• 한국농공학회지
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• 제28권4호
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• pp.57-65
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• 1986

A new method of determining the discharge coefficients and velocity which are very important factor to calculate the weight of riprap materials in the seadike closure gap can be derived through the hydraulic model test. On the basis of the results of this study, general hydraulic aspects between gradual horizontal and vertical closure method are compared, and also discharge and velocity computation procedures are presented.

• 한국군사과학기술학회지
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• 제10권3호
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• pp.34-42
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• 2007

It is very important for the combat system to process extensive data exactly at short time for the better situation awareness compared with the threats in these days. This paper suggests to add radial velocity on the decision factor of sensor data fusion in the existing algorithm for the accuracy enhancement of the sensor data fusion in the combat system.

• 대한의용생체공학회:의공학회지
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• 제33권2호
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• pp.72-77
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• 2012

Phase Contrast MR Angiography(PC MRA) is excellent MRA technique for measuring the velocity of vessels in the human body. PC MRA need to at least four images for angiogram reconstruction and it caused longer scan time. Therefore, we used keyhole imaging combined PC MRA to reduce the scan time. However, keyhole imaging can lead the erroneous effects as loss of phase information or frequency discontinuous. In this study, we applied the keyhole imaging combined 2D PC MRA for improving the temporal resolution and also measured the velocity to evaluate the accuracy of phase information. We used 0.32T MRI scanner(Magfinder II, Scimedix, Korea). Using the 2D PC MRA pulse sequence, the vascular images for a human brain targeted on the Superior Sagittal Sinus(SSS) were obtained. We applied tukey window function for keyhole images to minimize the ringing artifact and erroneous factors that are induced frequency discontinuous and phase information loss. We also applied zero-padded algorithm to peripheral missing k-space lines to compare keyhole imaging results and the artifact power(AP) value was measured on the complex difference images to validate the image quality. Consider as based on our results, heavy image distortions and artifacts were shown until using at least 50% keyhole factor. Using above the 50% keyhole factors are shown well reconstructed and matched for magnitude images and velocity information measurements. In conclusion, we confirmed the image quality and velocity information of keyhole technique combined 2D PC MRA. Especially, measured velocity information through the keyhole imaging combination was similar to the velocity information of full sampled k-space image despite of frequency discontinuous and phase information loss in the keyhole imaging reconstruction process. Consequently, the keyhole imaging combined 2D PC MRA will give some clinical usefulness and advantages as improving the temporal resolution and measuring the velocity information via selecting the appropriate keyhole factor at low tesla MRI system.

• 한국수자원학회논문집
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• 제38권2호
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• pp.143-153
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• 2005

최근 들어 자연형 하천과 하천생태계 복원에 대한 관심이 점증하면서 수리학적 기능 외에, 다양한 생태환경을 제공하고 하안 부근의 경관을 개선하는 기능을 가는 수제에 대한 관심이 커지고 있다. 그러나 현재 국내에는 수제설치에 대한 설계지침이 충분치 않을 뿐 만 아니라 국내 수행된 연구 자료가 매우 부족한 실정이다. 이에 본 연구에서는 수제 설계인자 해석을 위한 수리모형실험을 수행하였다. 실험조건은 수제선단 흐름변화와 수제하류부 재순환영역에 대한 고정상실험으로 수제길이와 투과율을 조절하여 수행하였다. 주요 분석은 수제 선단에서는 중앙부 유속증가와 세굴의 영향인자인 유속과 편향각을 측정하여 수제 선단유속비와 면적비에 대한 실험식을 제안하였다. 또한 수제하류부 재순환 영역에서는 수제 설치의 주요요인인 수제간격의 기초 자료를 해석하기 위해 흐름분리 길이와 입사각의 변화를 분석하였으며 투과율과 수제 설치각에 대한 실험식을 제안하였다.

• 한국콘텐츠학회논문지
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• 제15권2호
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• pp.499-506
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• 2015

마찰속도란 벽면 가까이의 흐름에서 벽면의 마찰 응력과 밀도로 정의되는 속도의 차원을 갖는 양이다. 또한 마찰속도는 바닥 흐름에서 전단력을 나타내는 수리학적 매개변수이다. 게다가 개수로 설계나 하천, 해안에서 유사 및 물질의 거동을 파악하는데 정확한 마찰속도의 산정이 매우 중요하며 주 흐름방향의 혼합계수를 결정하는데 필수적인 요소이다. 이러한 마찰속도를 산정하는 방법들은 하상경사를 이용하는 방법, 레이놀즈 응력분포를 이용하는 방법, 점성저층에서 평균유속의 선형법칙을 이용하는 방법, 벽 전단 응력의 직접적 측정방법 등이 있다. 본 연구에서는 기존 방법과 달리 확률통계 기법에 사용되는 엔트로피 개념에 접목하여 새로운 마찰속도공식을 제안하였고, 이를 검증하기 위해 Song의 실측 실험데이터를 이용하였다. 제안한 공식과 마찰속도 공식에 의해 산정된 마찰속도의 결정계수는 0.999-1.000로 잘 일치한 것으로 분석되었다.

