Techno Press


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CONTENTS
Volume 6, Number 7, September 2010
 

Abstract
In this paper, the optimal design of vibration control system for smart structures has been investigated semi-analytically via the optimization of geometric parameters like the placements and sizes of piezoelectric sensors and actuators (S/As) bonded on the structures. The criterion based on the maximization of energy dissipation was adopted for the optimization of the control system. Based on the sensing and actuating equations, the total energy stored in the system which is used as the objective function was analytically derived with design variables explicitly presented. Two cases of single and combined vibration modes were addressed for a simply supported beam and a simply supported cylindrical shell. For single vibration mode, the optimal distributions of the piezoelectric S/As could be obtained analytically. However, the Sequential Quadratic Programming (SQP) method has to be employed to solve those which violated the prescribed constraints and to solve the case of combined vibration modes. The results of three examples, which include a simply supported beam, a simply supported cylindrical shell and a simply supported plate, showed good agreement with those obtained by the Genetic Algorithm (GA) method. Moreover, in comparison with the GA method, the proposed method is more effective in obtaining better optimization results and is much more efficient in terms of computation time.

Key Words
optimization; vibration control; sequential quadratic programming; smart structures.

Address
Zhanli Jin: School of Electrical and Electronics Engineering, Nanyang Technological University (NTU), Singapore 639798
Yaowen Yang and Chee Kiong Soh: School of Civil and Environmental Engineering, Nanyang Technological University (NTU), Singapore 639798

Abstract
This paper addresses the control issue of vibratory MEMS-based gyroscopes. This study considers a gyroscope that can be modeled by an inner mass attached to an outer mass by four springs and four dampers. The outer mass itself is attached to the rotating frame by an equal number of springs and dampers. In order to measure the angular rate of the rotating frame, a driving force is applied to the inner mass and the Coriolis force is sensed along the y-direction associated with the outer mass. Due to micro-fabrication imperfections, including anisoelasticity and damping effects, both gyroscopes do not allow accurate measurements, and therefore, it becomes necessary to devise feedback controllers to reduce the effects of such imperfections. Given an ideal gyroscope that meets certain performance specifications, a feedback control strategy is synthesized to reduce the error dynamics between the actual and ideal gyroscopes. For a dual-mass gyroscope, it is demonstrated that the error dynamics are remarkably decreased with the application of four actuators applied to both masses in the x and y directions. It is also shown that it is possible to reduce the error dynamics with only two actuators applied to the outer mass only. Simulation results are presented to prove the efficiency of the proposed control design.

Key Words
control strategy; vibration; MEMS; gyroscope.

Address
S. Choura: Micro-Electro-Thermal-Systems Research Unit, National Engineering School of Sfax, University of Sfax, Route de Soukra, Sfax 3038, Tunisia
N. Aouni: Department of Mechanical Engineering, University of Houston, Houston 77204, USA
S. El-Borgi: Applied Mechanics and Systems Research Laboratory, Tunisia Polytechnic School, University of November 7th at Carthage, B.P. 743, La Marsa 2078, Tunisia

Abstract
Vibration control and health monitoring of building structures have been actively investigated in recent years but treated separately according to the primary objective pursued. This paper presents a general approach in the time domain for integrating vibration control and health monitoring of a building structure to accommodate various types of control devices and on-line damage detection. The concept of the time-domain approach for integrated vibration control and health monitoring is first introduced. A parameter identification scheme is then developed to identify structural stiffness parameters and update the structural analytical model. Based on the updated analytical model, vibration control of the building using semi-active friction dampers against earthquake excitation is carried out. By assuming that the building suffers certain damage after extreme event or long service and by using the previously identified original structural parameters, a damage detection scheme is finally proposed and used for damage detection. The feasibility of the proposed approach is demonstrated through detailed numerical examples and extensive parameter studies.

Key Words
parameter identification; vibration control; damage detection; integrated system; feasibility study.

