• Korean Journal of Microbiology
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• v.29 no.6
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• pp.361-370
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• 1991

Physical and chemical environmental factors influencing on the outbreak of freshwater red tide by Peridinium bipes (dinoflagellate) in Soyang Reservoir were studied. Red tide occured in the site of inflowing of tributary streams annually, but the extent and severity of red tide varied from year to year. Several environmental factors such as water level, nutrient releasing from sediment, cyst resuspension, and concentrations of $Ca^{2+}$ and $Mg^{2+}$were studiedin relation to development, extent, and duration of red tide. In June of 1989 and 1991, the red tides of Peridinium bipes were very severe, and these red tides coincided with notable and rapid drawdown of lake water in late spring. Nutrient releasing and cyst resuspension by turbulence during drawdown were suggested as main causes of red tide. The quanity of nutrient releasing from sediment and hydrometeorological factors such as run-off and wind may determine the extent and duration of red tide.

• Particle and aerosol research
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• v.10 no.4
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• pp.155-162
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• 2014

The internal temperature will change depending on operation conditions and material of cyclone dust collector. This study compares the results of collection efficiency and temperature distribution on the different heat flux at wall of dust collector. The previous researcher's experiment results were used to confirm the reliability of CFD(Computational Fluid Dynamics) model. Based on this verified CFD model, we extended the analysis on the cyclone dust collectors. In CFD study, we used RNG k-epsilon model for analysis of turbulence flow, fluid is air, the velocity at inlet is 10 m/s, the temperature of air is $600^{\circ}C$. Because of the difference of outer vortex and inner vortex temperature, the collection efficiency will reduce with the increase of heat flux, showed the highest collection efficiency at heat insulation.

• Environmental Engineering Research
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• v.19 no.2
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• pp.165-174
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• 2014

A model combining multi-dimensional discretized population balance equations with a computational fluid dynamics simulation (CFD-DPBE model) was developed and applied to simulate turbulent flocculation and sedimentation processes in sediment retention basins. Computation fluid dynamics and the discretized population balance equations were solved to generate steady state flow field data and simulate flocculation and sedimentation processes in a sequential manner. Up-to-date numerical algorithms, such as operator splitting and LeVeque flux-corrected upwind schemes, were applied to cope with the computational demands caused by complexity and nonlinearity of the population balance equations and the instability caused by advection-dominated transport. In a modeling and simulation study with a two-dimensional simplified pond system, applicability of the CFD-DPBE model was demonstrated by tracking mass balances and floc size evolutions and by examining particle/floc size and solid concentration distributions. Thus, the CFD-DPBE model may be used as a valuable simulation tool for natural and engineered flocculation and sedimentation systems as well as for flocculant-aided sediment retention ponds.

• Wind and Structures
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• v.13 no.1
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• pp.21-36
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• 2010

A new full scale testing apparatus generically named the Wall of Wind (WoW) has been built by the researchers at the International Hurricane Research Center (IHRC) at Florida International University (FIU). WoW is capable of testing single story building models subjected up to category 3 hurricane wind speeds. Depending on the relative model and WoW wind field sizes, testing may entail blockage issues. In addition, the proximity of the test building to the wind simulator may also affect the aerodynamic data. This study focuses on the Computational Fluid Dynamics (CFD) assessment of the effects on the quality of the aerodynamic data of (i) blockage due to model buildings of various sizes and (ii) wind simulator proximity for various distances between the wind simulator and the test building. The test buildings were assumed to have simple parallelepiped shapes. The computer simulations were performed under both finite WoW wind-field conditions and in an extended Atmospheric Boundary Layer (ABL) wind flow. Mean pressure coefficients for the roof and the windward and leeward walls served as measures of the blockage and wind simulator proximity effects. The study uses the commercial software FLUENT with Reynolds Averaged Navier Stokes equations and a Renormalization Group (RNG) k-${\varepsilon}$ turbulence model. The results indicated that for larger size test specimens (i.e. for cases where the height of test specimen is larger than one third of the wind field height) blockage correction may become necessary. The test specimen should also be placed at a distance greater than twice the height of the test specimen from the fans to reduce proximity effect.

