• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.113-118
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• 2004

Experiments are conducted to get basic information of under-expanded impinging jet in the near field. Experimental parameters are impinging angle and under-expanded ratio. As the under-expanded ratio increases, the maximum surface pressure decreases and the reducing effect of recovery factor increases. As the impinging angle decreases, the peak of surface pressure is displaced slightly from the geometric center of the plate to the upward region and the cooling region is expanded in the downward region, whereas it is contracted in the upward region.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.303-306
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• 2000

복잡한 형상을 지닌 터빈 블래이드의 결함을 검사하기 위해 현재 $35^\circ,\; 38^\circ,\; 40^\circ$의 횡파 굴절각을 지닌 탐촉자를 사용하고 있다. 이와 같은 굴절각은 초음파 빔의 경로를 Snell의 법칙에 의해 설정하고 있다. 그러나 터빈 블래이드 검사용 초음파 탐촉자를 제작하는 과정에서 $35^\circ$의 횡파 굴절각을 갖는 경사각 탐촉자는 제작이 어려움을 알았다. 이러한 원인은 철강재료의 종파임계각이 $33.2^\circ$의 횡과굴절각에 대응되며, 종파임계각 근처에서는 전반사 현상 때문에 에너지 투과율이 매우 작아 실제 시험대상체에 입사되는 에너지가 거의 없으며 또한 횡파굴절각이 약 $37.5^\circ$ 일때에 휭파의 에너지 투과율이 최대가 되어 wedge를 $37.5^\circ$ 이하의 횡파굴절각을 갖도록 설계하더라도 측정을 하면 $37.5^\circ$ 근처의 횡파굴 절각을 갖게된다. 즉, 종파임계각 근처에서는 전반사 현상에 의해 경계면에서의 에너지 투과가 매우 작아 횡파 굴절각은 Snell의 법칙이 아닌 초음파 에너지의 투과 정도를 나타내는 echo transmittance의 크기에 의해 결정된다.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1998.11a
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• pp.60-63
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• 1998

본 연구에서는 유류 오염토양 복원을 위한 효율적인 세척공정을 구성하여 현장적용 가능성을 검토하였다. 토양세척공정은 co-current식 전세척장치와 counter -current식 세척조로 구성된다. 물이 주입되는 co-current식 전세척장치에서는 스크류 축의 회전력에 의한 토양 이송 및 스크류의 각 pitch 사이에 부착된 임펠러의 기계적 교반력에 의한 세척이 동시에 이루어진다. 전세척장치를 통과한 토양과 물은 세척조로 유입되어 세척용액과 반대방향으로 이동하게 된다. 세척조의 내벽에 부착된 나선형 웨어에 의해 적정 운전조건하에서 일정 크기를 기준으로 토양이 분리되며, 각 웨어 사이에 부착된 임펠러의 교반력에 의해 오염토양이 세척된다. 실험결과, 운전시 고려해야 할 주요 영향인자들은 전세척장치에서의 토양주입량은 1 kg/min, 진탕비는 1, 회전속도는 50 rpm에서 최대 세척효율(#4-, 83.6%)을 보였으며, 세척조에서는 토양.물 주입위치 15 cm, 회전속도 5 rpm, 경사각 6$^{\circ}$, 세척용액 주입유량이 0.8 L/min일 때 최대 세척효율인 97.9%(#4-)를 나타냈다.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.11
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• pp.180-187
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• 2013

The dinger in solar generation is the amount of sunlight which the solar cells absorb. Various types of solar trackers, which rotate themselves in order to make the solar cells face the sun as much as possible, have been developed, and especially the method of tracking with two axes has greatly contributed in increasing the generation amount at work sites. Among theses 2-axis solar trackers, the inclination-dependent 2-axis solar tracker are widely utilized for its advantages of requiring less initial investment and easy maintenance due to a solid structure. However, the drawback is that the generation efficiency is relatively low because of the structural restriction that limits the rotation angle, thus making it less efficient when tracking the sun. This paper proposes a method to increase the generation efficiency of the inclination-dependent 2-axis solar tracker. It also contains the derived equations needed for precise controlling along with a method to keep tracking with the other axis even when one has reached its angle limit. To confirm that the proposed method increases the amount of incidence onto the solar cells, formulas needed for operation on the proposed method and tracking the exact position of the sun are derived, and applying this to the quarterly data of Korea Astronomy and Space Science Institute it shows maximum over 11.1% more incidence compared to existing methods.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1335-1341
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• 2011

The purpose of this research is to investigate how separated and reattached flow affects mass transfer, by comparing the local mass transfer characteristics on an inclined flat plate with those on a parallel flat plate. The local mass transfer coefficients for the flat plate were measured using the naphthalene sublimation technique; the inclined angle of the flat plate was varied from $-10^{\circ}$ to $10^{\circ}$ at $5^{\circ}$ intervals, and the free-stream velocity was varied from 2m/s to 15m/s. At positive inclined angles, the local Sherwood numbers decreased gradually because the boundary-layer thickness increased. On the other hand, for negative inclined angles, the local Sherwood numbers assumed the minimum value at the separation point of the recirculation flow and the maximum value at the reattachment point. The average Sherwood numbers for both positive and negative inclined angles were lower than those in the case of the parallel plate.

