• Journal of computational fluids engineering
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• v.11 no.3 s.34
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• pp.1-7
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• 2006

Euler and Navier-Stokes flow analyses for helicopter rotor in hover were performed as low and high fidelity analysis models respectively for the future multidisciplinary design optimization(MDO). These design-oriented analyses possess several attributes such as variable complexity, sensitivity-computation capability and modularity which analysis models involved in MDO are recommended to provide with. To realize PC-based analyses for both fidelity models, reduction of flow domain was made by appling farfield boundary condition based on 3-dimensional point sink with simple momentum theory and also periodic boundary condition in the azimuthal direction. Correlations of thrust, torque and their sensitivities between low and high complexity models were tried to evaluate the applicability of these analysis models in MDO process. It was found that the low-fidelity Euler analysis model predicted inaccurate sensitivity derivatives at relatively high angle of attack.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.240-245
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• 1996

높은 정지 비행 마하수를 갖는 로우터에 대해서 고속 충격 소음을 전산 유체역학파 Kirchhoff 공식의 결합으로서 해석하였고 그 해석 결과들이 실험값과 비교되었다. 첫째로, 고전적인 선형 Kirchhoff 공식이 제어면들의 위치와 지연시간의 방정식에 대해서 고려되었으며 이의 결과들은 기본적인 유동장의 물리적인 성질과 일치하는 것으로 나타났다. 제어면이 비선형 유동장의 바깥에 위치하였을 경우,선형 Kirchhoff 공식은 진폭과 파형이 실험 data와 잘 일치하는 것을 알 수 있었다. 또 제어면이 깃끝에 매우 가깝게 있을 경우 비선형 Kirchhoff 공식을 사용해서 좋은 결과들을 가져올 수 있었는데 즉 정확하게 음향학장(acoustic field)를 묘사할 수 잇는 것은 비선형 Kirchhoff 공식이라는 결론을 얻었다.

• The Optical Journal
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• s.158
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• pp.40-47
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• 2015

드론은 군사용으로 제일 먼저 개발되어 시장을 형성했지만, 오픈소스 드론의 제작이 많아지면서 소비자 시장도 급속도로 확대되고 있다. 최근 중국의 DJI는 기업가치 100억 달러 이상을 넘볼 정도로 급성장을 하였고, 드론용 소프트웨어나 플랫폼을 확보한 스타트업 기업들에 대한 투자도 활발하게 이루어지고 있다. 구글이나 페이스북, 아마존 등은 자사의 서비스 강화를 위한 목적으로 드론 기술을 적극적으로 활용하고 있으며, 드론의 시장 확대에 따른 드론 시장 생태계도 크게 확장되고 있다. 최근 드론에 대한 관심이 뜨겁다. 특히 중국의 DJI는 모형 헬리콥터의 비행조종 시스템을 만들다가 전격적으로 소비자 드론 시장에 뛰어들었는데, 2014년 약 5억 달러 정도의 매출을 올렸다고 한다. 이는 2013년과 비교할 때 4배가 증가한 것이며, 2015년에는 또 다시 2배 이상 성장을 할 것으로 보여 올해에는 소비자 드론을 만드는 기업중에서 세계 최초로 10억 달러 매출을 달성할 것으로 예측된다. 당연히 기업가치도 크게 상승해서, 실리콘밸리에서는 DJI의 기업 가치를 100억 달러 이상으로 보고 있다.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.389-394
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• 2007

Numerical simulations are conducted to investigate the mechanism for force generation of an insect with tandem wing configuration. Various stroke amplitudes, stroke plane angles and phase difference between the fore- and hind-wings are considered. The Reynolds number is 150 based on the chord length and maximum translation velocity of the wing. When an insect requires high lift such as takeoff, it flaps its wings in parallel at a lower stroke plane angle and a bigger stroke amplitude than those in the hovering. With wings in counter-stroke, the lift fluctuations decrease, and moreover mean lift force decreases. Interactions among the fore-wing, hind-wing and vortices are examined to explain the force variations

