Kyung Tae Jung

Internal solitary wave transformation over a bottom step: Loss of energy

In this paper, we extend the numerical study of Maderich et al. [“Interaction of a large amplitude interfacial solitary wave of depression with a bottom step,” Phys. Fluids 22, 076602 (2010)10.1063/1.3455984] on the interaction of an interfacial solitary wave with a bottom step, considering (i) the energy loss of solitary waves of both polarities interacting with a bottom step and (ii) features of the transformation of a large-amplitude internal solitary waves at the step. We show that the dependence of energy loss on the step height is not monotonic, but has different maximum positions for different incident wave polarities. The energy loss does not exceed 50% of the energy of an incident wave. The results of our numerical modeling are compared with some recent results from laboratory tank modeling.

Tidal regime change due to the large scale of reclamation in the west coast of the Korean Peninsula in the Yellow and East China Seas

ABSTRACT Kang, S.K., Jung, K.T., J.J. Park, Kim, E.J., and So, J.K., 2013. Tidal Regime Change of the Large Scale of Reclamation in the West Coast of the Korean Peninsula in the Yellow and East China Sea. A depth-averaged two-dimensional numerical model has been established in order to investigate tidal regime change by the large scale of reclamation in the west coast of Korean Peninsula. The fetched variable-grid system was used to discretize the complicated coastal region efficiently. Maximum six month integration of the model was carried to investigate the tidal change over 10 tidal components prescribed along the open boundaries consisting of the Ryuku Islands, Korea Strait, and Tiwan Strait. The tidal regime change appears widely in the whole Yellow Sea and its effect reaches to the shelf break region in the East China Sea. The Kelvin-wave type distribution of tidal amplitude along the west coast of KP is distorted and the propagation speeds of semi-diurnal and diurnal tidal waves increase around the reclamation and neighboring regions. The change of the propagation speed after reclamation seems to be due to weaker lateral friction by simplification of the land boundary. The tidal amplitudes decrease within several tens of km just around the reclamation area, while the amplitudes outside the region increase slightly. Such decreasing or increasing patterns appear alternatively. This implies that the change of tidal regime propagates toward the remote region far away from the reclamation site. Therefore, prescription of tidal components as open boundary condition should be carefully determined after considering any possible tidal regime change near the boundaries by reclamation of an inner model domain. The model result also confirms that friction at the lateral boundary affects the propagation of tidal waves as much as the bottom-friction effect.

Oil spreading in instantaneous and continuous spills on rotating earth

The effect of the Coriolis force on the oil spill spreading in the gravity-viscous regime is examined. A new shallow water model for the transport and spreading of oil slick of arbitrary shape is described in which the Coriolis force is included in the momentum equations and the oil–water friction is parameterized in a frame of the boundary layer theory including the Ekman friction. The numerical Lagrangian method based on smoothed particle dynamics is described. New similarity solutions of the model equations are obtained for unidirectional and axisymmetric spreading in gravity-viscous, gravity-turbulent and gravity-viscous-rotational regimes for instantaneous as well as continuous releases. The numerical simulation extends these results for the case of continuous release in the presence of currents. It was shown that Coriolis term in the momentum equation can be omitted if slick thickness is much less of the laminar Ekman layer thickness. However, the Ekman friction should be retained for slicks of any thickness for larger times. The Ekman friction results in the essential slowdown of the spreading as well as in the deflection of the oil spreading velocity at 45° from the direction of velocity in the non-rotation case. Numerical simulations of large-scale spills showed that after the 2xa0days the slick area with the Coriolis effect was approximately less than half of that without rotation. Therefore, the earth rotation can be also important in the oil weathering.

Internal breather-like wave generation by the second mode solitary wave interaction with a step

The transformation of an internal second mode solitary wave over a bottom step in a computational tank filled with a three-layer stratified fluid was studied. The convex waveforms were generated by a collapse mechanism for stratification with a thin mid-layer. The wave transformation depends on the blocking parameter B which is a ratio of the amplitude of the incident wave to the thickness of the lower water layer over the step. Three regimes of second mode wave transformation over the step are identified. In regime I (2 6. In regime II (0.5 < B < 2) the mode-2 wave is permanently disintegrated, generating a chain of waves of mode-1 ahead of wave of mode-2 and tail of short waves of mode-1 behind the wave. In regime III (B < 0.5) only waves of elevation of mo...

