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CONTENTS
Volume 18, Number 4, October 2016
 

Abstract
The monitoring of structural integrity of pipeline tapered thread connections is of great significance in terms of safe operation in the industry. In order to detect effectively the loosening degree of tapered thread connection, an active sensing method using piezoceramic transducers was developed based on time reversal technique in this paper. As the piezoeramic transducers can be either as actuators or sensors to generate or detect stress waves, the energy transmission for tapered thread connection was analyzed. Subsequently, the detection principle for tapered thread connection based on time reversal was introduced. Finally, the inherent relationship between the contact area and tightness degree of tapered thread connection for the pipe structural model was investigated. Seven different contact area scenarios were tested. Each scenario was created by loosening connectors ranging from 3 turns to 4.5 turns in the right tapered threads when the contact area in the left tapered threads were 4.5 turns. The experiments were separately conducted with a highly noisy environment and various excitation signal amplitudes. The results show the focused peaks based on time reversal have the monotonously rising trend with the increase of the contact areas of tapered threads within an acceptable monitoring resolution for metal pipes. Compared with the energy method, the proposed time reversal based method to monitor tapered threads loosening demonstrates to be more robust in rejecting noise in Structural Health Monitoring (SHM) applications.

Key Words
Structural Health Monitoring (SHM); pipeline tapered thread connections; piezoceramic transducers

Address
Xiaobin Hong: School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou, Guangdong, 510641, People\'s Republic of China;
Smart Material and Structure Laboratory, Department of Mechanical Engineering, University of Houston, Houston, TX 77004, USA
Gangbing Song: Smart Material and Structure Laboratory, Department of Mechanical Engineering, University of Houston, Houston, TX 77004, USA;
School of Civil Engineering, Dalian University of Technology, Dalian, Liaoning, 116023, People\'s Republic of China
Jiaobiao Ruan: Smart Material and Structure Laboratory, Department of Mechanical Engineering, University of Houston, Houston, TX 77004, USA
Zhimin Zhang: Smart Material and Structure Laboratory, Department of Mechanical Engineering, University of Houston, Houston, TX 77004, USA;
Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu,
Sichuan, 610054, People\'s Republic of China
Sidong Wu and Guixiong Liu: School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou, Guangdong, 510641, People\'s Republic of China



Abstract
Continuum manipulators as a kind of mechanical arms are useful tools in special robotic applications. In medical applications, like colonoscopy, a maneuverable thin and flexible manipulator is required. This research is focused on developing a basic module for such an application using shape memory alloys (SMA). In the structure of the module three wires of SMA are uniformly distributed and attached to the circumference of a flexible tube. By activating wires, individually or together, different rotation regimes are provided. SMA model is used based on Brinson work. The SMA model is combined to model of flexible tube to provide a composite model of the module. Simulating the model in Matlab provided a platform to be used to develop controller. Complex and nonlinear behavior of SMA make the control problem hard especially when a few SMA actuators are active simultaneously. In this paper, position control of the two degree of freedom module is under focus. An experimental control strategy is developed to regulate a desired position in the module. The simulation results present a reasonable performance of the controller. Moreover, the results are verified through experiments and show that the continuum module of this paper would be used in real modular manipulators.

Key Words
continuum manipulator; module; actuator; modeling; control; shape memory alloy

Address
Alireza Hadi and Hossein Akbari: Department of Mechatronics Engineering, Faculty of New Sciences and Technologies, University of Tehran, North Kargar St., Tehran, Iran

Abstract
A semi-active algorithm for edgewise vibration control of the spar-type floating offshore wind turbine (SFOWT) blades, nacelle and spar platform is developed in this paper. A tuned mass damper (TMD) is placed in each blade, in the nacelle and on the spar to control the vibrations for these components. A Short Time Fourier Transform algorithm is used for semi-active control of the TMDs. The mathematical formulation of the integrated SFOWT-TMDs system is derived by using Euler-Lagrangian equations. The theoretical model derived is a time-varying system considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar, mooring system and the TMDs, the hydrodynamic effects, the restoring moment and the buoyancy force. The aerodynamic loads on the nacelle and the spar due to their coupling with the blades are also considered. The effectiveness of the semi-active TMDs is investigated in the numerical examples where the mooring cable tension, rotor speed and the blade stiffness are varying over time. Except for excessively large strokes of the nacelle TMD, the semi-active algorithm is considerably more effective than the passive one in all cases and its effectiveness is restricted by the low-frequency nature of the nacelle and the spar responses.

