• Title/Summary/Keyword: Coefficient Pressure

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Performance analysis of hubless rim-driven thruster based on the number of blades: a CFD approach (날개수에 따른 허브리스 림 추진기의 성능 분석 : CFD를 이용한 접근)

  • Hyoung-Ho KIM;Chang-Je LEE
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.60 no.1
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    • pp.80-86
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    • 2024
  • We analyzed the performance of hubless rim propellers based on the number of blades, maintaining a fixed pitch ratio and expanded area ratio, using computational fluid dynamics (CFD). Thrust coefficient, torque coefficient and efficiency according to the number of blades were analyzed. In addition, the pressure distribution on the discharge and suction sides of the blade was analyzed. As the advance ratio increases, the thrust coefficient decreases. The highest thrust was shown when the advance ratio was lowest. For the three, four, five and six-blades, the torque coefficient tended to decrease as the advance ratio increased. In the case of seven and eight-blades, the torque coefficient tended to increase as the advance ratio increased. The maximum efficiency was found when the advance ratio was 0.8. When the three-blade, it showed high efficiency at all advance ratios. A high pressure distribution was observed at the leading edge of the discharge blade, and a low pressure distribution was observed at the trailing edge. Applying a hubless rim-driven thruster with the three-blade can generate higher thrust and increase work efficiency.

A Study on Factors Influencing to Coefficient of Consolidation in Horizontal Direction (수평압밀계수의 영향인자에 관한 연구)

  • Kim, Chang-Seop;Park, Byung-Soo;Yoo, Nam-Jae
    • Journal of Industrial Technology
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    • v.28 no.B
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    • pp.81-89
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    • 2008
  • This paper is results of investigating the dominant factors influencing to coefficient of consolidation in horizontal direction of Korean marine clays and their correlations through literature review. From the results of analyzing data obtained from field tests such as piezocone penetration and dilatometer tests as well as laboratory tests, coefficient of consolidation in the horizontal direction was found to increase with increase of stiffness index of soil while it decreases with the increase of dissipation time of pore pressure developed during field tests. In general, the coefficient of consolidation in the horizontal direction tends to increase with increase of undrained shear strength and preconsolidation pressure although correlation between them are relatively low. Friction ratio has a high correlation with coefficient of consolidation in the horizontal direction in case of friction ratio being greater than 1.0. For methods of estimating coefficient of consolidation in the horizontal direction with different testing device, values obtained from methods of P2-logt and DMT-A with dilatometer were quite similar to values from piezocone penetration test. Consistency of soil is quite proportional to coefficient of consolidation in the horizontal direction. Clear correlation between coefficients of consolidation in the horizontal and the vertical directions could not be found. coefficient of consolidation in the horizontal direction estimated from the results of field test tends to be 1.13~3.11 times greater than that obtained from laboratory tests.

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An Experimental Study on Condensation Heat Transfer Characteristics and Pressure Drop of Plate Heat Exchangers using the Alternative Refrigerant R410A (대체 냉매 R410A를 적용한 판형열교환기의 응축열전달 특성 및 압력강하에 대한 실험적 연구)

  • Kim, Y.H.;Han, D.H.;Lee, K.J.
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.220-225
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    • 2001
  • The plate heat exchanger is characterized. by low pressure drop and high heat transfer coefficient. The experimental study has been performed on the condensation heat transfer and pressure drop characteristics of the plate heat exchangers in this study. In the present study, a brazed type plate heat exchanger was investigated at a chevron angle of $45^{\circ},\;55^{\circ},\;and\;70^{\circ}$ with R410A. Condensation temperatures were varied from $20^{\circ}C\;and\;30^{\circ}C$, and mass flux was ranged from $13{\sim}34\;kg/m^{2}s$ with constant heat flux ($=5\;kw/m^{2}$). The heat transfer coefficient and pressure drop increased with the chevron angle. Average condensation heat transfer coefficients and pressure drops are decreased with increasing condensation tempeature.

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Earth Pressure Distribution on Retention Walls in the Excavation of Multi -Layered Ground (다층지반 굴착시 토류벽에 작용하는 토압분포)

  • 이종규;전성곤
    • Geotechnical Engineering
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    • v.9 no.1
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    • pp.59-68
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    • 1993
  • In deep excavations for creation of underground spaces, it would be difficult to predict earth pressure, especially multilayered ground including rock strata. The earth pressures and displacements on the retention walls are measured by load cell, strain gauge and inclinometer which were installed at struts or anchors at 4 deep excavation sites in Seoul area. In this paper, the measured earth pressure from the struts or anchors are compared with Peck's empirical values, and the coefficient of the earth pressures for each strata and horizontal wall displacement are investigated. The coefficient of earth pressure distribution, a(0.65zka), in the flexible and the rigid walls was about 74% and 88% of Peck's value respecitively. The measured earth pressure distributions for the 4 sites showed about 70%∼80% of Peck's empirical values and the average earth pressure coefficients based on the measured data were 0.3 for the felted layer, 0.23 for the weathered rock and 0.19 for the weak rock. The maximum w리1 displacements were found to be less 0.2% of excavation depth.

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The Effect of Oil Supply Pressure on the Performance of Vapor Cavitated Short Squeeze Film Dampers (증기 공동현상이 발생하는 무한 소폭 스퀴즈 필름 댐퍼 성능과 오일 공급압력의 영향)

  • Jung, Si-Young
    • Tribology and Lubricants
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    • v.24 no.3
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    • pp.147-153
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    • 2008
  • The effect of oil supply pressure on the performance of vapor cavitated short squeeze film dampers is examined. Vapor cavitation is characterized by film rupture occurring as a result of evaporating oils. The pressure of vapor cavity in the film is almost zero in absolute pressure and nearly constant. Pan's model about the shape of vapor cavity is utilized for studying the effect of vapor cavitation on the damping capability of a short squeeze film damper. As the level of oil supply pressure is increasing, vapor cavitation is suppressed so that the direct damping coefficient increases and the cross coupled damping coefficient decreases. Futhermore, the analysis of the unbalance responses of a rigid rotor supported on cavitated squeeze film dampers shows that a significant reduction in rotor amplitude and force transmissibility is possible by controlling the oil supply pressure into short squeeze film dampers.

