• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.38 no.9
• /
• pp.652-662
• /
• 2001

A WDM/SCM multiple access protocol suitable for optical double star networks is proposed. A node-grouping scheme is employed in the protocol, which is accomplished by connecting some nodes through passive star sub-hubs forming a group. The resulting multiple groups in a network are then connected through a central passive star hub resulting in a passive double star network. Each group is pre-assigned a WDM channel as its home channel, and SCM channels are used to identify the packet reception at each node. [n the proposed protocol, the average packet delay is remarkably reduced since the frame consists of the number of groups rather than the number of network nodes. Furthermore, additional reduction of the average packet delay is achieved by limiting the propagation paths of control packets to the roundtrip between source nodes and sub-hub using a double star network. It is shown in the performance evaluations using analytic and simulation model that the proposed protocol has the advantages of the higher channel utilization and excellent network throughput and average packet delay characteristic.

• Proceedings of the Korean Information Science Society Conference
• /
• 2003.04c
• /
• pp.377-379
• /
• 2003

본 논문은 문서검 색을 위한 온톨러지(Ontology)의 반자동 구축방안을 제시한다. 이를 위하여 우리는 다른 단어들과 특히 많은 관련이 있는 단어를 허브 단어(hub word)라고 정의하며 경제분야에 특정적인 온톨러지의 구축을 위하여 TREC 문서집합의 Wall Street Journal 문서들을 분석하였다. 문서집합 내의 모든 단어들의 tf, idf 값를 이용하여 허브 단어를 결정짓고 이렇게 선택된 허브 단어들을 중심으로 온톨러지를 구축하였다. 우리는 허브 단어와 다른 단어들간의 관계를 문서로부터 자동으로 추출하고 그 정보를 이용하여 온톨러지를 확장해나간다. 제안된 온톨러지는 전통적인 문서 검색의 인덱스 파일과 같은 역할을 하게 되며, 간단한 역파일(inverted file) 구조보다 더 많은 의미정보(semantic information)를 제공할 수 있다.

• Composites Research
• /
• v.16 no.5
• /
• pp.7-14
• /
• 2003

Modeling of thick composite structures for finite element analysis is relatively complicated. 2-D plane elements may cause inaccurate result since the plane stress condition cannot be applicable in these structures. Therefore a 3-D modeling should be used. However, the difficulty to model all the layers with different material properties and ply orientation arise in this case. In this paper, an equivalent modeling is proposed and numerically tested for analysis of thick composite structures. By grouping layers with same material and ply orientation, number of elements through the thickness is remarkably reduced and still the result is close enough to the one from a detail finite element model. MSC/NASTRAN and PATRAN are used for the analysis. The proposed modeling technique has been applied for analysis of composite rotor hub system designed by Korea Aerospace Research Institute(KARI). Using the proposed equivalent modeling technique, we could conduct stress analysis for the hub system and check the safety factor of each part.

• Journal of Korean Society of Transportation
• /
• v.24 no.6 s.92
• /
• pp.75-85
• /
• 2006

Recently. large number of countires have been focused on the construction of container seaport and hub airport to enrole as the center of logistics. In particular, the East Asian nations have been enhanced their airports' facilities in order to accommodate for demand of global market environment. In Korea, Incheon International Airport (ICN) was opened in 2001 to take leading role as the Northeast Asian main hub airport. The purpose of this research is to analyze the transferring connectivity at ICN. To analyze its connectivity, this research has been applies two methodologies ; wane structure and minimum or maximun connection time analysis It has analyzed the temporal configuration as the frequency and quality of indirect connections offered by an airline by adopting a wave-system structure in the airline flight schedule. As an empirical analysis, it also calculated the minimum and maximum connection time adopting Korean Air's flight information.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.06a
• /
• pp.183.2-183.2
• /
• 2010

본 개발에서의 해상용 풍력발전기는 크게 허브와 블레이드를 합한 상부 구조물, 전기 발전기와 연결 조인트의 중간구조물, 각종 제어 장치가 들어있는 제어박스로 나누어진다. 상부 구조물은 Circular Hub 타입의 Darrieus 형상으로 양력(lift)을 이용한 회전력이 발생하며, Circular Hub 타입은 기존의 허브와 블레이드를 연결하여주는 암(arm)에 의해 유발되는 항력토크를 최소화 하기 위한 신개념 형상설계가 이루어 졌으며, 저속에서 우수한 회전특성을 가진다. 이는 바람을 받아 기계적 에너지로 전환 하는 역할을 하며, 풍력발전기의 성능에 직접적인 영향을 미친다. 중간구조물의 전기발전기는, 상부에서 발생된 기계적 에너지를 이용하여 전기적 에너지로 전환 하는 역할을 수행한다. 이렇게 전환된 전기적 에너지는 하부의 제어박스를 거쳐서 해상용 부이(buoy)의 하단에 위치한 베터리 뱅크로 전달, 저장되어 부이에서 쓰이는 전력을 충당하게 된다. 한편 본 개발은 풍력발전기의 공력하중 해석과 로터블레이드의 설계, 풍력발전기의 구조, 진동해석, MPPT 제어컨트롤러와 Breaking controller, 풍동 및 차량시험을 통한 성능평가 및 분석 등의 순으로 개발을 수행하였다.

