• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.24 no.2
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• pp.282-297
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• 2019

Detection of mesoscale oceanic eddies using satellite data can utilize various ocean parameters such as sea surface temperature (SST), chlorophyll-a pigment concentration in phytoplankton, and sea level altimetry measurements. Observation methods vary for each satellite dataset, as it is obtained using different temporal and spatial resolution, and optimized data processing. Different detection results can be derived for the same oceanic eddies; therefore, fundamental research on eddy detection using satellite data is required. In this study, we used ocean color satellite data, sea level altimetry data, and infrared SST data to detect mesoscale eddies in the East Sea and compared results from different detection methods. The sea surface current field derived from the consecutive ocean color chlorophyll-a concentration images using the maximum cross correlation coefficient and the geostrophic current field obtained from the sea level altimetry data were used to detect the mesoscale eddies in the East Sea. In order to compare the eddy detection from satellite data, the results were divided into three cases as follows: 1) the eddy was detected in both the ocean color and altimeter images simultaneously; 2) the eddy was detected from ocean color and SST images, but no eddy was detected in the altimeter data; 3) the eddy was not detected in ocean color image, while the altimeter data detected the eddy. Through these three cases, we described the difficulties with satellite altimetry data and the limitations of ocean color and infrared SST data for eddy detection. It was also emphasized that study on eddy detection and related research required an in-depth understanding of the mesoscale oceanic phenomenon and the principles of satellite observation.

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.133-136
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• 2006

The mesoscale eddy field in the North Pacific Ocean, simulated by a high resolution eddy-resolving OGCM ($1/12^{\circ}C$ horizontal resolution), was analyzed, and compared with satellite altimetry data of TOPEX/Poseidon. High levels of eddy kinetic energy (EKE) appear near the Kurosho, North Equatorial Current (NEC), and Subtropical Countercurrent (STCC) in the western part of the subropical gyre. In particlure, it was found that the EKE level of the STCC has a well-defined annual cycle, but no distinct annual cycle of the EKE exists in any other zonal current of the North Pacific Ocean.

• Ocean and Polar Research
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• v.23 no.1
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• pp.1-10
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• 2001

Sea surface temperature derived from infrared images of NOAA satellites showed a warm eddy in the East Korean Bight(EKB) or Donghan Man during the winter 1997${\sim}$2000. To describe the warm eddy in the EKB, hydrographic data collected in 1934 and 1936 were also analyzed. The center of the warm eddy was located at about $39^{\circ}N$ and $129^{\circ}E$. The temperature and salinity of the eddy was about $4.0^{\circ}C$ and 34.0 psu, respectively, at 100m depth. The eddy rotated anticyclonically with a geostrophic current speed of about 20 cm/s. The mean state calculated from the data of 1922${\sim}$1960 showed the existence of a warm eddy over the EKB in winter. The eddy persists until late spring, and disappears from the previous location in summertime, only to be seen again in autumn.

• Ocean and Polar Research
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• v.34 no.3
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• pp.325-335
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• 2012

It is well known that sound waves in the sea propagates under the influence of sea surface and bottom roughness, the sound speed profile, the water depth, and the density of sea floor sediment. In particular, an abrupt change of sound speed with depth can greatly affect sound propagation through an eddy. Eddies are frequently generated in the East Sea near the Korean Peninsula. A warm eddy with diameter of about 150 km is often observed, and the sound speed profile is greatly changed within about 400 m of water depth at the center by the eddy around the Ulleung Basin in the East Sea. The characteristics of low-frequency sound propagation across a warm eddy are investigated by a sound propagation model in order to understand the influence of warm eddies. The acoustic rays and propagation losses are calculated by a range-dependent acoustic model in conditions where the eddy is both present and absent. We found that low-frequency sound propagation is affected by the warm eddy, and that the phenomena dominate the upper ocean within 800 m of water depth. The propagation losses of a 100 Hz frequency are variable within ${\pm}15$ dB with depth and range by the warm eddy. Such variations are more pronounced at the deep source near the sound channel axis than the shallow source. Furthermore, low-frequency sound propagation from the eddy center to the eddy edge is more affected by the warm eddy than sound propagation from the eddy edge to the eddy center.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.3 no.2
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• pp.91-103
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• 1999

According to numerical experiments, the Sokcho Eddy is produced at $37 5~39.0^{\circ}N$ by strong offshore winds, whereas the Ulleung Eddy is produced at $35~37^{\circ}N$ by an inflow variation of the Tsushima Current. These locations compare well with visual observations. The nonlinear 1$1/2$-layer model showed that most of the East Korea Warm Current (EKWC) driven by the Tsushima Current form the Ulleung Eddy that is larger and stronger than the Sokcho Eddy. In contrast, the nonlinear 2$1/2$-layer model showed that most of the EKWC travels further northward due to a strong subsurface current, thereby enhancing the Sokcho Eddy making it larger and stronger than the Ulleung Eddy. The Sokcho Eddy is also produced relatively offshore due to an eastward subsurface current in the frontal region. Using the 1$1/2$-layer model, when the mass of the Tsushima Current decreases, the two eddies are weakened and produce a circular shape. In the 2$1/2$-layer model the EKWC pushes the Ulleung Eddy northward after 330 days, next the Sokcho and Ulleung eddies begin to interact with each other, and then after 360 days the Ulleung Eddy finally disappears absorbed by the relatively stronger Sokcho Eddy. This behavior compares favorably with other visual observations.

• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.387-393
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• 2019

In this study, the free motion of a riser due to vortex shedding was numerically simulated with Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulence models. A numerical simulation program was developed by applying the Rhie-Chow interpolation method to the pressure correction of the OpenFOAM standard solver pimpleDyMFoam. To verify the developed program, the vortex shedding around the fixed riser at Re = 3900 was calculated, and the results were compared with the existing experimental and numerical data. Moreover, the vortex-induced vibration of a riser supported by a linear spring was numerically simulated while varying the spring constant. The results are compared with published direct numerical simulation (DNS) results. The present calculation results show that the numerical method is appropriate for simulating the vortex-induced motion of a riser, including lock-in phenomena.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.6
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• pp.406-418
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• 2015

The present modified FUNWAVE-TVD model, which is a modification to its previous version 2.1, is applied to solitary wave propagation and is tested against the experiments of Vincent and Briggs(1989) and Luth et al.(1994). The eddy viscosity breaking scheme is used for comparison with the existing study in the case of breaking experiment. The symmetry of wave-induced current is maintained when the modified model is employed to Vincent and Briggs(1989) breaking experiment, but the symmetry of wave-induced current in previous model is not maintained. A better agreement with the breaking experimental data is obtained in the modified model using eddy viscosity breaking scheme than the shock capturing breaking scheme using nonlinear shallow water equation. For comparison with the schemes in the model, the fourth order MUSCL-TVD scheme by Erduran et al.(2005) and the third order MUSCL-TVD scheme using minmod limiter is applied, and the numerical solutions of solitary wave are compared.

• Ocean and Polar Research
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• v.28 no.3
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• pp.245-258
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• 2006

We investigated seasonal variations of the upper ocean temperature and the mixed layer depth (MLD) in an eddy-permitting global ocean general circulation model (OGCM) to assess the OGCM perfermance. The OGCM is based on the GFDL MOM3 which has a horizontal resolution of 0.5 degree and 30 vertical levels. The OGCM was integrated for 68 years using a monthly-mean climatological wind stress forcing. The model sea surface temperature (SST) and sea surface salinity were restored to the Levitus climatology with a time scale of 30 days. Annual-mean model SST shows a cold bias $(<\;-2^{\circ}C)$ in the summer hemisphere and a warm bias $(>\;1^{\circ}C)$ in the winter hemisphere mainly due to the restoring boundary condition of temperature. The model MLD captures well the observed features in most areas, with a slightly deep bias. However, in the Ross Sea and Weddell Sea, the model shows significantly deeper MLD than the climatology-mainly due to weak salinity stratifications in the model. For amplitude of seasonal variation, the model SST is smaller $(1{\sim}3^{\circ}C)$ than the observation largely due to the restoring surface boundary condition while the model MLD has larger seasonal variation $({\sim}50m)$. It is suggested that for more realistic simulation of the upper ocean structure in the present eddy-permitting ocean model, more refinements in the surface boundary condition for the thermohaline forcing and parameterization for vertical mixing are required, together with the incorporation of a sea-ice model.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.10
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• pp.1639-1647
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• 2016

This paper deals with eddy current loss analysis of Slotless Double sided Cored type permanent magnet linear generator by using analytical method, space harmonic method. In order to calculate eddy current, this paper derives analytical solution by the Maxwell equation, magnetic vector potential, Faraday's law and a two-dimensional(2-D) cartesian coordinate system. First, we derived the armature reaction field distribution produced by armature wingding current. Second, by using derived armature reaction field solution, the analytical solution for eddy current density distribution are also obtained. Finally, the analytical solution for eddy current loss induced in permanent magnets(PMs) are derived by using equivalent, electrical resistance calculated from PMs volume and eddy current density distribution solution. The analytical result from space harmonic method are validated extensively by comparing with finite element method(FEM).

• Journal of Ocean Engineering and Technology
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• v.29 no.2
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• pp.199-206
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• 2015

Regular high-strength carbon steel is currently the most commonly used pipe material for onshore and offshore pipelines. The corrosion of offshore pipelines is a major problem as they age. The collapse of these structures as a result of corrosion may have a heavy cost is lives and assets. Therefore, their monitoring and screening is a high priority for maintenance, which may ensure the integrity and safety of a structure. Monitoring risers and subsea pipelines effectively can be accomplished using eddy current inspection to detect the average remaining wall thickness of corroded low-alloy carbon steel pipelines through corrosion scaling, paint, coating, and concrete. A test specimen for simulating the offshore pipeline is prepared as a standard specimen for an analysis and experiment with differential bobbin eddy current sensors. Using encircling coils, the signals for the defect in the simulated specimen are analyzed and evaluated in experiments. Differential bobbin eddy current sensors can diagnose the defects in a specimen, and experiments have been carried out using the developed bobbin eddy current sensor. As a result, the most optimum coil parameters were selected for designing differential bobbin eddy current sensors.