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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Smart Structures and Systems
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Volume 4, Issue 6 - Nov 2008
Volume 4, Issue 5 - Sep 2008
Volume 4, Issue 4 - Jul 2008
Volume 4, Issue 3 - May 2008
Volume 4, Issue 2 - Mar 2008
Volume 4, Issue 1 - Jan 2008
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Debonding monitoring of CFRP strengthened RC beams using active sensing and infrared imaging
Sohn, Hoon ; Kim, Seung Dae ; In, Chi Won ; Cronin, Kelly E. ; Harries, Kent ;
Smart Structures and Systems, volume 4, issue 4, 2008, Pages 391~406
DOI : 10.12989/sss.2008.4.4.391
This study attempts to develop a real-time debonding monitoring system for carbon fiber-reinforced polymer (CFRP) strengthened structures by continuously inspecting the bonding condition between the CFRP layer and the host structure. The uniqueness of this study is in developing a new concept and theoretical framework of nondestructive testing (NDT), in which debonding is detected without relying on previously-obtained baseline data. The proposed reference-free damage diagnosis is achieved based on the concept of time reversal acoustics (TRA). In TRA, an input signal at an excitation point can be reconstructed if the response signal measured at another point is reemitted to the original excitation point after being reversed in the time domain. Examining the deviation of the reconstructed signal from the known initial input signal allows instantaneous identification of damage without requiring a baseline signal representing the undamaged state for comparison. The concept of TRA has been extended to guided wave propagations within the CFRP-strengthened reinforced concrete (RC) beams to improve the detectibility of local debonding. Monotonic and fatigue load tests of large-scale CFRP-strengthened RC beams are conducted to demonstrate the potential of the proposed reference-free debonding monitoring system. Comparisons with an electro-mechanical impedance method and an inferred imaging technique are provided as well.
Active feedback control for cable vibrations
Ubertini, Filippo ;
Smart Structures and Systems, volume 4, issue 4, 2008, Pages 407~428
DOI : 10.12989/sss.2008.4.4.407
The nonlinear mechanics of cable vibration is caught either by analytical or numerical models. Nevertheless, the choice of the most appropriate method, in consideration of the problem under study, is not straightforward. A feedback control policy might even enhance the complexity of the system. Thus, in order to design a suitable controller, different approaches are here adopted. Devices mounted transversely to the cable in the two directions, close to one of its ends, supply the feedback control action based on the observation of the response in a few points. The low order terms of the control law are, at first, analyzed in the framework of linear models. Explicit analytic solutions are derived for this purpose. The effectiveness of high order terms in the control law is then explored by means of a finite element model(FEM), which accounts for high order harmonics. A suitably dimensional analytical Galerkin model is finally derived, to investigate the effectiveness of the proposed control strategy, when applied to a physical model.
Experimental identification of multiple faults in rotating machines
Mahfoud, Jarir ; Breneur, Claire ;
Smart Structures and Systems, volume 4, issue 4, 2008, Pages 429~438
DOI : 10.12989/sss.2008.4.4.429
The aim of this paper is to define the required measurements and processing tools necessary for developing a maintenance approach applied to rotating machines in the presence of multiple faults. The system responses measured were accelerations and transmission errors. Acceleration measurements provide most of the information on bearing conditions, while transmission error measurements provide pertinent information on gear conditions. The measurements were carried out for several operating conditions (loads and speeds). System responses were processed in several analyzing domains (Time, Spectrum, and Cepstrum domains). The approach developed enables the detection and identification of combined faults and it can be applied to other types of rotating machines once the critical elements and their associated faults have been defined.
Characterization of both adhesion and interfacial interaction between optical fiber coating and structural
Brotzu, A. ; Felli, F. ; Fiori, L. ; Caponero, M.A. ;
Smart Structures and Systems, volume 4, issue 4, 2008, Pages 439~448
DOI : 10.12989/sss.2008.4.4.439
Optical fiber sensors are by now broadly accepted as an innovative and reliable device for structural health monitoring, to be used either embedded into or bonded on structures. The accuracy of the strain measurement achievable by optical fiber sensors is critically dependent on the characteristics of the bonding of the various interface layers involved in the sensor bonding/embedding (structure material and gluing agent, fiber coating and gluing agent, fiber coating and fiber core). In fact, the signal of the bonded/embedded optical fiber sensor must correspond to the strain experienced by the monitored structure, but the quality of each involved interface can affect the strain transfer. This paper faces the characterization, carried on by both mechanical tests and morphological analysis, of the strain transfer function resulting with epoxidic and vinylester gluing agent on polyimide and acrylate coated optical fibers.
