• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.4
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• pp.40-46
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• 2006

It is required to develop a highly reliable attitude & orbit control system of satellite that is less expensive as the technology of satellite design & integration is recently matured dramatically. To accomodate this kind of needs, the two axis attitude control method for wheel-based momentum-biased satellite system whose momentum bias vector points to a certain direction(sun direction), is developed using simple but reliable sensors and actuator: three axis magnetometer and coarse sun sensor are used as sensors, and magnetic torque bars are used as actuator. Classical PD type controller design methodologies are applied on a satellite system for the two axis control with the proper assumptions. Nonlinear simulation results are included to demonstrate the long term stability and the performance of closed-loop system design results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.2
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• pp.36-47
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• 2006

The process of dual spin turn maneuver is introduced for attitude acquisition or recovery from flat spin state of a satellite. The physical principle of momentum transfer during dual spin turn is explained clearly. The case studies of special dual spin turn, in addition to the conventional dual spin turn, that are known as an acceptable cases, are performed to investigate the principle of dual spin turn and to provide a physical insight as well as the solution of dual spin turn. This study is done based on case-study simulation, which includes two-state control scheme composed of open-loop maneuver and energy dissipation device. Furthermore, we investigate the stability for the verification of all control cases after implementing two-stage control. We also provide the simulation scenario of flat spin recovery using dual spin turn method as an example.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.6
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• pp.413-422
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• 2022

In this paper, the fault analysis of the momentum wheel, which is a high-speed rotary machinery of 'Control Moment Gyro' for medium and large satellite, was described. For fault diagnosis, envelope spectrum analysis was performed using Hilbert transformation method and signal demodulation method to find the impact signals periodically generated from amplitude modulated signals. Through this, the fault of the momentum wheel was diagnosed by analyzing whether there was a harmonic component of the rotational frequency and a bearing fault frequency in a specific frequency band with a high peak.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.24-24
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• 2021

자연하천 바닥 경계층 내에서는 복잡한 난류 구조가 형성되며 이들은 하상에 강한 모멘텀을 전달한다. 바닥 부근에 분포하는 유사 입자들은 경계층 내에서 발생한 난류 흐름으로부터 모멘텀을 전달받아 소류사 혹은 부유사 형태로 이송되게 되며, 이러한 유사 이송 과정을 역학적으로 설명하기 위해서는 경계층 내 유체 흐름에 대한 이해가 선행되어야한다. 경계층 내 난류 흐름 특성이 유사 입자의 움직임에 미치는 영향에 대해 분석하기 위해서는 바닥 경계층 내 고해상도 유속 자료와 유사 움직임을 동시에 포착할 수 있는 기술이 요구된다. 하지만 현재까지 수행된 대부분의 선행 연구들은 점 유속을 측정할 수 있는 음파 도플러 유속계 (Acoustic Doppler Velocimetry) 혹은 2차원 입자 영상 유속계를 활용하였으며, 이들은 복잡한 3차원 난류 흐름 특성을 분석하기에는 한계가 있다. 본 연구의 목적은 실험실 실험을 통해 바닥 경계층 내 3차원 난류 흐름이 유사 이송에 미치는 영향에 대해 조사하는 것이다. 본 연구에서는 유사 주변에서의 고해상도 3차원 흐름 유동장 및 순간적인 유사 움직임에 대해서는 합성 개구 (synthetic aperture) 기반의 3차원 입자 영상 유속계 및 입자 추적 유속계를 활용하여 취득하였다. 취득된 흐름 유동장을 기반으로 레이놀즈 전단응력을 산정하였으며 이를 통해 유체가 하상에 미치는 모멘텀의 크기를 파악하였다. 복잡한 난류 흐름 구조에 대해서는 팔분원 분석 (octant analysis)을 통해 구분했으며, 유사가 움직이는 순간의 유속장을 기반으로 유사 이송을 발생시키는 지배적인 난류 흐름 특성에 대해 규명하였다. 본 연구는 바닥 경계층 내 복잡한 3차원 난류 흐름과 유사 입자의 움직임을 동시에 분석함으로써 기존에 수행되어왔던 선행 연구들의 한계점을 극복하고 보다 명확한 유사 이송의 발생 원인에 대해 분석했다는 점에 의의가 있다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.285-286
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• 2014

• Journal of the Society of Naval Architects of Korea
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• v.49 no.2
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• pp.109-115
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• 2012

Slamming phenomenon may occur when a ship navigates a high sea region, where the response of ship can be expected as elastic behaviour and the resultant wave loads may increase. In this paper, numerical analysis of ship motions and wave loads including momentum slamming was performed using the strip theory with regular waves. In order to analyze the effect of slamming force on the global ship motions, time histories of each mode of displacement and forces were simulated by using Newmark-beta time integration scheme. The added mass and damping coefficients calculated by Lewis form method were compared with the results of given references. For verification of numerical results, the motion RAOs of a S175 containership were calculated as an example of application and time histories of respective displacement and vertical bending moment were compared with the results of ITTC workshop benchmark test.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.54-60
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• 2006

This paper discusses wheel offloading approaches of the COMS which has a single solar array system for the accommodation of the optical payloads. First of all, in an effort to reduce fuel consumption and reflect practical implementation point of view, thruster sets for wheel offloading are proposed based on numerical analyses taking into account the COMS configuration. In this analysis, it is assumed that the wheel offloading is conducted twice a day. Secondly, in order to evaluate the effectiveness of the proposed thruster sets, orbit simulations are conducted for several wheel offloading approaches and compared.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.141-147
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• 2002

Estimation of thrusters efficiency is a very important process at the end of lifetime of a satellite. This paper introduces a technique to estimate the efficiency change of thrusters considering bubble effect for Koreasat I. During APEMAC(Automatic Pitch Error/ Momentum Adjust Control), the change in thruster efficiency is estimated to compare the attitude telemetry data of the Koreasat I with the results of the control logic using Simulink. The outcome of this study is expected to contribute to improving the operational load at the end of generic communication satellite mission.

• The Journal of the Korea Contents Association
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• v.8 no.1
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• pp.308-317
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• 2008

The objects real time rendered in the 3D cyber space can interact with each others according to the events which are happened when satisfying some conditions. But to representing the behaviors with these interactions, too many event conditions are considered because each behavior pattern and event must be corresponded in a one-to-one ratio. It leads to problems which increase the system complexity. So, in this paper, we try to physical method based on elasticity force for representing more realistic behaviors of AI fish and apply to the deformable multi-detection sensor, so we suggest the new method which can create the various behavior patterns responding to one evasion event.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.651-657
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• 2008

A new approach for maximizing torque capability of low efficient reaction wheel assembly is addressed in this paper. At first, to find out a solution in constrainted field, weighted pseudo-inverse and momentum minimized allocation are suggested instead of a general control allocation called pseudo-inverse. The second method is a structural manner to enlarge torque capability of specific axis by changing installed skew angle of wheels. Two proposed methods are applied to large angle maneuvers of satellite. Improvement of control performance and feasibility for applying to commercial satellite attitude control are demonstrated by numeric simulations.