• The KIPS Transactions:PartA
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• v.12A no.2 s.92
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• pp.103-108
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• 2005

The purpose of numerical analysis is to design an effective algorithm to realize some mathematical model on computer. In general the approximate value, which is obtained from computer operation, is not the same as the real value that is given by mathematical theory. Therefore the mr estimate measuring how approximate value is near to the real value, is the most significant task to evaluate the efficiency of algorithm. The limit of an error is used for mr estimation at the most case, but the exact mr evaluation could not be expected to get for there is no way to know the real value of the given problem. Wegmann's method has been researched, which is one of the solution to derive the numerical conformal mapping. We proposed an improved method for convergency by applying a low frequency filter to the Wegmann's method. In this paper we investigate error analysis based on some mathematical theory and propose an effective method which makes us able to estimate an error if the real value is not acquired. This kind of proposed method is also proved by numerical experiment.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.4
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• pp.385-394
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• 2006

The application areas of traditional push-pull converters are limited because the voltage stress of switches is high (twice of the input voltage). But the push - pull converter topology is suitable for unregulated low-voltage to high-voltage power conversion such as the fuel cell. This paper presents a novel power converter structure that is very suitable for the DC/DC converter in fuel cell systems. Based on this structure, a ZVS- ZCS push-pull converter is proposed. The switches of the proposed push-pull converter can operate under ZVS or ZCS condition with the help of a new passive clamping circuit. The passive clamping techniques solves the voltage overshoot problem. Because the buck converter circuit operates at twice the synchronous switching frequency of the push-pull converter, the peak current in the current-fed inductor and transformer is reduced. The operation principle of the proposed converter is analyzed and verified by simulations and experimental results. A 1 kW DC/DC converter was implemented with DSP TMS320F2812, from which experimental results have shown that efficiency improvement and surge suppression can be achieved effectively.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.8 no.3
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• pp.203-213
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• 2015

This study aims to figure out job stress and stress coping strategies for administrative personnel working in early childhood educational institution. The survey was conducted targeting 119 administrative personnel working in early childhood educational institution in Gyeonsangnam-do from September 10th, 2014 to December 20th, 2014. SPSS/WIN 18.0 Program for statistical processing, followed by frequency analysis, t-test, correlation analysis and multiple regression analysis. The result of socio-demographic characteristics had differences by factors ages, marriage status, religion and position. correlation. There was negative(-) correlation between lower variables of advices of experienced, change of problem recognition and lower variables of workload, job performance. Third, frequency of drinking and position at work were confirmed statistically as significant factors in regression model. This study is to be basic data to improve administrative personnel's task working in early childhood educational institution.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.3
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• pp.513-519
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• 2018

OFDM modulation has been used for a transmission scheme in 4G LTE (Long Term Evolution) and Wi-Fi systems to mitigate the effects of frequency selective fading channels. An OFDM modulation is a block transmission scheme because an OFDM symbol consists of multiple subcarriers with narrow bandwidth. Therefore, all OFDM symbols in a frame should be filled out with data and padding bits. Depending on the amount of data, more padding bits than information bits can occupy the last OFDM symbol. Such inefficiency causes the loss of throughput. To overcome this problem, an efficiency padding method is proposed by using the property of DFT (Discrete Fourier Transform). In the proposed method, symbol duration of the last symbol is changed depending on the number used data subcarriers in the last symbol. With numerical evaluation, it is examined that throughput enhancement achieved by the proposed method can be about 20% depending a transmission scheme and data length.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.1
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• pp.179-185
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• 2012

Since the eco-era is getting closer, the importance of noise reducing in the passenger cars of high-speed train is very important. The active noise control is best choice to reduce low frequency noise because the passive one is too heavy for high speed trains where weight is so critical. Also ANC is able to reduce the ambient noise when the environmental-factor changes. To reduce a three-dimensional closed-space sound field like a car of a high-speed rail is hard to do using single channel ANC control system. We used multi-channel FXLMS algorithm which calculation speed is fast and the secondary path estimation is possible in order to take into account the physical delay in electro acoustic hardware control loudspeaker and power amplifier. Firstly, we have measured interior noise of KTX and estimated noise path in KTX test-bed. However there was some problem related to algorithm divergence and increasing the filter order. We have made a simulation of interior environment of KTX car by using three frequency bands of 120Hz, 280Hz, 360Hz as the most important for KTX ANC system. During this research the interior noise reduction of KTX car was made by using the multi-channel FXLMS algorithm. Reduction performance was evaluated and compared each other for open space section and tunnel section. in-situ experiment for the KTX noise reduction by proposed ANC was performed based on data obtained in simulation and they were compared for open space section and tunnel section as well.

