• 터널과지하공간
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• 제9권4호
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• pp.328-336
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• 1999

본 연구에서는 암석절리에 대한 수리-역학적 거동이 동시에 가능한 실내시험장치로서 회전식 전단시험기를 제작 하였다. 회전식 전단시험기는 시료의 양 끝에 비틀림 모멘트를 가함으로써 전단응력을 발생시키도록 하였다. 실험결과 회전식전단시험에 의한 절리의 최대전단강도는 직접전단시험에 의한 값보다 과소평가되었다. 이는 비틀림에 의한 전단응력이 회전축의 반경에 따라 변하며 특히 회전축 중심부에서는 전단응력이 거의 작용하지 않기 때문인 것으로 판단된다. 절리에서의 유체유동은 절리 거칠기, 접촉 면적, 초기간극 등에 의해 주로 영향을 받는 것으로 알려져 있다. 이에 본 연구에서는 초기간극의 측정을 통하여 전단-유동에 대한 수리 간극과 역학적 간극사이의 관계를 알아보았다. 초기간극의 측정과 전단-유동 상호작용시험의 결과에 근거하여, 역학적 모델과 삼승법칙으로부터 계산된 역학적 간극과 수리 간극은 체적 팽창이 발생함에 따라 증가하며 이들 사이에는 좋은 선형관계가 있음을 보였다. 그러나 수리 간극과 역학적 간극사이에는 다소 차이가 발생하였는데 이는 평행 평판모델에 의해 예측된 거동으로부터 수리 간극이 벗어남을 나타낸다.

• 한국항공우주학회지
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• 제44권10호
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• pp.921-932
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• 2016

본 논문에서는 아리랑 5호의 고해상 SAR(Synthetic Aperture Radar) 영상 생성을 위해 수정된 주파수 스케일링 알고리듬(FSA: Frequency Scaling Algorithm)을 제안한다. 부 개구면(sub-aperture) 처리 과정에서 부정확한 기하 파라미터의 사용이 야기하는 방위압축 성능 저하문제를 개선하기 위해, 정확한 시간-주파수 분석을 통해 전 개구면(full-aperture) 신호처리 알고리듬을 설계한다. 이와 더불어, 아리랑 5호의 이동 집중조사(sliding-spotlight) SAR 신호처리에 적합한 전 개구면 신호처리 알고리듬을 위해 방위 스케일링 함수를 새롭게 제안하였다. 기존의 부 개구면 FSA 방식과 달리, 제안된 방법은 아리랑 5호의 모든 운용 모드에 적용 가능한 일관된 신호처리기 구조를 제공한다는 장점이 있다. 점표적 모의실험을 통해, 제안된 알고리듬이 기존의 전 개구면 데이터 처리 기법들에 비해 우수한 방위압축 성능을 제공함을 확인한다. 또한 아리랑 5호에서 획득된 실 데이터 처리 결과를 제시함으로써 제안된 기법의 유용성을 검증한다.

• 정보저장시스템학회논문집
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• 제11권1호
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• pp.1-5
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• 2015

The selective frequency analysis method is suggested in the holographic data storage system with the nyquist aperture to reduce the size of hologram. The image filter was designed with many different methods to improve the bit error rate caused by the nyquist aperture. In previous the methods of image restoration for HDS, an iteration time and a highly precise point spread function were necessary. In this paper, we describe the optical system with analytic method. Thereby, we expect our result help the researchers to design the filter.

• 한국소음진동공학회논문집
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• 제26권3호
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• pp.315-322
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• 2016

Room acoustic properties of coupled rooms connected by an aperture has been analyzed using statistical acoustic model based on the diffused sound field assumption, which has limitation in dealing with the parameters such an room geometries and non uniform absorptivity of the boundary surfaces. In order to overcome these difficulties the acoustic diffusion model has been introduced, by which distribution of the acoustic energy density can be analyzed for various shapes and wall absorptivity. In this study acoustic properties of coupled rooms connected by an aperture(e.g. door) is analyzed using acoustic diffusion equation, which is solved numerically. The mean energy densities of two rooms obtained by the diffusion model are compared with those from the statistical model. The results show good agreement for various coupling aperture sizes and absorption coefficients. For a limiting case when the partition wall is substituted by an aperture and the two rooms eventually forms a single room, results of coupled room analysis using diffusion model show good agreement with those of a single room.

• 터널과지하공간
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• 제24권2호
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• pp.176-186
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• 2014

절리면의 수리특성에 영향을 미치는 요소는 절리면의 거칠기, 절리면의 틈새, 충진물 등이 있다. 본 연구에서는 절리면의 거칠기에 따른 수리특성을 분석하고자 Barton and Choubey(1977)가 제안한 표준 프로파일을 이용하여 몬테카를로 시뮬레이션을 통해 인공 프로파일을 생성시켰다. 표준 프로파일과 인공 프로파일을 조합하여 유동채널 모델을 제작하였으며, 최소 간극의 변화와 유동채널의 형상에 따른 수리특성을 수치해석적으로 분석하였다. 두 프로파일이 이루는 최소 간극지점을 통과한 이후 유동면적이 증가하는 지점에서 최대 유동률을 나타냈으며, 최소 간극이 증가할수록 최대 유동률은 감소하였다. 또한 유동채널의 형상과 유동채널내의 최소 간극 지점의 위치가 모델마다 상이하기 때문에 단위면적당 최대 유동률은 모델마다 다른 값을 나타내고 있었다. 유동채널 내의 역학적 간극과 수리적 간극은 1.07 ~ 3.00 배 정도의 차이를 나타내고 있으며, 본 수리해석에서 분석된 $A_i$ 값과 역학적 간극은 $e_m=0.519A^{0.7169_i}$의 관계를 나타내고, 수리적 간극은 $e_h=0.6182A^{0.239}_i$의 관계를 나타는 것으로 분석되었다.

