• Title, Summary, Keyword: 팽창파

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Characteristics of Acoustic Emission by Expansive Cement Induced Rock Fractures (팽창성 시멘트에 의한 암석균열시의 AE 특성)

  • 김교원
    • The Journal of Engineering Geology
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    • v.8 no.3
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    • pp.207-213
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    • 1998
  • A study was conducted to determine the characteristics of acoustic emission(AE) events generated by the expansive cement induced rock fracturing. The dominant frequency and the maximum amplitude of the AE events are changed in relation to the rate of expansive pressure development in the hole. The dominant frequencies are in the range of 150∼230kHz for the small hole tests and 400∼500kHz for the large hole test. The maximum amplitudes are in the range of 0.015∼0.050cm/sec and 0.025∼0.064cm/sec, respectively. The fact that AE events of higher amplitude with higher frequency on the large hole test and lower amplitude with lower frequency on the small hole tests were detected, may strongly imply that the amount of energy consumed for a macro-crack in both tests may be similar. The expansive cement induced crack propagates stably without any distinguished event having higher amplitude and this implies that a macro-crack is a result of stable growth of micro cracks.

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Numerical Study on Under-Expanded Jets through a Supersonic Nozzle(II) (초음속 노즐을 통하는 부족팽창 제트에 관한 수치계산적 연구 (2))

  • Kim, Hui-Dong;Sin, Hyeong-Seung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.6
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    • pp.1994-2004
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    • 1996
  • Numerical calculation was applied to supersonic under-expanded jets, and compared with the results of a linear theory and other experiments. TVD difference scheme was employed to solve 2-dimensional and axisymmetric inviscid Euler equation. This paper aims to explore the effects of angle of divergence and design Mach number of nozzle on the structure of under-expanded jets. The angle of divergence was varied from 0 to 20 deg. The results show that the length of the first cell of the under-expanded jets decreases and Mach disk generates at lower nozzle pressure ratio, if the angle of divergence or design Mach number of nozzle increases. The distance from the nozzle exit to Mach disk in 2-dimensional jets becomes much larger than that of axisymmetric jets, and the widths of the jet boundary and the barrel shock wave are also larger than that of axisymmetric jets. Calculation results indicate that the configuration of the under-expanded jets is strongly dependent on the nozzle pressure ratio.

Center-of-Gravity Effect on Supersonic Separation from the Mother Plane (무게중심 변화에 따른 초음속 공중발사 로켓의 모선분리 연구)

  • Ji Young-Moo;Lee Jae-Woo;Byun Yung-Hwan;Park Jun-Sang
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.36-40
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    • 2006
  • An analysis is made of flow and rocket motion during a supersonic separation stage of air-launching rocket(ALR) from the mother plane. Three-dimensional compressible Navier-Stokes equations is numerically solved to analyze the steady/unsteady flow field around the rocket which is being separated from the mother plane configuration(F-4E Phantom). The simulation results clearly demonstrate the effect of shock-expansion wave interaction between the rocket and the mother plane. To predict the behavior of the ALR according to the change of the C.G., three cases of numerical analysis are performed. As a result, a design-guideline of supersonic air-launching rocket for the safe separation is proposed.

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Unsteady Separation Characteristics of Air-Launching Rocket from Full-Geometry Mother Plane (초음속 공중발사를 위한 전기체-로켓의 비정상 분리 유동특성)

  • Ji, Young-Moo;Byun, Yung-Hwan;Park, Jun-Sang;Lee, Jae-Woo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.6
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    • pp.474-482
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    • 2007
  • An analysis is made for flow and rocket motion during a supersonic separation stage of an air-launching rocket(ALR) from the mother plane. Three-dimensional compressible Navier-Stokes equations are numerically solved to analyze the steady/unsteady flow fields around the rocket which is being separated from the mother plane configuration(F-4E Phantom). Simulation results clearly demonstrate the effect of shock-expansion wave interaction around both of the rocket and the mother plane. To predict the behavior of the ALR by the change of the center-of-gravity, three cases of numerical analysis are performed. As a result, a design-guideline of supersonic air-launching rockets for safe separation is proposed.

