• 전력전자학회논문지
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• 제19권1호
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• pp.1-7
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• 2014

This paper proposes a current harmonic compensation method for the grid-connected inverter, especially caused by the grid impedance. Grid impedance causes low order harmonics in the grid current and deteriorates power quality. This paper analyzes the negative impact of the grid impedance, and proposes an active feedforward compensation method. Proposing method verified through simulation and experiment with 3-phase 1.5kW voltage source inverter prototype.

• 전력전자학회논문지
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• 제24권5호
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• pp.349-355
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• 2019

A grid-connected inverter with critical loads should be able to supply a stable voltage to critical loads at mode change and during clearing time while detecting unintentional islanding. This study proposes a mode transfer method for a grid-connected inverter with critical loads. The proposed method, which integrates the grid-connected and islanded mode control loops into one control block, provides an autonomous and seamless mode transfer from the current control to the voltage control. Therefore, the proposed scheme can supply a stable voltage to critical loads at mode change and during clearing time. Experimental results are provided to validate the proposed method.

• 한국항공우주학회지
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• 제35권8호
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• pp.661-669
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• 2007

지면효과에 대한 수치해석을 위한 격자생성 과정에서 발생하는 어려움을 해소하기 위하여 중첩격자 기법을 이용한 수치해석 기법의 타당성에 대한 연구를 수행하고 그 신뢰성을 검증하였다. 지면효과가 있는 경우와 없는 경우 RAE 101 익형주위의 저속 난류 유동장에 대한 수치해석을 수행하였고 다중블록격자 기법과 중첩격자 기법을 적용한 수치해석 결과를 실험결과와 비교하였다. 이를 통하여 중첩격자 기법을 이용함으로써 지면효과에 대한 수치해석과정을 정확하고 격자생성 문제없이 효과적으로 수행할 수 있음을 보였다.

• Journal of Information Processing Systems
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• 제15권5호
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• pp.1156-1170
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• 2019

In recent years, the problem of data drifted of the smart grid due to manual operation has been widely studied by researchers in the related domain areas. It has become an important research topic to effectively and reliably find the reasonable data needed in the Supervisory Control and Data Acquisition (SCADA) system has become an important research topic. This paper analyzes the data composition of the smart grid, and explains the power model in two smart grid applications, followed by an analysis on the application of each parameter in density-based spatial clustering of applications with noise (DBSCAN) algorithm. Then a comparison is carried out for the processing effects of the boxplot method, probability weight analysis method and DBSCAN clustering algorithm on the big data driven power grid. According to the comparison results, the performance of the DBSCAN algorithm outperforming other methods in processing effect. The experimental verification shows that the DBSCAN clustering algorithm can effectively screen the power grid data, thereby significantly improving the accuracy and reliability of the calculation result of the main grid's theoretical line loss.

• 한국수자원학회논문집
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• 제48권1호
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• pp.37-44
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• 2015

본 연구에서는 Grid method를 사용하여 베이지안 비정상성 확률강우량 산정 모형을 확립하였다. 강우 극치자료의 분포로 Gumbel 분포를 채택하였으며, 분포형의 매개변수에 사전분포를 적용하고, 사전분포에 포함된 매개변수에는 초사전 분포를 적용하여 계층적 베이지안 모형을 구성하였다. Grid method는 매개변수의 발생가능 전 구간에 대하여 확률적으로 더 높은 뒷받침이 있는 하위 구간에서 난수를 직접 생성하여 집합을 구성함으로써 잘못된 결과를 도출할 수 가능성이 높은 상황에서도 보다 정확한 매개변수의 추정을 가능케 하므로 매개변수의 추정과정에서 비표준분포로 나타나는 조건부 확률밀도함수를 통한 난수의 추출은 기존에 사용해 온 Metropolis Hastings 알고리즘이 아닌 Grid method를 사용하였다. 개발된 모형은 서울의 1973년부터 2012년까지의 시강우자료를 이용하여 미래에 대한 재현기간에 따른 확률강수량을 산정하였으며, 그 결과로 기존 정상성 가정에 비해 목표연도에 따라 5%에서 8%정도의 증가율을 나타냈다.

