• Journal of Power System Engineering
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• v.16 no.4
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• pp.51-59
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• 2012

The computational flow analysis using LES technique was carried out to investigate the flow characteristics of a sirocco fan under the maximum flowrate condition. The commercial SC/Tetra software was used for this unsteady and three-dimensional numerical analysis. In consequence, because a flow is unstable within the range of about 50% of a housing depth from a bellmouth around the cutoff region, the passing flow through the blade cascade occurred on the X-Y plane is a slow or a reverse with approaching to the housing inlet. Also, the secondary flow shows on the radial plane of a housing, and its vortex center exists within about 33% of a housing depth from a bellmouth except the cutoff region. Moreover, the flow occurring on the exit plane of a sirocco fan shows a complex secondary flow.

• Journal of computational fluids engineering
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• v.16 no.3
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• pp.88-94
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• 2011

The availability of the thermal energy has been deeply recognized recently to encourage the cascade usage of thermal energy from combustion. Within the framework, a 1 kW class Stirling engine based cogeneration system has been proposed for a unit of a distributed energy system. The capacity has been designed to be adequate for the domestic usage, which requires high compactness as well as low emission and noise. To develop a highly efficient system with satisfying these requirements, a premixed slot type short flame burner has been proposed and a series of numerical simulation has been performed to establish a design tool for the combustion chamber. The thermal radiation model has been found to highly affect the computational results and a proper resolution to analyze the heat transfer characteristics of the high temperature heat exchanger. Finally, the combustion characteristics of the premixed flame with the metal fiber type burner has been studied.

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.237-241
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• 2008

An all-optical encryption system built on the basis of electrical logic circuit design principles is proposed, using semiconductor optical amplifier (SOA) exclusive or (XOR) logic gates. Numerical techniques (steady-state and dynamic) were employed in a sequential manner to optimize the system parameters, speeding up the overall design process. The results from both numerical and experimental testbeds show that the encoding/decoding of the optical signal can be achieved at a 10 Gbps data rate with a conventional SOA cascade without serious degradation in the data quality.

• Journal of Power Electronics
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• v.19 no.1
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• pp.89-98
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• 2019

This paper analyzes the input side performance of a conventional three-phase to single-phase matrix converter (3-1MC). It also presents the input-side waveform quality under this topology. The suppression of low-frequency input current harmonics is studied using the 3-1MC plus capacitance compensation unit. The constraint between the modulation function of the output and compensation sides is analyzed, and the relations among the voltage utilization ratio and the output compensation capacitance, filter capacitors and other system parameters are deduced. For a 3-1MC without large-capacity energy storage, the system performance is susceptible to input voltage imbalance. This paper decouples the inner current of the 3-1MC using a Lyapunov function in the input positive and negative sequence bi-coordinate axes. Meanwhile, the outer loop adopts a voltage-weighted synthesis of the output and compensation sides as a cascade of control objects. Experiments show that this strategy suppresses the low-frequency input current harmonics caused by input voltage imbalance, and ensures that the system maintains good static and dynamic performances under input-unbalanced conditions. At the same time, the parameter selection and debugging methods are simple.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.6
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• pp.1193-1198
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• 2022

As unmanned processing systems emerged socially due to the rapid development of modern society, a face recognition attendance management system using Raspberry Pi 4 was studied and conceived to automatically analyze and process images and produce meaningful results using OpenCV. Based on Raspberry Pi 4, the software is designed with Python 3 and consists of technologies such as OpenCV, Haarcascade, Kakao API, and Google Drive, which are open sources, and can communicate with users in real time through Kakao API for face registration and face recognition.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.379-386
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• 2021

