• Nuclear Engineering and Technology
• /
• 제46권6호
• /
• pp.817-824
• /
• 2014

To ensure the safety of research reactors, the water level must be maintained above the required height. When a pipe ruptures, the siphon phenomenon causes continuous loss of coolant until the hydraulic head is removed. To protect the reactor core from this kind of accident, a siphon breaker has been suggested as a passive safety device. This study mainly focused on two variables: the size of the pipe rupture and the timing of air entrainment. In this study, the size of the pipe rupture was increased to the guillotine break case. There was a region in which a larger pipe rupture did not need a larger siphon breaker, and the water flow rate was related to the size of the pipe rupture and affected the residual water quantity. The timing of air entrainment was predicted to influence residual water level. However, the residual water level was not affected by the timing of air entrainment. The experimental cases, which showed the characteristic of partical sweep-out mode in the separation of siphon breaking phenomenon [2], showed almost same trend of physical properties.

• 한국군사과학기술학회지
• /
• 제13권4호
• /
• pp.577-585
• /
• 2010

The Military Tactical Communication technology for effective network-centric warfare is developing. Targeting broadband wireless transmission, core technology for connection, and Transmission technology that secure survivability under High-speed Movement environment. On the one hand, Tactical data communication system that reflects military characteristic is developing on the base of Legacy communication equipment which is used in the field. Because almost every military units in the field have used voice to communicate which lower efficiency of operation, they have made effort to Substitute voice communication which delays military Operation Tempo to digital communication. The Communications environment of troops in Forward edge of battle field area is very poor. Especially in terms of limited frequency allocation and bandwidth. Therefore, improving the efficiency of frequency is essential for Military Tactical Communication. This paper is about The Data Compression Method for increase of Efficiency in Tactical Data Communication over Legacy Radios which are UHF, VHF, HF Radio. I proposed and proved the most efficient Data Compression Method that reflects military characteristic, after analyzing the experimentation, which simulate CAS(Close Air Support mission) data transmission between Pilot and TACP.

• Journal of Electrochemical Science and Technology
• /
• 제5권1호
• /
• pp.1-18
• /
• 2014

Li-air cell is an exotic type of energy storage and conversion device considered to be half battery and half fuel cell. Its successful commercialization highly depends on the timely development of key components. Among these key components, the catalyst (i.e., the core portion of the air electrode) is of critical importance and of the upmost priority. Indeed, it is expected that these catalysts will have a direct and dramatic impact on the Li-air cell's performance by reducing overpotentials, as well as by enhancing the overall capacity and cycle life of Li-air cells. Unfortunately, the technological advancement related to catalysts is sluggish at present. Based on the insights gained from this review, this sluggishness is due to challenges in both the commercialization of the catalyst, and the fundamental studies pertaining to its development. Challenges in the commercialization of the catalyst can be summarized as 1) the identification of superior materials for Li-air cell catalysts, 2) the development of fundamental, material-based assessments for potential catalyst materials, 3) the achievement of a reduction in both cost and time concerning the design of the Li-air cell catalysts. As for the challenges concerning the fundamental studies of Li-air cell catalysts, they are 1) the development of experimental techniques for determining both the nano and micro structure of catalysts, 2) the attainment of both repeatable and verifiable experimental characteristics of catalyst degradation, 3) the development of the predictive capability pertaining to the performance of the catalyst using fundamental material properties. Therefore, under the current circumstances, it is going to be an extremely daunting task to develop appropriate catalysts for the commercialization of Li-air batteries; at least within the foreseeable future. Regardless, nano materials are expected to play a crucial role in this field.