• Journal of Korean Society of Steel Construction
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• v.21 no.3
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• pp.245-255
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• 2009

The low-rise buildings with gable roofs are commonly used in a number of industries. In order to study the characteristics of peak external pressure coefficient on low-rise buildings with gable roofs, wind-tunnel test have been carried out. Wind-induced pressures were measured simultaneously at many points on wind-pressure models, typical of simple low-rise buildings with gable roofs, which have seven different roof slope with constant width(D), height(H), and length(D). The pressure measurements were made in one kind of turbulent boundary layer, which simulated the natural winds over typical suburban terrains at a geometric scale of 1/150. The results indicate that peak external pressure coefficient on the roof and wall edges were increased. The results compared with wind standard of KBC-2005 and standards of various nations. The comparative resultant, experimental result appeared very similar at AIJ-2004. But the results were somewhat larger then wind standard of KBC-2005.

• Solar Energy
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• v.11 no.1
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• pp.61-68
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• 1991

Steady laminar natural convection heat transfer from the isothermal square beam attached to an adiabatic plate has been studied for various inclination angles of the adiabatic plate and Rayleigh number by using Mach-Zehnder interferometer in air. As the inclination angles change, the different temperature and fluid flow field were obtained by the ascending heated fluid and the adiabatic plate. In this study, the inclination angles were $0^{\circ}$(positive & negative), $45^{\circ}$(positive & negative), and $90^{\circ}$. The maximum total mean Nusselt number value was found at a positive inclination angle ${\theta}=45^{\circ}$.

• Journal of Power System Engineering
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• v.15 no.1
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• pp.32-38
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• 2011

2개의 경사 배플을 가진 사각 채널내의 열전달과 유동양상에 특성을 조사하기 위해 수치해석을 행하였다. 본 연구에서는 바닥에서만 가열된 채널 내 2개의 배플에 9개의 다이아몬드형 구멍을 설치하였다. 배플은 19.8 cm의 폭과 23.2 cm의 길이 그리고 0.5 cm의 두께의 플렉시 글라스를 사용하였다. 다이아몬드형 구멍의 크기는 $2.55\;cm{\times}2.55\;cm$이며 배플 경사각은 $5^{\circ}$를 유지하였다. 레이놀즈수의 범위는 23,000에서 57,000 이다. SST k-${\omega}$ 난류모델을 사용하였다. 누셀트(Nu) 수의 수치해석 결과는 실험 결과로 검증하였다. 유동장에 관한 수치해석으로부터 배플 구멍 근처의 유동 양상을 나타낼 수 있었고 이러한 유동장이 온도장의 특징에 크게 영향을 미친다는 것을 나타내었다. 국부 누셀트수는$x/D_h$=2.5 에서 최대가 되었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1509-1513
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• 2009

A semicircle antenna is presented for wideband communication system. The proposed antenna radiates linear polarized wave omnidirectionally in wide frequency band from 1.5 GHz to more than 5 GHz (110%). The frequency bands of the proposed antenna are investigated from the variable current path lengths by tilting angles. The overall radiation gain of the proposed antenna is 2-3 dBi.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2136-2149
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• 1992

The natural convection from an inclined ice flat plate immersed in cold water near its density maximum is studied numerically. Finite difference analysis has been performed for the heat and momentum transfer with respect to various inclined angles and ambient water temperatures. The results of the analysis are presented for ambient water temperatures, 1.0deg. C. leq. T／sub .inf.／.leq. 15.0deg. C and the inclined anales from 0deg to 60deg. They include velocity profiles, temperature profiles, melting velocities, and mean Nusselt numbers for entire flow fields, Generally, in the range of 0deg. C .leq.theta. .leq. 60.deg. C, the results show three distinct flow regimes, In the range of 1.0 deg. C .leq. T／sub .inf.／ .leq. 4.6 .deg. C, the greatest mean Nuselt number exists about 3.0deg. C. In the range of 5.7deg. C .leq. T／sub .inf.／ .leq. 15.0deg. C, mean Nuselt number increases as ambient water temperature increases. Also, the mean Nuselt number decreases as the inclined angle increases. This theoretical results are compared with previous experimental ones and multiple steady state ones.