• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.23 no.4
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• pp.204-217
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• 2018

This study proposes a cost-effective method to monitor coastal environments using e-Navigation-implemented domestic and international ferries, and to analyze big data of records such as wind, temperature, salinity, waves, and currents that are gathered through e-Navigation system. First, we present the concept and architecture of e-Navigation operation system based on the General Information Center on Maritime Safety and Security. Then, the marine observation system that can be applied to ferries operating in our nation's territory is discussed. Analytical methods, such as spatio-temporal mixed effects model, ensemble method, and meshfree method, in handling real-time big data obtained by the e-Navigation observing system are then explained in detail. This study will support the implementation of the Korean e-Navigation project that focuses on the safety of small vessels such as coasters and fishing vessels.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.28 no.1
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• pp.51-61
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• 2023

Sound can travel a long distance in the ocean; hence, acoustic instruments have been widely used for ocean observations in various fields such as bathymetric survey, object detection, underwater communication, and current measurements. Herein we introduce a pressure-recording inverted echo sounder (PIES) which is one of the most powerful instruments, moored at seafloor for ocean observation in physical oceanography. The PIES can measure various kinds of oceanic phenomena (currents, mesoscale eddies, internal waves, and sea surface height variabilities) and support acoustic telemetry and pop-up data shuttle (PDS) system for remote data acquisition. In this paper, we review uses of PIES and describe present and prospective system of PIES including remote data acquisition toward (quasi) real-time data recovery.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.3
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• pp.595-605
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• 1994

The field observations. data analyses and numerical experiments are performed to investigate the short and long term beach deformation mechanisms in Haeundae beach. The schematic diagrams of deposition and erosion mechanism due to the attack of typhoons are described from the analysis on the beach widths and profiles. The short term beach deformation depends strongly on the characteristics of incident waves and wave-induced currents. The main incident wave and the calibration parameters of the shoreline change model are determined using the beach width data. Beacause the main incident wave approaches obliquly from the SE direction, the net westward longshore sediment transport occurs. Therefore the unbalance of longshore sediment budget in the east of the beach where the sediment source dose not exist causes a beach erosion. On the other hand, the deposited sand in the west is lost offshore by the storm wave action.

• Journal of Navigation and Port Research
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• v.45 no.3
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• pp.165-172
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• 2021

Breaking wave is one of the important design factors in the design of coastal and port structures as they are directly related to various physical phenomena occurring on the coast, such as onshore currents, sediment transport, shock wave pressure, and energy dissipation. Due to the inherent complexity of the breaking wave, many empirical formulas have been proposed to predict breaker indices such as wave breaking height and breaking depth using hydraulic models. However, the existing empirical equations for breaker indices mainly were proposed via statistical analysis of experimental data under the assumption of a specific equation. In this study, a new Munk-type empirical equation was proposed to predict the height of breaking waves based on a representative linear supervised machine learning technique with high predictive performance in various research fields related to regression or classification challenges. Although the newly proposed breaker height formula was a simple polynomial equation, its predictive performance was comparable to that of the currently available empirical formula.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.2
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• pp.150-155
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• 2012

One of the primary purposes of tugs is for the towing of other ships in salvage operations. In order to conduct such a task safely, the tug should be capable of generating the appropriate towing forces. Therefore the prediction of resistance against a towed ship during towing operation is a very important and essential procedure. This paper studies the ship resistance calculation program to predict towing force. The calculation program consists of the functions that calculate basic hull resistance in calm water, added resistance due to wind, drifting, hull roughness, waves, shallow water and currents. All predictions are calculated by statistical and empirical methods by graph or formula. The calculation results made by this program are compared with the results from the U.S. Navy's Towing Manual. These results confirm that this computer program is quite capable of appropriately predicting the resistance of damaged ships.

