• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.395-398
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• 2009

Currently, a new generation of ducted fan UAVs (Unmanned Aerial Vehicles) is under development for a wide range of inspection, investigation and combat missions as well as for a variety of civil roles like traffic monitoring, meteorological studies, hazard mitigation etc. The current study presents extensive results obtained experimentally in order to investigate the tip clearance effects on performance characteristics of a ducted fan for small UAV systems. Three ducted fans having different tip clearance gap and with same rotor size were examined under three different yawed conditions of calibrated slanted hot-wire probe. Three dimensional velocity flow fields were measured from hub to tip at outlet of the ducted fan. The analysis of data were done by PLEAT (Phase locked Ensemble Averaging Technique) and three non-linear differential equations were solved simultaneously by using Newton -Rhapson numerical method. Flow field characteristics such as tip vortex and secondary flow were confirmed through axial, radial and tangential velocity contour plots. At the same time, the effects of tip clearance on axial thrust and input power were also investigated by using wind tunnel measurement system. For enhancing the performance of ducted fan, tip clearance level should be as small as possible.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권11호
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• pp.547-554
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• 2006

The detent force of a permanent magnet linear motor(PMLM) consists of the end force and cogging force, and should be reduced for high precision purpose applications. The cogging force comes from the electromagnetic interaction between the permanent magnets and interior teeth(or the slots) of the stator, and of which the magnitude depends on the ratio of the numbers of the armature and permanent magnet poles as well as the geometrical shape of the permanent magnet and armature pole. In order to reduce the cogging force of a PMLM, this paper proposes a new configuration which has 9 permanent magnet poles and 10 armature winding slots. By theoretical investigation of the principle of cogging force generation and simulating using finite element method, the proposed PMLM configuration is proven to give much less cogging force than the conventional configuration which has 8 permanent magnet poles and 12 armature winding slots. A proper winding algorithm, modified (A, A, A) winding method, for the proposed configuration is also suggested when the proposed PMLM is operating as a 3 phase synchronous machine. A theoretical and numerical calculation shows that the proposed configuration makes slightly bigger back-emf and thrust force under same exciting current and total number of winding turns condition.

• International Journal of Precision Engineering and Manufacturing
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• 제6권1호
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• pp.65-72
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• 2005

Drilling process is one of the most common, yet complex operations among manufacturing processes. The performance of a drill is largely dependent upon drilling forces, Many researches focused on the effects of drill parameters on drilling forces. In this paper, an effective theoretical model to predict thrust and torque in drilling is presented. Also, with the predicted forces, the stress analysis of the drill tool is performed by the finite element method. The model uses the oblique cutting model for the cutting lips and the orthogonal cutting model for the chisel edge. Thrust and torque are calculated analytically without resorting to any drilling experiment, only by tool geometry, cutting conditions and material properties. The stress analysis is performed by the commercial FEM program ANSYS. The geometric modeling and the mesh generation of a twist drill are performed automatically. From the study, the effects of the variation of the geometric features of the drill and of the cutting conditions of the drilling on the drilling forces and the stress distributions in the tool are calculated analytically, which can be applicable for designing optimal drill geometry and for improving the drilling process.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제31회 추계학술대회논문집
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• pp.67-71
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• 2008

추력조정이 유연한 차세대 고체추진기관 그리고 위성제어용 차세대 비냉각 액체엔진 소형추력기는 $2500^{\circ}C$급의 가혹한 작동조건에서 비삭마, 내열 내산화와 같은 내구성을 가진 내열부품을 요구하고 있다. 본 연구에서는 차세대 추진기관의 작동조건을 제시하고 그에 맞는 내열부품의 국내외 기술현황을 조사하였다. 또한 레늄(Re)을 기본으로하는, 고체 및 액체추진기관에 동시 적용이 가능한 $2500^{\circ}C$급 초고온 장수명 추력기(thruster) 내열부품의 국내연구 필요성과 방향을 제시하였다.

• 한국수소및신에너지학회논문집
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• 제32권6호
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• pp.542-550
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• 2021

As the application of multirotor grows, the demands for multirotor that can fly longer and load more are increasing. Hydrogen has a high energy density, so it can satisfy these demands when used in multirotor. In order to design hydrogen fueled multirotor that satisfies the desired flight time and payload, it is important to calculate the specifications of a fuel cell, battery, and hydrogen storage system. This paper contains detailed information on various energy systems used in multirotor and fuel cell powered multirotor research trends. This study proposed a sizing calculation method that meets the target flight time and payload using thrust and power equations. It has been explained how the two equations derive the particular specifications. The specifications of the multirotor were derived by assuming a payload of 50 kg and a flight time of 1 hour. In addition, the effects of the values of the fuel cell, hydrogen storage system, and motor propeller were analyzed.