THE ANALYSIS OF AERODYNAMIC CHARACTERISTICS FOR BUSEMANN BIPLANE WITH FLAP (초음속 조건의 플랩을 장착한 Busemann Biplane의 플랩 길이와 각도 변화에 따른 양항비 성능 비교)

  • Tai, Myungsik;Son, Chankyu;Oh, Sejong
    • Journal of computational fluids engineering
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    • v.18 no.3
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    • pp.42-50
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    • 2013
  • The supersonic airplane with flapped biplane, Busemann biplane equipped flap, is superior to drag and noise reduction due to wave cancelation effect between upper and lower airfoils. In this study, it is numerically calculated and analyzed the lift, drag and lift to drag ratio of flapped biplane with respect to various the length and angle of the flap. Euler solver of EDISON CFD, web based computational fluid dynamic solver for the purpose of education, is employed. Depending on the length of the flap, lift and drag increase linearly, and there exists the optimum flap angle which maximize the lift-to-drag ratio at the freestream mach 2.0 on-design condition. The predictable relational expression is driven as liner equation. As a results of comparison with drag of flapped biplane, Busemann biplane, and diamond airfoil with the same lift, the drag of flapped biplane is 88.76% lower than that of the Busemann biplane and 70.67% lower than that of the diamond airfoil. In addition, the change of pressure is compared to confirm the noise reduction effect of flapped biplane at h/c=5 of lower airfoil. The shock strength of flapped biplane is smaller than that of other airfoils.

A Numerical Study on Effects of Displacement of a Variable Area Nozzle on Flow and Thrust in a Jet Engine (가변노즐의 변위가 제트 엔진의 유동 및 추력특성에 미치는 영향에 관한 수치해석)

  • Park, Junho;Sohn, Chae Hoon;Park, Dong Chang
    • Journal of the Korean Society of Propulsion Engineers
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    • v.17 no.5
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    • pp.1-9
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    • 2013
  • Variable area nozzle, where both throat and exit area vary, is required for optimal expansion and optimal nozzle shape upon operation of after-burner. Steady-state and transient analyses are carried out for each condition with and without afterburner operation and as a function of the location of the nozzle flap. Effects of that nozzle displacement on flow and thrust characteristics are analyzed from numerical results. With variable area nozzle adopted, the combustion field is variable in time, leading to periodically variable thrust. For off-design conditions, flow separation shows up due to over expansion at the flap tips and shock wave does in the nozzle due to under expansion. The undesirable phenomena can be solved by control of variable area nozzle.

A Fast Analysis on Floating Wave Energy Conversion System (부유식 파랑 에너지 변환 시스템의 단순화된 열역학적 해석법)

  • Lee, Sang-Moo;Kim, Seoung-Gun
    • Journal of Ocean Engineering and Technology
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    • v.13 no.4
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    • pp.159-168
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    • 1999
  • 부유식 파랑에너지 변환시스템(Oscillating Water Column)에 대한 해석은 입력파와 챔버, 챔버내 공기의 상호작용으로 인하여 어려움이 많다. 이 논문은 이와 같은 요소를 고려하면서도 쉽고 간편한 해석법을 제시한다. 파랑에너지에 의한 자가발전은 파랑에너지를 기계적 운동으로 변환하고 이를 전기에너지로 변환함으로써 가능하다. 본 논문은 파랑에너지에서 기계적 에너지로 변환하는 과정에 집중하여 그 부분의 성능을 해석한다. 단일 진동수 규칙파가 입력되었을 때에 파에 의하여 챔버의 상하운동이 선형적으로 발생하는 것으로 보며, 이 상하운동에 챔버내의 압력 영향을 고려하였다. 상하운동과 챔버내로 투과한 파, 그리고 챔버내 압력에 의해 발생되는 파에 의해 챔버내의 상대운동을 정하고, 그 상대 운동에 의한 공기의 압축 팽창과 온도상승을 근사적 열역학적 방정식으로 해석하였고 오리피스를 통한 유량을 결정하였다. 얻어진 식은 간단하면서도 관련요소의 영향을 전반적으로 표현한다. 결과에 따르면 고정식의 에너지 변환식은 부유식의 특별한 경우로서 파악되었다. 또한 고정식의 시스템을 그대로 부유식으로 바꿨을 때 그 변환효율은 적어지는 것으로 나타났다. 본 해석법은 계산이 간편하므로 설계단계에서 유용하게 활용될 수 있을 것으로 기대된다.