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.763-766
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• 1996

A model helicopter is an unstable, multi-input multi-output nonlinear system exposed to strong disturbances and its system parameters change continually. In this paper, Time Delay Control(TDC) is adopted for these reasons. TDC uses past observation of the system's response and the control input to directly modify the control action rather than adjusting the controller gains leading to a model independent robust controller. TDC can force the plant to follow an appropriate reference model, but the reference model cannot be chosen arbitrarily. In this paper the procedure of choosing a reference model and the performance of the controller are presented.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.151-154
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• 2006

In the present paper, hovering performance analyses of proprotor and helicopter rotor blades were performed by using FLUENT software. As a proprotor, TRAM(Tilt Rotor Aeroacoustic Model) was selected and performance analysis was carried out with mesh adaptation for more elaborate solution. As a helicopter rotor blades, two bladed Caradonna and Tung's rotor and four-bladed BO-105 helicopter rotor blades were selected. In case of Caradonna and Tung's rotor, vortex trajectory was compared with experimental data to inspect the vortex convection capability of the present flow solver. For the final case, performance of BO-105 helicopter rotor blades was investigated and compared with experimental data. After performance analyses of proprotor and helicopter rotors, it was shown that the present solver showed reasonable vortex strength, wake geometry and thurst coefficient distributions. But power coefficient was somewhat overestimated about $10%{\sim}15%$ regard less of mesh adaptation.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.125-129
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• 2007

In this paper a method for the design optimization for helicopter rotor blade in hover is studied Numerical analysis of aerodynamic characteristics of the flow around a rotor blade is analysed by usign panel method and CFD code based on Navier-Stokes equation. The result is validated by comparing with existing experimental result. Optimization methods RSM(Response Surface Method) and DOE(Design of Experiments) are applied in combination. The object functions are power, twist angle, taper ratio, and thrust. The optimized result showed a decrease of 17% of the power required.

• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.2599-2601
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• 2000

A helicopter control problem has been researched with many control theory. Especially, study of the hovering flight attitude control of a helicopter has been brisked since 60s with multivariable control theory. In this paper, the modeling is interpreted through the 6-freedom equation. To getting a entire equation, species of parameters and charts are adapted. The $H_2/H_{\infty}$ controller is acquired by mixing the $H_2$ control theory and the $H_{\infty}$ control theory. The $H_2$ control theory is reasonable one to increase the performance of a plant, and the $H_{\infty}$ control theory secures the robust stability. The simulation shows that the helicopter system is being controlled while maintaining performance and robust stability against perturbation.

• Proceedings of the KIEE Conference
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• 1998.11b
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• pp.457-459
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• 1998

This paper presents a 3-DOF hovering flight controller for a model helicopter using the minimal order LQG/LTR technique. A model helicopter is an unstable multi-input multi-output nonlinear system strongly exposed to disturbances, so a robust multi-variable control theory should be applied to control it. The minimal order LQG/LTR technique which uses a reduced-order observer in the LTR procedure is used to design the controller. Performances for the 3-DOF hovering flight controller are evaluated through computer simulations.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.83-86
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• 2004

The aeroelastic stability analysis of composite bearingless rotors is investigated using a large deflection beam theory in hover. The bearingless rotor configuration consists of a single flexbeam with a wrap-around type torque tube and the pitch links located at the leading edge and trailing edge of the torque tube root. For the analysis of composite bearingless rotors, flexbeam is assumed to be a rectangular section made of laminate. Two-dimensional quasi-steady strip theory and Loewy's aerodynamic theory with the lift deficiency function are used for unsteady aerodynamic computation. The finite element equations of motion for beams are obtained using Hamilton's principle. Numerical results of selected bearingless rotor configurations are obtained for the lay-up of laminae in the flexbeam and pitch links location.