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3차원 솔리드 요소를 이용한 용접부 핫스팟 응력 계산에 대한 연구
오정식(Jung-Sik Oh),김유일(Yooil Kim),전석희(Seok-Hee Jeon) 한국해양공학회 2015 韓國海洋工學會誌 Vol.29 No.1
Because of the high stress concentration near the toe of a welded joint, the calculation of local stress using the finite element method which is relevant to the fatigue strength of the weld toe crack, is a challenging task. This is mainly caused by the sensitivity of finite element analysis, which usually occurs near the area of a dramatically changing stress field. This paper presents a novel numerical method through which a less mesh-sensitive local stress calculation can be achieved based on the 3D solid finite element, strictly sticking to the original definition of hot spot stress. In order to achieve the goal, a traction stress, defined at 0.5t and 1.5t away from the weld toe, was calculated using either a force-equivalent or work-equivalent approach, both of which are based on the internal nodal forces on the imaginary cut planes. In the force-equivalent approach, the traction stress on the imaginary cut plane was calculated using the simple force and moment equilibrium, whereas the equivalence of the work done by both the nodal forces and linearized traction stress was employed in the work-equivalent approach. In order to confirm the validity of the proposed method, five typical welded joints widely used in ships and offshore structures were analyzed using five different solid element types and four different mesh sizes. Finally, the performance of the proposed method was compared with that of the traditionally used surface stress extrapolation method. It turned out that the sensitivity of the hot spot stress for the analyzed typical welded joints obtained from the proposed method outperformed the traditional extrapolation method by far.
MVDC와 LVDC 연계를 위한 마이크로그리드 구축에 관한 연구
오정식(Jung-Sik Oh),구희석(Hui-Seok Gu),여서현(Seo-Hyun Yeo),정인성(In-Sung Jeong),최정훈(Jung-hoon Choi) 대한전기학회 2021 대한전기학회 학술대회 논문집 Vol.2021 No.10
In this paper, as a study on microgrid construction for MVDC and LVDC linkage, 5kV MVDC distribution line and lower LVDC system and load components are described. The microgrid composed of distributed power supply (solar power), ESS, DC-DC converter, and EMS will verify the effectiveness of an independent system composed of MVDC and LVDC.