• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.314-318
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• 2006

The interest on the detonation in small tubes, which can be applied to the ignition devices of propulsion system, is increasing. However, the propagation dynamics of detonation waves in small tubes has not been investigated clearly yet. In the present experiments, propagations of detonation waves in stoichiometric propane-oxygen mixture through transparent tubes were recorded using a high speed camera and average velocities were measured as well. In terms of average velocity, there exists a transition regime where the waves show smooth transition from the normal Chapman-Jouguet(CJ) detonation to the low velocity detonation$(\sim0.5V_{CJ})$ along the decreasing initial pressure. In this transition regime, the detonation waves are highly unstable and show cyclic or intermittent longitudinal velocity fluctuation.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.5
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• pp.467-477
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• 2004

A new scheme to estimate the moment of inertia in the servo motor drive system in very low speed is proposed in this paper. The typical speed estimation scheme in most servo system for low speed operation is sensitive to the variation of machine parameters, especially the moment of inertia. To estimate the motor inertia value, the observer using the Radial Basis Function Networks(RBFN) is applied. The effectiveness of the proposed inertia estimation method is verified by experiments. It is concluded that the speed control performance in the low speed region is improved with the proposed disturbance observer using RBFN.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1009-1015
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• 2011

In this study, in the high expansion cycle was conduced by variable valve timing system composition to close intake valve late, and in the intake air reduction on the low compression was solved by supercharging pressure. In this wise, by constituting Diesel-Atkinson cycle, this study looked into a possibility of thermal efficiency improvement. As a result, there was improvement in thermal efficiency and output in a whole range of closing timing from ABDC $40^{\circ}$ to ABDC $80^{\circ}$. However, after ABDC $70^{\circ}$ of closing timing, the thermal efficiency increase was getting smaller. As the result of the study, the optimum intake valve closing timing was about ABDC $70^{\circ}$, high loading territory of engine was more effective than low loading territory, and engine operation in middle loading territory was stable. At this time, brake thermal efficiency was 12.5% higher than ordinary engine on average.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.2
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• pp.97-104
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• 2005

A simple but efficient grid generation technique by using the modified compressible form of stream function has been formulated. Transformation of a physical plane to a streamline plane, the Von Mises Transformation, has been widely used to solve the differential equations governing flow phenomena, however, limitation arises in low velocity region of boundary layer, mixing layer and wake region where the relatively large grid spacing is inevitable. Modified Von Mises Transformation with simple mathematical adjustment for the stream function is suggested and applied to solve the confined coaxial turbulent jet mixing with simple $\kappa-\epsilon$ turbulence model. Comparison with several experimental data of axial mean velocity, turbulent kinetic energy, and Reynolds shear stress distribution shows quite good agreement in the mixing layer except in the centerline where the turbulent kinetic energy distributions were somewhat under estimated. This formulation is strongly suggested to be utilized specially for free turbulent mixing layers in axisymmetric flow conditions such as the investigation of mixing behavior, jet noise production and reduction for Turbofan engines.

• Electronics and Telecommunications Trends
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• v.21 no.5 s.101
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• pp.30-39
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• 2006

유비쿼터스 네트워크 시대가 도래함에 따라 위치인식 기반 응용 서비스 요구 증대에 따른 위치인식 무선 개인영역 네트워크(WPAN) 시스템이 주목을 받고 있다. 특히 초광대역(UWB) 기술은 저비용, 저소비 전력으로 통신뿐만 아니라 실내나 음영지역에서 수십 cm급 이내의 정밀한 위치인식/추적 기능을 줄 수 있어, 유비쿼터스 홈을 구축하기위한 핵심 기술로 인식되고 있으며, 저속 위치인식 WPAN 표준인 IEEE 802.15.4a의 물리계층(PHY)으로 채택되었다. 본 원고에서는 위치인식 UWB 기술과 관련한 IEEE802.15.4a 표준화 현황과 기술 동향에 대해서 살펴보고자 한다.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.3
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• pp.280-287
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• 2008

In this paper, a mathematical model for a ship manoeuvring with low forward speed in shallow water was suggested. Based on the cross flow model with low forward speed in deep sea, hull, propeller and rudder models were modified to consider the shallow water effects. Static drift and PMM tests were performed to obtain the cross flow drag coefficients and hydrodynamic coefficients. To validate suggested mathematical model, numerical simulation results were compared with those of sea-trials. Through comparisons, it was concluded that suggested mathematical model could give proper estimation on turning test results.

