• Title/Summary/Keyword: Oscillation chamber

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Analysis of Low Reynolds Number Flow in Nozzle and Diffuser (노즐-디류저 내에서의 저 Reynolds수 해독특성 해석)

  • Song, Gwi-Eun;Lee, Joon-Sik
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2672-2677
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    • 2007
  • An investigation of low Reynolds number flow in nozzles and diffusers which are widely used in the valveless micropump is presented. Flow characteristics in the nozzle and diffuser are explained in view of viscous effect and flow oscillation induced by pumping membrane. These calculation results show that the rectification property of valveless micropump is due to a flow separation in the diffuser and the separation is largely originated from the flow oscillation. Under the assumptions of steady flow velocity profile and flow separation in the diffuser, simplified analytical models are provided to see the dependency of rectification on the micropump geometry. Geometric parameters of channel length, nozzle throat, chamber size, and converging/diverging angle are depicted through the analytical models in low Reynolds number flow, and the prediction and experimental results are compared. This theoretical study can be used to determine the optimum geometry of valveless micropump.

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A Study on the Pressure Rising Considered Fluid Inertia in the Notch Area of Balanced Type Vane Pump (노치 영역에서 유체 관성을 고려한 압력 평형형 베인 펌프의 압력 상승에 관한 연구)

  • 조명래;한동철;문호지;박민호;배홍용
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1996.10a
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    • pp.168-175
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    • 1996
  • This paper reports on theoretical study of the pressure overshoot in the delivery ports and pressure rising within balanced type vane pump. Pressure overshoot occur due to the accelerated fluid through the notch, so, result in pressure ripple, flow ripple, and noise. For calculating the pressure rising and fluctuations of pressure, we have modeled mathematically used continuity equation based on compressibility and momentum equation considered fluid inertia in the notch, and analyzed simultaneously. As a results of analysis, we have found oscillation of pressure and compression chamber pressure depend on the rotational speeds, bulk modulus of working fluid, notches, number of vane and camring. Using the model, notches have been shown to be important design factor in relaxing the rapid pressure rising and reducing the amplitudes of pressure overshoot.

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Thrust Vector Control and Discharge Stabilization in a Hall Thruster by Azimuthal Division of Propellant Flow Rate

  • Fukushima, Yasuhiro;Yokota, Shigeru;Komurasaki, Kimiya;Arakawa, Yoshihiro
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.03a
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    • pp.574-578
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    • 2008
  • In order to achieve thrust vector control and discharge stabilization in Hall thrusters, the azimuthal nonuniformity of propellant flow rate in an acceleration channel was created. A plenum chamber was divided into two rooms by two walls and propellant flow rate supplied to each section was independently controlled. In a magnetic layer type Hall thruster, steering angle of up to ${\pm}2.3$ degree was achieved. In an anode layer type Hall thruster, discharge current oscillation amplitude was decreased with the normalized differential mass flow rate.

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An Experimental Study of Pneumatic Damping at the Air Chamber for OWC type Wave Energy Device (OWC형 파력발전 공기챔버의 공기감쇠력 실험연구)

  • CHOI Hark-Sun;LEW Jae-Moon;HONG Seok-Won;KIM Jin-Ha
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2004.05a
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    • pp.138-144
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    • 2004
  • Pneumatic damping through a orifice type duct for OWC type wave energy device is studied experimentally. Forced oscillation tests are made to measure chamber pressure and velocity of air flaw through orifice. Pneumatic damping coefficient are deducted from the experimental research, and discussion are made far the influence of frequency, heave amplitude, and orifice size. Finally two formula are proposed for the estimation of non-dimensional pneumatic damping coefficient by regression analysis. The proposed formula proves to be a reliable method far practical application.

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A Study of Pneumatic Reaction Force of Air Chamber for an OWC Type Wave Energy Device by Forced Heave Experiments (강제동요시 OWC형 파력발전 공기챔버의 공기반력 실험연구)

  • Hong, Seok-Won;Choi, Hark-Sun;Lew, Jae-Moon;Kim, Jin-Ha
    • Journal of Ocean Engineering and Technology
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    • v.19 no.3
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    • pp.11-17
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    • 2005
  • The effect of frequency and amplitude of the OWC (Oscillating Water Column) motion on the nonlinear reaction forces in an air duct are studied experimentally. Experimental owe model is idealized as a simple circular cylinder with an orifice type air duct located at the middle oj the top rid. Reaction forces due to forced heave oscillation are measured and analyzed. By subtracting the effect of inertia forces and restoring forces, pneumatic damping force and added spring force are deduced. The effects of the frequency and amplitude of the heave motion are discussed. Also, the effects of solidity of the duct on the reaction forces are discussed.

