• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.42.3-43
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• 2009

Triplets of identical cubesats will be built to carry out the following scientific objectives: i) multi-observations of ionospheric ENA (Energetic Neutral Atom) imaging, ii) ionospheric signature of suprathermal electrons and ions associated with auroral acceleration as well as electron microbursts, and iii) complementary measurements of magnetic fields for particle data. Each satellite, a cubesat for ion, neutral, electron, and magnetic fields (CINEMA), is equipped with a suprathermal electron, ion, neutral (STEIN) instrument and a 3-axis magnetometer of magnetoresistive sensors. TRIO is developed by three institutes: i) two CINEMA by Kyung Hee University (KHU) under the WCU program, ii) one CINEMA by UC Berkeley under the NSF support, and iii) three magnetometers by Imperial College, respectively. Multi-spacecraft observations in the STEIN instruments will provide i) stereo ENA imaging with a wide angle in local times, which are sensitive to the evolution of ring current phase space distributions, ii) suprathermal electron measurements with narrow spacings, which reveal the differential signature of accelerated electrons driven by Alfven waves and/or double layer formation in the ionosphere between the acceleration region and the aurora, and iii) suprathermal ion precipitation when the storm-time ring current appears. In addition, multi-spacecraft magnetic field measurements in low earth orbits will allow the tracking of the phase fronts of ULF waves, FTEs, and quasi-periodic reconnection events between ground-based magnetometer data and upstream satellite data.

• Journal of the Korean earth science society
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• v.27 no.4
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• pp.425-432
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• 2006

A seismic tomography using refraction waves is applied to provide information on depth of basement rocks and leachate distribution of the Noeun waste landfill site for the stage of preliminary environmental survey. This method is generally applied to civil and environmental areas. Three lines, apparently perpendicular to the potential leachate flow direction in this site, were installed to investigate the waste landfill site in pseudo three dimensional geometry. The results show that the site is composed of 3 layers and depth of basement becomes shallower at the upstream area of the landfill site than that of the downstream area. Moreover, some parts of the second layer and the basement at the down stream area are partially infiltrated by the leachate, probably related to the disturbed distribution of the different velocity materials within the second layer. In Conclusion, refraction wave tomography is found to be one of the most efficient way to investigate waste landfill site.

• Journal of Ocean Engineering and Technology
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• v.22 no.5
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• pp.52-60
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• 2008

This study investigates the applicability of CADMAS-SURF (Super Roller Flume for Computer Aided Design of a MArtime Structure) code basal on the Navier-Stokes solver to predict bore phenomena. The time variation of ware levels and velocities due to the bore propagation were computed for the different bore strength conditions. In order to verify the numerical results by CADMAS-SURF, laboratory experiments were also performed, using the DPIV and LDV measuring system. The numerical results were compared to the experimental data and the analytical predictions by the NSC method basal on fully nonlinear shallow-water theory by the method of characteristics. It appears that the CADMAS-SURF slightly overestimated the water-surface level measured by the laboratory experiments and its discrepancy becomes prominent as the bore strength increases. The predicted propagation speed for a bore was also slaver than that by the experiment and NSC method. However, the temporal variations in velocities were in relatively good agreement with the experimental data for all cases, except for overshooting and undershooting in the front face of a bore, which may be derived from the numerical instability. Further, CADMAS-SURF successfully simulated the decrease in the water level and velocity caused by the effects of negative waves reflected from the upstream end wall.

• 한국해양학회지
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• v.14 no.2
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• pp.71-77
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• 1979

Tidal waves and the fluctuation of current are studied by use of observed data on tidal level, flow velocity and river discharge in the estuarine region of the Nakdong River. Observed data on the tidal level at five stations are used to obtain the fluctuation of amplitude and phase of tides, and the change of the wave speed versus distance from the river mouth. Comnining these tidal data with the vertical distribution of horizontal velocity data, some characteristics of the periodic tidal flow are deduced: (1)Diminishing rates of the tidal amplitude ratio η / η$\_$0/ at high tide were 0.058η$\_$0H/ /Km at neap tides. The constant of phase change, K, was 0.035rad/km. (2)While proceeding landward, the shape of the tidal wave changes from symmetrical to asymmetrical. The traveling speed of the tidal wave crest was estimated to be 3.6∼5.2m/sec, while that of the tidal wave trough was 2.4∼ 3.5m/sec. (3)The flowing speed of the water varies periodically in accordance with the tidal period. The maximum speed of landward flow appeared approximately at two hours before the high tide, while that of seaward flow at two hours before the low tide. (4)The upstream boundary is deduced approximately to be 50km at spring tide and 44km at neap tide from the tidal velocity decreasing. the tidal influence area is estimated approximately to be 65km from the tidal amplitude damping.

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.311-314
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• 2006

The supersonic flow around tandem cavities was investigated by three- dimensional numerical simulations using the Reynolds-Averaged Navier-Stokes(RANS) equation with the $\kappa-\omega$ thrbulence model. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split using van Leer's limiter was used as the numerical method. Numerical calculations were performed by the parallel processing with time discretizations carried out by the 4th-order Runge-Kutta method. The aspect ratio of cavities are 3 for the first cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and $4.5{\times}10^5$, respectively. The characteristics of the dominant frequency between two-dimensional and three-dimensional flows were compared, and the characteristics of the second cavity flow due to the fire cavity flow cavity flow was analyzed. Both two dimensional and three dimensional flow oscillations were in the 'shear layer mode', which is based on the feedback mechanism of Rossiter's formula. However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter's 2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter's 1st mode frequency.

