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Park, Seunghee,Park, Gyuhae,Yun, Chung-Bang,Farrar, Charles R. SAGE Publications 2009 Structural health monitoring Vol.8 No.1
<P>The active sensing methods using piezoelectric materials have been extensively investigated for the efficient use in structural health monitoring (SHM) applications. Relying on high frequency structural excitations, the methods showed the extreme sensitivity to minor defects in a structure. Recently, a sensor self-diagnostic procedure that performs in situ monitoring of the operational status of piezoelectric (PZT) active sensors and actuators in SHM applications has been proposed. In this investigation, previously developed impedance models were revisited in order to investigate the effects of sensor and/or bonding defects on the admittance measurement. New parameters for sensor quality assessment of a PZT and coupling degradation effects between a PZT and bonding layer were incorporated into the traditional electromechanical impedance model for better estimation of the electromechanical impedance signatures and sensor diagnostics. The feasibility of the modified impedance model for sensor self-diagnosis using the admittance measurements was demonstrated by a series of parametric studies using a simple example of PZT-driven single degree of freedom spring-mass-damper system. This paper summarizes the description of the proposed modified electromechanical impedance model, parametric studies for impedance-based sensor diagnostics, and several issues that can be used as a guideline for future investigation.</P>
Health Monitoring of Pipeline Systems using Macro-fiber Composite Active-Sensors
Andrew B. Thien,Gyuhae Park,Charles R. Farrar 한국강구조학회 2007 International Journal of Steel Structures Vol.7 No.1
The objective of this research is to demonstrate the benefits and feasibility of a structural health monitoring (SHM) systemfor the sensor array. Because MFC patches are flexible and resilient, they can be permanently mounted to the curved surfaceof a pipeline’s main body. The presented Lamb wave methods using MFC transducers as sensors and actuators demonstratethe ability to correctly identify and locate the presence of damage in the main body of the pipeline system, including cracksand corrosion. By implementing a SHM system with pipelines, their structural integrity can be continuously monitored,
무인기 날개 변형 센싱을 위한 파일롯 팔 착용형 무선 햅틱 인터페이스 개발
이정률,김형철,강래형,박찬익,David L. Mascarenas,Charles R. Farrar 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.4
무인기는 지상에서 파일롯에 의해 비행 제어되는 데, 파일롯이 날개의 변형을 실시간으로 인지 하는 기술이 필요하며 일체형구조건전성모니터링에 의해 날개의 변형을 파일롯에게 전달되는 연구가 체계투입을 목표로 진행 중에 있다. 그러한 기체 변형 정보는 지상 파일롯의 시각을 통해 모니터링되는데, 본 논문에서는 시각이 아닌 촉각을 이용하여 파일롯이 보는 것이 아니라 느끼게 해주는 인터페이스(“Fly-by-Feel”)를 제안한다. 4 개의 광섬유브래그격자 변형률 센서가 날개시편에 설치되고 획득된 변형률은 베르누이-오일러 빔 모델 기반 변형률 및 변위 모드 형상에 입력된다. 획득된 날개 변형정보는 지상 파일롯의 팔에 착용할 수 있는 인터페이스에 설치된 다수의 진동햅틱모터를 가진하기 위해 무선으로 전달된다. When the flight of an unmanned air vehicle is controlled by a ground pilot, wing deformation monitoring technology is required. Therefore, integrated structural health monitoring technology is being developed to transfer such information to the pilot in real time for real world application. In general, the information is monitored by the vision of the ground pilot. In this paper, we propose an interface for “fly-by-feel” using not vision but haptic for the transfer of the wing deformation information. Four integrated fiber Bragg grating sensors were installed in a wing specimen to measure dynamic strains and the measured strains were input to displacement and strain mode shapes based on Bernoulli-Eulerbeam equation. The wing deformation information was wirelessly transferred to actuate vibro-haptic motors installed in a pilot arm-wearable haptic interface.
압전 페인트 센서를 기반으로 한 구조물 충돌 감지 시스템 개발
강상현(Sang-Hyeon Kang),Kevin Keller,Charles Farrar,강래형(Lae-Hyong Kang) 한국소음진동공학회 2016 한국소음진동공학회 학술대회논문집 Vol.2016 No.4
As transportation system gets lighter and faster, the structural collision monitoring and evaluation of its effects on the structures get more important. In order to detect collision events, in this study, the piezoelectric paint sensor-based collision monitoring system has been developed. Piezoelectric paint sensor itself has high electric impedance, so the impedance matching is needed for data acquisition systems. The signal conditioning system was composed of Texas Instruments’ TLV2771IDBVR OP Amp, resistors, and printed circuit board. Finally, 10-channel-signal conditioning system was applied to piezoelectric paint sensors coated on the aluminum specimen, and the sensitivity evaluation has been done for collision monitoring.