• Journal of Korea Multimedia Society
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• v.10 no.5
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• pp.623-630
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• 2007

With the development in IT technology and with growing demands of users, a ubiquitous environment is being made. Because of individuals identification is important in ubiquitous environment, RFID, a technology used frequently. RFID, a technology that radio frequency identification, reader send signer, then tag provide user information. RFID has various strengths, such as high recognition rates, quick recognition speed, but Eavesdropping is possible and problem that user information is revealed happens. To solve this, study is proceeded with activity, but, because of low-cost passive tag is limited operation capability, usually used hash function and random number. Also updates value that is used to present session and uses in next session. Therefore, this scheme protects user privacy using random number. And this sheme can offer synchronization by creating variable value without updating value.

• Journal of the Korean Institute of Gas
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• v.8 no.2 s.23
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• pp.48-53
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• 2004

Korea Gas Corporation(KOGAS) is a Liquified Natural Gas(LNG) supplier through out the Korea. LNG, which is imported wholly from foreign countries, is compressed 1/600 for easy transportation and is stored in a liquid state in the storage tanks at Incheon, Pyeongtaek and Tongyeong. At LNG receiving terminals, LNG is vaporized to natural gas before supplying to City Gas Consumer or Power Plant. The secondary pump is a equipment which compress LNG from $10 kgf/cm^2$ to $70 kgf/cm^2$. The secondary pump at Tongyeong LNG receiving terminal is consisted of two pumps in one underground PIT, and is connected to supporting structures. It is therefore expected that there is a vibration problem with the pump and was found that high level vibration was occurred in a low frequency band(5${\~}$10Hz). In this paper, the vibration of secondary pump was analyzed, and the main cause of vibration was found out.

• Journal of Ocean Engineering and Technology
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• v.30 no.5
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• pp.400-404
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• 2016

This paper presents experimental results for the vibration characteristics of the small unmanned underwater vehicle (UUV) OPKO 300, which was designed and manufactured by Daewoo ship and Marine Engineering Ltd. The autonomy of UUVs has led to an increase in their use in scientific, military, and commercial areas because their autonomy makes it possible for UUVs to be utilized instead of humans in hazardous missions such as mine countermeasure missions (MCM). Since it is impossible to use devices based on electromagnetic waves to gather information in an underwater environment, only sonar systems, which use sound waves, can be used in underwater environments, and their performance can strongly affect the autonomy of a UUV. Since a thruster system, which combines a motor and propeller in a single structure, is widely used as the propulsion system of a UUV and is mounted on the outside of a UUV’s stern, it can generate vibration, which can be transferred throughout the shell of the UUV from its stern to its bow. The transferred vibration can affect the performance of various sonar systems such as side-scan sonar or forward-looking sonar. Therefore, it is necessary to estimate the effect of the transferred vibration of the UUV on the sonar systems. Even if various numerical methods were used to analyze the vibration problem of a UUV, it would be hard to predict the vibration phenomena of a UUV at the initial design stage. In this work, an experimental study using OKPO 300 and an impact hammer was carried out to analyze the vibration feature of a small real UUV in the air. The frequency response function of the vibration based on the experimental results is presented.

• Journal of the Korea Convergence Society
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• v.12 no.9
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• pp.39-47
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• 2021

This study was conducted to propose a product planning prediction model using logistic regression algorithm to predict seasonal factors and rapidly changing product trends. First, we collected unstructured data of consumers in portal sites and online markets using web crawling, and analyzed meaningful information about products through preprocessing for transformation of standardized data. The datasets of 11,200 were analyzed by Logistic Regression to analyze consumer satisfaction, frequency analysis, and advantages and disadvantages of products. The result of analysis showed that the satisfaction of consumers was 92% and the defective issues of products were confirmed through frequency analysis. The results of analysis on the use satisfaction, system efficiency, and system effectiveness items of the developed product planning prediction program showed that the satisfaction was high. Defective issues are very meaningful data in that they provide information necessary for quickly recognizing the current problem of products and establishing improvement strategies.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.2
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• pp.247-254
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• 2021

Problems such as a limited frequency resource and interference between adjacent bands have been continuously raised because of rapidly developing wireless technology and communication service. In order to solve that problem, government has been developed and operating the Spectrum Management Intelligent System(SMIS). This paper compares the results simulated by SMIS with the ATDI and the Matlab coded provided by ITU-R for verification of SMIS operating for the public interests. The Recommendation ITU-R P.526, P.1546, and P.1812 among the propagation model loaded in SMIS were chosen because of the relation to the broadcasting service. The comparison and analysis result shows that the outputs derived by SMIS has the small error of less than 1 dB. This research could be utilized for the policy establishment and R&D for the frequency allocation and the interference between adjacent bands.