• Journal of Energy Engineering
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• v.4 no.1
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• pp.126-139
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• 1995

저속의 압축성 유동장에서의 원형 실린더 주위의 유동 및 열전달특성을 해석하였다. 비압축성 유동장에서의 실린더 주위의 유동 및 열전달현상에 대하여는 실험과 수치해석을 포함한 광범위한 연구가 진행되어 왔으며 매우 잘 알려져 있다. 실린더 벽면과 주위 유동장의 온도차가 큰 경우, 밀도의 변화가 커지므로 유동장은 압축성 유체가 되나 지배 방정식의 복잡함과 적절한 수치해석 방법의 부족으로 실린더 주위의 유동장을 압축성유체로 해석한 경우는 매우 드물다. 현재 압축성유동 해석에 널리 사용되는 time marching algorithm은 저속의 유동장 해석시 지배방정식에 나타나는 eigenvalue들의 괴리에 의하여 수렴속도가 현저히 떨어지게 된다. 본 연구에서는 이와 같은 난점을 극복할 수 있는 time-derivative preconditioning 방법을 사용하여 온도차가 큰 유동장에서의 강제 및 혼합대류에 대한 계산을 수행하였고 이들의 열전달특성을 비교하였다. 강제대류의 경우 실린더 벽면 온도의 증가에 따른 밀도 감소의 영향은 유동장의 Re수를 감소시켜 확산의 영향을 증가시키면서, 혼합대류의 경우 부력의 영향은 가열되는 유동장의 범위와 재순환 영역을 강제대류에 비해 현저히 감소시킨다.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1852-1853
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• 2007

지난 수 십년 동안 소량의 저속 데이터 통신 특성에 적합하게 개발되어온 현재의 전력 운영시스템은 각 전력회사로 부터 신뢰성 있는 전력설비 운영이라는 목표를 가장 잘 만족시키는 기술의 선택에 의해 전력회사의 요구를 훌륭히 만족시키며 운영되어 왔다. 하지만 저속 데이터 통신의 제약 뿐 아니라 이용 할 수 있는 데이터의 한계는 전력회사에게 계통운영의 신뢰성 유지 목표이외의 다른 것을 고려하도록 하지 않았을 뿐 아니라 이들 기술들이 지닌 상호 운영성 결여 및 배타적인 환경구성 요건은 전력회사에게 처음 선택한 기술이외의 다른 대안을 생각할 수 없게 만들어 왔다. 본 논문은 지능형 전력기기의 확산과 전력산업 디지털화가 확대되면서 전력시스템 전 영역에 걸쳐 발생되는 새로운 데이터의 활용과 전력회사들이 처음 선택한 기술에 의한 기술 종속으로부터 자신들의 요구에 맞는 다양한 기술을 취사선택할 수 있는 기술 독립적 전력시스템 참조 아키텍처에 대하여 기술하였다.

• Proceedings of the KAIS Fall Conference
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• 2011.12b
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• pp.551-553
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• 2011

본 논문에서는 유도전동기의 저속운전영역에서 고속운전영역에 이르기까지 모든 영역에 걸친 안정된 속도제어를 목적으로 전압 전류 모델 합성 자속 추정기를 구현하였다. 제시한 시스템의 유용성을 확인하기 위해 3.7[kW]용량의 농형 유도전동기에 적용하여 시뮬레이션의 편의를 위해 각각의 제어기를 Matlab/Simulink를 통해 모델링하여 검토하였으며, 실험을 통해 확인하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6C
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• pp.561-570
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• 2009

Ultra-wideband communication systems based on impulse radio have merits that are possible for the high data rate transmission, high resolution ranging are positioning system. Conventionally, in order to accomplish these features, the high-speed ADC (Analog to Digital Convertor) is necessary to apply radio determination system operating in time domain. However, considering low rate - wireless personal area network (LR-WPAN) aims to low-cost hardware implementation, the expensive ADC converting GHz sampling per second is not appropriate. So, this paper introduces a low complex AR (Auto Regressive) model based non-coherent ranging scheme operating in frequency domain with using low-speed ADC utilizing analog Voltage Control Oscillator (VCO) mode for the frequency domain transformation. To verify the superiority of the proposed ranging and location algorithm working in frequency domain, the suggested IEEE 802.15.4a TG channel model is used to exploit affirmative features of the proposed algorithm with conducting the simulation results.