• Journal of Navigation and Port Research
• /
• v.31 no.6
• /
• pp.479-484
• /
• 2007

For calculation of wave field for design of coastal and port structures, generally the wind fields from inland observation record or the predicted waves from deep water wave transformation model are being used. However, for the first case, as we should revise the wave data adopting correcting parameters depending on the distance from the coast and location, it is difficult to extract water waves from wind field. Furthermore, for the second case, because of the calculation which executed under very large grid sizes in the wide domain, the simulation(wave transformation) implied uncertainty in the near shore area and shallow region. So it's difficult to obtain exact data from the simulation. Thus, in this study the calculation of wave field on shallow water is accomplished using the observed data of typhoon 'Maemi' in the Korea Eastern South sea. Moreover, for the accuracy of the calculated wave field, we compared and studied the observed data of wave height and direction on the vicinity of the Ulsan waters. It is proved that the results of this study is more accurate than the existing method with showing ${\pm}1.3%$ difference between observed and calculated wave height distribution in Ulsan waters

• Journal of the Korean Association of Geographic Information Studies
• /
• v.18 no.1
• /
• pp.48-63
• /
• 2015

In this study, we introduce various hyperspectral data processing techniques for the monitoring of shallow and coastal waters to enlarge the application range and to improve the accuracy of the end results in Korea. Unlike land, more accurate atmospheric correction is needed in coastal region showing relatively low reflectance in visible wavelengths. Sun-glint which occurs due to a geometry of sun-sea surface-sensor is another issue for the data processing in the ocean application of hyperspectal imagery. After the preprocessing of the hyperspectral data, a semi-analytical algorithm based on a radiative transfer model and a spectral library can be used for bathymetry mapping in coastal area, type classification and status monitoring of benthos or substrate classification. In general, semi-analytical algorithms using spectral information obtained from hyperspectral imagey shows higher accuracy than an empirical method using multispectral data. The water depth and quality are constraint factors in the ocean application of optical data. Although a radiative transfer model suggests the theoretical limit of about 25m in depth for bathymetry and bottom classification, hyperspectral data have been used practically at depths of up to 10 m in shallow and coastal waters. It means we have to focus on the maximum depth of water and water quality conditions that affect the coastal applicability of hyperspectral data, and to define the spectral library of coastal waters to classify the types of benthos and substrates.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.9 no.4
• /
• pp.194-200
• /
• 1997

A two-dimensional shallow-water flow around a cavity driven by a sinusoidally oscillating external flow was studied numerically. A container model of "T" shape was constructed in the numerical computation for comparison with the experimental observation. The numerical computation shows that the aspect ratio of the cavity is not much affecting the overall flow pattern, and for the aspect ratio 2, the deep region of the cavity has a stagnant flow motion. At larger Reynolds number, the flow field is characterized by many small vortices which are not present in the flow visualization. The flow pattern in the external region is in good agreement with the experimentally recorded particle trajectories. It turns out that two large coherent vortices situated in the exterior region of the cavity are responsible for clockwise and counterclockwise drift motions, in large scale, of particles.particles.

• Ocean Science Journal
• /
• v.42 no.2
• /
• pp.103-116
• /
• 2007

Seasonal changes of tide signal(s), temperature, salinity and current were studied during the years 2004-2005 in the northernmost Gulf of Aqaba, which is under developmental activities, to obtain scientific bases for best management and sustainability. Spectrum analysis revealed permanent signals of tide measurements during all seasons, which represented semidiurnal and diurnal barotropic tides. The other signal periods of 8.13, 6.10-6.32, 4.16 and 1.02-1.05 h were not detected in all seasons, which were related to shallow water compound and overtides of principle solar and lunar constituent and to seiches generated in the Red Sea and the Gulf of Aqaba. Spatial and temporal distribution of temperature, salinity and density showed significant differences between months in the coastal and offshore region and no significant differences among the coastal sites, between the surface and bottom waters and between coastal and offshore waters. Therefore, the temporal and spatial variation of water properties in the northernmost Gulf of Aqaba behave similarly compared to other parts. The coastal current below 12 m depth was weak $(3-6\;cms^{-1})$ and fluctuated from east-northeastward to west-southwestward (parallel to the shoreline), which may be related to the effect of bottom topography and/or current density due to differential cooling between eastern and western parts in the study area, and wind-induced upwelling and downwelling in the eastern and western side, respectively. The prevailing northerly winds and stratification conditions during summer were the main causes of the southward current at 6 and 12 m depths with average speed of 28 and $12cms^{-1}$ respectively.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2004.05b
• /
• pp.463-467
• /
• 2004

Rosette-type diffusers with four-ports per riser are constructed in relatively shallow water in Korea. However, the trajectorial bending phenomena due to lower-pressure inside the surrounded buoyant jets on the riser was not considered in most models and was not observed without any experimental results. The buoyant jet behavior affected by the bending effect where there have been growing interests need to be verified experimentally and need to be preceded in the analysis of the characteristics of the buoyant jets oil a riser. The hydraulic model experiments have been carried out to investigate the characteristics of the behavior of horizontal buoyant jets discharged from a Rosette-type riser with four ports as well as single port over a certain range of the experimental conditions including initial momentum and initial buoyancy using LIF (Laser Induced Fluorescence) system to obtain concentration fields. The intensity of the fluorescent light in each pixel on the images obtained from LIF system with the tracer of Rhodamine H was converted to the local dye concentration with a set of calibration procedures to account for the non-uniform distribution of light intensity and the attenuation of light energy by water medium. The experimental results shows that the trajectories from Your ports tend to bend more and more to the inner side with the increase of the densimetric Froude number while the buoyant jet from a single port rises up without any bending phenomena. The previous models, VISJET and Seo et al. (2002), do not simulate the trajectories well except the region before the bending section. This study will focus on the analysis of the behavior of the buoyant jets for mainly a Rosette-type riser by conducting hydraulic model experiments using LIF system.

