• Journal of Ocean Engineering and Technology
• /
• v.24 no.6
• /
• pp.23-29
• /
• 2010

Korean shipbuilding companies have sometimes carried out sea trials to measure a vessel's speed performance around the western channel of the Straits of Korea, where the flow fields are very complicated because of the effect of various flows such as sea, tidal, geostrophic, and wind-driven currents. Because these flows seem to present significant interference to a ship, the numerical reproduction of the flow-fields in the vicinity of the target sites could provide a better understanding of the sea environments while performing sea trials. In this study, we used the MEC ocean model to simulate the tidal currents around Tsushima Island and compared the simulated tidal amplitudes and currents with the measurements of Teague et al. (2001). The tidal amplitudes of the present simulation results agreed well with the observations. Based on the numerical simulation, the optimal direction and proper sites for a speed trial are described.

• Proceedings of the KSRS Conference
• /
• 2007.10a
• /
• pp.22-24
• /
• 2007

Waterline extraction is the one of widely used methods for studying changes in tidal flat environment and coastlines using multi-temporal optical images such as Landsat TM and Landsat ETM+. High dynamics of tidal currents and land reclamation which accelerate sedimentation and/or erosion cause waterline change in tidal flats. The amount of sediment deposited or eroded can be evaluated by precisely estimating waterline changes in tidal flats. The objective of this study is to detect the change of waterlines during 17 years and analyze the trends of erosion and sedimentation in the study areas. The Ganghwado tidal flat on the west coast of the Korean Peninsula was selected. The study area is famous for high dynamics of tidal currents and vast tidal flats. Land reclamation which has been carried out on a large scale is also considered as one of elements that have accelerated the environmental changes in this tidal flat. In this study, we acquired 26 waterlines from Landsat TM and Landsat ETM+ images. We extracted the waterline from each satellite image to generate a digital elevation map (DEM) which was used for reference and to compare with the other waterline which was extracted from DEM having a same tide. The result of comparison well depicted the areas of dominant sedimentation and erosion, and general trends of sedimentation and erosion according to sub-regions are also revealed during the investigation time. Results showed that erosion during a decade was dominant at the west of the Southern Ganghwado tidal flat, while sedimentation was dominant at the wide channel between the Southern Ganghwado tidal flat and the Yeongjongdo tidal flat. This area has been commonly affected by high currents and sedimentation energy. Although we were not able to verify the accuracy of the waterline changes, this result clearly showed the waterline change and therefore, the waterline extraction method used in this study has proven as an effective tool for long term tidal change estimation.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.6 no.4
• /
• pp.421-438
• /
• 1994

Vertical distribution of tidal currents in the Korea Strait is computed by a tree-dimensional tidal model. The results are presented in the from of tidal charts (coamplitude and cophase chart) and (tidal ellipses charts for eight tidal constituents (M$_2$, S$_2$, $N_2$, $K_2$, $K_1$, $O_1$, P$_1$, Q$_1$) and of harmonic constants for predictions of tides and tidal currents during specified duration in the region. The computed tides were in general agreement with coastal observations and observation-based tidal charts of Odamaki (1989). Comparison between model computation and current observation by RIAM were also presented.

• Ocean and Polar Research
• /
• v.42 no.3
• /
• pp.211-223
• /
• 2020

With the increasing demand for improved marine environments and safety, greater ability to minimize damages to coastal areas from harmful organisms, ship accidents, oil spills, etc. is required. In this regard, an accurate assessment and understanding of current systems is a crucial step to improve forecasting ability. In this study, we examine spatial and temporal characteristics of current systems in the adjacent seas of Jeju Island using a high-resolution regional ocean circulation model. Our model successfully captures the features of tides and tidal currents observed around Jeju Island. The tide form number calculated from the model result ranges between 0.3 and 0.45 in the adjacent seas of Jeju Island, indicating that the dominant type of tides is a combination of diurnal and semidiurnal, but predominantly semidiurnal. The spatial pattern of tidal current ellipses show that the tidal currents oscillate in a northwest-southeast direction and the rotating direction is clockwise in the adjacent seas of Jeju Island and counterclockwise in the Jeju Strait. Compared to the mean kinetic energy, the contribution of tidal current energy prevails the most parts of the region, but largely decreases in the eastern seas of Jeju Island where the Tsushima Warm Current is dominant. In addition, a Lagrangian particle-tracking experiment conducted suggests that particle trajectories in tidal currents flowing along the coast may differ substantially from the mean current direction. Thus, improving our understanding of tidal currents is essential to forecast the transport of marine pollution and harmful organisms in the adjacent seas of Jeju Island.

• Journal of Advanced Marine Engineering and Technology
• /
• v.33 no.8
• /
• pp.1275-1280
• /
• 2009

Tidal currents were observed at 1 station of artificial reefs group during 15days. Maximum current was 82.4cm/s, and mean current showed 12.8~28.0cm/s, respectively. Flood currents magnitude were bigger than ebb ones due to wake region. To grasp sediment distributions, sediments were sampled at 4-direction(E, W, S, N) around each station. According to the results of sample analysis, sediments showed different distribution by main current direction. It showed that sediments distribution at front and back of artificial reefs were differently occurred by change of main current direction. It suggest that artificial reefs need to install after confirming tidal currents direction and sediments type.

• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.8
• /
• pp.856-862
• /
• 2015

Tidal current energy is an important alternative energy resource among the various ocean energy resources available. The tidal currents in the South-Western sea of Korea can be utilized for the development of tidal current power generation. Tidal power generation can be beneficial for many fishing nurseries and nearby islands in the southwest region of Korea. Moreover, tidal power generation is necessary for promoting energy self-sufficient islands. As tidal currents are always available, power generation is predictable; thus, tidal power is a reliable renewable energy resource. The selection of an appropriate hydrofoil is important for designing a tidal current turbine. This study concentrates on the selection and numerical analysis of four different hydrofoils (MNU26, NACA63421, DU91_W2_250, and DU93_W_210LM). Blade element momentum theory is used for configuring the design of a 50 W class turbine rotor blade. The optimized blade geometry is used for computational fluid dynamics (CFD) analysis with hexahedral numerical grids. Among the four blades, NACA63421 blade showed the maximum power coefficient of 0.45 at a tip speed ratio of 6. CFD analysis is used to investigate the power coefficient, pressure coefficient, and streamline distribution of a 50 W class horizontal axis tidal current turbine for different hydrofoils.

• 한국해양학회지
• /
• v.20 no.1
• /
• pp.56-73
• /
• 1985

The three-dimensional hydrodynamic numerical model of the Yellow Sea and the East China Sea has been further utilised to provide S$\sub$2/,K$\sub$1/,O$\sub$1/ tidal currents distribution in addition to previously provided M$\sub$2/ tidal current distribution(Choi, 1984), especially the vertical variation of horizontal current in the region. Model results have been compared with current meter data acquired from recent China-USA Marine Sedimentation Dyamics Programme (Larsen and Cannon, 1983). Results were also used to provide maps of the S$\sub$2/,K$\sub$1/,O$\sub$1/ tidal current constants and tidal ellipses at three depths to complement previous M$\sub$2/ tidal current information.

• Proceedings of the KSRS Conference
• /
• v.2
• /
• pp.692-694
• /
• 2006

X-SAR images taken on the coastal waters of Hwanghe province in Korea during SIR-C/X-SAR campaign in April and October 1994 are analysed. The SAR images show the peculiar signatures like nail marks, curved long string, and vortex streets patterns and they all seem to be produced by strong interactions between the topography in the coastal waters and tidal currents. The nail mark signatures are located at the same position of small scaled sand banks and the curved line patterns are almost identical to the outer boundary of large sand banks. Based on the tidal record, all the three images are taken at the almost same phase of tidal cycles, which are close to the low tide. It seems that bottom shapes are more strongly appeared on the SAR images when the tidal currents are slow. The front between two different current velocities caused by the flows along the steep boundaries of sandbanks is also the main factors imprinting the bottom features to the sea surface SAR images

• Journal of the Korea Institute of Military Science and Technology
• /
• v.14 no.2
• /
• pp.189-197
• /
• 2011

As a multidisciplinary study encompassing oceanography and history, we have attempted to reanalyze the course of a historical navel battle, Myungryang Naval Battle(September 16th, 1597 according to the lunar calendar) through hindcasting the paleo-tidal currents and -tides(PTC). Firstly, we conducted harmonic analysis using 6-month current data observed at Uldolmok and 1-year elevation data provided by Korea Ocean Research and Development Institute in order to understand their characteristics and to hindcast the PTC. Observation results show that Uldolmok, ~300m wide, relatively narrow channel, is characterized by a flood-dominant mixed mainly semidiurnal tidal regime induced by relatively-strong shallow water constituents, showing closely a standing wave type of tidal current. Further, we hindcasted PTC on the day of Myungryang Naval Battle. Our results were compared and discussed with results(time and speeds of maximum(flood and ebb) currents and high and low water times) of the previous studies estimated from different methods. Lastly, we reconstruct the course of the event of Myungryang Naval Battle recorded in the Admiral Sun-Sin Yi's War Diary(Nangjung Iigi in Korean) based on our hindcasting results.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.4 no.3
• /
• pp.146-155
• /
• 1992

It has been conventional to treat the land boundary as a fixed one in numerical modeling of tidal flows, particularly in the finite element scheme. However conventional models using the fixed land boundary result in unrealistic tidal flows in inter-tidal zones which exist over wide coastal area in Korea. In this study, a 2-dimensional hydrodynamic model, using finite element method for moving boundary problems was developed. The performance of the model was tested in a rectangular channel with an open boundary at one end and a moving boundary at the other end. The model was applied to calculate the tidal currents in Maro Hae, located in the southwestern part of Korea where wide tidal flats develop. The behavior of tidal currents in the Udolmok and near the tidal flats in the study area was satisfactory when compared with the observed data. Variation of tidal currents due to the construction of Kochunam sea-dyke which barrages large area of tidal flat was presented. The results of this study confirm the efficiency of moving boundary treatment in coastal numerical models.