• 한국강구조학회 논문집
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• 제11권1호통권38호
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• pp.23-31
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• 1999

결합부위의 해석을 위하여, 계산 효율과 정확성이 모두 뛰어난 단순모델의 사용이 필요한 경우가 많다. 이 단순모델은 결합부위의 특성을 잘 묘사하는 파라미터들로 구성된다. 이들 파라미터의 값은 실험을 통하여 얻어지게 된다. 따라서 단순모델은 실험에서 사용된 하중하에서는 결합부위의 거동을 잘 묘사하지만, 그외 다른 하중하에서는 결합부위의 거동을 어느 정도 구현할지 알 수 없다. 따라서 단순모델의 정확성을 객관적으로 얻을 수 있는 방법이 필요하게 된다. 본 연구에서는 역최적화 (antioptimization) 개념으로 최악의 하중조건을 정의하여, 이 하중하에서 단순모델의 정확성을 평가하는 방법을 제시하였다. 최악의 하중조건 하에서, 용접으로 체결된 3차원 결합부위의 단순모델과 2차원 구조물에서의 결합부위 단순모델의 정확성을 평가하였다.

• 대한조선학회논문집
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• 제41권6호
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• pp.91-101
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• 2004

For the grillage which is common types of structures in marine and land-based structural system, the elastic response and design methods are usually applied. However, plastic analysis and design methods are considered Tn those structures to maintain the structural stability at the limit states. In grillage design, the central intersection point load may be used as a worst loading condition. However, a point load may often move around on the grid system. in such case, the worst load point would not necessarily be at the central point. To investigate the variation of plastic collapse load according to the location of moving load between intersections, the plastic collapse loads are obtained for the three types of grillages with simply-supported ends. From the result of each case, it is confirmed that the worst load point is located between intersections. General formulae related with plastic collapse loads for the three groups of grillages with simply-supported boundaries are derived. Those plastic collapse formulae for the grillages are applied to the design of pontoon deck, and optimum design procedure is illustrated. Consequently, general formulae for the plastic collapse of grillages derived from this study can be easily applied to the plastic analysis and optimum design of similar grillages.

• Wind and Structures
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• 제4권6호
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• pp.455-468
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• 2001

This paper presents recent research on the experimental evaluation of wind loads on low buildings and the recommendations provided in the form of traditional codification. These mainly include the wind loads on buildings with geometries different from those examined in previous studies. This is followed by the evaluation of simulated wind loads on low building roofs. The overall application of a recently proposed simulation methodology for codification purposes is discussed in detail. The traditional codification provides for a group of roof geometries a single peak design pressure coefficient for each roof zone considering a nominal worst-case scenario; this may often lead to uneconomical loads. Alternatively, the presented methodology is capable of providing peak pressure coefficients corresponding to specific roof geometries and according to risk levels; this can generate risk consistent and more economical design wind loads for specific roof configurations taking into account, for instance, directional design conditions and upstream roughnesses.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.473-476
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• 2005

Mobility of tracked vehicles is dependent on performance of its power equipment and suspension systems. Especially, its road wheels, components of its suspension systems, play an important role in distributing the vehicle weight on the ground and preventing from misguiding tracks. In this study, the maximum force acted on multipurpose tracked vehicles driven on the worst condition was calculated. And then FE analyses were carried out to evaluate the strength of the road wheels under the maximum force condition. For quality evaluation of the road wheels, FE simulations and experimental works were carried out under specific slant loads. Residual deformation for the slant loads was investigated and commented upon.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제3B권2호
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• pp.103-110
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• 2003

With significant development of power electronics technology, the proliferation of nonlinear loads such as static power converters has deteriorated power quality in power transmission and distribution systems. Notably, voltage harmonics resulting from current harmonics produced by the nonlinear loads have become a serious problem in many countries. Many photovoltaic power generation systems installed in building systems have harmonics that are the worst object for distribution systems as a utility interactive system, and it tends to spread out continuously. Proposed and implemented in this paper is a multi-function inverter control strategy that allows a shunt active filter function to the power inverter of the photovoltaic power generation system established on a building system. The effectiveness of the proposed system is demonstrated through the simulation of a hypothetical power system using PSCAD/EMTDC.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.277-280
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• 2002

With significant development of power electronics technology, the proliferation of nonlinear loads such as static power converters has deteriorated power quality in power transmission and distribution systems. Notably, voltage harmonics resulting from current harmonics produced by the nonlinear loads have become a serious problem in many countries. There are already a lot of PV power generation systems installed in building systems whose harmonics are the worst object for distribution systems as a utility interactive system and also it tends to spread out continuously. In this paper, the authors propose a multy-function inverter control strategy which puts a shunt active filter function to the power inverter of the PV power generation system established on a building system. The effectiveness of the proposed system is demonstrated through the simulation of hypothetical power system using PSCAD/EMTDC.

