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.

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.

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.

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.

기하학적 재료적 비선형 특성을 고려한 스트라치 단위부재의 명시적 긴장설치 및 극한하중 해석

이경수,한상을,Lee, Kyoung-Soo,Han, Sang-Eul 한국강구조학회 2011 韓國鋼構造學會 論文集 Vol.23 No.4

본 연구에서는 스트라치 시스템의 긴장설치과정 및 극한하중 해석을 수행하기 위한 명시적 해석법을 제안하였다. 스트라치 시스템은 Stressed-Arch에서 유래한 용어로 슬리브와 갭이 도입된 유동하현재 내부의 긴장재에 초기장력을 도입함으로써 갭이 점차 닫히게 되며, 이에 따라 상현재에 곡률이 도입되면서 전체 구조물이 상승하여, 최종적인 아치형태의 구조물을 형성하는 독창적인 구조시스템이다. 스트라치 시스템의 초기장력 도입과정을 긴장설치(stress-erection) 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 강성행렬을 사용하지 않는 명시적 동적이완법을 사용하여 비선형 평형방정식의 해를 구하였고, 대변위 및 단면의 재료적 특성을 반영할 수 있는 필라맨트 보요소를 사용하여 연속된 상현재의 비선형 거동특성을 분석하였다. 필라맨트 보요소의 단면은 다수의 1차원 필라맨트로 구성되며, 각각의 필라맨트에 대해서 다양한 재료모델을 적용할 수 있다. 본 연구에서는 비선형 재료모델인 Ramberg-Osgood모델 및 Bi-linear 탄소성 모델을 적용하여 긴장설치 및 극한하중 해석을 수행하였고, 그 결과를 이전의 실험적 연구결과와 비교 분석하였다. 본 연구의 해석결과는 이전의 실험적 연구결과와 유사하였으며, 명시적 해석법의 특성상 효율적으로 후좌굴거동 특성까지 해석할 수 있었다. In this study, the explicit numerical algorithm was proposed to simulate the stress erection process and ultimate-load analysis of the strarch (stressed arch) system. The strarch system is a unique and innovative structural system and member prestress comprising prefabricated plane truss frames erected through a post-tensioning stress erection procedure. The flexible bottom chord, which has sleeve and gap details, is closed by the reaction force of the prestressing tendon. The prestress imposed on the tendon will enable the strarch system to be erected. This post-tensioning process is called "stress erection process." During this process, plastic rigid-body rotation occurs to the flexible top chord due to the excessive amount of plastic strain, and the structural characteristic is unstable. In this study, the dynamic relaxation method (DRM) was adopted to calculate the nonlinear equilibrium equation of the system, and a displacement-based finite-element-formulated filament beam element was used to simulate the nonlinear behavior of the top chord sections of the strarch system. The section of the filament beam element was composed by the amount of filaments, which can be modeled by various material models. The Ramberg-Osgood and bilinear kinematic elastic plastic material models were formulated for the nonlinear material behaviors of the filaments. The numerical results that were obtained in the present study were compared with the experiment results of the stress erection and with the results of the ultimate-load analysis of the strarch unit frame. The results of the present studies are in good agreement with the previous experiment results, and the explicit DRM enabled the analysis of the post-buckling behaviors of the strarch unit frame.

미사일-타깃해석법에 의한 콘크리트돔의 항공기 충돌해석에 관한 연구

이경수,하크 지아올,한상을,Lee, Kyoung-Soo,Huque, Ziaul,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.6

In this paper, the authors performed the missile-target interaction analysis for B747 airplane against prestressed concrete dome structure. The aircraft model was developed and verified from the previous researches that were done by the authors. Therefore, the FE aircraft model can be used for the aircraft impact loading case. The development of aircraft FE model is theoretically based on the Riera function which was proposed by Riera derived from the rigid wall impact hypothesis. When the aircraft impact to the freeform or circular section shaped structure, the resulting impact force and it's integral impulse force may be different from the theoretical values. In this paper, the authors developed the artificial prestress concrete dome structure which has circular section shape and usually using for the nuclear power plant containment building structure. And the aircraft impact analyses were performed using missile-target interaction method. The commercial Hydrocode AUTODYN was used for FE modelling and simulations. From the comprehensive numerical studies, the shape of target structure significantly affects the aircraft impact load and decreases it compared to the Riera function and rigid wall impact simulation.

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.

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.

자발성 뇌지주막하 출혈 환자에서 뇌동맥류 검출에 대한 고식적 혈관조영술과 3차원 전산화 단층 혈관조영술의 비교

이경수,강창구,허륭,이상훈,정의화,Lee, Kyoung Soo,Kang, Chang Gu,Huh, Ryoong,Lee, Sang Hoon,Chung, Ui Wha 대한신경외과학회 2001 Journal of Korean neurosurgical society Vol.30 No.6

Objectives : Three-dimensional computed tomographic angiography(3D-CTA) is recently developed diagnostic imaging modality. We have studied this noninvasive method for possible role in replacing conventional angiography( CA) in the detection of aneurysms of the circle of Willis in patients with subarachnoid hemorrahge(SAH). Methods : We studied retrospectively, the 100 patients with SAH or unruptured aneurysms admitted to our hospital from October 1997 to December 1998. Among there, 85 patients underwent CTA, 82 patients underwent CA and 67 patients underwent both of CTA and CA. 3D-CTA was obtained using maximum intensity projection(MIP) and shaded-surface display(SSD) reconstruction. Results : Total 107 aneurysms were detected in 92 patients, and 64 aneurysms were detected in 67 patients underwent both CTA and CA. In five cases of those 67 cases, aneurysms were detected by CA but not by 3D-CTA. The detection rate of aneurysms(91.8%) and the detection rate of parent artery in cases of anterior communicating artery aneurysms(86.9%) with total 3D-CTA were relatively compatible with that of CA. But 3D-CTA was not enough in detection of posterior communicating artery aneurysms, internal carotid artery aneurysms as well as small sized aneurysm(<3mm). Conclusion : We consider CTA is valuable in as a screening test for cerebral aneurysm and follow-up test. And it is also valuable in early surgery for patients with aneurysmal rebleeding because of simple, quick, non-invasive method.