and submitted to a biomechanical tensile test. The force necessary to induce tendon rupture was greater for tendons of the VEGF-111 group (p<0.05) while the section areas of the tendons were similar. The mechanical stress was similar at 5 and 15 days in the both groups but was improved for the VEGF-111 group at day 30 (p <0.001). No difference was observed in the mRNA expression of collagen III, tenomodulin and MMP-9. In conclusion, we observed that a local injection of VEGF-111 improves the early phases of the healing process of rat tendons after a surgical section. Further confirmatory experimentations are needed to consolidate our results. [less ▲] Detailed reference viewed: 67 (15 ULg) |
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