• Title/Summary/Keyword: 상사조건

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A Study on Self-Similarity in Turbulent Hydrogen Jet Flames with Coaxial Air (동축공기 수소확산 화염의 자기상사성에 대한 연구)

  • Kim, Mun-Ki;Kim, Seung-Han;Yoon, Young-Bin
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.30 no.5
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    • pp.71-78
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    • 2002
  • Experiments have been performed using two-color PIV in hydrogen non-premixed flames with various conditions of coaxial air, which was classified into three cases with/without reaction. Mean velocity, turbulence intensity and Reynolds stress were analyzed using flow fields from PIV measurement First, the similarity of pure jet had a good agreement with previous results of other researchers. It was found that the decay of centerline velocity was proportional to $x^{-1}$ in coaxial air conditions. By normalizing axial distance with effective jet diameter defined by effective density, the data of centerline velocity collapsed a single line. And the radial profiles of mean velocity showed that they didn't become self-similar because the curves differed from each other as coaxial air velocity increased at fixed fuel velocity. Also, turbulence intensity became self-similar further downstream than mean velocity.

Air Similarity Performance Test of Turbopump Turbine (터보펌프용 터빈 공기상사 성능시험)

  • Lim Byeung-Jun;Hong Chang-Uk;Kim Jin-Han
    • Journal of the Korean Society of Propulsion Engineers
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    • v.10 no.2
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    • pp.39-45
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    • 2006
  • In liquid rocket engine turbopump, it is difficult to evaluate turbine performance for high pressure, high temperature circumstance. Turbine test is often done by using air at similarity condition so that the turbine can be tested at lower risk. This paper describes an air similarity test program of liquid rocket engine turbopump turbine. A test facility has been built to evaluate aerodynamic performance of turbines. The test facility consists of high pressure air supply system, mass flow rate measuring nozzle, test section, hydraulic break, exit orifice for pressure control, instrumentation and control system. This paper also presents how to decide the similarity conditions of the turbine test and describes how to control test conditions. Relative standard deviation of measurement parameter was less than 1% and measured turbine efficiency corresponded with analysis result within 2%.

A benchmark experiment for analogue modeling of extensional basin formation and evaluation of applicability of centrifuge test (인장 분지 형성을 구현하기 위한 상사 모델링 벤치마크 실험 및 원심모형실험의 적용성 평가)

  • Lee, Sung-Bok;Park, Heon-Joon
    • Journal of the Geological Society of Korea
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    • v.54 no.6
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    • pp.605-614
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    • 2018
  • For physical experiments like analogue modeling that designed for studying geological deformation, reproducibility of the deformation is important to guarantee the reliability of the experiment. In this study, the normal fault generated by extensional stress is benchmarked using a sand box model. The scaling factors for the modeling test are considered and the experiments are conducted by setting the appropriate material, extensional stress, and boundary condition in the same way as in a benchmark experiment. In addition, a large centrifuge facility is used to vary the centrifugal acceleration and extension rate in the same sized model to account for the scaling factors of the physical quantity during extensional behavior. At 1 g benchmark condition and a centrifugal field at 10 g, a constant rate of the extensional stress is implemented and the topographic evolution is reliably measured. In this study, the reliability and applicability of large centrifuge model tests are evaluated for formulating experiments designed to study geological deformation.

상사이론에 의한 실험 응력해법에 있어서 2,3의 문제

  • 최선호
    • Journal of the KSME
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    • v.32 no.6
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    • pp.496-503
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    • 1992
  • 상사실험법(analogous experimental method)이라 함은 물리적현상을 다른 물리적현상으로 변환 하여, 후자를 실험적으로 측정하여 전자의 제반 물리량을 얻는 과정을 말한다. 이 때 두 물리량 사이에는 수학적 상사관계, 특히 미분방정식 상의 유사관계가 성립함을 전제로 한다. 일반적으로 임의형상의 내부응력을 실험적으로 해석하는 데는 탄소성 변위를 직접 전기적저항으로 바꾸어 측정하는 방법(strain gauge method)이나 광파의 간섭무늬(fringe)로 가시화하는 광탄성 법(photoelastic method), 또는 전자계산기를 이용하여 분할요소해석의 연계집적으로서 얻는 유 한요소법(F.E.M) 등이 널리 사용되고 있으나, 이들은 다같이 그 나름대로의 장단점을 지니고 있다. 전기저항식은 변형을 직접 측정할 수 있어 측정의 오차를 줄일 수 있고, 특히 실물측정과 동하중 해석에는 큰 강점이 있으나, 점해석(point by analysis)이기 때문에 전시야적인 분포를 파악하기 어렵다. 또한 광탄성법은 명료한 전시야적 분포를 얻을 수 있지만 모형해석(model analysis)이기 때문에 정밀한 모형제작의 어려움이 수반되며, F.E.M.(B.E.M.도 포함)은 복잡한 형상에서의 요소분할이 매우 어렵고, 경계조건의 정확한 설정에 문제가 있다. 따라서 여러 실험적 방법은 실측대상에 따라 그 장단점을 감안하여 선택되어야 하며, 이 글에서 논술하고자 하는 상사실험법에 의한 응력해석도 이러한 관점에서 지금까지의 일련의 연구결과를 종합하여 그 효 용적인 용도, 응용 및 그 전망과 더불어 장차 해결하여야 할 2,3의 문제를 제시하고자 한다.

