• Journal of the Korean earth science society
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• v.39 no.5
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• pp.436-457
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• 2018

In this study, we apply a three-dimensional circulation model, MOHID (MOdelo $HIDrodin{\hat{a}}mico$), and reproduce oceanic variation around the East Asian seas including Korea in 2016. Simulation results are verified by using objective analysis fields (EN4, ARMOR3D, AVISO, and SIO products) and in-situ observation data (serial oceanographic and buoy data). Verification results show that general characteristics of the water temperature, sea level anomaly, surface velocity, and mixed layer depths simulated by MOHID are similar with those of the objective analysis fields in the East Asian seas. Especially, when buoy data in the coastal areas are compared, correlation coefficients of sea surface temperature and sea level anomaly are both over 0.8 and normalized standard deviations are between 0.85 and 1.15, respectively. However, it is analyzed that additional improvement would be necessary in the representation of thermocline structure in the East Sea and strong stratification phenomena in the Yellow and South Sea in summer.

• Maritime Security
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• v.1 no.1
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• pp.61-92
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• 2020

This paper attempts to examine the changes in China's naval strategy and to analyze the goal, range, and method of each strategy during the Xi Jinping's era. Since the founding of New China, the People's Liberation of Army Navy(PLAN) has made four changes in the naval strategy. Under Xi Jinping's administration, China's naval strategy is far seas operation combined with near seas active defense. Now, China's naval strateg y is shifting from a defensive to an aggressive one, increasing the proportion of offensive weapon systems and the number of state-of-the-art warships, and the scope of the naval strategy has been specified in the second island chain including the Indian Ocean. With the changes of naval strategy, the PLAN will set a new strategic goal to secure maritime dominance and implement an assertive strategy to actively respond to the intervention and intrusion of external forces. Moreover, the PLAN will also improve its sea-based deterrence force and the maneuver force to block other countries in the long-distance maritime conflict zones. The operation method of China's future naval strateg y will gradually shift from 'interdiction' to 'rapid-response.'

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4265-4271
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• 2022

Determination of ¹³⁷Cs, ⁴⁰K and ²¹⁰Po in water, bottom sediments and suspended matter of river systems of the Can Gio Biosphere Reserve, Vietnam was carried out. The average activity concentration of ¹³⁷Cs in waters of Ca Gau and Long Tau was 0.89 ± 0.14 and 1.08 ± 0.15 Bq m^-3 and was comparable to the levels of this radioisotope in waters of the East Sea. The activity concentration of ¹³⁷Cs in bottom sediments was 2.23 ± 0.81 and 3.63 ± 1.24 Bq kg^-1. The activity concentration of ¹³⁷Cs in water and bottom sediments could be characterized as low. So, the water areas of the Ca Gau and Long Tau rivers could be attributed to areas with insignificant pollution by technogenic radionuclides. The ²¹⁰Po activity concentration in bottom sediments of the Ca Gau and Long Tau rivers ranged from 9.2 ± 1.2 to 25.5 ± 2.1 Bq kg^-1, which is typical for river bottom sediments. Such values indicate the absence of anthropogenic enhancement of the entry of this radionuclide into the Can Gio river systems. The ⁴⁰K activity concentration varied within 467 ± 42-651 ± 39 Bq kg^-1 and represented typical values of potassium content in the bottom sediments of coastal water bodies, subject to a significant influence of the lithogenic component of suspended matter.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.3
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• pp.325-331
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• 2018

This paper deals with the dynamical analysis of a vessel that leads to capsize in regular beam seas. The complete investigation of nonlinear behaviors includes sub-harmonic motion, bifurcation, and chaos under variations of control parameters. The vessel rolling motions can exhibit various undesirable nonlinear phenomena. We have employed a linear-plus-cubic type damping term (LPCD) in a nonlinear rolling equation. Using the fourth order Runge-Kutta algorithm with the phase portraits, various dynamical behaviors (limit cycles, bifurcations, and chaos) are presented in beam seas. On increasing the value of control parameter ${\Omega}$, chaotic behavior interspersed with intermittent periodic windows are clearly observed in the numerical simulations. The chaotic region is widely spread according to system parameter ${\Omega}$ in the range of 0.1 to 0.9. When the value of the control parameter is increased beyond the chaotic region, periodic solutions are dominant in the range of frequency ratio ${\Omega}=1.01{\sim}1.6$. In addition, one more important feature is that different types of stable harmonic motions such as periodicity of 2T, 3T, 4T and 5T exist in the range of ${\Omega}=0.34{\sim}0.83$.

