• Journal of computational fluids engineering
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• v.18 no.1
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• pp.49-57
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• 2013

Analysis of fluid-structure interaction for two nearby underwater vehicles immersed in the sea is quite challenging because simulation of flow around them is very difficult due to the complexity of underwater vehicle shapes. The conventional approach using body-fitted or unstructured grids demands much time in dynamic grid generation, and yields slow convergence of solution. Since an analysis of fluid-structure interaction must be based on accurate simulation results, a more efficient way of simulating flow around underwater vehicles, without sacrificing accuracy, is desirable. An immersed boundary method facilitates implementation of complicated underwater-vehicle shapes on a Cartesian grid system. An LES modeling is also incorporated to resolve turbulent eddies. In this paper, we will demonstrate the effectiveness of the immersed boundary method we adopted, by presenting the simulation results on the flow around a modeled high-speed underwater vehicle interacting with a modeled low-speed one.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.3
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• pp.386-398
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• 1998

The present experiment is conducted to investigate heat transfer characteristics on the impinging surface with secondary flows around circular nozzle jets. The changed vortex pattern around jet affects significantly the flow characteristics and heat transfer coefficients on the impinging surface. The effects of the jet vortex control are also considered with jet nozzle-to-plate distances and main jet velocities. The vortex pattern around a jet is changed from a convective instability to an absolute instability with a velocity suction ratio of the main jet and the secondary counterflow. With the absolute instability condition, the jet potential core length increases and the heat transfer on the impinging surface is increased by small scale eddies. The region of high heat transfer coefficients is enlarged with the high Reynolds number due to increasing secondary peak values. The effect of suction flows is influenced largely with collars attached the exit of the jet nozzle because the attached collar guides well the counterflow around the main jet.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.4
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• pp.430-436
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• 1997

Time-dependent Flow characteristics of a two-dimensional lid-driven square cavity flow of six high Reynolds numbers, $10^4 2{\times}lO^4., 3{\times}l0^4, 5{\times}lO^4, 7.5{\times}lO^4$ and $10^5$ were investigated. A convection conservative difference scheme based upon SOLA to maintain the nearly 2nd-order spatial accuracy was adopted on irregular grid formation. Irregular grid number is $80{\times}80$ and its minimum size is about 1/400 of the cavity height(H) and its maximum is about 1/53 H. The result shows that at Re= $10^4$, periodic migration of small eddies appearing in corner separation region and its temporal sinusoidal fluctuation are represented. And another critical Reynolds number which shows the commencement of flow randomness emerging from the periodic fluctuation is assumed to be around Re= $1.5{\times}10$. At five higher Reynolds numbers ($2{\times}lO^4., 3{\times}l0^4, 5{\times}lO^4, 7.5{\times}lO^4$ and $10^5$), an organizing structure of four consecutive vortices similar to a Moffat vortex at two lower corners is revealed from time-mean flow patterns.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.673-679
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• 2000

LNG Carriers are currently known as sole commercial means of shipping natural gas on the sea. They are designed to proven dangerous explosion for shipping a lot of gas over long distance. In this study. In this study, a scaled model chamber was made to investigate ventilation characteristics of the hood room in LNG carrier. Experimental study was performed in model using visualization equipments with laser apparatus and image intensifier CCD camera gated by an AOM controller Twelve different kinds of measuring area were selected as experimental condition. Instant simultaneous velocity vectors at whole field were measured by using 2-D PIV system which software adopts two-frame grey-level cross correlation algorithm. To look into stagnation area of hood room for LNG carrier, a three-dimensional numerical simulation with standard ${\kappa}-{\varepsilon}$ model was carried out by using PHOENICS for three kinds of Reynolds number, $6.5{\times}10^3$, $9.7{\times}10^3\;and\;1.29{\times}10^4$, based on the cavity inlet velocity and cavity height. The flow pattern showed the large scale counter-clockwise forced-vortex rotated at center area, small eddies at each corner and stagnation area located at left-back upper side of model.

• Water for future
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• v.27 no.2
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• pp.63-72
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• 1994

In this study, hydraulic characteristics for upstream migration of fish in a pool-and-weir fishway were analyzed through experiment. The results showed that streaming flow was preferable to plunging flow for upstream migration of fish and it was not good to make an orifice beneath the septum since it generates turbulent jet and eddies. Protrusions on the side wall of fishway were preferable to grooves since they decelerate flow velocity and make upstream migration easy. A vertically movable septum was necessary for a flushing of deposited bed material, and net installing over fishway was also needed for birds not to approach the fishway and eat fish.

