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李奉俊,金學奉 한국항공대학교 1982 論文集 Vol.20 No.-
유체의 흐름속에 놓인 날개의 상하면에는 壓力差가 생기고 자유흐름과 結合하여 날개Rmx 주위에는 trailing vortex라는 나선형 흐름이 생긴다. 이 날개끝 (과)流를 抑制하여 誘導抗力을 減少시키는 장치에는 여러가지가 있다. 實驗에 依하면 날개끝 次出이 날개의 揚ㆍ抗特性向上에 效果가 있음이 發見되었다. 本 論文에서는 이러한 次出인 境遇에 對하여 새로운 조건을 주고 V.L.M(Vortex Lattice Method)을 利用하여 날개의 揚ㆍ抗係數에 對한 數値解를 구하였다. 數値解와 잘 一致하는 傾向을 보였다. A wing moving through afluid induces a differential pressure field between the upper and lower surfaces. The resultant spanwise movement of fluid cmobined with the free stream velocity generates a helical movement of fluid about the wingtip called trailing vortex. A number of devices have been employed in an attempt to reduce the induced drag by controlling the trailing vortex. The experimental results showed that the wing tip blowing was more effective to increase aerodynamic characteristics of a wing. In this paper, a new numerical analysis was conducted by using vortex lattice method on the effect of a wing tip blowing on the lifyt and drag characteristics of a wing. The numerically predicted results agree closely with experimental data.
항공기용 제트엔진에 대한 가변구조 제어기 설계에 관한 연구
임흥식,이강웅,김학봉 한국항공대학교 1992 論文集 Vol.30 No.-
본 논문에서는 작동점에서 선형화하여 얻은 터보 제트엔진의 선형 모델에 대한 가변구조제어시스템을 설계하였다. 슬라이딩모드에서 발생하는 채터링을 제거하기 위하여 새로운 스위칭영역 설정방법을 제시하고 이 영역내에서 연속제어 입력이 가해지도록 하였다. 제안된 알고리즘을 적용하여 작동점에서 스텝함수로 변하는 명령을 따르도록 하였으며, 컴퓨터 시뮬레이션을 통하여 결과를 보였다. In this paper a variable structure controller is designed for the aircraft jet engine model which is linearized in operating point. In order to eliminate the chattering in the sliding mode, a new method of the switching region is proposed and a discontiuous control input is substituded by a continuous one in this region. The proposed control algorithm is applied to the engine model plant in the operating point. Simulation results show that good system responses for step changes of the command are obtained.
FA-200機의 wing tip sail에 依한 Vortex減衰의 可視化
李奉俊,金學奉 한국항공대학교 1981 論文集 Vol.18 No.-
A wing moving through a fluid induces a differential pressure field between the upper and lower surfaces. The resultant spanwise movement of fluid combined with the free stream velocity generates a helical movement of fluid about the wing tip called trailing vortex. The sails, small, stuffy vanes which stick out at different angles from the wing tip, are known to reduce a induced drag and to decay the trailing vortex effectively. This paper deals with the flow visualization studies of the decay of a trailing vortex about sails comparing with the basic wing without sails. Three sails were attached to the FA-200 airplane wing tip for smoke tunnel tests. Results showed the noticeable decay phenomena in trailing vortex close behind the wing tip sails than the wing tip without sails.
비정열 격자계에서 타원형 방정식의 수치해석을 위한 다중격자 가속
김학봉 한국항공대학교 1998 論文集 Vol.36 No.-
The multigrid method have been considered the most effective, especially when used to solve strongly eliptic problems. Unstructured grids have evolved over the recent years as a very variable approach for modeling complex geometries since they have been found to be very efficient means of generating body-conforming grids for complex configurations. The complete lack of order in unstructured grids precludes any possibility of generating suceccessively coarser grids. In the present works, the fine grids are created by division of trangular coarser grid cells. Thus, the cell-tree data structure is used to retrace the parents of fine cells on the adapted grid, and these parent cells along with the cells in the unembeded region of the flow domain constitute the coarser grid of multigrid of multigrid. The edge-tree data structure is used to interpolate the residuals back and forth between the fine and casrser level grids, and hence the scheme avoids relatively complicated intergrid transfer algorithms imployed in the other multigrid schemes. The purpose of this works is to extend the multigrid techniques historically employed by structured grid algorithms to unstructured solvers to accelerate convergence rates of the elliptic equation solver that is based on a finite volume cell-centered approach.