• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.11
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• pp.935-942
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• 2014

A numerical analysis of the effect of the Prandtl number on the natural convection in a cold outer tilted square enclosure with an inner hot circular cylinder is presented. Several Prandtl numbers (Pr=0.1, 0.7, 7) are considered, with different angles($0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$) for the enclosure and Rayleigh numbers ($Ra=10^3$, $10^4$, $10^5$). The effect of the Prandtl number on the natural convection is analyzed using isotherms and streamline and surface-averaged Nusselt numbers. The flow and heat transfer characteristics are found to be dependent on the time for $Ra=10^5$ and Pr=0.1 at angles of $0^{\circ}$ and $45^{\circ}$. However, in the other cases, the flow and heat transfer characteristics are independent of the time.The surfaceaveraged Nusselt number increases with an increase in the Prandtl number. As the Prandtl number increases, the Nusselt number becomes larger regardless of the angle for $Ra=10^5$. In particular, the Nusselt number steeply increases when the angle is $45^{\circ}$ for $Ra=10^5$ and Pr=0.1.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.1
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• pp.98-104
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• 1999

To investigate the relationships between ocean environmental characteristics, the time-series data of temperature and salinity observed at a station near at Hanlim set net in 1995 and 1996 are analyzed, and the results are as follow ; 1. In hanlim set net, the diurnal range of temperature and salinity variation in summer is very large and the amplitude of short-period fluctuation of temperature and salinity is very large. That is, not only the water of the middle and bottom layers (low temperature and high salinity) but also the coalstal water (high temperature and low salinity) appears alternatively depending on the current direction 2. from the result of mooring for 22 days in Hanlim set net, the mean speed and direction of tidal current in neap tide were 9.1 cm/sec and south westward in ebb time, and 11.6 cm/sec and north or northeastward in flood time, respectively. The highest speed of the current was 15cm/sec in ebb time, and 22.6 cm/sec in flood time. The mean speed and direction of tidal current in spring tide were 10.4 cm/sec, and southwestward in ebb time, and 12.3 cm/sec, and north or northestward in flood time, respectively. The highest speed of the current was 19.4 cm/sec in ebb time, and 20 cm/sec in flood time respectively. The mean speed of the current in flood time was larger than that in ebb time. The velocity vector along the major axis of semidiurnal tide ($M_2$) component was 1.5 times larger than that of diurnal tide ($K_1$), The major directions of two compornants were northwestward and east-southeastward and residiual current were 3.25 cm/sec and northwestward-directed. Result of TGPS Buoy tracer for 3 days between Biyang-Do and Chgui-Do showed that the mean speed was 1.6 knot in ebb time and 1.3 knot in flood time. Direction of tidal was southwestward in ebb time and northeastward in flood time respectively. The maximum current speed was 4.8 knot in ebb time and 3.7 knot in flood time respectively. The mean speed and direction of tidal in of offshore were 1.7 knot and northwestward in flood time. The residual current appeared 0.3 knot northeastward.

• Journal of Korean Society for Geospatial Information Science
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• v.11 no.3 s.26
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• pp.23-34
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• 2003

Currently, the efficiency of GPS has been increased in the various precise survey like as the control survey and the navigation etc. Also, it is widely used in the deformation analysis of the structure, the measurement of the marine tides, the measurement of the river level and the topographic monitoring of seabed or riverbed by combined the measurement equipment for depth. In this study, we intend to increase in efficiency of the topographic monitoring of seabed or riverbed by combined with DGPS, RTK GPS and echo sounder. For this study, we defined the error correction of the echo sounder with the experiment of water tank which is considered the characteristic of estuary riverbed and then we developed the s/w for 3-dimensional monitoring of estuary riverbed and applied the s/w to field test and improved the various problems. On analyzing topography of estuary riverbed by combined GPS with echo sounder, the draught error which is yielded to change of length from the water surface by the movement of survey vessel to the end of the transducer was eliminated by geometrical rearrangement and we defined the correction formula $z=BM+SAH-DBR_{(i)}-DRT-ED$. The sounding error about the echo sounder and characteristic of estuary riverbed was found by understanding the relation of average diameter ind residual error and we defined correction formula, $Y=0.00474{\ast}ln(X)-0.0045$ by the regression analysis. and then we verified applicability of correction formula.

• Journal of Biomedical Engineering Research
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• v.25 no.6
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• pp.489-496
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• 2004

Insertion of cannulae into vessels may disturb the blood flow doing non-physiological load and stress on blood cells such that ADP may increase and result in hemolysis. Authors used the computational method to simulate the 3-dimensional blood flow inside of the cannula using numerical method. We limited the research to within the drainage cannulae with side holes inserted through the human vein. In this paper, 9 different cannulae with side holes categorized by the number of side holes of 4, 12, and 20, and also categorized by the array type of side holes of staggered array, in-line array, and alternative in-line array were studied and compared to the cannula with no side holes by using CFD analysis. We evaluated the flow rate, the wall shear stress, and the shear rate and compared them with one another to estimate the effect of the side holes. The flow rate is not proportional to the number of the side holes. However, larger number of side holes can reduce the mean shear rate. Both the number and the array type of side holes play an important role on the fluid dynamics of the blood flow in cannulae.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.644-648
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• 2019

