• Journal of Korean Society of Disaster and Security
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• v.11 no.2
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• pp.61-67
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• 2018

Scour protection methods can be categorized as two types: The first is to reduce the horseshoe and wake vortices which are the main reasons for local scour. Either small cylindrical structures or separated vertical deflectors can be placed in front of the pier or the horizontal deflector (or collar) can be attached to the pier like the spoiler to reduce the dynamics of vortical structures. The second is to employ the protection layer to keep the bed material in place, which is a common method with a merit of immediate effect by using block mat or tetrapod. This study examined the effect of scour reduction using the former method. The relationship between the reflector interval and reduction of scour was not clear. It is assumed that the width of the reflector is somewhat correlated with the reduction of the scour. As the KC numbers increases, the Effect of Scour reduction rate is shown to decrease. Also, Scour reduction rate showed a rapid change at $U_R=25$ or KC = 8.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.2
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• pp.17-24
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• 2003

This paper presents results from steady wind tunnel test conducted on a $65^{\circ}$ delta wing at a root chord Reynolds number of $1.76{\times}10^6$. In these experiments, the wing was instrumented with 188 pressure taps, conjunction with powerful multi-channel data logging system, allowed the wing upper surface pressure distribution to be measured. Analysis indicates that the wing upper surface distribution can provide considerable insight into the comvined aerodynamic effects of angle of attack and sideslip on the wing. In a sideslip condition, the strength of the vortex on the windward side is much stronger than that of leeward side. This asymmetric pressure disstribution betwwen each side of wings result in a negative value of rolling moment. However, at a certatin range of angle of attck and sideslip angle(${\alpha}$=$24^{\circ}{\sim}36^{\circ}C$, ${\beta}$=$-5^{\circ}{\sim}-15^{\circ}C$) abrupt change of sign of rolling monent, rolling monent reversal, was observed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.649-652
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• 2011

A series of hybrid rocket combustion experiments were carried out with PMMA/GOx changing diameter and length of the disk installed at pre-chamber. The disk can generate vortex shedding flow and change flow conditions prior to entering the fuel grain which could also alter the combustion characteristics and pressure oscillations. Isolated dimple-like surface roughness patterns distributed all over the fuel surface, which can be thought of as a realization of the inherent flow instability. It is very likely that the formation of cell structures is originated from the modification of boundary layer characteristics of an entering oxidizer flow caused by a blowing effect mainly taking place near the wall. This coincided with our LES results. It would be a meaningful basis to understand combustion instability of hybrid rocket motor.

• Journal of Korea Water Resources Association
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• v.39 no.11 s.172
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• pp.961-968
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• 2006

Since a small harbor is often located near surf zone areas which have great influences of sediment transport, there is a great possibility that the sediment will be deposited inside of the harbor. The sediment transport occurring around the harbor entrance can't be explained by the wind wave and wave induced current. In this study, it was investigated the mechanism of the entrainment of sediment into a small harbor with permeable breakwater using hydraulic experiments in 3D wave basin. It is found out that the significant sediment entrainment produced when the mode of oscillation in the harbor became the 1st mode. In the case where the incident wave period was shorter than the period that caused higher mode oscillation in harbor, only a little amount of sediment entrainment took place. The vortex shedding from the top of secondary breakwater played very important roll in the entrainment of sediment into the harbor. It is also found that the small jetty attached at the top of secondary breakwater could effectively prevent the entrainment of sediment into the harbor.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.7
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• pp.489-498
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• 2019

The airloads and structural loads of Light Civil Helicopter (LCH) rotor are investigated using a loose CFD/CSD coupling. The structural dynamics model for LCH 5-bladed rotor cwith elastomeric bearing and inter-bladed damper is constructed using CAMRAD-II. Either isolated rotor or rotor-fuselage model is used to identify the effect of the fuselage on the aeromechanics behavior at a cruise speed of 0.28. The fuselage effect is shown to be marginal on the aeromechanics predictions of LCH rotor, though the effect can be non-negligible for the tail structure due to the prevailing root vortices strengthened by the fuselage upwash. A lifting-line based comprehensive analysis is also conducted to verify the CFD/CSD coupled analysis. The comparison study shows that the comprehensive analysis predictions are generally in good agreements with CFD/CSD coupled results. However, the predicted comprehensive analysis results underestimate peak-to-peak values of blade section airloads and elastic motions due to the limitation of unsteady aerodynamic predictions. Particularly, significant discrepancies appear in the structural loads with apparent phase differences.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.68-71
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• 2005

