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CONTENTS
Volume 1, Number 3, September 2005
 

Abstract
The non-linear behaviour of electrorheological (ER) and magnetorheological (MR) dampers makes it difficult to design effective control strategies, and as a consequence a wide range of control systems have been proposed in the literature. These previous studies have not always compared the performance to equivalent passive systems, alternative control designs, or idealised active systems. As a result it is often impossible to compare the performance of different smart damper control strategies. This article provides some insight into the relative performance of two MR damper control strategies: on/off control and feedback linearisation. The performance of both strategies is benchmarked against ideal passive, semi-active and fully active damping. The study relies upon a previously developed model of an MR damper, which in this work is validated experimentally under closed-loop conditions with a broadband mechanical excitation. Two vibration isolation case studies are investigated: a single-degree-of-freedom mass-isolator, and a two-degree-of-freedom system that represents a vehicle suspension system. In both cases, a variety of broadband mechanical excitations are used and the results analysed in the frequency domain. It is shown that although on/off control is more straightforward to implement, its performance is worse than the feedback linearisation strategy, and can be extremely sensitive to the excitation conditions.

Key Words
smart fluids; magnetorheological damper; semi-active control; benchmarking; mass isolator; vehicle suspension; skyhook; feedback linearisation.

Address
Department of Mechanical Engineering, The University of Sheffield, Sheffield, S1 3JD, UK

Abstract
In Lamb wave detection of damages in smart structures, the excitation pulse is usually designed as a narrow band burst wave for the convenience of analysis and recognition. However, the wideband excitation can excite more modes in plate/shell structure and thus provides extra information for changes of the structure. This paper presents a method that can extract information in wideband Lamb wave signals. By transforming the detected signals into various sub-frequency band, the measured signal can be converted to its equivalences of narrow band excitations, therefore, the information in different frequency bands can be acquired from a single test and in the same time the complicity of wideband signal can be simplified. Some test results are provided to verify this method.

Key Words
Lamb wave; wavelet transform; time-frequency analysis; damage detection; dispersion.

Address
Lihua Shi; Laboratory of Electromagnetics, Nanjing Engineering Institute, No.1 Haifuxiang, Nanjing 210007, China
Xinwei Wang and Gang Li; The Aeronautical Science Key Laboratory for Smart Materials and Structures,
Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Lingyan Zhang; Laboratory of Electromagnetics, Nanjing Engineering Institute, Nanjing 210007, China

Abstract
This work describes ongoing development of an embedded sensor system for the early detection and prevention of deterioration of reinforcing steel tendons within reinforced concrete. These devices will evaluate the condition of the steel tendon using ultrasonic techniques and then wirelessly transmit this data to the outside world without human intervention. The ultrasonic transducers and the interpretation of the sensed signals that allow detection and prognosis of tendon condition are detailed. Electrical characterization of concrete mixtures used in bridge construction is conducted and a wideband microstrip antenna is designed and fabricated to operate between 2.4 and 2.5 GHz when embedded in such a medium. Simulations and measurements of the embedded antenna element are presented. Transceiver selection and implementation are discussed as well as future work in operational protocols, sensor networking, and power sources. By implementing commercially available off-the-shelf components whenever possible, these devices have the potential to save millions of dollars a year in evaluation, repair and replacement of reinforced concrete.

Key Words
ultrasonic guided waves; structural concrete; corrosion; embedded wireless sensors; embedded antenna.

Address
University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA

Abstract
This paper features about the modeling and design of a fast output sampling feedback controller for a smart Timoshenko beam system for a SISO case by considering the first 3 vibratory modes. The beam structure is modeled in state space form using FEM technique and the Timoshenko beam theory by dividing the beam into 4 finite elements and placing the piezoelectric sensor/actuator at one location as a collocated pair, i.e., as surface mounted sensor/actuator, say, at FE position 2. State space models are developed for various aspect ratios by considering the shear effects and the axial displacements. The effects of changing the aspect ratio on the master structure is observed and the performance of the designed FOS controller on the beam system is evaluated for vibration control.

Key Words
: smart structure; Timoshenko beam; fast output sampling feedback control; finite element method; state space model; vibration control; aspect ratio; LMI.

Address
T. C. Manjunath; Interdisciplinary Programme in Systems and Control Engineering, Indian Institute of Technology Bombay, 101B, ACRE Building, Mumbai-400076, Maharashtra, India
B. Bandyopadhyay; Systems and Control Engineering, I.I.T. Bombay, Powai, Mumbai-76, India

Abstract
This paper presents an efficient and accurate coupled beam model for piezoelectric bimorphs based on improved first-order shear deformation theory (FSDT). The model combines the equivalent single layer approach for the mechanical displacements and a layerwise modeling for the electric potential. General electric field function is proposed to reasonably approximate the through-the-thickness distribution of the applied and induced electric potentials. Layerwise defined shear correction factor (k) accounting for nonlinear shear strain distribution is introduced into both the shear stress resultant and the electric displacement integration. Analytical solutions for free vibrations and forced response under electromechanical loads are obtained for the simply supported piezoelectric bimorphs with series or parallel arrangement, and the numerical results for various length-to-thickness ratios are compared with the exact two-dimensional piezoelasticity solution. Excellent predictions with low error estimates of local and global responses as well as the modal frequencies are observed.

Key Words
piezoelectric bimorph; beam model; first-order shear deformation theory; shear correction factor; electric potential; analytical solution.

Address
Department of Civil Engineering, Zhejiang University, Hangzhou 310027, P. R. China


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