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적응가변구조 방법을 이용한 DC MOTOR 제어에 관한 연구
하재해,한창훈,조용갑,최부귀 동아대학교 공과대학 부설 한국자원개발연구소 1994 硏究報告 Vol.18 No.1
Direct methods and indirect methods for the adaptive control of linear plant, DC motor, are currently well known. Recently, methods for combining direct and indirect methods have also been suggested. In this note the latter method is combined with the variable structure method. New adaptive laws are suggested which overcome the principal draw-backs of the variable structure method. While the direct and indirect components of the new method assure stability, the variable structure component improves the transient response of the system. Simulation results are presented to show that the overall system is asymptotically stable in the ideal case, and exhibits robustness and improved performance in the presence of perturbations.
가솔린-LP가스燃料가 單機筒 SI機關의 性能에 미치는 影響에 關한 實驗的 硏究
하재기 김천과학대학 1998 김천과학대학 논문집 Vol.24 No.-
This is a study to improve the performance of the SI engine. In this study, a existing gasoline was modified to a LPG-dedicated engine which can be operated with LPG. This modified model was tested with various load change, being compared with a gasoline engine, the results are as follows; 1. LPG-dedicated engine can be operated with better fuel economy (about 20~30%) and better thermal efficiency(about 10%). 2. The discharge density of hydrocarbon is not influenced by engine load, and carbon monoxide the is a lowest in the optimal combustion condition. 3. The attrition rate of lubricant does not change with load change, but gasoline engine is a little higher in lower load category.
하재기 김천과학대학 2005 김천과학대학 논문집 Vol.31 No.-
An experimental study was carried out to obtain fundamental data about liquid state gas fuel supply pump. Two types of pumps were used. One was a regenerative type which was generally used for gasoline engine fuel system. The other was a roller-vane type which was also used for automotive engine fuel system. The experiments were performed to obtain flow rate as a function of pressure differences and temperatures. The regenerative pump had low flow rate at some experimental conditions. Therefore, it is impossible to use this pump system for liquid state gas fuel supply system. On the other hand, the roller-vane type pump can be applied to the system only if its check valve is modified. Cavitation might occur in this system which can result in system noise, flow rate variation, and pump durability problem. To solve these problems the system is needed to increase NPSHre.
등방성체 동적 광탄성 하이브리드 법 개발 및 에너지 해방률에 대한 연구
하재기 김천과학대학 2001 김천과학대학 논문집 Vol.27 No.-
In this paper, dynamic photoelastic hybrid method is developed and its validity is certified. And dynamic energy release rate was calculated. The dynamic photoelastlic hybrid method can be used on the obtaining of dynamic stress intensity factors and dynamic stress components. The effect of crack length on the dynamic stress intensity factors is less than those on the static stress intensity factors. When structures are under the dynamic mixed mode load, dynamic stress intensity factor of mode I is almost produced.
AC4C재의 기계적 성질 및 균열 진전 특성에 관한 연구
하재기,이종형 金烏工科大學校 1992 論文集 Vol.13 No.-
This Study investigates the effect of the heat treatment on the mechanical property especially on the fatique strength of the AL casting alloy. The material which is used in the experiment is AL-Si-Mg alloy. It is the only treat-treatable non-corrosive alloy, and it is age-hardend as cast by the squeeze casting method.
동적 모드Ⅲ 하중을 받는 등방성체/직교이방성체 이종재료의 파이버 각도변화가 응력 및 위 성분에 미치는 영향
하재기,유재용 김천과학대학 2001 김천과학대학 논문집 Vol.27 No.-
In interpreting problems of bimaterial fracture mechanics, it is important to understand stress and displacement on the interface of bimaterial. Especially, a crack contained in the interface of the bimaterial has more complicated and dangerous fracture behavior than a crack contained in general material does. Therefore, the fracture problems of an interface crack in the bimaterial has been attracted by many researchers. In this paper, a crack on bond interface gets the load of dynamic modeⅢ and proceeds to the steady state when the mediums, i.e., isotropic/orthotropic material, are combined. In other words, we induce stress field and displacement field near a crack tip, and general stress field and displacement field apart from a crack tip in case that the velocity of a crack and direction are proportion to the change of time. And we then investigate the effect of the fiber direction of isotropic/orthotropic material to the stress and displacement fields of modeⅢ occured in the bi-material interfacial under constant velocity crack.
UN-GGIM 및 UN-GGIM-AP의 활동 동향 분석에 관한 연구
하재서(Ha, Jae Seo),정다운(Jeong, Da Woon),김경희(Kim, Kyung Hee),이명호(Lee, Myeoung Ho),신동빈(Shin, Dong Bin) 대한공간정보학회 2021 대한공간정보학회지 Vol.29 No.3
최근 UN과 중국이 상호 간에 협력하여 중국의 Deqing 지역에 세계 공간정보 지식혁신센터를 설립하기로 합의하였으며, 일본은 재난 및 통계와 관련한 공간정보 활용 사례들을 꾸준히 홍보하는 등 국제 무대에서의 입지를 넓히고 있다. 반면 우리나라의 경우, UN-GGIM 창립 총회를 개최한 이후 공간정보 관련 국제회의에서의 뚜렷한 입지를 선점하지 못하고 있으며, 현재는 공간정보 관련 국제 동향 정도를 모니터링하는 수준에 그치고 있는 실정이다. 향후에는 우리나라가 공간정보 관련 국제회의에서의 입지를 제고하고, 상시적으로 대응 가능한 방안을 마련하여 선도적인 지위 확보를 위한 기틀을 마련해야 한다. 이를 위해 본 연구는 UN-GGIM 및 UN-GGIM-AP의 활동 동향을 분석하고, 이에 따른 시사점을 통해 국제회의에서의 우리나라의 대응 방안에 대해 제시하는 것을 목적으로 한다. 이러한 대응 방안이 실제 계획에 반영된다면 공간정보 관련 국제사회에서 우리나라의 위상을 제고할 수 있을 것으로 전망한다. Recently, the United Nations and China agreed to establish a ‘global geospatial knowledge and innovation center’ in China’s Deqing area in cooperation with each other. In the case of Japan, it is expanding its presence on the international stage by continuously promoting cases of use of geospatial information related to disasters and statistics. However, since the inaugural UN-GGIM general meeting, Korea has not been able to occupy a clear position in international conferences related to geospatial data. Even now, it is only at the level of monitoring the degree of international trends related to geospatial data. In the future, Korea should improve its position in international conferences related to geospatial data. In addition, it is necessary to prepare a framework for securing a leading position by preparing a plan that can respond to international conferences on a regular basis. Therefore, this study analyzes the activity trends of UN-GGIM and UN-GGIM-AP, and suggests Korea’s response plan at international conferences. If these countermeasures are reflected in the plan, it is expected that Korea’s status will be improved in the international community related to geospatial data.