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CONTENTS
Volume 17, Number 2, February 2016
 

Abstract
This paper investigates the Synergetics based Damage Detection Method (SDDM) for frame structures by using surface-bonded PZT (Lead Zirconate Titanate) patches. After analyzing the mechanism of pattern recognition from Synergetics, the operating framework with cooperation-competition-update process of SDDM was proposed. First, the dynamic identification equation of structural conditions was established and the adjoint vector (AV) set of original vector (OV) set was obtained by Generalized Inverse Matrix (GIM).Then, the order parameter equation and its evolution process were deduced through the strict mathematics ratiocination. Moreover, in order to complete online structural condition update feature, the iterative update algorithm was presented. Subsequently, the pathway in which SDDM was realized through the modified Synergetic Neural Network (SNN) was introduced and its assessment indices were confirmed. Finally, the experimental platform with a two-story frame structure was set up. The performances of the proposed methodology were tested for damage identifications by loosening various screw nuts group scenarios. The experiments were conducted in different damage degrees, the disturbance environment and the noisy environment, respectively. The results show the feasibility of SDDM using piezoceramic sensors and actuators, and demonstrate a strong ability of anti-disturbance and anti-noise in frame structure applications. This proposed approach can be extended to the similar structures for damage identification.

Key Words
structural condition identification; Synergetics; lead zirconate titanate (PZT); frame structure; damage detection

Address
Xiaobin Hong: School of Mechanical and Automotive Engineering, South China University of Technology,
Guangzhou 510641, China;
Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA
Jiaobiao Ruan and Gangbing Song: Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA
Guixiong Liu: School of Mechanical and Automotive Engineering, South China University of Technology,
Guangzhou 510641, China
Tao Wang: Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA;
College of Mechanical Engineering and Automation, Wuhan University of Science and Technology, Wuhan, 430081, China
Youyong Li: College of Mechanical Engineering and Automation, Wuhan University of Science and Technology,
Wuhan, 430081, China





Abstract
Seismic isolation systems are essentially designed to preserve structural safety, prevent occupants injury and properties damage. An active saturated LMI-based control design is proposed to attenuate seismic disturbances in base-isolated structures under saturation actuators. Using a mathematical model of an eight-storied building structure, an active control algorithm is designed. Performance evaluation of the controller is carried out in a simplified model version of a benchmark building system, which is recognized as a state-of-the-art model for numerical experiments of structures under seismic perturbations. Experimental results show that the proposed algorithm is robust with respect to model and seismic perturbations. Finally, the performance indices show that the proposed controller behaves satisfactorily and with a reasonable control effort.

Key Words
vibration control; base-isolated structures; active control; linear matrix inequalities; saturation

Address
Francesc Pozo and Leonardo Acho: CoDAlab, Department of Applied Mathematics III, Escola Universitaria d\'Enginyeria Tecnica Industrial de Barcelona (EUETIB), Universitat Politecnica de Catalunya (UPC), Comte d\'Urgell, 187, 08036 Barcelona, Spain
Gisela Pujol: CoDAlab, Department of Applied Mathematics III, Escola d\'Enginyeria de Terrassa (EET), Universitat Politècnica de Catalunya (UPC), Colom, 1, 08222 Terrassa (Barcelona) Spain



Abstract
The Canton Tower is a high-rise slender structure with a height of 610 m. A structural health monitoring system has been instrumented on the structure, by which data is continuously monitored. This paper presents an investigation on the identified modal properties of the Canton Tower using ambient vibration data collected during a whole day (24 hours). A recently developed Fast Bayesian FFT method is utilized for operational modal analysis on the basis of the measured acceleration data. The approach views modal identification as an inference problem where probability is used as a measure for the relative plausibility of outcomes given a model of the structure and measured data. Focusing on the first several modes, the modal properties of this supertall slender structure are identified on non-overlapping time windows during the whole day under normal wind speed. With the identified modal parameters and the associated posterior uncertainty, the distribution of the modal parameters in the future is predicted and assessed. By defining the modal root-mean-square value in terms of the power spectral density of modal force identified, the identified natural frequencies and damping ratios versus the vibration amplitude are investigated with the associated posterior uncertainty considered. Meanwhile, the correlations between modal parameters and temperature, modal parameters and wind speed are studied. For comparison purpose, the frequency domain decomposition (FDD) method is also utilized to identify the modal parameters. The identified results obtained by the Bayesian method, the FDD method and a finite element model are compared and discussed.

