• International Journal of Fluid Machinery and Systems
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• 제8권2호
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• pp.102-112
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• 2015

In the Nordic grid, a trend observed the recent years is the increase in grid frequency variations, which means the frequency is outside the normal range (49.9-50.1 Hz) more often. Variations in the grid frequency leads to changes in the speed of rotation of all the turbines connected to the grid, since the speed of rotation is closely related to the grid frequency for synchronous generators. When the speed of rotation changes, this implies that the net torque acting on the rotating masses are changed, and the material of the turbine runners must withstand these changes in torque. Frequency variations thus leads to torque oscillations in the turbine, which become dynamical loads that the runner must be able to withstand. Several new Francis runners have recently experienced cracks in the runner blades due to fatigue, obviously due to the runner design not taking into account the actual loads on the runner. In this paper, the torque oscillations and dynamic loads due to the variations in grid frequency are simulated in a 1D MATLAB program, and measured grid frequency is used as input to the simulation program. The maximum increase and decrease in the grid frequency over a 440 seconds interval have been investigated, in addition to an extreme event where the frequency decreased far below the normal range within a few seconds. The dynamic loading originating from grid frequency variations is qualitatively found by a constructed variable $T_{stress}$, and for the simulations presented here the variations in $T_{stress}$ are found to be around 3 % of the mean value, which is a relatively small dynamic load. The important thing to remember is that these dynamic loads come in addition to all other dynamic loads, like rotor-stator interaction and draft tube surges, and should be included in the design process, if not found to be negligible.

• Structural Engineering and Mechanics
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• 제36권4호
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• pp.463-479
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• 2010

Based on damage accumulation of multi-grid composite walls, a method of dynamic reliability estimations is proposed. The multi-grid composite wall is composed of edge frame beam, edge frame columns, grid beams, grid columns and filling blocks. The equations including stiffness, shear forces at filling blocks cracking and multi-grid composite walls yielding, ultimate displacement, and damage index are obtained through tests of 13 multi-grid composite wall specimens. Employing these equations in reliability calculations, procedures of dynamic reliability estimations based on damage accumulation of multi-grid composite walls subjected to random earthquake excitations are proposed. Finally the proposed method is applied to the typical composite wall specimen subjected to random earthquake excitations which can be specified by a finite number of input random variables. The dynamic reliability estimates, when filling blocks crack under earthquakes corresponding to 63% exceedance in 50 years and when the composite wall reach limit state under earthquakes corresponding to 2-3% exceedance in 50 years, are obtained using the proposed method by taking damage indexes as thresholds. The results from the proposed method which show good agreement with those from Monte-Carlo simulations demonstrate the proposed method is effective.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제14권8호
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• pp.753-757
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• 2008

본 논문은 그리드 환경에서 동전계획법을 위한 새로운 스케줄링 정책을 제안한다. 이 스케줄링 정책의 특징은 동적 테이블의 지역성을 고려하여 테이블을 분할하고, 네트워크 지연이 최소인 노드에 작업을 할당함으로써 작업의 실행시간을 단축하는 것이다. 또한 최적의 병행성을 얻기 위해 분산 하향식으로 동적 테이블을 구성한다 시뮬레이션을 통하여 제안하는 그리드 스케줄링 정책이 그리드 환경의 성능 향상 면에서 기존의 분기-한정(branch-bound) 알고리즘에 비해 더 효과적임을 보인다

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제15권12호
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• pp.948-952
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• 2009

최근 공간 네트워크에서 대용량 이동객체의 위치정보를 관리하기 위한 DS-GRID(distributed S-GRID)가 제안되었다[1]. 그러나 DS-GRID는 균일 크기의 그리드 셀을 이용하기 때문에, 실제 응용에서 빈번히 발생하는 이동 객체의 쏠림 현상을 효율적으로 관리하지 못하는 단점을 지닌다. 이를 해결하기 위해, 본 논문에서는 이동객체의 밀도에 따라 그리드 셀을 동적으로 분할하는 동적 분산 그리드 기법을 제안한다. 아울러 이를 위한 k-최근접 질의처리 알고리즘을 제안한다. 마지막으로 성능 평가를 통해 이동객체의 쏠림 현상이 발생하였을 경우, 제안하는 동적 분산 그리드 기법이 검색 및 업데이트 성능 측면에서 DS-GRID 보다 우수함을 입증한다.

