• Journal of Electrical Engineering and Technology
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• v.13 no.5
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• pp.1852-1863
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• 2018

Direct current(DC) systems have recently attracted attention due to the increase in DC loads and distributed generations, such as renewable energy sources. Among these technologies, there has been much research into DC distribution systems or DC microgrids. Within this body of research, the main topics have been about optimum control and operation methods in terms of improving power efficiency. When DC systems are controlled and operated using power electronic devices such as converters, it is necessary to design and analyze them by considering the power electronics sections. For this reason, we propose a scalable DC system analysis algorithm, which considers various system configurations depending on the operating mode and location of the converter. The algorithm consists of power flow fault current calculations, and the results of the algorithm can be used for designing DC systems. The algorithm is implemented using MATLAB with defined input and output data. The verification of the algorithm is mainly performed using ETAP software, and the accuracy of the algorithm analysis can be confirmed through the results.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.6
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• pp.1305-1317
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• 2019

Although encryption for data protection is essential in the big data platform environment of public institutions and corporations, much performance verification studies on encryption algorithms considering actual big data workloads have not been conducted. In this paper, we analyzed the performance change of AES, ARIA, and 3DES for each of six workloads of big data by adding data and nodes in MongoDB environment. This enables us to identify the optimal block-based cryptographic algorithm for each workload in the big data platform environment, and test the performance of MongoDB by testing various workloads in data and node configurations using the NoSQL Database Benchmark (YCSB). We propose an optimized architecture that takes into account.

• Journal of KIISE:Software and Applications
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• v.29 no.5
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• pp.345-354
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• 2002

There have been many researches about monitoring and checking the implementations during run-time using formal requirement specification. They usually adopt temporal logics or their extensions to specify the requirements for the implementations. However, most of the systems fail to support the specification of requirements fir dynamic systems - systems whore components are created and removed during run-time. Unlike analysis or design models, most actual implementations are dynamic, so the notion of instances should be employed in the property specification language. In this paper, we show how we can monitor and check Java programs using our temporal logic for dynamic systems (HDTL). We suggest a framework in which the execution of Java programs are monitored and chocked against given HDTL requirements.

• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1643-1653
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• 2014

This paper presents the design and implementation of a wind-solar hybrid power system for LED street lighting and an isolated power system. The proposed system consists of photovoltaic modules, a wind generator, a storage system (battery), LED lighting, and the controller, which can manage the power and system operation. This controller has the functions of maximum power point tracking (MPPT) for the wind and solar power, effective charging/discharging for the storage system, LED dimming control for saving energy, and remote data logging for monitoring the performance and maintenance. The proposed system was analyzed in regard to the operation status of the hybrid input power and the battery voltage using a PSIM simulation. In addition, the characteristics of the proposed system's output were analyzed through experimental verification. A prototype was also developed which uses 300[W] of wind power, 200[W] of solar power, 60[W] LED lighting, and a 24[V]/80[Ah] battery. The control system principles and design scheme of the hardware and software are presented.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.10
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• pp.2462-2472
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• 2014

Recently, the computing paradigm has been changing and VoIP technology is being revisited to support various services. In this paper, we have designed and implemented the system of software PBX open source Asterisk, hardware platform, and mobile devices to support secured voice service based on VoIP. Specially, we designed the various platform from single board to servers based on XenServer in hardware platform. And we verified the delay test of network traffics and the secured voice communication test based on this platform.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.7
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• pp.1121-1127
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• 2016

In this paper, modeling of overcurrent relay(OCR) to protect domestic AC electric railway Auto Transformer(AT) feeding system and operation characteristic analysis on overload condition are described. The target system of this paper is actual site where overload trip of circuit breaker occurs frequently. Because this AT feeding system is made of parallel single track which had a load(electric train) respectively, and is connected with only T phase of Scott Transformer. In addition, this system has been feeding 66kV voltage by KEPCO, not 154kV. We focus on protective coordination of Scott Transformer primary side and secondary side OCR for Korea single track AC electrical railway system in operation currently. We modeled single track AT feeding system and OCR. Also we performed faults and overload analysis for verification of OCR's setting values and system modeling. To analyze above mentioned research, we used PSCAD/EMTDC software tool.

• Nuclear Engineering and Technology
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• v.52 no.1
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• pp.178-184
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• 2020

The traditional methods for radiation shield design always only focus on either the structure or the components of the shields rather than both of them at the same time, which largely affects the shielding performance of the facilities, so in this paper, a novel method for designing the structure and components of shields simultaneously is put forward to enhance the shielding ability. The method is developed by using the genetic algorithm (GA) and the MCNP software. In the research, six types of shielding materials with different combinations of elements such as polyethylene (PE), lead (Pb) and Boron compounds are applied to the radiation shield design, and the performance of each material is analyzed and compared. Then two typical materials are selected based on the experiment result of the six samples, which are later verified by the Compact Accelerator Neutron Source (CANS) facility. By using this method, the optimal result can be reached rapidly, and since the design progress is semi-automatic for most procedures are completed by computer, the method saves time and improves accuracy.

• Tunnel and Underground Space
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• v.15 no.3 s.56
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• pp.213-222
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• 2005

In this study, an artificial neural network was used to predict stability of weak rock slopes with various discontinuities and underground water conditions. Input data were provided by UDEC analyses on 108 cases of representative conditions of different slope heights, angles, discontinuity angles and water levels. The verification shows high correlation $(r^2-=0.97)$ between analyses and predictions. The program was able to predict safety factors with the same accuracy from unlearned data sets.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.12
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• pp.116-123
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• 2001

An automated injection molding design methodology has been developed to optimize multiple quality attributes, which are usually in conflict with each other, in injection molded parts. For the optimization, commercial CAE simulation tools and optimization techniques are integrated into the methodology. To decal with the multiple objective problem the relative closeness computed in TOPSIS(Technique for Order Preference by Similarity to Ideal Solution) is used as a performance measurement index for optimization multiple part defects. To attain robustness against process variation, Taguchi's quadratic loss function is introduced in the TOPSIS. Also, the modified complex method is used as an optimization tool to optimize objective function. The verification of the developed design methodology was carried out on simulation software with an actual model. Applied to production this methodology will be useful to companies in reducing their product development time and enhancing their product quality.

• Journal of Internet Computing and Services
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• v.5 no.6
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• pp.1-10
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• 2004

A web robot is a software that has abilities of tracking and collecting web documents on the Internet(l), The performance scalability of recent web robots reached the limit CIS the number of web documents on the internet has increased sharply as the rapid growth of the Internet continues, Accordingly, it is strongly demanded to study on the performance scalability in searching and collecting documents on the web. 'Design of web robot based on Multi-Agent to speed up documents collection ' rather than 'Sequentially executing Web Robot based on the existing Fork-Join method' and the results of analysis on its performance scalability is presented in the thesis, For collection speedup, a Multi-Agent based web robot performs the independent process for inactive URL ('Dead-links' URL), which is caused by overloaded web documents, temporary network or web-server disturbance, after dividing them into each agent. The agents consist of four component; Loader, Extractor, Active URL Scanner and inactive URL Scanner. The thesis models a Multi-Agent based web robot based on 'Amdahl's Law' to speed up documents collection, introduces a numerical formula for collection speedup, and verifies its performance improvement by comparing data from the formula with data from experiments based on the formula. Moreover, 'Dynamic URL Partition algorithm' is introduced and realized to minimize the workload of the web server by maximizing a interval of the web server which can be a collection target.