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Uncoupled spectral analysis with non-proportional damping Canor, Thomas ; Blaise, Nicolas ; Denoël, Vincent in Proceedings of the European-African Conference on Wind Engineering (2013, July 07) The use of normal modes of vibration in the analysis of structures with non-proportional damping reduces the number of governing equations, but does not decouple them. A common practice consists in ... [more ▼] The use of normal modes of vibration in the analysis of structures with non-proportional damping reduces the number of governing equations, but does not decouple them. A common practice consists in decoupling the equations by disregarding the off-diagonal elements of the modal damping matrix. This paper proposes a method based on the asymptotic expansion of the modal transfer matrix to take into account the modal coupling in Gaussian spectral analysis. First, the mathematical background is introduced, then the relevance of the method is illustrated within the context of the analysis of a large and real structure submitted to wind loadings. [less ▲] Detailed reference viewed: 66 (8 ULg)Equivalent static wind loads for structures with non-proportional damping Blaise, Nicolas ; Canor, Thomas ; Denoël, Vincent in Proceedings of the 11th International Conference on Recent Advances in Structural dynamics (2013, July) In current practice, wind structural design is often carried out using the concept of equivalent static wind loads. The main characteristic of such loadings is to reproduce, with static analyses, the same ... [more ▼] In current practice, wind structural design is often carried out using the concept of equivalent static wind loads. The main characteristic of such loadings is to reproduce, with static analyses, the same extreme structural responses as those resulting from a formal buffeting analysis. This paper proposes a method for the computation of equivalent static wind loads for structures with slight non-proportional damping in a modal framework. Because of the smallness of the out-of diagonal terms, this method is based on recent developments related to asymptotic expansion of the modal transfer matrix of such structures. As a main benefit, the static loading is described as a perturbation of the equivalent loading that would be obtained for the uncoupled system. The main contribution of this paper is to formalize the expression of the correction terms resulting from the non-proportionality of damping. The method is presented with a detailed illustrative example. [less ▲] Detailed reference viewed: 50 (13 ULg)Validation of an accelerometer-based approach to quantify gait events Boutaayamou, Mohamed ; Schwartz, Cédric ; et al Poster (2013, June) Researchers rarely provide solid performance and validation information about their acceleometer-based approaches to human gait analysis. We present here a novel signal processing and analysis algorithm ... [more ▼] Researchers rarely provide solid performance and validation information about their acceleometer-based approaches to human gait analysis. We present here a novel signal processing and analysis algorithm that automatically extracts four consecutive fundamental events of walking: heel strike (HS), toe strike (TS), heel off (HO), and toe off (TO). In addition, we validate this accelerometer-based technique by comparing these extracted gait events with those obtained by a kinematic 3D analysis system and a force plate, used as gold standards. [less ▲] Detailed reference viewed: 109 (43 ULg)Transient Fokker-Planck-Kolmogorov equation solved with smoothed particle hydrodynamics method Canor, Thomas ; Denoël, Vincent in International Journal for Numerical Methods in Engineering (2013), 94(6), 535553 Probabilistic theories aim at describing the properties of systems subjected to random excitations by means of statistical characteristics such as the probability density function (pdf). The time ... [more ▼] Probabilistic theories aim at describing the properties of systems subjected to random excitations by means of statistical characteristics such as the probability density function (pdf). The time evolution of the pdf of the response of a randomly excited deterministic system is commonly described with the transient Fokker-Planck-Kolmogorov equation (FPK). The FPK equation is a conservation equation of a hypothetical or abstract fluid, which models the transport of probability. This paper presents a generalized formalism for the resolution of the transient FPK equation using the well-known mesh-free Lagrangian method, Smoothed Particle Hydrodynamics (SPH). Numerical implementation shows notable advantages of this method in an unbounded state space: (i) the conservation of total probability in the state space is explicitly written, (ii) no artifact is required to manage far- eld boundary conditions , (iii) the positivity of the pdf is ensured and (iv) the extension to higher dimensions is straightforward. Furthermore, thanks to the moving particles, this method is adapted for a large kind of initial conditions, even slightly dispersed distributions. The FPK equation is solved without any a priori knowledge of the stationary distribution; just a precise representation of the initial distribution is required. [less ▲] Detailed reference viewed: 130 (50 ULg)L'apport de l'analyse biomécanique 3-D dans les stratégies préventives à partir de 2 exemples Schwartz, Cédric ; Croisier, Jean-Louis ; Tubez, François et al in Julia, M; Croisier, Jean-Louis; Perrey, S (Eds.) et al Prévention des troubles musculo-squelettiques chez le sportif (2013) De nouveaux outils de mesure permettent de quantifier la cinématique et la dynamique articulaire fonctionnelle des athlètes (systèmes optoélectroniques 3D, plateforme de forces, électromyographie, …). Ces ... [more ▼] De nouveaux outils de mesure permettent de quantifier la cinématique et la dynamique articulaire fonctionnelle des athlètes (systèmes optoélectroniques 3D, plateforme de forces, électromyographie, …). Ces données sont importantes dans le sens où elles donnent à l’équipe médicale et sportive des informations objectives sur le geste du sportif dans sa pratique réelle. Elles favorisent la compréhension et l’amélioration de la performance ainsi que la prévention lésionnelle et la détection de situations à risque. Dans le cadre d’un suivi longitudinal des sportifs, ces mesures sont intéressantes pour mettre en place des critères objectifs et spécifiques à l’athlète de retour sur le terrain après une blessure. Ce document a pour objectif de présenter les principaux outils disponibles dans les laboratoires de biomécanique et d’illustrer leurs utilisations à travers 2 exemples : l’influence de la raideur de l’épaule sur la mobilité de l’épaule et l’analyse cinématique du service au tennis. [less ▲] Detailed reference viewed: 292 (83 ULg)Principal static wind loads Blaise, Nicolas ; Denoël, Vincent in Journal of Wind Engineering & Industrial Aerodynamics (2013), 113 In current wind design practice, static wind loads are usually defined to obtain, by simple static analyses, the extreme values of any structural response that would be formally obtained with a strict ... [more ▼] In current wind design practice, static wind loads are usually defined to obtain, by simple static analyses, the extreme values of any structural response that would be formally obtained with a strict dynamic buffeting analysis. The minimum and maximum values that may reach any response define the envelope. Equivalent static wind loads (ESWLs) allow to recover extreme responses in the envelope. As a first objective, this paper formalizes a general method to determine ESWL, in a nodal basis, by extending the concept of load-response correlation, which is only valid in the background range. The general method, the displacement-response-correlation (DRC) method, covers the background and resonant contributions of the considered response. As a second objective, the paper addresses the problem of building a set of static wind loads that adequately reconstructs the envelopes of responses. The concept of principal static wind loads (PSWL) is introduced to form a reduced basis of representative loads well-suited for envelope reconstruction. Its optimality is demonstrated both analytically and with a detailed illustrative example. [less ▲] Detailed reference viewed: 105 (28 ULg)Elements de processus stochastiques Denoël, Vincent Learning material (2013) Detailed reference viewed: 25260 (1746 ULg)Dynamic Computation and Design of a World’s Record Death-Ride Denoël, Vincent ; Canor, Thomas ; in Proceedings of the 4th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (2013) A death-ride is a long cable anchored between two dead ends, allowing the crossing of wide valleys. Besides these mobility purposes, it is also operated in rescue operations, or simply for leisure. From a ... [more ▼] A death-ride is a long cable anchored between two dead ends, allowing the crossing of wide valleys. Besides these mobility purposes, it is also operated in rescue operations, or simply for leisure. From a serviceability viewpoint, a death-ride design should offer a comfortable and/or enjoyable journey to the riders, which is typically expressed in terms of maximum velocity. From a strength viewpoint, a death-ride should be designed in order to safely withstand the cable self-weight, wind forces, the rider’s load and at last but not least, the initial tension in the cable. Actually, the tensioning operation is usually subtle. Indeed, in case of a loose cable, the rider may be stopped in the in-span sagging area. Conversely a too tight cable will generate large stresses but also large outlet velocity at the end of the ride. The design of a death-ride is a tradeoff between all these aspects. The paper presents the dynamic model that was used for the design of a 1.2km long death-ride, with an only 10-mm diameter, a constraint fixed in the very first stages of this project for compatibility reasons, with the existing equipment. This death-ride, built and used in May 2010 in a Grimp competition [1], has a world record of the longest death-ride in urban area. The structural part of the dynamic model is rather common, with a co-rotational description of the cable by means of a chain-like model [2]. An interesting feature, however, concerns the interaction between the rider and the cable. In fact, because the pulley is rolling on the cable, the position of the force acting on the cable, resulting from the ride, depends on the rider’s velocity, which itself depends on the cable inclination. This coupling is solved in a staggered manner, and the details of the algorithm are given in the full paper. In some limiting cases, a comparison with analytical solutions is also provided, where these analytical solutions are available [3]. Experimental validation and observation of the operated death-ride will also be presented. [less ▲] Detailed reference viewed: 44 (1 ULg)Extension of Davenport's Background/Resonant decomposition for