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로터 굽힘의 국부적 교정을 위한 전자기 유도가열 공정의 다중물리해석
조황기(Hwangki Cho),박민규(Min-Gyu Park),박현구(Hyun-Ku Park),박광하(Kwang-Ha Park),손동우(Dongwoo Sohn) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
A bending deformation of steam turbine rotors can lead to serious accidences in the power plant. Therefore, the bent rotors should be straightened in an appropriate manner. Among several straightening methods, an electromagnetic induction heating is considered a promising tool in terms of efficiency and accuracy. In this study, we develop a finite element procedure for multi-physics simulation that includes electromagnetic induction, heat transfer, as well as thermo-elasto-plastic deformation. The difference in coupling strategies of multi-physics phenomena is also discussed. Subsequently, we conduct a series of numerical simulations for local straightening of bent rotors considering the states of initial residual stresses.
정사각형 콘크리트 구조물 분리를 위한 비폭성 파쇄제와 구멍의 효과적인 배치
조황기(Hwangki Cho),남윤민(Yunmin Nam),손동우(Dongwoo Sohn) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
As an alternative to conventional explosives for breaking rocks and concrete structures, the non-explosive demolition agents are used to reduce noise and vibration in the demolition process. This study is concerned with numerical simulations of quasi-static crack propagation, in which the thermal expansion of circular non-explosive demolition agents causes the formation of crack in a square concrete structure. The concrete damage plasticity model is used to predict the crack patterns. In addition, we consider empty holes that can affect the crack patterns. Consequently, we discuss the effective arrangement of non-explosive demolition agents and empty holes to increase the number of broken pieces.
비폭성 파쇄제를 이용한 구조물 파괴에서 재료강도에 따른 균열 진전 해석
남윤민(Yunmin Nam),조황기(Hwangki Cho),손동우(Dongwoo Sohn) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
One of traditional method for breaking large structures is the use of dynamite. However, such a blasting method has limitations due to noise and vibration problems. Recently, as an alternative to the blasting method, non-explosive demolition agents are considered to resolve the environment problems, In this study, we conduct a series of numerical simulations of breaking brittle structures that result from thermal expansion of the soundless chemical demolition agent (SCDA), one of non-explosive demolition agents. For two-dimensional semi-infinite structures, we observe the crack paths depending on the SCDA arrangement. Furthermore, we discuss the effect of material strength on breaking the structures.
화염 가열을 이용한 로터 굽힘교정 공정에서의 열변형 해석
김윤호(Yunho Kim),조황기(Hwangki Cho),박민규(Min-Gyu Park),박현구(Hyun-Ku Park),박광하(Kwang-Ha Park),손동우(Dongwoo Sohn) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
In power plants, bending deformation of turbine rotors can occur due to severe operating conditions such as high-speed rotation, high temperature and pressure. Therefore, it is necessary to straighten the bent rotors fast and effectively. This study focuses on a numerical simulation of the opposed heating and cooling method, which is one of simple straightening ways. First, an appropriate magnitude of heat flux, which is used as input data of numerical simulations, is estimated by comparing the simulation results with experimental ones of a flame heating. Next, we conduct finite element analysis of thermal deformation during the heating and cooling processes, and also predict the residual stress after straightening the bent rotors.