• 한국초전도ㆍ저온공학회논문지
• /
• 제6권4호
• /
• pp.27-31
• /
• 2004

This paper describes the development and fabrication of a high temperature superconducting motor which consists of HTS rotor and air-core stator. The machine was designed for the rated power of 100hp at 1800 rpm. The HTS field windings are composed of the double-pancake coils wound with AMSC's SUS-reinforced Bi-2223 tape conductor. These were assembled on the support structure and fixed by a bandage of glass-fiber composite. The cooling system is based on the heat transfer mechanism of the thermosyphon by using GM cryocooler as cooling source. The cold head is in contact with the condenser of a Ne-filled thermosyphon. The rotor assembly was tested independently at the stationary state and combined with stator. Characteristic parameters such as reactances, inductances, and time constants were determined to obtain a consistent overview of the machine operation properties. This motor has met all design parameters by demonstrating HTS field winding, cryogenic refrigeration systems and an air-core armature winding cooled with air. The HTS field winding could be cooled down below 30K. No-load test of open-circuit characteristics(OCC) and short-circuit characteristics(SCC) and load test with resistive load bank were conducted in generator mode. Maximum operating current of field winding at 30K was 120A. From OCC and SCC test results synchronous inductance and synchronous reactance were 2.4mH, 0.49pu, respectively. Efficiency of this HTS machine was 93.3% in full load(100hp) test. This paper will present design, construction, and basic experimental test results of the 100hp HTS machine.

• 태양에너지
• /
• 제15권1호
• /
• pp.85-94
• /
• 1995

본 연구는 2차원 충돌분류계의 포텐셜코어영역(H/B=2)내에서 전열증진을 목적으로 전열면 앞에 폭 6mm인 정 4각 rod군을 설치하고 rod와 전열면간의 간극(C=1, 2, 4, 6mm)과 rod와 rod사이의 피치(P=30, 40, 50mm)를 변화시킬때의 유동특성과 전열특성을 실험적으로 규명하고 rod를 설치하지 않았을 경우와 비교 검토한 것으로 간극변화시에는 C=1mm인 경우가 전열성능이 가장 우수하였으며, rod의 피치(P)를 변화시킨 경우에는 rod가 없는 평판에 비해 각각 약 1.6배의 평균전열증진율이 나타났다.

• 한국정보시스템학회지:정보시스템연구
• /
• 제14권3호
• /
• pp.63-70
• /
• 2005

Compared with land logistics and sea logistics, air logistics takes not only less transportation time, but also makes just-in-time delivery possible. Because of this, in spite of high freight rates, many shippers make good use of airlines. To cope with borderless competition in this global age, most shippers using air logistics want to receive diverse information including just-in-time cargo delivery and dangerous situation as well as convenience and speed in job handling. Nevertheless, most domestic forwarders, who perform many kinds of important businesses for air logistics, mainly put emphasis on demanding information from overseas partners through their business agreements, that is, focusing on horizontal integration, instead of sharing information or improving job performance among air logistics participants. As a result, it is almost impossible to satisfy the needs of shippers. Airline users want to remove the uncertainties over their cargo movement. And in time of emergency, they want to take immediate measures through speedy information sharing and decision-making. In order to satisfy shipper's needs, all the organizations participating in the air logistics supply chain-cargo senders, cargo receivers, forwarders, transporters, licensed customs brokers, airlines as well as foreign partners-have to set up a vertical cooperation system. For effective air logistics SCM, it is very important to remove overlapping jobs, strengthen the efficiency of job handling, and provide online monitoring on cargo information in order to support decision-making. To this end, this paper has applied the concept of RTE (Real Time Enterprise), a new business management system, which tries to maximize competitiveness by removing many hindrance factors on an ongoing basis in managing and fulfilling core business processes based on up-to-the-minute information. In order to realize RTE-based information system for air logistics SCM, this paper has analyzed the information required by business process and by air logistics participant, and suggested the method for information sharing, point of time for information input and output, and its means.

• 한국항공우주학회지
• /
• 제50권1호
• /
• pp.47-57
• /
• 2022

전장에서의 무인기 활용이 시작된 이후 무인기는 기만, 정찰, 공격 등 다양한 임무에 투입되어 인간을 대신하여 성공적인 임무를 수행하여 왔다. 과거, 기술의 제한으로 자율적 임무수행이나 유인기와의 협업을 통한 임무는 불가하였으나 데이터 통신, 인공지능 등의 기술 발전으로 인하여 자율임무 수행은 물론 유무인 협업을 통한 시너지 효과를 창출하는 수준까지 발전하였다. 본 연구에서는 공군의 항공우주작전 중 공대공 임무를 중심으로 유무인 협업이 가능한 임무를 식별하였으며, 많은 공대공 임무 중 가장 핵심이면서 기본 작전으로 판단된 전투기소탕에 관한 유무인 협업 전술 개발을 연구하였다. 전투기소탕 작전 중에서도 유무인 협업을 통한 비스텔스기 대응과 스텔스기 대응 전술로 구분하여 연구를 진행하였으며, 이후 간단한 공학시뮬레이션을 통하여 제시한 전술의 실효성(임무 성공과 유무인기 생존 가능성)을 증명하였다.

