• Journal of the Korean Society of Marine Environment & Safety
• /
• v.27 no.4
• /
• pp.538-549
• /
• 2021

In this study, a trim tab on the stern hull of a small high-speed vessel of approximately 10 m length sailing at a Froude number of 1.0 was designed for energy efficiency. The running attitude and resistance performance of the bare hull and trim tab hull at several angles to the base line were analyzed for model and full scale ships using computational fluid dynamics, and compared to investigate the scale effect. The analysis results for the bare hull were quite similar, but a difference in the attitude control under same conditions of the trim tab was observed, resulting in the total resistance error. However, there was no significant difference in tendency of the variation in the resistance with the attitude. Thus, the optimum running attitude could be determined from the tendency despite the scale effect, but a full scale analysis is required to analyze the control of the attitude by the trim tab and flow characteristics near the full scale ship.

• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.3074-3079
• /
• 2007

The conventional control valves have been used at the locations occurring high differential pressure and high temperature which causes cavitation, flashing, severe vibration due to abrupt flow change, and sudden pressure drop. Previous studies concerning control valves focused to prevent damage of valve trim due to the internal leak and low flow rate. The newly designed helical trim of control valve has been installed at the location of high pressure change and high temperature in a power plant, and operated for evaluation. It is confirmed that the new control valve developed in this study generates flow characteristics in comparison with previous helical trim of control valves.

• Journal of computational fluids engineering
• /
• v.20 no.2
• /
• pp.67-72
• /
• 2015

In this paper, study of high speed train pantograph arm shape and panhead cross-section for aerodynamic drag and noise reduction is performed. In previous research, it is known that knee of pantograph arm and panhead of pantogpraph are main sources of noise from high speed train pantograph. By numerical simulation using full scale pantograph model, pantograph arm and panhead optimization are performed. As a result, drag and noise are reduced at both studies about high speed pantograph.

• 한국전산유체공학회:학술대회논문집
• /
• 2009.11a
• /
• pp.77-83
• /
• 2009

In this study, we conducted resistance and propulsion performance test of ship composed of the Resistance Test, Propeller Open Water Test and Self Propulsion Test using the CFD(Computational Fluid Dynamics). We used commercial RANS(Reynolds Averaged Navier Stokes equation) solver, as a calculating tool. The unstructured grids were used in a bow and stern of ship, having complex shape, for a convenience of generating grids, and the structured grids were adopted in a central hull and rest of hull having a relatively simple shape which is called hybrid grid method. In addition, The sliding mesh method was adopted to rotate a propeller directly in the Propeller Open Water and Self Propulsion Test. The Resistance Test and Self Propulsion Test were calculated using Volume of Fluid (VOF) model and considering a free surface. And all The three cases were applied realizable k-epsilon model as the turbulence model. The results of calculations were verified for the suitability of calculations by comparing MOERI's EFD results.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.28 no.8 s.227
• /
• pp.968-975
• /
• 2004

Nanofluids have anomalously high thermal conductivities at very low fraction, strongly temperature-dependent and size-dependent conductivities, and three-fold higher critical heat flux than that of base fluids. Traditional conductivity theories such as the Maxwell or other macroscale approaches cannot explain why nanofluids have these intriguing features. So in this paper, we devise a theoretical model that accounts for the fundamental role of dynamic nanoparticles in nanofluids. The proposed model not only captures the concentration and temperature-dependent conductivity, but also predicts strongly size-dependent conductivity. Furthermore, we physically explain the new phenomena for nanofluids. In addition, based on a proposed model, the effects of various parameters such as the ratio of thermal conductivity of nanofluids to that of a base fluid, volume fraction, nanoparticle size, and temperature on the thermal conductivities of nanofluids are investigated.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2006.05a
• /
• pp.1275-1280
• /
• 2006

자연 저항체인 식생은 유체역학적으로 하천의 평균흐름과 난류량을 변화시키며, 이와 관련하여 유사, 영양 물질, 용존 산소, 그리고 서식 동물 등에 많은 영향을 미치는 것으로 알려져 있다. 과거에는 식생된 수로의 흐름을 식생에 의해 항력이 증가된 경계층 흐름으로 단순하게 보아 왔으나, 근래의 실험유체역학적 연구는 식생된 하천 흐름에 대한 미시적인 구조를 규명하였다. 본 연구는 식생수로에서 평균흐름 및 난류량에 관한 수리특성을 분석하고자 하며, 부유사의 퇴적, 유입, 이송 등의 거동에 큰 영향을 미치는 것으로 알려진 고유구조를 파악하였다. 식생된 개수로 흐름의 일반적인 평균흐름 및 난류구조는 기존의 연구결과와 동일하였으며, 본 연구에서 중점을 둔 고유구조의 경우, 식생높이를 기준으로 하여 상 하부의 흐름특성이 서로 상이한 것을 확인하였다. 식생높이 상부에서는 유속이 수면방향을 향하는 분출현상이 지배적으로 나타났으며, 식생높이 하부에서는 이와는 반대로 유속의 변동성분이 하상으로 향하는 쓸기현상이 지배적으로 나타났다. 이는 개수로에 식생이 존재할 경우 부유사의 농도분포가 수심에 따라 일정해지는 것에 대한 물리적인 근거로 파악된다.

