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CONTENTS
Volume 15, Number 6, June 2015
 

Abstract
An original sensor system based on Fiber Bragg Gratings (FBG) for the strain monitoring of an adaptive wing element is presented in this paper. One of the main aims of the SARISTU project is in fact to measure the shape of a deformable wing for performance optimization. In detail, an Adaptive Trailing Edge (ATE) is monitored chord- and span-wise in order to estimate the deviation between the actual and the desired shape and, then, to allow attaining a prediction of the real aerodynamic behavior with respect to the expected one. The integration of a sensor system is not trivial: it has to fit inside the available room and to comply with the primary issue of the FBG protection. Moreover, dealing with morphing structures, large deformations are expected and a certain modulation is necessary to keep the measured strain inside the permissible measure range. In what follows, the mathematical model of an original FBG-based structural sensor system is presented, designed to evaluate the chord-wise strain of an Adaptive Trailing Edge device. Numerical and experimental results are compared, using a proof-of-concept setup. Further investigations aimed at improving the sensor capabilities, were finally addressed. The elasticity of the sensor structure was exploited to enlarge both the measurement and the linearity range. An optimisation process was then implemented to find out an optimal thickness distribution of the sensor system in order to alleviate the strain level within the referred component.

Key Words
smart aircraft structures; Fiber Bragg Grating sensor; rotation angle; shape reconstruction

Address
Monica Ciminello, Salvatore Ameduri, Antonio Concilio: C.I.R.A.- Italian Aerospace Research Center, Smart Structures Lab, Via Maiorise 81043, Capua (CE), Italy
Domenico Flauto: University of Palermo, Aerospace Engineering Dept - Viale delle Scienze 90128, Palermo, Italy
Fabio Mennella: University of Napoli \"Federico II\", Composite Material Dept - P.le Tecchio 80100, Napoli, Italy


Abstract
The electro-magneto- thermo-elastic behavior of a rotating functionally graded long hollow cylinder with functionally graded piezoelectric (FGPM) layers is analytically analyzed. The layers are imperfectly bonded to its inner and outer surfaces. The hybrid cylinder is placed in a constant magnetic field subjected to a thermo-electro-mechanical loading and could be rested on a Winkler-type elastic foundation. The material properties of the FGM cylinder and radially polarized FGPM layers are assumed to be graded in the radial direction according to the power law. The hybrid cylinder is rotating about its axis at a constant angular velocity. The governing equations are solved analytically and then stresses, displacement and electric potential distribution are calculated. Numerical examples are given to illustrate the effects of material in-homogeneity, magnetic field, elastic foundation, applied voltage, imperfect interface and thermo-mechanical boundary condition on the static behavior of a FG smart cylinder.

Key Words
functionally graded piezoelectric (FGPM); functionally graded material (FGM); magnetic field; Imperfect bonding; elastic foundation

Address
M. Saadatfar and M. Aghaie-Khafri: Faculty of Mechanical Engineering, K.N. Toosi University of Technology, Postal Code: 1999143344, Tehran, Iran


Abstract
Design criteria, modeling rules, and analysis principles of seismic isolation systems have already found place in important building codes and standards such as the Uniform Building Code and ASCE/SEI 7-05. Although real behaviors of isolation systems composed of high damping or lead rubber bearings are nonlinear, equivalent linear models can be obtained using effective stiffness and damping which makes use of linear seismic analysis methods for seismic-isolated buildings possible. However, equivalent linear modeling and analysis may lead to errors in seismic response terms of multi-story buildings and thus need to be assessed comprehensively. This study investigates the accuracy of equivalent linear modeling via numerical experiments conducted on generic five-story three dimensional seismic-isolated buildings. A wide range of nonlinear isolation systems with different characteristics and their equivalent linear counterparts are subjected to historical earthquakes and isolation system displacements, top floor accelerations, story drifts, base shears, and torsional base moments are compared. Relations between the accuracy of the estimates of peak structural responses from equivalent linear models and typical characteristics of nonlinear isolation systems including effective period, rigid-body mode period, effective viscous damping ratio, and post-yield to pre-yield stiffness ratio are established. Influence of biaxial interaction and plan eccentricity are also examined.

