• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.33-36
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• 2010

Lots of studies about turbine loss have been done especially about tip leakage loss. But these studies deals with small tip clearances which is less than 5 percent chord. Now, like turbopumps, small turbines have larger tip clearance and it is hardly found related papers in open literature. On this study, with varying tip clearance 1% to 20% chord, loss is measured under inlet velocity at 30m/s and Reynolds number based on chord at 210000. It is found that maximum loss coefficient is 0.113 at 10% clearance, and when tip clearance is larger than 10%, loss is not linearly increased anymore.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.117-121
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• 2008

The effect of tip clearance on the performance of a supersonic impulse turbine was investigated experimentally. Test was performed using high pressure air in wide ranges of pressure ratio and rotational speeds. Test revealed that efficiency gradient of the subject turbine at a reference test point was a very low value of 0.05. Turbine efficiency was varied non-linearly with respect to tip clearance. It has been found that efficiency gradient is proportional to the cube of rotational speed at a fixed turbine pressure ratio. It also has been found that efficiency gradient shows its minimum at a reference test pressure ratio irrespective of rotational speeds.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.04b
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• pp.80-85
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• 1996

외부가압공기베어링중에서 Fig. 1과 같이 베어링 간극과 비슷항 크기의 간극을 갖는 슬롯을 통하여 공기를 공급하는 형태의 베어링을 슬롯 레스트릭터 공기베어링이라고 한다. 본 연구에서는 공기 윤활 외부가압 슬롯레스트릭터 저어널 베어링의 슬롯의 형상을 변화하는 방법을 이용하여 고속안정성이 우수한 또 다른 슬록의 형상을 제안하고 제안된 슬롯의 고속안정성을 해석하기로 한다.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.123-133
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• 2004

The magnitudes of wall thrust acting on quay walls can easily vary due to the development of excess pore pressure in backfill. In this research, a new displacement model was proposed to predict the displacement of the wall considering such magnitude variations of the wall thrust. This model is based on Newmark sliding block concept. The magnitude variation of the wall thrust is modelled by varying the magnitude of yield acceleration. The parametric study was performed to analyze the effects of input parameters on the seismic displacement of the wall, and the validity of this model was verified by comparing its predicted displacements with those of Is shaking table tests.

• The Journal of the Acoustical Society of Korea
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• v.34 no.3
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• pp.192-199
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• 2015

There is a gap between the inner wall of a pulse tube and an underwater acoustic material when the measurement for transmission loss by the pulse tube is carried out. In this paper, the effect, which is caused by the gap, for the measurement of transmission loss is analyzed. Transmission coefficient is derived from the ratio of the pressures between front and rear of the gap. Then, transmission loss for specimen with a gap is obtained by combining the transmission coefficients of the gap and specimen. The results of experiment and simulation for a specimen of stainless steel with 10 mm thickness are compared in order to evaluate the simulation model. Finally, simulations with respect to the gap size and transmission loss of a specimen are performed to analyze and evaluate the effect of the gap in measurement of transmission loss.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.277-285
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• 2009

A series of undrained cyclic triaxial tests were carried out to investigate the cyclic shear stress strength characteristics of sands with respect to the silt content. Silty sand was collected around the basin of Nak-Dong River and remolded in laboratory with the range of silt content 0~50% in sand located. As results, with the change of silt content cyclic shear stress ratio (CSR) at N=10 showed the maximum value at 5% and the minimum at 20% in all relative density. The development tendency of the pore water pressure analyzed by the relationship cyclic ratio and pore water pressure ratio is unrelated the change of CSR varying silt content. Comparing the results of the void ratio and skeleton void ratio after consolidation, CSR varying silt content was much affected by skeleton void ratio which is known to affect shear behavior of silty sand.

• Journal of the Korean Geotechnical Society
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• v.16 no.6
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• pp.141-151
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• 2000

본 연구에서는 토사나 사석을 이용하여 자체를 축조하는 과정에서 발생하는 연약지반의 강제치환거동을 연구하기 위하여 다양한 시험조건에 대한 원심모셩을 수행하였다. 제체축조에 따른 연약지반의 강제치환거동은 제체의 성토시공방법, 성토재의 입경, 연약지반의 종류와 강도 등에 따라 맣은 차이를 보였는데, 특히 성토과정 중에 발생하는 과잉간극수압의 크기와 밀접한 상관관계를 보였다. 급속시공인 경우에 연약지반의 파괴영역은 회적으로 확대되고 성토사면의 기울기는 완만해졌으며, 성토재의 입경이 클수록 치환깊이가 증가하고 성토사면의 기울기가 급하게 형성되었다. 그리고 동일점토에서는 지반의 강도가 클수록 치환량이 적었지만, 점토의 종류가 다른 경우에는 지반내 발생하는 과잉간극수압의 크기와 소산성조에따라 치환거동이 많은 영향을 받는 것으로 나타났다.