• Tunnel and Underground Space
• /
• v.5 no.4
• /
• pp.323-335
• /
• 1995

지열에너지 개발의 기본적 개념은 지하 심부의 고온건조암체에 시추공을 이용한 수압파쇄를 실시하여 고온건조암체내에 인공파쇄대를 형성함으로써 유체의 유동회로를 구축하여 지열에너지의 회수를 도모하는 것이다. 본 논문에서는 수압파쇄균열의 발전방향 조절문제와 관련하여, 초고압수 절삭장치를 이용, 수압파쇄공 내에 인공슬롯을 형성하여 수압파쇄를 실시함으로써 균열의 발전방향을 조사하였으며, 수압파쇄에 의한 파쇄대내로의 유체순환실험을 통해 지열수의 유동특성을 규명하였다. 이를 위해 모델에 종균열과 횡균열을 형성시키고 균열내에 주입되는 물의 주입률, 정상류압력, 흐름저항을 조사하고, 이 결과를 이용하여 전산모델링을 수행하였다. 인공절리면에 대한 투수시험에서는 10$0^{\circ}C$까지의 온도변화에 따라 투수계수가 증가하였으며, 봉압 증가에 따라 증가율이 현저히 감소하였다.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.15 no.2
• /
• pp.61-66
• /
• 1979

Skipjack, Katsuowonus vagans, yellow tail Seriola quinqueradiata and Scomberomorus sinensis are largely caught by trolling gear in the coastal waters of Jeju Island. The author determined the hydrodynamic resistance of the trolling gears uscd in the waters, estimated the pulling force of the fish species above mentioned by use of body weight, and then calculated the minimum diameter of the lines of trolling gears. The results obtained are as follows: 1. The hydrodynamic resistance of the trolling gears present linear relationship in accordance with the towing speed of the gears. 2. The diameter of seizing leader, leader gut and branch line used in the waters might be durable to catch skipjack and yellow tail, whereas the diameter of those must be weak in intensity for Scomberomorus zinensis.

• The KSFM Journal of Fluid Machinery
• /
• v.6 no.2 s.19
• /
• pp.15-22
• /
• 2003

Comprehensive study on a centrifugal blower for air-purifier involving a few physical filters for percolation process has been accomplished for an optimal design of the air handling system. The filtering media causes a flow resistance for induced flows by a rotating impeller. The present methodology is to adopt PIV system for velocity measurements and wind tunnel connected with an anechoic chamber for total performance test of the blower. Trial prototypes for the blades of a rotor and casing are presented for satisfaction of both flow rate and noise level set by design objectives. Tapered blades with a special casing for a fan show good performance data. The results of velocity fields also explain the reason of improvements of the blower performance.

• 한국전산유체공학회:학술대회논문집
• /
• 1998.11a
• /
• pp.175-184
• /
• 1998

본 연구에서는 제한된 수로를 운항하는 선체주위의 유동특성에 관한 연구를 수행하고자 하였다. 일반적으로 운하 또는 하천을 운항하는 선박의 경우 제한된 수심의 영향으로 천수효과가 발생하게 된다. 이러한 천수의 효과와 제한된 폭의 영향으로 선수부분에서 선체보다 선행하는 파도가 전파되어 나아가기도 하며, 이로 인하여 선박은 보다 많은 조파저항을 받게 된다. 본 연구에서는 임의의 형상을 갖는 선체가 폭과 수심이 제한된 운하를 임계속도 근처에서 운항하는 경우에 관하여 폭과 수심을 변화시켜가며 수치계산을 수행하여, 제한수로에서의 임의의 선체주위의 유동특성을 관찰하고자 하였다. 수치계산은 MAC(Marker And Cell)법을 기초로 한 유한차분법(Finite Difference Method)을 사용하였으며, 계산에 사용된 격자계는 임의의 형상에 관하여 격자생성이 용이한 직사각형 격자계(Rectangular Grid System)를 사용하였다.