• Journal of Environmental Science International
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• v.8 no.2
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• pp.151-154
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• 1999

To verify the accuracy of the numerical experiment of Part I, measurements at the matured rice canopy located around Junam reservoir were performed at August 14, 1995. According to the measured data, the foliage temperature recorded the highest value, and the ground temperature was the lowest around noon, and these results coincided with those of the numerical experiment using the combined model of Part I. From the estimation using measured data, the maximum value of the latent heat flux was 380$Wm^2$, the highest value among energy balance terms, and the energy redistribution ratio of the latent heat flux was averaged as 0.5, the highest values among redistribution ratios. These results are the same as those of the numerical experiment in tendency, but they reveals a little lower in the absolute values than those from the numerical experiment.

• Journal of Ocean Engineering and Technology
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• v.20 no.5 s.72
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• pp.23-29
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• 2006

A quasi depth-varying mathematical model for wind-generated circulation in coastal areas, expressed in terms of the depth-averaged horizontal velocity components and free surface elevation was validated and used to understand the diurnal circulation process. The wind velocity is considered as a dominant factor for driving the current. In this paper, three-dimensional numerical experiments that included the land topography were used to investigate the mesoscale air flaw over the coastal regions. The surface temperature of the inland area was determined through a surface heat budget consideration with the inclusion of a layer of vegetation.A series of numerical experiments were then carried out to investigate the diurnal response of the air flaw and wind-generated circulation to various types of surface inhomogeneities.

• Journal of computational fluids engineering
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• v.3 no.1
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• pp.63-72
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• 1998

The numerical simulations of flowfield and pollutant dispersion over two-dimensional hills of various shapes are described. The Reynolds-averaged Wavier-Stokes equations and concentration diffusion equation based on the gradient diffusion theory have been applied to the atmospheric shear flow over the bell-shaped hills which are basic components of the complex terrain. The flow characteristics such as velocity profiles of the geophysical boundary layer, speed-up phenomena, mean pollutant concentration profiles are compared with experimental data to validate the present numerical procedure and it has been found that the present numerical results agree well with experiments and other numerical data. It has been also found that the distributions of ground level concentration are strongly influenced by the source location and height.

• Wind and Structures
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• v.4 no.2
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• pp.119-130
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• 2001

The paper addresses the suitability of wind pressure coefficients specified in contemporary design standards and codes of practice for gable roofs of intermediate slope (roof angle $10^{\circ}-30^{\circ}$). In a recent research study, a series of low building models with different roof slopes in this intermediate range were tested in a boundary layer wind tunnel under simulated open country terrain conditions. This was different from the original study in the 70's, which produced the current provisions on the basis of a model tested only for a single roof slope (4:12) in this range. The results of the study suggest that a modification to the American wind provisions would be warranted to make them more representative of the true local and area-averaged wind loads imposed on gable roofs of intermediate slope.

• Wind and Structures
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• v.16 no.2
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• pp.193-211
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• 2013

This paper presents results from a wind tunnel study that examined the drag coefficient and wind flow over an asymmetric wave train immersed in turbulent boundary layer flow. The modeled wavy surface consisted of eight replicas of a statistically-valid hurricane-generated wave, located near the coast in the shoaling wave region. For an aerodynamically rough model surface, the air flow remained attached and a pronounced speed-up region was evident over the wave crest. A wavelength-averaged drag coefficient was determined using the wind profile method, common to both field and laboratory settings. It was found that the drag coefficient was approximately 50% higher than values obtained in deep water hurricane conditions. This study suggests that nearshore wave drag is markedly higher than over deep water waves of similar size, and provides the groundwork for assessing the impact of nearshore wave conditions on storm surge modeling and coastal wind engineering.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1663-1674
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• 2018

We propose the Poynting vector analysis of the air mode in a top-emitting organic light-emitting diode (OLED) by combining the transfer matrix method and dipole source term. The spatial profiles of the time-averaged optical power flow of the air mode are calculated inside and outside the multilayer structure of the OLED with respect to the thickness of the semi-transparent top cathode and capping layer (CPL). We elucidate how the micro-cavity effect controlled by the thickness variation of the semi-transparent top cathode or CPL affects the internal optical power and absorption loss inside the OLED multilayer and the external optical power coupled into the air. When the calculated absorption loss and external power obtained by the proposed Poynting vector and currently-used point dipole models are compared, two calculation results are identical, which demonstrates the validity of the two models.