• Fire Science and Engineering
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• v.15 no.2
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• pp.91-95
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• 2001

Decays of the ceiling jet front velocity under a circular ceiling are investigated. To simulate the ceiling jet in fires He and $N_2$gas were injected from a nozzle to the center of the ceiling. The jet fronts in the form of turbulent eddies were traced by a high-speed camera system. The instantaneous locations of the front were obtained from visual readings of visualized front, and the radial velocity was calculated from the information of the time and the location with respect to the front. The similarity and dimensional analysis were also carried out to reveal the relationship between the velocity decay and the radial distance. It was shown that the radial velocity of the front was inversely proportional to the radial distance in the fully developed region from the experimental results and the theoretical analysis.

• Proceedings of the KSRS Conference
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• 1998.09a
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• pp.64-69
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• 1998

The chlorophyll-a concentration measured by OCTS could be used for observing the physical phenomena such as eddies, fronts, and up welling in the oceans as well as for studying the ecology of phytoplankton. In this study, biological and physical features in the East Sea/Japan Sea (the East Sea) and the Yellow Sea observed by OCTS are analyzed in comparison with other satellite data. And in situ chlorophyll data were compared with OCTS Level 2 chlorophyll data. There was a striking correspondence between the satellite chlorophyll structure and other satellite data in the East Sea in the spring. Very complicated ring structures in the 557 are reflected in chlorophyll structure. In the Yellow Sea, the surface structure was rather simple. While the discrepancies between in situ and OCTS algorithm version 3 chlorophyll were small in the East Sea, those for the Yellow Sea were rather big. Comparison with CZCS data for similar time of the year (May-June) shows that OCTS chlorophyll is higher in general. Although the error is partly due to the fact that NASDA chlorophyll algorithm is an empirical algorithm for case 1 water, how much of this error is also due to the errors in sensor calibration or in atmospheric correction is not clear.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.2 no.4
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• pp.200-207
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• 1990

This study is concerned with the meandering of plume axis in oceanic waters. The process is understood that it is a consequence of the differential contribution by the multiple harmonics of local velocity field to variances of center of mass of crossplume as a function of distance from the source point. A diagnostic model is proposed which is aimed to delineate the eddying motions and furthermore the amplified meandering of plumeaxis. From the data base of dye plumes, wave lengths of meandering eddies are estimated to range between 5.5 to 60.3 (m) in coastal surface waters. A numerical simulation is conducted to predict the concentration field of meandering plume.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.233-237
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• 2007

Recent experimental data shows that an irregular fuel surface pops up during the combustion test. This may contribute to the agitated boundary layer due to blowing effect of fuel vaporization. Blowing effect can be of significance in determining the combustion characteristics of solid fuel within the oxidizer flow. LES was implemented to investigate the flow behavior on the fuel surface and turbulence evolution due to blowing effect. Simple channel geometry was used for the investigation instead of circular grain configuration without chemical reactions. This may elucidate the main mechanism responsible for the formation of irregular isolated spots during the combustion in terms of turbulence generation. The interaction of turbulent flow with blowing mass flus causes to breakup turbulent coherent structures and to form the small scale isolated eddies near the fuel surface. This mechanism attributes to the formation of irregular isolated sopt on the fuel surface.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.6
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• pp.1021-1032
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• 1997

Satellite-tracked drifters deployed in the East Sea since 1991 are used to study the Tsushima Current (TC). It is found that the TC is a steady current with a mean speed of 10 cm/s before it enters the East Sea. Only during the summer, the TC flows along Honshu Island with a mean speed of $30\~40\;cm/s$ and then exits through the Tsugaru Strait. In fall and winter, the TC does not follow the coast along Honshu Island but it enters into the interior of the East Sea before it reaches the Tsugaru Strait. The water that passes the West Channel of the Korea Strait mostly comes from the western East China Sea and spreads into the interior of the East Sea. It also forms the large eddies in the southern East Sea. The outflow through the Tsugaru Strait comes from the interior of the East Sea in all seasons except summer. The mean speed of the Tsugaru Strait outflow is about 60 cm/s. The largest current variability is found in the eastern central area of the East Sea, south of sub-polar front.