• 한국전산구조공학회논문집
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• 제18권4호통권70호
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• pp.405-416
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• 2005

본 연구에서는 경수로용 핵연료집합체의 전체지지격자(Full Size Grid)와 부분지지격자(Small Size Grid)에 대한 정적 좌굴강도 실험과 전체 지지격자와 부분지지격자를 구성하는 지지격자판(Grid Strap)에 대한 정적 좌굴해석을 수행하여 지지격자의 좌굴특성을 분석하였으며, 분석결과를 이용하여 전체지지격자와 부분지지격자에 대한 좌굴하중값의 예측 가능성을 평가하였다. 좌굴강도 실험은 웨스팅하우스형 연료의 $17{\times}17$셀을 갖는 전체지지격자와 $1{\times}1,\;1{\times}2,\;1{\times}3,\;1{\times}4,\;1{\times}5,\;1{\times}17\;,2{\times}1,\;2{\times}2,\;2{\times}3,\;2{\times}9,\;2{\times}17,\;3{\times}17$ 등의 셀을 갖는 부분지지격자에 대하여 수행하였으며, 실험결과를 이용하여 지지격자의 좌굴강도와 지지격자의 행(rows)과 열(columns) 사이의 관계식을 제시하였다. 좌굴강도 해석은 범용 유한요소해석코드인 ANSYS를 이용하여 수행하였으며, 해석결과를 이용하여 지지격자의 좌굴특성을 분석하고 실험결과와 비교평가 하였다.

• 전력전자학회논문지
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• 제17권6호
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• pp.495-499
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• 2012

Recently, DC distribution systems become hot issues since DC type loads increase rapidly according to the expansion of IT equipment such as computers, servers, and digital devices; DC type loads will cover 50% for all electricity loads in 2020 which was mere 10% in 2000. DC distribution systems are also accelerated by the expansion of renewable power systems since they are easy to be interfaced with DC grids rather than AC grids. However, removing the fault current in DC grids is comparably difficult since the current in DC grids has non zero-crossing point like in AC grids. Thus, developing dedicated DC circuit breakers for DC grids is necessary to get safety for human and electrical facilities. Magnet arc extinguishing method is proper to small size DC circuit breakers. However, simple Magnet arc extinguishing method is not enough to break inductive fault currents. This paper proposed a novel DC circuit breaker against inductive fault current defined by IEEE C37.14-2004 Standard for Low-Voltage DC Power Circuit Breakers Used in Enclosures. The performance of the proposed DC circuit breaker was verified by an experimental circuit breaker test system built in this research.

• 대한기계학회논문집B
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• 제34권9호
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• pp.817-824
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• 2010

본 연구에서는 개선된 액막 분열 모델을 개발하였고 그에 따른 계산격자 의존성을 고찰하였다. 액막 및 액적 추적을 위해 라그랑지-오일러 액적 추적 모델을 사용하였기 때문에 계산격자의 크기에 한계가 있으므로 매우 작은 격자를 사용하는데 제약을 받는다. 또한 유동장내로의 분사기의 액막 주입 시선회유동이 존재하므로 선회 유동을 정확히 예측하기 위해서는 계산격자가 충분히 작아야 한다. 이러한 상반된 조건으로부터 두 목적을 달성하기 위해 10$\times$10mm부터 0.625$\times$0.625mm까지 다양한 계산격자를 구성하여 수치적 고찰을 수행하였고 가장 효율적인 격자의 크기는 1.25$\times$1.25mm인 것을 알 수 있었다.

• 한국지반환경공학회 논문집
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• 제16권3호
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• pp.49-55
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• 2015

