• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.85-94
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• 2003

A geosynchronous Satellite in general, has two momentum management logics to maintain its wheel momentum tin the stable region. The one is applied in order to control accumulative wheel momentum in the momentum dumping mode and the other is utilized in order to control attitude errors during the stationkeeping. In this paper, the momentum management logics are explained for dumping/sationkeeping mode and the logics are verified by simulation on the 3 attitude subsystem.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.48-59
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• 2019

In recent years, the type of bridge where cables such as suspension bridge and cable-stayed bridge are the main factors in the construction of long-range bridges has been soaring. The effects of cables on these structures are very large, and for structural analysis, it is necessary to study the cable and the structural changes according to the mode characteristics of the cables. In particular, cables are directly connected to camber adjustment, which conveys load effects on girders to tower, and are important components in the overall structure, and since the initial tension on the construction is compared with the tension over time, this study was conducted to help identify the condition of the bridge's aging and abnormalities. Therefore, in this study, the characteristics of the mode from the mode analysis through the impact hammer to the mass of the cable and the change in the length of the cable are analyzed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.6
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• pp.113-123
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• 2006

As Cable-stayed bridges were constructed to the long span, they have become bigger and had weaknesses to vibration induced by earthquake, wind and vehicle loads. Structural damages induced by these loads affect the characteristic of vibration modes of structure. Damage detection of cable-stayed bridges by using existing safety diagnosis is difficult to detect the characteristic change of overall structural action. Also it requires very much time and cost. So in this study, the investigation of characteristic change of structural action and the detection of structural damages is analyzed by using characteristic properties of vibration mode before and after structural damage.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.56-64
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• 2013

The wind resistant capacity of bridges with a span of less than 200m is typically evaluated by Wind Resistant Design Manual for Highway Bridges in Japan. Also, the first vertical frequency plays an important role in the evaluation of their aerodynamic performance. An unexpected vortex-induced vibration of Nielsen arch bridge with span of 183m designed by this manual has been measured by monitoring system during typhoon. The amplitude of vibrations was about 2 times than the allowable vibration displacement. This paper presents the feature of vortex-induced vibration of this Nielsen arch bridge based on measured wind velocity, wind direction, and responses at midspan of main girder. From the result of FFT, the $1^{st}$ mode shape of the bridge is antisymmetric and the $2^{nd}$ is symmetric. Also, the dominant vibration of the bridge is the $2^{nd}$ vertical mode. According to these results, the $2^{nd}$ vertical vibration mode of this Nielsen arch bridge is prior to the first for the estimation of wind resistance capacity.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.27 no.6
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• pp.1307-1315
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• 2017

While the PSK mode of the DTLS is the most efficient in terms of the performance, it is not easy to pre-distribute and manage the symmetric key pairs as the number of sensor devices increases. On the other hand, both the RPK and certificate modes offer a convenient key management tool, but they do not guarantee a good computational performance. In this paper, the end-to-end security protocol suitable for the constrained devices is proposed, based on both the ECQV certificate and the PSK mode. Namely, the initial DTLS handshake is performed using the ECQV certificate, and the subsequent DTLS handshakes with the other CoAP servers in the same group are performed using the PSK mode for the purpose of reducing the overall computational load. Furthermore, a fine-grained access control for the CoAP client can be enforced to allow access to the limited number of CoAP servers.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.2
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• pp.87-94
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• 2012

A damage estimation method of wind turbine tower using natural frequency and mode shape is presented for effective condition monitoring. Dynamic analysis for a wind turbine was carried out to obtain the response of tower from which modal properties were identified. A neural network was learned based on training patterns generated by the changes of natural frequency and mode shape due to various damages. The changes of modal property were calculated using a program for modal parameter estimation. Damage locations and severities could be successfully estimated for 10 damage cases including multi-damage cases using the trained neural network. The damage severities for very small damages generally tends to be slightly under-estimated however, the identified damage locations agreed reasonably well with the accurate locations. Enhancement of the estimation result for very small damage and verification of the proposed method through experiment will be carried out by further study.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.3 s.55
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• pp.101-109
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• 2009

An algorithm is proposed for estimating dynamic displacements of a bridge by using FBG sensors and by superposing some measurable low modes. Modal displacements are obtained from the beam theory and the generalized coordinates are deduced from the strains measured by FBG sensors. By considering flexural and torsional modes occurred in bridges only as flexural modes of a simply supported beam by separating a bridge into multiple girders or parts, the proposed algorithm can be applied to various types of bridges. Guidelines are provided theoretically for determining the number of modes and the number of strain gages to be used. The proposed algorithm has been examined through simulation studies on various types of bridges, laboratory experiments on a model bridge, and field tests on a simple span PC Box girder bridge. Through the simulation study, the effects of the error in the vibration modes and measurement noise on estimating the dynamic displacements are analyzed.

• Journal of Korean Society of Archives and Records Management
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• v.2 no.1
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• pp.119-131
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• 2002

The study designs and implements a KORMARC/EAD integrated system for the Myongji Digital Library Collections. The purpose of this paper is to design the metadata to Myongji Korean History Collections to provide digital information of high quality to clients, and to develop and implement a model for managing digital library collections. In order to test the model and the quality of the derived metadata, we built a metadata management system, which is connected to the existing KORMARC system. The system consists of two modules- a retrieval and an input module. While in the retrieve mode, one can retrieve KORMARC records of books and archival items, with links to modified EAD files for archival items or to image files for books, in the input mode, one can type two types of data such as a catalog data and an inventory data. Finally, we evaluated the proposed system via mail questionnaires, and propose three suggestions to make this system a much more comprehensive and effective system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4C
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• pp.581-593
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• 2004

The interest in wireless LAN security is on the increase owing to a role of high-speed wireless Internet infrastructure of wireless LAN. Wi-Fi has released WPA standard in order to overcome drawbacks of WEP algorithm that is security element of current IEEE 802.11-based wireless LAN system. Pairwise key management and group key management in a mixed-mode which supports both terminals running WPA and terminals running original WEP security are very complicate. In this paper, we analyze flaws in WPA authenticator key management state machine for key distribution and propose the countermeasures to overcome the analyzed problems. Additionally, WPA authenticator key management state machine to which the solutions are applied is described. The reconstructed WPA authenticator key management state machine helps the AP perform efficiently group key exchange and group key update in the mixed-mode.

• 건강소식
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• v.36 no.10
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• pp.32-33
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• 2012

수능이 한 달 앞으로 바짝 다가왔다. 수험생들의 스트레스 지수가 가장 높은 시기인 만큼 지금부터 수능까지의 꾸준한 건강관리가 필수다. 최적의 컨디션을 위해서 지금부터 잘 먹고 잘 자고 화장실도 잘 가야한다. 한마디로 신체를 수능 모드로 바꿔야 한다. 수험생에게 꼭 필요한 막판 건강관리요령을 알아보자.