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Al-Si 도금된 보론강 레이저 소스에 따른 레이저 용접부의 미세조직과 기계적 성질에 미치는 핫스탬핑 처리의 영향
오명환,공종판,권민석,강정윤,Oh, Myeong-Hwan,Kong, Jong-Pan,Kwon, Min-Suck,Kang, Chung-Yun 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.6
In this study, the effect of laser source($CO_2$ and Nd:YAG) on the microstructure and tensile properties of laser welded Al-Si coated boron steel(1.2mmt) was investigated with before and after hot-stamping. In case of as welds condition, fracture occurred in base metal unrelated to the laser source. It could be explained that tensile strength of fusion zone composed of martensite and bainite is higher than that of base metal that contains a lot of ferrite despite dilution of Al and Si from coating layer to fusion zone. In case of hot-stamping condition, the fracture occurred in fusion zone irrelevant to laser source and the tensile strength was lower than hot stamped base metal. In the $CO_2$ laser welds, $Fe_3$(Al,Si) formed near the bond line was transformed into ferrite during hot-stamping. Therefore tensile strength of bond line is lower than that of base metal and center of fusion zone and the fracture occurred in the bond line. On the other hand, in the Nd:YAG laser welds, the higher concentration of Al formed the ferrite in the fusion zone during hot-stamping treatment. Also, the thickness of centerline was thinner than that of base metal. Therefore, it is considered that fracture occurred in centerline of fusion zone due to effect of concentration stress, and it leaded to a lower tensile strength and elongation.
A Frozen Time Receding Horizon Control for a Linear Discrete Time-Varying System
오명환,오준호,Oh, Myung-Hwan,Oh, Jun-Ho Institute of Control 2010 제어·로봇·시스템학회 논문지 Vol.16 No.2
In the case of a linear time-varying system, it is difficult to apply the conventional stability conditions of RHC (Receding Horizon Control) to real physical systems because of computational complexity comes from time-varying system and backward Riccati equation. Therefore, in this study, a frozen time RHC for a linear discrete time-varying system is proposed. Since the proposed control law is obtained by time-invariant Riccati equation solved by forward iterations at each control time, its stability can be ensured by matrix inequality condition and the stability condition based on horizon for a time-invariant system, and they can be applied to real physical systems effectively in comparison with the conventional RHC.
Al-Si 용융 도금된 보론강 CO<sub>2</sub> 레이저 용접부의 미세조직과 기계적 성질에 미치는 핫스탬핑 처리의 영향
오명환,공종판,신현정,권민석,정병훈,강정윤,Oh, Myeonghwan,Kong, Jongpan,Shin, Hyeonjeong,Kwon, Minsuck,Jung, Byunghun,Kang, Chungyun 한국레이저가공학회 2013 한국레이저가공학회지 Vol.16 No.3
In this study, Al-Si coated boron steel(1.2 mm) were laser welded by $CO_2$ laser and hot-stamping was applied to the laser joints. Tensile properties and microstructures of the joints were investigated before and after hot-stamping. Tensile and yield strengths of the as welded specimen similar with base metal and fracture occurred base metal of boron steel. Although, in case of heat treated specimen, fracture occurred fusion zone that Al segregated zone near the bond line. These could be explained by the existence of ferrite, in the Al segregated zone near the bond line and base metal of boron steel. Before hot-stamping, hardness of base metal is lower than fusion zone and heat affected zone in spite of exist Al segregation zone($Fe_3$(Al,Si)). So fracture occurred base metal. Although, after hot-stamping, microstructure of base metal and welds zone transformed to martensite and bainite except in Al segregation zone near the bond line that $Fe_3$(Al,Si) transformed to a-ferrite. So fracture occurred Al segregation zone near the bond line.