This study was undertaken to develop a cascade-type continuous culture system (CCCS) that combines both ICT and biotechnology (BT), for the mass production of microalgae. This system is capable of maintaining the essential culture conditions of pH, temperature, carbon dioxide, and illuminance control, which are key parameters for the growth of microalgae, and is economical for producing microalgae regardless of the season or location. It has the added advantage of providing stable and high productivity. In the current study, this system was applied to culture microalgae for 71 days, with subsequent analysis of the experimental data. The initial O.D. of the culture measured from incubator 1 was 0.006. On the 71st day of culture, the O.D.s obtained were 0.399 (incubator 1), 0.961 (incubator 2), 0.795 (incubator 3), and 0.438 (incubator 4), thereby confirming the establishment of continuous culture. Thus, we present a smart-farm based on ISMC (in-situ monitoring and control) for a mass culture method. We believe that this developed technology is suitable for commercialization, and has the potential to be applied to hydroponics-based cultivation of microalgae and cultivation of high-value-added medicinal plants as well as other plants used in functional foods, cosmetics, and medical materials.

• Journal of Korean Society for Atmospheric Environment
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• v.9 no.1
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• pp.44-50
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• 1993

The suspended particulate matters had been collected by a cascade impactor having 9 size fragnated stages for 2 years (Dec. 1989 to Nov. 1991) in Kyung Hee University-Suwon Campus. The particulate matters were then collected on each stage by membrane filters. The weight concentration on each stage was estimated by a microbalance and further chemical element concentrations were determined by an XRF system. The study focused on developing of a receptor model using the TTFA (target transformation factor analysis) to apportion aerosol mass with the 30 ambient data sets. Each data set consists of the 8 size-ranged subdata sets characterized by 13 element variables. Even though a couple of sources could not be identified, three to five sources were extracted from each aerosol size-range, and then 9 statistical source profiles were generated. Finally, source contribution of particulate matters on each size-range could be estimated in Suwon area.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.576-580
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• 2001

This paper presents a casca multilevel PWM rectifier without the isolation transformers for energy build-up at each inverter modules; The features and advantages of the proposed PWM rectifier can be summarized as follows; 1) It realizes the high power high voltage AC/DC power conversion, 2) It uses no transformer which is bulky and heavy, 3) It has hybrid structure so that switching devices can be effectively utilized, 4) It produces high quality AC current even in high power high voltage applications, 5) The input power factor remains unity by simple modulation index control. The multilevel rectifier is analyzed by using the circuit DQ transformation whereby the characteristics and control equations are obtained. Finally, it will be shown that the system simulation reveals the validity of analyses

• The KSFM Journal of Fluid Machinery
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• v.1 no.1 s.1
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• pp.72-80
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• 1998

Computational analysis of incompressible flows by numerically solving Navier-Stokes equations using multi-block finite volume method is conducted on a parallel computing system. Numerical algorithms adopted in this study $include^{(1)}$ QUICK upwinding scheme for convective $terms,^{(2)}$ central differencing for other terms $and^{(3)}$ the second-order Euler differencing for time-marching procedure. Structured grids are used on the body-fitted coordinate with multi-block concept which uses overlaid grids on the block-interfacing boundaries. Computational code is parallelized on the MPI environment. Numerical accuracy of the computational method is verified by solving a benchmark test case of the flow inside two-dimensional rectangular cavity. Computation in the axial compressor cascade is conducted by using 4 PE's md, as results, no numerical instabilities are observed and it is expected that the present computational method can be applied to the turbomachinery flow problems without major difficulties.

• Journal of Environmental Health Sciences
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• v.21 no.2
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• pp.1-6
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• 1995

Authors investigated the size distribution and mass fraction of dusts in work environment of Changwon industrial complex. Size distribution of suspended dusts in welding and grinding processes were evaluated using ambient cascade impactors. The mass median diameters of dusts were 0.25 to $0.60 \mu m$ at welding sites and 1.20 to $1.92 \mu m$ at grinding sites. Respirable mass fractions were 63.68 to 73.50% at welding sites and 43.24 to 51.47% at grinding sites. Respirable fractions were calculated from the size distribution data for the ACGIH criteria by the respirable particle mass. In case of dust removal system, electrostatic precipitator and bag filter were appropriate for welding process and grinding process, respectively.