• 한국해양학회지
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• v.9 no.2
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• pp.59-64
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• 1974

Relative light intensity was observed with underwater illuminometer (Cs Photoelectric cell, glass window) at the mouth of Yeong-il Bay, and relative vertical clearness and extinction coefficient were calculated from the relative light intensity data. Relationship between extinction coefficient and transparency in this region is also shown.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.2_2
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• pp.199-207
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• 2020

These days, many different types of valves are developed in the industrial area according to their use purpose. Multiple kinds of valves are installed to control a flow and pressure of the pipe conveying fluid. Valves serve as critical roles in land plants such as power plants. The performance of equipment varies depending on valve characteristics. In this study, the internal flow analysis on Cone-type valve is conducted to analyze flow field and secure a value of the flow coefficient Cv. According to the internal flow analysis, when the flow distribution of the middle cross-section of valve was open 100%, flow field was relatively and smoothly taken out. If it was open 50%, flow recirculation region increased and a little complex flow field occurred. Unlike ball valve or butterfly valve, this valve had flow recirculation in its outlet depending on a valve opening amount. Therefore, it was found that there was no flow recirculation in the outlet of Cone-type valve.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.93-99
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• 2005

Performed were 2-phase numerical studies on two types of fuel atomizers, plain orifice and pressure swirl atomizer. In case of plain orifice, cavitation model was applied so that discharge coefficient, cavitation size, and magnitude of cavitation region characterized and compared with experimental results for several different pressure enforced to the orifice. In case of swirl atomizer, VOF model was applied to analyze air core size, spray angle, and wall pressure distributions with comparison of experimental results.

• The Journal of Korea Robotics Society
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• v.7 no.2
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• pp.142-149
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• 2012

The camera has limitations of poor visibility in underwater environment due to the limited light source and medium noise of the environment. However, its usefulness in close range has been proved in many studies, especially for navigation. Thus, in this paper, vision-based object detection and tracking techniques using artificial objects for underwater robots have been studied. We employed template matching and mean shift algorithms for the object detection and tracking methods. Also, we propose the weighted correlation coefficient of adaptive threshold -based and color-region-aided approaches to enhance the object detection performance in various illumination conditions. The color information is incorporated into the template matched area and the features of the template are used to robustly calculate correlation coefficients. And the objects are recognized using multi-template matching approach. Finally, the water basin experiments have been conducted to demonstrate the performance of the proposed techniques using an underwater robot platform yShark made by KORDI.

• Journal of the Korean Wood Science and Technology
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• v.34 no.5
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• pp.98-103
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• 2006

Radial and tangential diffusion coefficients of boron in wood under water leaching conditions were determined from the change of concentration profiles of boron. Egner's solution was used to obtain variable diffusion coefficients of boron because it has been known to be the only method to determine variable diffusion coefficients with no cumbersome assumption. The values of diffusion coefficients were between $0.18{\times}10^{-6}m^2/sec$ and $25.6{\times}10^{-6}cm^2/sec$. They increased with the increase of sample thicknesses, and decreased with the increase of leaching times. There was a region where Egner's method was not valid. However, Egner's solution illustrates a convenient way to evaluate diffusion characteristics of boron from wood under water leaching conditions. The diffusion coefficients at wood surface may be regarded as leaching coefficients.

• KSTLE International Journal
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• v.4 no.2
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• pp.66-72
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• 2003

This paper presents the hydrodynamic effect by the journal speed, eccentricity and source positions in order to overcome the defects of air bearing such as low stiffness and damping coefficient. Choosing the two row source position of air bearing is different from existing investigations in the side of pressure distribution of air film because of the high speed of journal and the wedge effects by the eccentricity. These optimal choices of the two row source positions enable us to improve the performance of the film reaction force and loading force as making the high-speed spindle. In this paper, The pressure behavior in theory of air film in high speed region of journal according to the eccentricity of journal and the source positions analyzed. The theoretical analysis has been identified by experiments. The results of investigated characteristics may be applied to precision devices like ultra-precision grinding machine and ultra high-speed milling.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.2
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• pp.169-174
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• 2001

The electron transport coefficients(the electron drift velocity, W, and the longitudinal and transverse diffusion coefficient, D$_{L}$ and D$_{T}$) in SiH$_4$-Ar mixtures containing 0.5% and 5.0% monosilane were calculated over the E/N range from 0.01 to 300 Td and over the gas pressure range 0.5, 1.0 and 1.5 Torr by the time-of-flight(TOF) method of the Boltzmann equation(BE.) and Monte-Carlo simulation(MCS). The electron energy distribution function in each SiH$_4$-Ar mixtures at E/N=10 Td and L=0.2 cm, which in equilibrium region in the mean electron enregy were compared.red.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.223-226
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• 2006

Computational Study of a sphere subjected to free stream flow and simultaneously subjected to spinning motion is carried out. Three dimensional compressible Navier-Stokes equations are solved using fully implicit finite volume scheme. SST(Shear Stress Transport) $k-{\omega}$ turbulence model is used. Aerodynamic characteristics being affected are studied. Validation of the numerical process is done for the no spin condition. Variation of drag coefficient and shock wave strength with increase in spinning rate is reported. Changes in the wake region of the sphere with respect to spinning speed are also observed.

• 한국전산유체공학회:학술대회논문집
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• 1995.10a
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• pp.203-212
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• 1995

In this paper the upwind flux difference splitting Navier-Stokes method has been applied to study the perfect gas and the equilibrium chemically reacting hypersonic flow over an axisymmetric sphere-cone($5^{\circ}$) geometry. The effective gamma($\bar{r}$), enthalpy to internal energy ratio was used to couple chemistry with the fluid mechanics for equilibrium chemically reacting air. The test case condition was at altitude(30Km) and Mach number(15). The equilibrium shock thickness over the blunt body region was much thinner than that of perfect gas shock. The pressure difference between perfect gas and equilibrium gas was about $3\sim5$ percent. The skin friction coefficient and heat transfer coefficient were also calculated.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.246-247
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• 2005

The paper presents the heat transfer characteristics during cooling process of carbon dioxide($CO_2$) in a helically coiled tube. The main components of the apparatus consist of a receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section with the inner diameter 4.55 [mm] is a tube in tube type heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. The main results were summarized as follows : The heat transfer coefficient increases with respect to the decrease of the gas cooler pressure in a supercritical region and the increase of the refrigerant mass flux. The pressure drop decreases in increases of the gas cooler pressure and increases with respect to increases the refrigerant mass flux.