• 한국지반공학회논문집
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• 제19권2호
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• pp.189-197
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• 2003

본 논문은 공진주시험과 삼축압축시험을 이용하여 소변형률(0.0001%~l%) 범위에서 섬유혼합토의 변형 특성을 규명하였으며, 최대전단탄성계수를 잣대로 보강효과를 평가하였다. 또한 단섬유의 직경에 대한 길이의 비(형상비), 흙의 중량에 대한 섬유 중량의 섬유혼합비, 단섬유의 종류에 따른 보강효과를 비교 검토하였다. 시료는 주문진 표준사에 폴리프로필렌 재질의 단섬유를 무작위로 배합하여 사용하였다. 섬유혼합토의 최대전단탄성계수는 비혼합토에 비해 최대 30%까지 증가하였고, 비선형 영역에서의 전단탄성계수 감소량도 억제되었다. 형상비가 증가할수록 최대전단 탄성계수는 증가하고, 단사에 비해 망사의 보강 효과가 큰 것으로 나타났다. 섬유혼합비는 0.3 % 부근에서 보강효과가 가장 커, 최적인 것으로 확인되었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.842-847
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• 2001

In order to reinforce the plate in bending spot-welding method is usually used. To analyze the effect of the reinforcement of the plates spot-welded, finite element method was employed to take advantage of the deflection obtained with respect to the change of the aspect ratio and area ratio. The reinforcement effect represented by the equivalent thickness. Was maximum when the aspect ratio was around $1.2{\sim}1.6$ and the area ratio was 0.05.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1522-1527
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• 2004

The purpose of this study is to investigate the effect of swirler angle and swirl chamber aspect ration of nozzle on the characteristics of single and twin spray. The performances of nozzle has been investigated by measurements of spray angle, droplet size, velocity and Weber number at a water pressure 0.4MHz. Visualization of spray was conducted to obtain the spray angle and breakup process. The spray characteristics such as droplet size and velocity were measured by Phase Doppler Anemometry(PDA). It was found that the smaller swirler angle, the larger axial velocity became. It was also shown that the larger aspect ratio, the smaller droplet diameter became.

• 한국항만학회지
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• 제14권1호
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• pp.87-95
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• 2000

This stability of a plate structure is very crucial problem which results in wrinkle and buckling. In this study, the effect of the pattern of spot-welding points of the two rectangular plates on the compressive and shear buckling load is studied with respect to the thickness, aspect ratio of plates and number of welding spots. Buckling coefficient of the plate not welded was compared with that of two plates with various thickness to extract the effect of thickness. The effect of number of welding spots are studied in two directions, longitudinal and transverse directions. The conclusions obtained were that the reinforcement effect was maximized when the aspect ratio was close to 1.75 at compressive load condition and that the effect of number of welding spots in transverse direction was larger than that in longitudinal direction at shearing load condition.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 1999년도 추계학술대회논문집
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• pp.265-272
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• 1999

This stability of a plate structure is very crucial problem which results in wrinkle and bucking. In this study, the effect of the pattern of spot-welding points of the two rectangular plates on the compressive and shear bucking load is studied with respect to the thickness, aspect ratio of plates and number of welding spots. Buckling coefficient of the plate not welded was compared with that of two plates with various thickness to extract the effect of thickness. The effect of number of welding spots are studied in two directions, longitudinal and transverse directions. The conclusions obtained were that the reinforcement effect was maximized when the aspect ratio was close to 1.75 at compressive load condition and that the effect of number of welding spots in transverse direction was larger than that in longitudinal direction at shearing load condition.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.247-252
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• 2001

