Papers by Author: Young Jin Kim

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Authors: Seong In Moon, Ja Choon Koo, Jae Boong Choi, Young Jin Kim, Sung Sik Choi, Jeoung Gwen Lee
1773
Authors: Nam Su Huh, Ludwig Stumpfrock, Eberhard Roos, Yun Jae Kim, Young Jin Kim
Abstract: Application of the leak-before-break concept to nuclear piping requires accurate fracture mechanics assessment on pipes with postulated circumferential through-wall crack subject to combined tension and bending. One important element is determination of relevant J-resistance curve for pipes under combined loading. This paper provides experimental J estimation method for the circumferential through-wall cracked pipe under combined tension and bending, based on the load-crack opening displacement (COD) record to estimate J-resistance curve. To give confidence in the proposed method, the J results from detailed elastic-plastic finite element (FE) analysis are also compared with estimated J based not only on proposed method but also on conventional method using load-load line displacement, which shows that estimated J based on the proposed method provides reliable J estimates regardless of analysis condition, on the other hand, the conventional method using the load-load line displacement record gives erroneous results for shallow cracks.
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Authors: Yong Hoon Rim, Young Jin Kim, Sang Sik Lee, Joung H. Mun
Abstract: Equinus gait, defined as walking on one forefoot or both forefeet, has long been considered an undesirable characteristic in patients with a variety of neuromuscular disorders. In the equinus gait, the heel contact pattern is changed according to the severity, because an excessive ankle plantar flexion instigates rearfoot lifting in patients. However, no biomechanical severity index exists to evaluate the rehabilitation procedure of equinus gait. Therefore, we developed an SIEG (Severity Index of Equinus Gait) for nondestructive evaluation of the equinus gait and to validate the index with regard to 11 kinematic and kinetic factors of gait analysis. In this study, the 3-D heel contact pattern was considered for the development of a severity index. In order to verify the result, we compared the developed severity index values with ankle joint kinematic and kinetic factors in 3 test groups. As a result, the average SIEG values ranged between 10.45 (Normal group) and 26.61 (Severe group) and the highest correlation with regard to the 3 groups was shown in the developed severity index. Additionally, we also presented a fuzzy model using Takagi-Sugeno-Kang(TSK) logic with regard to the 12 factors in order to more accurately classify equinus gait.
1086
Authors: Nam Su Huh, Young Jin Kim, Y.H. Choi, J.S. Yang
195
Authors: Chang Sung Seok, Jae Sil Park, Young Jin Kim
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Authors: Young Jae Park, Yoon Suk Chang, Jae Boong Choi, Young Jin Kim
Abstract: Class 1 piping components of a certain old vintage nuclear power plant were designed by ANSI B31.1 code without a detailed fatigue evaluation such as the one required by recent ASME Section III code. These components may undergo fatigue damage when considering the continued operation beyond the design life whilst the inherent fatigue resistances of those may satisfy the corresponding implicit limits. In this paper, the alternative fatigue evaluation has been carried out explicitly for Class 1 piping of old nuclear power plant. At first, four representative nuclear piping systems were selected to check the operational adequacy. After characterization of conservative loading conditions based on design features, a series of finite element analyses have been performed and the cumulative usage factors were calculated to guarantee if the components at each system sustain adequate fatigue resistance. Finally, comparisons were drawn between the implicit fatigue design specifications and alternative explicit fatigue analysis results. Even though there were some exceptions, it was demonstrated that most components satisfied the current explicit fatigue criterion.
1659
Authors: Yun Jae Kim, Ja Choon Koo, Seong In Moon, Young Jin Kim
1767
Authors: Ja Choon Koo, H.S. Kim, Jae Boong Choi, Young Jin Kim
Abstract: Application of Hamilton’s theorem is limited to rigid body dynamics problems in spite of its benefit that always yield a set of first order differential equations as a model. From the fundamental formulation procedure, introduction of Hamilton’s principle to continuum problems differs from the traditional continuum modeling methodology that relies upon partial differential field equation. For the analysis of impact problems where highly nonlinear coupled models are norm, massively distributed computation schemes are usually employed and they significantly reduce computational cost and improve accuracy. With the parallel resources in mind, the present work applies Hamiltonian modeling approach to a shock propagation problem in continuous media. The formulated model which is in first order ordinary differential equations is efficiently calculated on a Beowulf based Linux parallel machines.
716
Authors: Young Jae Park, H.K. Kim, Yoon Suk Chang, Jae Boong Choi, Young Jin Kim
Abstract: A seamless analysis of complex geometry is one of greatly interesting topic. However, there are still gaps between the industrial applications and fundamental academic studies owing to time consuming modeling process. To resolve this problem, an auto mesh generation program based on grid-based approach has been developed for IT-product in the present study. At first, base mesh and skin mesh are generated using the information of entities which extracted from IGES file. Secondly the provisional core mesh with rugged boundary geometry is constructed by superimposing the skin mesh as well as the base mesh generated from the CAD model. Finally, the positions of boundary nodes are adjusted to make a qualified mesh by adapting node modification and smoothing techniques. Also, for the sake of verification of mesh quality, the hexahedral auto mesh constructed by the program is compared with the corresponding tetrahedral free mesh and hexahedral mapped mesh through static finite element analyses. Thereby, it is anticipated that the grid-based approach can be used as a promising pre-processor for integrity evaluation of various IT-products.
631
Authors: Young Jae Park, Byung Sun Kim, Han Ok Ko, Yoon Suk Chang, Jae Boong Choi, Young Jin Kim, Joon Seong Lee, C.S. Kim
Abstract: A seamless analysis of IT-related products, such as cellular phone, LCD monitor and note PC etc., which are thin and complex geometry is one of great concerns in product design. However, there is a considerable amount of gap between the industrial application and fundamental academic studies due to a time consuming detailed mesh generation. In order to settle the bottleneck, an auto mesh generation program based on a modified grid-based approach is proposed in this paper. At first, base mesh and skin mesh were generated using informations on entities which extracted from an IGES (Initial Graphics Exchange Specification) file. Secondly, a provisional core mesh with a rough boundary geometry was constructed by superimposing the skin mesh into the base mesh generated from CAD model. And then, positions of boundary nodes were redistributed to delineate exact geometry of the provisional mesh. Finally, good qualified meshes were constructed by moving the positions of the nodes and splitting elements along boundary edges. In conclusion, it is anticipated that the developed program can be used as a promising pre-processor for static or dynamic analysis of various IT-related products.
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