• 한국항해학회지
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• 제22권1호
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• pp.79-89
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• 1998

When an automatic course-keeping is concerned , as is quite popular in modern navigation, the closed-loop steering system consists of autopilot device, power unit(or telemotor unit), steering gear, magnetic or gyro compass and ship dynamics. In order to estimate steering system of ship in open seas, we need to know the characteristics of each component of the system and also to know the characteristics of disturbance to ship dynamics. Calculation methods of irrgular disturbances are based on the linear superposition principle. In this paper, for the purpose of evaluation of automatic steering of ships , the influences of linear control constants of autopilot on propulsive energy loss are investigated bya performance index is introduced from the viewpoint of energy saving. Numberical calculations are carried out for an are carrier and for a fishing boat in multi-directional waves.

• 디지털융복합연구
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• 제11권11호
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• pp.85-94
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• 2013

본 논문에서는 기존 DTV 커버리지 측정차량의 문제점을 해결하고 효율적으로 전파 음영지역을 찾아내기 위해 고정식 DTV전파측정차량의 기능을 포함하면서도 이동하며 전파수신현황 및 수신상태를 측정할 수 있는 다중 안테나 이동측정시스템을 제안한다. 제안된 시스템은 모두 4개의 무지향성(omni-directional)안테나와 고정측정을 위한 1개의 지향성(directional)안테나를 포함하며, 공간 다이버시티(space diversity)를 활용하여 운용할 수 있도록 각각의 안테나마다 측정장비를 배치하고 각각의 측정값을 실시간으로 수집하고 처리한다. 제안된 시스템의 효용성을 보이기 위해 국내 수신 전파 환경을 3가지 유형으로 모델링하고 이들 지역에서 집중적인 측정을 실시하였다. 또한 측정 결과의 상세한 분석을 토대로 이동측정 및 고정측정간의 상관관계를 밝히고자 하였다. 특히 제안된 시스템의 적용을 위한 실험에는 방송사 현업 실무자들이 측정 및 결과 정리에 공동으로 참여하는 등 객관성을 확보하고자 하였으며 개발 장비를 국책 연구기관의 인위적 난시청 조사사업에 일부 적용하는 등 실제 방송 커버리지 관리 업무에 적극적으로 활용하고 있다.

• 한국통신학회논문지
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• 제35권2A호
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• pp.134-141
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• 2010

본 논문에서는 지향성 안테나를 사용하는 IEEE 802.16 기반 무선 메쉬 네트워크(wireless mesh networks)의 성능 향상을 위한 스케줄링 알고리즘을 제안한다. 성능은 사용자 수에 따른 시스템의 수율과 각 노드 간의 지연으로 나타낸다. 분석 결과를 통해 제안된 알고리즘이 메쉬 네트워크 시스템의 지연을 줄여 시스템의 성능을 향상시킬 수 있음을 보인다. 본 논문의 결과는 향후 메쉬 네트워크, 멀티 홉 중계기 등의 다중 홉 시스템에서 각 SS(subscribe station)들의 공정성을 고려한 지향성 안테나 도입 시에 참고할 만한 가이드라인을 제시할 수 있을 것이다.

• 조명전기설비학회논문지
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• 제28권10호
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• pp.16-26
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• 2014

This paper proposes new 13-level inverter topology and DC/DC converter buck-boost structure topology for multilevel, compounding uni-directional and bi-directional switches, and proposes high-efficient multilevel inverter system in which the proposed two PCS(Power Conditioning System) was connected in series. In proposed multilevel inverter of forming a output 13-level phase voltage by using total 18 switching parts, Then bi-directional switch has a characteristic of reducing conduction loss and controlling the reactive power effectively by separating electrically from the neutral point. DC/DC converter for supplying in dependent 3 DC voltage to the proposed multi-level inverter generates 180-degree phase shifted PWM by the symmetrically combined structure of 2 buck-boost converter and twice switching frequency efficiency can be obtained, meanwhile, the converter can step up/down the output voltage and 20% output can be generated comparing the input voltage. This proposed system is verified with the simulation and laboratory test.