• 한국자동차공학회논문집
• /
• 제16권1호
• /
• pp.37-44
• /
• 2008

The global warming potential (GWP) of $CO_2$ refrigerant is 1/1300 times lower than that of R134a. Furthermore, the size and weight of the automotive heat pump system can decrease because $CO_2$ operates at high pressure with significantly higher discharge temperature and larger temperature change. The presented $CO_2$ heat pump system was designed for both cooling and heating in fuel cell vehicles. In this study, the performance characteristics of the heat pump system were analyzed for heating, and results for performance were provided for operating conditions when using recovered heat from the stack coolant. The performance of the heat pump system with heater core was compared with that of the conventional heating system with heater core and that of the heat pump system without heater core, and thus the heat pump system with heater core showed the best performance among the selected heating systems. On the other hand, the heating performance of two different types of coolant/air heat pump systems with heater core was compared each other at various coolant inlet temperatures. Furthermore, to use exhausted thermal energy through the radiator, experiments were carried out by changing the arrangement of a radiator and an outdoor evaporator, and quantified the heating effectiveness.

• 대한기계학회논문집B
• /
• 제35권4호
• /
• pp.425-429
• /
• 2011

원자로의 노심 손상에 따른 노심 용융물의 노외 유출시 코어캐처라고 불리는 설비를 통해 용융물을 억제하고 냉각시키게 된다. 이 때 노외 노심용융물의 거동은 희생물질과의 반응을 포함한 복잡한 물리적, 화학적 현상에 의해 결정된다. 이 연구는 기존의 용융물 거동 실험결과에 대해 용융물의 유동과 열전달의 세부적인 특성을 상용코드를 이용해 해석하여 검증함으로써 코어캐처의 설계에 활용할 수 있도록 하기 위한 것이다. 단순화된 채널에서 시간에 따른 용융물과 공기의 이상유동과 복사열전달을 VOF 모델과 구분종좌법을 적용하여 비정상상태에서 해석한 결과, 열전달에 따른 용융물 내부의 온도 변화 및 이에 따른 점성 변화 등을 예측할 수 있음을 확인하였다. 이러한 접근방식을 기초로 향후 용융물의 조성, 유량 및 용도 등의 조건에 따른 용융물의 거동에 대한 자세한 평가가 필요하다.

• 한국융합학회논문지
• /
• 제12권2호
• /
• pp.29-34
• /
• 2021

본 논문에서는 중심에 동공을 갖는 원통형태 광결정 도파로가 제안되어지고, 이 전송로의 도파 특성에 대한 분석이 수행되어진다. 여기서 동공은 일반적인 공기이거나 임의의 액체나 고체 물질들에 의한 저지수 유전체로써 형성되게 된다. 베셀 함수를 이용한 분석적 방법으로 전자장에 대한 엄밀한 해를 구하기 위하여, 행렬 기법이 고유치 방정식의 유도에 사용되고, 실효 굴절률, 분산, 전자장 분포 등의 기본 모드의 중요한 전송 성질들이 조사된다. 또한 분석 결과 정확도의 검증을 위하여 엄밀한 완전 벡터 유한 차분법을 적용해보고, 광결정 도파로의 설계와 제조 상의 문제를 해결하는데 용이하게 활용하고자 한다. 설계된 중심-동공 광도파관의 실효 모드 면적이 2.6056 ㎛2에서 5.9673 ㎛2까지 동작 파장에 따라 다양하게 변하며, 일반적으로 광도파로의 중심으로부터 바깥쪽으로 원통형의 층수가 적을수록 그리고 굴절률 n1이 약간 큰 저지수일수록 실효 면적은 작아지므로, 비선형 소자 응용의 관점에서 훨씬 더 최적화된 결과를 나타낸다.