• Ocean Systems Engineering
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• 제2권4호
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• pp.297-314
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• 2012

Power-take-off through inner dynamic system inside a floating buoy is suggested. The power take-off system is characterized by mass, stiffness, and damping and generates power through the relative heave motion between the buoy and inner mass (magnet or amateur). A systematic hydrodynamic theory is developed for the suggested WEC and the developed theory is illustrated by a case study. A vertical truncated cylinder is selected as a buoy and the optimal condition of the inner dynamic system for maximum PTO (power take off) through double resonance for the given wave condition is systematically investigated. Through the case study, it is seen that the maximum power can actually be obtained at the optimal spring and damper condition, as predicted by the developed WEC theory. However, the band-width of high performance region is not necessarily the greatest at the optimal (maximum-power-take-off) condition, so it has to be taken into consideration in the actual design of the WEC.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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• pp.211-218
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• 2000

Off-design experimental performance was investigated for a small centrifugal compressor, whose impeller diameter is about 125mm, used in an industrial gas turbine. Test rig was designed and manufactured with a radial inflow turbine and a combustor to supply driving power to the compressor. Static pressure was measured on the casing of the impeller, vaneless diffuser, vaned diffuser and volute. Total pressure was obtained using specially fabricated rakes at the vaned diffuser throat and exit. Circumferential nonuniformity was found, near surge, in the Impeller, vaned diffuser and volute region. Spanwise nonuniform flow from the impeller affected the total pressure defects in the vaned diffuser region. Static pressure distortion in the circumferential direction in the volute was found near surge, where the minimum occurred near 140 degree position.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.134-140
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• 1999

A three-dimensional CSCM upwind flux difference splitting Navier-stokes code with two-equation turbulence models was developed to predict the transonic flows in centrifugal compressor diffuser. The k-$\epsilon$ model of Abe et al. performed well in predicting the pressure distribution in the shock wave/turbulent boundary-layer interaction. Three turbulence models predicted the similar distribution of static pressure through the diffuser and showed a good agreement with the experimental results. The secondary flows in the corner were predicted well by these turbulence models. The pressure increase before the throat of the diffuser vane is important for the overall pressure recovery. As the mass flow rate increased the blockage decreased at the throat. The pressure coefficient distribution through the diffuser depended on the throat blockage not on the rotational speed of the impeller.

• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.272-285
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• 2004

The losses at off-design points from a compressor cascade occur due to the deviation from a design incidence angle at the inlet of the cascade. The self-noise from the blade cascade at off-design points comes from a separated boundary layer and vortex sheddings. If the incidence angle to the cascade increases, stalling in blades may occur and the noise level increases significantly. This study applied Large-Eddy Simulations (LES) using deductive and deductive dynamic SGS models to low Mach-number, turbulent flow with each incidence angle to the cascade ranging from -40$^{\circ}$ to +20$^{\circ}$ and compared numerical predictions with measured data. It was observed that the oscillating separation bubbles attached to the suction surface do not modify wake flows dynamically for cases of negative incidence angles. However, an incidence angle greater than 8$^{\circ}$ caused a separated vortex near the leading edge to be shed downstream and created stalling. The computed performance parameters such as drag coefficient and total pressure loss coefficient showed good agreement with experimental results. Noise from the cascade of the compressor is summarized as sound generated by a structure interacting with unsteady, turbulent flows. The hybrid method using acoustic analogy was observed to closely predict the measured overall sound powers and directivity patterns at design and off-design points of blade cascade.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 A
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• pp.274-277
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• 1995

Recent environmental pollutions have intensified the need to develop zero emission vehicles. The most effect method of such solutions is EV. EV is high energy efficiency, easy to maintain, repair and is possible to make high performance control. However, because energy density of batteries is constrained and the distance covered one charge is short range. Also because EV has disadvantage of poor accelation ability, development of high performance battery is required for large scale use of EV. EV charger analogous to gas apparatus must also be developed immediately. Charger is discriminate between on-vehicle type and off-vehicle type. As off-vehicle type is able to charge fast and safe, inductive charging is considered. This paper aims to develope off-vehicle inductive charging system. Therefore, it achieved power factor correction converter, high frequency DC/AC inverter control algorithm development which gives proof validity through simulation and formulated the basic concept of high frequency transformer design for inductive charging.