• 전기학회논문지
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• 제56권5호
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• pp.841-847
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• 2007

This paper deals with the micro-grid consisting of micro-sources which adopt voltage sourced inverters with independent real and reactive power control capability for providing premium power quality. This paper presents dynamic modeling and the stable operating range of the micro-grid system varying the parameters of the micro-sources. The fundamental frequency model of the micro-source inverters are considered to form a dynamic model of the micro-grid system. Stability analysis is performed based on the linearized dynamic model of the micro-grid system. Case study results show the parameters affecting the stability of the micro-grid and the stable operating range of the micro-sources.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권6호
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• pp.1689-1705
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• 2023

To deal with the potential XSS vulnerabilities in the source code of the power communication network, an XSS vulnerability detection method combining the static analysis method with the dynamic testing method is proposed. The static analysis method aims to analyze the structure and content of the source code. We construct a set of feature expressions to match malignant content and set a "variable conversion" method to analyze the data flow of the code that implements interactive functions. The static analysis method explores the vulnerabilities existing in the source code structure and code content. Dynamic testing aims to simulate network attacks to reflect whether there are vulnerabilities in web pages. We construct many attack vectors and implemented the test in the Selenium tool. Due to the combination of the two analysis methods, XSS vulnerability discovery research could be conducted from two aspects: "white-box testing" and "black-box testing". Tests show that this method can effectively detect XSS vulnerabilities in the source code of the power communication network.

• 조명전기설비학회논문지
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• 제21권7호
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• pp.46-53
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• 2007

Micro-Grid는 높은 전력품질을 제공하기 위해 독립적으로 유효 및 무효전력 제어가 가능한 연료전지와 마이크로터빈과 같이 친환경적이고 신뢰할 수 있는 전력원을 채용하는 Micro-Source들로 구성된다. 본 논문은 Micro-Grid시스템의 동특성 모델링과 안정도 해석의 기본적 해석 방법에 관하여 연구하였다. Micro-Source 인버터의 기본주파수 모델을 이용하여 Micro-Grid 시스템의 동특성 모델을 구성하였다. Micro-Grid 시스템의 선형화된 동특성 모델을 기초로 하여 안정도 해석을 수행하였다. 사례연구 결과로부터 Micro-Grid 시스템의 안정도에 영향을 미치는 파라미터를 식별하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제35권1호
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• pp.82-88
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• 2011

본 연구의 목적은 실용연소기를 대상으로 한 복잡한 난류 연소장에의 Dynamic SGS G-방정식의 유용성을 확인하는 데에 있다. 본 연구에서는 sub-grid 난류확산과 화염 두께에 근거한 새로운 난류화염 전파속도 모델을 제안하였으며, sub-grid 난류강도를 이용한 기존 모델과의 비교, 검증을 수행하였다. 해석결과는 실험결과와의 비교를 통해 속도와 온도분포를 잘 예측하고 있음을 확인하였다.

• Journal of Information Processing Systems
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• 제11권4호
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• pp.538-555
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• 2015

Event detection based on using features from a static grid can give poor results from the viewpoint of two main aspects: the position of the camera and the position of the event that is occurring in the scene. The former causes problems when training and test events are at different distances from the camera to the actual position of the event. The latter can be a source of problems when training events take place in any position in the scene, and the test events take place in a position different from the training events. Both issues degrade the accuracy of the static grid method. Therefore, this work proposes a method called a dynamic grid for event detection, which can tackle both aspects of the problem. In our experiment, we used the dynamic grid method to detect four types of event patterns: implosion, explosion, two-way, and one-way using a Multimedia Analysis and Discovery (MAD) pedestrian dataset. The experimental results show that the proposed method can detect the four types of event patterns with high accuracy. Additionally, the performance of the proposed method is better than the static grid method and the proposed method achieves higher accuracy than the previous method regarding the aforementioned aspects.

• Journal of Advanced Marine Engineering and Technology
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• 제34권8호
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• pp.1084-1093
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• 2010

화염 전파 특성을 나타내는 G 방정식에 기초한 Sub-grid Scale연소 모델을 이용하여 보염기 주위의 난류 예혼합 연소 해석에 관한 대 와동 모사를 수행하였다. Dynamic SGS 모델이 G방정식에 도입되었으며, 삼각형의 보염기 배면의 예혼합 연소 유동에 의해 검증되었다. 해석결과는 실험결과와의 비교를 통해 속도와 온도분포를 잘 예측하고 있음을 확인하였다.