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Electromechanical impedance-based long-term SHM for jacket-type tidal current power plant structure
Min, Jiyoung,Yi, Jin-Hak,Yun, Chung-Bang Techno-Press 2015 Smart Structures and Systems, An International Jou Vol.15 No.2
Jacket-type offshore structures are always exposed to severe environmental conditions such as salt, high speed of current, wave, and wind compared with other onshore structures. In spite of the importance of maintaining the structural integrity for an offshore structure, there are few cases to apply a structural health monitoring (SHM) system in practice. The impedance-based SHM is a kind of local SHM techniques and to date, numerous techniques and algorithms have been proposed for local SHM of real-scale structures. However, it still requires a significant challenge for practical applications to compensate unknown environmental effects and to extract only damage features from impedance signals. In this study, the impedance-based SHM was carried out on a 1/20-scaled model of an Uldolmok current power plant structure in Korea under changes in temperature and transverse loadings. Principal component analysis (PCA)-based approach was applied with a conventional damage index to eliminate environmental changes by removing principal components sensitive to them. Experimental results showed that the proposed approach is an effective tool for long-term SHM under significant environmental changes.
Development of a low-cost multifunctional wireless impedance sensor node
Min, Jiyoung,Park, Seunghee,Yun, Chung-Bang,Song, Byunghun Techno-Press 2010 Smart Structures and Systems, An International Jou Vol.6 No.5
In this paper, a low cost, low power but multifunctional wireless sensor node is presented for the impedance-based SHM using piezoelectric sensors. Firstly, a miniaturized impedance measuring chip device is utilized for low cost and low power structural excitation/sensing. Then, structural damage detection/sensor self-diagnosis algorithms are embedded on the on-board microcontroller. This sensor node uses the power harvested from the solar energy to measure and analyze the impedance data. Simultaneously it monitors temperature on the structure near the piezoelectric sensor and battery power consumption. The wireless sensor node is based on the TinyOS platform for operation, and users can take MATLAB$^{(R)}$ interface for the control of the sensor node through serial communication. In order to validate the performance of this multifunctional wireless impedance sensor node, a series of experimental studies have been carried out for detecting loose bolts and crack damages on lab-scale steel structural members as well as on real steel bridge and building structures. It has been found that the proposed sensor nodes can be effectively used for local wireless health monitoring of structural components and for constructing a low-cost and multifunctional SHM system as "place and forget" wireless sensors.
Min, Jiyoung,Park, Seunghee,Yun, Chung-Bang Institute of Physics Publishing 2010 Smart materials & structures Vol.19 No.12
<P>The impedance-based structural health monitoring (SHM) method has come to the forefront in the SHM community due to its practical potential for real applications. In the impedance-based SHM method, the selection of optimal frequency ranges plays an important role in improving the sensitivity of damage detection, since an improper frequency range can lead to erroneous damage detection results and provide false positive damage alarms. To tackle this issue, this paper proposes an innovative technique for autonomous selection of damage-sensitive frequency ranges using artificial neural networks (ANNs). First, the impedance signals are obtained in a wide frequency band, and the signals are split into multiple sub-ranges of this wide band. Then, the predefined damage index is evaluated for each sub-range by comparing impedance signals between the intact and the concurrent cases. Here, the cross correlation coefficients (CCs) are used as the predefined damage index. The ANN is constructed and trained using all CC values at multiple frequency ranges as multi-inputs and the real damage severity as the single output for various preselected damage scenarios, so that subsequent damage estimations may be carried out by selecting the governing frequency ranges autonomously. The performance of the proposed approach has been examined via a series of experimental studies to detect loose bolts and cracks induced on real steel bridge and building structures. It is found that the proposed approach autonomously determines the damage-sensitive frequency ranges and can be used for effective evaluation of damage severity in a wide variety of damage cases in real structures.</P>
Jiyoung Min,Hyojin Shim,Chung-Bang Yun,홍정욱 국제구조공학회 2016 Smart Structures and Systems, An International Jou Vol.17 No.1
We propose an effective methodology using electromechanical impedance characteristics for estimating the remaining tensile force of tendons and simultaneously detecting damages of the anchorage blocks. Once one piezoelectric patch is attached on the anchor head and the other is bonded on the bearing plate, impedance responses are measured through these two patches under varying tensile force conditions. Then statistical indices are calculated from the impedances, and two types of relationship curves between the tensile force and the statistical index (TE Curve) and between statistical indices of two patches (SR Curve) are established. Those are considered as database for monitoring both the tendon and the anchorage system. If damage exists on the bearing plate, the statistical index of patch on the bearing plate would be out of bounds of the SR curve and damage can be detected. A change in the statistical index by damage is calibrated with the SR curve, and the tensile force can be estimated with the corrected index and the TE Curve. For validation of the developed methodology, experimental studies are performed on the scaled model of an anchorage system that is simplified only with 3 solid wedges, a 3-hole anchor head, and a bearing plate. Then, the methodology is applied to a real scale anchorage system that has 19 strands, wedges, an anchor head, a bearing plate, and a steel duct. It is observed that the proposed scheme gives quite accurate estimation of the remaining tensile forces. Therefore, this methodology has great potential for practical use to evaluate the remaining tensile forces and damage status in the post-tensioned structural members.
