• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.295-302
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• 2009

The flow in the draft tube cone of Francis turbines operated at partial discharge is a complex hydrodynamic phenomenon where an incoming steady axisymmetric swirling flow evolves into a three-dimensional unsteady flow field with precessing helical vortex (also called vortex rope) and associated pressure fluctuations. The paper addresses the following fundamental question: is it possible to compute the circumferentially averaged flow field induced by the precessing vortex rope by using an axisymmetric turbulent swirling flow model? In other words, instead of averaging the measured or computed 3D velocity and pressure fields we would like to solve directly the circumferentially averaged governing equations. As a result, one could use a 2D axi-symmetric model instead of the full 3D flow simulation, with huge savings in both computing time and resources. In order to answer this question we first compute the axisymmetric turbulent swirling flow using available solvers by introducing a stagnant region model (SRM), essentially enforcing a unidirectional circumferentially averaged meridian flow as suggested by the experimental data. Numerical results obtained with both models are compared against measured axial and circumferential velocity profiles, as well as for the vortex rope location. Although the circumferentially averaged flow field cannot capture the unsteadiness of the 3D flow, it can be reliably used for further stability analysis, as well as for assessing and optimizing various techniques to stabilize the swirling flow. In particular, the methodology presented and validated in this paper is particularly useful in optimizing the blade design in order to reduce the stagnant region extent, thus mitigating the vortex rope and expending the operating range for Francis turbines.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 B
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• pp.1148-1150
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• 2003

Power conversion system must be increased switching frequency in order to achieve a small size, a light weight and a low noise. However, the switches of converter are subjected to high switching power losses and switching stresses. As a result of those, the power system brings on a low efficiency. To improved these, a large number of soft switching topologies included a resonant circuit has been prosed. But these circuits increase number of switch in circuit and complicate sequence of switching operation. In this paper, the authors propose a high power factor and high efficiency DC-DC converter using single-pulse soft switching by partial resonant switching node. The switching devices in a prosed circuit are operated with soft switching by the partial resonant method, that is, Partial Resonant Switch Mode Power Converter. The partial resonant circuit makes use of a inductor using step up and a condenser of loss-less snubber. The result is that the switching loss is very low and the efficiency of system is high. Also the proposed converter is deemed the most suitable for high power applications where the power switching devices are used. Some simulative results on computer results are included to confirm the validity of the analytical results.

• 전자공학회논문지
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• 제50권1호
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• pp.21-26
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• 2013

본 논문에서는 그룹(group)을 2개의 심볼(symbol)로 나누는 시스템을 제안하는데, 이 두 개의 더해진 심볼들은 다중화에 의해 분리된 후 역다중화 기술을 이용해 다시 합해진다. 제안된 시스템에서 간단한 PIC(Partial Interference Cancelation) 그룹 복호화 기술은 Double-ABBA(D-ABBA) 유사 직교(Quasi-Orthogonal) 시공간 부호(Space Time Code)를 위해 사용된다. 이 부호는 고차 MIMO(Multiple Input Multiple Output) 시공간 블록 부호화에서 복호화시에 복잡도를 줄여준다. 그리고 기존의 방법과 제안된 방법과의 성능을 비교한다.

• Journal of Platform Technology
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• 제8권3호
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• pp.10-21
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• 2020

부분 방전 현상은 배전반, 트랜스포머, 스위치 기어 등 고압전력기기에서 많이 발생한다. 부분 방전은 절연체의 수명을 단축하고 절연파괴를 가져오게 되고 이로 인해 정전사고 등 대형피해가 발생하게 된다. 부분 방전 현상은 제품 내부에서 발생하는 경우와 표면에서 발생하는 여러 가지 유형을 가지고 있다. 본 논문에서는 부분 방전 현상에 대한 패턴 및 발생할 확률을 예측할 수 있는 예측 모델을 설계하는 것이다. 설계된 모델을 분석하기 위하여 부분 방전 현상을 발생시키는 시뮬레이터를 활용하여 각각의 부분 방전 유형에 대한 학습 데이터를 UHF 센서를 통하여 수집하였다. 본 논문에서 설계된 예측 모델은 딥 러닝 중 CNN을 기반으로 설계를 하였으며 학습을 통하여 모델을 검증하였다. 설계된 모델에 대한 학습을 위하여 5,000개의 훈련데이터를 만들었으며 훈련데이터의 형태는 UHF센서에서 입력되는 3차원의 원시데이터를 2차원 데이터로 전 처리하여 모델에 대한 입력데이터로 사용하였다. 실험결과, 학습을 통하여 설계된 모델에 대한 정확도는 0.9972의 정확도를 갖는 것을 알 수 있었으며 데이터를 2차원 이미지로 만들어 학습한 경우 보다 그레이 스케일 이미지 형태로 만들어 학습한 경우가 제안된 모델에 대해 정확도가 높음을 알 수 있었다.