Key Words
floating offshore wind turbine; spar-type; edgewise vibration; tuned mass damper; semi-active control

Address
Van-Nguyen Dinh: Software Division, Wood Group Kenny, Galway Technology Park, Parkmore, Galway, Ireland
Biswajit Bas: Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, Ireland
Satish Nagarajaiah: Departments of Civil and Environmental Engineering and Mechanical Engineering, Rice University, Houston, TX, United States


Abstract
A unified mathematical model of the equations of generalized magneto-thermoelasticty based on fractional derivative heat transfer for isotropic perfect conducting media is given. Some essential theorems on the linear coupled and generalized theories of thermoelasticity e.g. the Lord- Shulman (LS) theory, Green-Lindsay (GL) theory and the coupled theory (CTE) as well as dual-phase-lag (DPL) heat conduction law are established. Laplace transform techniques are used. The method of the matrix exponential which constitutes the basis of the state-space approach of modern theory is applied to the non-dimensional equations. The resulting formulation is applied to a variety of one-dimensional problems. The solutions to a thermal shock problem and to a problem of a layer media are obtained in the present of a transverse uniform magnetic field. According to the numerical results and its graphs, conclusion about the new model has been constructed. The effects of the fractional derivative parameter on thermoelastic fields for different theories are discussed.

Key Words
generalized magneto-thermoelasticity; fractional calculus; laplace transforms; state space approach; numerical results

Address
M.A. Ezzat: Department of Mathematics, Faculty of Education, Alexandria University, Alexandria, Egypt
A.A. El-Bary: Arab Academy for Science and Technology, P.O. Box 1029, Alexandria, Egypt

Abstract
Structural optimization involves a large number of structural analyses. When optimizing large structures, these analyses require a considerable amount of computational time and effort. However, there are specific types of structure for which the results of the analysis can be achieved in a much simpler and quicker way thanks to their special repetitive patterns. In this paper, frequency constraint optimization of cyclically repeated space trusses is considered. An efficient technique is used to decompose the large initial eigenproblem into several smaller ones and thus to decrease the required computational time significantly. Some examples are presented in order to illustrate the efficiency of the presented method.

Key Words
optimal analysis; optimal design; frequency constraint; truss; cyclic symmetry

Address
A. Kaveh and A. Zolghadr:Centre of Excellence for Fundamental Studies in Structural Engineering, Iran University of Science and Technology, Narmak, Tehran, P.O. Box 16846-13114, Iran


Abstract
The hygro-thermo-mechanical bending behavior of sigmoid functionally graded material (S-FGM) plate resting on variable two-parameter elastic foundations is discussed using a four-variable refined plate theory. The material characteristics are distributed within the thickness direction according to the two power law variation in terms of volume fractions of the constituents of the material. By employing a four variable refined plate model, both a trigonometric distribution of the transverse shear strains within the thickness and the zero traction boundary conditions on the top and bottom surfaces of the plate are respected without utilizing shear correction factors. The number of independent variables of the current formulation is four, as against five in other shear deformation models. The governing equations are deduced based on the four-variable refined plate theory incorporating the external load and hygro-thermal influences. The results of this work are compared with those of other shear deformation models. Various numerical examples introducing the influence of power-law index, plate aspect ratio, temperature difference, elastic foundation parameters, and side-to-thickness ratio on the static behavior of S-FGM plates are investigated.

Key Words
refined plate theory; moisture concentration; thermal effect; functionally graded plate; variable elastic foundation

Address
Youcef Beldjelili: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology,
Civil Engineering Department, Algeria
Abdelouahed Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology,
Civil Engineering Department, Algeria;
Laboratoire de Modélisation et Simulation Multi-échelle, Département de Physique, Faculté des Sciences Exactes, Département de Physique, Université de Sidi Bel Abbés, Algeria
S.R. Mahmoud: Department of Mathematics, Faculty of Science, King Abdulaziz University, Saudi Arabia;
Mathematics Department, Faculty of Science, University of Sohag, Egypt


