Kyu-Nam Hwang

The Laboratory Study on Estimation of Depositional Properties of Kaolinite Sediments on Saltwater Condition

In this study, a series of deposition tests have been conducted on saltwater condition(salinity 32 %o) using an annular flume, in order to estimate depositional properties of kaolinite sediments and to analyze the effect of the initial concentration on them. Total 37 deposition tests have been carried out in three different initial concentrations (1000, 5000, 15000 ppm) with varying the bed shear stress. From these test results, minimum shear stress (or critical shear stress for deposition; ) and the deposition rate parameters () for kaolinite sediments have been quantified, and the effects of the initial concentration and salinity on depositional properties of cohesive sediments have been analyzed qualitatively. As the results, are found to be 0.147, 0.74 and respectively. Through comparing with results from previous studies, the performance of this study and tests results are shown to be good enough to verify.

A Field Report on the Impact of the 2004 Sumatra Tsunami Along the Southeast Coast of India

A field survey to document the event that occurred in the coast of the Andaman and Nicobar Islands, India on December 26, 2004 was undertaken along the Tamil Nadu coast to estimate several items, including the wave run-up height, damage assessment and inundation areas in the different parts of the affected regions. The results of this field survey indicate that the tsunami inundation was heavier in the southern region along the Nagapattinam coast than the northern coast near Chennai; this was most likely due to differences in onshore topography. Consequently, the role of the onshore topography and its relationship with near-shore bathymetry needs to be evaluated in detail in order to prevent future catastrophes.

Using Inclined Walls to Control the Bottom Shear Stress Distribution in an Annular Flume

This study proposes a method to alter secondary flow pattern in a rotating annulus flume and obtain a resulting uniform bottom shear stress distribution along the radial direction by changing the shape of the channel cross section. Two or three wall angles, except for the bottom wall angle, are simultaneously changed up to 25° for different cross-sectional shapes. The flow characteristics in the channel are analyzed using the computational fluid dynamics technique to find the most effective configuration of the walls, including the rotating top ring. The results show that the bottom shear stress decreases and becomes uniform as the outer wall and the top ring angles increase. In the case of the inner wall, the wall angle has little effect on the bottom shear stress. The stress distribution is most uniform when the top ring, the outer wall, and the inner wall angles are 25, 25, and 5°, respectively.

Estimation of Net Flux of Water Mass and Tidal Prism at a Tidal Entrance through Bottom Tracking with ADCP

In this study, the bottom tracking observation in the tidal entrance within Mokpo coast is performed using ADCP in order to estimate net flux of water mass and tidal prism. First of all, observed rawdata was conducted coordinate rotation considering rotation of the cross-section in order to derive the predominant velocity component. And observed rawdata is converted into Sigma coordinate with normalization and blank zone data near the water surface and bottom is interpolated using von-Karman equation. Net flux of water mass is calculated quantitively from the interpolated data, calculated results show that these represent well characteristic of ebb superiority at Mokpo coast as well as change of net flux of water mass with tide. Also, by complementing the definition of tidal prism proposed in past studies, the definition of tidal prism including tidal condition was re-established. Based on the new definition, tidal prism at a tidal entrance using bottom tracking data with ADCP is estimated quantitively for the first time domestically. The results are compared with those for results of previous study, calculated results were in good agreement with previous studies.

An Experimental Study on Depositional Properties of Cohesive Sediments in Masan Port

In this study, a series of deposition tests have been performed using an annular flume in order to estimate depositional parameter of natural sediments. The sediment of Masan Port has been collected for deposition tests, and total 18 deposition tests have been carried out on different bed shear stress respectively but with the same initial concentration. As the results, the minimum bed shear stress , standard deviation and time scale parameter are found to be , 0.54 and 0.87 respectively. Through comparing with results from previous studies for other sediments, the results of this study are shown to be good enough to verify.

Numerical Simulations of Scalar Transport with Fully Derived Diffusion Terms in Sigma-Coordinate

Abstract A two-dimensional numerical model employing a fully transformed σ-coordinate system in the vertical direction is developed to analyze the scalar transport in an estuary. For a preliminary step of developing the numerical model, the influence of a coordinate transformation on the accuracy of the numerical simulation is investigated by comparing the computational results in both z- and σ-coordinates with analytical solutions. In addition, the numerical errors due to the transformation are investigated according as whether the diffusion term is fully derived or not. The numerical accuracy attributable to the full transformation is examined by comparing predicted results with those of the model employing only the partial transformation in a simply sloped topography. Finally, the numerical model developed in this study is applied to the Keum River estuary in Korea, for a salinity intrusion simulation. The calculated results showed good agreement with the observed field data, both of which clearly indicate that the tidal effect on the salinity intrusion are clearly discerned in the estuary.

Estimation of Tsunami Run-up Heights with Parameters

Since many islands are located in the South Sea, unexpected damage by tsunamis could be caused by mutual interferences between adjacent islands. In this study, the variation of run-up heights is investigated by using different crest lengths of incident waves and different distances between two adjacent islands. The run-up height sharply increases when the crest length of Incident waves is greater than the distance bewteen outer boundaries of two islands. The run-up height also increases as the distance between two adjacent islands decreases.