• 한국항공우주학회지
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• 제38권3호
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• pp.207-212
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• 2010

본 논문에서는 고정익 무인항공기의 그물망 자동착륙을 위한 나선형 강하궤적과 종말 유도기법을 설계하였다. 시야가 확보된 좁은 지역에서 착륙하도록 고정익 항공기의 나선형 강하궤적을 설계하였고, 나선형 강하의 끝점에서 그물망 입사방향을 향하도록 비행경로각 명령을 생성하였다. 종말유도 단계에서는 그물망 중심으로의 정밀한 유도를 위하여 시선각 정보 기반 의사추적 유도기법을 설계하였다. 고정익 무인항공기의 시스템 인식 모델을 이용한 6자유도 수치 시뮬레이션을 수행하여 제안한 나선형 착륙비행의 성능을 검증하였다.

• Journal of Platform Technology
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• 제10권3호
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• pp.44-50
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• 2022

얼굴 영상에서 나이를 인식하는 기술은 여러 응용분야에서 활용되면서 그에 대한 연구가 활발히 진행되고 있다. 다양한 환경에서 촬영된 얼굴 영상은 얼굴의 일부가 가려지는 경우가 많으며 이는 나이 인식 성능에 영향을 미치게 된다. 따라서 본 논문에서는 가림이 있는 얼굴 영상의 나이 인식 성능을 개선하기 위해, Image Extrapolation 기술을 이용하여 가려진 부분을 생성하여 나이를 인식하는 방법을 제안한다. 영상에서의 가림이 나이 인식 성능에 미치는 영향을 확인하기 위해서 마스크 이미지를 적용하여 가림이 있는 얼굴 영상을 생성하였다. 가림에 의해 나이 인식 성능이 저하되는 문제를 해결하기 위해, Image Extrapolation 기술 중 영상의 가장자리를 순회하면서 가려진 부분을 생성하는 SpiralNet 을 사용하여 가려진 부분을 예측하여 생성하고 얼굴 나이 인식에 사용하였다. 실험을 통해 가림이 있는 영상에서 나이 인식 성능이 저하되는 문제가 있고, SpiralNet으로 가림 부분을 생성한 영상으로 나이를 인식하면 나이 인식 성능이 개선되는 것을 확인하였다.

• 한국기계가공학회지
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• 제16권1호
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• pp.118-123
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• 2017

It is well known that water jetting is now widely used in the advanced cutting processes of polymers, metals, glass, ceramics, and composite materials because of some advantages, such as heatless and non-contacting cutting different from the laser beam machining. In this paper, we proposed the simulation model of waterjet by lengths and the inner spiral structure of the nozzle. The simulation results show that the outlet velocity of the nozzle is faster than the inlet. Furthermore, we found rapid velocity reduction after passing through the outlet. The nozzle of diameter ${\phi}500$ and length 70mm, shows the optimal fluid width and velocity distribution. Also, the nozzle with inner spiral structure shows a Gaussian distribution of velocity and this model is almost twice as fast as the model without spiral structure, within the effective standoff distance (2.5 mm). In the future, when inserting abrasive material into the waterjet, we plan to analyze the fluid flow and the particle behavior through a simulation model.

• Tribology and Lubricants
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• 제2권1호
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• pp.30-38
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• 1986

In the paper, static characteristics of spiral grooved seal is theoretically obtained by Using Navier-Stokes equation. In the analysis, inertia term of fluid is considered and the flow and pressure in the steady state are obtained for the groove direction and vertical to the groove direction. As the journal rotating frequency increases, the leakage flow decreases. Therefore, zero net leakage flow is possible at the region of some rotating frequency.