토석류가 발생할 때는 강우패턴, 강우강도 및 해석을 위한 지형여건에 따라 토석류의 발생량과 흐름의 속도가 달라진다. 지형여건의 고려는 일정규모의 격자로 지형을 구분하고 구분된 격자 내의 지형경사는 평균경사로 가정하여 계산하므로 굴곡이 심한 지형에서는 분할되는 격자를 세분할수록 실제와 근접한 결과를 얻을 수 있게 된다. 그러나 지금까지는 해석알고리즘 및 컴퓨터 계산능력, 해석수행 시간 등의 한계로 인해 지형분할 격자를 상당히 크게 구분하여 수행하고 있다. 그러나 토석류 해석의 정확도를 위해서는 지형구분 격자크기를 가급적 작게 하여야 하므로, 실무적 접근을 위한 적절한 격자규모의 제안이 필요하게 된다. 따라서 본 논문에서는 기존 연구에서 논의되었던 누가 강우량, 강우강도, 강우지속시간 및 선행 강우량 등의 강우 특성 이외에 지형분할 격자크기가 토석류 흐름에 미치는 영향을 평가하고 이로부터 합리적이고 현실성 있는 지형분할규모를 제시하였다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.41-49
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• 2003

Tube oscillation behaviour is experimentally investigated for the study on the fuel rod fretting that is caused by the flow-induced vibration in nuclear reactor. The experiment was conducted in all at room temperature. The specimen of tube assembly was supported by plate springs which simulated the spacer grids and fuel rods of a fuel assembly. To investigate the influence of contact condition between the grids and rods, normal load of 10 and 5 N, gaps of 0.1 and 0.3 mm were applied. The range of the oscillation at the center of the fuel rod specimen was varied as 0.2, 0.3 and 0.4 mm to simulate the fuel rod vibration due to flow. Displacements near the contact were measured with four displacement sensors during the tube oscillation. As results, the shape of oscillation (phase) varied depending on the contact condition. The oscillation displacement increased considerably from the contact to gap condition. The displacement increased further as the gap size increased. It is regarded that the spring shape influences the tube oscillation behaviour. Simple calculation showed that the slip displacement was very small. Therefore, cumulative damage concept is necessary for the fuel rod wear. The mechanism of plowing is thought required to explain the severe wear in the case of gap existence.

• Journal of Biosystems Engineering
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• 제33권5호
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• pp.362-369
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• 2008

There is developing interest in precision agriculture in Korea, despite the fact that typical Korean fields are less than 1 ha in size. Describing within-field variability in typical Korean production settings is a fundamental first step toward determining the size of management zones and the inter-relationships between limiting factors, for establishment of site-specific management strategies. Measurements of rice (Oriza Sativa L) yield, chlorophyll content, and soil properties were obtained in a small (100-m by 30-m) Korean rice paddy field. Yield data were manually collected on 10-m by 5-m grids (180 samples with 3 samples in each of 60 grid cells) and chlorophyll content was measured using a Minolta SPAD 502 in 2-m by 2-m grids. Soil samples were collected at 275 points to compare results from sampling at different scales. Ten soil properties important for rice production in Korea were determined through laboratory analyses. Variogram analysis and point kriging with and without median polishing were conducted to determine the variability of the measured parameters. Influence of variogram model selection and other parameters on the interpretation of the data was investigated. For many of the data, maximum values were greater than double the minimum values, indicating considerable spatial variability in the small paddy field, and large-scale spatial trends were present. When variograms were fit to the original data, the limits of spatial dependency for rice yield and SP AD reading were 11.5 m and 6.5 m, respectively, and after detrending the limits were reduced to 7.4 m and 3.9 m. The range of spatial dependency for soil properties was variable, with several having ranges as short as 2 m and others having ranges greater than 30 m. Kriged maps of the variables clearly showed the presence of both large-scale (trend) variability and small-scale variability in this small field where it would be reasonable to expect uniformity. These findings indicate the potential for applying the principles and technology of precision agriculture for Korean paddy fields. Additional research is needed to confirm the results with data from other fields and crops.d similar tendency with the result for the frequency less than 20 Hz, but the width of change was reduced highly.