Holder exponent analysis for discontinuity detection
Sohn, Hoon,Robertson, Amy N.,Farrar, Charles R. Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.17 No.3
In this paper, a Holder exponent, a measure of the degree to which a signal is differentiable, is presented to detect the presence of a discontinuity and when the discontinuity occurs in a dynamic signal. This discontinuity detection has potential applications to structural health monitoring because discontinuities are often introduced into dynamic response data as a result of certain types of damage. Wavelet transforms are incorporated with the Holder exponent to capture the time varying nature of discontinuities, and a classification procedure is developed to quantify when changes in the Holder exponent are significant. The proposed Holder exponent analysis is applied to various experimental signals to reveal underlying damage causing events from the signals. Signals being analyzed include acceleration response of a mechanical system with a rattling internal part, acceleration signals of a three-story building model with a loosing bolt, and strain records of an in-situ bridge during construction. The experimental results presented in this paper demonstrate that the Holder exponent can be an effective tool for identifying certain types of events that introduce discontinuities into the measured dynamic response data.
Taylor, Stuart G.,Farinholt, Kevin M.,Park, Gyuhae,Todd, Michael D.,Farrar, Charles R. Techno-Press 2010 Smart Structures and Systems, An International Jou Vol.6 No.5
This paper presents recent developments in an extremely compact, wireless impedance sensor node (the WID3, $\underline{W}$ireless $\underline{I}$mpedance $\underline{D}$evice) for use in high-frequency impedance-based structural health monitoring (SHM), sensor diagnostics and validation, and low-frequency (< ~1 kHz) vibration data acquisition. The WID3 is equipped with an impedance chip that can resolve measurements up to 100 kHz, a frequency range ideal for many SHM applications. An integrated set of multiplexers allows the end user to monitor seven piezoelectric sensors from a single sensor node. The WID3 combines on-board processing using a microcontroller, data storage using flash memory, wireless communications capabilities, and a series of internal and external triggering options into a single package to realize a truly comprehensive, self-contained wireless active-sensor node for SHM applications. Furthermore, we recently extended the capability of this device by implementing low-frequency analog-to-digital and digital-to-analog converters so that the same device can measure structural vibration data. The compact sensor node collects relatively low-frequency acceleration measurements to estimate natural frequencies and operational deflection shapes, as well as relatively high-frequency impedance measurements to detect structural damage. Experimental results with application to SHM, sensor diagnostics and low-frequency vibration data acquisition are presented.
Sohn, Hoon,Hyun Woo Park,,Law, Kincho H.,Farrar, Charles R. Sage Science Press (UK) 2007 Journal of intelligent material systems and struct Vol.18 No.4
<P>A structural health monitoring system is developed for continuous online monitoring of delamination initiation and growth in composite structures. Structural health monitoring problems are often cast in the context of a statistical pattern recognition paradigm, in which a damage state of a structure is inferred by comparing test data with baseline data. However, subtle signal changes due to damage can often be masked by larger ambient variation of operational and environmental conditions of an in-service structure. Therefore, it is critical for the development of a robust monitoring system to minimize false-positive indications of damage caused by the undesired operational and environmental variation of the structure. The issue of minimizing damage misclassification has been addressed in this article by developing an instantaneous damage detection scheme that does not rely on past baseline data. The proposed instantaneous damage diagnosis is based on the concepts of time reversal acoustics and consecutive outlier analysis, and the proposed damage diagnosis has been tested for detecting delamination in composite plates.</P>
Design and performance validation of a wireless sensing unit for structural monitoring applications
Lynch, Jerome Peter,Law, Kincho H.,Kiremidjian, Anne S.,Carryer, Ed,Farrar, Charles R.,Sohn, Hoon,Allen, David W.,Nadler, Brett,Wait, Jeannette R. Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.17 No.3
There exists a clear need to monitor the performance of civil structures over their operational lives. Current commercial monitoring systems suffer from various technological and economic limitations that prevent their widespread adoption. The wires used to route measurements from system sensors to the centralized data server represent one of the greatest limitations since they are physically vulnerable and expensive from an installation and maintenance standpoint. In lieu of cables, the introduction of low-cost wireless communications is proposed. The result is the design of a prototype wireless sensing unit that can serve as the fundamental building block of wireless modular monitoring systems (WiMMS). An additional feature of the wireless sensing unit is the incorporation of computational power in the form of state-of-art microcontrollers. The prototype unit is validated with a series of laboratory and field tests. The Alamosa Canyon Bridge is employed to serve as a full-scale benchmark structure to validate the performance of the wireless sensing unit in the field. A traditional cable-based monitoring system is installed in parallel with the wireless sensing units for performance comparison.