Swell Prediction for the Korean Coast

ABSTRACT Yuk, J.-H.; Kim, K.O.; Jung, K.T., and Choi, B.H., 2016. Swell prediction for the Korean coast. The accurate prediction of abnormally high waves occurring in the East Sea during winter is important in terms of the prevention of coastal disasters along the east Korean coast. This study attempts to hindcast the abnormally high swell wave events that occurred in October 2006 and February 2008 using the unstructured grid wave model UnSWAN with high-resolution reanalysis data from the European Centre for Medium-Range Weather Forecasts as meteorological inputs. The model used in this study incorporates an additional weighting factor for the relative wave-number in dissipation source term to improve swell propagation and wave period. Wave heights and periods are well reproduced compared with the observational data. Examination of the meteorological data and model results shows that the abnormally high waves in October 2006 were induced by the overlap of a swell wave and a wind-generated wave with nearly the same heading directions; the wave generated in February 2008 was, however, induced by the swell that propagated over very long distances from the northeastern area of the East (Japan) Sea due to enhanced atmospheric low pressure. Use of the reanalysis meteorological data and a wave model equipped with a weighting factor is found to be useful in identifying the generation mechanisms as well as reasonable estimates of abnormally high wave events.

Three-dimensional simulation of 2011 East Japan-off Pacific coast earthquake tsunami induced vortex flows in the Oarai port

ABSTRACT Kim, K.O., Choi, B.H., Pelinovsky, E. and Jung, K.T., 2013. Three-dimensional simulation of 2011 East Japan-off Pacific coast earthquake tsunami induced vortex flows in the Oarai port. The huge tsunami was generated by the 11 March 2011 off coast of the Pacific side of East Japan, recording a maximum 40 meter run up in Iwate prefecture. The tsunami wave attacked the Oarai port of Ibaraki prefecture within 30 minutes, and created an enormous vortex flow within the harbor. A similar feature was observed in the Imwon port, in the Eastern Korean coast during the 1983 tsunami event in the East (Japan) Sea. A set of simulations have been performed to investigate the generation of the powerful vortex caused by the 2011 tsunami event at the Oarai Port. The application of numerical models has successfully reproduced the formation of the vortex in the center of the port, which can be clearly identified in a photograph taken during the tsunami. The simulation of tsunami generation and propagation at the outer sea is performed with a hydrostatic model and, for the investigation of a more detailed transient pattern of water flows, the model which uses full Reynolds-averaged Navier–Stokes equations is applied. Examination of the Oarai and Imwon vortexes implies that the generation and strength of a vortex due to tsunami wave is strongly related in the size and the shape of port and breakwater layouts. The present work indicates that time-variation the inflow through the mouth of a harbor controls the transient pattern of the vortex.

Propagation of a tsunami wave generated by an earthquake in the Nankai Trough onto the South Korean coast

ABSTRACT Kim, K.O., Jung, K.T. and Choi, B.H., 2013. Propagation of a tsunami wave generated by an earthquake in the Nankai Trough onto the South Korean coast. The earthquake of magnitude 9.0 that occurred in March 2011 and the ensuing crisis at the Fukushima Daiichi nuclear power plant prompted sweeping reviews of Japans disaster preparedness and criticism over apparent failures to take into account potential risks. Based on studies conducted after the catastrophes, the Japanese government revised its tsunami projections in a report posted on a government website. While the earlier forecast in 2003 put the potential maximum height of a tsunami runup at less than 20 m, a governmental panel of experts in Japan recently reported that the occurrence of a magnitude-9.0 earthquake in the Nankai trough, which runs east of Japans main island of Honshu to the southern island of Kyushu, might generate a tsunami runup with a height of more than 34 m, which would inundate much of Japans Pacific coast. A chronicle of Cheju Island (Tamraji) reports that a tsunami was propagated by the 1707 Hoei earthquake. The tsunami from the 2011 earthquake event was also propagated to the southern shore of Korea. In this study, we conducted a numerical simulation of the propagation of the tsunami from Japans Pacific coast to the southern shore of the Korean Peninsula. Simulation results are presented for 11 scenarios of initial water displacement identified by the Japanese government. The simulation results indicate that after an earthquake in the Nankai Trough, tsunami waves would reach Cheju Island in approximately 3.5 hours and the southern coast of Korea in approximately 4 hours, with a maximum runup height of approximately 1.5 m.