• 한국멀티미디어학회논문지
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• 제23권6호
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• pp.729-737
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• 2020

Screening with low-dose spiral computed tomography (LDCT) has been shown to reduce lung cancer mortality by about 20% when compared to standard chest radiography. One of the problems arising from screening programs is that large amounts of CT image data must be interpreted by radiologists. To solve this problem, automated detection of pulmonary nodules is necessary; however, this is a challenging task because of the high number of false positive results. Here we demonstrate detection of pulmonary nodules using six off-the-shelf convolutional neural network (CNN) models after modification of the input/output layers and end-to-end training based on publicly databases for comparative evaluation. We used the well-known CNN models, LeNet-5, VGG-16, GoogLeNet Inception V3, ResNet-152, DensNet-201, and NASNet. Most of the CNN models provided superior results to those of obtained using customized CNN models. It is more desirable to modify the proven off-the-shelf network model than to customize the network model to detect the pulmonary nodules.

• 소성∙가공
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• 제16권8호
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• pp.621-628
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• 2007

Nowadays, Exhaust Gas Recirculation(EGR) Cooler is one of the most favorite systems for reducing the generation amount of $NO_x$ and other particle materials from vehicles burning diesel as fuel. Efficiency of the system is mainly dependent on its heat transfer efficiency and this ability is affected by net heat transferring area of the system. For that reason, several types of heat transfer tube such as dimple, wrinkle and spiral types that have large net area are used. However, it is difficult to manufacture the rectangular tube with dimpled type structure because it experiences too much strain around the rectangular tube surface during the forming process. For that reason, in this study, numerical simulation for forming process of non-symmetric dimple shape on a thin sheet metal was carried out. Furthermore, theoretical forming limit curves(forming limit diagram, forming limit stress diagram) were proposed as criteria of formability evaluation. From the results of finite element simulation in view of stress and strain distribution, it is found that the designed process has robustness and feasibility to safely manufacture the dimpled rectangular tube.

• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1378-1389
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• 2021

TRIUMF, Canada's particle accelerator centre, is constructing a new high-power ISOL (Isotope Separation On-Line) facility called ARIEL (Advanced Rare IsotopE Laboratory). Thick porous targets will be bombarded with up to 48 kW of 480 MeV protons from TRIUMF's cyclotron, or up to 100 kW of 30 MeV electrons from a new e-linac, to produce short-lived radioisotopes for a variety of applications, including nuclear astrophysics, fundamental nuclear structure and nuclear medicine. For efficient release of radioisotopes, the targets are heated to temperatures approaching 2000 ℃, and are exposed to GSv/h level radiation fields resulting from intended fissions and spallations. Due to these conditions, the operational life for each target is only about five weeks, calling for frequent remote target exchanges to limit downtime. A few days after irradiation, the targets have a residual radiation field producing a dose rate on the order of 10 Sv/h at 1 m, requiring several years of decay prior to shipment to a national disposal facility. TRIUMF is installing new remote handling infrastructure dedicated to ARIEL, including hot cells and a remote handling crane. The system design applies learnings from multiple existing facilities, including CERN-ISOLDE, GANIL-SPIRAL II as well as TRIUMF's ISAC (Isotope Separator and ACcelerator).

• Nuclear Engineering and Technology
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• 제52권5호
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• pp.897-907
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• 2020

The flow characteristics of reactor fuel assembly always intrigue the designers and the experimentalists among the myriad phenomena that occur simultaneously in a nuclear core. In this work, the visual experimental method has been developed on the basis of refraction index matching (RIM) and particle image velocimetry (PIV) techniques to investigate the detailed flow characteristics in China fast reactor fuel subassembly. A 7-rod bundle of simulated fuel subassembly was fabricated for fine examination of flow characteristics in different subchannels. The experiments were performed at condition of Re=6500 (axial bulk velocity 1.6 m/s) and the fluid medium was maintained at 30℃ and 1.0 bar during operation. As for results, axial and lateral flow features were observed. It is shown that the spiral wire has an inhibitory effect on axial flow and significant intensity of lateral flow mixing effect is induced by the wire. The root mean square (RMS) of lateral velocity fluctuation was acquired after data processing, which indicates the strong turbulence characteristics in different flow subchannels.

• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1119-1126
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• 2021

Spacer grid with mixing vane had been widely used in nuclear reactor core. One of the main feather of spacer grid with mixing vane was that strong swirl flow was formed after the spacer grid. The swirl flow not only changed the bubble generation in the near wall field, but also affected the bubble behaviors in the center region of the subchannel. The interaction between bubble and the swirl flow was one of the basic phenomena for the two phase flow modeling in fuel assembly. To obatin better understanding on the bubble behaviors in swirl flow, full three dimension numerical simulations were conducted in the present paper. The swirl flow was assumed in the cylindral calculation domain. The bubble interface was captured by Volume Of Fluid (VOF) method. The properties of saturated water and steam at different pressure were applied in the simulation. The bubble trajectory, motion, shape and force were obtained based on the bubble parameters captured by VOF. The simulation cases in the present study included single bubble with different size, at different angular velocity conditions and at different pressure conditions. The results indicated that bubble migrated to the center in swirl flow with spiral motion type. The lateral migration was mainly related to shear stress magnitude and bubble size. The bubble moved toward the center with high velocity when the swirl magnitude was high. The largest bubble had the highest lateral migration velocity in the present study range. The effect of pressure was small when bubble size was the same. The prelimenery simulation result would be beneficial for better understanding complex two phase flow phenomena in fuel assembly with spacer grid.

• 국제지역연구
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• 제20권1호
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• pp.105-125
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• 2016

일본은 21세기에 들어와서 경기침체와 디플레이션을 극복하기 위하여 확산적 화폐금융정책을 실시하였으며, 최근 아베정부는 무제한적으로 화폐공급을 증가시키고 있다. 그러나 이와 같은 정책의 효과는 아직 뚜렷이 나타나지 않고 있다. 본 연구의 목적은 2001년 이후 일본금융정책의 효과를 검증하는데 있다. 이를 위하여, 일본에서는 1990년 이후 버블형성과 붕괴이후 민간경제주체의 기대형성 과정이 변하고 있다는 사실에 기인하여, 기대가설을 내포하고 있는 거시모형을 설정하였다. 본 연구에서 사용된 거시모형은 통화량이 환율에 미치는 영향을 포함하였으며, 이를 IVM와 VAR를 이용하여 통계적으로 분석하였다. 통계분석 결과는 다음과 같다. 화폐금융정책의 효과는 2001.01-2015.03 기간에서 1985.01-1994.04.기간보다 낮아졌으며 효과가 미치는 기간도 짧아지고 있다. 이는 버블형성과 붕괴를 경험한 일본 민간경제주체가 더 이상 화폐금융정책의 효과를 믿지 않고 있기 때문인 것으로 판단된다. 통화량의 증가에도 불구하고 총수요는 영향을 받지 않고 있으며, 기대하지 못한 환율의 변화는 순수출을 증가시키고 있지만 통화 증가가 환율의 기대오차에 영향을 주지 못하고 있는 것으로 판단된다. 본 연구의 결과가 금융정책에서 의미하는 바는 중요하다고 할 수 있다. 일본의 버블형성과 붕괴, 그 후의 금융정책의 실패 등은 민간경제주체의 정책에 대한 신뢰를 변화시켰고, 화폐금융정책의 효과는 점차 낮아지고 있으며 불확실성은 커지고 있다. 확산적 화폐금융정책은 효과가 미흡할 경우 그 정책에 내재해 있는 위험성은 높아지므로 정책실시에 보다 신중한 결정이 요구된다. 또한 정부부채를 이용하는 재정정책을 배합하는 방향도 고려할 필요가 있다. 문제는 일본 정부부채 비율이 250%에 달한 것인데, 그렇다고 해서 재정정책을 사용하지 못한다는 근거는 없으므로, 이에 대한 또 다른 연구가 요구되는 시점이다.