Address
B. Chen, Y.L. Xu and X. Zhao: Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong, China

Abstract
This study investigated propagation characteristics of piezo-activated guided waves in an aluminium rectangular-section tube for the purpose of damage identification. Changes in propagating velocity and amplitude of the first wave packet in acquired signals were observed in the frequency range from 50 to 250 kHz. The difference in guided wave propagation between rectangular- and circular-section tubes was examined using finite element simulation, demonstrating a great challenge in interpretation of guided wave signals in rectangular-section tubes. An active sensor network, consisting of nine PZT elements bonded on different surfaces of the tube, was configured to collect the wave signals scattered from through-thickness holes of different diameters. It was found that guided waves were capable of propagating across the sharp tube curvatures while retaining sensitivity to damage, even that not located on the surfaces where actuators/sensors were attached. Signal correlation between the intact and damaged structures was evaluated with the assistance of a concept of digital damage fingerprints (DDFs). The probability of the presence of damage on the unfolded tube surface was thus obtained, by which means the position of damage was identified with good accuracy.

Key Words
guided waves; damage identification; tubular structures; active sensor networks; piezoelectric element.

Address
Ye Lu: State Key Laboratory of Mechanical System and Vibration, Shanghai Jiao Tong University, Shanghai 200240, China
Lin Ye and Dong Wang: Laboratory of Smart Materials and Structures (LSMS), Centre for Advanced Materials Technology (CAMT), School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006, Australia
Limin Zhou and Li Cheng: Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, China

Abstract
This paper presents a new concept of using PZT (lead zircornate titanate) transducers as a non-destructive testing (NDT) tool for evaluating quality of concrete. Detection of defects in concrete is very important in order to check the integrity of concrete structures. The electro-mechanical impedance (EMI) response of PZT transducers bonded onto a concrete specimen can be used for evaluating local condition of the specimen. Measurements are carried out by electrically exciting the bonded PZT transducers at high frequency range and taking response measurements of the transducers. In this study, the compression test results showed that concrete specimens without sufficient compaction are likely to fall below the desired strength. In addition, the strength of concrete was greatly reduced as the voids in concrete were increased. It was found that the root mean square deviation (RMSD) values yielded between the EMI signatures for concrete specimens in dry and saturated states showed good agreement with the specimens compressive strength and permeable voids. A quality metric was introduced for predicting the quality of concrete based on the dry-saturated state of concrete specimens. The simplicity of the method and the current development towards low cost and portable impedance measuring system, offer an advantage over other NDE methods for evaluating concrete quality.

Key Words
electro-mechanical impedance; PZT transducers; non-destructive testing; concrete quality.

Address
R. Tawie and H.K. Lee: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, South Korea
S.H. Park: Department of Civil and Environmental Engineering, Sungkyunkwan University, Suwon, Gyeonggi 440-746, South Korea

Abstract
An energy-based variational approach is used for structural dynamic modeling of the IPMC (Ionic Polymer Metal Composites) flapping wing. Dynamic characteristics of the wing are analyzed using numerical simulations. Starting with the initial design, critical parameters which have influence on the performance of the wing are identified through parametric studies. An optimization study is performed to obtain improved flapping actuation of the IPMC wing. It is shown that the optimization algorithm leads to a flapping wing with dimensions similar to the dragonfly Aeshna Multicolor wing. An unsteady aerodynamic model based on modified strip theory is used to obtain the aerodynamic forces. It is found that the IPMC wing generates sufficient lift to support its own weight and carry a small payload. It is therefore a potential candidate for flapping wing of micro air vehicles.

Key Words
ionic polymer metal composites; dynamics; flapping wing; optimization; unsteady aerodynamics; micro air vehicles.

Address
Sujoy Mukherjee and Ranjan Ganguli: Department of Aerospace Engineering, Indian Institute of Science, Bangalore-560012, India


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