• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.90-99
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• 2002

The main purpose of this study lies on the development of micro dilution tunnel based on the Sierra Dilution chamber model. As a primary examination, characteristics of flow and temperature distributions during the steady dilution process in dilution chamber are observed with numerical analysis. The penetration of dilution air through porous tube as well as wall temperature and temperature gradient inside porous tube are examined. The thermophoretic velocity in terms of temperature behavior inside porous tube are defined and examined. Based on the ratio of penetration and thermophoretic velocities, all part of porous tube are shown to be safe from the particulate depositions. However, The inlet portion of porous tube in addition to the portion of impinging of dilution air are marginally safe from the particulate depositions. Generally the safer design against particulate deposition is required in provision f3r steady dilution process and for transient process as well.

• Laser Solutions
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• v.3 no.3
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• pp.21-29
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• 2000

For the direct metal shape processing the powder feed device which is different from the widely used in rapid prototyping. is developed, The three dimensional object is shaped with the melting metal powder. The developed research has applied to rapid prototyping in ultraprecision for MEMS and medical science fields required of rapid manufacture of complex shape. The goal of this study make 3D model which has precision accuracy. Powder spreading apparatus has been more improved because that the control of powder spread is very important in layer manufacturing. It consists of the vibration motor, nozzle and tube which supplies various metal powder. This apparatus could control the spreading velocity that could control powder spreading thickness. Laser on/off switch was adapted because laser scanning velocity must be preserved constantly to prevent heat transformation of laser overheating. The error between sintered thickness md experimental one occurred by shrinkage in sintering melting process. The problem of heat transformation was solved by On/Off switching system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.2
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• pp.147-155
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• 2005

For a long road tunnel, a tunnel ventilation system may be used in order to reduce the pollution level below the required level. To control the tunnel pollution level, a closed loop control algorithm may be used. The cascade control algorithm, which composed of a jet fan control algorithm and an air velocity setpoint algorithm, was developed to regulate the CO level in a tunnel. The verification of control algorithms was carried out by dynamic models developed from real tunnel data sets. The simulation results showed that control algorithms developed for this study were effective to control the tunnel ventilation system.

• The Journal of the Acoustical Society of Korea
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• v.19 no.5
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• pp.71-78
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• 2000

Quickness and precision are the two most important requirements for an industrial scale used in production lines. In this paper, a new approach, "Mass-estimation algorithm by vibration-response measurement of dynamic balance", is presented to improve some of drawbacks in conventional scales. The system, consisted of velocity and displacement sensors, spring scale, analog-digital converter and microcomputer, is based on full utilization of dynamic mass measurement of velocity and displacement via microcomputer-assisted real time monitoring. The resulting system, when combined with appropriate mass estimation algorithm software, has shown its effectiveness in terms of two desirable characteristics required.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.7
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• pp.1050-1060
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• 1994

This paper is a study on the computer simulation of the characteristics of the superconducting fault current limiter. Input variable parameters are apparent power, load resistance value, line resistance value and so on. Initial fault current 2 times larger than the trigger current is required to reduce the switching time of SFCL. The propagation velocity increases abruptly, the transport current is several times larger than the ciritical current. In this paper, the switching time is calculated to be 323$\mu$ sec, and the initial fault current is 19 times larger than the critical current. Because the trigger coils are bifilar winding, they have little impedance in superconducting state. After fault occurred, the limiting coil acts as a superconducting reactor and the trigger coils quench at a critical current. Without the SFCL in the circuit, fault current after the load impedence is shorted might be increased to 1100A. The fault current is, therefore, successfully limited by the superconducting limiting coil to 100A determined by the coil inductance.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.69-76
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• 1991

A design method based on the surface vorticity distribution is developed to generate a two-dimensional blade section for prescribed velocity distribution in potential flow. The boundary condition used to determine the strength of vorticity distribution requires that the surface of blade section should be a streamline of the resulting flow. In order to obtain the required final geometry of a two-dimensional blade section, an iterative procedure is used. A computer program is developed and several numerical results are presented.

• Journal of the Korean Society of Safety
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• v.10 no.2
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• pp.56-63
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• 1995

A simulation of contaminant dispersion in a water reservoir has been done using 2-D finite difference method(FDM). The steady state velocity field of the reservoir was computed using stream function-vorticity formulation of Wavier-Stokes equation and continuity equation. Based on the computed steady state velocity field, the transient convective diffusion equation of the contaminant dispersion was computed. For the 1m$\times$1m reservoir model with inlet and outlet attached, it was shown that the center of circulation located toward right. For the numerical values of v =0.01($\textrm{cm}^2$/s) and D=0.6($\textrm{cm}^2$/s) and the flow of 50($\textrm{cm}^3$/s ), it was determined that the outflow had to be shut down in 18 seconds to prevent from severe pollution. Also the required time was computed to be 6 seconds for the inflow of 100 ($\textrm{cm}^3$/s). The result of this study is considered, hopefully, to be useful for the design of the water reservoir systems that are the subjects to various contamination.

• Journal of the Korean Society of Combustion
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• v.18 no.3
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• pp.54-60
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• 2013

This paper shows a general development process for aircraft gas turbine combustors. As a first step for developing the preliminary combustor design program, several combustor sizing methodologies using reference area concepts are reviewed. There are three ways to determine the reference area; 1) combustion efficiency approach, 2) pressure loss approach, 3) velocity assumption approach. The current study shows the comparisons of the calculated results of combustor reference values from the pressure loss and velocity assumption approaches. Further works are required to add iterative steps in the program using more reasonable values of pressure loss and velocities, and to evaluate the sizing results using data for actual combustor performance and sizes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.879-882
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• 2004

Two-phase flow exists in many industrial components. Characteristics of two-phase flow have been studied by many researchers; however, a further study of the two-phase is required for flow-induced vibration. Characteristics of two-phase flow were measured by force sensor at the end of a vertical pipe. The predominant frequency of fluctuation was obtained for various speeds of flow pattern. A correlation to slug frequency for horizontal flow was obtained by Heywood & Richardson (1979), while Legius et al (1997) for vertical flow. A coefficient based on the correlation is estimated and then compared to the existing ones. The existing empirical formulations for average void fraction were proposed by Wallis (1969), Zuber et al (1967) and Ishii (1970). In the present result, flow parameters, such as flow quality and real velocity, are evaluated with void fraction.

• Journal of Sensor Science and Technology
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• v.30 no.3
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• pp.125-130
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• 2021

In this study, the degree of alignment of polymer microfibers produced by electrospinning using a rotating water collector was evaluated. Aligned micro- and nano-fibers are required in various practical applications involving anisotropic properties. The degree of fiber alignment has many significant effects; hence, and accurate quantitative analysis of fiber alignment is necessary. Therefore, this study developed a simple and efficient method based on two-dimensional fast Fourier transform, followed by ellipse fitting. As a demonstrative example, the polymer microfibers were electrospun on the rotating water collector as the alignment of microfibers can be easily controlled. The analysis shows that the flow velocity of the liquid collector significantly affects the electrospun microfiber alignment, that is, the higher the flow velocity of the liquid collector, the greater is the degree of microfiber alignment. This method can be used for analyzing the fiber alignment in various fields such as smart sensors, fibers, composites, and textile engineering.