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Study for J-integral analysis with re-distributed residual stress by cutting in welded pipe
노지선,김명현 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11
In the structural integrity assessment based on existing BS 7910 code, the residual stress near the weld metal is very conservatively calculated and applied as the yield strength level based on the empirical equation of BS 7910 code. However, when a plate is welded, cooling and cut, the residual stress is re-distributed, resulting in a lower level of residual stress than the existing value. This study predicts J-integral at crack tip by considering the redistributed residual stress according to the cutting methods. This study also proposes a reasonable method to reduce a conservatism of the existing ECA (Engineering critical assessment).
산불 지역 인공·자연복원에 따른 Landsat영상 기반 식생지수 비교
노지선,최재용,Noh, Jiseon,Choi, Jaeyong 한국환경복원기술학회 2022 한국환경복원기술학회지 Vol.25 No.5
This study aims to classify forest fire-affected areas, identify forest types by the intensity of forest fire damage using multi-time Landsat-satellite images before and after forest fires and to analyze the effects of artificial restoration sites and natural restoration sites. The difference in the values of the Normalized Burned Ratio(NBR) before and after forest fire damage not only maximized the identification of forest fire affected and unaffected areas, but also quantified the intensity of forest fire damage. The index was also used to confirm that the higher the intensity of forest fire damage in all forest fire-affected areas, the higher the proportion of coniferous forests, relatively. Monitoring was conducted after forest fires through Normalized Difference Vegetation Index(NDVI), an index suitable for the analysis of effects by restoration type and the NDVI values for artificial restoration sites were found to no longer be higher after recovering the average NDVI prior to the forest fire. On the other hand, the natural restoration site witnessed that the average NDVI value gradually became higher than before the forest fires. The study result confirms the natural resilience of forests and these results can serve as a basis for decision-making for future restoration plans for the forest fire affected areas. Further analysis with various conditions is required to improve accuracy and utilization for the policies, in particular, spatial analysis through forest maps as well as review through site checks before and immediately after forest fires. More precise analysis on the effects of restoration will be available based on a long term monitoring.
Welding Deformation Characteristics and Mitigation Method of Hub Flange
노지선,박창우,박중구 대한용접접합학회 2022 대한용접·접합학회지 Vol.40 No.5
This paper considers a 3-D thermos-mechanical analysis to investigate the effect of welding direction, tack weld, root gap and welding process on welding deformation in hub flange and pipe joint. Multi-pass welding for a single ‘V’ butt-weld joint geometry is simulated and 3-D weld path analysis is used with realistic weld bead. 3 different welding direction (2-path, 4-path diagonally, 4-path from the bottom) are analyzed and how the presence or absence of tack weld affects deformation was analyzed. Also, 3 different cases for root gaps (2, 3, 4mm) are considered and finite element analysis results are compared. In addition, the effects of the welding process on the hub flange face are determined. From the results, perpendicularity of the hub flange face is found to be strongly dependent on the welding direction and tack welds. On the other hand, root gap has small influence for tilting. The results also showed the feasibility of mitigating and controlling the welding deformation, and optimum selection of welding method was confirmed.
해양레저용 요트의 마스트 러그 형상에 따른 응력집중계수 추정
노지선,오동진,김명현,Roh, Ji-Sun,Oh, Dong-Jin,Kim, Myung-Hyun 대한용접접합학회 2012 대한용접·접합학회지 Vol.30 No.1
Recently, according to the increase of income and development of quality of life, the leisure industry has been developed. In particular, the interest of design and manufacture technology of leisure yacht has significantly increased. However, domestic market of leisure ships is currently in its initiating stage. So research and development for structural strength of leisure yacht need to be investigated. In this study, lug of yacht's mast which is known for a critical damage region is explicitly considered. This paper deals with the estimation of stress concentration factors (SCFs) for lug of yacht's mast depending on dimensions of lug using hot spot stress. Also, SCF formulae is suggested using parametric study.
Study for re-distributed residual stress by cutting in welded pipe
노지선 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
Welded piping made of seam welding using rolling steel plates produces more roundness deformation than seamless piping. This is mainly due to the re-distributed of the existing residual stress by cutting process in the presence of residual stress by seam welding for pipe construction. In this study, the characteristics of re-distributed residual stress is identified depending on the method of cutting and constraints of pipe, cutting angle, correcting pipe shapes according to pipe materials. It also plans to propose a mitigation of conservatism for selecting of secondary stress at yield stress level in structural integrity assessment (ECA, Engineering critical assessment).
용접배관 절단에 따른 잔류응력 재분포 특성 및 구조건전성평가 연구
노지선,이명수,김명현 대한용접접합학회 2022 대한용접·접합학회지 Vol.40 No.2
Welded rolled up steel pipe plates undergo more roundness deformation than seamless pipes. The main reason is that the existing residual stress after welding was re-distributed by the cutting process. The objective of this research is to investigate the effect of the constraint on the cutting process through finite element analysis (FEA) to minimize deformation. To include the effect of the cutting simulation, the external constraint was used as the mechanical restraint, and a welded pipe without constraints was used for comparison purposes. The results show that the cutting deforma- tion and residual stress were both significantly reduced under the effect of external constraints. Moreover, the method of reducing conservatism in engineering critical assessment (ECA) was proposed using residual stress re-distribution.
핫 스팟 응력을 이용한 요트 알루미늄 마스트 러그의 피로강도 평가
노지선(Ji-Sun Roh),김명현(Myung-Hyun Kim) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6
Recently, according to the increase of income and quality development of life, a variety of leisure boats and facilities has been invigorated. So interests about development of design and the production technology have been increased. However, research & development about yachts has been neglected due to its situation that market of domestic leisure ships is in level of beginning. Also, skill of technology lags behind compare to advanced country. Therefore, it is required to evaluate the local strength of yacht. In case of accident of yacht, the major failure region is a connection between mast and deck or lug of mast. This paper deals with the fatigue strength assessment for lug of yacht's mast using hot spot stress.