• Journal of Ocean Engineering and Technology
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• v.27 no.4
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• pp.33-44
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• 2013

IIn this study, a wave-surge-tide coupling numerical model was developed to consider nonlinear interaction. Then, this model was applied and calculations were made for a storm surge on the southeast coast. The southeast coast was damaged by typhoon "Maemi" in 2003. In this study, we used a nearshore wind wave model called SWAN (Simulating WAves Nearshore). In addition, the Meyer model was used for the typhoon model, along with an ocean circulation model called POM (Princeton Ocean Model). The wave-surge-tide coupling numerical model could calculate exact parameters when each model was changed to consider the nonlinear interaction.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.5
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• pp.65-70
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• 2015

Lightning is one of hazards affecting the rapid-transit railway system. There are two effects, which are direct lightning surge to electric car line and induced lightning surge. Protection methods for the direct lightning surge are studied with various occasions, however, study of induced lightning surge is insufficient in spite of a large or small effects. In this paper, it is analysed the way that serge voltage is induced to electric car line by lightning strikes. By modeling the propagation process and the coupling phenomenon of electromagnetic wave produced by lightning strikes, it is achieved to make integrative circuit model combined with existing electric car model. The study is conducted into three different waveform of electromagnetic wave produced by lightning; rectangular wave, double exponential distribution wave, triangle wave. It is also simulated that the inducing serge is coupled to electric car line in an arbitrary location. The simulation results in that, when rapidly changing rectangular wave is supplied, maximum power is induced to electric car line.

• Journal of Ocean Engineering and Technology
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• v.21 no.2 s.75
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• pp.35-41
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• 2007

In general, coastal damage is mostly occurred by the action of complex factors, like severe water waves. If the maximum storm surge height combines with high tide, severe water waves will overflow coastal structures. Consequently, it can be the cause of lost lives and severe property damage. In this study, using the numerical model, the storm surge was simulated to examine its fluctuation characteristics at the coast in front of Noksan industrial complex, Korea. Moreover, the shallow water wave is estimated by applying wind field, design water level considering storm surge height for typhoon Maemi to SWAN model. Under the condition of shallow water wave, obtained by the SWAN model, the wave overtopping rate for the dike in front of Noksan industrial complex is calculated a hydraulic model test. Finally, based on the calculated wave-overtopping rate, the inundation regime for Noksan industrial complex was predicted. And, numerically predicted inundation regimes and depths are compared with results in a field survey, and the results agree fairly well. Therefore, the inundation modelthis study is a useful tool for predicting inundation regime, due to the coastal flood of severe water wave.

• Journal of Ocean Engineering and Technology
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• v.19 no.2 s.63
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• pp.12-18
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• 2005

Typhoon Maemi landed on the southeast coast of Korea and caused a severe storm surge in Jinhae Bay and Masan Bay. The tide gage in Masan Port recorded the storm surge of a maximum of more than 2m and the area of more than 700m from the Seo Hang Wharf was flooded by the storm surge. They had not met such an extremely severe storm surge since the opening of the port. Then storm surge was hindcasted with a numerical model. The typhoon pressure was approximated by Myers' empirical model and super gradient wind around the typhoon eye wall was considered in the wind estimation. The land topography surrounding Jinhae Bay and Masan Bay is so complex that the computed wind field was modified with the 3D-MASCON model. The motion of seawater due to the atmospheric forces was simulated using a one-layer model based on non-linear long wave approximation. The Janssen's wave age dependent drag coefficient on the sea surface was calculated in the wave prediction model WAM cycle 4 and the coefficient was inputted to the storm surge model. The result shows that the storm surge hindcasted by the numerical model was in good agreement with the observed one.

• International Journal of Ocean System Engineering
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• v.4 no.1
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• pp.19-28
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• 2014

The tension leg platform (TLP) is a vertically moored structure with excess buoyancy. The TLP is regarded as moored structure in horizontal plan, while inherit stiffness of fixed platform in vertical plane. In this paper, a numerical study using modified Morison equation was carried out in the time domain to investigate the influence of nonlinearities due to hydrodynamic forces and the coupling effect between surge, sway, heave, roll, pitch and yaw degrees of freedom on the dynamic behavior of TLP's. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables and the nonlinear equations of motion were solved utilizing Newmark's beta integration scheme. The effect of tethers length and wave characteristics such as wave period and wave height on the response of TLP's was evaluated. Only uni-directional waves in the surge direction was considered in the analysis. It was found that for short wave periods (i.e. 10 sec.), the surge response consisted of small amplitude oscillations about a displaced position that is significantly dependent on tether length, wave height; whereas for longer wave periods, the surge response showed high amplitude oscillations about that is significantly dependent on tether length.

