• Nuclear Engineering and Technology
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• v.30 no.6
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• pp.485-495
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• 1998

Migration characteristics of tracers in a rock fracture in a case of line-source and line-collection was studied. The fracture plane was discretized into a square mesh to which variable apertures were assigned. The spatially varying apertures of a fracture were generated using a geostatistical method, based on a given aperture probability density distribution and a specified spatial correlation length. The flow potential and pressure at each node were computed. Calculations showed that fluid flow occurs predominantly through a few preferred paths. Hence, the large range of apertures in the fracture gives rise to flow channeling. The solute transport was calculated using a particle tracking method. The migration plumes of tracer between injection line and withdrawal line are displayed in contour plots. The elution curves are shown to be controlled by the aperture density distribution and to be insensitive to statistical realization and spatial correlation length.

• Journal of Power Electronics
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• v.10 no.1
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• pp.79-84
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• 2010

This paper presents a grid connected photo-voltaic system using a quasi-Z-source inverter (QZSI) for power stage reduction. The power stage can be reduced because of an additional shoot-through stage which is a characteristic of QZSI. Therefore, by utilizing a QZSI the system's efficiency can be increased. In this paper, for applying a QZSI to a PV system, control methods such as maximum power point tracking (MPPT), point of common coupling (PCC) current control and PWM are studied and verified through simulation and experiment. In order to explain the above controllers, the characteristics of a QZSI are first analyzed. Then the MPPT control technique with a modified P&O method, the PCC current control for the regulation of the dc-link capacitor voltage and the PWM methods for the proposed system are explained. The feasibility of the proposed algorithm is verified through simulation and experiment with a 3kW system.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.5
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• pp.53-57
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• 2008

Diesel generator is most widely used for supplying of emergency electrical power. There have been extensive research efforts to develop ways to Ensure stable electrical power delivery to the loads using hybrid power sutures, such as power source, storage batteries, fuel cells and solar cells. Furthermore, as the role of these diesel generators for emergency electrical power supply has recently become very important, they should assure high reliability and flexibility according to the operation load. Therefore, in this paper, we introduce a controller to be used in diesel generator toenable tracking control of maximum power according to the load variation and suppressing high-order harmonics while maintaining stable frequency.

• Journal of Korean Society on Water Environment
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• v.39 no.1
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• pp.87-101
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• 2023

The constituents of a watershed control a wide range of ecosystem processes, such as, carbon sequestration, nutrient retention, and biodiversity preservation. Maintenance of a healthy watershed is advantageous to humans in many direct and indirect ways. Dissolved organic matter fluorescence analysis is one of the most commonly utilized parameters for water quality measurement, pollution source tracking, and determination of the ecological state of a watershed. Throughout the recent decades, the advancement in data processing, instrumentation, and methods has resulted in many improvements in the area of watershed study with fluorescence analysis. The current trend of coupling advanced instrumentations and new comparative parameters, such as, microplastics of different types, antibiotics, and specific bacterial contaminants have been reported in watershed studies. However, conventional methodologies for obtaining fluorescence excitation emission matrices and for calculating the fluorescence and spectral indices are preferred to advanced methods, due to their easiness and simple data collection. This review aims to gain a general understanding of the use of dissolved organic matter fluorescence analysis for diagnosis and source identification of watershed pollutions, by focusing on how the studies have utilized fluorescence analysis to improve existing knowledge and techniques in recent years.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.4
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• pp.300-309
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• 2007

In this paper, a grid-interactive photovoltaic (PV) system with the function of the power quality improvement is presented. The proposed system requires only one current-controlled voltage source inverter, which control the current flow at low total harmonic distortion and unity power factor, as well as simultaneously provide reactive power support. The proposed system operation has been divided into two modes (sunny and night). In night mode, the system operates to compensate the reactive power demanded by nonlinear or variation in loads. In sunny mode, the system performs power quality control (PQC) to reduce harmonic current and to improve power factor as well as maximum power point tracking (MPPT) to supply active power from the PV arrays, simultaneously. To verify the proposed system a comprehensive evaluation included simulation and experimental results are presented.

