• Computational Structural Engineering
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• v.11 no.3
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• pp.253-262
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• 1998

본 연구에서는 경부고속철도의 주요 교량형식인 PSC 박스교량을 3차원 뼈대요소를 사용하여 모형화하였으며, 궤도불규칙성의 형상은 지수 스펙트럴 밀도함수를 사용하여 생성시켰다. 경부고속철도차량(K-TGV)중 동력차는 17자유도의 3차원 주행열차로 모형화하였고, 이러한 교량, 궤도불규칙성 및 차량 모형을 이용하여 교량과 차량의 상호작용을 해석할 수 있는 프로그램을 개발하였다. 동적해석을 위한 교량과 차량의 운동방정식은 Lagrange 방정식을 사용하여 유도하였으며, 운동방정식의 수치해석에는 Newmark-β법을 사용하였다. 개발된 프로그램을 이용하여 동력차의 주행에 의한 교량의 시간이력곡선을 구하였으며, 궤도불규칙성의 영향을 분석하였다. 또한 도상의 유무에 따른 교량동적거동의 특성과 함께 열하중의 편심의 영향도 분석하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.7
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• pp.684-692
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• 2010

Based on the planar restricted three body problem formulation, optimized trajectories for the Earth-Moon transfer are obtained. Mixed impulsive and continuous thrust are assumed to be used, respectively, during the Earth departure and Earth-Moon transfer/Moon capture phases. The continuous, dynamic trajectory optimization problem is reformulated in the form of discrete optimization problem by using the method of direct transcription and collocation, and then is solved using the nonlinear programming software. Representative results show that the shape of optimized trajectory near the Earth departure and the Moon capture phases is dependent upon the relative weight between the impulsive and the continuous thrust.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.1
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• pp.63-70
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• 2017

In this paper, we design and fabricate a de-orbiter using drag-sail and evaluate deployment characteristics. Without employing an actuator to deploy, the de-orbiter is activated by the SMA wire based the release mechanism and driven by the restoring force of the tape-spring. For efficient storage and deployment of drag-sail, an origami method of original ISO flasher is chosen and low priced mylar film is used as the material of the drag-sail. In addition, through the fault tree analysis method which is one of the one-shot device reliability evaluation methods, we confirm the reliability of the de-orbiter(0.997572) and the Roller failure has the highest criticality. Finally, we find feasibility of the proposed de-orbiter through the deployment demonstration of drag-sail.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.1
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• pp.39-47
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• 2005

In this paper, a method of station keeping strategy using relative orbital motion and numerical optimization technique is presented for geostationary spacecraft. Relative position vector with respect to an ideal geostationary orbit is generated using high precision orbit propagation, and compressed in terms of polynomial and trigonometric function. Then this relative orbit model is combined with optimization scheme to propose a very efficient and flexible method of station keeping planning. Proper selection of objective and constraint functions for optimization can yield a variety of station keeping methods improved over the classical ones. Results from the nonlinear simulation have been shown to support such concept.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.2
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• pp.165-171
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• 2016

The attitude control, station keeping and wheel off-loading at GEO-KOMPSAT-2 are realized by thrusters firings. Thrusters 1, 2 and 3 are mounted on the same axis as the solar array, which generates the plume disturbance largely. Therefore the effect of plume disturbance should be analyzed from satellite design phase. In this paper, we described the calculation method of plume disturbance and analyzed the plume disturbance of thruster 1,2 and 3 using GEO-KOMPSAT-2 initial configuration.

• Aerospace Engineering and Technology
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• v.7 no.2
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• pp.88-94
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• 2008

In this study, triaxial velocity is analyzed for COMS(Communication, Ocean and Meteorological Satellite) configuration, which is generated when thrusters are used to dump wheel momentum. Since COMS is designed to periodically change the thruster set in order to uniformly decrease the performance of thrusters, triaxial velocity would be different during the change of thruster set. So, the triaxial velocity generated due to the change of thruster set is optimized.

• Journal of Aerospace System Engineering
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• v.16 no.5
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• pp.8-16
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• 2022

This paper presents the orbital control for positioning micro synthetic aperture radar (SAR) satellites for all-weather monitoring around the Korean Peninsula. In Small SAR technology experimental project (S-STEP) developed in Korea, multiple satellites are placed at equal intervals in multiple orbital planes to secure an average revisit period for the region around the Korean Peninsula. Satellites entering the same orbital plane use ion thrusters to control their orbits and the separation velocity from the launch vehicle to distribute them evenly across the orbit. For an orbital that places the satellites equally spaced in the same orbital plane, the shape of the satellite constellation is formed by adjusting the difference in drift rates between the satellites. This paper presents, different types of satellite constellations, and the results of satellite constellation placement according to launch strategies are presented. In addition, a method and limitations in shortening the duration of orbital deployment are presented.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.1
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• pp.20-27
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• 2001

A variable configuration tracked vehicle(VCTV) is developed to reduce turning energy and improve climbing ability for stairs. This mechanism has four track T-type frames. By changing the driving direction, each track T-type frame rotates to minimize the contact area with ground. It also has better performance than other VCTV in energy consumption of turning. Futhermore this mechanism is more stable than other VCTV on the rough terrain. When climbing stairs, each track T-type frame rotates to obtain a front attack angle and keep stability on steep stairs. The design parameters of components of track T-type frames are optimized to enhance the performance of climbing stairs. Performance indices include a stable angle, a climbing ability, a height of the vertical obstacle. In case that the overall length of the mechanism is 0.2m, it is required that the radius of the wheels should be 5mm and the length track contacted with he ground should be 0.09m to climb higher and steeper stairs.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.207-208
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• 2009

In this study, floating slab system which is one of the solution to avoid noise and vibration in railway has been introduced, and preliminary analysis and vibration absorber of floating slab system according to the isolator has been introduced.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.3
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• pp.50-55
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• 2008

In this paper, we propose a new shape compensation scheme to make up for the difference in groove radius between the formed tools and the machined bearing raceways, which inherently takes place during machining the ball bearing raceways by the turning process using conventional formed tools. The associated conventional methods of the formed tool design and its modification such as a simple depth compensation method and a graphical compensation method are introduced and the latter, which has been known to be the better of the two, is experimentally investigated in detail to reveal its drawback. The algorithm is given and it is applied to develop a formed tool design program. The program developed by the presented approach is successfully applied to design the formed turning tool for the bearing raceways.