• International Journal of Aeronautical and Space Sciences
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• 제16권1호
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• pp.102-109
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• 2015

In Korea, Lunar exploration program has been prepared with the aim of launching in the 2020's. As a part of it, a lunar lander demonstrator was developed, which was the model for verifying the system such as structure, propulsion, and control system, before launching into the deep space. This paper deals with the path tracking performance of the lunar lander demonstrator with respect to the thruster controller based on Pulse Width Pulse Frequency Modulator (PWPFM) and Pulse Width Modulator (PWM). First, we derived equations of motion, considering the allocation of the thrusters, and designed the path tracking controller based on Euler angle. The signal generated from the path tracking controller is continuous, so PWPFM and PWM modulator are adopted for generating ON/OFF signal. Finally, MATLAB simulation is performed for evaluating the path tracking ability. We compared the path tracking performances of PWPFM and PWM based thrust controller, using performance measures such as the total impulse and the position error with respect to the desired path.

• 한국항공운항학회지
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• 제22권4호
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• pp.75-80
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• 2014

A lunar lander demonstrator developed for the purpose of demonstrating lunar landing technologies recently in Korea. The thruster control system of the lunar lander demonstrator adopted the main thrusters for altitude control and the reaction thrusters for attitude control. In this paper, we propose a path tracking controller base on Euler angles. The control signals of the controller are of continuous type. And Pulse Width Modulator(PWM) is adopted to provide On/Off signals. We perform MATLAB simulation for evaluating the path tracking performance and the final landing velocity of the lunar lander demonstrator.

• International Journal of Aeronautical and Space Sciences
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• 제16권2호
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• pp.148-156
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• 2015

A continuous type side jet controller which has four nozzles with thrust control devices was considered. It is deployed to a missile for high maneuverability and fast controllability in the terminal guidance phase. However, it causes more complex aerodynamic jet interactions between the side jet and the supersonic free stream than does the conventional impulse type side jet with a small single thruster. In this paper, a numerical investigation of the jet interference effects for the missile equipped with a continuous type side jet thruster is presented. A three-dimensional flow field was simulated by using a commercial unstructured-based CFD solver. The numerical simulation method was validated through comparison with wind tunnel test results for the single jet. The method of defining jet direction for this type of side jet control to minimize simulation cases was also introduced. Flow fields investigation and jet interaction effects for various flow conditions, jet pressure ratios and defined jet direction conditions were performed. From the numerical simulation for the continuous type side jet, extensive aerodynamic interference data were obtained to construct an aerodynamic coefficients database for precise missile control.

• 한국전산구조공학회논문집
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• 제24권6호
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• pp.699-705
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• 2011

고기동 유도탄은 짧은 시간에 큰 추력을 필요로 하는 발사체이다. 유도탄의 비행에 필요한 추력을 얻기 위하여 고체 연료를 폭발적으로 연소시키면 고온, 고압의 연소 가스가 발생되고, 이 연소 가스를 초음속 노즐을 통하여 팽창시킴으로서 큰 추력을 얻게 된다. 로켓 모터의 작동 시간은 수초 미만에 지나지 않으나 큰 추력을 내기 위해 고온 고압의 연소 가스가 이용됨으로 평창 과정 중 시스템 부품의 파손 혹은 노즐목 부근에서 삭마현상이 발생되기도 한다. 즉, 탄의 정확한 제어를 위해서는 연소 가스와 벽면과의 열전달에 따른 열응력과 유동장 내의 압력의 변화에 따른 구조체 응력이 동시에 고려된 정확한 응력해석이 선행되어야만 한다. 본 논문에서는 예비 설계된 추력 발생장치에 고온 고압의 연소 가스가 유동할 때 모터의 작동시간에 따른 구조체의 안전성을 응력과 재료의 용융온도의 측면으로부터 구명하였다.