• Journal of the Korea Society of Computer and Information
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• v.27 no.1
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• pp.91-96
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• 2022

With the development of the cloud industry, various efforts are being made to improve resource efficiency and environmental continuity in software development and operation methods. However, in constructing a conventional structure of structural scheme, if the functionality is improved and added, it has a problem that the efficiency of full build arrangement is reduced for the changed source. In this paper, if a problem occurs in a solution service company, communication between the development department and the operation department can be facilitated and responded quickly, and the latest source updated during processing of the problem is the management system, provided is a system that can take advantage of CI tools and continuously integrate them. As communication through the proposed system is smooth, it is expected that unnecessary work can be reduced and the speed of development can be improved.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.2
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• pp.231-242
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• 2014

It is throwing the spotlight on the cultivation crops about high quality crops and productivity improvement per unit area because of rapid climate change caused by global warming. Therefore, we propose a water culture management of circulation nutrient method control system applies to solar tracking method not using traditional method of deep flow technique and artificial light source. We design it in the form of the circulation nutrient method in waterway of a certain amount of nutrient solution and water flowed into the way of circular. In addition, we design a multistage structure in pyramid shape which be possible continuous photosynthesis action to crops of water culture bottom part. Also, solar tracking method is designed five sensor method of center hole sensor method for tracking shadow of solar light not using traditional two hole, four hole sensor method. Finally, through the water culture device applies to solar light tracking method was not introduced in existing study yet, we can reduce growth speed of crops which be possible continuous photosynthesis action to crops. Moreover, We can expect high productivity of per unit area which be possible all crops can be offered growth environment of same type by using form of pyramid shape of multistage structure without top or bottom part.

• Journal of the Institute of Convergence Signal Processing
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• v.13 no.4
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• pp.220-232
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• 2012

In this paper, we investigate the correlation result due to the problems of delay tracking and fringe rotation module in the VCS(VLBI Correlation Subsystem). The VCS, FX-type correlator, adopts the delay tracking and fringe rotation module in order to compensate the delay change and fringe phase of wave signal from the radio source by Doppler's effect. The phase of observed data is also compensated by means of delay tracking and fringe rotation in the correlator, but we confirmed that the phase is unstable by applying long integration period of AIPS(Astronomical Image Processing System) rather than correlator. And the delay value of observed data has the errors of several tens nanoseconds than normal case at the analysis of correlation result. In addition, we found that the phase of correlation results is not connected as the unit of FFT-segment because the initial fringe phase at the fringe rotation module is not correctly determined. In this paper, in order to solve these problems, the original direction of 90 degree phase jump is reversely modified when the bit-shift occurred at the delay tracking. And the initial fringe phase at the fringe rotation module is correctly modified by using the initial phase of observed data. In addition, the parameter calculation module was abnormally operated as designed in the fringe rotation. So, the logical program by the VCS is modified so as to calculate the parameters correctly. Through the experiments of correlation processing over the above problems, the modified proposal algorithm is adequately corrected to the data analysis results, so that the experimental results make it clear for us to operate the developed VCS hardware correlator normally.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.389-394
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• 2004

A Fuzzy Logic Sliding Mode Control or FLSMC for the uninterruptible power system (UPS) is presented, which is tracking a sinusoidal ac voltage with specified frequency and amplitude. The FLSMC algorithm combines feedforward strategy with the Variable Structure Control (VSC) or Sliding Mode Control (SMC) and fuzzy logic control. The control function is derived to guarantee the existence of a sliding mode. FLSMC has an advantage that the stability of FLSMC can be proved easily in terms of VSC. Furthermore, the rules of the proposed FLSMC are independent of the number of system state variables because the input of the suggested controller is fuzzy quantity sliding surface value. Hence the rules of the proposed FLSMC can be reduced. The simulation results illustrate that the purposed approach gives a significant improvement on the tracking performances. It has the small overshoot in the transient and the smaller chattering in the steady state than the conventional VSC. Moreover, its can achieve the requirements of robustness and can supply a high-quality voltage power source in the presence of plant parameter variations, external load disturbances and nonlinear dynamic interactions.

• Journal of the Speleological Society of Korea
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• no.89
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• pp.27-33
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• 2008

Solar energy is most green and clean, unlimited and sustainable energy source on the earth. It is almost 97% of imported consumer energy in Korea. Because of resource poor nation, it is necessary to do their best to make alternative energy to allot their deficiency of the matter in hand of energy resources of petroleum. In a point of view of this problems, the natural solar energy should be improved by any methods as much, possible as we need. Photovoltaic generation with solar tracking system for obtaining optimal power is one of most benefit equipment to improve power of solar-cell panel producing clean electric power efficiently. Solar tracker is a device for orienting a solar photovoltaic panel toward the sun perpendicularly to sunlight, especially in widely separated place. For this reason, we are very interested in developing the equipment system of tracker, specially in solar cell applications, obtaining a high degree of accuracy to ensure that the optimal sunlight could be directed precisely against to the powered device. As a result, it was obtained of 12.46 volts at 90$^\circ$toward solar panel and 9.44 volts at 45$^\circ$, furthermore, improved efficiency more than 30% of average output voltage between tracker system (12.41V) and fixed system (8.55V), respectively. It is also very useful for optimum power system of widely separated cave.