Key Words
nonlinear isolation systems; equivalent linear modeling; effective stiffness; effective damping; base isolation; seismic isolation

Address
Cenk Alhan and Murat Özgür: Department of civil Engineering, Istanbul University, 34320 Avcilar, Istanbul, Turkey

Abstract
Lamb waves have been a promising candidate for quantitative damage identification for various engineering structures, taking advantage of their superb capabilities of traveling for long distances with fast propagation and low attenuation. However, the application of Lamb waves in damage identification so far has been hampered by the fact that the characteristic signals associated with defects are generally weaker compared with those arising from boundary reflections, mode conversions and environmental noises, making it a tough task to achieve satisfactory damage identification from the time series. With awareness of this challenge, this paper proposes a time reversal-based technique to enhance the strength of damage-scattered signals, which has been previously applied to bulk wave-based damage detection successfully. The investigation includes (i) an analysis of Lamb wave propagation in a plate, generated by PZT patches mounted on the structure; (ii) an introduction of the time reversal theory dedicated for waveform reconstruction with a narrow-band input; (iii) a process of enhancing damage-scattered signals based on time reversal focalization; and (iv) the experimental investigation of the proposed approach to enhance the damage identification on a composite plate. The results have demonstrated that signals scattered by delamination in the composite plate can be enhanced remarkably with the assistance of the proposed process, benefiting from which the damage in the plate is identified with ease and high precision.

Key Words
time reversal; damage detection; Lamb waves; signal focalization; imaging damage

Address
Qiang Wang:School of Automation, Nanjing University of Posts and Telecommunications, 9 Wen Yuan Road, Nanjing,
P.R. China, 210046
Shenfang Yuan: The Aeronautical Science Key Laboratory for Smart Materials and Structures, Nanjing University of Aeronautics and Astronautics, 29 Yu Dao Street, Nanjing, P.R. China, 210016
Ming Hong: Department of Mechanical Engineering, The Hong Kong Polytechnic University, Kowloon,
Hong Kong SAR
Zhongqing Su:The Hong Kong Polytechnic University Shenzhen Research Institute, 18 Yue Xing Road, Shenzhen, P.R. China, 518057


Abstract
MR-TLCD (Magneto-Rheological Tuned Liquid Column Damper) is a new developed vibration control device, which combines the traditional passive control property with active controllability advantage. Based on traditional TLCD governing equation, this study further considers MR-fluid viscosity in the equation and by transforming the non-linear damping term into an equivalent linear damping, a solution can be obtained. In order to find a countable set of parameters for the design of the MR-TLCD system and also to realize its applicability to structures, a series of experimental test were designed and carried out. The testing programs include the basic material properties of the MR-fluid, the damping ratio of a MR-TLCD and the dynamic responses for a frame structure equipped with the MR-TLCD system subjected to strong ground excitations. In both the analytical and experimental results of this study, it is found that the accurately tuned MR-TLCD system could effectively reduce the dynamic response of a structural system.

Key Words
MR-TLCD; viscosity of MR-fluid; vibration mitigation; shaking-table testing on TLCD; magnetic power control

Address
Chih-Wen Cheng, Hsien Hua Leeand Yuan-Tzuo Luo: Department of Marine Environment and Engineering, National Sun Yat-sen University, 70 Lienhai Rd., Kaohsiung 80424, Taiwan, R.O.C.


Abstract
This paper provides a novel solution for thick-walled cylinders made of functionally graded materials (FGMs). In the formulation, the cylinder is divided into N layers. On the individual layer, the Young\'s modulus is assumed to be a constant. For an individual layer, two undetermined constants are involved in the elastic solution. Those undetermined coefficients can be evaluated from the continuation condition along interfaces of layers and the boundary conditions at the inner surface and outer surface of cylinder. Finally, the solution for thick-walled cylinders made of functionally graded materials is obtainable. This paper provides several numerical examples which are useful for engineer to design a cylinder made of FGMs.

