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단일추진체 추진시스템의 비정상 마찰을 고려한 과도기유체 해석
채종원 한국전산유체공학회 2006 한국전산유체공학회지 Vol.11 No.1
A fluid transient analysis on the Koreasat 1 & 2 pipeline system is conducted through numerical parametric studies in which unsteady friction results are compared with quasi-steady friction results and show relatively accurate prediction of the response curve with the unsteady friction. The code developed and used in this analysis has finished verification through comparing with the original Zielke model, the full and recursive convolution model and quasi-steady model as a reference. The unsteady friction is calculated by the recursive convolution Zielke model in which a complete evolution history of velocity field is no longer required so that it makes the fluid transient analysis on the complicated system possible. The results show that the application of quasi-steady friction to model cannot predict the entire response curve properly except the first peak amplitude but the application of unsteady friction to model can predict reasonably the response curve, therefore it is to know the characteristics of the propulsion system.
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Jongwon Chae(채종원) 한국전산유체공학회 2006 한국전산유체공학회지 Vol.11 No.1
A fluid transient analysis on the Koreasat 1 & 2 pipeline system is conducted through numerical parametric studies in which unsteady friction results are compared with quasi-steady friction results and show relatively accurate prediction of the response curve with the unsteady friction. The code developed and used in this analysis has finished verification through comparing with the original Zielke model, the full and recursive convolution model and quasi-steady model as a reference. The unsteady friction is calculated by the recursive convolution Zielke model in which a complete evolution history of velocity field is no longer required so that it makes the fluid transient analysis on the complicated system possible. The results show that the application of quasi-steady friction to model cannot predict the entire response curve properly except the first peak amplitude but the application of unsteady friction to model can predict reasonably the response curve, therefore it is to know the characteristics of the propulsion system.
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이원추진제 추진시스템의 배관망에 대한 비정상 마찰을 고려한 과도기유체 해석
채종원(Jongwon Chae),한조영(Cho Young Han),김정훈(Jung-Hoon Kim),전형열(Hyoung Yol Jun) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.5
A fluid transient analysis on the pipe network of bipropellant propulsion system is conducted through numerical parametric studies in which unsteady friction results are compared with quasi-steady friction results and also show the pressure drop results during the liquid apogee engine firing. The fluid transient analysis program has verified through comparing with the original Zielke model, the full and recursive convolution model and quasi-steady model as a reference. And the pressure drop program also has verified through comparing with results of the well-known program, EPANET2. The bipropellant propulsion system has two different fluids as fuel and oxidizer, and mostly they are hypergolic combination so that the valve opening and closing of the thrusters, that cause the pressure waves, shall take place simultaneously to get proper performance. The different physical properties of the fuel and oxidizer result in the different responsive to the same valve opening and closing. The response results may be helpful to know the characteristics of the bipropellant propulsion system and design it.
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주파수 도약 통신위성 중계기의 다상 DFT 필터뱅크 과도기 응답 분석
이대일(Daeil Lee),주재관(Jaikwan Joo) 한국항공우주학회 2014 韓國航空宇宙學會誌 Vol.42 No.7
통신위성 중계기에서 효과적인 다중채널 처리를 위하여 여러 가지 필터뱅크들이 사용되어져 왔다. 특히 구현의 간단함으로 인하여 대역폭이 일정한 복수의 다중채널을 다루는 경우 다상 DFT 필터뱅크가 광법위하게 사용되어져 왔다. 하지만 주파수도약 통신위성 중계기에서 Polyphase DFT 필터뱅크를 사용하여 다중채널 처리를 할 경우 주파수 도약 홉과 홉 사이에서 발생하는 비정상적인 과도기 응답으로 인하여 다상 DFT 필터뱅크의 사용에 있어 제약이 발생할 수 밖에 없다. 본 논문에서는 주파수 도약 환경에서의 비정상적인 다상 DFT 필터뱅크의 과도기 응답을 분석하고 해당 문제를 해결 할 수 있는 방법을 제시하며 모의실험을 통하여 제안된 방법의 효율성을 보인다. Filterbanks have been widely used in the field of multi-channel signal processing for their simple efficient implementation architectures. Especially, the polyphase DFT(Discrete Fourier Transform) filterbank is the most preferred filterbank for the uniform spaced multi-channel processing due to its simplicity. In frequency hopped communication systems, however, the use of the polyphase DFT filterbank is limited due to its undesirable transient response from hop-to-hop transitions. In this paper, the transient response of polyphase DFT filterbanks in the hop-to-hop transition was analyzed, and the efficient methods to overcome such a problem was proposed. Simulation results showed that the proposed schemes could resolve this issue efficiently.
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공기 유량 변화에 따른 이온교환막 연료전지용막 가습기의 동특성응답
배호준(Hojune Bae),김용모(Yongmo Kim),유상석(Sangseok Yu),안국영(kookyoung Ahn),이영덕(Youngduk Lee) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
The efficiency and life time of the proton exchange membrane (PEM) fuel cell system is critically changed with its humidity which should be maintained properly during dynamic operation. Membrane humidifier is used for the water management of the PEMFC due to its reliable performance and the feature of zero parasitic power loss. In the PEMFC system, membrane humidifier is required to regulate proper humidity level for the design point of the fuel cell. During transient operation of the PEMFC system, it is difficult to control the humidity of the PEMFC system properly. However, few literatures are reported for the dynamic response of the membrane humidifier even though it is very important for durability of the system. In this study, we presented the performance variation of the membrane humidifier during transient conditions. Dry air pressure, water flow temperature, and air flow rate were chosen as the operating parameters. Results shows that time constant for dynamic response of membrane humidifier is small enough. Flow rate and differential pressure between dry air and water are important factor in the performance of membrane humidifier.
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허재영(Heo, Jae-young) 한국어문학회 2011 語文學 Vol.0 No.114
In modern enlightened times, the writing of Korean, various forms of character were used. In all traditional books, Chinese characters were used, but the native characters(Eonmun=Korean Alphabet) were relegated to daily life or literary works. In this time, the Korean written language did not correspond with spoken language. This is a very important question about accepting the new-knowledge or advanced ideas. So many pioneers in the Korean language field developed the mixed style of writing Korean with Chinese characters. But the Korean language standards were not established and the disagreement(spoken language and written language) intensified in this time. Many Korean language scholars regarded the problem as the using of Korean characters, so called KUKMUNROM(國文論: national written language). But the unification of the written problem was spoken language. I will focus on the various mixed styles that were developed by the discovering of the spoken language. I divided these styles into eight forms this time. Specially, the style of BUSOKMUNCHE(附屬文體: the style is the Korean alphabet annex of the Chinese character’s upper or contrast method) were developed as a transient state.
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