• Aerospace Engineering and Technology
• /
• v.2 no.2
• /
• pp.33-44
• /
• 2003

This paper describes the design and analysis technology of composite flexure and composite paddle-type blade which are all key technologies on hingeless rotor system. Through replacing the existing metal or engineering plastic flexure part with composite part, Several required structural analysis were accomplished, which are static analysis by using NASTRAN and dynamic analysis by using FLIGHTLAB. The dynamic characteristics of composite hingeless hub attached with paddle-type blade was also investigated. Further more, small-scaled paddle-type blade was designed using froude scaled properties of existing full size blade. Through this design procedure of composite paddle-type blade, the structural design method was achieved. These results will be applied to accomplishing current project named as "the development of next-generation helicopter rotor system."

• Journal of Digital Convergence
• /
• v.11 no.6
• /
• pp.175-185
• /
• 2013

For effective information sharing, data provenance semantics need to be managed effectively. Based on a scheme to represent data provenance semantics, we propose a model to calculate information sharing costs. Information sharing costs are derived from probabilities of type I and type II errors that occur in organizational information sharing, costs related to these errors, and information sharing distances between organizational units which are determined by information sharing workflows. We apply the model to various types of information sharing workflows including departmental information systems, hierarchical information systems, a hub and a stand-alone system. The calculated information sharing costs show that the hub with data standardization is best in information sharing; however without standardization its information sharing cost deteriorates to that of a departmental information system. And, any information sharing workflow is better than a stand-alone system. It is proved that the model is useful in analyzing effectiveness of information sharing workflows and their characteristics.

• Journal of Korean Society of Transportation
• /
• v.26 no.6
• /
• pp.103-112
• /
• 2008

Implementing hub networks in logistics is generally attractive and effective because of cost savings derived from economies of scale on network transportation, and objective of the hub network design problem is to decide optimal hub locations, and the transportation route of each origin-destination pair. This problem is generally a NP-complete problem not to solve easily, and it is almost impossible to find optimal solutions considering the big-sized network within a reasonable time. This research tried to find optimal logistics strategy in the given big-sized real network and the freight origin-destination data. The objective function, which was proposed by Honor and O'kelly (2001), that rewards economies of scale on network links with increase of transportation volumes, is applied. This thesis proposed the optimal hub network of korea within a reasonable time based on engineering approaches. And it is expected that this thesis can contribute to plan freight policies which can improve to have competitive power in the level of a company or nation by reducing logistic costs.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.7
• /
• pp.561-568
• /
• 2013

After we designed Bearingless rotor hub system for 7,000lb class helicopter, flexbeam fatigue analysis was conducted for validation of requirement life time 8,000 hours. sectional structural analysis method applying elastic beam model was used. Fatigue analysis for two sections of flexbeam which were expected to weak to fatigue damage from result of static analysis was conducted. Extension, bending and torsion stiffness of flexbeam section shape was calculated using VABS for structure analysis. S-N curve of two composite material which composed flexbeam was generated using wohler equation. Load analysis of bearingless rotor system was conducted using CAMRAD II and load analysis result was applied HELIX/FELIX standard load spectrum to generate bearingless rotor system load spectrum which was used flexbeam fatigue safe life analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.46 no.3
• /
• pp.237-243
• /
• 2018

In this study, the hub vibration load characteristic is evaluated for a rotor in high advance ratio conditions while investigating blade loads through the structural load prediction and harmonic analysis. Numerical studies are performed to validate the wind tunnel test data performed in NASA as the rotor advance ratios are varied from 0.40 to 0.71. A good correlation is obtained for rotor performance calculation at the range of advance ratios considered. It is observed that the hub vibration loads remain almost unchanged when the advance ratios are higher than 0.5, even though the amplitudes of blade structural loads become larger with increasing advance ratios. A harmonic analysis on blade moments is confirmed that the dominant structural mode is 3/rev component for flap bending moments and 4/rev for lag bending moments. The reason is due to the tendency of the second flap and lag mode frequencies which approach 3/rev and 4/rev, respectively, as the advance ratios are increased.