In the case of wind turbine design, Optimization of tower structure is very important because tower generally takes about $20\%$ of overall turbine cost. In this paper, we calculated wind loads considering vortex shedding, and optimized tower flange using the calculation results. For optimization, we used FEM to analyze structural strength of the flange and blade momentum theory to calculate wind loads.

• Proceedings of the Membrane Society of Korea Conference
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• 1997.10a
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• pp.120-122
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• 1997

1. 서론 : 본 연구에서는 매우 안정된 유동의 하나로 막 표면의 전단력을 향상시켜 여과가 진행됨에 따라 막의 표면에서 발생하여 여과선속을 저하시키는 케이크층의 형성을 억제하는 데에 효과가 있다고 알려진 Taylor와류를 응용한 회전막 여과기를 사용하여 여과실험을 수행함으로써 이러한 유동이 케이크층의 형성에 미치는 영향을 살펴보았다. 또한 여과선속에 영향을 미치는 여러 매개인자들을 포함하는 새로운 모델식을 제안하고 실험결과와 비교해봄으로써 그 타당성을 살펴보았다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.130-135
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• 1995

본 연구에서는 30000rpm으로 회전하는 진공청소기 원심팬의 유동장을 임펠러, 디퓨저, 케이싱을 모두 고려하여 해석하였다. 또한 삼차원으로 배출되는 출구를 간단한 sink 패널로 모델하여 출구의 효과를 충분히 고려하였다. 해석된 유동장 자료를 이용하여 먼 거리에서의 음압을 예측하였다. 예측된 음압자료는 FFT를 이용하여 측정된 값과 주파수 영역에서 비교하였다. 또한 진공청소기 원심팬의 측정자료에서 보이는 광역소음특성이 임펠러에서 흘려지는 후류와류의 교란에 의한 임펠러와 디퓨저 깃의 비정상 힘이 주된 원인임을 밝혔다.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2001.10a
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• pp.75-76
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• 2001

산업적으로 강제 Swirl 유동은 난류를 촉진하기 위하여 많이 이용된다. 특히 Swirl유동은 난류 강도를 증가시켜 물질과 열의 전달 효과를 증진시켜 터빈 연소기, 열교환기 및 각종 산업용 버너 등의 공업분야에 폭넓게 이용되고 있다. Swirl강제 유동 발생 방법은 원추형 덕트방식, 베인형, 프로펠러형 등이 많이 이용되고 있으나 대부분의 방법은 강제로 와류(Swirl)를 발생, 촉진 및 증가 시키므로 유동손실 및 압력 손실 등을 수반하게 되어 많은 에너지 손실을 가져온다. (중략)

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.508-513
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• 1998

가압경수로에서 열여유도를 평가하는 당대의 접근 방범이 고찰되었다. 통상적으로 열여유도 평가는 국부 열속이 임계열속(CHF: Critical Heat Flux)으로부터 떨어진 거리로부터 도출된 핵비등이탈률(DNBR: Departure from Nucleate Boiling Ratio) 개념을 사용하여 수행된다. 본 연구에서는 열여유도 정가에 대하여 제기되는 문제가 당대의 접근 방법에 이러한 영향을 주는 지 평가하고 이에 대한 향후 연구 방향을 살펴 보고자 하는 것이다. 혼합날게 그리드에 의해 야기되는 와류 효과가 크면 클수록 현재의 부수로 분석 방법의 신뢰성이 제고되며 상관식의 예측 성능을 평가할 때 데이터 분포가 중요하다는 착안점이 얻어졌다.