• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.115-121
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• 2010

Cavitating flow is widely shown in many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work focuses on the numerical analysis of the multiphase flow around the underwater vehicle which was launched from a submarine. The governing equation is the Navier-Stokes equation with a homogeneous mixture mode. The multiphase flow solver uses an implicit preconditioning scheme in curvilinear coordinate. For the code validation, the results from the present work are compared with the existing experimental and numerical results, and a reasonably good agrements are obtained. The multiphase flow around an underwater vehicle is simulated which includes submarine wake effects.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.341-346
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• 2010

In this paper, viscous flow calculation of pump-jet that is used as underwater propulsor was made by using RANS equation. For the validation, calculation for DTRC4119 marine propeller was made and reasonable agreements were obtained between the present results and the experiment. An unstructured overset mesh technique is used for analysis of relative motion between rotor and stator in pump-jet propulsor. Results for pump-jet propulsor were compared with computational results of another researcher.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.252-255
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• 2011

Supercavitating torpedo uses the supercavitation technology that can reduce dramatically the skin friction drag. The present work focuses on the numerical analysis of the non-condensable cavitating flow around the supercavitating torpedo. The governing equations are the Navier-Stokes equations based on the homogeneous mixture model. The cavitation model uses a new cavitation model which was developed by Merkle(2006). The multiphase flow solver uses an implicit preconditioning scheme in curvilinear coordinates. The ventilated cavitation is implemented by non-condensable gas injection on backward of cavitator cone and the base of the torpedo. The comparison between the without and with ventilated cavitation numerical results, with ventilated cavitation using non-condensable gas injection is more efficient method.

• Journal of the Korean Society of Marine Environment & Safety
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• v.2 no.1
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• pp.1-10
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• 1996

초음파는 액체 및 고체의 매질 속에서도 그 전달 특성이 우수하여 수중 물체의 감지, 지질 조사 자원탐사뿐만 아니라, 의학 분야에서도 널리 사용되고 있다. 물체유동정보 측정방식에는 연속파를 이용한 도플러식과 펄스 신호를 이용한 도플러는 거리 분해능이 좋으므로 깊이에 따른 속도 정보를 쉽게 얻을 수 있는 장점이 있으나, 수신되는 도플러 신호가 탐촉자의 특성과 매질 속에서의 전파특성 등에 의하여 송신된 신호와 파형이 다르고 복잡한 주파수 특성을 가지므로 연속파에서와 같이 도플러 주파수를 직접 측정하기 곤란하다. 도플러 주파수를 검출하기 위하여 여러 방법이 개발되어 있으나, 측정거리와 측정속도의 제약과 더불어, 실시간(real time) 처리에 의한 분포적 측정이 어려운 실정이다. 본 연구에서는 시간 영역에서 국소 데이터를 이용하여 펄스 신호의 위상을 정의하고 실시간에서 펄스 신호를 위상으로 변환하는 신호 처리법을 제안하였다. 또한 이 신호 처리법을 응용하여 측정 범위의 위상 곡선에서 위상 차를 계산함으로써 평균 가속도와 유동속도정보를 분포적으로 얻을 수 있는 새로운 펄스 도플러 기법을 제안하였으며, 모델 신호를 만들어 제안된 방법의 유용성을 검토하였다.

• The KSFM Journal of Fluid Machinery
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• v.11 no.3
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• pp.7-13
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• 2008

The cavitating flow simulation is of practical importance for many engineering systems, such as pump, turbine, nozzle, Infector, etc. In the present work, a solver for two-phase flows has been developed and applied to simulate the cavitating flows past hydrofoils. The governing equation is the two-phase Navier-Stokes equation, comprised of the continuity equation of liquid and vapor phase. The momentum and energy equation is in the mixture phase. The solver employs an implicit, dual time, preconditioned algorithm using finite difference scheme in curvilinear coordinates. An experimental data and other numerical data were compared with the present results to validate the present solver. It is concluded that the present numerical code has successfully accounted for two-phase Navier-Stokes model of cavitation flow.

• Journal of the Korean Society of Visualization
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• v.19 no.2
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• pp.48-55
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• 2021

In order to design a propeller with high efficiency and excellent cavitation performance, theoretical and experimental studies on the cavitation and noise characteristics according to the blade section shape are essential. In general, sheet cavitation, bubble cavitation, and cloud cavitation are the main causes of hull vibration and propeller surface erosion. However vortex cavitation, which has the greatest influence on the noise level because the fastest CIS in ship propeller, has been researched for a long time and studies have been conducted recently to control it. In this experiment, the development process of cavitation was measured by using three dimensional wings with two different wing section and wing tip shapes, and the noise level at that time was evaluated. In addition, we evaluated the relationship between cavitation inception and hydrodynamic force using three component load cell and we measured the velocity field of wing wake using LDV.

• Proceedings of the Korean Nuclear Society Conference
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• 2002.05a
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• pp.335.2-335
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• 2002

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.403-410
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• 2021

There are positive effects, such as pain reduction, when rheumatism patients exercise in water, but the cause of the pain reduction is unclear, and research on this is inadequate. This study examined the flow of the surface of the foot and the principles of pain relief. Unsteady simulations were conducted to analyze the flow, which was performed by repeatedly setting the movement of the foot raising and descending three times. Pressure fluctuations and frequencies were analyzed by designating pressure points at the painful location. The results showed that a positive and negative pressure of approximately ±500Pa was applied overall. A pressure of approximately ±2000Pa was applied when the direction of movement was changed. A frequency of approximately 35 to 80Hz was generated in the area where rheumatoid arthritis pain frequently occurs. The effects of reducing pain could be predicted when continuous pressure fluctuations and frequencies are applied repeatedly to the painful location, blood circulation promotion. The results could be used as basic data to understand the principles of aquatic exercise and support the development of underwater exercise programs and developing related medical equipment.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.5
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• pp.542-548
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• 2005

A fluidized bed reactor containing porous media has been known to be effective for nitrogen and organic matters removal in wastewater. The porous media which attached microbes plays important roles in simultaneous nitrification/denitrification (SND) due to coexistence of oxic, anaerobic and anoxic zone. For SND reaction, oxygen and organic substrates should be effectively diffused from wastewater into the intra-carrier zone. However, the overgrowth heterotrophic microbes at the surface of porous media may restrict from substrates diffusion. From these viewpoints, the existence and effect of heterotrophic bacteria at surface of porous media might be the key point for nitrogen removal. A porous media-membrane hybrid process was found to have improved nitrogen removal efficiency, due to stimulated denitrification as well as nitrification. Microelectrode studies revealed that although intra-media denitrification rate in a conventional fluidized bed was limited by organic carbon, this limitation was reduced in the hybrid process, resulting in the increased denitrification rate from 0.5 to $4.2\; mgNO_3-N/L/hr$.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.2
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• pp.241-246
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• 2014

The purpose of this study is to investigate the flow characteristics around underwater triangular structure with various inclination and Reynolds number. A flow fields around the triangular structure model were measured by visualization method and PIV in the circulating water channel. The result of the experiment is where the triangular structure that has a inclination of $45^{\circ}$ and the reynolds number at $Re=2.9{\times}10^3$ showed rising velocity component to 2.7 times of the structure height. When the reynolds number is steady and when the inclination is greater the descending velocity component of the structure's rears current form is greatly shown and for the areas where it's more than y/hs=1.75 has a change in the angle of inclination but it doesn't give a great effect to it.