The flow around free end of a finite circular cylinder(FC) embedded in an atmospheric boundary layer has been investigated experimentally. The experiments were carried out in a closed-return type subsonic wind tunnel with varying aspect ratio of the finite cylinder mounted vertically on a flat plate. The wake structures behind a 2-D cylinder and a finite cylinder located in a uniform flow were also measured for comparison. Reynolds number based on the cylinder diameter was about Re=20,000. A hot-wire anemometer was employed to measure the wake velocity and the mean pressure distributions on the cylinder surface were also measured. The flow past the FC free end shows a complicated three-dimensional wake structure and flow phenomenon is quite different from that of 2-D cylinder. The three-dimensional flow structure was attributed to the downwashing counter rotating vortices separated from the FC free end. As the FC aspect ratio decreases, the vortex shedding frequency is decreased and the vortex formation length is increased compared to that of 2-D cylinder. Due to the descending counter-rotating twin-vortex, in the region near the FC free end, regular vortex shedding from the cylinder is suppressed and the vortex formation region is hardly established. In the wake center region, the mean velocity for the FC located in atmospheric boundary layer has large velocity deficit, compared to that of uniform flow.

• 한국기계가공학회지
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• 제16권2호
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• pp.63-68
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• 2017

Friction occurs when surfaces that are in contact move relatively between solid surfaces, fluid layers, and materials slide against one another. This friction force causes wear on the contact surface, generates unwanted heat and leads to performance degradation. Thus, much research has been performed to avoid friction reduction. Among these studies, a textured surface that has micro patterns on the surface has drawn attention for its ability to reduce friction. A mathematical model is developed in this study to examine friction reduction due to the texture of a surface. Numerical simulations are carried out with respect to various factors such as the shape aspect ratio and texture depth of a diamond-shaped texture in the hydrodynamic lubrication regime. As a result, a shape aspect ratio of 1 is best for friction reduction.

• International Journal of Fluid Machinery and Systems
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• 제5권3호
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• pp.117-125
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• 2012

In the present experimental study, the authors try to clarify the characteristics of the flow around and inside a cross-flow impeller in a typical geometry, over a wide parameter range of an aspect ratio $L/D_2$. In order to eliminate the complicated casing factors, the impeller rotates in open space without any casings. As a result, by using hot wire anemometer measurements and by conventional flow visualisations with a particle image velocimetry technique, the authors show that both the outflow rate and the maximum vorticity attain the maximum for $L/D_2$ = 0.6. In order to investigate the aspect-ratio effect, we further reveal minute fluctuating pressures on an impeller end wall for a singular $L/D_2$ = 0.6. Especially in these pressure measurements, the eccentric vortex is prevented to revolute by the insertion of a tongue, in order to consider the spatial structure of flow more precisely.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.55-65
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• 2017

Underwater torpedo has control fin with very low aspect ratio due to launching from limited size of cylindrical torpedo tube. If the aspect ratio of control fin of underwater vehicle is very low three-dimensional flow around control fin largely reduces control forces. In this study, the end plate was applied to reduce the three-dimensional flow effects of partially movable control fin of underwater vehicle. Through numerical simulations the flow field around control fin was examined with and without end plate for different flap angles. The pressure, vorticity, lift and torque on the control fin were analyzed and compared to experiments. The comparison have shown a reasonable agreement between numerical and experimental results and the effect of end plate on a low aspect ratio control fin. When the end plate was attached to the movable control fin, the lift increased and the actuator shaft torque did not significantly change. As this means less consumption of the actuator shaft torque compared to the control fin that has the same control force, the inner actuator capacity can be reduced and energy consumption can be saved. Considering this, it is expected to be effectively applied to the control fin design of underwater vehicles such as torpedoes.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2012년도 제38회 춘계학술대회논문집
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• pp.259-261
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• 2012

본 연구에서는 3점 굽힘시험 및 DMA 시험을 통해 온도환경이 에폭시 수지의 굽힘탄성계수에 미치는 영향을 조사하였다. 굽힘 시험의 온도 조건은 $30^{\circ}C$, $100^{\circ}C$, $140^{\circ}C$의 세 가지 조건을 적용하였으며 시편은 종횡비 16, 32, 40배의 세 가지 종류가 고려되었다. 연구결과에 따르면 DMA를 통한 저장탄성계수와 굽힘시험을 통해 얻은 강성은 주어진 온도조건에서 서로 유사한 경향을 보였다. 또한 종횡비가 증가함에 따라 굽힘탄성계수도 증가 하였으며, 고온환경에서는 32배 이상의 종횡비가 적합하다고 판단된다.