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Aerodynamic Characteristics of Supersonic Jets Impinging on $60^{\cire}$ Wedge (꼭지각이 $60^{\cire}$인 쐐기에 충돌하는 초음속 제트의 공기역학적 특성)

  • 박종호;이택상;김윤곤
    • Journal of the Korean Society of Propulsion Engineers
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    • v.8 no.1
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    • pp.8-15
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    • 2004
  • Supersonic jets impinging on $60^{\cire}$ wedge were investigated to obtain fundamental design data for jet deflector It was of interest to study flow phenomena such as shock interaction and separation induced by shear layer. Experiments using supersonic cold flow system were conducted for Schlieren flow visualization and measurement of surface pressure. Numerical results were compared with the experimental results. The major parameters are underexpansion ratio, distance from nozzle to apex and design Mach number. Flow conditions were obtained for the wedge shock to attach on or detach from the wedge. The dominant feature of flow-field is shock pattern induced by the Interaction between the wedge shock and the barrel shock.

A comparative study of field measurements of the pressure wave with analytical aerodynamic model for the high speed train in tunnels (고속철도 터널내 압력파 측정과 공기압 해석모델에 대한 기초연구)

  • Kim, Hyo-Gyu;Choi, Pan-Gyu;Hong, Yoo-Jung;Yoo, Ji-Oh
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.17 no.3
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    • pp.319-332
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    • 2015
  • The pressure wave formed by the piston effects of the train proceeds within the tunnel when a train enters the tunnel with a high speed. Depending on the condition of tunnel exit, the compression waves reflect at a open end, change to the expansion waves, transfer to tunnel entrance back. Due to interference in the pressure waves and running train, passengers experience severe pressure fluctuations. And these pressure waves result in energy loss, noise, vibration, as well as in the passengers' ears. In this study, we performed comparison between numerical analysis and field experiments about the characteristics of the pressure waves transport in tunnel that appears when the train enter a tunnel and the variation of pressure penetrating into the train staterooms according to blockage ratio of train. In addition, a comparative study was carried out with the ThermoTun program to examine the applicability of the compressible 1-D model(based on the Method of Characteristics). Furthermore examination for the adequacy of the governing equations analysis based on compressible 1-D numerical model by Baron was examined.

An Experimental Study on the Effects of Tabs and Small Proturbances Inside Nozzle on Supersonic Jet Flowfield (노즐 탭과 노즐 내부 낮은 돌출부가 초음속 제트유동장에 미치는 영향에 관한 연구)

  • Jin, Won-Jin;Cho, Chang-Kwon;Lee, Yeol;Yoon, Woong-Sup
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.30 no.5
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    • pp.24-31
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    • 2002
  • The effects of vortex generators, in the form of small delta-shaped tabs or thin tapes at an axi-symmetric supersonic nozzle exit, on the characteristics of supersonic jet flowfields are investigated by Schlieren images and Pitot-tube measurements. Small tabs as small as 1 % of the nozzle exit area can introduce streamwise vortices and produce a significant effect on the jet flowfield downstream of the nozzle. The effect is stronger for the cases of under-expanded jet than over- and perfect-expanded cases, introducing a larger flow entrainment. The effects of the angle of tabs with respect to the flow direction are also investigated, and for over-expanded jet cases, it is found that the tabs bended toward upstream can weaken the interaction strength and remove the Mach disc in the jet flowfield. Introduction of small proturbances inside the nozzle surface by attachment of thin tapes is also found to change the pressure distribution in the circumferential direction of the flowfield. Its effect is also found to be dependent on the jet expansion ratio.