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김진환(J. H. KIM),남기우(K. W. Nam),안석환(S. H. Ahn),강창룡(C. R. Kang),박인덕(I. D. Park) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
Even if duplex steel made improvement the strength and corrosion resistance properties, the necessity of steel which has long life in severe environment increases with industrial development. Newly developed duplex stainless steel is the super duple stainless steel which contain 25% of chromium. We investigated the fatigue crack propagation of heat affected zone(HAZ) in super duplex stainless steel. The HAZ of super duplex stainless steel propagated more faster base metal of super duplex stainless steel. And we analysed acoustic emission signals during the fatigue test by time-frequency analysis method. And as a result of time-frequency was 200-400 ㎑ was obtained by fatigue crack propagation and 500 ㎑ was obtained by dimple and separate of inclusion.
김진환(J.H. Kim),안석환(S.H. Ahn),김현수(H.S. Kim),남기우(K.W. Nam),김선진(S.J. Kim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
Fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. However, effects of local wall thinning on strength and fracture behaviors of piping system were not well studied. Acoustic emission(AE) has been widely used in various fields, because of its extreme sensitivity, dynamic detection ability and location of growing defects. In this study, we investigated failure modes of local wall thinning pipes and AE signals by bending test. As results of test, we could divide four types of failure modes of ovalization, ovalization+cracking, local buckling and buckling+cracking. And fracture behaviors of Elastic range, yield range, plastic range and cracking progress could be evaluated in bending test by AE counts, accumulation counts and time frequency analysis. It is expected to be basic data that can protect a risk according to local wall thinning of pipes, as a real time test of AE.
김진환(J.W. Kim) 한국전산유체공학회 2007 한국전산유체공학회 학술대회논문집 Vol.2007 No.-
This paper is a continuation of the recent development on the hermite-based divergence free basis function and deals with a non-isothermal fluid flow thru the buoyancy driven flow in a square cavity with temperature difference across the two sides. The basis functions for the velocities consist of the hermite function and its curl. However, the basis for the temperature are the hermite function and its gradienst. Hence, the number of degrees of freedom at a node becomes 6, which are the stream function, two velocities, the temperature and its x- and y-derivatives. Numerical results for the streamlines, the temperatures, the x-velocities and the y-velocities show good agreements with those of De vahl Davis[7].
이차원 비압축성 유동 계산을 위한 Hermite 쌍 3차 유동 함수법
김진환(J.W. Kim) 한국전산유체공학회 2008 한국전산유체공학회 학술대회논문집 Vol.2008 No.-
This paper is an extension of previous study[9] on a development of a divergence-free element method using a hermite interpolated stream function. Divergence-free velocity bases defined on rectangles derived herein produce pointwise divergence-free flow fields. Hence the explicit imposition of continuity constraint is not necessary and the Galerkin finite element formulation for velocities does not involve the pressure. The divergence-free element of the previous study employed hermite serendipity cubic for interpolation of stream function, and it has been noted a possible discontinuity in variables along element interfaces. This deficiency can be removed by use of a hermite bicubic interpolated stream function, which requires at each element corners four degrees-of-freedom such as the unknown variable, its x- and y-derivatives and its cross derivative. Detailed derivations are presented for both solenoidal and irrotational bases from the hermite bicubic interpolated stream function. Numerical tests are performed on the lid-driven cavity flow, and results are compared with those from hermite serendipity cubics and a stabilized finite element method by Illinca et al[7].