• 대한기계학회논문집A
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• 제37권8호
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• pp.1007-1013
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• 2013

이 논문은 터빈 로터의 형상변화에 따른 공력 특성에 대하여 분석하였다. 본 논문의 터빈은 헬리콥터의 보조동력 장치로 사용되는 소형엔진이다. 소형엔진은 팁 형상의 구조적 취약성 때문에 성능을 향상시키기 어렵다. 그러므로, 터빈의 허브를 개선하는 것이 여러 가지 측면에서 유리하다. 터빈의 작동유체는 고온 고압의 가스이다. 터빈표면의 열전달률이 고려되었을 때, 열부하에 의한 블레이드의 손상을 줄이기 위해서는 블레이드 표면의 열전달률 분포를 고찰하여야 한다. 수치모사 결과를 검증용 실험값과 비교하였을 때, SST난류모델은 공력 특성을 잘 반영하고 열전달 예측성능도 우수하였다. 결론적으로, 허브측 선단에서 구륜설계(bulbous design)를 적용하였을 때 공력효율이 향상되었고, 전체 공력 손실 중 끝벽 손실은 15% 감소되었다.

• 한국정밀공학회지
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• 제16권2호통권95호
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• pp.23-30
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• 1999

This paper investigates the radial performance of self-acting spiral-grooved air bearing, used to support small high-speed rotating bodies. Repeatable runout, nonrepeatable runout, stiffness and supporting load are selected as the performance. The clearance between rotor and stator, the stator groove depth, and the rotating speed are chosen as three main parameters affecting the performances. Force application and displacement measurement are done in a noncontact manner, in order not to disturb operation: electromagnetic force is applied to the rotor and gap sensors are used to measure the displacement of the rotor. Experimental results show that repeatable runout decreases as speed, groove depth and clearance decrease. Nonrepeatable runout decreases as clearance decreases, and it has a minimum value at $5.5{\mu}m$ of grove depth and a maximum value at speed of 18.000rpm. Stiffness increases as speed increases and clearance decreases, and has a maximum value around $5.5{\mu}m$ of groove depth. The relationship between force and displacement is linear for small displacement, but becomes nonlinear for large displacement. Supporting load is linearly proportional to the stiffness, and it is a maximum value around $4.75{\mu}m$ of clearance.

• 항공우주기술
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• 제8권1호
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• pp.32-41
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• 2009

본 연구에서는 한국형기동헬기(KUH) 주로터 블레이드의 축소 설계를 수행하였다. 축소 모델은 공력하중, 익단 와류 및 소음원 측정 시험을 위해 설계되었다. 실제 로터와 동일한 공력 하중을 모사하기 위하여 마하스케일링 기법이 적용되었다. 마하스케일 모델은 블레이드의 익단 마하수가 동일하며, 정규화된 진동수 또한 동일하다. 즉, 마하스케일된 모델은 공력하중 및 구조동역학적 과점에서 상사된 모델이다. 공기역학적 축소과정은 외형 치수의 축소와 회전수의 증가를 통해 완료된다. 구조동역학적 측면에서는 블레이드 단면 설계를 통해 생성된 강성 및 관성 분포가 실제 로터의 회전고유진동수 분포를 나타내는지 확인하는 과정을 통해 완료된다. 본 연구에서는 국내에서 수급 가능한 복합재 프리프레그를 이용한 블레이드 단면 설계를 수행하고, 설계된 모델의 동역학적 특성을 고찰하였다.

• 동력기계공학회지
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• 제20권3호
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• pp.22-28
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• 2016

Energy consumption rapidly increases with industrial development. therefore an interest in the efficiency of various power converters is increasing. Especially, the field of high-efficiency small motors widely distributed for industrial and family use is considered a very important field in terms of efficient energy usage, and accordingly, in the field of small electric equipment, the use of BLDC that allows high-efficiency drive in an inductor gradually increases. However, for the BLDC drive, information on the position of the rotor is essential. Both methods using a magnetic encoder and an optical encoder to detect the information on the position of the rotor obtain the information by three position sensitive devices, and if any one of these position sensitive devices fails to function, no positional information can be obtained, so there is a limitation in implementing a position sensor with high reliability. In the paper, proposes a new type of encoder that can obtain the positional information on the position of the rotor using a single position sensor in order to overcome the issues that it has to use numerous signal flows and that the reliability is reduced for the acquisition of positional information generated by using multiple position detectors. The encoder in the proposed method replaced the function of generating positional information from multiple sensors with the shape of the encoder plate and the capture function of MICOM. In order to verify the validity of the position detection technique by the proposed encoder, a prototype was produced, and an experiment using the capture function of DSP was conducted through this.

