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박재학(Jai Hak Park),Gennadiy P. Nikishkov 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
A SGBEM-FEM alternating method is extended to analyze a through-thickness crack problem. The effect of shape of boundary element mesh on the accuracy of stress intensity factor is examined. It is noted that the fictitious portion of the boundary element mesh, which is located outside the body, plays an important role in the method. Also the effect of the boundary condition imposed on the edge of boundary element mesh is examined. In order to check the accuracy of the method, we considered a sample problem of a through-thickness crack with unequal surface lengths. The obtained stress intensity factors are compared with the known solutions or the results obtained from finite element method. Using the proposed method stress corrosion crack growth simulation is performed for a through-thickness crack with unequal surface lengths.
선형적으로 변하는 단면적을 가진 균열에서의 누설률 평가
박재학(Jai Hak Park) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.9
원자력 배관 설계에는 파단전 누설(leak before break, LBB) 개념이 사용되고 있다. LBB 개념의 적용을 위해서는 관통균열을 통한 누설률을 정확하게 예측할 수 있어야 한다. 단면적이 일정한 관통균열에 대한 누설률 해석은 많이 이루어지고 있으나 실제 관찰되는 관통균열에서는 배관 내면 쪽과 외면 쪽의 단면적이 다른 경우가 많이 발생된다. 따라서 본 논문에서는 유동경로를 따라 선형적으로 변화하는 단면적을 가진 관통균열에 대하여 누설률을 평가하여 단면적의 분포가 누설률에 미치는 영향을 살펴보았다. 또한 클래딩 등에 의하여 두께 방향으로 이중 재료로 된 배관에 존재하는 관통균열에 대해서도 누설률을 평가하여 유동경로를 따라 달라지는 균열면 형태학적 변수가 누설률에 미치는 영향을 살펴보았다. The leak before break (LBB) concept is used in pipe line design for nuclear power plants. For application of the LBB concept, leak rates through cracks should be evaluated accurately. Usually leak late analyses are performed for through-thickness cracks with constant cross-sectional area. However, the cross-sectional area at the inner pipe surface of a crack can be different from that at the outer surface. In this paper, leak rate analyses are performed for the cracks with linearly-varying cross-sectional areas. The effect of varying the cross-sectional area on leak rates was examined. Leak rates were also evaluated for cracks in bi-material pipes. Finally, the effects of crack surface morphology parameters on leak rates were examined.
박재학(Jai Hak Park),이재봉(Jae Bong Lee),최영환(Young Hwan Choi) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
A probabilistic integrity assessment program of pipes in nuclear power plants is developed. The program is named by P-PIE (Piping Probabilistic Integrity Evaluation) and based on existing PRAISE program. Using the program, the probabilities of leakage, big leak and fracture of pipes in nuclear power plants can be obtained. Preexisting cracks and initiated crack during the operation due to stress corrosion can be considered and growth of cracks due to stress corrosion cracking (SCC) and fatigue can be simulated. Operating stresses, thermal stresses, residual stresses and varying operation conditions can be considered in the program. Crack growth simulation is performed based on stress intensity factors and fracture is determined based on J integral or net section yielding. In order to check the accuracy of the program several example problems are solved and compared with the results from PRAISE. And the effects of several variables on the leak or failure probability are examined.
박재학(Park, Jai-Hak),강병진(Kang, Byung-Jin),임상호(Lim, Sang-Ho) 한국산학기술학회 2012 한국산학기술학회논문지 Vol.13 No.4
본 논문은 인천광역시 소재 직업교육훈련 기관의 직업훈련 만족도와 진로성숙도에 영향을 미치는 요인에 대 해서 알아보았다. 자비로 교육을 받는 직업교육훈련생이 직업교육훈련과정에서 직무능력을 향상시키기 위해 노력하고 있는 것으로 나타났다. 또한 “친지, 가족, 지인”의 권유로 직업교육훈련을 받으러 왔으며. 교육훈련을 장기를 선호하 고 학력이 낮을수록 진로성숙도가 높고 미혼자가 진로성숙도가 높게 나타났다. 회귀분석에서는 직업교육훈련 내용 만 족도는 진로성숙도에 영향을 미치는 것으로 나타났다. 따라서 관계당국에서는 직업교육훈련과정 프로그램이 충실하게 운영할 수 있는 방안을 모색하여야 할 것이다. In this paper, in Incheon, vocational education and training satisfaction of vocational training institutions and on the factors affecting the career maturity were investigated. Mercy Vocational trainees receive training in vocational education and training to improve skills in the process it was found that commitment. In addition, "friends, family, acquaintances," with the encouragement of vocational education and training has been to collect. Prefer long-term training and career maturity and high educated singles with lower career maturity were higher. Regression analysis of satisfaction in the vocational education and training information, influence on career maturity. Therefore, the authorities concerned in the vocational education and training program faithfully find ways to operate should be.
유한요소 교호법을 이용한 삼차원 균열의 탄소성 J 적분 해석
박재학(Jai Hak Park) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.2
SGBEM(Symmetric Galerkin Boundary Element Method)-FEM alternating method has been proposed by Nikishkov, Park and Atluri. In the proposed method, arbitrarily shaped three-dimensional crack problems can be solved by alternating between the crack solution in an infinite body and the finite element solution without a crack. In the previous study, the SGBEM-FEM alternating method was extended further in order to solve elastic-plastic crack problems and to obtain elastic-plastic stress fields. For the elastic-plastic analysis the algorithm developed by Nikishkov et al. is used after modification. In the algorithm, the initial stress method is used to obtain elasticplastic stress and strain fields. In this paper, elastic-plastic J integrals for three-dimensional cracks are obtained using the method. For that purpose, accurate values of displacement gradients and stresses are necessary on an integration path. In order to improve the accuracy of stress near crack surfaces, coordinate transformation and partitioning of integration domain are used. The coordinate transformation produces a transformation Jacobian, which cancels the singularity of the integrand. Using the developed program, simple three-dimensional crack problems are solved and elastic and elastic-plastic J integrals are obtained. The obtained J integrals are compared with the values obtained using a handbook solution. It is noted that J integrals obtained from the alternating method are close to the values from the handbook.