• Journal of Ocean Engineering and Technology
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• v.19 no.6 s.67
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• pp.22-28
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• 2005

We investigated the characteristics of the overflow/wave overtopping, induced by the storm surge and high waves in Masan bay and Busan Coast during Typhoon 'Maemi', which landed at the southeast coast of the Korean peninsula on September, of 2003, causing a severe inundation disaster. Characteristics of the water level, increase by the overflow / wave overtopping, were discussed in two patterns. One is the increase of water level in the region, located inside of a bay, like Masan fishing port, and the waves are relatively small. The other is in the open sea, in which the waves act directly, as on the seawall in Suyong bay. In the former region, the water level increase was affected by the storm surge, as well as the long period oscillation and waves. In Masan fishing port, about $80\%$ of the water level increase on the quay wall was caused by the storm surge. In the latter one, it was greatly affected by the wave run-up. In Suyong bay, about $90\%$ of the water level increase on the seawall was caused by the wave run-up.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.2
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• pp.196-208
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• 2009

In this paper, wave responses of buoyant flap-typed storm surge barriers was studied numerically. Wave motions were modeled by using a linear potential wave theory, and behaviors of structures were represented as a Newton's 2nd law of motion. The near field region of the fluid was discretized as conventional quadratic iso-parametric elements, while the far field was modeled as infinite elements. Comparisons with the results from hydraulic model tests show that the present model gives good results. By using the model, the applicability of a buoyant flap-typed storm surge barrier in Masan bay was investigated considering field environmental conditions.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.3
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• pp.81-87
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• 2015

In order to effectively protect electrical and electronic circuits which are extremely susceptible to lightning surges, multi-stage surge protection circuits are required. This paper presents the operational characteristics of the two-stage hybrid surge protection circuit in extra-low voltage DC power lines. The hybrid surge protective device consists of the gas discharge tube, transient voltage suppressor, and series inductor. The response characteristics of the proposed hybrid surge protective device to combination waves were investigated. As a result, the proposed two-stage surge protective device to combination wave provides the tight clamping level of less than 50V. The firing of the gas discharge tube to lightning surges depends on the de-coupling inductance and the rate-of-change of the current flowing through the transient voltage suppressor. The coordination between the upstream and downstream components of the hybrid surge protective device was satisfactorily achieved. The inductance of a de-coupler in surge protective circuits for low-voltage DC power lines, relative to a resistance, is sufficiently effective. The voltage drop and power loss due to the proposed surge protective device are ignored during normal operation of the systems.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.2
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• pp.178-183
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• 2013

The study of lightning surge have been conducted on information and communications equipment and power system. However, the research on SMPS itself is an inactive field. This paper analyzes surge current path of flyback converter with the combination wave generator by lightning surge. Also, this paper discloses that there exists the surge current with high-frequency component besides the low-frequency component based on the standard surge current. This high-frequency surge current is the major reason to damage the semiconductor devices such as FET and IC. To confirm the validity of the proposed issue, the analysis and experimental results are presented.

• Ocean Systems Engineering
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• v.2 no.2
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• pp.115-135
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• 2012

The very low natural frequencies of tension leg platforms (TLP's) have raised the concern about the significance of the action of hydrodynamic wave forces on the response of such platforms. In this paper, a numerical study using modified Morison equation was carried out in the time domain to investigate the influence of nonlinearities due to hydrodynamic forces and the coupling effect between surge, sway, heave, roll, pitch and yaw degrees of freedom on the dynamic behavior of TLP's. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables and the nonlinear equations of motion were solved utilizing Newmark's beta integration scheme. The effect of wave characteristics such as wave period and wave height on the response of TLP's was evaluated. Only uni-directional waves in the surge direction was considered in the analysis. It was found that coupling between various degrees of freedom has insignificant effect on the displacement responses. Moreover, for short wave periods (i.e., less than 10 sec.), the surge response consisted of small amplitude oscillations about a displaced position that is significantly dependent on the wave height; whereas for longer wave periods, the surge response showed high amplitude oscillations about its original position. Also, for short wave periods, a higher mode contribution to the pitch response accompanied by period doubling appeared to take place. For long wave periods, (12.5 and 15 sec.), this higher mode contribution vanished after very few cycles.