Key Words
supertall structure; ambient vibration; modal identification; Bayesian method; uncertainty

Address
Feng-Liang Zhang and Yan-Chun Ni: Research Institute of Structural Engineering and Disaster Reduction, Tongji University, 1239 Siping Road, Shanghai, China
Yi-Qing Ni and You-Wu Wang: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

Abstract
This study concerns the derivation of optimum tuning formulas for a passive Tuned Mass Damper (TMD) device, for the case of benchmark ideal excitations acting on a single-degree-of-freedom (SDOF) damped primary structure. The free TMD parameters are tuned first through a non-linear gradient-based optimisation algorithm, for the case of harmonic or white noise excitations, acting either as force on the SDOF primary structure or as base acceleration. The achieved optimum TMD parameters are successively interpolated according to appropriate analytical fitting proposals, by non-linear least squares, in order to produce simple and effective TMD tuning formulas. In particular, two fitting models are presented. The main proposal is composed of a simple polynomial relationship, refined within the fitting process, and constitutes the optimum choice. A second model refers to proper modifications of literature formulas for the case of an undamped primary structure. The results in terms of final (interpolated) optimum TMD parameters and of device effectiveness in reducing the structural dynamic response are finally displayed and discussed in detail, showing the wide and ready-to-use validity of the proposed optimisation procedure and achieved tuning formulas. Several post-tuning trials have been carried out as well on SDOF and MDOF shear-type frame buildings, by confirming the effective benefit provided by the proposed optimum TMD.

Key Words
Tuned Mass Damper (TMD); harmonic excitation; white noise excitation; tuning formulas; optimisation; nonlinear least squares; fitting models

Address
Jonathan Salvi and Egidio Rizzi: Universita di Bergamo, Dipartimento di Ingegneria e Scienze Applicate,
viale G. Marconi 5, I-24044 Dalmine (BG), Italy


Abstract
The nonlocal static bending, buckling, free and forced vibrations of graphene nanosheets are examined based on the Kirchhoff plate theory and Taylor expansion approach. The nonlocal nanoplate model incorporates the length scale parameter which can capture the small scale effect. The governing equations are derived using Hamilton\'s principle and the Navier-type solution is developed for simply-supported graphene nanosheets. The analytical results are proposed for deflection, natural frequency, amplitude of forced vibration and buckling load. Moreover, the effects of nonlocal parameter, half wave number and three-dimensional sizes on the static, dynamic and stability responses of the graphene nanosheets are discussed. Some illustrative examples are also addressed to verify the present model, methodology and solution. The results show that the new nanoplate model produces larger deflection, smaller circular frequencies, amplitude and buckling load compared with the classical model.

Key Words
bending; buckling; free vibration; forced vibration; nonlocal theory; graphene nanosheets

Address
Jinjian Liu, Ling Chen, Feng Xie, Xueliang Fan and Cheng Li: School of Urban Rail Transportation, Soochow University, Suzhou 215131, China

Abstract
This paper focuses on developing a new configuration on magnetorheological (MR) brake damper as prosthetic knee. Prosthetic knee uses magnetic fields to vary the viscosity of the MR fluid, and thereby its flexion resistance. Exerted transmissibility torque of the knee greatly depends on the magnetic field intensity in the MR fluid. In this study a rotary damper using MR fluid is addressed in which a single rotary disc will act as a brake while MR fluid is activated by magnetic field in different walking gait. The main objective of this study is to investigate a prosthetic knee with one activating rotary disc to accomplish necessary braking torque in walking gait via T-shaped drum with arc surface boundary and implementing of Newton\'s equation of motion to derive generated torque at the inner surface of the rotary drum. For this purpose a novel configuration of a T-shaped drum based on the effects of a material deformation process is proposed. In this new design, the T-shaped disc will increase the effective areas of influences in between drum and MR fluid together and the arc wall crushes the particles chains (fibrils) of the MR fluid together instead of breaking them via strain in a conventional MR brake. To verify the proposed MR brake, results of the proposed and conventional MR brakes are compared together and demonstrated that the resisting torque of the proposed MR brake is almost two times greater than that of the conventional brake.