• Journal of Mechanical Science and Technology
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• 제17권5호
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• pp.654-667
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• 2003

This paper presents a consequence of the systematic approach to identify the aerodynamic parameters of an unmanned aerial vehicle (UAV) equipped with the automatic flight control system. A 3-2-1-1 excitation is applied for the longitudinal mode while a multi-step input is applied for lateral/directional excitation. Optimal time step for excitation is sought to provide the broad input bandwidth. A fully automated programmed flight test method provides high-quality flight data for system identification using the flight control computer with longitudinal and lateral/directional autopilots, which enable the separation of each motion during the flight test. The accuracy of the longitudinal system identification is improved by an additional use of the closed-loop flight test data. A constrained optimization scheme is applied to estimate the aerodynamic coefficients that best describe the time response of the vehicle. An appropriate weighting function is introduced to balance the flight modes. As a result, concurrent system models are obtained for a wide envelope of both longitudinal and lateral/directional flight maneuvers while maintaining the physical meanings of each parameter.

• 센서학회지
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• 제9권6호
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• pp.448-454
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• 2000

This paper describes the implementation of a multi-subject, multi-channel optical telemetry system for the short range measurement of electrocardiograms (EKGs) a system which receives command signals and transmits physiological signals to the external system using LED (Light Emitting Diode) and PD (Photodiode). This system decreases the dependency of power supply voltage to the CMOS IC chips and a new enforced synchronization technique using infrared bi-directional communication has also been proposed. The telemetry IC with the size of $5.1{\times}5.1mm^2$ has the following functions: receiving of command signal, initialization of internal state of all functional blocks, decoding of subject selection signal, time division multiplexing of 4-channel modulated physiological signals, transmission of modulated signals to external system, and auto power down control.

• 전기학회논문지
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• 제60권8호
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• pp.1523-1528
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• 2011

This paper proposes buck-type charging method using motor inductance, 3-phase inverter and bi-directional converter without an additional charger in plug-in hybrid electric vehicles. The proposed system has advantages over the conventional system such as high charging efficiency, high power factor, and low total harmonic distortion. The validity of each methods are verified by theoretical analysis and simulation.

• 수산해양기술연구
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• 제37권1호
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• pp.35-44
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• 2001

본 논문에서 취급한 계산모델 및 계산조건하에서 얻어진 주요한 결론은 다음과 같다. (1) 다방향 불규칙파중에서 TLP에 작용하는 파강제력 및 정상표류력의 유의치를 구할 수 있는 프로그램을 개발하였다. (2) 한방향파중에서 파강제력 및 정상표류력이 큰 모-드에 대해서는 다방향파의 영향으로 감소하는 경향을 보이고, 한방향파중에서 작은 모-드에 대해서는 다방향파의 영향이 무시할 수 없을 정도로 나타났다. (3) 다방향파의 상호작용에 의해 실해역을 재현할 수 있으며, 다방향파의 영향으로 최대 파강제력 및 정상표류력의 크기가 감소한다는 결과에 따라 다방향파의 영향을 고려하면 보다 현실적인 결과를 얻을 수 있을 것으로 사료된다.

• 한국환경과학회지
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• 제29권5호
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• pp.457-468
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• 2020

With continuous industrial development, the types, and amount of particulate matter (PM) have been increasing. Since 2018, environmental standards regarding PM have become more stringent. Pulse air jet bag filters are suitable for PM under the 20 ㎛ and, can function regardless of size, concentration and type. Filtration velocity and shape are important factors in the operation and design of the pulse air jet bag filters however, few established studies support this theory. In this research, numerical simulations were conducted based on experimental values and, several methods were employed for minimizing the pressure drop. In the pilot system, as the inlet duct velocity was faster than 19 m/sec, flow was not distributed equally and, re-entrainment occurred due to the hopper directional vortex. The multi-inlet system decelerated the hopper directional vortex by 25 ~ 30%, thereby decreasing total pressure drop by 6.6 ~ 14.7%. The guide vane system blocked the hopper directional vortex, which resulted optimal vane angle of 53°. The total pressure of the guide vane system increased by 0.5 ~ 3% at 1.5 m/min conditions. However, the filtration pressure drop decreased by 4.8 ~ 12.3% in all conditions, thereby reducing the operating cost of filter bags.

• 한국해양공학회지
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• 제20권4호
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• pp.83-90
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• 2006

Recently, as the technology of utilization for the ocean space is being advanced, floating structures are asked for being mare and mare huge-scale. A very large floating structure(VLFS) is considered as a flexible structure, because of a quite large length-to-breadth ratio and its geometrical flexibility. The main object of this study is to develop an accurate and convenient method on the hydroelastic response analysis of very large offshore structures on the real sea states. The numerical approach for the hydorelastic responses is based on the combination of the three dimensional source distribution methods, the dynamic response analysis method and the spectral analysis method. A model is considered as many rigid bodies connected elastic beam elements. The calculated results shaw good agreement with the experimental and calculated ones by Ohta.