• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.2
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• pp.167-172
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• 2011

In physical engineering, the turbulent flow on the surface roughness is very important. With the welding, design and paint, the hull surface roughness at each stage in the various aspects are important factors to be considered. In this study, the hull surface roughness geometry that was generalized to the PIV was applied to the tank test. The roughness of the surface changed the distance of the interval. Experimental velocity is Re = $1.1{\times}10^4$, Re = $2.0{\times}10^4$ and Re = $2.9{\times}10^4$. The turbulent intensity at the time-average were examined The roughness coefficient occurred with increasing turbulence intensities was stronger. The turbulence intensity away from the roughness in the shape was zero. The variation of turbulence intensity at the experimental flow conditions change was not affected.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.3 s.153
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• pp.267-278
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• 2007

This experimental study investigated on the eddy making effect on the roll motion of a rectangular barge in a two-dimensional wave tank. The structure was used to simulate a simplified rectangular barge in the beam sea condition. The structure with a draft one half of its height was hinged at the center of gravity and free to roll by waves. The rectangular barge was tested with regular waves with a range of wave periods that are shorter, equal to, and longer than its roll natural period. Particle image velocimetry (PIV) was employed to obtain the velocity field in the vicinity of the structure. The coupled interactions between the incident wave and the barge were demonstrated by examining the vortical flow fields to elucidate the eddy making effect during the roll motion. For incoming wave with a wave period same as the roll natural period, the barge roll motion was reduced by the eddy making damping effect. At the wave period shorter than the roll natural period, the structure roll motion was slightly reduced by the vertical flow around the barge. However, at the wave period longer than the roll natural period, the eddy making effect due to flow separation at structure corners indeed amplifies the roll motion. This indicates that not only can the eddy making effect damp out the roll motion, it can also increase the roll motion.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.5
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• pp.523-529
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• 2018

Two liquids which are generally used as fuels of rockets are mixed and their mixing process is quantitatively investigated by the use of particle image velocimetry (PIV). As working fluids for the liquid mixing, Dimethylfuran (DMF) and JetA1 oils have been used. Since the specific gravity of DMF is larger than that of JetA1 oil, the DMF oil has been set at the lower part of the JetA1 oil. For better visualization of the mixing process, Rhodamin B powder has been blended into the DMF oil. An agitator having 3 blades has been used for mixing the two liquids. For quantitative visualization, a LCD monitor has been used as a light source. A color camera, camcoder, has been used for recording the mixing process. The images captured by the camcoder have been digitized into three color components, R, G, and B. The color intensities of R, G, and B have been used as the inputs of the neural network of which hidden layer has 20 neurons. Color-to-concentration calibration has been performed before commencing the main experiments. Once this calibration is completed, the temporal changes of the concentration of the DMF has been quantitatively analyzed by using the constructed measurement system.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.5
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• pp.493-499
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• 2013

This paper presents are experimental investigation to figure out impact pressure and flow characteristics of a wedge type structure in free fall. The flow field has been obtained by 2-frame grey level cross correlation PIV(Particle Image Velocimetry) method, the impact pressure of free fall structure by a pressure acquisition system apply to Dewetron system. The angles between a model and the free surface are adapted $15^{\circ}$, $25^{\circ}$, $35^{\circ}$ and $45^{\circ}$ respectively. Velocity field of water exit has higher better than water entry. The impact pressure under the bottom of the model has been appeared higher values at $15^{\circ}$ than $45^{\circ}$, and also at P1.

• 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.

• Journal of Navigation and Port Research
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• v.34 no.5
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• pp.331-336
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• 2010

The free surface influenced the wake behind a circular cylinder and its effects were investigated experimentally in a circulating water channel with the variation of water depth. Instantaneous velocity fields were measured in this paper. The measured results has been compared with each other to investigate the flow characteristics of the circular cylinder's 2-dimensional section at $Re=1.0{\times}10^3$ using 2-frame grey level cross correlation PIV method. The flow around the circular cylinder with free surface affected the wake structure. Especially, in case of d=1.0D, the boundary layer was measured in the whole area. The separation point and boundary layer of the circular cylinder could be controlled by the water depth.

• Journal of Navigation and Port Research
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• v.32 no.10
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• pp.771-776
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• 2008

The main purpose in having a control surface on a ship is to control the motion of it. It is the important element to determine the maneuvering characteristics of the ship. In this paper, the measured results has been compared with each other to predict the performance characteristics of flapped rudder's 2-dimensional section at $Re=3.0{\times}10^4$ using 2-frame grey level cross correlation PIV method. The side force of the rudder could be mainly improved by the lift force at 10 degrees angle of attack and the drag force at 20 degrees angle of attack. The separation point and boundary layer could be controlled by the change of the only flap's angle at 10 degrees angle of attack.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.72-72
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• 2015