• Journal of the Korean earth science society
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• v.24 no.1
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• pp.7-21
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• 2003

The state-of-art third generation wave prediction model WAM was applied to the Korean seas for a winter monsoon period of January 1997. The wind field used in the present study is the global NSCAT-ERS/NCEP blended winds, which was further interpolated using a bi-cubic spline interpolator to fine grid limited area shallow water regime surrounding the Korean seas. To evaluate and investigate the accuracy of WAM, the hindcasted wave heights are compared with observed data from two shallow water buoys off Chil-Bal and Duk-Juk. A detailed study has been carried with the various meteorological parameters in observed buoy data and its inter-dependency on model computed wave fields was also investigated. The RMS error between the observation and model computed wave heights results to 0.489 for Chil-Bal and 0.417 for Duk-Juk. A similar comparison between the observation and interpolated winds off Duk-Juk show RMS error of 2.28 which suggest a good estimate for wave modelling studies.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.1
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• pp.94-108
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• 1994

As satellite altimetry is being progressed to apply with higher precision to maginal seas. it is necessary to improve correction procedures for tidal signals in altimetry with more accurate tidal model than the well-known model of Schwiderski for studying marginal sea dynamics. As a first step, tidal regime of semidiurnal tides (M$_2$, S$_2$, $N_2$, $K_2$) and diurnal tides (K$_1$, $O_1$, P$_1$, Q$_1$) were computed with finer details of formulation of tidal model over the East Asian Marginal Seas covering the Okhotsk Sea and South China Sea and part of Northwest Pacific Ocean with mesh resolutions of 1/6$^{\circ}$. Computed results were discussed with observations, previous tidal charts and Schwiderski's tidal map of the region.

• Journal of the Korean Institute of Navigation
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• v.14 no.2
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• pp.15-31
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• 1990

Recently, there is a tendency to design the large full ships with lower-powered engine as the means for energy saving in ship's navigation at seas. Such a lower-powered ship is anticipated to show the different propulsive performance in rough seas, because the fluctuation of main engine load of lower powered ship is relatively large as compared with higher-powered ship is relatively large as compared with higher-powered ship. The fluctuation of propeller load is nonlinear at racing condition in waves. It is due to the variation of inflow velocity into propeller, the propeller immersion and the characteristics of engine governor. In this paper, the theoretical calculation of the nominal speed loss and the numerical simulation for the nonlinear load fluctuation of a model ship in rough seas are carried out. From the results of calculation, the following are discussed. (1) The ratio of nominal speed loss to the speed in still water. (2) The manoeuvring ability of ship and the operational ability of main engine in a seaway. (3) A method of the evaluation for the fluctuation of propeller torque and revolution on the engine characteristics plane. (4) The effect of engine governor characteristics on the propeller load fluctuation.

• Ocean and Polar Research
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• v.23 no.4
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• pp.379-388
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• 2001

Ch1 a abundance, Ch1 a-specific productivity and phytoplankton growth rate in each size fraction (pico, $<2{\mu}m$; nano, $2-10{\mu}m$; micro, > $10{\mu}m$) in the waters around the South Shetland Islands (Ant-arctic Peninsula Area) were analysed. Although Ch1 a-specific productivity and growth rate were highest in micro-size fractions, ChI a abundance was highest in pico-size fractions. Selective removal of nano- and micro-size phytoplankton especially by krill and salp grazing, but not limitation of phytoplankton growth, seemed to be the major reason to explain this miss match between productivity and abundance of the phytoplankton community.

• Proceedings of the KSRS Conference
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• v.2
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• pp.977-980
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• 2006

Ships and industries damage the delicate coastal ecosystem in many parts of the world by releasing oil or pollutants into rivers, coastal and offshore waters. After a tanker accident the biggest problem is to get a clear idea of the extent of the oil slick and predict the way it will move. For natural and man-made oil spills it is necessary to operate a regular and operational monitoring. In the Mediterranean, North and Baltic seas aircrafts or ships normally carry it out. This is expensive and is constrained by the limited availability of these resources, borders between countries, daylight hours, good weather conditions, etc. Satellite imagery can help greatly identifying probable spills over large areas and then guiding aerial surveys for precise observation of specific locations. The Synthetic Aperture Radar (SAR) instrument, which can collect data almost independently of weather and light conditions, is an excellent tool to monitor and detect oil on water surfaces. SAR is currently on board the ENVISAT, ERS-2 and RADARSAT satellites. The application of this technology to the investigation of oil pollution in the Caspian, Black, Mediterranean, North and Baltic seas is shown.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.3
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• pp.292-304
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• 2017

High-speed vessels are prone to the surf-riding in adverse quartering seas. The possibility of mitigating the surf-riding of the ITTC A2 fishing vessel in the design stage is investigated using the 6-DOF weakly non-linear model developed for surf-riding simulations in quartering seas. The longitudinal position of the ship's center of buoyancy (LCB) is chosen as the design parameter. The adjusting of LCB is achieved by changing frame area curves, and hull surfaces are reconstructed accordingly using the Radial Basis Function (RBF). Surf-riding motions in regular following seas for cases with different LCBs and Froude numbers are simulated using the numerical model. Results show that the surf-riding cannot be prevented by the adjusting of LCB. However, it occurs with a higher threshold speed when ship's center of buoyancy (COB) is moved towards stem compared to moving towards stern, which is mainly due to the differences on wave resistance caused by the adjusting of LCB.