• International Journal of Naval Architecture and Ocean Engineering
• /
• v.12 no.1
• /
• pp.468-478
• /
• 2020

The wave interaction problem with a vertical slotted breakwater, consisting of impermeable upper, lower parts and a permeable middle part, has been studied theoretically. An analytical model was presented for the estimation of reflection and transmission of monochromatic waves by a slotted breakwater. The far-field solution of the wave scattering involving nonlinear porous boundary condition was obtained using eigenfunction expansion method. The empirical formula for drag coefficient in the near-field, representing energy dissipation across the slotted barrier, was determined by curve fitting of the numerical solutions of 2-D channel flow using CFD code StarCCM+. The theoretical model was validated with laboratory experiments for various configurations of a slotted barrier. It showed that the developed analytical model can correctly predict the energy dissipation caused by turbulent eddies due to sudden contraction and expansion of a slotted barrier. The present paper provides a synergetic approach of the analytical and numerical modelling with minimum CPU time, for better estimation of the hydrodynamic performance of slotted breakwater.

• Korean Journal of Hydrosciences
• /
• v.8
• /
• pp.19-30
• /
• 1997

The hydraulics of flow within the covered reach of urban streams is very complicated due to the accumulation and interference effect of eddies around the multipli piers supporting the covering slab. An extensive experimental study is done to quantitatively estimate the backwater rise effect caused by various arrays of multiple piers. The factors governing the backwater rise are found out to be the contraction ratio due to the piers. Foude number of the flow, longitudinal pier spacing, and the length of the covered reach. For a single section of lateral pier arralyzed and a multiple regression equation derived. The effect of multiple piers, arrayed in both lateral and longitudinal directions. on the backwater rise is analyzed in terms of the contraction ratio. Froude number, longitudinal pier spacing and the total length of the covered reach. A multiple regression equation for the backwater rise estimation is proposed based on the experimental data collected in this study.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.25 no.6
• /
• pp.374-385
• /
• 2013

Sediment particle motions have been numerically simulated over a sinusoidal ripple. Turbulent boundary layer flows are generated by Large Eddy Simulation, and the sediment particle motions are simulated using Lagrangian particle tracking method. Two unsteady flow conditions are used in the experiment by employing two different wave amplitudes while keeping other conditions such as wave period same. As expected, the amount of suspended sediment particles is clearly dependent on the wave amplitude as it is increasing with increasing flow intensity. However, it is also observed that the pattern of suspension may be different as well due to the only different condition caused by wave amplitude. Specially, the time of maximum sediment suspension within the wave period is not coincident between the two cases because sediment suspension is strongly affected by the existence of turbulent eddies that are formed at different times over the ripple between the two cases as well. The role of these turbulent eddies on sediment suspension is important as it is also confirmed in previous researches. However, it is also found the time of these eddies' formation may also dependent on the wave amplitude over rippled beds. Therefore, it has been proved that various flow as well as geometric conditions under waves has to be considered in order to have better understanding on the sediment suspension process over ripples. In addition, it is found that high turbulent energy and strong upward flow velocities occur during the time of eddy formation, which also supports high suspension rate at these time steps. The results indicate that the relationship between the structure of flows and bedforms has to be carefully examined in studying sediment suspension at coastal regions.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.24 no.2
• /
• pp.351-373
• /
• 2019

The cold eddies around the Ulleung Basin in the East Sea were identified from satellite altimeter sea level data using the Winding-Angle method from 1993 to 2015. Among the cold eddies, the Dokdo Cold Eddies (DCEs), which were formed at the first meandering trough of the East Korea Warm Current (EKWC) and were pinched off to the southwest from the eastward flow, were classified and their migration patterns were analyzed. The vertical structures of water temperature, salinity, and flow velocity near the DCE center were also examined using numerical simulation and observation data provided by the Hybrid Coordinate Ocean Model and the National Institute of Fisheries Science, respectively. A total of 112 DCEs were generated for 23 years. Of these, 39 DCEs migrated westward and arrived off the east coast of Korea. The average travel distance was 250.9 km, the average lifespan was 93 days, and the average travel speed was 3.5 cm/s. The other 73 DCEs had moved to the east or had hovered around the generated location until they disappeared. At 50-100 m depth under the DCE, water temperature and salinity (T < $5^{\circ}C$, S < 34.1) were lower than those of ambient water and isotherms made a dome shape. Current faster than 10 cm/s circulates counterclockwise from the surface to 300 m depth at 38 km away from the center of DCE. After the EKWC separates from the coast, it flows eastward and starts to meander near Ulleungdo. The first trough of the meander in the east of Ulleungdo is pushed deep into the southwest and forms a cold eddy (DCE), which is shed from the meander in the south of Ulleungdo. While a DCE moves westward, it circumvents the Ulleung Warm Eddy (UWE) clockwise and follows U shape path toward the east coast of Korea. When the DCE arrives near the coast, the EKWC separates from the coast at the south of DCE and circumvents the DCE. As the DCE near the coast weakens and extinguishes about 30 days later after the arrival, the EKWC flows northward along the coast recovering its original path. The DCE steadily transports heat and salt from the north to the south, which helps to form a cold water region in the southwest of the Ulleung Basin and brings positive vorticity to change the separation latitude and path of the EKWC. Some of the DCEs moving to the west were merged into a coastal cold eddy to form a wide cold water region in the west of Ulleung Basin and to create a elongated anticlockwise circulation, which separated the UWE in the north from the EKWC in the south.

