• Title/Summary/Keyword: Flaw criteria

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Application of FAD on Pressure Tube for the Probabilitic Integrity Assessment (파손평가선도를 이용한 압력관 결함의 확률론적 건전성 평가)

  • Kwak, Sang-Log;Wang, Jong-Bae;Park, Youn-Won;Lee, Joon-Seong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.3
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    • pp.289-295
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    • 2004
  • Pressure tubes are major component of nuclear reactor, but only selected samples are periodically examined due to numerous numbers of tubes. Current in-service inspection result show there is high probability of flaw existence at uninspected pressure tube. Probabilistic analysis is applied in this study for the integrity assessment of uninspected pressure tube. All the current integrity evaluations procedures are based on conventional deterministic approaches. So it is expected that the results obtained are too conservative to perform a rational evaluation of lifetime. More realistic failure criteria, based on FAD are also proposed for the probabilistic analysis. As a result of this study failure probabilities for various conditions are calculated, and examined application of FAD and LBB concept.

Comparison of vessel failure probabilities during PTS for Korean nuclear power plants

  • Jhung, M.J.;Choi, Y.H.;Chang, Y.S.
    • Structural Engineering and Mechanics
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    • v.37 no.3
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    • pp.257-265
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    • 2011
  • Plant-specific analyses of 5 types of domestic reactors in Korea are performed to assure the structural integrity of the reactor pressure vessel (RPV) during transients which are expected to initiate pressurized thermal shock (PTS) events. The failure probability of the RPV due to PTS is obtained by performing probabilistic fracture mechanics analysis. The through-wall cracking frequency is calculated and compared to the acceptance criterion. Considering the fluence at the end of life expected by surveillance test, the sufficient safety margin is expected for the structural integrity of all reactor pressure vessels except for the oldest one during the pressurized thermal shock events. If the flaw with aspect ratio of 1/12 is considered to eliminate the conservatism, the acceptance criteria is not exceeded for all plants until the fluence level of $8{\times}10^{19}\;n/cm^2$, generating sufficient margin beyond the design life.

Availability Verification of Feature Variables for Pattern Classification on Weld Flaws (용접결함의 패턴분류를 위한 특징변수 유효성 검증)

  • Kim, Chang-Hyun;Kim, Jae-Yeol;Yu, Hong-Yeon;Hong, Sung-Hoon
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.16 no.6
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    • pp.62-70
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    • 2007
  • In this study, the natural flaws in welding parts are classified using the signal pattern classification method. The storage digital oscilloscope including FFT function and enveloped waveform generator is used and the signal pattern recognition procedure is made up the digital signal processing, feature extraction, feature selection and classifier design. It is composed with and discussed using the distance classifier that is based on euclidean distance the empirical Bayesian classifier. Feature extraction is performed using the class-mean scatter criteria. The signal pattern classification method is applied to the signal pattern recognition of natural flaws.

Fatigue Life Evaluation of Butt-Welded Tubular Joints

  • Kim, Dong-Su;Nho, In-Sik
    • Journal of Ocean Engineering and Technology
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    • v.17 no.2
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    • pp.34-39
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    • 2003
  • Recent deepwater offshore structures in the Gulf of Mexico utilize butt welded tubular joints. Application of a welded tubular joint includes tendons, production risers, and steel catenary risers. Fatigue life assessment of these joints becomes more critical, as the structures to which they are attached are allowed to undergo cyclic and sometimes large displacements around an anchored position. Estimation of the fatigue behavior of these tubular members in the design stage is generally condrcted by using S-N curves, as specified in the codeds and standards. Applying the stress concentration factor of the welded structure to the S-N approach often results in a very conservative assessment, because the stress field acting on the tubular has a non-uniform distribution through the thickness. Fatigue life analysis using fracture mechanics has been applied in the design of the catenary risers. This technology enables the engineer to establish proper requirements on weld quality and inspection acceptance criteria to assure satisfactory structural integrity during its design life. It also provides guidance on proper design curves and a methodology for accounting for the effects of non-uniform stress distribution through the wall thickness. Still, there is inconsistency when designing tubular joints using a conventional S-N approach and when specifying weld flaw acceptance criteria using fracture mechanics approach. This study developed fatigue curves that are consistent with both the S-N approach and the fracture mechanics approach. Accounting for non-uniform stress distribution and threshold stress intensity factor were key parameters in relating both approaches. A series of S-N curves, generated from the fracture mechanics approach, were compared to the existing S-N curves. For flat plate butt joint, the S-N curve generated from fracture mechanics matches with the IIW class 100 curve when initial crack depth was 0.5 mm (0.02 ). The new curves for tubular joint agree very well with the experimental results. The comparison also indicated the degree of conservatism built into the API X design curve.