Al-Cu 합금의 일방향 응고조직과 기계적 성질에 미치는 냉간압연의 영향
오명환,나형용 ( Myung Hwan Oh,Hyong Yong Ra ) 한국주조공학회 1983 한국주조공학회지 Vol.3 No.1
The influence of columnar dendirtes on the mechanical properties of Al-1% Cu alloys as unifirectionalloy solidified under the conditions of controlled crystal growth rate (R) and temperature gradient (G) was investigated. And the change of metallography and mechanical properties when unifirectionalloy solidified alloys and cast alloys were cold-rolled from 10% to 90% in reduction ratio was studied. The results are as follows: 1. The elongation and yield strength of unifirectionalloy solidified alloy are higher then those of cast alloy, but there is a little decrease in ultimate tensile strength. 2. The metallography and mechanical properties are changeable with the primary arm spacings when the unidirectionalloy solidified alloys were cold-rolled from 10% to 90% in reduction ratio. An alloy with larger primary arm spacings was easily changeable in metallography and mechanical properties when it was cold-rolled. 3. The tensile strength of transversely cold-rolled to 90% in reduction ratio was higher then that of longitudionalloy cold-rolled to 90% in reduction ratio. In the case, the fractorgraphs of fractured surface showed that the cast alloy and the unifirectionalloy solidified alloy was ductile-fractured, but the surface of transversely cold-rolled to 90% reduction of unidirection alloy solidified was slip plane qracture.
심장질환 및 당뇨병의 재발 위험요인의 예측을 위한 SVM 기반 회귀분석의 성능비교
오명환(Myeong Hwan Oh),정용규(Yong Gyu Jung) 한국IT마케팅학회 2014 한국IT마케팅학회 학술대회 Vol.2014 No.1
Recently, as the Korean Digital equipment and technology develops, by analyzing the stored data, in order to provide my users know the new information, data mining techniques have been utilized. Data mining techniques are verified according to the purpose to be used, confirmation, discovered, are used for purposes such as prediction. In this paper, not only patients with no cardiovascular or coronary artery disease is blood sugar valued dye in the risk factors that provided, blood pressure, aspirin, to evaluate the risk of heart disease and diabetes to have a non smoking, and to predict the risk, that give us the user is desired, using a regression analysis. Regression analysis, are suitable for predictive analytics, you will be able to perform a variety of regression analysis. Typically there is an SVM-based regression analysis. SVM is analysis capability for performing error generalized in a direction to a minimum is evaluated as excellent. By analyzing the SVM-based regression and general multiple regression analysis to compare the performance SVM.
홈 네트워크 게이트웨이용 HAVi - Jini Bridge 설계
오명환(Myounghwan Oh),최훈(Hoon Choi) 한국정보과학회 2003 한국정보과학회 학술발표논문집 Vol.30 No.2Ⅲ
홈 네트워크란 가정 내 정보 가전 기기들이 하나의 네트워크로 통합되어 정보를 공유하고 제어하는 시스템으로서, 많은 홈 네트워크용 미들웨어들이 개발되어 표준화 되었다. 그러나 한가지 미들웨어로 가정내의 제어 네트워크, 데이터 네트워크 및 엔터테인먼트 네트워크 모두를 통합할 수 있는 방안은 아직 제시되지 않았으며, 둘 이상의 미들웨어를 연동하는 브릿지로 상호 연동하고자 하는 연구가 진행 중이다. 본 논문은 가정 내 엔터테인먼트 네트워크를 위한 미들웨어인 HAVi 를 데이터 네트워크를 위한 미들웨어인 Jini를 중심으로 통합하여 상호 연동하는 브릿지를 설계, 제시한다.
재실자의 시쾌적과 건물에너지성능을 고려한 슬랫형 블라인드 자동제어전략
오명환(Oh, Myung-Hwan),윤종호(Yoon, Jong-Ho),신우철(Shin, U-Cheol) 한국태양에너지학회 2011 한국태양에너지학회 학술대회논문집 Vol.2011 No.11
Glass Envelope is vulnerable to insulation performance and controling solar radiation. Insulation performance is consistently improving these days due to recent building energy saving policy in South Korea. However, solar control at glass envelope is still limited to meeting requirements of ideal high performance. Generally, Inside Blind plays an important role of solar controlinstead of glass which have a characteristics of transmitted solar.Unfortunately, most of them are controled by occupants and which method is not resonable in building energy. Therefore, achieving the high efficient performance building, automated control blind system considering reduction of building loads have to be adopted. Furthermore, considering occupants visual comport about removing discomfort glare is also essential.