• Journal of Periodontal and Implant Science
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• v.34 no.1
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• pp.83-91
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• 2004

2-piece 임플란트에서는 초기 치유 기간 동안 0.9-1.6mm의 골 소실이 일어나는데 2-piece 임플란트의 미세 간극과 그에 따른 생물학적 폭경의 형성이 중요한 원인이다. 최근 수직적으로 미세 간극의 위치를 변화시킴으로 골 소실의 양을 줄일 수 있다는 보고가 있다. 이번 실험의 목적은 미세 간극의 수평적 위치 변화에 따른 골 소실의 양을 비교하는데 있다. 하악에서 인접하여 최소 2개의 임플란트를 식립할 수 있는 7 무치악 부위에 총 15개의 Osseotitie XP 4/5를 식립하였다. 이때 임플란트의 상연이 주위 치조골과 일치하게 식립하였고 무작위로 선택하여 한 그룹(W군)에서는 wide diameter healing abutment를 연결하였고 다른 한 그룹(S 군)에서는 standard diameter healing abutment를 연결하였다. 3개월의 치유 기간후 보철 과정을 시작하였으며 이 때 healing abutment와 같은 크기의 prosthetic component를 이용하였다. 임플란트 식립 직후, 3개월의 치유 기간이 지난 보철 직전(Interval I)에, 보철 과정 직후(Interval II)에 각각 치근단 방사선 사진을 찍어 각 단계에서의 골 소실 양을 비교하였다. W 군의 경우 골 소실의 양이 Interval I에서 $1.60{\pm}0.78$, Interval I+II에서 $2.36{\pm}0.29$이었고 S 군에서는 Interval I에서 $1.5810{\pm}0.3030$, Interval I+II에서는 $1.7346{\pm}0.4199$이었다. W군에서는 Interval I와 I+II에서의 골 소실 양이 통계학적으로 유의할 만한 차이를 보였으며, Interval I+II에서의 W 군과 S 군에서의 골 소실 양도 통계학적으로 유의할 만한 차이를 나타내었다. Interval I에서는 두 그룹에서 골 소실의 차이가 없었는데 이는 1 stage surgery시 healing abutment 주위로 mucoperiosteal flap 접합의 어려움 때문으로 생각된다. 한편 Interval II에서는 abutment manipulation 등의 과정이 추가적인 골 소실을 야기한 것으로 생각된다. Interval I+II에서 W 군과 S 군 사이의 골 소실 양 차이는 미세 간극의 수평적 위치 변화의 양과 유사한 결과를 나타내었는데 이로 미루어 미세 간극의 수평적 이동은 임플란트 주위의 골 소실 양에 영향을 미칠 수 있다고 생각된다.

• The Journal of Engineering Geology
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• v.31 no.1
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• pp.55-66
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• 2021

Hydraulic-mechanical (H-M) coupled numerical modeling was used to evaluate the evolution of hydrogeological properties in response to the installation and expansion of a borehole. A domain with a discrete fracture network was adopted for discontinuum modeling to simulate changes in fracture apertures. Comparison with real hydraulic test data shows that the effects of principal stress direction and expansion of borehole diameter were reasonably simulated by H-M coupled numerical modeling. The modeling confirmed that aperture changes depended on the principal stress direction, with an increase in aperture size due to vertical displacement being the dominant effect. A concentration of shear dilation around the borehole had an additional, subsidiary, effect on the hydrogeological evolution. These results show that the permeability of fractured rock can be increased by changing the hydraulic properties of a fracture through stress redistribution caused by the installation and expansion of a borehole.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.2 s.152
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• pp.101-110
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• 2007

Recently, rudder erosion due to cavitation frequently has occurred at large high speed container carriers. Especially, in the case of a horn-type rudder, the rudder erosion is severe around a gap. The gap-flow characteristics are investigated through a computational method to understand the effects of a gap on the cavitation and rudder efficiency. A viscous flow theory utilizing a cavitation model is applied to calculate the flow around idealized 2-dimensional rudder sections in a full scale. The effects of gap clearance and flow-control projection are also investigated. From the computational results, the mass flow rate through a gap is found to be one of the important parameters to affect the cavitation and rudder efficiency.