최근 이상기후로 집중호우와 강우패턴이 변화하고 있다. 하지만 변화하는 환경을 고려하지 않은 내배수시설 설계로 내수 침수 피해가 증가하여 인명 및 재산 피해가 급증하고 있다. 이에 도시지역의 내수침수에 대한 대책으로 재내지의 초과 우수를 하천으로 강제 배수시키기 위한 빗물펌프장의 역할이 점점 중요해지고 있다. 도심지역의 집중호우에 대응하기 위해서는 빗물펌프장의 목표 배수량을 실제 배수할 수 있는지에 대한 여부가 도시지역의 내수침수를 효율적으로 방어하는데 있어 중요한 요소가 될 것이다. 하지만 현재 빗물펌프장의 설계 시 펌프 흡입부 내 흐름특성을 고려하지 못하고 있어 펌프의 효율에 대한 불확실성이 큰 것이 사실이다. 따라서 펌프 가동 시 흡입부 주변의 흐름특성에 대한 연구가 필요하다. 기존 펌프 흡입부의 실험적 연구에서는 색소를 이용한 vortex의 생성 위치 및 경향을 정성적으로 파악하거나 ADV등의 유속계를 이용하여 흡입부 주변의 흐름특성을 지점별로 분석하는 연구들이 수행되었다. 하지만 빗물펌프장의 펌프 흡입부 주변의 흐름은 펌프 가동에 따라 매우 복잡한 와류가 발생하기 때문에 이를 방지하기 위해서는 정량적인 유속장 분석이 필요하다. 이에 본 연구에서는 비접촉식 유속 측정이 가능하고 유속장 측정이 가능하다는 장점을 갖고 있는 입자영상유속계(PIV: Particle Image Velocimetry)를 이용하여 펌프 흡입부 주변의 흐름특성을 분석하였다. 펌프 흡입부의 흐름특성을 분석한 결과 흡입관 내 유속분포의 편중 현상에 접근유속의 영향이 큰 것으로 나타났다. 또한 흡입유속에 비해 접근유속이 빠른 경우 흡입관 내 유속분포는 상류측에서 횡방향 와류가 발생하여 흡입에 방해가 되는 것을 확인하였고, 하류측으로는 흡입 방향으로 유속이 발생하는 것으로 나타났다. 따라서 향후 펌프 흡입관내 상류측부분의 와류를 감소시키기 위한 연구가 필요할 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.454-454
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• 2016

하천의 치수안정성 확보 및 수심유지, 생태복원 등과 같은 다양한 요구를 충족하기 위한 보의 성능 개선에 대한 연구가 필요하며, 계단형 보는 재료에 의한 폭기효과 및 서식처 효과 등의 환경적요소를 내포하고 있다. 기존 연구는 표면류 흐름특성을 검증하고 유량변화에 따른 하류단 도수발생위치 변화를 분석하는 등 계단형 보에 대해 수리특성을 정량화한 연구가 대부분이며 흐름변화에 따른 유속장에 관한 연구는 미흡한 실정이다. 따라서 본 연구는 기능성 친환경 횡단 구조물 유형 중 하나인 계단형 보의 안정성 검토를 위한 수리적 특성을 분석하고자 함으로써 구조물 안정성에 영향을 줄 수 있는 자체 및 하류 보호공 주변의 유속 분석을 통한 흐름 특성을 검토하고 설계시 외력 고려를 위한 자료를 제공하기 위한 목적이 있다. 이를 위해 계단형 보모형에 대해 수리모형실험을 수행하였다. 폭 0.24 m, 총 길이 3.70 m, 높이 0.30 m인 순환실험수로를 이용하였으며, 계단형 보 모형은 5단으로 단 높이 2 cm와 단 길이 5 cm이며, 보 높이는 10 cm, 보 길이는 25 cm 모형으로 실험하였다. 하류에 전도식 게이트를 설치하여 하류 수위를 증가시키면서 보 하류부에서 발생하는 완전도수부터 하류수심이 보 높이를 초과하는 잠김흐름 조건에 대해 실험하였다. 측정기법은 입자영상측정계(Particle Image Velocimetry; PIV)를 이용하였으며, 상류영역부터 하류영역에 대해 보 주변 흐름의 순간적 유속분포를 확인하였다. 또한 측정된 전반적 흐름 양상에 대해 통계적 수리분석을 수행하였다. 흐름특성에 대한 연구는 향후 계단형 보의 물받이 길이 및 보의 적정 규모 설계시 중요한 자료가 될 것으로 기대한다.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.6
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• pp.642-647
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• 2018

Gas compressors are mostly driven by motors. It is important to measure the power of motors to evaluate their power efficiency, because the mechanical loads of gas compressors are always varied. In order to measure the power given to the driving motors, the torque should be measured. Manufacturers of compressors usually use the torque data to calculate the compressors qualities such as power consumption, efficiencies and failures. In general, measurements for the shaft torque of the compressors have been based upon contact types, strain gauges. In the cases of larger compressors, the contact type of strain gauges have several disadvantages such as large size and high cost. In this study, a relatively inexpensive and simple torque sensing technique that is not restricted to shaft diameter is introduced using visualization technique. Particle image velocimetry (PIV) has been adopted to complete non-contact torques measurements for rotating motors. In order to compare the performance of the newly constructed torque measurement technique, torque measurement by a transducer based on MEMS technology has been performed simultaneously during experiments.