• Journal of the Korean Society for Marine Environment & Energy
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• v.4 no.2
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• pp.35-42
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• 2001

We demonstrated the importance of initial estimates of model parameters and the utility of an optimization approach of the uncertain forcing of wind-driven circulation off the southeastern coastal waters of Korea. The wind stress represents the upper boundary condition in this model and enters in the model equation as a forcing term in the numerical formalism. The wind field contributes to maintain the almost time-independent distribution of the upper layer thickness feature in a north-south direction and negative wind stress curl to maintain the formation of warm eddy off the southeastern coastal waters of Korea. Elucidated is the variational characteristics of the East Korean Warm Current due to the variations of the zonally averaged wind stress (southward transport) from the seasonal variations of the meridional transport by the Ekman transport.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.10
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• pp.955-966
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• 2009

DES method is applied to an axisymmetric base flow at supersonic mainstream. The model is based on the Spalart-Allmaras (S-A) turbulence model in the RANS mode, and is based on the subgrid scale model in the Large-eddy simulation (LES) mode. Accurate predictions of the base flowfield and base pressure are successfully achieved by using the DES methodology which is less expensive than LES. Flow properties at the edge of base, such as boundary layer thickness, momentum thickness and skin fraction are compared with Dutton et al [experimental data to proper prediction of base flowfiled. From the present results, The DES accurately resolves the physics of unsteady turbulent motions, such as shear layer rollup, large-eddy motions in the downstream region and small eddy motions inside the recirculating region. Moreover, The present results of using an empirical constant $C_{DES}$ of 1.2 shows good agreement with experimental data than conventional empirical constant $C_{DES}$ of 0.65.

• Wind and Structures
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• v.35 no.1
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• pp.1-20
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• 2022

This research work presents an experimental study's outcomes to reveal the impact of an O-ring on the flow control over a sphere placed in a turbulent boundary layer. The investigation is performed quantitatively and qualitatively using particle image velocimetry (PIV) and dye visualization. The sphere model having a diamater of 42.5 mm is located in a turbulent boundary layer flow over a smooth plate for gap ratios of 0≤G/D≤1.5 at Reynolds number of 5 × 10³. Flow characteristics, including patterns of instantaneous vorticity, streaklines, time-averaged streamlines, velocity vectors, velocity fluctuations, Reynolds stress correlations, and turbulence kinetic energy (), are compared and discussed for a naked sphere and spheres having O-rings. The boundary layer velocity gradient and proximity of the sphere to the flat plate profoundly influence the flow dynamics. At proximity ratios of G/D=0.1 and 0.25, a wall jet is formed between lower side of the sphere and flat plate, and velocity fluctuations increase in regions close to the wall. At G/D=0.25, the jet flow also induces local flow separations on the flat plate. At higher proximity ratios, the velocity gradient of the boundary layer causes asymmetries in the mean flow characteristics and turbulence values in the wake region. It is observed that the O-ring with various placement angles (𝜃) on the sphere has a considerable alteration in the flow structure and turbulence statistics on the wake. At lower placement angles, where the O-ring is closer to the forward stagnation point of the sphere, the flow control performance of the O-ring is limited; however, its impact on the flow separation becomes pronounced as it is moved away from the forward stagnation point. At G/D=1.50 for O-ring diameters of 4.7 (2 mm) and 7 (3 mm) percent of the sphere diameter, the -ring exhibits remarkable flow control at 𝜃=50° and 𝜃=55° before laminar flow separation occurrence on the sphere surface, respectively. This conclusion is yielded from narrowed wakes and reductions in turbulence statistics compared to the naked sphere model. The O-ring with a diameter of 3 mm and placement angle of 50° exhibits the most effective flow control. It decreases, in sequence, streamwise velocity fluctuations and length of wake recovery region by 45% and 40%, respectively, which can be evaluated as source of decrement in drag force.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.2
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• pp.99-110
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• 2010

The DES analysis of strong compressibility flow, LES mode is intentionally performed in boundary layer with the conventional empirical constant $C_{DES}$ value of 0.65. In this study, an expression is suggested to determine the $C_{DES}$ value dynamically by using a distribution function of the ratio of turbulence length scale and wall distance which is used in S-A DDES model for RANS mode protection. The application of the dynamic $C_{DES}$ presents better prediction than previous results those used constant but different $C_{DES}$ values.