• 천문학회지
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• 제27권1호
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• pp.13-29
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• 1994

We have constructed a 3-dim hydrodynamics code called BTSPH. The fluid dynamics part of the code is based on the smoothed particle hydrodynamics (SPH), and for its Poisson solver the binary tree (BT) scheme is employed. We let the smoothing length in the SPH algorithm vary with space and time, so that resolution of the calculation is considerably enhanced over the version of SPH with fixed smoothing length. The binary tree scheme calculates the gravitational force at a point by collecting the monopole forces from neighboring particles and the multipole forces from aggregates of distant particles. The BTSPH is free from geometric constraints, does not rely on grids, and needs arrays of moderate size. With the code we have run the following set of test calculations: one-dim shock tube, adiabatic collapse of an isothermal cloud, small oscillation of an equilibrium polytrope of index 3/2, and tidal encounter of the polytrope and a point mass perturber. Results of the tests confirmed the code performance.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 Proceedings of 2004 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.81-90
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• 2004

A zonal embedded grid technique has been developed for computation of the two-dimensional Navier-Stokes equations with cylindrical coordinates. The fundamental idea of the zonal embedded grid technique is that the number of azimuthal grids can be made small near the origin of the coordinates so that the grid size is more uniformly distributed over the domain than with the conventional regular-grid system. The code developed using this technique combined with the explicit, finite-volume method was then applied to calculation of the spin-up flows within a semi-circular cylinder. It was shown that the numerical results were in good agreement with the experimental results both qualitatively and quantitatively.

• 대한치과보철학회지
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• 제51권4호
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• pp.261-268
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• 2013

연구 목적: 본 연구는 납형의 크기 및 형태 변화가 티타늄의 주조성에 어떠한 영향을 미치는지 확인하고자 하였다. 연구 재료 및 방법: 납형의 크기에 따라 Small Pattern군과 Large Pattern군으로 나누었고, 각각 Flat, Semicircular, Horse-shoe 및 V-shape형으로 납형의 형태에 따라 4개의 하위군으로 나누어 총 8개의 군으로 분류하였다. 모든 납형의 주입선은 Runner-bar형으로 하였다. 티타늄 주조 전용 매몰재인 실리카계 매몰재(Rematitan Plus$^{(R)}$, Dentarum, Germany)를 이용하여 매몰하였고, 아크용융 방식의 원심 주조기(Ti Cast Super R$^{(R)}$, Selec, Japan)를 사용하여 주조하였다. 주조성 평가는 완전한 형태로 주조 된 격자의 개수를 척도로 재현 정도를 확인하였다. 통계처리는 SPSS ver. 19.0 for WIN (SPSS. Inc. Chicago, IL, USA)를 사용하였다. 납형의 크기 및 형태에 따른 티타늄의 주조성을 이원변량 분산분석(Two-way ANOVA)을 이용하여 분석하였다. 결과:납형의 평균 재현율은 Small Pattern군은 95.14%, Large Pattern군은 94.30%로 Small Pattern군의 주조성이 유의하게 높았다(P<.05). 납형의 형태 변화에 따른 주조성은 Small Pattern군에서 Semicircular군 133.20개(96.52%), Horse-shoe군 132.40개(95.94%), Flat군 132.00개(95.65%), V-shape군 127.60개(92.46%) 순으로 감소하였다. Large Pattern군은 Flat군 198.60개(95.94%), V-shape군 197.80개(95.56%), Semicircular군 196.40개(94.88%), Horse-shoe군 188.00개(90.82%)순으로 감소하였다. Small Pattern군과 Large Pattern군 모두에서 납형의 형태변화에 따른 주조성은 유의할 만한 차이를 보이지 않았다(P>.05). 결론:주조체의 크기가 작을수록 주조성이 높아짐을 알 수 있었고 형태에 따른 주조성에서는 큰 영향을 받지 않는 것을 알 수 있었다.

• Journal of Biosystems Engineering
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• 제24권2호
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• pp.153-158
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• 1999

As a basic research for the development of the automatic grading and sorting system for dried oak mushrooms, the device to acquire both cap and gill side images of mushroom has been developed and neural network based side recognition and quality grading has been proposed via inputting both side images. 20 quality grades have been selected considering the requirement of grade classifications imposed by the mushroom company. Developed DC motor driven‘V’type reversing device for the image acquisition of both side images of mushroom showed more than 95% success. Most error was caused by very small size mushrooms with a radius of around 1cm. However, it required a further research to reduce the reversing time. Grading and side recognition were performed via inputting normalized size factors and average gray levels of $8{\times}8$ grids converted from the raw images of both surfaces to the multi-layer back propagation(BP) network. Accuracy of the grading showed about 88.5% and the total grading time including reversing operation was around 2 seconds.