• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 학술대회 논문집 전문대학교육위원
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• pp.6-8
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• 2002

Generally in solar air conditioning system, the diode rectifier is used to build up DC link voltage from AC source. The diode rectifier is simple and cheap but it brings out the problems of low power factor and plentiful harmonics at the AC source. Also It can degrade the utilization rate of solar energy because the reverse of power flow cannot be made. Hence, in this paper to overcome the peak power problems in summer and to endure good AC input characteristics, solar air conditioning system using the PWM converter is proposed. A high input power factor of 97[%] and an efficiency of 98[%] are also obtained. The harmonic guide lines of proposed rectifier is no interfered with inverter switching, resulting in a simple, reliable and low cost ac to dc converters in comparison with the boost type current improving circuits.

• 한국연소학회지
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• 제9권1호
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• pp.25-31
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• 2004

Various types of the air/fuel pre-mixer have been designed and tested to investigate the combustion characteristics of the lean-premixed gas turbine combustor, such as NO emission and flame stability. One type of the pre-mixers has been selected and installed to a 70 kW lean-premixed gas turbine combustor. The concentrations of CO and NO were measured with varying equivalence ratios in the combustion chamber at ambient pressure. The result shows that the emissions of CO and NO are heavily affected by the shape of the pre-mixer. The NO and CO emissions decreased, as the mixing ratio of air and fuel increased. In addition, the NO emission of the lean-premixed low NOx combustor is more dependent on the equivalence ratio than that of the conventional combustor.

• 한국산학기술학회논문지
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• 제17권12호
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• pp.120-127
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• 2016

본 연구에서는 수문의 설치방향에 따른 최적의 설치방향을 규명하기 위하여, 모형 제작에 의한 수문 진동실험을 수행하고, 진동특성이 연구되어진다. 47.5m 원형게이트가 아크릴을 사용하여 1:31 축척으로 제작되고, 납으로 질량이 보완된다. 먼저 모형을 검증하기 위하여 모형의 고유진동수가 측정되고, 원형 수문의 유한요소 해석 값으로 부터 환산된 고유진동수와 비교된다. 모형은 1.6m 폭을 갖는 콘크리트 수로에서 정방향과 역방향 설치에 따른 각각의 실험이 이루어 졌다. 각 방향 실험에서는 수문 개방고와 상하류 수위에 따른 여러 조건에서 수직진동이 측정되어 졌다. 실험결과를 바탕으로 정뱡향과 역방향 설치에 대한 진동현상을 서로 비교 분석하였다. 정방향 모형은 수문이 많이 열렸을 때 하단부의 수평트러스 부재를 치는 뒤돌아 치는 와류에 의하여 진동이 크게 발생하였고, 작은 개방고에서 suction force에 의한 진동이 발생하였다. 그러나 역방향 모형에서는 이러한 현상이 발생하지 않는다. 마지막으로 95m 수문의 진동실험결과와 본 47.m의 실험결과를 같이 비교하여 평가하였다. 실험결과 여러 실험 조건에서 진동이 작게 측정되는 역방향 배치 모형이 더 합리적인 것으로 분석되었다.

• Journal of Advanced Marine Engineering and Technology
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• 제38권3호
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• pp.246-252
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• 2014

본논문은 150마력급 선내형 소형 워터제트 추진시스템 개발에 대한 연구이다. 워터제트는 흡입부, 임펠러, 디퓨저(공기확산기), 후진부와 메인 샤프트로 구성되어 있다. 워터제트의 구성품은 사형 주조후 정밀가공을 거쳐 개발하였다. 워터제트 추진기관의 개발은 각각의 부품에 대한 설계-제작-검사의 과정을 거쳐 최종 완성하였으며, 육상 시험 풀에서는 선체의 이동 없이 워터제트의 펌프 특성을 확인한 결과, 최대 37m/s의 유속과 0.29m3/s의 유량을 배출할 수 있는 성능을 확보하였다. 본 연구에서 개발된 워터제트 추진장치를 설치한 21ft 시험선을 사용하여 실증 연구를 수행하였다. 그 결과, 국내 연안에서 시험시 선체무게와 엔진등 기타 부수적인 무게가 대략 1.2ton 가량 이였으며 이 상태에서 엔진회전수 3,700rpm에서 최대시속 45km/h의 운항속도를 기록하였다.

• 한국농공학회논문집
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• 제54권3호
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• pp.113-124
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• 2012

Reliable estimation of energy load inside the greenhouse and the selection of cooling and heating facilities are very important preceding factors to save energy as well as initial and maintenance costs of operating a greenhouse. Recently, building energy simulation (BES) technique to simulate a model similar to the actual conditions through a variety of dynamic simulation methods, and predict and analyze the flow of energy is being actively introduced and developed. As a fundamental research to apply the BES technique which is mainly used for analysis of general buildings, to greenhouse, this research designed four types of naturally-ventilated greenhouses using one of commercial programs, TRNSYS, and then compared and analyzed their energy load properties, by applying meteorological data collected from six regions in Korea. When comparing the greenhouse load of each region depending on latitude and topographical characteristics through simulation, Chuncheon had nearly 9~49 % higher heating load per year than other regions, but its annual cooling load was the reverse to it. Except for Jeju, 1-2W type greenhouses in five regions showed about 17 % higher heating load than a widespan type greenhouse, and 1-2W type greenhouses in Chuncheon, Suwon, Cheongju, Daegu, Cheonju and Jeju had 23 %, 20 %, 17 %, 16 %, 18 % and 20 % higher cooling load respectively than a wide span-type one. Glasshouse and vinyl greenhouse showed 8~11 % and 10~12 % differences respectively in heating load, while 2~10 % and 7~10 % differences in cooling load respectively.