• Journal of the Korean association of regional geographers
• /
• v.17 no.2
• /
• pp.150-166
• /
• 2011

This study aims to investigate the differences of synoptic characteristics and frontal structures over East Asia according to the main path types of water vapor flux (WVF) of 850hPa surface in cases of the heavy rainfall in the south coastal region of Korea during the Changma season (June and July), In the cases of type A in which the main path of WVF is running from the South china Sea via the South china to the South Sea of Korea, the North Pacific subtropical anticyclone (NPSA) expands to the South China and strong cyclones appear in the Yellow Sea. In cases of type B and C in those the main paths of WVF are running from the South China Sea via the Western Pacific Ocean near Taiwan to the South Sea and from the Western North Pacific Ocean to the South Sea respectively, tropical cyclones appear frequently near Taiwan and the NPSA shifts northward. In the case of type D in which the main path of WVF appear only near the South Sea, strong cyclones appear near the Yellow Sea. In all cases upper jets are intensified in the northern part of the heavy rainfall region and low-level jets appear near the main paths of WVF. In the view of frontal structure, deep active-type of the Changma front is identified in most cases of all types. In this point the Changma season is different from the Baiu season in Western Japan where many cases of shallow active-type of the Baiu front appear.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.56 no.6
• /
• pp.889-898
• /
• 2023

This study was conducted to estimate the abundance of narrow-ridged finless porpoises Neophocaena asiaeorientalis in the West Coast of Korea, where they predominantly inhabit. Sighting surveys were conducted in March and November 2021-2022 using vessels and aircraft during the same time periods and along the same survey transects. The aerial surveys yielded significantly more sightings than shipboard surveys, with 8.5-21.6 times the abundance and 6.3-16.9 times the number of observations. The detection rates were 0.000-0.047 and 0.0103 to 0.539 per km² for shipboard and aerial surveys, respectively. The densities were estimated to be 0.003-0.061 and 0.236-1.898 individuals per km² in the shipboard and aerial surveys, respectively. The shipboard survey conducted in March 2022 and the aerial survey conducted in November 2021 had the highest detection rates and abundance. In the coastal waters, shipboard sighting surveys face numerous challenges due to factors such as fishing gear, islands, and shallow water depths. In contrast, aerial surveys have the advantage of a shorter survey period and are less affected by weather, fisheries, coastal lines, and other variables. Thus, they are highly suitable for studying narrow-ridged finless porpoises in the coastal areas of the West Sea.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.6 no.4
• /
• pp.234-241
• /
• 2001

The degree of saturation of calcium carbonate in the East Sea was calculated from the data obtained from'99 expedition using R/V Roger Revelle. The calcium concentrations in seawaters were estimated from salinity data, and the carbonate ion concentrations were calculated from total alkalinity and pH data. The results suggest that the crossover from the supersaturation to undersaturation for calcium carbonate occur at the depth of approximately 200-400 m for calcite, and 100-300 m for aragonite. Compared to the Pacific and Atlantic oceans, these levels in the East Sea are shallow due to most likely lower temperature of sea water in this region.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.3 no.3
• /
• pp.176-183
• /
• 1991

In this paper. boundary element method is applied to the analysis of nonlinear free surface wave. A particular concern is given to the treatment of the open boundaries at the in-flow boundary and out-flow boundary, which uses the mass-flux and energy-flux considering the continuity of fluid. By assuming the fluid to be inviscid and incompressible and the flow to be irrotational. the problem is formulated mathematically as a two-dimentional nonlinear problem in terms of a velocity potential. The equation(Laplace equation) and the boundary conditions are transformed into two boundary integral equations. Due to the nonlinearity of the problem. the incremental method is used for the numerical analysis. Numerical results obtained by the present boundary element method are compared with those obtained by the finite element method and also with experimental values.

• Journal of the Society of Naval Architects of Korea
• /
• v.39 no.4
• /
• pp.32-41
• /
• 2002

Present study aims to investigate draft effects on hydro-elastic response of pontoon type VLFS(Very Large Floating Structure). A three dimensional higher-order boundary element method(HOBEM: Hong et al;1999, Choi, Hong and Choi; 2001) is extended to analyze elastic response of structures. Intensive numerical calculations were carried out for box type structure to investigate the draft effect on hydrodynamic forces on pontoon type VLFS. Main attention was paid to wave run-up along the waterline for various cases of draft scantling. It is found that the draft effects on the hydro-elastic response of pontoon type VLFS are important especially in short wave range and shallow water region.