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.

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.

유한변형과 굽힘 효과가 고려된 공간프레임요소에 분기좌굴해석

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

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.

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.

수압시험 및 운전조건이 가압기 안전노즐의 용접잔류응력에 미치는 영향 평가

이경수,이성호,김완재,Lee, Kyoung Soo,Lee, Sung Ho,Kim, Wan Jae 한국압력기기공학회 2012 한국압력기기공학회 논문집 Vol.8 No.1

This paper presents the results of finite element analysis for the effects of hydrostatic test and operating condition on the weld residual stress at dissimilar metal weld of a pressurizer safety nozzle in a nuclear power plant. For the study, the weld residual stress at ambient condition was analyzed using ABAQUS in the first place. After the weld residual stress analysis, the hydrostatic test condition and operating condition was applied to the same model one after another. The weld residual stress was observed to change due to the successive hydrostatic test and operating condition. The axial residual stresses on inner surface of the dissimilar metal weld and HAZ region were decreased by hydrostatic test and operating condition, which gives beneficial effect on preventing primary water stress corrosion cracking.

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.

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.