( Min Sung Yoon ),( Hee Seung Lee ),( Chang Moo Kang ),( Woo Jung Lee ),( Jiyoung Keum ),( Min Je Sung ),( Seungseob Kim ),( Mi-suk Park ),( Jung Hyun Jo ),( Moon Jae Chung ),( Jeong Youp Park ),( Seu 대한소화기학회 2022 Gut and Liver Vol.16 No.1
Background/Aims: Controversy regarding the effectiveness of neoadjuvant therapy for resectable pancreatic ductal adenocarcinoma (PDAC) still exists. Here, we aimed to identify the potential benefits of neoadjuvant therapy followed by surgery for resectable PDAC. Methods: We reviewed radiologically resectable PDAC patients who received resection with curative intent at a tertiary hospital in South Korea between January 2012 and August 2019. A total of 202 patients underwent curative resection for resectable PDAC: 167 underwent surgical resection first during this period, and 35 received neoadjuvant chemotherapy/chemoradiation therapy followed by surgery. Resectable PDAC patients were subdivided, and 1:3 propensity score matching (PSM) was performed to reduce selection bias. Results: Compared with the group that received surgery first, the group that received neoadjuvant treatment followed by surgery had significantly smaller tumors (22.0 mm vs 27.0 mm, p=0.004), a smaller proportion of patients with postoperative pathologic T stage (p=0.026), a smaller proportion of patients with lymphovascular invasion (20.0% vs 40.7%, p=0.022), and a larger proportion of patients with negative resection margins (74.3% vs 51.5%, p=0.049). After PSM, the group that received neoadjuvant therapy had a significantly longer progression-free survival than those in the group that underwent surgery first (29.6 months vs 15.1 months, p=0.002). Overall survival was not significantly different between the two groups after PSM analysis. Conclusions: We observed significantly better surgical outcomes and progression-free survival with the addition of neoadjuvant therapy to the management of resectable PDAC. However, despite PSM, there was still selection bias due to the use of different regimens between the groups receiving surgery first and neoadjuvant therapy. Large homogeneous samples are needed in the future prospective studies. (Gut Liver 2022;16:118-128)
국내 해안가 비래염분량 추정을 위한 인공신경망 기술 적용
민지영 ( Min Jiyoung ),김률리 ( Kim Ryulri ),이종석 ( Lee Jong-suk ) 한국구조물진단유지관리공학회 2023 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.27 No.1
염화물은 콘크리트 구조물 표면 또는 내부에 침투하여 축적되면서 구조물 내부 철근 부식을 야기해 내구성을 저하시키는 주요 요인 중 하나이다. 해상 혹은 해안가에 위치한 콘크리트 구조물은 바람, 파도와 같은 환경적 영향으로 인해 염화물에 쉽게 노출된다. 그러나, 공기중 염분량은 측정이 매우 까다로우며 장기적으로 측정해야 하므로 비래염분의 영향과 관련한 연구 수행에 어려움이 존재한다. 이에 본 연구에서는 비교적 데이터 확보가 용이한 기상과 해양환경 데이터를 활용하여 베이지안 정규화를 적용한 인공신경망으로부터 동·서, 남해안에서의 비래염분량을 추정하는 기술 개발을 목표로 하였다.
민지영 ( Min Jiyoung ),진승섭 ( Jin Seung-seop ),박민수 ( Park Min-su ),김영택 ( Kim Young-taek ),김성태 ( Kim Sung-tae ) 한국구조물진단유지관리공학회 2022 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.26 No.2
4차 산업혁명 시대가 도래함에 따라, 센서, 드론, 로봇, AI 등 첨단 기술을 활용한 점검을 수행하고, 측정된 데이터 및 과거 이력 데이터를 기반으로 시설물의 안전성 및 사용성을 평가하여, 선제적으로 유지관리가 가능한 체계로 패러다임이 변화하고 있다. 본 연구에서는 항만시설물에서 계측되는 모니터링 데이터를 실시간으로 분석할 수 있는 기술을 개발하기 위하여, 항만시설의 거동 특성을 검토하고, 실제 항만시설 및 축소모형 등으로부터 정상 및 이상상태 학습 데이터를 계측·확보하였다. 이로부터 이상상태 발생 지점을 실시간으로 판단할 수 있도록 온라인 학습과 선택적 샘플링 기법을 함께 도입한 비지도 학습 기반 이상상태 알고리즘을 제안·검증하였다.