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Local Mean Water Layer Thickness in Countercurrent Stratified Two -Phase Fllow
김효정,김갑,Kim, Hho-Jung,Kim, Kap The Korean Society of Mechanical Engineers 1986 대한기계학회논문집 Vol.10 No.6
물-증기 역류 성층이상유동에서의 평균 액체층 두께가 여러가지 경사각과 종횡비에 따라 측정되었다. 난류유동에 있어서 전단응력분포의 선형화와 von Karman의 혼합길이 이론을 근거로 평균 액체층의 두께에 대한 관계식이 제시되었으며 실험결과와 잘 일치하였음을 보였다. 접촉면에서의 조파저항이 고려되지 않은 해석결과는, 수평 성층유동의 경우에, 평균 액체층 두께보다는 오히려 파곡까지의 액체층 두께를 예측하고 있는 것으로 나타났다. 또한 평균 액체층 두께에 대한 실험 상관관계식이 계산시 편의를 위해 쉽게 인지할 수 있는 매개변수들의 항들롤 제시되었다.
조강래,김효정,Kim, Hho Jung 대한기계학회 1979 대한기계학회논문집 Vol.3 No.1
In order to improve the load capacity of externally pressurized air-lubeicatedjournal bearings, a new type(doubly-stepped type) bearing was revised and experimented. Through the results of experiment, the load capacity of doubly-stepped bearings was discussed and compared with equivalent conventional circular journal bearings. Results were obtained for speed up to 18000rpm and for supply pressure ratio(Ps/Pa) 4.8,6,7. Compared with equivalent conventional bearings, doubly-stepped bearings resultd a high gain in load capacity. It is also shown that the increasing rate of load capacith increases with decreasing the eccentricity ratio. Furthermore, the increasing rate is higher in the case of great clearanceratio than small dleatance ratio of doubly-stepped bearings. Such an increase in load capacity is confirmed by pressure distributions in the bearings.
피로하중을 받는 구조물의 결함분포에 대한 확률론적 해석
곽상록(Sang-Log Kwak),최영환(Young-Hwan Choi),김효정(Hho-Jung Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
Flaw geometries, applied stress, and material properties are major input variables for the fracture<br/> mechanics analysis. Probabilistic approach can be applied for the consideration of uncertainties within<br/> these input variables. But probabilistic analysis requires many assumptions due to the lack of initial<br/> flaw distributions data. In this study correlations are examined between initial flaw distributions and<br/> in-service flaw distributions on structures under cyclic load. For the analysis, LEFM theories and Monte<br/> Carlo simulation are applied. Result shows that in-service flaw distributions are determined by initial<br/> flaw distributions rather than fatigue crack growth rate. So initial flaw distribution can be derived from<br/> in-service flaw distributions.
Turbulence Induced Fretting Wear Characteristics of Steam Generator Helical Tubes
정명조(Myung Jo Jhung),조종철(Jong Chull Jo),김효정(Hho Jung Kim),윤영길(Young Gill Yune),유선오(Seon Oh Yu) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
This study addresses safety assessment of the potential for fretting wear damages on steam generator helical tubes due to turbulence induced vibration in operating nuclear power plants. To get the natural frequency, corresponding mode shape and participation factor, modal analyses are performed for helical type tubes with various conditions. Special emphases are put on the effects of coil diameter and the number of turns on the modal and fretting wear characteristics of tubes. Also, investigated are the effects of external pressure on the tube modal characteristics as well as the effects of turbulence induced vibration on the fretting wear characteristics of tubes.