• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2007년도 한국컴퓨터종합학술대회논문집 Vol.34 No.1 (D)
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• pp.100-104
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• 2007

라디오 주파수를 이용하여 사물의 정보를 인식할 수 있는 RFID 기술은 다양한 분야에 활용되고 있는데 이러한 RFID 망을 All-IP 기반의 이동통신망과 연동할 경우 RFID의 각종정보와 휴대단말기의 위치정보 및 이동성, 그리고 다양한 IP 기반의 정보서버를 활용한 새로운 형태의 위치기반 서비스의 창출이 가능하다. 즉, RFID 태그에 태그 리더기 역할을 하는 단말기의 위치를 부여하고 이를 RFID 서버에서 지속적으로 관리함으로써 RFID 태그의 Code와 위치를 기반으로 한 위치기반서비스를 제공할 수 있다. 본 연구에서는 RFID망과 이동통신망의 연동을 기반으로 한 위치기반서비스 모델로 Mobile Information Retrieval Service (MIRS), Mobile Location Tracking Service (MLTS), Localization Service by Fixed Tag (LSFT) 세 가지 모델을 제시하였으며 이러한 서비스 모델은 실제 서비스를 개발하는데 있어 다양한 방식으로 활용될 수 있다.

• 천문학회보
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• 제39권2호
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• pp.77.2-77.2
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• 2014

Questions of how our Milky Way evolves through the interaction with its environment have been constantly raised. One particularly interesting question is how the metallicity would change as our Milky Way goes through collision with HVCs. Because of the possibility of HVCs providing fuel for star formation in the Galactic disk, we simulate the collision between HVCs and the Galactic disk. More specifically, we trace how the Galactic metallicity changes throughout the process of HVCs colliding with our Milky Way based upon a specific scenario that HVCs are primordial gas left-overs from an ancient galaxy formation. Such mixing between metal-rich gas (disk) and metal-poor HVC can be traced by running numerical simulations with the FLASH code due to its capability of tracking down the abundance change of a specific element such as carbon at each time step of the hydrodynamic evolution. As for now, we give how this mixing depends on model parameters that we choose such as collision speed, initial metallicities, temperature and so on.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.460-463
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• 2010

Ice accretion on aircraft surface can greatly impair the aerodynamic performance of aircraft. As an alternative to the traditional Lagrangian particle tracking approach, an Eulerian-based droplet impingement and ice accretion code for air flows containing water droplets was developed A CFD solver was also developed to solve the clean airflow. The results of present method were compared with experimental data and previous icing codes such as LEWICE and FENSAP-ICE and were confirmed to show good agreement each other in qualitative and quantitative ways.

• 제어로봇시스템학회논문지
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• 제11권3호
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• pp.233-239
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• 2005

This paper presents the design and evaluation of a tiltrotor attitude controller. The implemented response type of the command augumentation system is Attitude Command Attitude Hold. The controller architecture can alleviate the need for extensive gain scheduling and thus has the potential to reduce development time. The control algorithm is constructed using the feedback linearization technique. And an on-line adaptive architecture that employs a neural network compensating the model inversion error caused by the deficiency of full knowledge tiltrotor aircraft dynamics is applied to augment the attitude control system. The use of Lyapunov stability analysis guarantees boundedness of the tracking error and network parameters. The performance of the controller is evaluated against ADS-33E criteria, using the nonlinear tiltrotor simulation code for Bell TR301 developed by KARI. (Korea Aerospace Research Institute)

• 한국전산유체공학회지
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• 제14권3호
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• pp.63-68
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• 2009

The motion of a rising liquid droplet is different that of a bubble motion. Treatment of liquid drops is more complex because internal motion must be considered. A 3D unstructured CFD code has been developed to solve incompressible N-S equation for the droplet simulation. This front-tracking consideration which the interface is tracked explicitly is very available to apply for not only exact interface topology but also the high schmidt number issue, such as $CO_2$ dissolution. This paper is forced on the zig-zag motion of the liquid droplet. The simulation shows that if the rising droplet is located at the corner of the zig-zag path, the velocity is low and shape of the droplet is more spherical shape, results in the less drag coefficient. Twin horse shoe vortexes behind the rising droplet are presented and the topology of the droplet is compared with an experimental result during one period of the path.

