• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.65-70
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• 2003

In this work variations of orbital parameters are first derived from the perturbation equations using difference equation method under Earth oblateness and atmospheric drag. A simple and effective scheme is proposed to compute the required delta v and fuel consumption to compensate for atmospheric drag. The scheme is applied to KOMPSAT example. And by means of numerical simulations we quantitatively analyze influences due to each perturbation source, i.e., nonspherical Earth, atmospheric drag, third body gravities (Sun, Moon), and solar radiation.

• Journal of Advanced Navigation Technology
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• v.3 no.2
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• pp.147-155
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• 1999

In this work variations of orbital parameters are derived from the perturbation equations under Earth oblateness and atmospheric drag. A simple and effective scheme is proposed to compute the required delta v and fuel consumption to compensate for atmospheric drag. The scheme is applied to KOMPSAT example.

• Journal of Astronomy and Space Sciences
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• v.7 no.1
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• pp.23-35
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• 1990

Resonance effect on the orbital elements of geosynchronous artificial satellite due to the non-zonal geopotential has been calculated. For the perturbation of a artificial satellite, perturbation effects due to the non-zonal geopotential is less than due to the $J_2$ or Luni-Solar perturbation, but non-zonal harmonics resonance exist. So, we calculate the perturbation of geosynchronous artificial satellite orbit due to the non-zonal harmonics resonance. The effect on the orbit eccentricity of non-zonal harmonics resonance is represented by a phase plane plot of ec. The effect on the orbit eccentricity of non-zonal harmonics resonance is represented by a phase plane plot of $e_c$ verse $e_s$. The evolution of mean longitude and semi-major axis are obtained.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.705-712
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• 2022

A sudden pressure drop caused by the pressure relief valve acts as a strong noise source and propagates the compressible pressure fluctuation along the pipe wall, which becomes a excitation source of Acoustic Induced Vibration (AIV). Therefore, in this study, the numerical methodology is developed to evaluate the reduction effect of compressible pressure fluctuation due to curved pipe in the pressure relief valve system. To describe the acoustic wave caused by density fluctuation, unsteady compressible Large Eddy Simulation (LES) technique, which is high accuracy numerical method, Smagorinsky-Lilly subgrid scale model is applied. Wavenumber-frequency analysis is performed to extract the compressible pressure fluctuation component, which is propagated along the pipe, from the flow field, and it is based on the wall pressure on the upstream and downstream pipe from the curved pipe. It is shown that the plane wave and the 1st mode component in radial direction are dominant along the downstream direction, and the overall acoustic power was reduced by 3 dB through the curved pipe. From these results, the noise reduction effect caused by curved pipe is confirmed.

• Information and Communications Magazine
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• v.9 no.11
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• pp.34-36
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• 1992

여러 개의 문자(혹은 여러 개의 자소로 구성된 한개의 문자)를 인식할때에는 문자(혹은 자소) 상호간에 영향을 미쳐서 오인식이 발생할 가능성이 높다. 개개의 숫자인식에 기초한 숫자열 인식이나, 개개의 자소인식을 바탕으로한 필기체 한글인식이 그 좋은 보기일 것이다. 예를 들어 단순한 한글 '그'를 Neocognitron으로 인식한다고 생각해 보자, 조합 가능한 글자를 모두 기억시키려면 방대한 규모의 회로가 필요하므로 현실적으로 불가능하다. 따라서 기본 자소(자음 14개, 모음 10개)를 인식하도록 학습시키고 이를 바탕으로 한글을 인식하는 것이 효율적이다. 이때, 회로의 각 세포가 보는 receptive field가 유한하여 '?'의 끝 세로부분 'I'가 '?'에 영향을 미쳐서 '?'로 인식된다 즉, 자소간의 섭동에 의해 '그'가 '고'로 인식되는 것이다. 이와같은 예는 '니'가 '넉'으로, '41'이 '4H'로 인식되는 등 매우 많지만 그 해결에 대한 연구는 거의 없다. 이 논문에서는 필기체 한글 자소를 인식하는 Necognitron외에 자소간의 섭동현상을 제거하기 위한 high-level constraint 회로를 Lotka-Volterra동역학에 기초하여 설계하였다. 이로써 off-line필기체 한글인식을 보다 효과적으로 할 수 있음을 컴퓨터 시뮬레이션으로 보인다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.1144-1147
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• 2017

It was reviewed about the pressure oscillation on the inlet of turbo-pump at the moment of engine startup and shutdown. Specially, This research was performed how much is the effect of PSD(Pogo Suppression Device) about the pressure oscillation on the inlet of turbo-pump at the moment of engine startup and shutdown. For analysis, propellant tank PSD and Engine are modelled with Flowmaster which is the commercial 1D program. As the analysis results, even though the PSD is installed in the pipeline, the pressure drop or rising at the moment of engine startup and shutdown is same compared to the case without PSD. However, it was confirmed that PSD reduces the pressure oscillation of the high frequency band as the original purpose of PSD.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.3
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• pp.50-57
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• 2009

A gas mechanical pulsator is developed for the study of combustion instabilities in various combustors such as LRE combustor. First, it shows that the mass flow rates and the perturbation frequencies can be successively controlled by the inlet pressure and the rotating speed of a rotating disk with many holes. Second, the device is used as an acoustic amplification source as a substitute for the speaker in the previous acoustic tests and its results show almost the same resonant frequency and damping characteristics compared with the previous results. In conclusion, the result shows that it can be used as a substitute for a speaker in the studies of LRE combustion instabilities, which has a flow and no limitation of amplification, and a device for making a perturbation source in gas flow.

• Proceedings of the Optical Society of Korea Conference
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• 1990.02a
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• pp.199-203
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• 1990

원자와 강력한 빛이 상호작용을 하면 섭동이론으로 취급되지 않는 형광선들이 나타나게 된다. Nd:YAG 레이저로 펌핑된 색소레이저를 열 파이프 오븐에 발생시킨 Na 원자 기체의 D1 및 D2 흡수선에 입사시켜 Na 원자를 공명여기 시켰다. 그결과 빛 싸인 원자 모델에서 예측한 7개의 형광선을 얻었고 이들 형광선에 대한 입사광의 세기 및 detuning에 의한 효과에 대해 논의 검토하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.1
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• pp.29-34
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• 1999

In the paper, the extened Huygens-Fresnel principle has been used to make an analysis of the statistics the received intensity for speckle propagation though the turbulent atmosphere. The results of these formulations include of the log-amplitude covariance as well as the wave structure functions, and It was found that the normalized variance is dependent on the turblence strength and rises above unity.

• Journal of the Korean Vacuum Society
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• v.2 no.4
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• pp.433-438
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• 1993

전자의 파동성에 기인하는 여러 가지 양자간섭 현상을 연구하기 위하여, 금속의 미세고리구조을 제작하였다. 전자의 양자간섭과 가간섭 역충돌 효과에 의한 자기저항의 진동형상이 관측되었으며, 자기저항의 비주기 섭동 현상과 비국재현상도 관찰되어 중시적 전기 전도도의 일반식에 의하여 설명되었다. 또한 AlGaAs/GaAs 의 이차원 전자가스총을 이용한 고리구조도 제작되어, 양자 효과와 탄동적 수송의 영역에서 자기저항이 측정되었다.