• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.1
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• pp.9-20
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• 1989

This paper presents an analysis to predict thermal behaviors of water in ice storage tank during the coldness release process. To deal with complicated transient phenomena due to ice-water phase change and the density inversion, a theoretical model which consists of initial perfectly mixed, stratified and thermal diffusion state was introduced and a criterion on the growth of thermal boundary layer was developed. The analysis includes considerations on the type of ice-making heat exchanger, refrigerator on/off and tank arrangement. Also, discussions on the various parameters and operating conditions which have influence on the performance of the system were made. Finally, simulated results were shown, which agreed with experiments in trends reasonably.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.1
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• pp.65-75
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• 1996

A pilot plant, which is simplified the hot water heating control system of a large scale residential building, is used to investigate the effects of control methods and operating conditions on the system performance and to compare control characteristics. Digital variable structure controller(DVSC) and digital PI controller are implemented to control the speed of the circulating pump for the pilot plant using PC. For the DVSC, a control algorithm is suggested, which using a nonlinear sliding surface and a PID sliding surface outside and inside of output error boundary layer, respectively. Smith predictor algorithm is used for the compensation of long dead time. The suggested DVSC yields improved control performance compared with existing DVSC using linear sliding surface only. the system responses with the suggested DVSC shows good responses without overshoot for various operating conditions and robust under external disturbances compared with digital PI controller.

• 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.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.71-80
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• 2001

In order to consider the sediment layer's effect to total acoustic field, we composed a 3 layered fluid model of 2 sediment layers by adding an additional layer to the Pekeris model and found solutions by using Green's function, boundary conditions and Sommerfeld radiation condition. The modes were divided into discrete modes and virtual modes, and confirmed that the characteristic equation to find discrete modes was same as that of Tolstoy and Clay for normal modes. Also, we confirmed that under similar conditions the 3 layered model showed same results as that of Pekeris model. We believe this 3 layered model can be used to study the sediment's effect on the virtual mode of near field.

• 한국해양학회지
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• v.9 no.2
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• pp.52-58
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• 1974

The water temperature distribution and the water movement closely related with it, in the east side of Korea, was condidered. Special emphasis was paid on the low temperature phenomenon near Ulgi. It was known from the temperature distribution in the east side of Korea that the Tsushima current continues to flow northward at the surface near Sokcho. Also the influence of the cold water extends from the North to the South with increasing depth. The formation of the cold core near Ulgi was explained as due mainly to the existence of the boundary layer near the surface, and partly to the effect of the wind. This inclination of the boundary layer has the value of about 3.0m/Km, and the lower cold current velocity computed using this value lies in the range of those observed by Nishida(1926, 1927). The upwelling velocity was computed approximately as 1.4 10$\^$-3/ cm/sec, and the maximum distance to which the boundarylayer can rise or fall from it's equilibrium position was considered as below 10m.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.15 no.1
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• pp.41-50
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• 2010

We have developed an in-situ benthic chamber (BelcI) for use in coastal studies that can be deployed from a small boat. It is expected that BelcI will be useful in studying the benthic boundary layer because of its flexibility. BelcI is divided into three main areas: 1) frame and body chamber, 2) water sampler, and 3) stirring devices, electric controller, and data acquisition technology. To maximize in-situ use, the frame is constructed from two layers that consist of square cells. All electronic parts (motor controller, pA meter, data acquisition, etc.) are low-power consumers so that the external power supply can be safely removed from the system. The hydrodynamics of BelcI, measured by PIV (particle image velocimetry), show a typical "radial-flow impeller" pattern. Mixing time of water in the chamber is about 30 s, and shear velocity ($u^*$) near the bottom layer was calculated at $0.32\;cm\;s^{-1}$. Measurements of diffusivity boundary layer thickness showed a range of $180-230\;{\mu}m$. Sediment oxygen consumption rate, measured in-situ，was $84\;mmol\;O_2\;m^{-2}\;d_{-1}$, more than two times higher than on-board incubation results. Benthic fluxes assessed from in-situ incubation were estimated as follows: nitrate + nitrite = $0.18\;{\pm}\;0.07\;mmol\;m^{-2}\;d^{-1}$ ammonium $23\;{\pm}\;1\;mmol\;m^{-2}\;d^{-1}$ phosphate = $0.09\;{\pm}\;0.02\;mmol\;m^{-2}\;d^{-1}$ and silicate = $23\;{\pm}\;1\;mmol\;m^{-2}\;d^{-1}$.