the estimation of higher response moments Denoël, Vincent in Proceedings of the Sixth European-African Conference on Wind Engineering (2013) The non Gaussian buffeting analysis of a structure subjected to turbulent wind may be advantageously performed with a Volterra approach. Although this concept may be applicable to nonlinear structures ... [more ▼] The non Gaussian buffeting analysis of a structure subjected to turbulent wind may be advantageously performed with a Volterra approach. Although this concept may be applicable to nonlinear structures, the scope of this paper is limited to structures with a deterministic linear behavior. In this case, the Volterra kernels take a simple explicit expression and the statistical moments of the structural response are simply recovered by a multi-dimensional integration of the corresponding spectra. Because the multi-dimensional spectra of the loading are usually determined numerically, these integrals have to be computed numerically too. The computational burden necessary for the estimation of these integrals turns out to be prohibitive as soon as high order moments are required (beyond and including 4th moment). The numerical conditioning is in fact again worse when the structural damping is low as the Volterra kernels then exhibit very large gradients in the frequency space, which are difficult to capture properly. Because the timescales related to the dynamics of the structure and to the random wind loading are well distinct, a nowadays customary decomposition of the response into Background and Resonant contributions (dating back to A. Davenport's earliest works) provides a very good estimation of the second statistical moment. Recently the concept has been extended to the Background/biResonant decomposition for the estimation of the third statistical moment of the response. This paper presents the extension to the computation of the fourth statistical moment, with the only assumptions of slight damping and low-frequency loading such as those that made Allan Davenport's Background/Resonant (B/R) decomposition fruitful. After some multiple scales considerations, the fourth moment of the response is approximated as the sum of a background component, a tetraresonant component and a mixed background-biresonant component. Mathematical developments will be presented in the full paper along with illustrative examples, while the current 4-page abstract just presents of a flavour of it. [less ▲] Detailed reference viewed: 27 (4 ULg)Patching Asymptotics Solution of a Cable with a Small Bending Stiffness Denoël, Vincent ; Canor, Thomas in Journal of Structural Engineering (2013), 139 The analysis of a cable with a small bending stiffness is a problem encountered in many engineering applications such as the fatigue assessment of stay cables, the modeling of pipeline laying operation or ... [more ▼] The analysis of a cable with a small bending stiffness is a problem encountered in many engineering applications such as the fatigue assessment of stay cables, the modeling of pipeline laying operation or the determination of bending stresses in drillpipe assemblies. Because this phenomenon is modeled by a singularly perturbed equation, standard numerical techniques fail to solve these problems efficiently. As an alternative, provided the complexity of the analytical developments does not preclude their application, these problems may be tackled with appealing analytical procedures such as matching asymptotics or multiple scales. Otherwise advanced numerical simulations combining patching asymptotics within a numerical framework are the only possible approach for problems where the governing equations are too complex. Patching asymptotics also features a number of merits such as the possibility of using a boundary layer with a finite extent. Aiming at a better understanding of this latter technique, it is considered here to determine the solution of a cable with a small bending stiffness. Interesting details about patchability conditions and about how to restore higher derivatives continuity are included. The accuracy of the patching asymptotics approach is also compared with that of matched asymptotics. [less ▲] Detailed reference viewed: 62 (14 ULg)Transient Fokker-Planck equation with SPH method : Application in seismic design Canor, Thomas ; Denoël, Vincent in Papadrakakis, M; Papadopoulos, V; Plevris, V (Eds.) Proceedings COMPDYN2013 (2013) Detailed reference viewed: 21 (10 ULg)Shoulder injury prevention in sports using 3D motion capture Schwartz, Cédric ; HAZEE, Amandine ; Denoël, Vincent et al Poster (2012, December 07) In sports, where regular and intensive training could progressively lead to traumatic situations, accurate measurement of kinematic parameters can help to predict and anticipate injuries. Overhead ... [more ▼] In sports, where regular and intensive training could progressively lead to traumatic situations, accurate measurement of kinematic parameters can help to predict and anticipate injuries. Overhead throwing athletes may develop an increased stiffness of the shoulder capsule. The resulting diminution of the gleno-humeral range of motion is usually associated with decreased performance and injury risks. This study illustrates the detection of these situations that put the athlete at risk. [less ▲] Detailed reference viewed: 164 (24 ULg)Validated Extraction of Gait Events from 3D Accelerometer Recordings Boutaayamou, Mohamed ; Schwartz, Cédric ; et al in IEEE International Conference on 3D Imaging (IC3D) (2012, December) This work is part of a project that deals with the three-dimensional (3D) analysis of normal and pathological gaits based on a newly developed system for clinical applications, using low-cost wireless ... [more ▼] This work is part of a project that deals with the three-dimensional (3D) analysis of normal and pathological gaits based on a newly developed system for clinical applications, using low-cost wireless accelerometers and a signal processing algorithm. This system automatically extracts relevant gait events such as the heel strikes (HS) and the toe-offs (TO), which characterize the stance and the swing phases of walking. The performances of the low-cost accelerometer hardware and related algorithm have been compared to those obtained by a kinematic 3D analysis system and a force plate, used as gold standard methods. The HS and TO times obtained from the gait data of 7 healthy volunteers (147 trials) have been found to be (mean ± standard deviation) 0.42±7.92 ms and 3.11±10.08 ms later than those determined by the force plate, respectively. The experimental results demonstrate that the new hardware and associated algorithm constitute an effective low-cost gait analysis system, which could thus be used for the assessment of mobility in routine clinical practice. [less ▲] Detailed reference viewed: 150 (55 ULg)Principal Static Wind Loads on a large roof structure Blaise, Nicolas ; Hamra, Lotfi ; Denoël, Vincent in Proceedings of the 12th ANIV conference of wind engineering In Vento (2012, October 07) Usually, structural wind design is realized using static wind loads. Such loadings are expected, as a main property, to recover by static analyses, the envelope values that would be obtained by a formal ... [more ▼] Usually, structural wind design is realized using static wind loads. Such loadings are expected, as a main property, to recover by static analyses, the envelope values that would be obtained by a formal buffeting analysis. For simple structures, equivalent static wind loads might be used but they are established in order to reproduce envelope values of specific structural responses and are thus not suitable to reconstruct efficiently the entire envelope. Recently, more general methods were derived to propose global static loadings that reconstruct the entire envelope but several drawbacks remained as their robust applicability for any structure and accuracy. This paper addresses a new type of static loadings, the principal static wind loads, derived in a strict mathematical way, the singular value decomposition, to make it optimum for the envelope reconstruction problem. The method is illustrated with a large roof and the reconstruction accuracy is analysed by studying the rate of envelope reconstruction, envelope previously obtained by a rigourous stochastic analysis. The way principal loadings are derived makes them suitable for combinations in order to increase the rate of the envelope reconstruction. As a major outcome, the method provides a finite number of design load cases that matches a desired level of accuracy in the envelope reconstruction. [less ▲] Detailed reference viewed: 236 (101 ULg)Introduction aux statistiques et probabilités Denoël, Vincent Learning material (2012) Le document annexé contient les slides du cours donné en 2012-2013 aux étudiants du 3eme Bac Ingénieur Architectes de l'Université de Liège. Le cours est donné en 30 heures. Detailed reference viewed: 2633 (624 ULg)Extension of the Background/biResonant decomposition to the estimation of the kurtosis coefficient of the response Denoël, Vincent in Proceedings of the Conference on Uncertainty in Structural Dynamics (2012, September) Based on the observation of the existence of diﬀerent timescales, this paper provides an approximate method to compute the kurtosis coeﬃcient of the response of a linear-time-invariant system subjected to ... [more ▼] Based on the observation of the existence of diﬀerent timescales, this paper provides an approximate method to compute the kurtosis coeﬃcient of the response of a linear-time-invariant system subjected to a low-frequency non Gaussian input. While the kurtosis coeﬃcient is formally obtained by a multidimensional integration of the corresponding spectrum, the proposed method only requires the estimation of a single deﬁnite integral. The speedup performance is three to four orders of magnitude and the approximation is very accurate as it corresponds to the leading order expansion of the formal solution, with the ratio of the identiﬁed timescales considered as a small parameter. [less ▲] Detailed reference viewed: 8 (0 ULg)Nonlinear Dynamics Of A Drill Bit Under Percussive Activation Depouhon, Alexandre ; Denoël, Vincent ; in Proceedings of ICTAM 2012, Beijing (2012, August) Detailed reference viewed: 59 (6 ULg)Limit cycling behavior of a hybrid system: Application to percussive drilling Depouhon, Alexandre ; ; Denoël, Vincent in Proceedings of the 2nd International Colloquium on Non-Linear Dynamics and Control of Deep Drilling Systems, Eindhoven, May 2012 (2012, May) Detailed reference viewed: 68 (18 ULg)Recent advances in the modeling of a drillstring inside a curved borehole Denoël, Vincent ; in Proceedings of the 3rd International Colloquim on Nonlinear Dynamics and Control of Deep Drilling Systems (2012) Detailed reference viewed: 12 (1 ULg)Structural Dynamics Denoël, Vincent Learning material (2012) Detailed reference viewed: 1222 (411 ULg) |
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