• 한국정보과학회논문지:시스템및이론
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• 제26권9호
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• pp.1064-1072
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• 1999

크기가 n인 하이퍼큐브 다중컴퓨터를 위한 대표적인 동적인 재분배 방법인 DEM(Dimension Exchange Method) 기법으로 양자화된 부하를 분배할 때 분배 후 각 프로세서가 갖는 부하의 크기는 최악의 경우, logn~단위부하 만큼 분배오차를 갖게 된다. 이러한 오차를 억제하기 위하여 본 논문에서는 두 프로세서간에 부하를 분배할 때, 가능하면 동일 유형(홀수개 또는 짝수개)의 단위부하를 동일 방향으로 재분배하는 기법을 제안하였다. 그 결과 최대 분배 오차를 LCEIL logn over {2} RCEIL 까지 줄일 수 있었다. 시뮬레이션에 의한 실험을 통해 기존 DEM 방법에 비해 약 30% 정도 시스템의 속도가 향상됨을 보임으로써 제안된 기법이 DEM 기법보다 타당성함을 입증하였다.

• KEPCO Journal on Electric Power and Energy
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• 제8권2호
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• pp.159-179
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• 2022

Often a network becomes complex, and multiple entities would get in charge of managing part of the whole network. An example is a utility grid. While the entire grid would go under a single utility company's responsibility, the network is often split into multiple subsections. Subsequently, each subsection would be given as the responsibility area to the corresponding sub-organization in the utility company. The issue of how to make subsystems of adequate size and minimum number of interconnections between subsystems becomes more critical, especially in real-time simulations. Because the computation capability limit of a single computation unit, regardless of whether it is a high-speed conventional CPU core or an FPGA computational engine, it comes with a maximum limit that can be completed within a given amount of execution time. The issue becomes worsened in real time simulation, in which the computation needs to be in precise synchronization with the real-world clock. When the subject of the computation allows for a longer execution time, i.e., a larger time step size, a larger portion of the network can be put on a computation unit. This translates into a larger margin of the difference between the worst and the best. In other words, even though the worst (or the largest) computational burden is orders of magnitude larger than the best (or the smallest) computational burden, all the necessary computation can still be completed within the given amount of time. However, the requirement of real-time makes the margin much smaller. In other words, the difference between the worst and the best should be as small as possible in order to ensure the even distribution of the computational load. Besides, data exchange/communication is essential in parallel computation, affecting the overall performance. However, the exchange of data takes time. Therefore, the corresponding consideration needs to be with the computational load distribution among multiple calculation units. If it turns out in a satisfactory way, such distribution will raise the possibility of completing the necessary computation in a given amount of time, which might come down in the level of microsecond order. This paper presents an effective way to split a given electrical network, according to multiple criteria, for the purpose of distributing the entire computational load into a set of even (or close to even) sized computational loads. Based on the proposed system splitting method, heavy computation burdens of large-scale electrical networks can be distributed to multiple calculation units, such as an RTDS real time simulator, achieving either more efficient usage of the calculation units, a reduction of the necessary size of the simulation time step, or both.

• 전기학회논문지
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• 제66권3호
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• pp.513-521
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• 2017

Robust optimal operation of a microgrid is required since the increase of the penetration level of renewable generators in the microgrid raises uncertainty due to their intermittent power output. In this paper, an application of probabilistic optimization method to economical operation of a microgrid is studied. To simplify the treatment of the uncertainties of renewable generations and load, the new 'band of virtual equivalent load variation' is introduced considering their uncertainties. A simplified robust optimization methodology to generate the scenarios within the band of virtual equivalent load variation and to obtain the optimal solution for the worst scenario is presented based on Monte Carlo method. The microgrid to be studied here is composed of distributed generation system(DGs), battery systems and loads. The distributed generation systems include combined heat and power(CHP) and small generators such as diesel generators and the renewable energy generators such as photovoltaic(PV) systems and wind power systems. The modeling of the objective function for considering interruption cost by the penalty function is presented. Through the case study for a microgrid with uncertainties, the validity of proposed robust optimization methodology is evaluated.

• International Journal of Contents
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• 제3권1호
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• pp.9-13
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• 2007

This paper proposes a policy on efficient load balancing that can reduce the network game server load burdened by surging number of users. The study adopted a contents-based clustering technique. Recently, skyrocketing number of clients in on-line games causes overloads on specific game servers, and the consequent server-instability brings the worst situation: a server failure. To cope with this problem, one can install more high-powered servers or be equipped with back-up servers, which is often inefficient in terms of cost performance. To solve this problem, the present study examined the technology enhancing the performance and efficiency of game servers by reducing the loads of specific game servers. In doing this, this study used the clustering technology to compose game servers classified by their contents and carried out appropriate load balancing to numerous clients with load balancers in each region.