• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.7
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• pp.536-541
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• 2008

The Flow characteristics of a ship's propulsion mechanism of Weis-Fogh type, in which a airfoil(NACA0010) moves reciprocally in a channel, were investigated by the PIV. Velocity vectors and velocity profiles around the operating and stationary wings were observed at opening angles of ${\alpha}=15^{\circ}$ and $30^{\circ}$, velocity ratios of $V/U=0.5{\sim}1.5$ and Reynolds number of $Re=0.52{\times}104{\sim}1.0{\times}104$. As the results the fluid between wing and wall was inhaled in the opening stage and was jet in the closing stage. The wing in the translating stage accelerated the fluid in the channel. And the flow fields of this propulsion mechanism were unsteady and complex, but those were clarified by flow visualization using the PIV.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.69-74
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• 2001

The Wells turbine has hysteresis characteristics in a reciprocating flow. In this paper, in order to understand unsteady flow characteristics of the Wells turbine, a sinusoidal flow condition is simulated. The flow conditions and hysteresis characteristics, including blade thickness, are investigated over a period of time. The pressure distributions along the blade surface are investigated at mid-span to clarify the cause of the hysteresis. The result has shown that the hysteresis characteristics become more pronounced as blade thickness becomes larger. The occurrence of these characteristics depends on the varying behavior of wakes between an accelerating flow and a develerating flow.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1995.10a
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• pp.51-56
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• 1995

일방향 흐름에 표면파가 중복하여 작용할 때 해저면 마찰력의 증가로 토사이동량의 증대가 예상된다. 표면파는 왕복운동 특성을 갖고 있으며, 유속과 해저전단력간의 위상차와 해저잔단력과 토사이동발생 시각간의 위상차가 존재하기 때문에 토사이동량 산정에 많은 어려움이 따른다. 그러나 이렇게 복잡한 현상이 내포되어 있음에도 불구하고 일반적인 기법으로 하천 토사이동량 산정식을 수정하거나 비례상수를 재조정하여 파와 해류에 의한 토사이동량을 산정해 왔다. (중략)

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.1014-1021
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• 2002

Analysis of two-dimensional secondary flows given by an oscillatory motion of a liquid with a free surface in a rectangular container subject to a linear reciprocating force is performed by numerical and experimental methods. FVM is used for the numerical computation of the two-dimensional flows. We considered the effects of the free-surface properties such as the surface tension and the dilatational viscosity. The boundary-layer analysis as well as an experiment is used in establishing the free surface properties. The secondary flow patterns are visualized by a laser sheet. It is shown that the secondary flow patterns predicted by the numerical methods are in good agreement with the experimental results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.673-678
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• 2014

In a compressor, highly impulsive pressure fluctuations induced by a reciprocating piston and valves cause noise and vibration to be so critical issues that low noise requirement always challenges engineers developing it. A muffler is frequently used for reducing these impulsive noise components, but has adverse effects on compressor's performance due to additional pressure drop and heat transfer of refrigerant when it pass through the muffler. In this study, compressible full 3-dimensional CFD simulations are performed to investigate both of flow and acoustic performances of a muffler in use for compressors. On a basis of the analysis results, a parametric study using design factors introduced to improve flow and acoustic performances of the existing muffler is carried out. Finally, improved designs are suggested to confirm the current results.

• Journal of the Korean Society of Visualization
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• v.21 no.1
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• pp.40-46
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• 2023

For application to drag-based propulsion system, the dynamics of a segmented structure with multiple hinges undergoing oscillatory motion are investigated. The side flaps are connected to a centre rod with elastic plates acting as hinges. The hinges bend to only one direction so that the structure behave asymmetrically between the power stroke and the recovery stroke. An analytical model is proposed, which estimates the asymmetric deformation of the segmented structure coupled with hinges. Using the proposed model, the effects of key geometric and kinematic parameters on the dynamics of the structure are analyzed.

