기계가공이 이종용접부의 잔류응력에 미치는 영향에 관한 연구

이경수,이정근,이성호,박치용,이승건,박재학,Lee, Kyoung-Soo,Lee, Jeong-Geun,Lee, Seong-Ho,Park, Chi-Yong,Lee, Seung-Geon,Park, Jai-Hak 대한용접접합학회 2011 대한용접·접합학회지 Vol.29 No.2

his paper aimed to understand the residual stress in the dissimilar metal welds of nuclear power plant. Two kinds of residual stress were considered, which caused by welding and machining. Residual stress due to mechanical machining was measured by hole-drilling technique and x-ray diffraction method for the SA508 and F316L. Weld residual stress at dissimilar metal weld between SA508 and F316L was evaluated by FEA. Residual stress profiles were obtained for the inside surface and through thickness of welds. Machining effect was also analyzed by FEA. According to the residual stress measurement, it was observed that mechanical machining can generate tensile stress on the surface of the test material. However, FEA results showed that mechanical machining did not increase the tensile stress on the surface of weld region. Further study with more elaborate measurement and numerical analysis is required to identify the effect of machining on residual stress in the dissimilar metal weld region.

원전재료 모재 및 용접부 잔류응력측정 연구

이경수,이정근,이성호,박재학,Lee, Kyoung-Soo,Lee, Jeong-Keun,Lee, Seong-Ho,Park, Jae-Hak 한국압력기기공학회 2011 한국압력기기공학회 논문집 Vol.7 No.1

Primary water stress corrosion cracking (PWSCC) has been found in the weld region of the nuclear power plant. Welding can produce tensile residual stress. Tensile residual stress contributes to the initiation and growth of PWSCC. It is important to estimate weld residual stress accurately to predict or prevent the initiation and growth of PWSCC. This paper shows the results of finite element analysis and measurement experiment for weld residual stress. For the study, four kinds of specimen were fabricated with the materials used in the nuclear power plant. Residual stresses were measured by four kinds of methods of hole drilling, x-ray diffraction, instrumented indentation and sectioning. Through the study, numerical analysis and measurement results were compared and the characteristics of each measurement technique were observed.

원자로 상부헤드 관통노즐 균열에 대한 원인분석 및 건전성 평가

이경수,이성호,이정석,이재곤,이승건,Lee, Kyoung-Soo,Lee, Sung-Ho,Lee, Jeong-Seog,Lee, Jae-Gon,Lee, Seung-Gun 한국압력기기공학회 2013 한국압력기기공학회 논문집 Vol.9 No.1

This paper presents the results of integrity assessment for the cracks happened in reactor vessel upper head penetration nozzles. The crack morphology for a boat sample from crack area was analyzed through microscope. The stress condition including weld residual stress around crack was analyzed using finite element analysis. From the results of crack morphology and stress condition, the crack was concluded as primary water stress corrosion cracking. The integrity of the cracked nozzle was assessed by the methodology provided in ASME Section XI. According to the assessment results, the remaining life of the cracked nozzle was 1.43 yrs. and the plant decided to repair it.

유한변형과 굽힘 효과가 고려된 공간프레임요소에 분기좌굴해석

이경수,김현수,Lee, Kyoung-Soo,Kim, Hyun-Su 한국공간구조학회 2012 한국공간구조학회지 Vol.12 No.4

동적이완법과 탄소성 보-기둥요소를 이용한 스트라치 시스템의 긴장설치과정 해석

이경수,한상을,Lee, Kyoung-Soo,Han, Sang-Eul 대한건축학회 2011 대한건축학회논문집 Vol.27 No.4

In this paper, the stress-erection process of STRARCH system was simulated by using dynamic relaxation method(DRM) and elasto-plastic beam-column element. The Stressed-Arch(STRARCH) system is a unique and innovative structural form and member prestress comprising prefabricated plane truss frames which are erected by a post-tensioning stressing procedure. The shape and member force of erected STRARCH frame are determined from the initially unstable assembled STRARCH frame by using so called stabilizing process analysis. The plastic hinge concept are applied with large deformable elasto-plastic beam-column element for the tubular top chord becoming to be curved, often causing yielding over a substantial portion of its length, during the post-tensioning stress-erection process. Finally, the verification of proposed approach for stress-erection of STRARCH is evaluated by comparing the numerical results with predicted value of tendon force and member forces.