• Journal of the Korean Society for Railway
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• v.15 no.1
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• pp.71-79
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• 2012

The main purpose of this study is to depict the causal relationship among Market Orientation(MO), Marketing Capabilities(MC), and Organizational Performance(OP) with the moderating effect of Environmental Turbulence(ET), especially comparatively highlighting the differences between Korail and Subway firms. Findings show that there partly existed significant interactions effects between ET and MO in case of subway firms, whereas Korail did not reveal any significant results. When considering the strong relationship between MO and MC shown in the subway firms' case, it can be inferred that subway firms continuously have attempted to adapt to the external environment facing them more flexibly and actively over their counterpart, by which the degree of their MC became positively enhanced over Korail. These results give us some implication that MO should be internalized and also MC should get a higher consideration than ever throughout the railway public enterprises in order to strengthen their performance.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.1 no.2
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• pp.105-117
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• 1997

The formation mechanism of the vortex streets in the lee of the mountain is investigated by a three-dimensional numerical model. The model is based upon the hydrostatic Boussinesq equations in which the vertical turbulent momentum flux is estimated by a turbulence parameterization scheme, but the horizontal viscosity is assumed to be constant. The results show that Karman vortex streets can form even without surface friction in a constant ambient flow with uniform stratification. The vortex formation is related to breaking of the mountain wave, which depends on the Froude number (Fr). In the case of a three-dimensional bell-shaped mountain, the wave breaking occurs when Fr is less than about 0.8, while a Karman vortex forms when Fr is less than about 0.22. Vortex formation also depends on Reynolds number, which is estimated from the horizontal diffusivity. The vortex formation can be explained by the wave saturation theory given by Lindzen (1981) with some modification. Simulations in this study show that in the case of Karman vortex formation the momentum flux in the lower level is much larger than the saturated momentum flux whereas it is almost equal to the saturated momentum at the upper levels as expected from the saturation theory. As a result, large flux divergence is produced in the lower layer, the mean flow is decelerated behind the mountain, and the horizontal wind shear forms between unmodified ambient wind. The momentum exchange between the mean flow and the mountain wave is produced by the turbulence within a breaking wave. From the result, well developed vortices like Karman vortex can be formed. The results of the momentum budget calculated by the hydrostatic model are almost the same as nonhydrostatic results as long as horizontal scale of the mountain is 10 km. A well developed Karman vortex similar to the hydrostatic one was simulated in the nonhydrostatic case. Therefore, we conclude that the hydrostatic assumption is adequate to investigate the origin of the Karman vortex from the viewpoint of wave breaking.

• Journal of Environmental Science International
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• v.18 no.8
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• pp.927-932
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• 2009

Wind turbine noise become main environmental problem as wind energy have been installed all around. Noise from large wind turbine give annoyance to listener, moreover it increase loading to whole system by restricting blade tip speed. However accurate noise mechanism of wind turbine is not yet examined. This paper reviewed noise source and analysis theory. Broadband noise if main component of wind turbine noise and airfoil self noise is main noise source. These make acoustic analogy hard to apply for analysis. For this reason, experimental equation is method for wind turbine noise prediction up to now. Spectrum analysis shows that vortex shedding noise exists around $1k{\sim}2k$ Hz. This region is most sensitive frequency range to human. Thus it is necessary to reduce this noise source.

• Wind and Structures
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• v.20 no.6
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• pp.793-810
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• 2015

Tests were conducted at the Florida International University (FIU) Wall of Wind (WOW) to investigate the susceptibility of Variable Message Signs (VMS) to wind induced vibrations due to vortex shedding and galloping instability. Large scale VMS models were tested in turbulence representative of the high frequency end of the spectrum in a simulated suburban atmospheric boundary layer. Data was measured for the $0^{\circ}$ and $45^{\circ}$ horizontal wind approach directions and vertical attack angles ranging from $-4.5^{\circ}$ to $+4.5^{\circ}$. Analysis of the power spectrum of the fluctuating lift indicated that vertical vortex oscillations could be significant for VMS with a large depth ratio attached to a structure with a low natural frequency. Analysis of the galloping test data indicated that VMS with large depth ratios, greater than about 0.5, and low natural frequency could also be subject to galloping instability.

• Environmental Engineering Research
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• v.21 no.1
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• pp.1-14
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• 2016

Flocculation is a widely used phase separation technique in industrial unit processes and is typically observed in many natural flow systems. Advances in colloidal chemistry over the past decades has vastly improved our understanding of this phenomenon. However, in many practical applications, process engineering still lags developments in colloidal science thereby creating a gap in knowledge. While significant progress has been made in environmental process engineering research over the past decades, there is still a need to align these two inter-dependent fields of research more closely. This paper provides a comprehensive review of the flocculation mechanism from empirical and theoretical perspective, discuss its practical applications, and examines the need and direction of future research.

• Wind and Structures
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• v.8 no.4
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• pp.235-250
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• 2005

The paper describes the work of the Working Group on Wind Structure, one of the International Codification Working Groups set up by the International Association of Wind Engineering in 1999. The topics of terrain and exposure, shielding and shelter, topographic effects, tropical cyclone and hurricane wind structure, and thunderstorm wind structure, are described with emphasis on their codification in wind loading codes and standards. Recommendations from the working group are given.