• 한국통신학회논문지
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• 제21권8호
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• pp.2043-2054
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• 1996

In this paper, Digital Delay Locked Loop(DDLL) is designed, implemented and analysed by experiment whose results show that it is possible to track the received signal by this scheme. Designed digital DLL has an advantage that it is not needed to maintain gain balance between early and late channels, which has been problem with an analog DLL. Also DDLL has more improved noise performance compared to analog DLL due to noise level limitation and noise cancellation characteristics. For various loop parameters, their effects on loop performance are analysed and simulated. Proposed DDLL is the first attempt as a digital approach in code tracking loop and it is expected to be a good reference for spread spectrum communication research.

• 제어로봇시스템학회논문지
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• 제12권10호
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• pp.1050-1055
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• 2006

Since the muiltipath signal arrives at the GPS receiver later than the line-of-sight signal, the multipath signal makes the shape of the correlation function asymmetric. This paper proposes a multipath mitigation method through asymmetry estimation of the correlation function, in which multiple correlators are utilized. The asymmetry is estimated from correlation values of correlators which have different chip spacings. Based on the estimated asymmetry, the correlation function is modified in order to get a better code tracking performance. Even through the proposed method uses multiple correlators including the narrow correlator, the acquisition performance is not degraded since the number of search cell of the narrow correlator part can be reduced in the algorithm of the proposed method. The simulation results show that the proposed method gives better performance than the generic correlator in multipath environment.

• 동력기계공학회지
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• 제18권3호
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• pp.5-13
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• 2014

In order to control emissions from engine, it is necessary to understand the mixture formation process of diesel spray. In this study, analysis of diesel fuel(n-Tridecane, $C_{13}H_{28}$) spray under a high temperature and pressure was performed by a general-purpose program, ANSYS CFX release 11.0, and the results of these are compared with experimental results of diesel fuel spray using the Exciplex Fluorescence Method. The simulation results of diesel spray is analyzed by using the combination of Large-Eddy Simulation(LES) and Lagrangian Particle Tracking(LPT), and then injection pressure was selected as an analysis parameter. Consequently, it was found that the experimental results and the numerical results are consistent with each other, and then in order to investigate the behavior characteristics of evaporative diesel spray, the effectiveness of the use of CFX of commercial code is definitely validated.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2007년도 하계종합학술대회 논문집
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• pp.71-72
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• 2007

대역 제한된 DS/SS 시스템의 상관 함수는 최고 값이 나타나는 시점과 함께 이른 또는 늦은 상관시간 옵셋 영역에서 극소 또는 극대로 나타나는 시점을 특징점으로 갖는다. 이 가운데 이른 상관시간옵셋 영역의 상관 함수는 다중경로 신호에 의해 덜 왜곡되기 때문에 이 영역의 상관 함수를 이용해 부호 동기를 추적하여 유지할 수 있다면 EL-DLL (delay lock loop with early minus late discriminator) 보다 추적편이를 줄일 수 있다. 본 논문에 이런 특성을 이용하는 추적편이 완화 기법을 제안하고, 모의실험을 통해 성능을 알아본다.

• Journal of Electrical Engineering and Technology
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• 제7권6호
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• pp.869-875
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• 2012

Because of the nature of wind, the output power of wind turbines fluctuates according to wind speed variation. Therefore, many countries have set up wind-turbine interconnection standards usually named as Grid-Code to regulate the output power of wind farms to improve power system reliability and power quality. This paper proposes three operation modes of wind farms such as maximum power point tracking (MPPT) mode, single wind turbine control mode and wind farm control mode to control the output power of wind turbines as well as overall wind farms. This paper also proposes an operation scheme of wind farm to alleviate power fluctuation of wind farm by choosing the appropriate control mode and coordinating multiple wind turbines in consideration of grid conditions. The performance of the proposed scheme is verified via simulation studies in PSCAD/EMTDC with doubly-fed induction generator (DFIG) based wind turbine models.