Key Words
functionally graded materials; thick-walled cylinder; numerical technique; multiply-layered cylinder

Address
Y.Z. Chen: Division of Engineering Mechanics, Jiangsu University, Zhenjiang, Jiangsu, 212013, P.R. China

Abstract
The use of shape memory alloys (SMAs) in dynamical systems has an increasing importance in engineering especially due to their capacity to provide vibration reductions. In this regard, experimental tests are essential in order to show all potentialities of this kind of systems. In this work, SMA springs are incorporated in a dynamical system that consists of a one degree of freedom oscillator connected to a linear spring and a mass, which is also connected to the SMA spring. Two types of springs are investigated defining two distinct systems: a pseudoelastic and a shape memory system. The characterisation of the springs is evaluated by considering differential calorimetry scanning tests and also force-displacement tests at different temperatures. Free and forced vibration experiments are made in order to investigate the dynamical behaviour of the systems. For both systems, it is observed the capability of changing the equilibrium position due to phase transformations leading to hysteretic behaviour, or due to temperature changes which also induce phase transformations and therefore, change in stiffness. Both situations are investigated by promoting temperature changes and also pre-tension of the springs. This article shows several experimental tests that allow one to obtain a general comprehension of the dynamical behaviour of SMA systems. Results show the general thermo-mechanical behaviour of SMA dynamical systems and the obtained conclusions can be applied in distinct situations as in rotor-bearing systems.

Key Words
shape memory alloys; dynamic systems; stiffness changes; phase transformation; experimental tests

Address
Soren Enemark and Ilmar F. Santos: Technical University of Denmark, Department of Mechanical Engineering, DK-2800 Kgs. Lyngby, Denmark
Marcelo A. Savi: Universidade Federal do Rio de Janeiro, COPPE – Department of Mechanical Engineering,
21.941.972 – Rio de Janeiro – RJ – Brazil, P.O. Box 68.503


Abstract
In this study, a wireless crack sensor is developed for monitoring cracks propagating in two dimensions. This sensor is developed by incorporating a laser-based optical navigation sensor board (ADNS-9500) into a smart wireless platform (Imote2). To measure crack propagation, the Imote2 sends a signal to the ADNS-9500 to collect a sequence of images reflected from the concrete surface. These acquired images can be processed in the ADNS-9500 directly (the navigation mode) or sent to Imote2 for processing (the frame capture mode). The computed crack displacement can then be transmitted wirelessly to a base station. The design and the construction of this sensor are reported herein followed by some calibration tests on one prototype sensor. Test results show that the sensor can provide sub-millimeter accuracy under sinusoidal and step movement. Also, the two modes of operation offer complementary performance as the navigation mode is more accurate in tracking large amplitude and fast crack movement while the frame capture mode is more accurate for small and slow crack movement. These results illustrate the feasibility of developing such a crack sensor as well as point out directions of further research before its actual implementation.

Key Words
crack monitoring; optical flow; opticalnavigation

Address
S.H. Man and C.C. Chang: Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Clear Way Bay, Kowloon, Hong Kong
M. Hassan and A. Bermak: Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Way Bay, Kowloon, Hong Kong

Abstract
Two hyperbolic displacement models are used for the bending response of simply-supported orthotropic laminated composite plates resting on two-parameter elastic foundations under mechanical loading. The models contain hyperbolic expressions to account for the parabolic distributions of transverse shear stresses and to satisfy the zero shear-stress conditions at the top and bottom surfaces of the plates. The present theory takes into account not only the transverse shear strains, but also their parabolic variation across the plate thickness and requires no shear correction coefficients in computing the shear stresses. The governing equations are derived and their closed-form solutions are obtained. The accuracy of the models presented is demonstrated by comparing the results obtained with solutions of other theories models given in the literature. It is found that the theories proposed can predict the bending analysis of cross-ply laminated composite plates resting on elastic foundations rather accurately. The effects of Winkler and Pasternak foundation parameters, transverse shear deformations, plate aspect ratio, and side-to-thickness ratio on deflections and stresses are investigated.

Key Words
hyperbolic expressions; cross-ply laminated plate; elastic foundations

Address
Ashraf M. Zenkour: Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia;
Department of Mathematics, Faculty of Science, Kafrelsheikh University, Kafrelsheikh 33516, Egypt


Abstract
When natural disasters occur, including earthquakes, tsunamis, and debris flows, they are often accompanied by various types of damages such as the collapse of buildings, broken bridges and roads, and the destruction of natural scenery. Natural disaster detection and warning is an important issue which could help to reduce the incidence of serious damage to life and property as well as provide information for search and rescue afterwards. In this study, we propose a novel computer vision technique for debris flow detection which is feature-based that can be used to construct a debris flow event warning system. The landscape is composed of various elements, including trees, rocks, and buildings which are characterized by their features, shapes, positions, and colors. Unlike the traditional methods, our analysis relies on changes in the natural scenery which influence changes to the features. The \"background module\" and \"monitoring module\" procedures are designed and used to detect debris flows and construct an event warning system. The multi-criteria decision-making method used to construct an event warring system includes gradient information and the percentage of variation of the features. To prove the feasibility of the proposed method for detecting debris flows, some real cases of debris flows are analyzed. The natural environment is simulated and an event warning system is constructed to warn of debris flows. Debris flows are successfully detected using these two procedures, by analyzing the variation in the detected features and the matched feature. The feasibility of the event warning system is proven using the simulation method. Therefore, the feature based method is found to be useful for detecting debris flows and the event warning system is triggered when debris flows occur.