A Study of Pneumatic Reaction Force of Air Chamber for an OWC type Wave Energy Device by Forced Heave Experiments (강제동용시 OWC형 파력발전 공기챔버의 공기반력 실험연구)

  • CHOI Hark-Sun;LEW Jae-Moon;HONG Seok-Won;KIM Jin-Ha
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2004.11a
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    • pp.212-219
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    • 2004
  • The effect of frequency and amplitude of the OWC (Oscillating Water Column) motion on the nonlinear reaction forces in an air duct arc studied experimentally. Experimental OWC model is idealized as a simple circular cylinder with an orifice type air duct located at the middle of the top rid. Reaction forces due to forced heave oscillation are measured and analyzed. By subtracting the effect of inertia forces and restoring forces, pneumatic damping force and added spring force are deduced. The effects of the frequency and amplitude of the heave motion are discussed. Also, the effects of solidity of the duct on the reaction forces are discussed.

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Experimental Investigation of a Regression rate On Hybrid Rocket Engine

  • Park, J. W.;S. Krishnan;Lee, C. W.;M. W. Yoon
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2004.03a
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    • pp.524-527
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    • 2004
  • Hybrid rocket had many advantage with compared to solid and liquid rockets. However, the engines have not yet been used in practical rocket systems, due mainly to the disadvantage of hybrid combustion, such as low fuel regression rate. In this study, lab-scale hybrid motor was designed and manufactured. And the methods of regression rate improvement were considered. Test firings with thrusts up to 300 N were conducted with GOX and transparent PMMA. Thrust was calculated with the pressure of the combustion chamber and the regression rate was measured in with variation of oxidizer flow rate. The regression rates showed a strong dependency on GOX mass flux. The frequency analysis technique of the bulk-mode oscillation of motor was applied to a hybrid rocket motor and was based on the principle that this frequency was inversely proportional to the square root of the chamber volume. Several problems and solutions of operating hybrid rocket were presented.

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An Experimental Study of Pneumatic Damping at the Air Chamber for an OWC-type Wave Energy Device (OWC형 파력발전 공기챔버의 공기감쇠력 실험 연구)

  • CHOI HARK-SUN;HONG SEOK-WON;KlM JIN-HA;LEW JAE-MOON
    • Journal of Ocean Engineering and Technology
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    • v.18 no.4 s.59
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    • pp.8-14
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    • 2004
  • Pneumatic damping through an orifice-type duct for an OWC-type wave energy device is studied experimentally. Forced oscillation tests are used to measure chamber pressure and velocity of air-flow through an orifice. Pneumatic damping coefficients are deducted from the experimental research, and the influence of frequency, heave amplitude, and orifice size are discussed. Finally, two formulas are proposed for the estimation of non-dimensional pneumatic damping coefficient by regression analysis. The proposed formula proves to be a reliable method for practical application.

Numerical Study of Nonlinear Acoustic Damping Induced by Acoustic Resonators in a Combustion Chamber (음향공명기의 비선형 음향감쇠 특성에 관한 수치적 연구)

  • Sohn, Chae-Hoon;Park, I-Sun
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2007.04a
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    • pp.13-16
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    • 2007
  • Nonlinear acoustic damping of a half-wave acoustic resonator in a combustion chamber is investigated numerically. First, in a baseline chamber without any resonators, acoustic behavior is investigated over the wide range of acoustic amplitude from 80 dB to 150 dB. Decay rate increases nonlinearly with acoustic amplitude and nonlinearity becomes appreciable at acoustic amplitude above 125 dB. Next, damping effect of a half-wave resonator is investigated. Nonlinear acoustic excitation does not affect optimum tuning condition of the resonator, which is derived from linear acoustics. A half-wave resonator is effective even for acoustic damping of high-amplitude pressure oscillation, but its function of acoustic damper is relatively weakened compared with the case of linear acoustic excitation.

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Numerical hydrodynamic analysis of an offshore stationary-floating oscillating water column-wave energy converter using CFD

  • Elhanafi, Ahmed;Fleming, Alan;Macfarlane, Gregor;Leong, Zhi
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.9 no.1
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    • pp.77-99
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    • 2017
  • Offshore oscillating water columns (OWC) represent one of the most promising forms of wave energy converters. The hydrodynamic performance of such converters heavily depends on their interactions with ocean waves; therefore, understanding these interactions is essential. In this paper, a fully nonlinear 2D computational fluid dynamics (CFD) model based on RANS equations and VOF surface capturing scheme is implemented to carry out wave energy balance analyses for an offshore OWC. The numerical model is well validated against published physical measurements including; chamber differential air pressure, chamber water level oscillation and vertical velocity, overall wave energy extraction efficiency, reflected and transmitted waves, velocity and vorticity fields (PIV measurements). Following the successful validation work, an extensive campaign of numerical tests is performed to quantify the relevance of three design parameters, namely incoming wavelength, wave height and turbine damping to the device hydrodynamic performance and wave energy conversion process. All of the three investigated parameters show important effects on the wave-pneumatic energy conversion chain. In addition, the flow field around the chamber's front wall indicates areas of energy losses by stronger vortices generation than the rear wall.