• Journal of the Optical Society of Korea
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• 제17권4호
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• pp.317-322
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• 2013

We have proposed and demonstrated a low numerical aperture technique to measure the depth of through silicon vias (TSVs) using white-light scanning interferometry. The high aspect ratio hole like TSV's was considered to be impossible to measure using conventional optical methods due to low visibility at the bottom of the hole. We assumed that the limitation of the measurement was caused by reflection attenuation in TSVs. A novel interference theory which takes the structural reflection attenuation into consideration was proposed and simulated. As a result, we figured out that the low visibility in the interference signal was caused by the unbalanced light intensity between the object and the reference mirror. Unbalanced light can be balanced using an aperture at the illumination optics. As a result of simulation and experiment, we figured out that the interference signal can be enhanced using the proposed technique. With the proposed optics, the depth of TSVs having an aspect ratio of 11.2 was measured in 5 seconds. The proposed method is expected to be an alternative method for 3-D inspection of TSVs.

• Current Optics and Photonics
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• 제5권3호
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• pp.229-237
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• 2021

The capabilities of the near-field scanning optical microscope (NSOM) for obtaining high resolution lateral topographical images as well as for mapping the spectroscopic and optical properties of a sample below the diffraction limit of light have made it an attractive research field for most researchers dealing with optical characteristics of materials in nano scales. The apertured NSOM technique involves confining light into an aperture of sub-wavelength size and using it to illuminate a sample maintained at a distance equal to a fraction of the sub-wavelength aperture (near-field region). In this article, we present a setup for developing NSOM using a cantilever with a sub-wavelength aperture at the tip. A single laser is used for both cantilever deflection measurement and near-field sample excitation. The laser beam is focused at the apex of the cantilever where a portion of the beam is reflected and the other portion goes through the aperture and causes local near-field optical excitation of the sample, which is then raster scanned in the near-field region. The reflected beam is used for an optical beam deflection technique that yields topographical images by controlling the probe-sample in nano-distance. The fluorescence emissions signal is detected in far-field by the help of a silicon avalanche photodiode. The images obtained using this method show a good correlation between the topographical image and the mapping of the fluorescence emissions.

• Journal of Astronomy and Space Sciences
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• 제40권4호
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• pp.225-235
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• 2023

This paper presents the structural design of a planar synthetic aperture radar (SAR) antenna applied to a microsatellite. For micro-satellite applications, the SAR antenna structure must be lightweight, flat, and designed to withstand the launch environment. To satisfy these conditions, our novel antenna structure was designed using aluminium (AL) alloy. Structural analysis was performed for quasi-static load, random vibration, and shock load to verify its robustness in the launch environment, and the results are presented here.

• 한국입자에어로졸학회지
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• 제13권2호
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• pp.53-63
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• 2017

As semiconductor process was highly integrated, particle contamination became a major issue. Because particle contamination is related with process yields directly, particles with a diameter larger than half pitch of gate should be controlled. PBMS (Particle beam mass spectrometry) is one of powerful nano particle measurement device. It can measure 5~500 nm particles at ~ 100 mtorr condition in real time by in-situ method. However its usage is restricted to research filed only, due to its big device volume and high price. Therefore aperture changeable aerodynamic lenses (ACALs) which can control particle focusing characteristics by changing its aperture diameter was proposed in this study. Unlike conventional aerodynamic lenses which changes particle focusing efficiency when operating condition is changed, ACALs can maintain particle focusing efficiency. Therefore, it can be used for a multi-monitoring system that connects one PBMS and several process chambers, which greatly improves the commercialization possibility of the PBMS. ACALs was designed based on Stokes number and evaluated by numerical method. Numerical analysis results showed aperture diameter changeable aerodynamic lenses can focus 5 to 100 nm standard particles at 0.1 to 10 torr upstream pressure.

• 한국태양에너지학회 논문집
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• 제27권4호
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• pp.113-120
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• 2007

The 5kWt dish solar collector is designed and the preliminary performance test for this is carried out. The diameter of the parabolic dish is 3.2 m, and its focal length is 2 m. It consists of 10 small reflectors which have their own curvatures, and the effective reflecting area is $5.9\;m^2$, and the rim angle of the dish is $43.85^{\circ}$. The reflectivity of reflectors is 0.95, and the thermal capacity of the system is about 5 kW thermal. The aperture diameter of the cylindrical-shape receiver which is made of stainless steel is 100 mm, and the height is 210 mm. A quartz window is installed at the receiver aperture to minimize the convective heat loss and prevent air leakage. In order to increase the heat transfer area, porous materials (nickel-alloy) are inserted into the receiver. Air flows into the upper part of the receiver which is the opposite side of the aperture. After the air flows through the inside of the receiver, that goes out of the receiver through 3 exits which are located near the aperture. The volumetric flow rates of air are varied from 600 to 1200 L/min. The results show that the system efficiency and receiver efficiency increase as the volume flow rate increases.