• Ocean and Polar Research
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• v.39 no.3
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• pp.169-179
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• 2017

The "GeoDrifter" is a newly-developed surface drifter with high temporal resolution. It is the first time that high-frequency drifters have been deployed in the East/Japan Sea. The purpose of this study is to introduce the phenomena experienced by these drifters flowing along with the Tsushima Current across the East/Japan Sea, focusing on high-frequency variability, and to discuss them in comparison with previous observations. The observed basin-scale circulation of the Tsushima Current generally coincides well with the known schematic circulation. The GeoDrifter trajectories also show inertial oscillations almost everywhere in the oceanic regions of the East/Japan Sea, strong semi-diurnal tidal currents in the western part of Korea Strait, diurnal currents much stronger than semi-diurnal currents in the upstream region of the Nearshore Branch off the Japanese coast, and many warm eddies in the Yamato Basin, all comparable to the observational results reported in the previous studies. An interesting point is that the semi-diurnal tidal currents undergo a great spatial variation in the western part of the Korea Strait. The observed features that cannot be explained are, among others, strong counter-clockwise motions with oscillating period about 51 hours appearing in the upstream region of the Nearshore Branch off the Japanese coast and the different tidal behaviors between upstream and downstream regions of the latter.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.4
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• pp.295-307
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• 2012

In order to understand the flow properties of the South Sea of Korea, tidal currents, wind-driven currents, density-driven currents and residual flows were investigated by using 3-dimensional numerical model(POM). In offshore regions, tide-induced residual current tends to flow eastward during the spring tide and westward during the neap tide. Total residual flow is irregular due to the bottom topography in the coastal area. The density-driven currents in the coastal area showed to be relatively weak, with little seasonal differences. The special tendency was apparent in the open sea. That is, the flow in the offshore regions showed results similar to that of the Tsushima current. The wind-driven currents in the coastal area showed to be much stronger than in offshore regions. Vertically, the flow of the surface layer was much stronger than that of the bottom layer. Through these results, material transport and diffusion in the south coast, as a basis for predicting the spread of use is expected to be available.

• Ocean and Polar Research
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• v.38 no.4
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• pp.325-330
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• 2016

Partial high frequency bands were allocated to the operation of ocean surface radars that monitor the sea surface currents and waves in WRC-12. On that basis, government-related organizations revised the table of domestic frequency allocation. In order to study radio environments in the allocated bands for ocean radar, tests of the radio signal spectrum were carried at 7-sites using the receiver of the ocean surface radar system operated with a shutdown of the transmitter for 10-60 min. The results showed that no serious radio noises occur at 25 and 43 MHz bands, indicating a good radio environment for the ocean surface radar operation. However, at 13 MHz band, it was difficult to generate stable and confidential data from the ocean surface radar because serious radio noises occurred continuously.

• 한국해양학회지
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• v.30 no.2
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• pp.125-137
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• 1995

CTD, light transmission and tidal current data obtained off the Keum estuary in August, 1991 and 1992 were analyzed to look into the plume movement and the vertical structure of the plume changing with tidal currents. When the river plume was developed by a localized torrential downpour, the initial plume showed a surface lens of low salinity in the section south of the Yeon-Do. The axis of surface lens moved with tidal currents which flows mainly northeastward and southwestward tn the study area and the excursion of the lens axis reached 7 km. The plume during the ebb period showed a symmetric lens structure of low salinity which extends vertically to 3 m below the surface. During the flood period the plume deepened to 6 m below the surface in its northen side forming a sharp salinity front, which results in an asymmetric lens. We suggest that the salinity front with deepened plume moved to the north repeatedly, resulting in temperature increase and salinity decrease in the northern region off the estuary. When the river discharged continuously the large volume over 20 days, the plume forming surface lens extended to the Sybidongpa-Do and deflected to the north.