This study examined effects of the wall thermal conductivity coefficients on the thermal fluid phenomenon of a compartment fire. The reduced scale compartment was 0.4 m in width, 0.6 m in length and 0.6 m in height with a fire-board, which has a thermal conductivity coefficient of $0.18W/m{\cdot}K$. The local temperature at a 0.37 m height and the overall heat release rate were measured under the following experiment conditions: a $0.12m^2$ opening area and $0.01m^2$ pool size of a gasoline fire. The numerical results obtained by the Fire Dynamic Simulation were compared with the experimentally measured temperature. The deviations were within 10 % in the period of the steady state for maximum heat release rate (4.8 kW). The numerical results show that the average temperature of the compartment wall decreases by approximately 71 % with increasing thermal conductivity coefficient from $0.1W/m{\cdot}K$ to $100.0W/m{\cdot}K$ on the fixed heat release rate.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.70-82
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• 1995

A multi-layer simulation program is developed to estimate the ocean current considering sea bottom geometry. The so-called $\sigma$ coordinate system is introduced in vertical direction to describe sea bottom topography more accurately and effectively. Leapfrog scheme combined with Euler backward scheme is used to reduce computation error which may be possibly accumulated in time evolution by Leapfrog scheme alone. In this paper, very simple examples of rectangular basins with various bottom geometries were taken and the effect of sea bottom geometry on vertical structure of the ocean tidal current and its direction were investigated. Through comparisons between the present three dimensional calculation in which bottom topography is directly taken into consideration and the two dimensional calculation in which depth average concept is employed, it was found that magnitude of surface current and its direction could be largely affected by the sea bottom topography, particularly in shallow region with complex bottom shape.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1113-1120
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• 2013

A numerical analysis of the effect of the position of a circular cylinder in a $45^{\circ}$ tilted enclosure on natural convection in the enclosure is presented. The location of the cylinder is changed between -0.4 and 0.4. The Rayleigh number is varied between $10^3$ and $10^5$. The effect of the location of the cylinder on natural convection in the enclosure is analyzed by the isothermal line, stream line, and surface-averaged Nusselt number. The flow and heat transfer characteristics are independent of time in the range of the Rayleigh number and cylinder location that is considered in this study. The surface-averaged Nusselt number of the cylinder and enclosure increases as the cylinder gets closer to the wall of the enclosure.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.53-67
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• 2001

In this study the pilot test of CGS as injection method by low slump mortar was performed and the results were analyzed in order to find out the application of this method and effect of settlement restraint. The site far pilot test is adjacent to apartments supported by pile foundations. Sand drain method was performed previously as countermeasures against settlement, but settlement occur continuously because this ground is very soft. Site investigations such as SPT, DCPT and vane shear test were performed to determine the characteristics of ground improvement. Field measurements and FDM analysis were performed on purpose to find out the displacement of ground during injection works. From the results of this study, CGS method can be optimized by the control of diagram, space, depth, injection material, and injection pressure. CGS improved soft ground compositely by the bearing effect of CGS columns and reinforcement of adjacent ground. Considering that increase of N value is about 2.1, CGS can be considered as an effective method to increase the bearing capacity as well as to stop the settlement of soft ground. It is also expected to be economic and effective in improvement of ground when it is used in applicable sites.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.12
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• pp.1111-1118
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• 2010

Combustion measurements based on optical techniques have recently become of major interest as tools not only for clarifying the combustion mechanism but also for validating the computational results for the combustion fields. In this study, the particle behavior in turbulent pulverized coal flame are investigated using advanced optical diagnostics. A laboratory-scale pulverized coal combustion burner is specially fabricated as open type in order to apply various optical measurement techniques. The detailed particle behavior is performed by LDV (laser Doppler velocimetry) and SDPA (shadow Doppler particle analyzer). It is observed that the particle mean diameter increase as the distance from burner increases, and this is found to be caused by the decrease of small particles' diameter and increase of large particles' diameter. This is because of result in the char reaction and the particle swelling due to devolatilization, respectively. The size-classified streamwise velocities of pulverized coal particles in the central region of the jet show the same magnitude, whereas those in the outer region are different depending on the particle size. The results show that the velocity and size-classified diameter of the pulverized coal particles in the flame can be measured well by SDPA.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.59-67
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• 2003

In this study, the change in hydraulic conductivity according to the changes in the contact area, aperture, confining pressure and temperature was observed to improve the reliability of the analysis of underground water flow. Also, the mechanical and thermal properties of domestic crystalline rocks in a great depth were obtained. It was found that the averaged intial aperture ranged from 544.33${\mu}{\textrm}{m}$ to 898.62${\mu}{\textrm}{m}$ and it followed a log-normal distribution. The hydraulic conductivity decreased with the increase of normal stress on the fracture surface and the hydraulic conductivity decreased as temperature increased. The change in hydraulic conductivity was strongly correlated with the change in contact area. It was verified by experiments that hydraulic conductivity was inversely proportional to the contact area. The measured mechanical and thermal properties were very close to the existing typical properties of domestic granites.