Migration of radioactivity in multi-fraction sediments

A new 3D radioactivity transport model coupled with multiscale circulation and multi-fractional sediment transport modules is presented. The sediment transport module simulates the transport of a mixture of one cohesive sediment fraction and a number of fractions of non-cohesive sediments of different sizes and densities. The model of radionuclide transport describes the key transport and exchange processes in the system of water-suspended and bottom multi-fraction sediments. Two-step kinetics with two successive reversible fast and slow reactions is used in the model. A noticeable feature of the model is approximation of the sediment and contamination profiles in the bed by multiple well-mixed layers to describe the vertical migration of radioactivity within bottom sediments due to erosion/deposition, molecular diffusion and bioturbation. The model accurately reproduced a laboratory experiment on the uptake of radiocesium by lake sediments. An analytical solution describing mutual adjustment of the concentrations of radioactivity in the pore water and in the multi-fraction sediment showed that activity was redistributed between different fractions of sediments far slower than between water and the total concentration in the sediment. The extended one-layer model of bottom contamination of multi-fraction sediments was derived from a general model and compared with a multi-layer model. It was found, however, that the one-layer approximation was not capable of correctly predicting the inventory due to the fact that one-layer averaged concentration can essentially differ from the near-surface value in the multi-layer model. Radionuclide transport in channel with bottom depression was simulated to estimate the effects of erosion/deposition and the multi-fractionality of sediments on the transport process. It was shown that these factors affect the distribution of sediments by forming local maxima and minima of activity at the beginning and end of the depression, respectively, due to the redistribution of contaminated bottom sediments by flow. The developed model can also be used to simulate the transport of a wide class of toxic substances sorbed on sediments.

3D numerical model of ecohydrodynamics for shallow waters

ABSTRACT Bezhenar R.; Jung K.T.; Maderich V., and Kim K.O., 2016. 3D numerical model of ecohydrodynamics for shallow waters. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 820–824. Coconut Creek (Florida), ISSN 0749-0208. A new modeling system for the calculation of ecohydrodynamics in shallow water bodies is developed. It consists of three interacting components: hydrodynamics, sediment transport and ecodynamics. The system takes into account changes in the light absorption in the water due to presence of phytoplankton and suspended sediments as well as in the bottom friction due to presence of bottom vegetation. The bottom friction in turn affects the currents and turbulence that govern the transport and dispersion of nutrients which are necessary for the growth of phytoplankton and bottom vegetation. The turbulent mixing influences the resuspension of sediments that changes absorption of light in the water, affecting the bottom vegetation growth. The influence of model feedbacks on the biochemical characteristics of shallow Lake Markermeer (the Netherlands) was studied. Results of modeling show good quantitative agreement with measurements of temperature, nutrients, and dissolved oxygen. Good qualitative agreement of bottom concentration of periphyton with measured field of bottom plants was also obtained.

Swell Propagation Caused by Typhoon Passage to the Yellow and East China Seas

ABSTRACT Kim, K.O.; Yuk, J.-H.; Jung, K.T., and Choi, B.H., 2017. Swell propagation caused by typhoon passage to the Yellow and East China Seas. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 144–148. Coconut Creek (Florida), ISSN 0749-0208. Typhoons generate big swells frequently propagating over the East China Sea, the wide continental shelf sea with depth shallower than 200 m. The characteristic features of swell propagation into the Yellow and East China Seas caused by typhoon Herb in 1996 has been investigated applying a ray-tracing technique and a spectral wave model (SWAN) with an unstructured-mesh grid system. This study discusses the generation and propagation of the swells into the Yellow and East China Seas using the integration of ray trajectories and model-based simulated wave. Calculated and observed wave heights and periods at Gadeokdo, Korea are found to be in reasonable agreement with each other.