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경수로 핵연료 열-구조 연계 해석을 위한 다차원 간극 열전도도 모델 개발
김효찬(Hyo Chan Kim),양용식(Yong Sik Yang),구양현(Yang Hyun Koo) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.2
경수로 핵연료가 원자로내에서 연소되는 동안 핵연료 펠릿에서부터 피복관까지 온도해석은 핵연료 안전 해석에 있어 중요한 요소이며, 경수로 핵연료 온도 해석을 하기 위해서는 간극 모델 개발이 필수적이다. 간극 열전도도는 특성상 간극 두께값에 의존적이게 되며 이러한 특성으로 인해 다차원 간극 열전도도 모델이 비선형적 거동을 보인다. 본 연구에서는 선형화된 다차원 간극 열전도도 모델 개발을 위해 가상 연결 간극 요소를 제안하였다. 제안된 간극 연결 요소에 간극 열전도도를 적용하기 위해 등가 열전달 계수를 정의하였다. 제안된 모듈을 평가하기 위해 상용코드 ANSYS APDL 을 이용하여 열-구조 연계 해석 모듈을 구현하였으며, 다양한 예제를 통해 정확성과 수렴성을 평가하였다. A light water reactor (LWR) fuel rod consists of zirconium alloy cladding tube and uranium dioxide pellets with a slight gap between them. The modeling of heat transfer across the gap between fuel pellets and the protective cladding is essential to understanding fuel behavior under irradiated conditions. Many researchers have been developing fuel performance codes based on finite element method (FE) to calculate temperature, stress and strain for multidimensional analysis. The gap conductance model for multi-dimension is difficult issue in terms of convergence and nonlinearity because gap conductance is function of gap thickness which depends on mechanical analysis at each iteration step. In this paper, virtual link gap element (VLG) has been proposed to resolve convergence issue and nonlinear characteristic of multidimensional gap conductance. In terms of calculation accuracy and convergence efficiency, the proposed VLG model has been evaluated for variable cases.
하지근력강화 운동프로그램이 노인의 근력과 균형수행력에 미치는 영향
김효찬(Kim Hyo-Chan) 한국체육과학회 2003 한국체육과학회지 Vol.12 No.2
The purpose of this study is to offer materials about efficient exercises that increase & maintain sense of balance for old people and prevent them from falling and hurting themselves by executing exercises to develop muscular strength legs of aged people. In order to achieve study goals, 40 old people who are over 65 were selected; the program of exercises to develop muscular strength legs 3 times a week, for 6 weeks in total, then, walking capacity, muscular strength of legs, and sense of balance were measured. In order to examine homogeneity of two groups, an experimental group and a control group, t-test were conducted. In order to verify hypotheses, Repeated ANOVA was used in their analysis works. Following conclusions were obtained through the analysis on data collected by these researches. First, muscular strengths of legs like femoral joints' extensor muscles and trunk flexor, knee joints' extensor muscles and trunk flexor, ankle joints' ankle plantar flexor and excessive ankle dorsiflexion muscles significantly improved. It was proved that muscular strengths of legs like femoral joints, knee joints, ankle joints improved. Second, with respect to the static balance executing capacity in balance executing capacity, after the experiment, the time of standing on one leg and closing eyes is not different from the time of before the experiment, whereas the time of standing on one leg and opening eyes significantly increased. Therefore, it was proved that the static balance executing capacity improved after conducting the program of exercises to develop muscular strength of legs. Third, with respect to the dynamic balance executing capacity in balance executing capacity, it was measured by the action of standing up from a chair, walking 3 meters, and coming back to the chair; after the experiment, the time of the action significantly reduced. Therefore, after conducting the program of exercises to develop muscular strength of legs, the dynamic balance executing capacity improved.