• Journal of the korean society of oceanography
• /
• v.39 no.1
• /
• pp.57-71
• /
• 2004

Based on the data obtained under the China-Korea joint project (1997-2001) and historic observations, the distribution, transportation and sedimentation of sediment in the southern Yellow Sea (SYS) are discussed, and the controversial formation mechanism of muddy sediments is also explored. The sediment transport trend analysis indicates that the net transport direction of sediment in the central SYS (a fine-grained sediment deposited area) points to $123.4^{\circ}E,\;35.1^{\circ}N$, which is a possible sedimentation center in the central SYS. The sediment transport pattern is verified by the distribution of total suspended matter (TSM) concentration and ${\delta}^{13}C$ values of particulate organic carbon (POC), the latter indicates that the bottom water plays a more important role than the surface water in transporting the terrigenous material to the central deep-water area of the SYS, and the Yellow Sea circulation is an important control factor for the sediment transport pattern in the SYS. The carbon isotope signals of organic matter in sediments indicate that the Shandong subaqueous delta has high sedimentation rate and the deposited sediments originate mainly from the modern Yellow River. The terrigenous sediments in deep-water area of the SYS originate mainly from the old Yellow River and the modern Yellow River, and only a small portion originates from the modern Yangtze River. The analytical results of TSM and stable carbon isotopes are further confirmed by another independent tracer of sediment source, polycyclic aromatic hydrocarbons (PAHs). Five light mineral provinces in the SYS can be identified and they indicate inhomogeneity in sources and sedimentary environment. The modern shelf sedimentary processes in the SYS are controlled by shelf dynamic factors. The muddy depositional systems are produced in the shelf low-energy environments, which are controlled by some meso-scale cyclonic eddies (cold eddies) in the central SYS and the area southwest of the Cheju Island. On the contrary, an anticyclonic muddy depositional system (warm eddy sediment) appears in the southeast of the SYS (the area northwest of the Cheju Island). In this study, we give the cyclonic and anticyclonic eddy sedimentation patterns.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2003.10a
• /
• pp.339-342
• /
• 2003

Sea level variations and sea surface circulations inthe Korean seas were observed by Topex/Poseidon altimeter data from 1993 through 1997. In sea level variations, the West and South Sea showed relatively high variations with comparison to the East Sea. Then, the northern and southern area in the West Sea showed the range of 20-30cm and 18-24cm, and the northern west of Jeju island and the southern west of Tsushima island in the South Sea showed the range of 15-20cm and 10-15cm, respectively. High variations in the West Sea was results to the inflow in sea surface of Yellow Sea Warm Current (YSWC) and bottom topography. Sea level variations in the South Sea was due to two branch currents (Jeju Warm Current and East Korea Warm Current) originated from Kuroshio Current (KC). In sea surface circulations, there existed remarkably three eddies circulations in the East Sea that are mainly connected with North Korea Cold Current (NKCC), East Korea Warm Current (EKWC) and Tushima Warm Current (TWC). Their eddies are caused basically to the influence of currents in sea surface circulations; Cyclone (0.03 cm/sec) in the Wonsan bay on shore with NKCC, and anticyclone (0.06 cm/sec) in the southwestern area of Ulleung island with EKWC, and cyclone (0.01 cm/set) in the northeastern area of Tushima island with TWC, respectively.

• Korean Journal of Remote Sensing
• /
• v.27 no.3
• /
• pp.235-258
• /
• 2011

The purpose of this study is to investigate climatological variations from the temporal and spatial surface particulate organic carbon (POC) estimates based on SeaWiFS spectral radiance, and to determine the physical mechanisms that affect the distribution of pac in the Gulf of Mexico. 7-year monthly mean values of surface pac concentration (Sept. 1997 - Dec. 2004) were estimated from Maximum Normalized Difference Carbon Index (MNDCI) algorithm using SeaWiFS data. Synchronous 7-year monthly mean values of remote sensing data (sea surface temperature (SST), sea surface wind (SSW), sea surface height anomaly (SSHA), precipitation rate (PR)) and recorded river discharge data were used to determine physical forcing factors. The spatial pattern of POC was related to one or more factors such as river runoff, wind-derived current, and stratification of the water column, the energetic Loop Current/Eddies, and buoyancy forcing. The observed seasonal change in the POC plume's response to wind speed in the western delta region resulted from seasonal changes in the upper ocean stratification. During late spring and summer, the low-density river water is heated rapidly at the surface by incoming solar radiation. This lowers the density of the fresh-water plume and increases the near-surface stratification of the water column. In the absence of significant wind forcing, the plume undergoes buoyant spreading and the sediment is maintained at the surface by the shallow pycnocline. However, when the wind speed increases substantially, wind-wave action increases vertical motion, reducing stratification, and the sediment were mixed downward rather than spreading laterally. Maximum particle concentrations over the outer shelf and the upper slope during lower runoff seasons were related to the Loop Current/eddies and buoyancy forcing. Inter-annual differences of POC concentration were related to ENSO cycles. During the El Nino events (1997-1998 and 2002-2004), the higher pac concentrations existed and were related to high runoffs in the eastern Gulf of Mexico, but the opposite conditions in the western Gulf of Mexico. During La Nina conditions (1999-2001), low Poe concentration was related to normal or low river discharge, and low PM/nutrient waters in the eastern Gulf of Mexico, but the opposite conditions in the western Gulf of Mexico.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.25 no.4
• /
• pp.207-218
• /
• 2013