Key Words
debris flow; natural disaster; feature based; computer vision; natural disasters detection; event warning system

Address
Chih-Wei Lin: Department of Computer Science and Information Engineering, National Taiwan University, Taipei, Taiwan, R.O.C.;
Faculty of Engineering, King Abdulaziz University, Jeddah 21589, Saudi Arabia
Wen-Ko Hsu: Research Center for Hazard Mitigation and Prevention, National Central University, Jhung-li,
Taoyuan, Taiwan, R.O.C.
Cheng-Wu Chen: Department of Maritime Information and Technology, National Kaohsiung Marine University, Kaohsiung, Taiwan, R.O.C.;
Faculty of Engineering, King Abdulaziz University, Jeddah 21589, Saudi Arabia
Wei-Ling Chiang: Department of Civil Engineering, National Central University, Jhung-li, Taoyuan, Taiwan, R.O.C.





Abstract
Electroactive polymers have attracted considerable attention in recent years due to their sensing and actuating properties which make them a material of choice for a wide range of applications including sensors, biomimetic robots, and biomedical micro devices. This paper presents an effective modeling strategy for nonlinear large deformation (small strains and moderate rotations) dynamic analysis of polymer actuators. Considering that the complicated electro-chemo-mechanical dynamics of these actuators is a drawback for their application in functional devices, establishing a mathematical model which can effectively predict the actuator\'s dynamic behavior can be of paramount importance. To effectively predict the actuator\'s dynamic behavior, a comprehensive mathematical model is proposed correlating the input voltage and the output bending displacement of polymer actuators. The proposed model, which is based on the rigid finite element (RFE) method, consists of two parts, namely electrical and mechanical models. The former is comprised of a ladder network of discrete resistive-capacitive components similar to the network used to model transmission lines, while the latter describes the actuator as a system of rigid links connected by spring-damping elements (sdes). Both electrical and mechanical components are validated through experimental results.

Key Words
polymer actuators; large deformation dynamic analysis; rigid finite element method

Address
Amir Ali Amiri Moghadam, Abbas Kouzani and Akif Kaynak: School of Engineering, Deakin University, Geelong, Victoria 3216, Australia
Reza Zamani: School of Information Systems and Technology, EIS, University of Wollongong, NSW 2522, Australia
Kevin Magniez: Institute for Frontier Materials, Deakin University, Geelong, Victoria 3216, Australia

Abstract
We propose an electrically self-reliant structural health monitoring (SHM) system that is able to wirelessly transmit sensing data using electrical power generated by vibration without the need for additional external power sources. The provision of reliable electricity to wireless SHM systems is a highly important issue that has often been ignored, and to expand the applicability of various wireless SHM innovations, it will be necessary to develop comprehensive wireless SHM devices including stable electricity sources. In light of this need, we propose a new, highly efficient vibration-powered generator based on a tuned-mass-damper (TMD) mechanism that is quite suitable for vibration-based SHM. The charging time of the TMD generator is shorter than that of conventional generators based on the impedance matching method, and the proposed TMD generator can harvest 16 times the amount of energy that a conventional generator can. The charging time of an SHM wireless transmitter is quantitatively formulated. We conduct wireless monitoring experiments to validate a wireless SHM system composed of a self-reliant SHM and a vibration-powered TMD generator.

Key Words
wireless health monitoring; self-reliant energy harvester; vibration-powered generator; tuned-mass-damper mechanism

Address
Kanjuro Makihara, Yuta Yamamoto and Hisao Fukunaga: Tohoku University, Department of Aerospace Engineering, 6-6-01 Aramaki-Aza-Aoba, Aoba-Ward, Sendai, 980-8579 Japan
Hidekazu Hirai: Shinko Electric Industries Co., Ltd., 80, Oshimada-Machi, Nagano, 381-2287 Japan


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