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정휘권,이인규,김재민,Jung, Hwee Kwon,Rhee, Inkyu,Kim, Jae-Min 한국전산구조공학회 2020 한국전산구조공학회논문집 Vol.33 No.4
Ultrasonic investigation of damage detection has been widely used for non-destructive testing of various concrete structures. This study focuses on damage detection analysis with the aid of wave propagation in two-phase composite concrete with aggregate (inclusion) and mortar (matrix). To fabricate a realistic simulation model containing a variety of irregular aggregate shapes, the mesh generation technique using an image processing technique was proposed. Initially, the domains and boundaries of the aggregates were extracted from the digital image of a typical concrete cut-section. This enables two different domains: aggregates and mortar in heterogeneous concrete sections, and applied the grids onto these domains to discretize the model. Subsequently, finite element meshes are generated in terms of spatial and temporal requirements of the model size. For improved analysis results, all meshes are designed to be quadrilateral type, and an additional process is conducted to improve the mesh quality. With this simulation model, wave propagation analyses were conducted with a central frequency of 75 kHz of the Mexican hat incident wave. Several void damages, such as needle-shaped cracks and void-shaped holes, were artificially introduced in the model. Finally, various formats of internal damage were detected by implementing energy mapping based signal processing. 초음파 탐상은 다양한 콘크리트 구조물의 비파괴검사에서 활용된다. 본 연구에서는 골재형상을 고려한 골재-모르타르 모델 생성과 초음파 전파 해석을 수행하였다. 실제 골재형상을 반영하기 위해 이미지처리를 통한 골재-모르타르 단면으로부터 모르타르와 골재 영역을 파악하고, 영역 경계형상을 보존하면서 격자를 생성하는 기법을 개발하였다. 개발된 기법에서는 모든 격자가 4각형으로 생성된다. 골재-모르타르 모델을 통해 초음파 전파 해석을 수행하였고 모델을 반무한체로 간주하기 위해 CALM 기반 경계흡수 조건을 적용하였다. 골재 및 결함을 포함한 이미지로부터 격자를 생성한 뒤, 결함 영역에 포함된 격자를 제거하여 공극결함을 모사하였다. 본격적인 결함탐지 전 선행 해석을 통해 모델 동특성을 고려한 적절한 가진 주파수를 결정 및 가진 신호형상을 설계하였다. 이후 case 별초음파 전파 해석을 통해 신호를 획득하고 신호 에너지 맵핑 작업을 통해 내부 결함을 가시화 하였다. 가시화 결과, 골재에 의한 다수반사 및 산란현상이 관찰되지만 결함부에서 신호 에너지는 가장 높게 나타났으며 모든 해석 case에서 결함위치 추정이 가능하였다. 또한 균열의 경우 형상파악도 가능하였다.
L-형상 압전체 센서 배열을 이용한 충격 및 손상 탐지 기법 개발
정휘권(Hwee-Kwon Jung),이명준(Myung-Jun Lee),박규해(Gyuhae Park) 한국비파괴검사학회 2014 한국비파괴검사학회지 Vol.34 No.5
항공기 구조물 표면에 발생하는 외부 충격은 크랙과 같은 손상을 발생시킬 수 있으며 이는 차후 큰 결함을 야기하기 때문에 충격과 손상을 탐지하고 위치를 추정하는 것은 구조 안정성 모니터링에 있어 중요한 부분이다. 본 연구에서는 능동, 수동 센싱기법을 조합한 L-형상 압전체 센서 배열을 사용하여 충격과 손상을 탐지할 수 있는 기법을 개발하였다. 수동 센싱기법으로 1개 센서군 당 3개의 센서를 L-형상으로 배치하여 충격 발생 각도를 추정하고 2개의 센서군을 사용하여 충격위치를 탐지하는 방법을 도입하였다. 이 수동 센싱기법을 유도초음파 기반의 능동 센싱기법에 확대 적용하여 동일한 압전소자로 충격 탐지와 더불어 손상을 탐지할 수 있는 방법을 개발하였다. 이 기법은 방향에 따른 파동의 속도 변화와 같은 구조물에 대한 정보 없이도 위치 추정이 가능하여 비등방성 구조 내에서도 정확한 충격 및 손상 위치 정보를 얻을 수 있다. 개발된 기법을 날개 형태 구조물 및 CFRP 판에 적용하여 실험적으로 정확한 충격 및 손상 위치를 추정할 수 있음을 증명하였다. This paper presents a method that integrates passive and active-sensing techniques for the structural health monitoring of plate-like structures. Three piezoelectric transducers are deployed in a L-shape to detect and locate an impact event by measuring and processing the acoustic emission data. The same sensor arrays are used to estimate the subsequent structural damage using guided waves. Because this method does not require a prior knowledge of the structural parameters, such as the wave velocity profile in various directions, accurate results could be achieved even on anisotropic or curved plates. A series of experiments was performed on plates, including a spar-wing structure, to demonstrate the capability of the proposed method. The performance was also compared to that of traditional approaches and the superior capability of the proposed method was experimentally demonstrated.