풍력터빈의 구조특성 평가에 관한 연구-Part1

이경수,한상을,Lee, Kyoung-Soo,Huque, Ziaul,Kommalapati, Raghava,Han, Sang-Eul 한국공간구조학회 2014 한국공간구조학회지 Vol.14 No.4

This paper presents the structural model development and verification processes of wind turbine blade. The National Renewable Energy Laboratory (NREL) Phase VI wind turbine which the wind tunnel and structural test data has publicly available is used for the study. The wind turbine assembled by blades, rotor, nacelle and tower. The wind blade connected to rotor. To make the whole turbine structural model, the mass and stiffness properties of all parts should be clear and given. However the wind blade, hub, nacelle, rotor and power generating machinery parts have difficulties to define the material properties because of the composite and assembling nature of that. Nowadays to increase the power generating coefficient and cost efficiency, the highly accurate aerodynamic loading evaluating technique should be developed. The Fluid-Structure Interaction (FSI) is the emerging new way to evaluate the aerodynamic force on the rotating wind blade. To perform the FSI analysis, the fluid and structural model which are sharing the associated interface topology have to be provided. In this paper, the structural model of blade development and verifying processes have been explained for Part1. In following Part2 paper, the processes of whole turbine system will be discussing.

풍력터빈의 구조특성 평가에 관한 연구-Part2

이경수,한상을,Lee, Kyoung-Soo,Huque, Ziaul,Kommalapati, Raghava,Han, Sang-Eul 한국공간구조학회 2015 한국공간구조학회지 Vol.15 No.1

This paper presents the structural model verification process of whole wind turbine blade including blade model which proposed in Part1 paper. The National Renewable Energy Laboratory (NREL) Phase VI wind turbine which the wind tunnel and structural test data has publicly available is used for the study. In the Part1 of this paper, the processes of structural model development and verification process of blade only are introduced. The whole wind turbine composed by blade, rotor, nacelle and tower. Even though NREL has reported the measured values, the material properties of blade and machinery parts are not clear but should be tested. Compared with the other parts, the tower which made by steel pipe is rather simple. Since it does not need any considerations. By the help of simple eigen-value analysis, the accuracy of structural stiffness and mass value of whole wind turbine system was verified by comparing with NREL's reported value. NREL has reported the natural frequency of blade, whole turbine, turbine without blade and tower only models. According to the comparative studies, the proposed material and mass properties are within acceptable range, but need to be discussing in future studies, because our material properties of blade does not match with NREL's measured values.

명시적 호장법을 이용한 공간프레임의 반강접 탄소성 후좌굴 해석

이경수,한상을,Lee, Kyoung-Soo,Han, Sang-Eul 한국강구조학회 2011 韓國鋼構造學會 論文集 Vol.23 No.5

본 연구에서는 다양한 명시적 호장법을 사용하여 공간프레임의 반강접 탄소성 후좌굴 해석을 수행하였다. 이를 위해 이전 연구를 발전시켜 다양한 명시적 알고리즘의 호장법과 명시적, 묵시적 해석법에 동시에 적용 가능한 반강접 탄소성 공간프레임요소를 제안하였다. 다양한 명시적 호장법은 예측단계와 수렴단계에 명시적 해석법인 동적이완법을 적용한 것을 의미한다. 따라서 명시적 호장법에는 명시적(예측단계)-명시적(예측단계) 호장법, 명시적(예측단계)-묵시적(수렴단계) 호장법, 묵시적(예측단계)-명시적(수렴단계) 호장법으로 구분된다. 또한 명시적 호장법에 적용 가능하도록 수정된 반강접 탄소성 공간프레임요소는 오일러리안 유한변형이론에 의해 강체회전변형을 고려하였기 때문에 대변위가 발생하는 기하학적 비선형 문제에 적용될 수 있고, 완전 탄소성 소성힌지 알고리즘에 의한 재료적 비선형성을 고려하였으며, 부재내부에 정적 응축된 회전 및 축방향 성분의 선형 스프링에 의해 접합부 반강접 특성을 반영하였다. 제안된 해석법을 이용하여 검증예제를 수행함으로써 본 연구에서 제안된 다양한 명시적 호장법 및 공간프레임요소의 정확성을 검증한다. In this paper, semi-rigid elasto-plastic post-buckling analysis of a space frame was performed using various explicit arc-length methods. Various explicit arc-length methodsand a large-deformation and small-strain elasto-plastic 3D space frame element with semi-rigid connections and plastic hinges were developed. This element can be appliedto both explicit and implicit numerical algorithms. In this study, the Dynamic Relaxation method was adopted in the predictor and corrector processesto formulate an explicit arc-length algorithm. The developed "explicit-predictor" or "explicit-corrector" were used in the elasto-plastic post-buckling analysis. The Eulerian equations for a beam-column with finite rotation, which considers the bowing effects, were adopted for the elastic system and extended to theinelastic system with a plastic hinge concept. The derived tangent stiffness matrix was asymmetrical due to the finite rotation. The joint connection elements were introduced for semi-rigidity using a static condensation technique. Semi-rigid elasto-plastic post-buckling analyses were carried out to demonstrate the potential of the developed explicit arc-length method and advanced space frame element in terms of accuracy and efficiency.

