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유도 초음파를 이용한 교량 구조물의 무기저 비파괴 검사
손훈 ( Sohn Hoon ),이창길 ( Lee Chang Gil ),김승범 ( Kim Seung Bum ),염철민 ( Yeum Chulmin ) 한국구조물진단유지관리공학회 2008 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.12 No.2
Recently, a reference-free damage detection technique based on guided wave and the characteristics of piezoelectric ceramic has been proposed by author's group and the developed technique is applied to in-service bridges, Samseung Bridge in Yeoju, Gyeonggi-do, Korea, Buffalo Creek Bridge in Armstrong County, Pennsylvania, US. First, raw signals using attached collocated PZT pairs are measured and then individual Lamb modes are decomposed. Finally, instantaneous damage classification technique is performed using the decoupled signals.
램파의 분산성과 파 반사가 시간반전과정에 미치는 영향의 이해
박현우,김승범,손훈,Park, Hyun-Woo,Kim, Sung-Bum,Sohn, Hoon 한국전산구조공학회 2009 한국전산구조공학회논문집 Vol.22 No.1
이 연구에서는 얇은 판형구조물의 손상탐지에 널리 사용되어오는 램파에 시간반전(time reversal)개념의 적용성을 이론적으로 규명한다. 고전적 시간반전 음향학에 의하면, 센서에서의 출력신호를 시간영역에서 반전 후 재입사시켜 원래의 가진점으로 돌려보내면, 그 가진점에서 원래 입력신호가 복원된다. 그러나 램파에 시간반전과정을 적용하게 되면 램파 고유의 분산성과 판 경계에서의 파 반사로 인해 시간반전성이 복잡한 양상을 띠게 된다. 이러한 램파의 시간반전성을 보다 잘 이해하기 위해 이 연구에서는 램파의 시간반전과정을 이론적으로 규명한다. 특히, 램파의 내부모드분산, 다중모드분산, 그리고 판 경계면에서의 램파의 반사가 시간반전성에 미치는 영향을 정식화하였다 간단한 수치예제를 통해 이 연구에서 제시된 이론적 발견들의 타당성을 검증한다. This study investigates the applicability of the time reversal concept in modem acoustics to the Lamb waves, which have been widely studied for defect detection in plate-like structures. According to conventional time reversal acoustics, an input signal can be reconstructed at an excitation point if an output signal recorded at another point is reversed in the time domain and emitted back to the original source point. However, the application of a time reversal process(TRP) to Lamb wave propagations is complicated due to velocity and amplitude dispersion characteristics of Lamb waves and reflections from the boundaries of a structure. In this study, theoretical investigations are presented to better understand the time reversibility of Lamb waves. In particular, the effects of within-mode dispersion, multimode dispersion, amplitude dispersion, and reflections from boundaries on the TRP are theoretically formulated. Simple numerical case studies are conducted to validate the theoretical findings of this study.
압전소자가 부착된 보의 고주파수 동적응답에 대한 스펙트럼 요소 해석의 실험적 검증
김은진(Kim, Eun-Jin),손훈(Sohn, Hoon),박현우(Park, Hyun-Woo) 한국소음진동공학회 2009 한국소음진동공학회 논문집 Vol.19 No.12
This paper demonstrates the validity of spectral element analysis for modeling the high-frequency dynamic behaviors of a beam with a surface-bonded piezoelectric wafer through a laboratory test. In the spectral element analysis, the high-frequency electro-mechanical interaction can be considered properly with relatively low computational cost compared to the finite element analysis. In the verification test, a cantilever beam with a surface-bonded piezoelectric wafer is forced to be in steady-state motion by exerting the harmonic driving voltage signal on the piezoelectric wafer. A laser scanning vibrometer is used to obtain the overall dynamic responses of the structure such as resonance frequencies, the associated mode shapes, and frequency response functions up to 20 kHz. Then, these dynamic responses from the test are compared to those computed by the spectral element analysis. A two-dimensional finite analysis is conducted to obtain the asymptotic solutions for the comparison purpose as well.