Abstract
The aim of the paper is to analyze nonlinear transverse vibration of an embedded piezoelectric plate reinforced with single walled carbon nanotubes (SWCNTs). The system in rested in a Pasternak foundation. The micro-electro-mechanical model is employed to calculate mechanical and electrical properties of nanocomposite. Using nonlinear strain-displacement relations and considering charge equation for coupling between electrical and mechanical fields, the motion equations are derived based on energy method and Hamilton\'s principle. These equations can\'t be solved analytically due to their nonlinear terms. Hence, differential quadrature method (DQM) is employed to solve the governing differential equations for the case when all four ends are clamped supported and free electrical boundary condition. The influences of the elastic medium, volume fraction and orientation angle of the SWCNTs reinforcement and aspect ratio are shown on frequency of structure. The results indicate that with increasing volume fraction of SWCNTs, the frequency increases. This study might be useful for the design and smart control of nano/micro devices such as MEMS and NEMS.

Key Words
nonlinear vibration; piezoelectric plate; SWCNT; pasternak foundation; DQM

Address
Ali Ghorbanpour Arani: Faculty of Mechanical Engineering, Institute of Nanoscience & Nanotechnology, University of Kashan, Kashan, Iran
Reza Kolahchi: Department of Mechanical Engineering, Kashan Branch, Islamic Azad University, Kashan, Iran
Masoud Esmailpour: Young Researchers and Elite Club, Damavand Branch,Islamic Azad University, Damavand, Iran




Abstract
To estimate structural displacement, a visually servoed paired structured light system (ViSP) was proposed in previous studies. The ViSP is composed of two sides facing each other, each with one or two laser pointers, a 2-DOF manipulator, a camera, and a screen. By calculating the positions of the laser beams projected onto the screens and rotation angles of the manipulators, relative 6-DOF displacement between two sides can be estimated. Although the performance of the system has been verified through various simulations and experimental tests, it has a limitation that the accuracy of the displacement measurement depends on the alignment of the laser pointers. In deriving the kinematic equation of the ViSP, the laser pointers were assumed to be installed perfectly normal to the same side screen. In reality, however, this is very difficult to achieve due to installation errors. In other words, the pose of laser pointers should be calibrated carefully before measuring the displacement. To calibrate the initial pose of the laser pointers, a specially designed jig device is made and employed. Experimental tests have been performed to validate the performance of the proposed calibration method and the results show that the estimated displacement with the initial pose calibration increases the accuracy of the 6-DOF displacement estimation.

Key Words
structural health monitoring; displacement measurement; visually servoed paired structured light system (ViSP); laser pose calibration

Address
Jae-Uk Shin, Suyoung Choi and Youngjae Kim: Robotics Program, KAIST, Daejeon 34141, Republic of Korea
Haemin Jeon:Department of Civil and Environmental Engineering, Hanbat National University, Daejeon, 34158, Republic of Korea
Hyun Myung: Robotics Program, KAIST, Daejeon 34141, Republic of Korea;
Department of Civil and Environmental Engineering, KAIST, Daejeon 34141, Republic of Korea



Abstract
The quality of vibration pattern reproduction of elastic structures by the modal expansion method is influenced by the modal expansion method and the sensor placement as well as the accuracy of measured natural modes and the total number of vibration sensors. In this context, this paper presents an improved numerical method for reproducing the vibration patterns by introducing a block-wise modal expansion method (BMEM), together with the genetic algorithm (GA). For a given number of vibration sensors, the sensor positions are determined by an evolutionary optimization using GA and the modal assurance criterion (MAC). Meanwhile, for the proposed block-wise modal expansion, a whole frequency range of interest is divided into several overlapped frequency blocks and the vibration field reproduction is made block by block with different natural modes and different modal participation factors. A hollow cylindrical tank is taken to illustrate the proposed improved modal expansion method. Through the numerical experiments, the proposed method is compared with several conventional methods to justify that the proposed method provides the improved results.

Key Words
vibration pattern reproduction; block-wise modal expansion method (BMEM); sensor placement optimization; modal assurance criterion (MAC); genetic algorithm (GA)

Address
B.K. Jung and W.B. Jeong: School of Mechanical Engineering, Pusan National University, Busan 609-735, Korea
J.R. Cho: Department of Naval Architecture and Ocean Engineering, Hongik University, Sejong 339-710, Korea

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