• Journal of the Korean Society for Marine Environment & Energy
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• v.8 no.3
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• pp.140-147
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• 2005

We investigated the interactions between coastal waters of the Yeongil Bay, Korea, and oceanic waters of the Eastern Sea, as wet 1 as the development mechanism of vertical circulation currents in the bay. The oceanic waters of the bay have an average water temperature of $12.2{\sim}18.4^{\circ}C$ and salinity of $33.32{\sim}34.43$ PSU. Results of spectral analysis have shown that the period of revolution between oceanic and coastal waters is about 0.84-0.91 years in the surface waters and 1.84 years in the bottom layer. The wind direction in the bay shifts between SW and NE, with the main wind direction being SW during the winter period, and water mass movement is influenced by such seasonal variations in wind direction. Vertical circulation currents in the bay are structured by two phenomena: the surface riverine outflow layer from the Hyeong-san River into the open sea and the bottom oceanic inflow layer with high-temperature and salinity into the bay. These phenomena start the spring when the water mass is stable and become stronger in the summer when the surface cold water develops over a 10-day period. Consequently, tidal currents have little influence in the bay; rather, these vertical and horizontal circulation currents play an important role in the transport of the pollutant load from the inner bay to the open sea.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.331-335
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• 2001

This paper presents the self-commissioning for surface-mounted permanent magnet synchronous motor. The proposed strategy executes three tests with a standard inverter drive system. To do this, synchronous d-q axes currents are appropriately controlled for each test. From the three tests, armature resistance, armature inductance, equivalent iron loss resistance, and emf coefficient are identified automatically. The validity of the proposed strategy is confirmed by experimental results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.521-527
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• 2020

In offshore structures, the mean viscous drift force due to drag is considered to be a design part that has not been considered until recently. In particular, it is most important to calculate the drift force acting on a vertical cylinder considering both waves and currents in the low frequency region. This paper presents a process for deriving analytical solutions for the drift forces acting on a fixed vertical cylinder considering waves and currents. The area of the cylinder was considered by dividing it into a splash zone above the free surface and a submerged zone below the free surface. The presence of waves is considered only in the Splash Zone, and in the case of waves and currents, the equations were obtained for both the splash and submerged zones. The results show that drift forces occur due to the significant viscous effects in both the splash zone and the submerged zone. Therefore, the analytical solutions derived in this study can be used to calculate the drift force using the given design variables and form a theoretical basis for judging whether the magnitude of the drift force in each case has a dominant influence within a specific physical range.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.503-509
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• 2020

In offshore floating structures, the viscous mean drift force due to drag is considered a design part that has not been considered until recently. In this paper, an analytical solution for the viscous mean drift forces on a floating vertical cylinder considering the waves and currents was obtained. The area was considered by dividing it into a splash zone above the free surface and a submerged zone below the free surface. In the case of waves, only the splash zone was considered; in the case of waves and currents, equations were obtained in both the splash zone and the submerged zone. The RAO results of previous studies were used to compare the calculated results with the drift forces acting on the fixed cylinder. Except for the case in only waves in the splash zone, the viscous mean drift force acting on the floating cylinder was larger than the drift force acting on the relatively fixed cylinder in most frequencies. In particular, the increase was greater when the currents were considered to be more important. Therefore, these results provide the inference for the viscous drift force due to drag in the design of floating offshore structures.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.371-374
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• 1998

The Scattering of arbitrarily shaped gratings covered with dielectric slab is considered. The total field in each region is expressed in terms of incident field and scattered field by induced currents on the surface of the grating. Some numerical results is presented nd compared with previous ones in cases of several gratings.

• Journal of Environmental Science International
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• v.3 no.3
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• pp.185-195
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• 1994

Masan bay is one of the polluted enclosed bays, which has red tides problem and the formation of oxygen deficient water in the bottom layer. Most important factors that cause eutrophication and red tide is nutrient materials containing nitrogen and phosphorus which stem from terrestrial sources and nutrients released from sediment. Therefore, to improve of water quality, reduction of these nutrient loads should be indispensible. At this study, the three-dimensional numerical hydrodynamic and eutrophication model, which were developed by Institute for Resources and Environment of Japan, were applied to analyze the processes affecting the phytoplankton production and also to evaluate the effect of water quality improvement plans on phytoplankton production. In field sorvey, the range of concentrations of chlorophyll-a at surface area was found to be 29.17 - 212.5mg/m3, which were exceeding eutrophication criteria. The constant currents defined by integrating the simulated tidal currents over 1 tidal cycle showed the counterclockwise eddies in the southern part of Budo. The general directions of constant currents were found to be southward at surface and northward at bottom over all the bay. The eutrophication model was calibrated with the data surveyed in the field area in June, 1993. The calculated results are in fairly good agreement with values within relative error of 30%. The pollutant load from the sources such as the input from terrestrial release from the sediment was reduced by the rate of 50, 70, 90, 98% to effect of phytoplankton production. Phytoplankton production was reduced to of the 90% reduction of the input loads from terrestrial sources and 8% in 90% reduction of the load from sediment.