Experiment on condensation heat transfer and pressure drop characteristics in the multi-channel flat tube (다채널 편평관의 응축 열전달 및 압력강하특성에 관한 실험)

  • Jeon, C.D.;Chung, J.W.;Lee, J.H.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.9 no.3
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    • pp.376-388
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    • 1997
  • In this study, an experiment was performed to investigate the characteristics of pressure drop and heat transfer of multi-channel tubes for automotive condenser using HFC-134a as an alternative refrigerant. The mass flux and inlet saturation pressure of the refrigerant were controlled, respectively, in the range of 200 to $500kg/m^2s$ and 1.0 to 1.6MPa. Pressure drop and heat transfer coefficient were compared with the previously proposed correlations and new correlations based on Traviss' correlation were suggested. Prediction of pressure drop and heat transfer coefficient based on the new correlations agrees with experimental results within ${\pm}9%$ and -18~+11%, respectively.

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Optimum electrode selection for measuring the abdominal pressure using bio-impedance method (비침습적 복압 측정을 위한 생체 임피던스 전극의 최적 위치 선정)

  • An, Yang-Su;Kim, Keo-Sik;Song, Chul-Gyu
    • Proceedings of the KIEE Conference
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    • 2007.04a
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    • pp.46-48
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    • 2007
  • In this study, we determined the optimum electrode pair for measuring the abdominal pressure using bio-impedance method. Because impedance changes differ from a weight, a height, contractile force, volume of muscle and blood other or whatever of individuals, it was quantified using values of impedance change, correlation coefficient and SNR. Our results showed the optimum electrode pair (1, 9) which could detect impedance changes due to an increase of the intensity of the abdominal pressure. The correlation coefficient and quadratic function between the RMS values of EMG and the impedance changes were 0.87 and $y=0.0014x^2$+0.0620x+0.6958, respectively. It demonstrated that the abdominal pressure could be measured non-invasively and simply using bio-impedance method. We propose that this optimum electrode configuration would be useful for future studies involving the convenient measurement of abdominal pressure by ambulatory urodynamics monitoring study.

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Identification of ambient pore pressure and rigidity index from piezocone dissipation test (피에조콘 소산시험을 이용한 평형간극수압과 강성지수의 역해석)

  • 김영상
    • Proceedings of the Korean Geotechical Society Conference
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    • 2002.03a
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    • pp.49-54
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    • 2002
  • This paper describes a systematic way of simultaneously identifying the ambient pore pressure and the rigidity index (=G/s$\_$u/) of soil by applying an optimization technique to the piezocone dissipation test result. An ambient pore pressure and optimal rigidity index were determined by minimizing the differences between theoretical excess pore pressures developed by Randolph & Wroth(1979) and measured excess pore pressures from piezocone using optimization technique. The effectiveness of the proposed back-analysis method was examined against the well-documented performance of piezocone dissipation tests (Tanaka & Sakagami, 1989), from the viewpoints of proper determination of selected target parameters and saving of test duration. It is shown that the proposed back-analysis method can evaluate properly the ambient pore pressure and the rigidity index by using only the early phase of the dissipation test data. Also, it is shown that with the optimized rigidity index and ambient pore pressure the proposed back-analysis method permits the horizontal coefficient of consolidation to be identified rationally.

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A Numerical Study on the Off-Design Performance of Three-Dimensional Transonic Centrifugal Compressor Diffusers (3차원 천음속 원심압축기 디퓨저의 탈설계 성능에 관한 수치적 연구)

  • Kim, Sang Dug;Song, Dong Joo
    • 유체기계공업학회:학술대회논문집
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    • 1999.12a
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    • pp.134-140
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    • 1999
  • A three-dimensional CSCM upwind flux difference splitting Navier-stokes code with two-equation turbulence models was developed to predict the transonic flows in centrifugal compressor diffuser. The k-$\epsilon$ model of Abe et al. performed well in predicting the pressure distribution in the shock wave/turbulent boundary-layer interaction. Three turbulence models predicted the similar distribution of static pressure through the diffuser and showed a good agreement with the experimental results. The secondary flows in the corner were predicted well by these turbulence models. The pressure increase before the throat of the diffuser vane is important for the overall pressure recovery. As the mass flow rate increased the blockage decreased at the throat. The pressure coefficient distribution through the diffuser depended on the throat blockage not on the rotational speed of the impeller.

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A Study on the Estimation of Frictiom Coefficient between Tire and Road Surface Using Running Car data (실차 데이터를 이용한 차륜과 노면간의 마찰계수 예측에 관한 연구)

  • 우관제;산기준일
    • Transactions of the Korean Society of Automotive Engineers
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    • v.7 no.6
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    • pp.207-213
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    • 1999
  • In this study, the possibility of estimation of friction coefficient between tire and road surface using running car data are checked. To get necessary data, such as tire and car velocities and braking force, a test car is driven with certain magnitude of decelerations from pre-set initial velocities to stop . The data are used to estimate friction coefficient with property chosen parameters , e.g,, driving stiffness, pressure distribution functions, etc. Experimental results show that running data car be used with properly chosen parameters to estimate friction coefficient.

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