Evaluation of Limit Loads for Circumferentially Cracked Pipes Under Combined Loadings (원주방향 표면 결함이 존재하는 배관에 가해지는 비틀림을 포함한 복합하중에 대한 한계하중식 제시)

  • Ryu, Ho-Wan;Han, Jae-Jun;Kim, Yun-Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.5
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    • pp.453-460
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    • 2015
  • Since the Fukushima nuclear accident, several researchers are extensively studying the effect of torsion on the piping systems In nuclear power plants. Piping installations in power plants with a circumferential crack can be operated under combined loading conditions such as bending and torsion. ASME Code provides flaw evaluations for fully plastic fractures using limit load criteria for the structural integrity of the cracked pipes. According to the recent version of Code, combined loadings are provided only for the membrane and bending. Even though actual operating conditions have torsion loading, the methodology for evaluating torsion load is not established. This paper provides the results of limit load analyses by using finite element models for circumferentially cracked pipes under pure bending, pure torsion, and combined bending and torsion with tension. Theoretical limit load solutions based on net-section fully plastic criteria are suggested and verified with the results of finite element analyses.

Fatigue Life Evaluation of Butt-Welded Tubular Joints

  • Kim, Dong-Sup;Nho, In-Sik
    • International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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    • v.6 no.1
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    • pp.69-74
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    • 2003
  • Recent deepwater offshore structures in the Gulf of Mexico utilize butt welded tubular joints. Application of a welded tubular joint includes tendons, production risers, and steel catenary risers. Fatigue life assessment of these joints becomes more critical, as the structures to which they are attached are allowed to undergo cyclic and sometimes large displacements around an anchored position. Estimation of the fatigue behavior of these tubular members in the design stage is generally conducted by using S-N curves, as specified in the codes and standards. Applying the stress concentration factor of the welded structure to the S-N approach often results in a very conservative assessment, because the stress field acting on the tubular has a non-uniform distribution through the thickness. Fatigue life analysis using fracture mechanics has been applied in the design of the catenary risers. This technology enables the engineer to establish proper requirements on weld quality and inspection acceptance criteria to assure satisfactory structural integrity during its design life. It also provides guidance on proper design curves and a methodology for accounting for the effects of non-uniform stress distribution through the wall thickness. Still, there is inconsistency when designing tubular joints using a conventional S-N approach and when specifying weld flaw acceptance criteria using fracture mechanics approach. This study developed fatigue curves that are consistent with both the S-N approach and the fracture mechanics approach. Accounting for non-uniform stress distribution and threshold stress intensity factor were key parameters in relating both approaches. A series of S-N curves, generated from the fracture mechanics approach, were compared to the existing S-N curves. For flat plate butt joint, the S-N curve generated from fracture mechanics matches with the IIW class 100 curve when initial crack depth was 0.5 mm (0.02). The new curves for tubular joint agree very well with the experimental results. The comparison also indicated the degree of conservatism built into the API X design curve.