A migration based reconstruction algorithm for the imaging of defects in a plate using a compact array
Muralidharan, Ajith ; Balasubramaniam, Krishnan ; Krishnamurthy, C.V. ;
Smart Structures and Systems, volume 4, issue 4, 2008, Pages 449~464
DOI : 10.12989/sss.2008.4.4.449
An array based, outward monitoring, ultrasonic guided wave based SHM technique using a single transmitter and multiple receivers (STMR), with a small footprint is discussed here. The previous implementation of such SHM arrays used a phase-reconstruction algorithm (that is similar to the beam-steering algorithm) for the imaging of reflectors. These algorithms were found to have a limitation during the imaging of defects/reflectors that are present in the "near-field" of the array. Here, the "near-field" is defined to be approximately 3-4 times the diameter of the compact array. This limitation is caused by approximations in the beam-steering reconstruction algorithm. In this paper, a migration-based reconstruction algorithm, with dispersion correction in the frequency domain, is discussed. Simulation and experimental studies are used to demonstrate that this algorithm improves the reconstruction in the "near-field" without decreasing the ability to reconstruct defects in the "far-field" in both isotropic and anisotropic plates.
Optimal sensor placement techniques for system identification and health monitoring of civil structures
Rao, A. Rama Mohan ; Anandakumar, Ganesh ;
Smart Structures and Systems, volume 4, issue 4, 2008, Pages 465~492
DOI : 10.12989/sss.2008.4.4.465
Proper pretest planning is a vital component of any successful vibration test on engineering structures. The most important issue in dynamic testing of many engineering structures is arriving at the number and optimal placement of sensors. The sensors must be placed on the structure in such a way that all the important dynamic behaviour of a structural system is captured during the course of the test with sufficient accuracy so that the information can be effectively utilised for structural parameter identification or health monitoring. Several optimal sensor placement (OSP) techniques are proposed in the literature and each of these methods have been evaluated with respect to a specific problem encountered in various engineering disciplines like aerospace, civil, mechanical engineering, etc. In the present work, we propose to perform a detailed characteristic evaluation of some selective popular OSP techniques with respect to their application to practical civil engineering problems. Numerical experiments carried out in the paper on various practical civil engineering structures indicate that effective independence (EFI) method is more consistent when compared to all other sensor placement techniques.
Semi-active friction dampers for seismic control of structures
Kori, Jagadish G. ; Jangid, R.S. ;
Smart Structures and Systems, volume 4, issue 4, 2008, Pages 493~515
DOI : 10.12989/sss.2008.4.4.493
Semi-active control systems have attracted a great deal of attention in recent years because these systems can operate on battery power alone, proving advantageous during seismic events when the main power source of the structure may likely fail. The behavior of semi-active devices is often highly non-linear and requires suitable and efficient control algorithm. This paper presents the comparative study and performance of variable semi-active friction dampers by using recently proposed predictive control law with direct output feedback. In this control law, the variable slip force of semi-active variable friction damper is kept slightly lower than the critical friction force, which allows the damper to remain in the slip state during an earthquake, resulting in improved energy dissipation capability. This control algorithm is able to produce a continuous and smooth slip forces for a variable friction damper. The numerical examples include a structure controlled with multiple variable semi-active friction dampers and with multiple passive friction dampers. A parameter, gain multiplier defined as the ratio of damper force to critical damper control force, is investigated under four different real earthquake ground motions, which plays an important role in the present control algorithm of the damper. The numerically evaluated optimum parametric value is considered for the analysis of the structure with dampers. The numerical results of the variable friction dampers show better performance over the passive dampers in reducing the seismic response of structures.