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Brussels, Belgium

El Ouni M.H.,University of Carthage | El Ouni M.H.,University of Sousse | Ben Kahla N.,University of Carthage | Ben Kahla N.,University of Sousse | Preumont A.,Active Structures Laboratory
Engineering Structures | Year: 2012

In cable-stayed bridges, the occurrence of parametric excitation is very probable due to the presence of many low frequencies in the deck or tower and in the stay cables. When a local (cable) and a global (structure) mode are coupled, even very small motion of the deck or tower may cause dynamic instability and extremely large vibration amplitudes of the stay cables. This paper presents a nonlinear dynamic study of a three dimensional cable stayed bridge in construction phase under parametric excitation. A nonlinear inclined cable with small sag which takes into account the quadratic and cubic nonlinear couplings between in-plane and out-of-plane motion, is coupled with a finite element model of a cable stayed bridge. Active damping is successfully added to the structure using collocated displacement actuator-force sensor pairs located on each cable and a robust control strategy based on decentralized collocated Integral Force Feedback. The effect of the amplitude of excitation as well as the added active damping on the steady state response of the stay cable under parametric excitation is studied numerically and experimentally. A phenomenon of energy transfer between the cable and the deck is observed. The experimental results are qualitatively in good agreement with the numerical ones. © 2012 Elsevier Ltd. Source

Deraemaeker A.,Active Structures Laboratory | Preumont A.,Active Structures Laboratory | Reynders E.,Issyk-Kul State University | De Roeck G.,Issyk-Kul State University | And 10 more authors.
Smart Structures and Systems | Year: 2010

Recent advances in hardware and instrumentation technology have allowed the possibility of deploying very large sensor arrays on structures. Exploiting the huge amount of data that can result in order to perform vibration-based structural health monitoring (SHM) is not a trivial task and requires research into a number of specific problems. In terms of pressing problems of interest, this paper discusses: the design and optimisation of appropriate sensor networks, efficient data reduction techniques, efficient and automated feature extraction methods, reliable methods to deal with environmental and operational variability, efficient training of machine learning techniques and multi-scale approaches for dealing with very local damage. The paper is a result of the ESF-S3T Eurocores project "Smart Sensing For Structural Health Monitoring" (S3HM) in which a consortium of academic partners from across Europe are attempting to address issues in the design of automated vibration-based SHM systems for structures. Source

Bastaits R.,Active Structures Laboratory | Mokrani B.,Active Structures Laboratory | Preumont A.,Active Structures Laboratory
Proceedings of ISMA 2010 - International Conference on Noise and Vibration Engineering, including USD 2010 | Year: 2010

This paper examines the active optics of future large segmented telescopes from the point of view of dynamic simulation and control. The first part of the paper is devoted to the modelling of the mirror. The model has a moderate size and separates the quasi-static behavior of the mirror (primary response) from the dynamic response (secondary or residual response). The second part of the paper is devoted to control. The control strategy considers explicitly the primary response of the telescope through a singular value controller. The control-structure interaction is addressed with the general robustness theory of multivariable feedback systems, where the secondary response is considered as uncertainty. This approach is very fast and allows extensive parametric studies. The study is illustrated with an example involving 90 segments, 270 inputs, and 654 outputs. Source

Collette C.,Active Structures Laboratory | Collette C.,CERN | Janssens S.,Active Structures Laboratory | Janssens S.,CERN | And 7 more authors.
International Conference on Noise and Vibration Engineering 2012, ISMA 2012, including USD 2012: International Conference on Uncertainty in Structure Dynamics | Year: 2012

The measurement of low frequency and small amplitude seismic vibrations with a high accuracy is critical in two scientific disciplines: seismology and structural vibration control. In both fields, there is a constant necessity to develop sensors with a better resolution, robust to temperature variations and magnetic fields, with a low consumption and, of course, at an affordable price. This is particularly valid in frontier science facilities, like future particle colliders and gravitational wave detectors. So far, the vibration sensor industry has not been interested to develop absolute displacement sensors, to measure low frequency and small amplitude vibrations. Such sensors are required in active isolation based on the so-called sky-hook spring strategy. In this paper, we show some recent developments and tests of such sensors. Basically, two prototypes are compared. The first one is based on a commercial low cost geophone, which has been modified to measure the displacement. The second one is based on a pendulum. The two sensors are compared on the following aspects: resolution, dynamic range, linearity, spurious high frequency modes, robustness and price. © (2012) by the Katholieke Universiteit Leuven Department of Mechanical Engineering All rights reserved. Source

Avraam M.,Active Structures Laboratory | Horodinca M.,Active Structures Laboratory | Romanescu I.,Active Structures Laboratory | Preumont A.,Active Structures Laboratory
Journal of Intelligent Material Systems and Structures | Year: 2010

This aricle presents a novel, computer controlled, magneto-rheological (MR) brake actuated, muscular rehabilitation, and evaluation device. The first part discusses various MR brake architectures and compares them. Simple analytical formulae are developed for a set of figures of merit, which point out the role played by the various parameters. Based on this analysis, a prototype with a T-shaped rotor has been designed, built and integrated into a portable rehabilitation device. In the second part of the article, the various exercise modes of the device and its control are described. Finally, results validating the performances of the device for the pronation/supination motion of the wrist are shown. © 2010 The Author(s). Source

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