• Journal of Navigation and Port Research
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• v.31 no.1 s.117
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• pp.29-33
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• 2007

An OWC-type Wave Energy Conversion passes through 3 steps energy conversion process. This paper deal with the internal oscillating flow and effect of shape of air chamber and duct at setting place of turbine by numerical analysis using commercial CFD code, FLUENT. Air chamber and duct in OWC-type wave energy conversion are adopting sudden expanded and contracted form for high-efficiency. So, whole oscillating flow from OWC-type chamber to outlet duct through duct was solved by steady and unsteady analysis in order that flow efficiency of air chamber and duct was made better.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.3
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• pp.6-13
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• 2006

Aerodynamic characteristics for two-dimensional cyclic motion profile of flapping airfoil in low Reynolds number flows are investigated. Plunging motion and lead-lag motion in the two dimensional space with different plunging and lead-lag amplitudes are combined to cyclic motion profile and the flow around the airfoil is simulated. Present result shows that the improved aerodynamic efficiencies for a given flapping airfoil by adding periodic lead-lag motion of airfoil rather than the pure plunging case. The thrust coefficient and lift coefficient are compared with each cycle during the flapping period and aerodynamic characteristics are obtained on upstroke motion and downstroke motion.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.3
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• pp.395-408
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• 1987

Turbulent flows in an axisymmetric reciprocating engine are numerically simulated at it's suction and compression stage. Amounts of heat transfer through the wall of the cylinder are also estimated. k-.epsilon. turbulence model is adopted and the law of the wall is applied at grid-points near the wall. More than 40 * 40 grids are reguried to reasonably predict flows and the 3-level finite difference scheme for the time derivative term appears to be effective rather than the 2-level scheme. Calculated mean velocity distributions shows good agreements with an available experimental data. The program reasonably simulates flow patterns and pressures throughout the suction and the compression stages of the reciprocating engine. Predicted intensities of turbulence are still deviated from measured data. Further researches for turbulence modeling are expected.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.98.1-98.1
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• 2015

G-M극저온냉동기의 구동으로 인해 발생되는 크라이오 펌프의 진동 저감을 위해 각 요소에 해당하는 부품의 소재 및 모델 변경으로 설계에 반영하고자 한다. G-M극저온냉동기는 헬륨냉매를 사용하여 2개의 정압과정과 2개의 정적과정으로 구성되는 냉동사이클을 구성하는데, 구조적 특성상 내부 왕복기의 운동과 고저압변환에 따른 압력차이가 냉동기의 진동을 유발하므로 진공성능에 영향을 줄 수 있으므로, 이를 최소화하는 기술 개발이 필요하다. 헬륨냉매의 고압 유동에 따른 관로 압력증가로 인한 유동소음이 발생하는데, 이로 인한 소음을 줄이기 위해 관로의 최적화 설계/방진구조반영(DAMPER)으로 진동 안정화(Vibration Stabilization)설계를 수행 하고자 하며, 이에 따른 최적화 연구을 수행하고자 한다. 일차적으로, 기존 시스템의 진동측정을 통해 진동의 가진원을 밝히고 진동 전달경로를 파악하고자한다. 진동 가진원의 가진 최소화, 진동전달경로의 전달률 최소화, 고압유동에 따른 관로 설계 최적화를 진동해석, 탄성체 동역학해석, 그리고 유동해석을 통해 진동 및 소음의 최소화 방안을 도출하고자 한다. 해석결과를 토대로 진동가진원의 최소화를 위한 제품설계변경과 진동전달경로에 대한 방진을 위한 dmper 적용(전달률 최소화) 및 유동소음 최소화를 위한 damper나 관로 최적화 설계를 수행한다. 상기 기존시스템 측정/분석, CAE해석을 통한 진동/소음의 최적화방안도출 및 실제품 적용기술은 저진동 크라이오펌프 개발을 위한 기반 기술 확립에 크게 기여할것이며, 향후 크라이오펌프 고도화 및 최신 기술 제품 개발에 큰 기여가 기대된다.