• Wind and Structures
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• 제10권3호
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• pp.287-300
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• 2007

Wind action is a factor of fundamental importance in the structural design of light or slender constructions. Codes for structural design usually assume that the incident mean wind velocity is parallel to the ground, which constitutes a valid simplification for frequent winds caused by meteorological phenomena such as Extratropical Storms (EPS) or Tropical Storms. Wind effects due to other phenomena, such as thunderstorms, and its combination with EPS winds in so-called squall lines, are simply neglected. In this paper a model that describes the three-dimensional wind velocity field originated from a downburst in a thunderstorm (TS) is proposed. The model is based on a semi empirical representation of an axially-symmetrical flow line pattern that describes a stationary field, modulated by a function that accounts for the evolution of the wind velocity with time. The model allows the generation of a spatially and temporally variable velocity field, which also includes a fluctuating component of the velocity. All parameters employed in the model are related to meteorological variables, which are susceptible of statistical assessment. A background wind is also considered, in order to account for the translational velocity of the thunderstorm, normally due to local wind conditions. When the translation of the TS is caused by an EPS, a squall line is produced, causing the highest wind velocities associated with TS events. The resulting vertical velocity profiles were also studied and compared with existing models, such as the profiles proposed by Vicroy, et al. (1992) and Wood and Kwok (1998). The present model predicts horizontal velocity profiles that depend on the distance to the storm center, effect not considered by previous models, although the various proposals are globally compatible. The model can be applied in any region of interest, once the relevant meteorological variables are known, to simulate the excitation due to TS winds in the design of transmission lines, long-span crossings, cable-stayed bridges, towers or similar structures.

• 설비공학논문집
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• 제19권8호
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• pp.593-598
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• 2007

The present study has dealt with the measuring method of ice slurry viscosity using falling sphere viscometer. The experimental apparatus was composed by test section and high-speed video system. And the spheres used in this study were alumina and glass. The main parameters were ice packing factor (IPF) and falling velocity of sphere so the acquired results were discussed for these parameters. The viscosity of ice slurry was calculated by using measured falling velocity and moving distance at instantaneous time and the Stokes hypothesis was used for this calculation. It was clarified that possible measuring range was $IPF\;=\;0.06{\sim}0.14$ of this type of measuring device and measuring method. In addition, it was clarified that the viscosity of ice slurry increased to increase of ice packing factor (IPF) of ice slurry.

• Journal of Advanced Marine Engineering and Technology
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• 제32권1호
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• pp.50-56
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• 2008

Experimental results for forced convection condensation of Refrigerant-22 and ternary Refrigerant-407C(HFC-32/125/134a 23/25/52 wt%) which is being considered as a substitute R-22 inside a horizontal micro-fin tube are presented. The test section was horizontal double-tube counterflow condenser with a length 4,000 mm micro-fin tube, having 8.53 mm ID, 0.2 mm fin height and 60 fins. The range of parameters of mass velocity were varied from 102.1 to 301.0 kg/(m2.s) and inlet quality 1.0. At the given experimental conditions. the average heat transfer coefficients for R-407C were lower than that for R-22 at a micro-fin tube. Over the mass velocity range tested. the PF(penalty factor) for R-22, R-407C were lower than the increasing ratio of heat transfer area by fins, and the EF(enhancement factor) for R-22, R-407C were higher than the increasing ratio of heat transfer area by fins.

• 설비공학논문집
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• 제19권3호
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• pp.220-227
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• 2007

Heat transfer and momentum transfer under conditions of both oscillating flow and oscillating pressure within pulse tubes show very different behavior from those for steady state conditions. The analytic solutions of axial velocity and temperature of the gas within pulse tubes were obtained by assuming that the variations in pressure and temperature were purely sinusoidal and small. The shear stress and the heat flux at the tube wall obtained from the solutions are expressed in terms of the cross-sectional averaged velocity, the difference between mean temperature and instantaneous cross-sectional averaged temperature and the difference between mean pressure and instantaneous pressure. It is shown that the complex shear factor, which has been applied to momentum transfer of incompressible oscillating flow, and the complex Nusselt number, which has been applied to either heat transfer with oscillating pressure only or heat transfer of incompressible oscillating flow, could also be used for momentum transfer and heat transfer subjected to both oscillating flow and oscillating pressure, respectively.

• 한국군사과학기술학회지
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• 제10권3호
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• pp.208-216
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• 2007

As the propellant mass is being accelerated out of the gun chamber along with the projectile, a continuous pressure gradient exists between the end of chamber and the base of the projectile. For this reason, the base pressure-travel curve is very important to design a conventional gun barrel in the interior ballistics, but it is not obtained briefly by empirical or theoretical method. In this paper, a simple relation between chamber pressure and base pressure was determined by the factor of base pressure(Cb) obtained from the experimental method. The simple relation gives a reasonable prediction for the reduction of pressure between the breech and the base of projectile owing to the axial gradient in the gun tube. The predictions have been validated by the infrared screen sensor and the PRODAS(PROjectile Design and Analysis System) for interior ballistic systems. Therefore, the base pressure-travel curve could be calculated from the chamber pressure measured by piezoelectric sensor. The base pressure-travel curve obtained from the simple relation offers initial information to gun barrel designer and is used for calculation of muzzle velocity.