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Fretting cracking behavior of nub of laststage blade for steam turbine
Kihyeon Kim,Sung-SanCho,Dong Hyeon Hwang 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.4
Nub-and-sleeve of last-stage blade for steam turbine is a part-span damper. The nub is vulnerable to fretting cracking since it is in contact with the sleeve under centrifugal force, and a small-amplitude oscillatory movement occurs at the nub-sleeve contact interface due to the blade vibration during operation of turbine. The present study developed a rig test that mimics fretting behavior at the nub-sleeve contact interface and reproduces fretting cracking of the nub. The rig tests reveal that fretting cracking occurs if the contact interface is in partial slip state and the tangential contact force amplitude is sufficiently large. The minimum tangential contact force amplitude for cracking increases with the normal contact force. Moreover, under the partial slip condition, the tangential contact force amplitude increases with the imposed displacement amplitude and its maximum value increases with the normal contact force.
Kihyeon Bae,Kyungmo Jung,Baeksuk Chu,Daehie Hong,Hoonjai Chun,Yongsik Kim,Bora Keum 한국정밀공학회 2009 International Journal of Precision Engineering and Vol.10 No.2
The large number of patients who suffer from diseases such as gastritis, obesity, and chronic gastro-esophageal reflux disease has made the development of a new suture device using an endoscope instrument channel an important priority. This paper deals with a novel design of an endoscopic instrument that facilitates suture operations on the stomach and esophagus. Unlike a laparoscope, it is very difficult to transfer forces and moments to the end of a gastrointestinal endoscope from the outside handle dues to its extreme flexibility. The only feasible forces are pushing and pulling using wires and tubes. This new design requires only the push-pull action from the outside handle to complete suture operations. Furthermore, several stitches can be performed with a single endoscope insertion. This new endoscope suturing methodology thus significantly reduces the time for surgical operations and the pain that patients experience. The feasibility of the instrument was demonstrated through in vitro and in vivo animal experiments.
Analysis of fretting cracking condition for nub of steam turbine blade
Kihyeon Kim,조성산,Dong Hyeon Hwang 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.3
Nub-and-sleeve of last-stage blade for steam turbine is a part-span damper. The nub is susceptible to fretting cracking since the nub is in contact with the sleeve under centrifugal force and vibration of blade causes a small-amplitude oscillatory movement at the nub-sleeve contact interface. Previous study of the authors achieved the experimental result that the minimum tangential contact force amplitude for cracking increases almost proportionally to the normal contact force when the nub-sleeve contact interface is in partial slip state. Present study aims at establishing the fretting cracking condition for nub that can be applicable to design of nub-and-sleeve. For this purpose, the experimental result was analyzed with fatigue damage parameters: Smith-Watson-Topper, Fatemi-Socie and Crossland. Finite element analyses were carried out to obtain stress and strain data for estimation of fatigue damage. It is demonstrated that the fretting cracking of nub can be predicted with a single fatigue damage parameter value in a range of the normal contact force if plasticity is considered. However, if plasticity is ignored, the minimum fatigue damage parameter value for cracking increases with the normal contact force.
대형 강입자 충돌가속기(LHC) 실험의 자료 분산 처리
조기현(Kihyeon Cho),한대희(Daehee Han),권기환(Kihwan Kwon),김진철(Jincheol Kim),손동철(Dongchul Son) 한국정보과학회 2005 한국정보과학회 학술발표논문집 Vol.32 No.2
고에너지물리학의 거대강입자충돌실험(LHC)에서 생산되는 데이터양은 연간 12~14PetaByte이므로 이러한 데이터를 분석하기 위해서 기존의 전산개념으로는 자료 처리하기가 불가능하다. 그러므로 새로운 개념의 대용량 자료 처리를 위한 분산 처리 시스템이 필요하며, 이와 관련하여 고에너지 물리 실험분야에서는 계층적 구조의 Tier-0, 1, 2의 지역데이터센터의 개념 및 그리드 개념을 도입하였다. LCG(LHC Computing Grid) 및 OSG(Open Science Grid)등의 그리드 팜을 이용하여 자료를 처리한다.
조기현(Kihyeon Cho),김현우(Hyunwoo Kim) 한국콘텐츠학회 2007 한국콘텐츠학회 종합학술대회 논문집 Vol.5 No.2_1
고에너지물리 e-Science 연구 환경 구축은 데이터가 생산되는 외국의 가속기 연구소에 가지 않더라도, 언제나 어디서나 실제 가속기 연구소에서 고에너지물리 연구를 수행하는 것과 같은 연구 환경을 만드는 것이다. 그 구성요소로서 1) 데이터 생산, 2) 데이터 프로세싱, 3) 데이터 publication이 있다. 데이터 생산은 원격 제어시스템을 활용하여 원격으로 데이터 생산에 참여하는 것이며 데이터 프로세싱은 그리드 팜을 활용하여 job을 언제나 어디서나 수행하는 것이며 데이터 publication은 EVO(Enabling Virtual Organzation) 시스템을 활용하여 공동 협업 환경으로 연구 결과물을 얻는 것이다. 이러한 개념을 고에너지물리 실험의 하나인 CDF 실험에 적용하여 구현하였다. The e-Science for High Energy Physics is to study high energy physics anytime and anywhere even if we are not on-site of accelerator latboratories. The concepts are 1) data production, 2) data processing and 3) data publication. The data production is to do remote control and take shifts remotely. The data processing is to run jobs anytime, anywhere with grid farms. The data publication is to work together to publish papers using collaborative environment such as EVO (Enabling Virtual Organization) system. We apply this concept to high energy physics, espessically, CDF experiment and show the results.
Optimal Gain Filter Design for Perceptual Acoustic Echo Suppressor
KIM, Kihyeon,KO, Hanseok The Institute of Electronics, Information and Comm 2009 IEICE transactions on information and systems Vol.92 No.6
<P>This Letter proposes an optimal gain filter for the perceptual acoustic echo suppressor. We designed an optimally-modified log-spectral amplitude estimation algorithm for the gain filter in order to achieve robust suppression of echo and noise. A new parameter including information about interferences (echo and noise) of single-talk duration is statistically analyzed, and then the speech absence probability and the a posteriori SNR are judiciously estimated to determine the optimal solution. The experiments show that the proposed gain filter attains a significantly improved reduction of echo and noise with less speech distortion.</P>