• 한국기계가공학회지
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• 제11권2호
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• pp.27-33
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• 2012

A marine propeller is designed for preventing cavitation priority. Cavitation is a phenomenon which is defined as the vibration or noise by dropping the pressure on the high-speed rotation of the propeller. There has to be a enough thrust on the low-speed rotation for preventing cavitation. Thus, it has to be considered in the increasing of the number of blade and the angle of wing to design the propeller. In addition, flow resistance will be increasing by narrowing the width between blades. So high quality surface roughness of the hub to minimize flow resistance is required. Interference problems with tool and neighboring surfaces often take place from this kind of characteristics of the propeller. During 5-Axis machining of these propellers, the excessive local interference avoidance, necessary to avoid interference, leads to inconsistency of cutter posture, low quality of machined surface. Therefore, in order to increase the surface quality, it is necessary to minimize the cutter posture changes and create a continuous tool path while avoiding interference. This study, by using a MC-space algorithm for interference avoidance and a MB-spline algorithm for continuous control, is intended to create a 5-Axis machining tool path with excellent surface quality. Also, an effectiveness is confirmed through a verification manufacturing.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국제학술편); Seoul National University, Seoul; 20-22 Oct. 1993
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• pp.480-485
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• 1993

A method for obtaining optimal orbital maneuvers of a space vehicle has been developed by combining feedback linearization method with the elegance of the Lambert's theorem. To obtain solutions to nonlinear orbital maneuver problems. The full nonlinear equations of motion for space vehicle in polar coordinate system are transformed exactly into a controllable linear set in Brunovsky canonical form by using feedback linearization by choosing position vector as fully observable output vector. These equations are used to pose a linear optimal tracking problem with a solutions to Lambert's problem and a linear analytical solution of continuous low thrust problem as reference trajectories.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1998년도 봄 학술발표회 논문집
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• pp.335-340
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• 1998

The apparently different physical problems of lateral vibration and elastic stability of a linear member are limiting cases of a single phenomenon, the more general expression being the mode of vibration with end thrust. For a single-span beam-column, it is generally known that the square of the frequency of lateral vibration is approximately linearly related to compressive axial force. In this paper the relationship between the frequency and axial force of multi-span compression members is investigated by means of the finite element method.

• 제어로봇시스템학회논문지
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• 제10권2호
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• pp.145-152
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• 2004

In this paper, an S(stochastic)-eigenvalue and its corresponding S-eigenvector concept for linear continuous-time systems with probabilistic uncertainties are proposed. The proposed concept is concerned with the perturbation of eigenvalues due to the stochastic variable parameters in the dynamic model of a plant. An S-eigenstructure assignment scheme via the Sylvester equation approach based on the S-eigenvalue/-eigenvector concept is also proposed. The proposed control design scheme based on the proposed concept is applied to a longitudinal dynamics of an open-loop-unstable aircraft with possible uncertainties in aerodynamic and thrust effects as well as separate dynamic pressure effects. These results explicitly characterize how S-eigenvalues in the complex plane may impose stability on the system.

• 한국항공운항학회지
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• 제19권2호
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• pp.52-57
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• 2011

The procedures of Continuous Descent Approach(CDA) is designed to minimize the thrust required during landing, thereby reducing fuel consumption, noise and emissions compared to conventional approach procedures. Widespread implementation of CDA would result in significant reductions in the environmental impact and aircraft operation costs. This paper estimated the possible economic effects from the perspective of airliners through cost-benefit analysis, provided that the CDA is introduced. It is now proposed that a more comprehensive analysis model, which includes the reduced ATC communication burden between controllers and pilots, not to mention the economic aspect, should be established for the improvement.

• 한국항해학회지
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• 제15권3호
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• pp.73-97
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• 1991

The analysis and investigation are described for White's[2] equations compared to the equations of Runeburg[3] and Milano[5] for continuous icebreaking mode, Tunik[8-1] and Ghoneim[8-2] for ramming icebreaking mode. Calculation results compare reasonably well with published model-scale and full-scale icebreaker data by Baker[1] and Dick[11]. During continuous and ramming mode operation, using characteristics of an incebreaker, down ward force on ice and standard ice thickness broken are predicted. Additionally draft, trim and extraction difficulty are also predicted. The bow part line of an icebreakin $g^{ply}$ vessel is designed aiming to maximize the ice breaking capabiltiy as following conditions-low bow angle[20 degrees] at designed waterline, small spread angle complement [6 degrees] at designed waterline, small spread angle complement [6 degrees] and high propeller thrust [220tons]. with plow, two reamers and wave type bumper.