• 대한기계학회논문집B
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• 제26권11호
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• pp.1521-1530
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• 2002

This article proposes a pressure based method for predicting flows at all speeds. The compressible SIMPLE algorithm is extended to unstructured grid framework. Convection terms are discretized using second-order scheme with deferred correction approach. Diffusion term discretization is based on structured grid analogy that can be easily adopted to hybrid unstructured grid solver. This method also uses node centered scheme with edge based data structure for memory and computing time efficiency of arbitrary grid types. Both incompressible and compressible benchmark problems are solved using the above methodology. The demonstration of this method is extended to slip flow problem that has low Reynolds number but compressibility effect. It is shown that the proposed method can improve efficiency in memory usage and computing time without losing any accuracy.

• 한국전산유체공학회지
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• 제17권1호
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• pp.70-77
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• 2012

In this paper, diagonal implicit harmonic balance method with overset grid technique is applied to analyze helicopter rotor blade flow in hover and forward flight condition. The chimera grid need interpolation time with sub-grid and background grid in moving problem such as forward flight on every time step. Present method is available enough to reduce the grid module interpolation time. In order to demonstrate present method, Caradonna & Tung's and AH-1G rotor blades are used and the results are compared to other researchers' result and experimental data.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 추계 학술대회논문집
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• pp.145-151
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• 1999

An Interactive grid generation program(KGRID) with graphical user interface(GUI) has been improved. KGRID works on the UNLX environment and GUI has been implemented with OSF/Motif and X Toolkit and the graphics language is Open GL for visualization of the 3D objects. It supports more convenient user environment to generate 2D and 3D multi-block structured grid systems. It provides various useful field grid generation methods, which are the algebraic methods, the elliptic partial differential equations method and the predictor-corrector method. It also supports 3D surface grid generation with NURBS(Non-Uniform Rational B-Spline) and various stretching functions to control grid points distribution on curves and surfaces. And some menus are added to perform flexible management, for the objects. We generated surface and field grid system about full aircraft configuration using KGRID. The performance and stability of the KGRID is verified through the generation of the grid system about a complex shape.

• 한국CDE학회논문집
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• 제1권1호
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• pp.56-64
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• 1996

A quadrilateral-triangular mixed grid method for the solution of incompressible viscous flow is presented. The solution domain near the body surface is meshed using elliptic grid geneator to acculately simulate the viscous flow. On the other hand, we used unstructured triangular grid system generated by advancing front technique of a simple automatic grid generation algorithm in the rest of the computational domain. The present method thus is capable of not only handling complex geometries but providing accurate solutions near body surface. The numerical technique adopted here is PISO type finite element method which was developed by the present author. Investigations have been made of two-dimensional unsteady flow of Re=550 past a circular cylinder. In the case of use of the unstructured grid only, there exists a considerable amount of difference with the existing results in drag coefficient and vorticity at the cylinder surface; this may be because of the lack of the grid clustering to the surface that is a inevitable requirement to resolve the viscous flow. However, numerical results on the mixed grid show good agreements with the earlier computations and experimental data.

• 스마트미디어저널
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• 제12권4호
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• pp.47-57
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• 2023

육각 그리드(hexagonal grid) 구조는 지리정보시스템에서 공간정보 데이터를 처리하고 표현하기에 우수하여 많은 연구가 이루어지고 있다. 육각 그리드를 이용한 시각화는 다른 그리드 표현 방법 대비 시인성이 높지만, 이에 표현된 공간정보 데이터에 따라 양적 정보와 그리드 간 데이터 차이를 효과적으로 전달하는 데 어려움이 있다. 따라서, 본 연구에서는 육각 그리드 외곽에 그림자를 생성하여 시각적으로 육각 그리드를 강조하는 방법을 제안한다. 이를 위해 강조하고자 하는 육각 그리드들의 최외곽 선분들을 오프셋 시키고, 그 정보를 바탕으로 베지어 곡선을 생성하여 최종적인 그림자 형상을 결정한다. 그림자는 육각 그리드에서 멀어질수록 서서히 옅어진다는 특성을 활용하여, 그림자의 가장자리로 갈수록 투명도를 가변적으로 적용한다. 제안하는 방법을 이용하여 하나의 육각 그리드뿐만 아니라 여러 개의 육각 그리드가 주어지더라도 그림자 영역을 효과적으로 생성할 수 있음을 보였으며, 사용자 인터페이스의 입력에 따라 다양한 그림자 형상을 생성할 수 있다. 서울특별시의 행정구 중 용산구에 제안하는 방법을 활용하여 그림자를 생성한 후 시각적으로 강조한 결과를 보인다.