• Wind and Structures
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• 제25권6호
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• pp.507-535
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• 2017

In the strong wind shutdown state, the blade position significantly affects the streaming behavior and stability performance of wind turbine towers. By selecting the 3M horizontal axis wind turbine independently developed by Nanjing University of Aeronautics and Astronautics as the research object, the CFD method was adopted to simulate the flow field of the tower-blade system at eight shutdown positions within a single rotation period of blades. The effectiveness of the simulation method was validated by comparing the simulation results with standard curves. In addition, the dynamic property, aerostatic response, buckling stability and ultimate bearing capacity of the wind turbine system at different shutdown positions were calculated by using the finite element method. On this basis, the influence regularity of blade shutdown position on the wind-induced response and stability performance of wind turbine systems was derived, with the most unfavorable working conditions of wind-induced buckling failure of this type of wind turbines concluded. The research results implied that within a rotation period of the wind turbine blade, when the blade completely overlaps the tower (Working condition 1), the aerodynamic performance of the system is the poorest while the aerostatic response is relatively small. Since the influence of the structure's geometrical nonlinearity on the system wind-induced response is small, the maximum displacement only has a discrepancy of 0.04. With the blade rotating clockwise, its wind-induced stability performance presents a variation tendency of first-increase-then-decrease. Under Working condition 3, the critical instability wind speed reaches its maximum value, while the critical instability wind speed under Working condition 6 is the smallest. At the same time, the coupling effect between tower and blade leads to a reverse effect which can significantly improve the ultimate bearing capacity of the system. With the reduction of the area of tower shielded by blades, this reverse effect becomes more obvious.

• 대한기계학회논문집B
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• 제34권5호
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• pp.491-498
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• 2010

연료전지 자동차는 성능과 수명 측면에서, 전해질막의 가습이 필요하며, 이를 위해 반응기체인 공기, 수소의 높은 가습이 요구된다. 본 연구에서는 내경 75 mm공기공급관 내에 직접 삽입된 인젝터(노즐)과 액적제거를 위한 사이클론을 통한 가습장치를 고안하여 실험을 수행하였다. 충돌형 노즐 3 종류를 이용하여 분사압력, 공기 유량, 분사방향각도를 달리하여 실험을 수행하였다. 가습 성능을 분석하기 위해, 가습효율이라는 개념을 정의하였다. 별도의 외부 열공급원 없이 분사되는 물과 공기의 엔탈피가 자체 기화열 공급원으로, 분사되는 물의 양이 가습에 가장 중요한 변수임을 볼 수 있었다. 사이클론은 높은 공기유량에서 재비산이 발생되는 것을 볼 수 있었다. 노즐타입 PJ24, 분사방향 각도 90도, 분사압력 1200 kPa, 공기 유량 6000 nlpm에서 절대습도 $21.29\;kJ/kg_{da}$, 가습 효율 86.57%를 얻을 수 있었다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.497-501
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• 2001

Unbundled power quality service is paid much attention under the circumstances of deregulation and diversification of needs of customers for quality and price of electric power. Moreover, distributed generators (DGs) such as photovoltaic generations and wind turbines will be introduced to distribution system more and more, and reverse flow of active power has possibility to cause new problems in the distribution system such as voltage rise of distribution line and protection problem. Flexible, Reliable and Intelligent Electrical eNergy Delivery System, which is called FRIENDS, has been proposed as one of promising distribution system for such requirements, and intensive studies are under way. One of features of the system is introducing Quality Control Center (QCC) into the system for unbundled power quality service and easy installation of DGs. Two types of QCCs for such purposes are proposed, and simulation results are shown in this paper.

• 항공우주기술
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• 제11권2호
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• pp.57-64
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• 2012

보조동력장치 개발에서 성공적인 연소기 개발이 이루어졌다고 하더라도 엔진에 조립되어 실제 환경에서 운용될 경우, 예상하지 못한 문제나 현상들이 발생하는 사례가 많이 있다. 하지만, 엔진 또는 체계단위의 개발단계에서는 연소기의 유동장이나 하드웨어의 구조적 변경은 불가능하거나 아주 작은 범위 내에서 가능하다. 따라서 체계 운용 중 발생한 문제에 대하여 시험과 유동해석을 통해 원인 규명 및 해결 방안을 제시하고, 이를 반복시험을 통해 확인, 검증하여야 한다. 본 논문에서는 엔진 및 체계 시험과정 동안 발생한 환형 역류형 연소기 관련 문제들을 유동해석과 엔진시험을 통해 해결, 검증한 과정에 대하여 기술하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.314-319
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• 2003

The concept of lean-premixed combustion in gas turbine combustor operation has become a standard in recent years as an effective means to meet stringent enviromental standards on NOx emissions. The combustion characteristics of 75 kW class lean premixed combustor were investigated at the conditions of high temperature and ambient pressure. The exit temperature and emissions of CO and NOx were measured at the center of exit plane. The high temperature air of $550K{\sim}650K$ was supplied through air preheater. As expected, experimental results indicate that NOx emission was increased and CO emission was decreased by increasing inlet air temperature. But CO emission measured at the center of exit plane was increased because of the non-uniform radial direction profiles. The Semi-Empirical Correlation method was applied to obtain the design point emissions of NOx and CO. Also the flame temperature, CO and NOx emissions were measured along the centerline of liner at 650K inlet air temperature to determine the position of dilution holes.