• International Journal of Fluid Machinery and Systems
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• 제9권2호
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• pp.169-174
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• 2016

A cross-flow wind turbine has a high torque coefficient at a low tip speed ratio. Therefore, it is a good candidate for use as a self-starting turbine. Furthermore, it has low noise and excellent stability; therefore, it has attracted attention from the viewpoint of applications as a small wind turbine for an urban district. However, its maximum power coefficient is extremely low (10 %) as compared to that of other small wind turbines. In order to improve the performance and flow condition of the cross-flow rotor, the symmetrical casing with a nozzle and a diffuser are proposed and the experimental research with the symmetrical casing is conducted. The maximum power coefficient is obtained as $C_{pmax}=0.17$ in the case with the casing and $C_{pmax}=0.098$ in the case without the casing. In the present study, the power characteristics of the cross-flow rotor and those of the symmetrical casing with the nozzle and diffuser are investigated. Then, the performance and internal flow patterns of the cross-flow wind turbine with the symmetrical casings are clarified. After that, the effect of the side boards set on the symmetrical casing is discussed on the basis of the analysis results.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.265-270
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• 2005

This paper presents a new attitude stabilization and control of an unmanned helicopter based on neural network compensation. A systematic derivation on the dynamics of an unmanned small-scale helicopter is performed. Combined rotor-fuselage-tail dynamics is derived in body-fixed reference frame with its origin at the C.G. of the helicopter. And the resulting nonlinear equation of motion consists of 6-DOF air vehicle dynamics as well as the rotor flapping and engine torque equations. A simulation model was modified using the existing simulator for an unmanned helicopter dynamic model, which reflects the unmanned test helicopter(CNUHELI). The dynamic response of the refined model was compared with the flight test data. It can be shown that a good coincidence was accomplished between the real unmanned helicopter system and the mathematical model. This dynamic model was linearized for classical controller design using small perturbation method. A Neuro-PD control system was designed for both longitudinal and lateral flight modes, and the results were compared with the PD-only control response. Simulation results show that the proposed Neuro-PD control system demonstrates better performance.

• 대한기계학회논문집B
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• 제33권8호
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• pp.580-588
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• 2009

This paper summarizes the experimentally-measured performance of small-scale, vertical-axis wind turbine for the purpose of improving the aerodynamic efficiency and its controllability. The turbine is designed to have a Savonius-Type rotor with an inlet guide-vane and an side guide-vane so that it achieves a higher efficiency than any lift- or drag-based turbines. The main design factors for this high-efficient, vertical wind turbine are the number of blades (Z), and the aspect ratio of Height/Diameter (H/D) among many. The basic model has the diameter of 580mm, the height of 464mm, and the blade number of 10. The maximum power coefficient of 0.50 was experimentally measured for the above-mentioned specifications. The inlet-guide vane ensures the maximum efficiency when the angle of attack to the rotor blade lies between $15^{\circ}$ and $20^{\circ}$. This experimental results for the vertical-axis wind turbine can be applied to the preliminary design of turbine output curve based on the wind characteristics at the proposed site by controlling its aerodynamic performance given as a priori.

• International Journal of Fluid Machinery and Systems
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• 제7권2호
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• pp.60-67
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• 2014

In order to clarify the effect of inlet bellmouth size of semi-opened type axial fan on its performance and flow fields around rotor, fan test and flow field measurements using hotwire anemometer were carried out for 6 kinds of bellmouth size. As results of fan test, the shaft power curve hardly changed, even if the bellmouth size changed. On the other hand, the pressure-rise near best efficiency point became small with the bellmouth size decreasing. Therefore, the value of maximum efficiency became small as the bellmouth size decreased. As results of flow field measurements at fan inlet, the main flow region with large meridional velocity existed near blade tip when the bellmouth size was large. As bellmouth size became smaller, the meridional velocity at fan inlet became smaller and the one at outside of blade tip became larger. As results of flow field measurements at fan outlet, the main flow region existed near rotor hub side.

• 대한기계학회논문집A
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• 제24권10호
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• pp.2597-2602
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• 2000

The most effective means of evaluating remaining life is through the creep testing of samples removed from the component. But sampling of large specimen from in-service component is actually impossible. So, sampling device and small-specimen creep tester have been applied. Sampling device has been devised to extract mechanically small samples by hemispherical, diamond -coated cutter from the surface of turbine rotor bores and thick-walled pipes without subsequent weld repairs requiring post weld heat treatment. A method of manufacturing small creep specimen, 2min gage diameter and 10min gage length, using electron beam welding to attach grip section, has been proven. Small-specimen creep tester has been designed to control atmosphere to prevent stress increment by oxidation during experiment. To determine whether the small specimens successfully reproduce the behavior of large specimens, creep rupture tests for small and large specimens have been performed at identical conditions. Creep rupture times based on small specimens have closely agreed within 5% error compared with that of large specimen. The errors in rupture time have decreased at longer test period. This comparison validates the procedure for fabricating and testing on small specimen. This technique offers potential as an efficient method for remaining life assessment by direct sampling from in -service high temperature components.

• 항공우주기술
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• 제13권1호
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• pp.153-165
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• 2014

멀티로터 비행체는 헬리콥터와 같은 제자리 비행이 가능하면서 구조적으로 간단한 형태를 가지며 상대적으로 높은 추력을 가지는 장점으로 인해 다양한 분야에서 활용되고 있다. 최근 레저용으로 개발된 Parrot사의 AR.Drone은 사용자를 위한 내부 안정화 루프를 탑재하고 있기 때문에 초보자들도 쉽게 조정할 수 있으며, SDK(Software Development Kit)를 제공함으로서 멀티로터를 이용한 연구에 쉽게 활용할 수 있는 특징이 있다. 또한 크기가 상대적으로 작으면서 저가이기 때문에 군집비행에 적용되기 적합한 비행체이다. 이에 본 논문에서는 다수의 AR.Drone을 이용하여 실내 군집비행을 위한 제어기 개발과정에 대해서 소개하고자 한다.