Hyoseob Kim

Effective Form Roughness of Ripples for Waves

Abstract The effective roughness of ripple beds under a wave regime is investigated. An existing numerical model, KU-2DVW-00, with a mixing length hypothesis is used to simulate the wave boundary layer flow over ripples. The ripple-length-average bed shear stress or form drag friction is obtained from integration of the computed pressure field. The wave friction factor is generally expressed in terms of the ripple profile shape, the ratio between the amplitude of wave orbital velocity, and the representative amplitude of bed shear stress. The effects of three factors, the bed form shape, orbital velocity amplitude over ripple length, ripple steepness on the wave friction factor or form drag are examined. Three bed profiles were tested. Results show that the drag force at the bed for the sharp-crested arc is much larger than for other shapes. The computed bed friction for the sharp-crested shape is about two times larger than that for the sinusoidal shape. Then, the effective roughness for the sharp-crested ripple becomes about 3 times larger than that for the sinusoidal shape. The model results also show that the effective roughness over ripple height is proportional to the ripple steepness up to a limit, and remains almost constant above the limit.

Modelling Siltation at Chukpyon Harbour, Korea

The present paper describes the application of a range of computer models to describe the seasonal variation of seabed bathymetry in the vicinity of Chukpyon Harbour, which is situated on the east coast of Korea. The coastal conditions at the harbour site are dominated by waves and wave-induced currents. Consequently, wave-period-average models were used to predict waves and wave-induced-currents for three wave conditions for two wave directions. A new three-dimensional wave-period-average sediment model was then used to describe particular patterns of seabed change, which were, in turn, combined to predict seasonal changes. Use was made of a variety of field data on waves, currents, and sediment transport rates to set up and calibrate the model. Comparison of model results with field data confirmed the presence of residual sediment movement towards the harbour entrance and the location of shoal zones near the west groyne and east breakwater. The model was subsequently used to study new additions to the existing structures to control nearshore siltation.

Simulation of Seasonal Bathymetric Change at Haeundae Beach with Two Representative Wave Settings

ABSTRACT Kim, H.; Jin, J.Y.; Jang, C.; Yoo, H.J., and Hwang, D.H., 2014. Simulation of seasonal bathymetric change at Haeundae Beach with two representative wave settings. Long-term shoreline position of Haeundae Beach has been quite stable notwithstanding seasonal oscillatory movement. Bathymetry around Haeundae Beach was surveyed on 7 August 2007 and 12 November 2007 by using an echo-sounder, while wave, tide, and tidal current were measured between the two survey days, so that bathymetric change at Haeundae Beach was obtained from the two surveys. According to the surveys the east part of the beach was eroded, and the west part of the beach was accreted. Measured waves from SSE, SE, ESE, E during the period were stronger than measured waves from S, SSW, SW, WSW. A numerical model system CST3D was adopted to reproduce the bathymetric change at Haeundae Beach during the period. Two representative wave settings are chosen for the period as a minimum number to represent the time-series of wave record, based on equivalent sediment flux concept contained in the CERC formula. Wave field, wave-induced force field, wave-induced current field, sediment transport field, and bathymetric change are computed from individual modules, SWAN, WIF, FLOW, SED in CST3D, respectively. Computed bathymetric change agrees reasonably well with measured one. It is believed that selection of two representative wave settings is useful for simulation of seasonal bathymetric change for fairly straight morphology like Haeundae. CST3D is thought to effectively describe overall seasonal sediment transport pattern and consequent bathymetric change at Haeundae Beach.

Regular grids dynamic nesting model TIFLOW-2DN for inter-tidal zones

A technique to combine different size grids in a computational domain is proposed. While existing nesting methods which link two or more grids for hydrodynamic problems cannot treat the inter-tidal zones, the present model can be applied to the areas which repeat dry and wet conditions.