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김지수(Jeesoo Kim),신동익(Dongik Shin),손영창(Youngchang Shon) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
The impeller is routinely proof loaded during manufacture to verify the strength capability. Over-speed test is one of the proof tests for the rotating part. This kind of proof test could be overload to the normal operation cyclic loading. In general, overload when it comes tensile has a good effect to the product life, since the overload sequence generate compressive residual stress. Under these load history, the effective stress level is decreased by residual stress on unloaded condition. Therefore, fatigue life applied tensile overload could be larger than the normal load. Although there are many of papers to show the overload effect to the life in coupon test or theoretical approach, it has not been prepared for the product base application. In this paper, the residual stress and effective stress on life limited location of the impeller are investigated by applying different levels of over-speed which is overload. Then, fatigue strength estimated according to the amount of overload. Finally, the relation between level of overload and fatigue life is prepared in this specific impeller application. The FE analysis is used to estimate the amount of stress/residual stress by applying each load steps. These stress results are correlated to the fatigue life curve of the material.
김지수(Jeesoo Kim),박기훈(Kihoon Park),성옥석(Okseok Sung) 한국추진공학회 2011 한국추진공학회 학술대회논문집 Vol.2011 No.5
본 논문에서 Compressor 및 turbine 에서의 Blade failure등의 내부파손이 이를 둘러싸고 있는 케이스 내부에 머무르게 하는 엔진설계의 방법에 대한 이론 및 Simulation 등을 기술 하였다. 가장 무거운 부품 중에 하나인 케이스의 두께 최적화는, 항공기의 안정성뿐만 아니라 항공 효율을 높이기 위한 경량화의 목적을 위해서도 매우 중요한 설계목표 이다. 이러한 목적을 위하여 이론적 접근방법으로 에너지 밸런스 방법을 사용하였으며, 파손된 블레이드의 거동특성 및 영향성 평가를 위한 유한요소해석을 위하여 LS-DYNA가 사용 되어졌다. On the basis of the paper described herein, rotor blade failure in the compressor, gas generator turbine, and power turbine and the resulting internal damage is contained within the peripheral hardware and engine casings. For the safety reason, the blade containment was regulated by aviation authority. For reducing the weight of the case, a heaviest single component of a jet engine, the blade containment capability was analyzed by engine manufacturer. The procedure established for containment design involves an energy balance method based on the comparison of the kinetic energy of released blade and the strain energy of the containment zone. The LS-DYNA simulation can also be introduced to predict behavior of released blade and case. All of the analytic and numerical result are described ...
조윤경 ( Cho Yunkyoung ),김지수 ( Kim Jeesoo ),오준일 ( Oh Junil ) 글로벌영어교육학회(구 호남영어교육학회) 2016 Studies in English education Vol.21 No.2
The present study sought to examine the use of grammar learning strategies of Korean college students in two aspects. First, it explored the relationship between learner background factors and their use of grammar learning strategies. Second, it investigated to what extent the learners’ use of grammar learning strategies would predict their grammatical knowledge and whether it would have different effects on their grammatical knowledge measured by two grammar tests with a differing level of vocabulary and readability. To this end, 107 Korean college students were asked to complete a grammar learning strategy questionnaire and take the two grammar tests. The results show that the learners reported using more explicit discovery strategies and more implicit strategies over explicit consolidation strategies, and that higher grade students reported more uses of grammar strategies than did lower grade students. Furthermore, the use of explicit discovery strategies was found to positively predict the scores of grammar tests with a lower level of vocabulary and readability. On the other hand, the results suggest that the use of implicit strategies would predict grammatical knowledge measured by the grammar test loaded with difficult vocabulary and higher readability. Theoretical, methodological and pedagogical implications are discussed.
고온 터빈 노즐에서 발생하는 크리프가 피로수명에 미치는 영향에 대한 연구
박훤(Hwun Park),김지수(Jeesoo Kim),신동익(Dongick Shin),류시양(Shiyang Ryu),신종섭(Jongsub Shin),김용련(Yongryun Kim) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.12
터빈노즐은 고온, 고압의 연소가스에 노출되기 때문에 크리프가 발생한다. 크리프에 의한 손상과 교번응력에 의해 발생하는 피로손상 모두 터빈노즐의 수명을 감소시키므로 두 현상을 동시에 고려하여서 수명 평가를 해야 한다. 본 연구에서는 유한요소 해석을 사용하여서 터빈노즐이 가스터빈 작동환경에서 크리프 파단시간과 저주기 피로 수명을 산출하였다. 해석결과는 최대 크리프 손상이 발생하는 곳과 최대 피로손상이 발생하는 곳은 일치하지 않는다는 것을 보여준다. 이런 경우 크리프와 피로파괴 손상의 합을 총 수명이라고 보는 것은 타당하다. Turbine nozzles have creep because they are exposed to high-temperature and high-pressure combustion gas. Since the damage by creep and the damage caused by alternating stress reduce the life simultaneously, life assessment should count the both damage mechanism. This study employs finite element analyses to compute the creep-rupture life and the low-cycle fatigue of a turbine nozzle in its operating conditions. The results show that the maximum damage by creep and the maximum damage by fatigue do not occur at the same part of nozzle. In these conditions, the superposition of creep damage and fatigue damage can be reasonably estimated to be total damage.