• Current Optics and Photonics
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• 제6권1호
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• pp.44-50
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• 2022

An off-axis zone plate is able to focus on a single order while neglecting the zeroth order in a visible imaging system. This allows one to enhance the contrast quality in diffractive images, which is the major advantage of this type of zone plate. However, most previous reflection zone plates are used in focusing X-rays with a small grazing incident angle and are intricately designed with the use of a local grating period. In this study, we suggest the design of an off-axis elliptical zone plate (EZP) that is used to focus a monochromatic light beam with separation between the first and unfocused orders under a large grazing incident angle of 45°. An assumption using the total grating period, which depends on the average and constant grating period, is proposed to calculate the desired distance between the first and zeroth order and to simplify the construction of a novel model off-center EZP. Four diffractive optical elements (DOEs) with different parameters were subsequently fabricated by direct laser lithography and then verified using a performance evaluation system to compare the results from the assumption with the experimental results.

• 대한기계학회논문집B
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• 제26권1호
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• pp.55-65
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• 2002

In this study, the procedures for the preliminary design of the turbo-shaft engine for the light multi-purpose helicopter are established. The engine specifications are determined through the performance analysis on the on-design and off-design conditions by the use of simulation program. In addition, the effect of humidity on the engine performance is examined by considering the change of the gas properties and characteristic maps due to moisture contents. The calculation results show that the engine power is reduced by the existence of moisture in working fluid.

• 한국정보통신학회논문지
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• 제6권4호
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• pp.574-581
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• 2002

기존의 큐잉분석은 네트워크 용량설계 및 성능 예측시 상당히 유용하지만, 실제의 경우 큐잉 분석으로부터 예측된 결과는 실제 관측된 성능과는 상당히 다르다. 또한 LAM, WAN 및 VBR 트래픽 특성에 관한 최근의 실험적 연구들은 기존의 Poisson 가정에 의한 모델들이 네트워크 트래픽의 장기간 의존성 및 self-similar 특성을 과소평가 함으로써, 실제 트래픽의 특성을 제대로 나타낼 수 없다는 것을 지적해 왔다. 본 논문에서는 exactly self-similar 모델링인 Pareto-like ON/OFF 소스 모델링에 의한 트래픽과 기존의 Poisson 모델링에 의한 트래픽을 비교 분석함으로써, self-similar 트래픽이 실제의 Ethernet 트래픽 특성을 잘 반영한다는 것을 보임으로써 최적화된 ATM 네트워크 설계 및 성능분석을 이루고자 한다.

• International Journal of Aeronautical and Space Sciences
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• 제4권1호
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• pp.88-98
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• 2003

Compared to the noise limits (CAN7) specified in ICAO Annex 16 for civil helicopters, the Lynx helicopter equipped with BERP blades has only 0.2 EPNdB margin in the approach case although it has more than 4 EPNdB margin in fly-over and take-off conditions. The objectives of the study described in this paper were to devise a low noise main rotor blade for the Lynx using UEAF combined with the high resolution airload model ACROT. A design requirement is that the new blade, KBERP (Korean BERP) blade should achieve a significant reduction in noise during approach(at least 6EPNdB margin) without any noise penalty in fly-over and take-off conditions and minimal performance penalty. It was decided to investigate a tip modification to the BERP blade, employing the twin vortex concept to reduce the BVI noise and to retain the excellent high speed performance characteristics of BERP. Through the parametric study, the KBERP blade with optimized twin vortices has at least a 9 EPNdB noise margin in approach flight condition with only a small penalty in fly-over and take-off conditions. The KBERP tip is thus a very cost effective wav to reduce BVI noise during approach.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1987년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 16-17 Oct. 1987
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• pp.547-549
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• 1987

The purpose of this paper is to present an efficient and practical method for a Hissle autopilot design problem. The method emphasizes on the use of a modern design technique to classical flight control specifications and the trade-off between dynamic performance and robustness of the Missle autopilot control system.