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A Comprehensive Performance Evaluation in Collaborative Filtering (협업필터링에서 포괄적 성능평가 모델)

  • Yu, Seok-Jong
    • Journal of the Korea Society of Computer and Information
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    • v.17 no.4
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    • pp.83-90
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    • 2012
  • In e-commerce systems that deal with a large number of items, the function of personalized recommendation is essential. Collaborative filtering that is a successful recommendation algorithm, suffers from the sparsity, cold-start, and scalability restrictions. Additionally, this work raises a new flaw of the algorithm, inconsistent performance of recommendation. This is also not measurable by the current MAE-based evaluation that does not consider the deviation of prediction error, and furthermore is performed independently of precision and recall measurement. To evaluate the collaborative filtering comprehensively, this work proposes an extended evaluation model that includes the current criteria such as MAE, Precision, Recall, deviation, and applies it to cluster-based combined collaborative filtering.

Effect of tack of Fusion Defects on Short-Term Performance of Polyethylene Electrofusion Joints (폴리에틸렌 배관 전기융착부 단기성능 평가를 위한 융합물량 영향 평가)

  • Kil, Seong-Hee;Kwon, Jeong-Rock;Jo, Ji-Hwan
    • Journal of Energy Engineering
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    • v.14 no.2 s.42
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    • pp.153-158
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    • 2005
  • In order to investigate the short-term performance of polyethylene electrofusion joints, the mechanical tests and stress analysis have been conducted to the artificially defected weld joints. The defects of lack of fusion with a square-type were fabricated with 10, 20, 30, 40, 50, 60$\%$ size of the width of heat-ing wire zone, respectively. In this defect sires range, both tensile and bending test results showed the dependence of defect size to the electrofusion joints performance, but both sustained pressure and crush test results didn't. The numerical stress analysis results including the soil and internal pressures, tensile and bend-ing stresses clearly showed the dependence of fusion defect size. Based on both mechanical test and stress analysis results, the maximum acceptable defect size in polyethylene electrofusion joints is discussed.

Classification of Smartphone Game based on Mechanics (게임 메커니즘에 따른 스마트폰 게임 분류 연구)

  • Chun, Yeonbi;Chang, Sung Kyun;Woo, Tack
    • Journal of Korea Game Society
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    • v.12 no.6
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    • pp.15-24
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    • 2012
  • The recent growth of smartphone users and high speed network has fueled the expansion of the market for mobile application. Among these applications with various purposes, smartphone games are the hottest contents on this market. Smartphone games are far different from former games due to their new input and output interface (e.g. touch sensors and gyro sensors).It is possible that the most resonable way to categorize these new smartphone games is comparisons of different objects, in this case, various smarphone games. But there exists no classification of the games neither for the use of the market nor the purpose of researches. Even though there are few classifications for games, those classifications have a major flaw that their criteria are derived from superficial features of games. In this paper, we propose a new method to categorize smartphone games through game mechanics of principal design components.

Development of an Integrity Evaluation System (WIES) for Fuel Channels in CANDU Reactors (중수로 연료관 건전성 평가시스템(WIES) 개발)

  • Choi, Sung-Nam;Kim, Hyung-Nam;Yoo, Hyun-Joo;Kwon, Dong-Kee;Hwang, Won-Gul
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.9
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    • pp.1273-1279
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    • 2010
  • Pressure tubes at the CANada Deuterium Uranium (CANDU) nuclear power plants are periodically inspected in accordance with the CSA N285.4 code. If flaws that do not satisfy the criteria given in CSA N285.4 are detected, the code permits a fitness-for-service assessment to determine the acceptability of the flawed pressure tubes. In this paper, the Wolsong In-service Evaluation System (WIES) is introduced; this system has been developed for the assessment of the flawed pressure tubes and is based on CSA N285.8. Since the system evaluates the integrity of flawed pressure tubes exactly and promptly during an in-service inspection, it will help in operating the Wolsong nuclear power plants without prolonging the outage period.