Sami El-Borgi

International Conference on Advances in Mechanical Engineering and Mechanics 2010

The use of active-fiber composites (AFC) instead of traditional ceramic piezoelectric materials is motivated by flexibility and relatively high actuation capacity. Nevertheless, their energy harvesting capabilities remain low. As a first step toward the enhancement of AFC&#x2019;s performances, a mathematical model that accurately simulates the dynamic behavior of the AFC is proposed. In fact, most of the modeling approaches found in the literature for AFC are based on finite element methods. In this work, we use homogenization techniques to mathematically describe piezoelectric properties taking into consideration the composite structure of the AFC. We model the interdigitated electrodes as a series of capacitances and current sources linked in parallel; then we integrate these properties into the structural model of the AFC. The proposed model is incorporated into a vibration based energy harvesting system consisting of a cantilever beam on top of which an AFC patch is attached. Finally, analytical solutions of the dynamic behavior and the harvested voltage are proposed and validated with finite element simulations.

A. Jemai

F. Najar

M. Chafra

Z. Ounaies

Mathematical Modeling of an Active-Fiber Composite Energy Harvester with Interdigitated Electrodes

This paper investigates numerically the active tendon control of a cable-stayed bridge in a construction phase. A linear Finite Element model of small scale mock-up of the bridge is first presented. Active damping is added to the structure by using pairs of collocated force actuator-displacement sensors located on each active cable and decentralized first order positive position feedback (PPF) or direct velocity feedback (DVF). A comparison between these two compensators showed that each one has good performance for some modes and performs inadequately with the other modes. A decentralized parallel PPF-DVF is proposed to get the better of the two compensators. The proposed strategy is then compared to the one using decentralized integral force feedback (IFF) and showed better performance. The Finite Element model of the bridge is coupled with a nonlinear cable taking into account sag effect, general support movements, and quadratic and cubic nonlinear couplings between in-plane and out-of-plane motions. Finally, the proposed strategy is used to control both deck and cable vibrations induced by parametric excitation. Both cable and deck vibrations are attractively damped.

M. H. El Ouni

N. Ben Kahla

Numerical Study of the Active Tendon Control of a Cable-Stayed Bridge in a Construction Phase

In this paper, we propose a novel strategy for controlling a flexible nonlinear beam with the confinement of vibrations. We focus principally on design issues related to the passive control of the beam by proper selection of its geometrical and physical parameters. Due to large deflections within the regions where the vibrations are to be confined, we admit a nonlinear model that describes with precision the beam dynamics. In order to design a set of physical and geometrical parameters of the beam, we first formulate an inverse eigenvalue problem. To this end, we linearize the beam model and determine the linearly assumed modes that guarantee vibration confinement in selected spatial zones and satisfy the boundary conditions of the beam to be controlled. The approximation of the physical and geometrical parameters is based on the orthogonality of the assumed linear mode shapes. To validate the strategy, we input the resulting parameters into the nonlinear integral-partial differential equation that describes the beam dynamics. The nonlinear frequency response curves of the beam are approximated using the differential quadrature method and the finite difference method. We confirm that using the linear model, the strategy of vibration confinement remains valid for the nonlinear beam.

W. Gafsi

S. Choura

S. El-Borgi

Confinement of Vibrations in Variable-Geometry Nonlinear Flexible Beam

Multisensor information fusion, when applied to fault diagnosis, the time-space scope, and the quantity of information are expanded compared to what could be acquired by a single sensor, so the diagnostic object can be described more comprehensively. This paper presents a methodology of fault diagnosis in rotating machinery using multisensor information fusion that all the features are calculated using vibration data in time domain to constitute fusional vector and the support vector machine (SVM) is used for classification. The effectiveness of the presented methodology is tested by three case studies: diagnostic of faulty gear, rolling bearing, and identification of rotor crack. For each case study, the sensibilities of the features are analyzed. The results indicate that the peak factor is the most sensitive feature in the twelve time-domain features for identifying gear defect, and the mean, amplitude square, root mean square, root amplitude, and standard deviation are all sensitive for identifying gear, rolling bearing, and rotor crack defect comparatively.

Ling-li Jiang

Hua-kui Yin

Xue-jun Li

Si-wen Tang

Fault Diagnosis of Rotating Machinery Based on Multisensor Information Fusion Using SVM and Time-Domain Features

We study a capacitive MEMS switch composed of two clamped-clamped exible microbeams. We first develop a mathematical model for the MEMS switch where the upper microbeam represents the ground transmission line and the lower one represents the central transmission line. An electrostatic force is applied between the two microbeams to yield the switch to its ON and OFF states. We derive the equations of motion of the system and associated boundary conditions and solve the static and dynamic problems using the differential quadratic method. We show that using only nine grid points gives relatively accurate results when compared to those obtained using FEM. We also examine the transient behavior of the microswitch and obtain results indicating that subsequent reduction in actuation voltage, switching time, and power consumption are expected along with relatively good RF performances. ANSYS HFSS simulator is used in this paper to extract the RF characteristics of the microswitch. HFSS simulation results show that the insertion loss is as low as &#x2212;0.31&#x2009;dB and that the return loss is better than &#x2212;12.41&#x2009;dB at 10&#x2009;GHz in the ON state. At the OFF state, the isolation is lower than &#x2212;23&#x2009;dB in the range of 10 to 50&#x2009;GHz.

Hatem Samaali

Fehmi Najar

Slim Choura

Dynamic Study of a Capacitive MEMS Switch with Double Clamped-Clamped Microbeams

The modal parameters of a structure that is estimated from ambient vibration measurements are always subject to bias and variance errors. Accordingly the concept of the stabilization diagram is introduced to help users identify the correct model. One of the most important problems using this diagram is the appearance of spurious modes that should be discriminated to simplify modes selections. This study presents a new stabilization criterion obtained through a novel numerical implementation of the stabilization diagram and the discussion of model validation employing the power spectral density. As an application, an aircraft skeleton is used.

E. Mrabet

M. Abdelghani

A New Criterion for the Stabilization Diagram Used with Stochastic Subspace Identification Methods: An Application to an Aircraft Skeleton

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Shock and Vibration publishes papers on all aspects of shock and vibration, especially in relation to civil, mechanical and aerospace engineering applications, as well as transport, materials and geoscience.&nbsp;

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Chief Editor&nbsp;Dr Tai Thai&nbsp;is based at the University of Melbourne and his current research focuses on high strength materials for sustainable construction of buildings, bridges and other infrastructure.

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Shock and Vibration

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Shock and Vibration

International Conference on Advances in Mechanical Engineering and Mechanics 2010

International Conference on Advances in Mechanical Engineering and Mechanics 2010

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