Key Words
prosthetic knee; magnetorheological (MR) brake; T-shaped drum

Address
Hassan Sayyaadi and Seiyed Hamid Zareh: School of Mechanical Engineering, Sharif University of Technology, Tehran, 11155-9567, Iran

Abstract
Based on the distributed fiber optic sensing (DFOS) technique, plastic optical fibers (POFs) are attractive candidates to measure deformations of geotechnical structures because they can withstand large strains before rupture. Understanding the mechanical interaction between an embedded POF and the surrounding soil or rock is a necessary step towards establishing an effective POF-based sensing system for geotechnical monitoring. This paper describes a first attempt to evaluate the feasibility of POF-based soil deformation monitoring considering the POF–soil interfacial properties. A series of pullout tests were performed under various confining pressures (CPs) on a jacketed polymethyl methacrylate (PMMA) POF embedded in soil specimens. The test results were interpreted using a fiber–soil interaction model, and were compared with previous test data of silica optical fibers (SOFs). The results showed that the range of CP in this study did not induce plastic deformation of the POF; therefore, the POF–soil and the SOF–soil interfaces had similar behavior. CP was found to play an important role in controlling the fiber–soil interfacial bond and the fiber measurement range. Moreover, an expression was formulated to determine whether a POF would undergo plastic deformation when measuring soil deformation. The plasticity of POF may influence the reliability of measurements, especially for monitored geo-structures whose deformation would alternately increase and decrease. Taken together, these results indicate that in terms of the interfacial parameters studied here the POF is feasible for monitoring soil deformation as long as the plastic deformation issue is carefully addressed.

Key Words
distributed geotechnical monitoring; soil deformation; plastic optical fiber (POF); plasticity; interfacial behavior

Address
Cheng-Cheng Zhang, Bin Shi, Jun-Kuan She and Dan Zhang: School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
Hong-Hu Zhu: School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China;
Nanjing University High-tech Institute at Suzhou, Suzhou 215123, China


Abstract
The paper provides a comprehensive procedure for the mechanical and magnetic design of Langevin transducer based on giant magnetostrictive material. The the transducer is designed to work at its second mode of vibration, having high mechanical quality factor and low damping coefficient. The design procedure is based on an analytical model and it is verified by finite-element analysis. Experimental tests based on impedance response analysis in first and second modes are carried out on the prototype. Results confirm the appropriate design of this transducer, demonstrating the highest mechanical quality factor between the resonant transducers in the literature.

Key Words
magnetostrictive; terfenol-D; resonant transducer; mechanical quality factor

Address
Mohammad R. Sheykholeslami: Department of Mechanical Engineering, Faculty of Engineering, Arak University, Arak, Iran
Yousef Hojjat and M. Karaf: Mechanical Eng., Dep., Tech and Eng. Faculty, Tarbiat Modares University, Iran
Simone Cinquemani: Department of Mechanical Engineering, Politecnico di Milano, Milan, Italy
Mojtaba Ghodsi: Mechanical and Industrial Eng., Dep., College of Eng. Sultan Qaboos University, Oman

Abstract
The existence of SH-wave in a piezomagnetic layer overlying an initially stressed orthotropic half-space is investigated. The coupled of differential equations are solved for piezomagnetic layer overlying an orthotropic elastic half-space. The general dispersion equation has been derived for both magnetically open circuit and magnetically closed circuits under the four types of boundary conditions. In the absence of the piezomagnetic properties, initial stress and orthotropic properties of the medium, the dispersion equations reduce to classical Love equation. The SH-wave velocity has been calculated numerically for both magnetically open circuit and closed circuits. The effect of initial stress and magnetic permeability are illustrated by graphs in both the cases. The velocity of SH-wave decreases with the increment of wave number.

Key Words
piezomagnetic; orthotropic; initial stress; magnetic permeability;dispersion equations

Address
Rajneesh Kakar: Chotti Baradari, 163/1, Jalandhar-144022, India
Shikha Kakar: Department of Electronics, SBBSIET, Padhiana, India

Abstract
A two-stage method for damage detection in truss systems is proposed. In the first stage, a modal residual vector based indicator (MRVBI) is introduced to locate the potentially damaged elements and reduce the damage variables of a truss structure. Then, in the second stage, a differential evolution (DE) based optimization method is implemented to find the actual site and extent of damage in the structure. In order to assess the efficiency of the proposed damage detection method, two numerical examples including a 2D-truss and 3D-truss are considered. Simulation results reveal the high performance of the method for accurately identifying the damage location and severity of trusses with considering the measurement noise.

Key Words
damage detection; truss structure; modal residual vector; damage indicator; differential evolution

Address
Seyed Mohammad Seyedpoor and Maryam Montazer: Department of Civil Engineering, Shomal University, Amol, Iran

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