• Journal of Mechanical Science and Technology
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• v.20 no.8
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• pp.1256-1265
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• 2006

The supersonic flows around tandem cavities were investigated by two-dimensional and three-dimensional numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) equation with the k- ω turbulence model. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split with van Leer's limiter was used as the numerical method. Numerical calculations were performed by the parallel processing with time discretizations carried out by the 4th-order Runge- Kutta method. The aspect ratios of cavities are 3 for the first cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and $4.5{\times}10^5$, respectively. The characteristics of the dominant frequency between two- dimensional and three-dimensional flows were compared, and the characteristics of the second cavity flow due to the first cavity flow was analyzed. Both two dimensional and three dimensional flow oscillations were in the 'shear layer mode', which is based on the feedback mechanism of Rossiter's formula. However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter's 2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter's 1st mode frequency.

• Journal of Climate Change Research
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• v.34 no.22
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• pp.9093-9113
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• 2021

This study examines the role of the relative wind (RW) effect (wind relative to ocean current) in the regional ocean circulation and extratropical storm track in the south Indian Ocean. Comparison of two high-resolution regional coupled model simulations with and without the RW effect reveals that the most conspicuous ocean circulation response is the significant weakening of the overly energetic anticyclonic standing eddy off Port Elizabeth, South Africa, a biased feature ascribed to upstream retroflection of the Agulhas Current (AC). This opens a pathway through which the AC transports the warm and salty water mass from the subtropics, yielding marked increases in sea surface temperature (SST), upward turbulent heat flux (THF), and meridional SST gradient in the Agulhas retroflection region. These thermodynamic and dynamic changes are accompanied by the robust strengthening of the local low-tropospheric baroclinicity and the baroclinic wave activity in the atmosphere. Examination of the composite life cycle of synoptic-scale storms subjected to the high-THF events indicates a robust strengthening of the extratropical storms far downstream. Energetics calculations for the atmosphere suggest that the baroclinic energy conversion from the basic flow is the chief source of increased eddy available potential energy, which is subsequently converted to eddy kinetic energy, providing for the growth of transient baroclinic waves. Overall, the results suggest that the mechanical and thermal air-sea interactions are inherently and inextricably linked together to substantially influence the extratropical storm tracks in the south Indian Ocean.

• Journal of Korea Water Resources Association
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• v.45 no.3
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• pp.291-300
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• 2012

We conducted a three-dimensional numerical simulation by using the FLOW-3D, with RANS as the governing equation, in an effort to track the dam-break wave.immediately after a dam break.in areas surrounding where the dam break took place as well as the bed change caused by the dam-break wave. In particular, we computed the bed change in the movable bed and compared the variation in flood wave induced by the bed change with our analysis results in the fixed bed. The analysis results can be summarized as follows: First, the analysis results on the flood wave in the L-shaped channel and on the flood wave and bed change in the movable-bed channel successfully reproduce the findings of the hydraulic experiment. Second, the concentration of suspended sediment is the highest in the front of the flood wave, and the greatest bed change is observed in the direct downstream of the dam where the water flow changes tremendously. Generated in the upstream of the channel, suspended sediment results in erosion and sedimentation alternately in the downstream region. With the arrival of the flood wave, erosion initially prove predominant in the inner side of the L-shaped bend, but over time, it tends to move gradually toward the outer side of the bend. Third, the flood wave in the L-shaped channel with a movable bed propagates at a slower pace than that in the fixed bed due to the erosion and sedimentation of the bed, leading to a remarkable increase in flood water level.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.23-29
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• 2003

Transonic two-phase flow of Saturated humid air, in which relative humidity is 100%, with various condensation processes around thin airfoils is investigated. The study uses an extended transonic small-disturbance(TSD) model of Rusak and Lee [11, 12] which includes effects of heat addition to the flow due to condensation. Two possible limit types of condensation processes are considered. In the nonequilibrium and homogeneous process, the condensate mass fraction is calculated according to classical nucleation and droplet growth rate models. In the equilibrium process, the condensate mass fraction is calculated by assuming an isentropic process. The flow and condensation equations are solved numerical1y by iterative computations. Results under same upstream conditions describe the flow structure, field of condensate, and pressure distribution on airfoil's surfaces. It is found that flow characteristics, such as position and strength of shock waves and airfoil’s pressure distribution, are different for the two condensation processes. Yet, in each case, heat addition as a result of condensation causes significant changes in flow behavior and affects the aerodynamic performance of airfoils.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3B
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• pp.205-209
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• 2011

The low carrying capacity caused by the deposition in a sewer line is one of the main reason of the urban flood. Therefore, an efficient maintenance and management of the storm water drainage system is very important to prevent urban flood. In this research, the sediment transport characteristics through a pressure pipeline were examined with laboratory experiments. Bed-forms in a pipeline, sediment rates, roughness due to sediments were examined. Experimental system consists of flow circulation system with a pump and a sediment feeder at the upstream of the pipeline. Sediments were supplied into a 60 mm-diameter and 8 m-long pipe. Maximum flow rate is $30m^3/hr$, and the sediment feeding rate range is 5 g/s~19 g/s. Governing parameters and estimation equation for sediment transport rate were developed. The mean velocity (U), coefficient of viscosity (${\mu}$), unit width bed load ($q_b$), mean diameter of particle ($d_{50}$), unit weight of sediment in water (${\gamma}^{\prime}_s$) were adopted as the most influencing factors of sediment transport patterns. The prediction equation for sediment transport rate were developed with two dimensionless terms. These two dimensionless terms showed a linear relationship with high correlation coefficient.