• Korean Journal of Mathematics
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• 제23권4호
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• pp.537-555
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• 2015

This paper is concerned with the existence of solutions to the following fractional differential inclusion $$\{-{\frac{d}{dx}}\(p_0D^{-{\beta}}_x(u^{\prime}(x)))+q_xD^{-{\beta}}_1(u^{\prime}(x))\){\in}{\partial}F_u(x,u),\;x{\in}(0,1),\\u(0)=u(1)=0,$$ where $_0D^{-{\beta}}_x$ and $_xD^{-{\beta}}_1$ are left and right Riemann-Liouville fractional integrals of order ${\beta}{\in}(0,1)$ respectively, 0 < p = 1 - q < 1 and $F:[0,1]{\times}{\mathbb{R}}{\rightarrow}{\mathbb{R}}$ is locally Lipschitz with respect to the second variable. Due to the general assumption on the constants p and q, the problem does not have a variational structure. Despite that, here we study it combining with an iterative technique and nonsmooth critical point theory, we obtain an existence result for the above problem under suitable assumptions. The result extends some corresponding results in the literatures.

• 정보처리학회논문지D
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• 제15D권4호
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• pp.581-588
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• 2008

오래된 필름이나 영상들은 물리적 또는 화학적으로 많은 손상을 받기 때문에 손상부분에 대한 특별한 처리가 요구된다. 영상 손상은 손상의 범위에 따라, 영상 전체에 걸쳐 나타나는 전역 손상과, 영상 일부분이 손상되어 나타나는 지역손상으로 구분할 수 있으며, 오래된 영상은 지역 손상 부분의 복구만으로도 상당한 화질 향상이 가능하다. 기존의 연구는 긁힘으로 인한 line scratch 검출 알고리즘의 연구와 얼룩, 긁힘, 또는 의도적인 손상으로 인해 손상된 영역을 복원하는 복원 알고리즘이 연구되고 있다. 오래된 영상 복원 연구의 대표적인 방법은 편미분방정식을 적용한 인페인팅 기법이며, 영상의 형태를 편미분방정식으로 모델링하기 때문에, 편미분 차수의 제한에 의해 복잡한 형태의 영상 복원 화질이 좋지 못하고, 계산복잡도가 높은 단점을 가지고 있다. 본 논문에서는 오래된 영상에서 주로 나타나는 필름의 긁힘으로 인해 생기는 line scratch를 검출하고, 영상의 특성을 반영하는 에지검출연산자의 일종인 Sobel 연산자를 이용하는 인페인팅 기법을 제안한다. 실제 영상 복원실험을 위해 오래된 한국영화인 1945년 작 "자유만세" 와 1976년 작 "로보트 태권V" 영상을 사용하였으며, 기존의 연구결과와 비교하여 화질개선 뿐만이 아니라, 개선된 복원 속도를 얻을 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
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• pp.35-38
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• 1991

Recent, problems on the voltage-instability have been paid attention in power system and methods to find the limit of voltage-stability, concerned with these problems, were developed. However, these methods are short of precision on the limit of voltage-instability. Here, using the second-order load flow, constraint equation(d Pi/d Vi=0) and its patial differentiations are precisely formulated. Also, since the taylor series expansion of power flow equations terminates at the second-order terms, partial differentiations of constraint equation, that is Hessian, are constant. Then, Hessian matrix are calculated once during iteration process.

• 한국유체기계학회 논문집
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• 제10권1호
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• pp.26-33
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• 2007

Four design candidates for a partial admission turbine have been chosen from a preliminary design process. Their performance were estimated through the 3-D numerical analyses using a frozen rotor method. In order to select the optimum design, each flow analysis result was compared with others. Flow characteristics in the passages and some types of losses induced by shocks and wakes were found from calculation results. Based on these calculations, a new rotor blade was redesigned and compared with previous one through flow analysis.

• 설비공학논문집
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• 제9권3호
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• pp.323-332
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• 1997

It was reported by some researchers that two-stage parallel-plate ESPs, commonly called electronic air cleaners, show decreasing behavior of collection efficiency as particle size decreases below about $0.03{\mu}m$. This phenomenon is attributed to partial particle charging characteristics, where some of incoming particles are not charged in the charging cell of 2-stage parallel-plate ESP. One way to improve the decreasing collection efficieny in that particle size range is to enforce particle charging quantity in the charging cell. In the present study, in order to do this a 2-wire series-type charging cell modified from a 1-wire normal-type one was suggested and investigated theoretically and experimentally concerning improvement of the collection efficiency. It was confirmed from the experimental and theoretical works that the collection efficiency was apparently improved.

• 한국컴퓨터산업교육학회:학술대회논문집
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• 한국컴퓨터산업교육학회 2003년도 제4회 종합학술대회 논문집
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• pp.55-58
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• 2003

Stability of inside power equipments are required for electron equipment in order to operate those safely. Also, the power circuits for these have been developing, but research of dielectric strength of power supply is insufficient. In this paper, for test insulation condition variation by void it is tested insulation characteristics variation, using $\phi-q-n$ distribution variation in partial discharge test.