스트라치 시스템의 긴장응력해석을 위한 명시적 해석법의 개발

이경수,한상을,Lee, Kyoung-Soo,Han, Sang-Eul 한국전산구조공학회 2011 한국전산구조공학회논문집 Vol.24 No.5

본 연구에서는 스트라치 시스템의 긴장설치과정 해석을 수행하기 위한 개선된 명시적 해석법을 제안하였다. 스트라치 시스템은 Stressed-Arch에서 유래한 용어로 슬리브에 의한 갭이 도입된 유동 하현재가 내부의 긴장재에 의한 초기장력의 도입으로 서서히 닫히게 되고, 이에 따라 전체 구조물이 상승하여 최종적인 아치형태의 구조물을 형성하는 독창적인 구조시스템이다. 스트라치 시스템의 초기장력 도입과정을 긴장설치(stress-erection process) 과정이라 하며, 초기곡률의 도입에 따라 유동 상현재에는 과도한 초기변형이 발생하여 소성거동에 의한 강체회전이 발생하는 불안정 구조물이 된다. 본 연구에서는 이러한 스트라치 시스템의 불안정 거동특성을 해석하기 위해서 소성힌지가 적용된 보-기둥요소를 사용하여 유동상현재를 모델링하였고, 불안정 구조물의 해석법에 효과적으로 사용되는 동적이완법의 개선된 알고리즘을 개선하여, 실제 스트라치 구조물의 긴장설치과정 해석을 수행하였으며, 실제 프로젝트에 대한 해석결과의 분석을 통하여 제안된 해석법의 적용성을 검증하였다. In this paper, the advanced explicit algorithm is proposed to simulate the stress-erection process analysis of Strarch system. The Strarch(Stressed-Arch) system is a unique and innovative structural system and member prestress comprising prefabricated plane truss frames which are erected by a post-tensioning stress-erection procedure. The flexible bottom chord which have sleeve and gap detail are closed by the reaction force of prestressing tendon. The prestress imposing to the tendon will make the Strarch system to be erected. This post tensioning process is called as "stress-erection process". During the stress-erection process, the plastic rigid body rotation is occurred to the flexible top chord by the excessive amount of plastic strain, and the structural characteristic becomes to be unstable. In this study, the large deformational beam-column element with plastic hinge is used to model the flexible top chord, and the advanced Dynamic Relaxation method(DRM) are applied to the unstable problem of stress-erection process of Strarch system. Finally, the verification of proposed explicit algorithm is evaluated by analysing the stress-erection of real project of Strarch system.

항공연료 질량을 고려한 대형항공기 충돌하중모델의 개발

이경수,하크 지아올,전두진,한상을,Lee, Kyoung-Soo,Huque, Ziau,Jeon, Doo-Jin,Han, Sang-Eul 大韓建築學會 2014 大韓建築學會論文集 : 構造系 Vol.30 No.8

In this paper, the aircraft impact force models of large commercial B747 aircraft were developed by using so called Missile-Target Interaction Method. The Lagrangian meshfree SPH concept was adopted to the fuel mass for impact force calculation. 240ton, 320ton, 420ton of aircraft mass were considered to meet with the previously proposed aircraft impact force model by OECE/NEA(2002) and Arros & Doumbalski(2007). The model of present studies are based on the model of OECE/NEA originally, and extended to the model of Arros & Doumbalski. To calculate and evaluate the aircraft impact force, the impact analyses were simulated by using commercial Hydrocde AUTODYN considering the fuel mass effect. The resultant reaction force of symmetric rigid wall is considered as the impact force of aircraft. The preparation of refined FE mesh and impact simulation were done by using AUTODYN. The aircraft and fuel debris and secondary trajectory effects were considered by the eroding effect on the FE shell element and the explicitly modeled fuel mass. To evaluate and verify the impact force of aircraft, the Riera approach were used for the reference impact time history graph. The rigid wall impact test shows that the finite element model of a B747 which considering the explicit fuel mass effect is good agreement with reference values and the applicability of fuel modelling approaches of this study.