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An Experimental Study of Mutual Relation between Wake and Boundary Layer of a Flat Plate; Mean Velocity Field (평판 경계층과 후류와의 상호관계에 관한 연구; 평균속도장)

  • Kim, Dong-Ha;Chang, Jo-Won
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.32 no.10
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    • pp.1-11
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    • 2004
  • An experimental study was carried out to investigate the influence of flow conditions of a boundary layer on the near-wake of a flat plate. Various attaching positions of tripping wires were selected to change flow conditions on a boundary layer. Laminar, transitional, and turbulent boundary layer conditions at 0.98C from the leading edge are imposed to investigate the evolution of symmetric and asymmetric wake. An x-type hot-wire probe(55P61) is employed to measure at 8 stations of the near-wake region. Measured mean velocity distributions are presented in terms of similarity parameter. It is found that the symmetric wake collapses well to the universal profile in the central part of the wake. However, the universal profile is not suitable in describing an asymmetric wake.

An Economic Analysis of Commercial Arbitration from the Game Theory Perspective: Theoretical Analysis and a Case Study (게임이론을 통한 상사중재의 경제학적 분석: 이론과 사례)

  • Kim, Sung-Ryong;Hwang, Seok-Joon;Hwang, Uk
    • Korea Trade Review
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    • v.43 no.6
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    • pp.1-24
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    • 2018
  • This study analyzes the dispute settlement of between arbitration and litigation using a game theoretical approach. Many studies on arbitration have so far focused on the relevant institutions. However, there are few theoretical studies that have focused on the demand side of arbitration. The model presented here suggests conditions under which arbitration form a perfect Bayesian Nash equilibrium, provided that the players strategically choose a dispute settlement tool. Furthermore, the suggested model is used to analyze simple cases of international commercial dispute cases.

담수 와편모조 Peridinium bipes 휴면포자의 발아 특성

  • 박명환;김백호;고춘주;한명수
    • Proceedings of the Korean Environmental Sciences Society Conference
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    • 2004.11a
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    • pp.161-162
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    • 2004
  • 주암호와 상사호의 담수와편모조 P. bipes 휴면포자의 환경조건에 따른 발아특성을 밝하기 위하여, 매월 채집된 휴면포자를 다양한 수온, 광조건, 영양염, pH 등에서 발아실험을 실시하였다. 실험결과, P. bipes 휴면포자는 수온 $20^{\circ}C$, 광도 $20{\mu}E/m^2/s$, 풍부한 영양원, pH 6-8 등이 최적발아조건으로 밝혀졌다. 특히, 환경요인 중 수온과 광조건은 휴면포자의 발아에 상대적으로 좀더 큰 영향을 주는 것으로 판단된다.

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Modified Similitude Law for Pseudodynamic Test on Small-scale Steel Models (철골 축소모헝의 유사동적실험을 위한 수정된 상사법칙)

  • Kim, Nam-Sik;Kwak, Young-Hak;Chang, Sung-Pil
    • Journal of the Earthquake Engineering Society of Korea
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    • v.7 no.6
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    • pp.49-57
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    • 2003
  • Although there are several experimental techniques to evaluate the seismic behavior and performance of civil structures, small-scale models in mast of physical tests, instead of prototypes or large-scale models, would be used due to a limitation on capacities of testing equipments. However, the inelastic seismic response prediction of small-scale models has some discrepancies inherently because the similitude law is generally derived in the elastic range. Thus, a special attention is required to regard the seismic behavior of small-scale models as one of prototypes. In this paper, differences between prototypes and small-scale models pseudodynamically tested on steel column specimens are investigated and an alternative to minimize them is suggested. In general, small-scale models could have the distorted stiffness induced from some experimental errors on test setup, steel fabrication and so on. Therefore, a modified similitude law considering both a scale factor for length and a stiffness ratio of small-scale model to prototype is proposed. Using the modified similitude law to compensate experimental errors, the pseudodynamic test results from modified small-scale model are much improved as compared with the results of prototype. According to the pseudodynamic test results of small-scale steel models, it can be concluded that the modified similitude law proposed could be effective in simulating the seismic response of prototype structures.