This study is based on a series of numerical modeling experiments to understand the circulation and its change in the Chunsu Bay (CSB), Yellow Sea of Korea. A skill analysis was performed for the tidal height and tidal current of the observation data using the amplitude and phase of the 4 major tidal constituents respectively for verification of modeling experimental results. As a result, most of the skill score was seen to be over 90%, so numerical model experiment results can be said to be in good agreement with the observed tidal height and tidal current. Tidal wave proceeded from the entrance of the CSB towards inside, and the tidal range gradually increased to the north. It took about 10 to 30 minutes for the tidal wave to reach to northern end. The tidal wave showed a characteristic to rotate counter-clockwise in the southern part. The tidal current flowed to the north-south direction along the bottom topography; the angle of the major axis appeared alongside the isobath. It showed the characteristics of reversing tidal current with the minor axis less than 10% of the major axis. The strength of the tidal residual current that is influenced by geographical factors including bathymetry and coastline showed the range of 1~30 cm/sec, greater in the south channel and smaller in northern Bay. Two pairs of cyclonic/anti-cyclonic eddies around Jukdo and 3~4 pairs of strong eddies at the southern part of CSB in hundreds of m to a few km size by relative vorticity derived from the tidal residual current.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.24 no.2
• /
• pp.179-187
• /
• 2018

In order to understand the flow of currents around Aphae Island and the surrounding Archipelago, the numerical model experiments on tidal currents and tide-induced residual currents were carried out. Dominant semidiurnal tidal currents have a reversing form and flow along the narrow channels of the archipelago. During periods of flood, currents flow from the west of Hwawon Peninsula to the archipelago to the northwest together with the currents flowing from the channels at Palgeum Island to Amtae Island and Amtae Island to Jeung Island. Ebb currents flow from the northwest archipelago to the channel of Amtae Island and Jeung Island as well as Amtae Island to Palgeum Island, further flowing south between Palgeum Island and Hwawon Peninsula. Flood currents are separated from east and west at the southern coast of Aphae Island, but flow south from both the west and east of Aphae Island to the channel found between Palgeum Island and Hwawon Peninsula at ebb. Flow speed is high between Amtae Island and Aphae Island where the flows meet and join. Lee wakes or topographical eddies are formed around the islands due to the high speed of the currents flowing along the narrow channel in the archipelago, manifesting as a tide-induced residual current. A weak cyclonic wake and anti-cyclonic eddy both exist at the west and northwestern coast of Aphae Island individually. The speed of the tide-induced residual current become slow on account of the wide littoral zone at exists around Aphae Island.

• Korean Journal of Remote Sensing
• /
• v.16 no.3
• /
• pp.211-220
• /
• 2000

Even though recurring eddies at the terminal end of the East Korean Warm Current have been identified in the thermal infrared imagery from the NOAA/AVHRR sensor and ocean color data from Orbview-2/SeaWiFS sensor, it is difficult to make observation in the field regarding recurring eddies located around the Wonsan coastal area in North Korea. But we could get in situ data related to an eddy from an ARGOS satellite tracking drifter trapped in the eddy on January 4th, 1999. An ARGOS drifter, a NOAA satellite tracked buoy was trapped by the eddy during January 4th.March 18, 1999. The ARGOS drifter rotated 10 times per 72 days on the edge of the eddy located at $39^{\circ}N$, $129^{\circ}E$. The diameter of the eddy was about 100 km. The horizontal rotation velocity of the recurring cold-core anti-cyclonic eddy was 1.53 km/h(42 cm/sec). The sea surface temperatures of the eddy varied from $14.7^{\circ}C$ on January 5, 1999 to $9.6^{\circ}C$ on March 18,1999. To study the mechanism of the recurring eddy. we tried to find out the relationship between the vector of the drifter moving in the eddy and the wind vector in Sokcho and Ulleung Island located near the eddy in southern Korea, and the difference in sea level between Ulleung Island and Mukho. We hope the results of this study would be useful for calibration and validation data of simulation and numerical modeling studies of the recurring eddy.