• Computational Structural Engineering
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• v.10 no.4
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• pp.239-249
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• 1997

The method to distinguish chaotic attractors in the perturbed response behaviors of a piecewise-linear system under combined regular and external randomness is provided and examined. In the noisy fields such as the ocean environment, excitation forces induced by wind, waves and currents contain a finite degree of randomness. Under external random perturbations, the system responses are disturbed, and consequently chaotic signatures in the response attractors are not distinguishable, but rather look just random-like. Mean Poincare map can be utilized to identify such chaotic responses veiled due to the random noise by averaging the noise effect out of the perturbed responses. In this study, the procedure to create mean Poincare map combined with the direct numerical simulations is provided and examined. It is found that mean Poincare maps can successfully distinguish chaotic attractors under stochastic excitations, and also can give the information of limit value of noise intensity with which the chaos signature in system responses vanishes.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.25 no.1
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• pp.65-72
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• 1992

It is believed that the lower cold water is formed by winter cooling in the north of the East(Japan) Sea. To examine its effect on the general circulation of the East Sea, we performed a two-layer numerical model with realistic bottom topography. First a circulation is generated by imposing only an inflow and an outflow which is then modified by adding the cooling effect in the north. The interface between the two layers rises due to cooling and propagates along the coast as internal Kelvin waves. About 7 months after the cooling starts, all coastal areas of the basin have higher elevation than that in offshore region. This induces baroclinic currents resulting in clockwise(anticlockwise) circulation in upper (lower) layer of the basin. It is concluded that the East Korean Warm Current strengthens as a result of lower cold water formation.

• Proceedings of the KSRS Conference
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• v.1
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• pp.21-24
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• 2006

Processes controlling the interannual variation of mixed layer temperature (MLT) averaged over the NINO3 domain ($150-90^{\circ}W$, $5^{\circ}N-5^{\circ}S$) are studied using an ocean data assimilation product that covers the period of 1993 to 2003. Advective tendencies are estimated here as the temperature fluxes through the domain's boundaries, with the boundary temperature referenced to the domain-averaged temperature to remove the dependence on temperature scale. The overall balance is such that surface heat flux opposes the MLT change but horizontal advection and subsurface processes assist the change. The zonal advective tendency is caused primarily by large-scale advection of warm-pool water through the western boundary of the domain. The meridional advective tendency is contributed mostly by Ekman current advecting large-scale temperature anomalies though the southern boundary of the domain. Unlike many previous studies, we explicitly evaluate the subsurface processes that consist of vertical mixing and entrainment. In particular, a rigorous method to estimate entrainment allows an exact budget closure. The vertical mixing across the mixed layer (ML) base has a contribution in phase with the MLT change. The entrainment tendency due to temporal change in ML depth is negligible comparing to other subsurface processes. The entrainment tendency by vertical advection across the ML base is dominated by large-scale changes in wind-driven upwelling and temperature of upwelling water. Tropical instability waves (TIWs) result in smaller-scale vertical advection that warms the domain during La Ni? cooling events. When the advective tendencies are evaluated by spatially averaging the conventional local advective tendencies of temperature, the apparent effects of currents with spatial scales smaller than the domain (such as TIWs) become very important as they redistribute heat within the NINO3 domain. However, such internal redistribution of heat does not represent external processes that control the domain-averaged MLT.

• Journal of Biosystems Engineering
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• v.12 no.1
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• pp.45-52
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• 1987

In order to improve the thermal efficiency of an internal combustion engine, various ignition timing control systems were examined and the best one was chosen. The parts used for the systems were a microcomputer system with DAS, 8 bit output port (D-FLIP FLOP), three types of isolation circuit, two types of ignition timing pulse generator, three types of switching circuit and two types of high voltage ignition circuit. Most systems did not operate well due to the effects of electromagnetic waves and surge currents occurring when the ignition began or ended with resulting high voltage. The best ignition timing control system was found to be the combination of (microcomputer system)-(ignition timing pulse generator using step motor position control pick-up)-(switching circuit using TR logic)-(high voltage ignition circuit using CDI).

• Journal of the Korean Vacuum Society
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• v.20 no.4
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• pp.307-312
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• 2011

As a technique for removing cancerous tumors from normal tissue, radio-frequency electromagnetic waves were employed to heating target cells up to the critical temperature, which kills the cancerous cells. However, its use in treating tumors in soft organs is limited by inconvenient factors, which are use of high-currents and long time operation. In this work, the feasibility of the localized heating by inserting four conducting electrodes with tiny direct current is investigated. The heat source is resulting from the electric field as known as resistive heating. We have investigated the temperature distribution as a function of applying DC voltages ranging from 10 V to 30 V with 10 V step. From the simulation results, the mushroom-like lesion shape by applying 20 V is generated by four electrodes within a few minutes, that is proper to the clinical application.