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Taehoon Heo,Jaeha Park,Bongyoung Ahn,Seung Hyun Cho 한국비파괴검사학회 2011 한국비파괴검사학회지 Vol.31 No.3
The on-line monitoring for the wall thinning in secondary system has been considered one of main issues for the safety of nuclar power plants. To establish the on-line monitoring technique for the pipe wall thinning, the development of the ultrasonic transducer working in high-temperature is very important. In this investigation, the magnetostrictive transducer is concerned for high temperature condition up to 300℃. The magnetostrictive transducer has many advantages such as high working temperature, durability, cost-effectiveness, and shear waves, most of all. A thin Fe-Co alloy patch whose Curie temperture is over 900℃ was employed as a ferromagnetic material for magnetostriction. Wave transduction experiments in various temperature were carried out and the effect of bias magnets was considered together with the dry coupling performance of the transducer. From experimental results, consequently, it was found that the magnetostrictive transducer works stable even in high temperature up to 300℃ and can be a promising method for the on-line monitoring of the wall thinning in nuclear power plants.
전자기 음향 공진을 이용한 강선의 표면 미세 결함 탐상 타당성 연구
허태훈(Taehoon Heo),조승현(Seung Hyun Cho),안봉영(Bongyoung Ahn),임종수(Zhong Soo Lim) 한국비파괴검사학회 2013 한국비파괴검사학회지 Vol.33 No.1
철강 생산 제품 중 강선 (steel wire rod)은 제조 과정 중 종방향으로 미세한 표면 결함이 매우 빈번하게 발생하는데 이중 깊이가 수 십 마이크로미터 이상인 결함들은 최종 생산품의 불량을 유발하는 심각한 원인이 되고 있다. 이와 같은 이유로 강선의 제조 단계에서 표면의 미세 결함의 깊이를 평가하는 방법의 개발이 절실히 요구된다. 표면 미세 결함을 평가할 수 있는 여러 가지 방법 중에서, 본 연구에서는, 전자기 음향 공진법의 적용 가능성을 고찰하고자 한다. 전자기 음향 공진 (electromagnetic acoustic resonance, EMAR)은 전자기 음향 트랜스듀서 (electromagnetic acoustic transducer, EMAT)을 이용하여 시편의 공진 특성을 측정하는 방법으로서, 대상의 작은 변화에도 민감하게 반응하고 비접촉 측정이 가능하여 현장 적용에 용이하다는 장점이 있다. 전자기 음향 공진 실험을 통하여 표면 미세결함과 잔향특성의 변화를 관찰하여 깊이 약 100 마이크로 미터 내외의 결함은 탐상 가능함을 확인하였다. The surface microcrack over a few tens of micrometers is one of severe problems of a steel wire rod to lead to the failure of the final products, so the method to evaluate crack depth has been required to develop. This work investigates the feasibility of electromagnetic acoustic resonance (EMAR) for this problem. EMAR is the method for measurement of resonant features using electromagnetic acoustic transducer (EMAT). Generally, EMAR is sensitive to small variation of the structures and easy to apply it to the industrial field because of the feature of noncontact measurement. Through several EMAR experiments, the change of the resonant frequencies and attenuation in reverberation has been observed. The results confirms that the surface cracks of around 100 micrometer depth can be detected successfully with the present method.
매설형 자기변형 초음파 트랜스듀서를 이용한 고온 구조물 두께 감시
허태훈(Taehoon Heo),조승현(Seung Hyun Cho) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
Wall thinning is one of severe problems of the secondary piping systems in nuclear power plants, so it is very essential to monitor the thickness of the pipe periodically. However, the monitoring in operation is very difficult to execute due to high temperature about to 270 degrees Celsius and thick insulating layers. This work presents a thickness monitoring method using an embedded magnetostrictive transducer which comprises an Fe-Co element, a PCB coil, and bias magnets. It was designed to be installed under insulating layers since it has considerably thin structure less than 5 mm. It can endure over 300 degrees Celsius since magnetostriction of Fe-Co occurs well during temperature region. Also a portable pulser/receiver was developed to operate the transducer. The present method was verified through experiments with high temperature specimens and shows successful results to detect the thickness of the structure.
허현동(Hyundong Heo),황태훈(Taehoon Hwang),이경수(Kyongsu Yi) 한국자동차공학회 2010 한국자동차공학회 학술대회 및 전시회 Vol.2010 No.11
This paper presents an Electronic Stability Control (ESC) algorithm to improve vehicle stability using individual tire force information. The objective of the proposed ESC algorithm is to determine the optimal distribution of individual wheel braking forces based on tire forces being exerted on the road to improve the performance of the controller. This ESC algorithm consists of an upper level controller and a lower level controller. The upper level controller uses the measured or estimated signal from vehicle to calculate the desired yaw moment for satisfying the driver’s intention. On this occasion, lateral tire forces are approximated by using the measured and estimated signals. The lateral dynamic model can be more accurate by getting rid of the uncertainties caused by complex tire model when you directly apply the current tire forces to the model. The controller which is used to improve vehicle steerability and to maintain vehicle stability under extreme driving situations is then designed by using the Sliding Mode Control (SMC) technique, respectively. In the lower level controller, the individual braking forces are determined by the optimal strategy. The closed loop computer simulation results with driver-vehicle-controller system confirm the effectiveness of the proposed control system and the improvements in vehicle handling and stability.
입구 벨마우스 형상에 따른 냉장고 원심홴의 성능에 대한 수치적 분석
김상현(Sanghyeon Kim),허승(Seung Heo),정철웅(Cheolung Cheong),김태훈(Taehoon Kim) 한국소음진동공학회 2011 한국소음진동공학회 학술대회논문집 Vol.2011 No.10
Because of complex structure of inlet and outlet flows, the performance of centrifugal fans used in a household refrigerator is affected by many parameters of duct system surrounding the fans. In this paper, the performance of a centrifugal fan is numerically analysed according to shapes of inlet bell-mouth. To improve performance of the centrifugal fan, some design parameters are selected for comparison. On a basis of these comparison, optimum shape of inlet bell-mouth is proposed to maximise the flow rate of the fan.