• Journal of Korea Water Resources Association
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• v.45 no.4
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• pp.349-360
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• 2012

A horizontally curvilinear non-hydrostatic free surface model that was applicable to three-dimensional viscous flows was developed. The proposed model employed a top-layer equation to close kinematic free-surface boundary condition, and an isotropic k-${\varepsilon}$ model to close turbulence viscosity in the Reynolds averaged Navier-Stokes equation. The model solved the governing equations with a fractional step method, which solved intermediate velocities in the advection-diffusion step, and corrects these provisional velocities by accounting for source terms including pressure gradient and gravity acceleration. Numerical applications were implemented to the wind-driven currents in a two-dimensional closed basin, the flow in a steep-sided trench, and the flow in a strongly-curved channel accounting for secondary current by the centrifugal force. Through the numerical simulations, the model showed its capability that were in good agreement with experimental data with respect to free surface elevation, velocity, and turbulence characteristics.

• The Journal of Engineering Geology
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• v.17 no.4
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• pp.517-523
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• 2007

Geophysical surveys(seismic refraction, electrical resistivity, and ground penetrating radar) were performed to delineate the weathering zone associated with vadose water in Chojeong area and investigate the fault related fracture zones. On the basis of seismic velocity structures, weathering layer for the southwestern part is interpreted to be deeper than for the northeastern part. The depth to bedrock(i.e., thickness of weathered zone) from seismic refraction data attempted to be correlated with drill-core data and groundwater level. As for the investigation of geological discontinuities such as fault related fracture zone, seismic refraction, electrical resistivity, and ground penetrating data are compositely employed in terms of velocity and resistivity structures for mapping of surface boundary of the discontinuities up to shallow depth. Surface boundaries of fracture zone are well indicated in seismic velocity and electrical resistivity structures. Accurate estimation of weathered zone and fracture zone can be successfully available for mapping of attitude of vadose water layer.

• Journal of the Society of Disaster Information
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• v.15 no.1
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• pp.84-97
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• 2019

Purpose: The consolidation settlement of soft ground is dependent on the distribution of pore water pressure which is also affected by hydraulic conductivities (boundary condition) of layers, thickness of clayey soil layer and surcharge. Results: However, the current consolidation analyses are mostly based on Terzaghi's consolidation theory that assumes the initial pore water pressure ratio with depth to be constant. In this study, numerical analysis are carried out to investigate the variation of pore water pressure dissipation with depth and thickness of clayey soil layer, time, surcharge as well as drainage conditions. Conclusion: Comparative study with Terzaghi's consolidation theory is also conducted. The result shows that Terzaghi's consolidation theory should be used with caution unless it is ideally corresponded to the isochrone.

• Journal of Korean Society of Forest Science
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• v.85 no.2
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• pp.210-224
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• 1996

The SLODSVAT consists of interrelated submodels that simulate : the transfer of radiation, water vapour, sensible heat, carbon dioxide and momentum in two canopy layers determined by environmental conditions and ecophysiological properties of the vegetation ; uptake and storage of water in the "root-stem-leaf" system of plants ; interception of rainfall by the canopy layers and infiltration and storage of rain water in the four soil layers. A comparison of the results of modeling experiments and field micro-climatic observations in a spruce forest(Picea abies [L].Karst) in the Soiling hills(Germany) shows, that the SLODSVAT can describe and simulate the short-term(diurnal) as well as the long-term(seasonal) variability of water vapour and sensible heat fluxes adequately to natural processes under different environmental conditions. It proves that it is possible to estimate and predict the transpiration and evapotranspiration rates for spruce forest ecosystems on the patch and landscape scales for one vegetation period, if certain meteorological, botanical and hydrological information for the structure of the atmospheric boundary layer, the canopy and the soil are available.