• 설비공학논문집
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• 제17권4호
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• pp.325-332
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• 2005

This paper addresses the development of a scroll expander for power generation from relatively low temperature steam source. It has a double-sided orbiting scroll member so that no thrust bearing is needed to support the base plate of the orbiting scroll. Three power transmission shafts are placed at the periphery of the orbiting scroll base plate, and these shafts can also function as anti-rotation devices. Final output is obtained from the main central shaft engaged with the three power transmission shafts through gear assembly. The clearance between the fixed and orbiting scroll elements was estimated by comparing measurement of the mass flow rate with calculation results of a computer simulation. Due to large clearance, the expander total and volumetric efficiencies were measured to be $34\%\;and\;43\%$, respectively. It has been shown through the computer simulation that the total and volumetric efficiencies could be improved to $65\%\;and\;83\%$, respectively, if the current clearance is reduced by half.

• Nuclear Engineering and Technology
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• 제49권4호
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• pp.825-837
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• 2017

Due to the severe impacts of recent earthquakes, the use of seismic isolation is paramount for the safety of nuclear structures. The diversity observed in seismic events demands ongoing research to analyze the devastating attributes involved, and hence to enhance the sustainability of base-isolated nuclear power plants. This study reports the seismic performance of a seismically-isolated nuclear reactor containment building (NRCB) under strong short-period ground motions (SPGMs) and long-period ground motions (LPGMs). The United States Nuclear Regulatory Commission-based design response spectrum for the seismic design of nuclear power plants is stipulated as the reference spectrum for ground motion selection. Within the period range(s) of interest, the spectral matching of selected records with the target spectrum is ensured using the spectral-compatibility approach. NRC-compliant SPGMs and LPGMs from the mega-thrust Tohoku earthquake are used to obtain the structural response of the base-isolated NRCB. To account for the lack of earthquakes in low-to-moderate seismicity zones and the gap in the artificial synthesis of long-period records, wavelet-decomposition based autoregressive moving average modeling for artificial generation of real ground motions is performed. Based on analysis results from real and simulated SPGMs versus LPGMs, the performance of NRCBs is discussed with suggestions for future research and seismic provisions.

• 한국정밀공학회지
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• 제22권12호
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• pp.190-197
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• 2005

For precise micro-grooving and surface machining, a mechanism for creating elliptical vibration cutting (EVC) motion is proposed which uses two parallel piezoelectric actuators. And based on its kinematical analysis, variations of EVC path are investigated as a function of dimensional changes in the mechanism, phase difference and amplitude of excitation sinusoidal voltages. Using the proposed PZT mechanism, various types of two dimensional EVC paths including one dimensional vibration cutting path along the cutting direction and thrust direction can be easily obtained by changing the phase lag, the amplitude of the piezoelectric actuators, and the dimension of the mechanism.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 후기학술대회논문집
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• pp.31-32
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• 2005

It is known that an oscillating airfoil can produce a driving force through the generation of a reversed $K\acute{a}rm\acute{a}n$ vortex street, and this can be expected to be a new highly effective propulsion system. We have been examined various conditions such as frequency number, amplitude in NACA 0010. As Strouhal number is greater than 0.08, wake profile with velocity deficit can be transformed into the wake with velocity excess. We also presented the experimental results on the unsteady vortices structure of the heaving airfoil at various parameters.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2001년도 제16회 학술발표회 논문초록집
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• pp.35-38
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• 2001

차세대 추진 기관으로 연구되고 있는 스크램제트 엔진의 열역학적 특성들을 검토하였다. 유동이 엔진을 통과하면서 연소에 의해 전압력이 손실되고 노즐 출구 마하수가 감소하지만, 고온 연소 가스가 배출되기 때문에 실질적인 속도는 증가하게 되고 추력이 발생한다. 초음속 연소를 모사하기 위해 blowdown 형태의 초음속 연소 풍동 설계를 위한 개념 설계가 이루어졌다. 초음속 풍동 시험부에서 마하 2.5의 속도를 유지하기 위한 작동 압력과 질유량이 계산되었다.