수위변화에 따른 파이프 시스템의 진동 특성 변화에 대한 연구
정휘권(Hwee Kwon Jung),김종윤(Jong yoon Kim),박규해(Gyuhae Park) 한국소음진동공학회 2013 한국소음진동공학회 학술대회논문집 Vol.2013 No.10
This paper presents vibration testing, control, and finite element analysis of a piping system, which is subjected to the changes in fluid levels. Nuclear power plants typically employ a cooling system that uses sea water. These systems are subjected to dynamic characteristic changes caused by sea-level variations, which introduces failures of cooling system components. Therefore in this study, analytical and experimental studies were performed to understand the effect of sea-level changes on the dynamic characteristics of piping systems. It was shown that, as the sea-level increases, pipe’s natural frequencies decreases in relation to its mode shape. A 1/14 scale model was also built to compare the results obtained by the analytical study. A good agreement between experiment and analytical studies were observed. Finally, an on-line resonant frequency identification system was proposed and developed, which utilizes piezoelectric transducers as sensors and actuators, in order to avoid catastrophic failure of piping systems.
특수목적 차량용 샤시의 내구성능 평가를 위한 등가하중 신호 개발
정휘권(Hwee Kwon Jung),박규해(Gyuhae Park),강지상(Jisang Kang),고환규(Hwan Kyu Kho),박병식(Byung Sik Park),정명철(Myungchuel Jung),정길성(Gilsung Jung) 한국자동차공학회 2018 한국자동차공학회 지부 학술대회 논문집 Vol.2018 No.5
Assessment of durability is an essential in early stages of development. In these stages, tuning parts and geometry of a vehicle are not determined. In addition there are no available physical prototypes. Therefore, numerical durability analysis with a reasonable load signal is required. We propose several techniques to produce an equivalent load signal for numerical durability analysis. The acceleration signals are measured through a prototype vehicle test on various road conditions and converted into force and displacement signals, respectively. The signals are then refined and a representative segment of the signal is selected by considering the statistical characteristics, frequency component and fatigue damage. Finally the equivalent load signals are produced from the selected representative signal based on a time correlated damage editing method. For validation of the proposed techniques, comparison of the signal characteristics and a series of numerical analysis are planed to be carried out.
Hwee Kwon Jung(정휘권),Myung Jun Lee(이명준),Jun Young Jeon(전준영),Gyuhae Park(박규해),To Kang(강토),Soon Woo Han(한순우) 한국소음진동공학회 2016 한국소음진동공학회 학술대회논문집 Vol.2016 No.4
Condition Monitoring(CM) methods encounter a big data problem in processing the data collected through dense sensor networks with a high sampling rate. For this reason, compressive sensing technique has been introduced to improve efficiency and scalability of todays CM procedures parallel to data acquisition improvement. In this study, Compressive sensing approach for condition monitoring is proposed to demonstrate efficiency in handling a large amount of data. For experiments, a built-in system was used for condition monitoring of a rotating system. During the experiments, all data were sampled with compressive sensing to obtain compressed data. Then we had performed condition monitoring only using compressed data without the reconstruction process. Experimental results show that the proposed method could effectively improve the speed of data processing and reduce energy consumption of sensing networks.