• 한국위성정보통신학회논문지
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• 제8권3호
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• pp.47-51
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• 2013

본 논문에는 Ka 대역 VSAT용 반사판 안테나의 급전부에 사용하기 위한 이중대역 직교모드변환기의 설계와 실험 결과를 보였다. 설계된 직교모드변환기는 20Ghz의 수신대역 주파수 영역과 30GHz의 송신대역 주파수 영역에서 동작하는 두 개의 선형 직교 편파된 신호를 분리하기 위해서 광대역 특성을 갖는다. 또한, 급전 부품의 부피를 작게 하기 위해서 Boifot 접합 기반의 직교모드변환기를 이중 대역을 갖도록 설계를 하였다. 설계 검증을 위한 실험결과 수평편파에 대해서 수신대역과 송신대역의 반사손실은 각각 20dB와 21dB 이상의 특성을 나타냈으며, 수직편파에 대해서는 20dB와 24dB 이상의 특성을 보였다. 수평편파와 수직편파에 대한 격리도 특성은 수신대역과 송신대역에서 각각 43dB와 52dB 이상을 보였다.

• 한국측량학회지
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• 제38권5호
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• pp.415-423
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• 2020

GNSS (Global Navigation Satellite System) is mostly used for high-precise surveys due to its accuracy and efficiency. But this technique does not always fulfill the demanding accuracy in harsh operational environments such as urban canyon and forest. One of the remedies for overcoming this barrier is to compose a heterogeneous surveying network by adopting terrestrial measurements (i.e., distances and angles). Hence, this study dealt with the adjustment of heterogeneous surveying networks consisted of GNSS baseline vectors, distances, horizontal and vertical angles with a view to enhancing their accuracy and so as to derive an appropriate scheme of the measurement combination. Reviewing some technical issues of the network adjustments, the simulation, and experimental studies have been carried out, showing that the inclusion of the terrestrial measurements in the GNSS standalone overall increased the accuracy of the adjusted coordinates. Especially, if the distances, the horizontal angles, or both of them were simultaneously adjusted with GNSS baselines, the accuracy of the GNSS horizontal component was improved. Comparing the inclusion of the horizontal angles with those of the distances, the former has been more influential on accuracy than the latter even though the same number of measurements were employed in the network. On the other hand, results of the GNSS network adjustment together with the vertical angles demonstrated the enhancement of the vertical accuracy. As conclusion, this paper proposes a simultaneous adjustment of GNSS baselines and the terrestrial measurements for an effective scheme that overcomes the limitation of GNSS control surveys.

• 한국전자파학회논문지
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• 제18권11호
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• pp.1279-1290
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• 2007

본 논문에서는 복합 빔 패턴들을 형성하기 위해 오프셋 선형 급전 배열에 의해 공간 급전되는 원통형 하이브리드 안테나에 대하여 기술한다. 선형 급전 배열은 12개의 마이크로스트립 패치 소자들로 구성되며, 수평면에서 $90^{\circ}$의 구형 빔 패턴을 형성한다. 그리고, 수직면에서 $-5^{\circ}{\sim}-25^{\circ}$ 범위에 걸쳐 코씨컨트 빔 패턴을 형성하기 위해 선형 급전 배열에 의해 원통형 반사판상의 수직 곡선이 성형화 된다. IMT-2000 서비스 대역에서 동작하는 $140{\times}50\;cm$ 크기의 원통형 반사판 개구면을 갖는 하이브리드 안테나 시제품을 설계 및 제작하였으며, 또한 안테나의 전기적 성능들을 측정하고 그 결과들을 분석하였다.

• 한국지반공학회논문집
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• 제19권3호
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• pp.5-13
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• 2003

쏘일네일링 공법은 작업공간의 확보가 용이하고 네일길이가 어스앵커보다 비교적 짧아 도심지 지하굴착에 매우 이로운 장점이 있다. 이 공법이 도입된 이후 쏘일네일링 벽체의 거동에 관한 연구는 토조에 의한 모형실험과 이론적 연구가 진행되고 있지만 지반조건이 다층토로 구성된 현장에 대한 연구는 미흡한 실정이다. 본 연구는 국내 다층토 지반에 시공된 쏘일네일링 현장에서 시공중 측정된 수평변위를 토대로 한 역해석적 방법에 의해 배면지반의 이완영역거리와 이완영역계수를 고찰하였다. 연구결과에 의하면 쏘일네일링 벽체 배면지반의 이완 영역거리는 최종굴착깊이의 증가에 따라 증가함을 보였으며, 그 비율은 최종굴착깊이의 94% 정도로 나타났다. 토사층과 암층이 혼합되어 있는 다층토 지반에서 토사층의 비율이 클수록 이완영역계수도 증가하였으나, 약 1.05값에서 수렴하는 경향을 나타냈다. 벽체 최대수평변위에 대한 지표면 최대수직변위와의 관계는 역해석결과에서 지표면 최대수직변위가 최대수평변위의 80%이하로 나타났으며, Caspe방법에 의한 지표면 최대수직변위는 최대수평변위의 150~280%의 범위로 나타나 역해석결과보다는 매우 큰 값을 나타내 Caspe방법이 매우 보수적임을 확인하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제39권2호
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• pp.136-142
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• 2015

The shell and tube heat exchanger is an essential part of a power plant for recovering transfer heat between the feed water of a boiler and the wasted heat. The baffles are also an important element inside the heat exchanger. Internal materials influence the flow pattern in the bed. The influence of baffles in the velocity profiles was observed using a three-dimensional PIV (Particle Image Velocimetry) around baffles in a horizontal circular tube. The velocity of the particles was measured before the baffle and between them in the test tube. Results show that the velocity vectors near the front baffle flow along the vertical wall, and then concentrate on the upper opening of the front baffle. The velocity profiles circulate in the front and rear baffle. These profiles are related to the Reynolds number (Re) or the flow intensity. Velocity profiles at lower Re number showed complicated mixing to obtain the velocities and concentrate on the lower opening of the rear baffle as front wall. Numerical simulations were performed to investigate the effects of the baffle and obtain the velocity profiles between the two baffles. In this study, a commercial CFD package, Fluent 6.3.21 with the turbulent flow modeling, k-${\epsilon}$ are adopted. The path line and local axial velocities are calculated between two baffles using this program.

• 한국전자파학회논문지
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• 제12권7호
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• pp.1057-1066
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• 2001

본 논문에서는 전자기적으로 결합하는 다이폴을 이용하여 직선편파를 복사하는 마이크로스트립 안테나의 설계에 관하여 기술하였다. 다이폴의 위치에 의해 서로 다른 직선편파를 가지는 안테나의 해석 및 설계는 FDTD 법으로 행하였다. 급전선로와 복사소자간의 상호결합을 고려한 단일 소자 안테나의 설계로부터 각 편파에 대한 설계파라미터들을 구했으며, 이를 이용한 어레이 설계에서 Offset을 변화시켜 복사전력을 조절할 수 있었다. 또한 어레이 소자간의 간격을 조정함으로써 원하는 방향으로의 지향각을 설계할 수 있었다. 5 소자 어레이 안테나를 제작하여 측정을 행하였고, 이들 결과는 이론치와 잘 일치하였다.

• 한국정밀공학회지
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• 제21권7호
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• pp.62-69
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• 2004

This paper presents an experimental study on the dimensional error in ball-end milling. In the 3D free-formed surface machining using ball-end milling, while machining conditions are varied due to the Z component of the feed and existing hemisphere part of the ball-end mill, the mechanics of ball-end milling are complicated. In the finishing, most of cutting is performed the ball part of the cutter and the machined surface are required the high quality. But the dimensional errors in the ball-end milling are inevitably caused by tool deflection, tool wear, thermal effect and machine tool errors and so on. Among these factors, the most significant one of dimensional error is usually known as tool deflection. Tool deflection is related to the instantaneous horizontal cutting force and varied the finishing cutting path. It lead to decrease cutting area, thus resulting cutting forces but the dimensional precision surface could not be obtained. So the machining experiments are conducted fur dimensional error investigation and these results may be used for decrease dimensional errors in practice.

• 한국표면공학회지
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• 제47권6호
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• pp.347-353
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• 2014

We present a synthesis of single-walled carbon nanotubes(SWNTs) for enhancement of parallel-alignment and density using chemical vapor deposition with methane feed gas. As-purchased ST-cut quartz substrates were heat-treated and line-patterned by electron-beam lithography in order to grow SWNTs with parallel alignment. We investigated the effects of various synthesis parameters such as catalyst oxidation, reduction, and synthesis conditions in order to enhance both tube density and degree of parallel alignment. The condition of $1{\AA}$ of Fe catalyst film, atmospheric oxidation at $750^{\circ}C$ for 10 min, reduction under 400 Torr for 5 min, and growth at $865^{\circ}C$ under 300 Torr yields $33tubes/10{\mu}m$, which is the highest tube density with parallel alignment. Based on the results of atomic force microscope and Raman spectroscopy, it was found that SWNTs have diameter range of 0.8-2.0 nm. We believe that the present work would contribute to the development of SWNTs-based flexible functional devices.

• Journal of Biosystems Engineering
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• 제23권3호
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• pp.259-270
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• 1998

An automatic seedling transplanter, employed an innovative plug-seedling feeder was developed by improving the problems of conversational feeding and transplanting mechanisms. With conventional methods, missing and damage rates of seedling were high for long seedlings over 20cm and also breaking seed-bed was frequently observed. Thus, a pushout-bucket slide-hopper type trandsplanter was devised and tested. Test results of picking and transferring accuracies of the developed transplanter are as follows : A prototype transplanter performed with 1.5% of missing rate. The deviations of horizontal feed ranged from -0.3mm to 2.8mm and averaged 0.673mm for the 128-hoe test tray : and ranged from -lmm to ＋3mm and averaged 0.785mm for the 200-hole test tray. The deviations could decrease with precise manufacturing and lightening the mechanism. The maximum and deviations of vertical feed were -2.3mm and + 1mm, respectively, for the 128-hole test tray ; and were ＋3mm and ＋2.5mm, respectively, for the 200-hole test tray. The missing rate, seeding bruise rate and seed-bed damage rate were esitmate to be 1.3％, 0.4% and 3.5％, respectively, with the developed automatic transplanter.

• 대한기계학회논문집A
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• 제30권12호
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• pp.1634-1641
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• 2006

High-precision centerless grinding machines are emerging as a means of finishing the outer diameter grinding process required for ferrules, which are widely used as fiber optic connectors. In this study, a sensitivity analysis for structural and thermal characteristics was carried out using a virtual prototype of a centerless grinding machine to realize systematic design technology and performance improvements required to manufacture ferrules. The prototype consisted of a concrete-filled bed, hydrostatic grinding wheel (GW) and regulating wheel (RW) spindle systems, a hydrostatic RW table feed mechanism, a RW swivel mechanism, and on-machine GW and RW dressers. The results of the structural sensitivity analysis illustrated that the vertical stiffness of hydrostatic guideway for the RW table feed system greatly influenced the horizontal loop stiffness, and the results of the thermal sensitivity analysis illustrated that the heat generation rates at hydrostatic bearings and belt pulley greatly influenced the temperature rise of hydrostatic bearings and the deviation of thermal displacement between GW and RW.