• Journal of Wind Energy
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• v.15 no.1
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• pp.21-29
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• 2024

In order to respond to environmental changes and various events in the nearby sea area due to the operation of an offshore wind substantiation farm in the Southwest Sea, X-band radar has been installed and operated on a fixed platform since 2018. The X-band radar's monitoring system produces wave and current data through Rutter's Ocean WaveS wave and current (Sigma S6 WaMoS II). In this study, to verify the reliability of the produced data, the accuracy of current and wave data was evaluated by analyzing the correlation with the results obtained by an acoustic doppler current profiler (ADCP). The selected analysis period was a total of 30 days from November 29 to December 28, 2021, the period during which the ADCP survey was conducted. As a result of comparative verification, the current, wave height and peak wave period (H_s > 0.69 m) data observed from the X-band radar showed a high correlation with the results investigated from ADCP. In the future, current and wave data produced by X-band radar are expected to be used as basic data to analyze environmental changes in sea areas and provide information on various events.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.3
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• pp.170-176
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• 2012

This paper analyzes the sea state and characteristics during the August 2011 passage of Typhoon Muifa based on data measured at four ocean weather/wave observation stations (buoys) located on the southwestern coast of Korea. When the typhoon arrived in the area approximately 230 km west of Mokpo at 9 PM on August 7, the decrease in air pressure led to increases in sea level of 25.64 cm at the Chilbal-do buoy, 16.43 cm at the Geomun-do buoy, and 9.60 cm at the Geoje-do buoy. The maximum wave height increased at the Geomun-do buoy about seven times faster than at the Chilbal-do buoy. The low water temperature at Chilbaldo during the typhoon passage probably reduced the wave energy. In the face of the oncoming typhoon, the southwest direction of the wind and waves may have been the result of external forces transporting seawater (energy) from the open sea toward the coast. The weather and ocean data from the Mara-do buoy were negatively correlated with those of Chilbal-do, whereas the data from Geomun-do had a positive correlation with those of Geoje-do.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.2
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• pp.158-168
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• 2001

A numerical model based on the wide-angle parabolic approximation equation is developed for the accurate simulation of the directional spreading and partial breaking of irregular waves. This model disintegrates the irregular waves into a series of monochromatic wave components, and the simultaneous calculations are made for each wave component. Then, the computed wave components are superposed to get the wave height of irregular waves. To consider the partial breaking of irregular waves in the computation the amount of energy dissipation due to breaking is estimated using the superposed wave height. The accuracy of the developed model is tested by comparing the numerical results with the experimental measurements reported earlier. In the case of non-breaking waves a considerable accuracy of the model is observed for both regular and irregular waves. On the contrary it is found that the accuracy is significantly degenerated for the case of breaking waves. Some analyses for the accuracy degeneration are presented.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.6_2
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• pp.801-808
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• 2021

In this paper, a numerical analysis was conducted on the effect of the flow control valve of a oscillation water column(OWC) type wave power generator turbine. The OWC wave power turbine operates with compressed air in the air chamber according to the change of wave height. When the wave height changes rapidly, a flow control valve is required due to overload of the turbine and reduced efficiency. Therefore, in this paper, a flow control valve with an opening angle of 60 degrees was installed in the front of the turbine, and the pressure drop, torque, and overall performance were calculated according to the change of turbine RPM and flow rate of turbine inlet. In conclusion, the flow control valve with an opening angle of 60 degrees affects when the turbine rotates at low rotation and the inlet flow rate is large. But it does not have a significant effect on overall turbine performance and it is necessary to find the optimal angle in the future works.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1700-1706
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• 2016

In this paper, a dual-stator, spoke-type linear vernier machine (DSSLVM) for wave energy extraction application was proposed. This machine is capable of producing a competitively high thrust force and force density at a low operation speed in direct drive systems. The operation principal and working of the proposed DSSLVM were studied. The stator core height is adjusted to improve the overall force density of the proposed machine while reducing the force ripple. To evaluate the advantages of the proposed DSSLVM, the main performance was compared with that of a recently developed linear primary permanent magnet vernier machine (LPPMVM). The proposed machine exhibited greater thrust force and force density, an improved power factor and lower force ripple with the same permanent magnet (PM) volume compared to the LPPMVM.

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.795-805
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• 2006

Tuned Liquid damper and Tuned Liquid Column are kind of passive mechanical damper which relies on the sloshing of liquid in a rigid tank for suppressing structural vibrations. TLD and TLCD are attributable to several potential advantages - low costs ; easy to install in existing structures : effective even for small-amplitude vibrations. In this paper, the shaking table experiments were conducted to investigate the characteristics of water sloshing motion in TLD (rectangular, circular) and TLCD. The parameter obtained from the experiments were wave height, base shear force and energy dissipation. The shaking table experiments show that the liquid sloshing relies on amplitude of shaking table and frequency of tank. The TLCD was more effective control vibration than TLD.

• Journal of the Korean Society of Marine Environment & Safety
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• v.14 no.2
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• pp.119-125
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• 2008

The aim of this study was to determine the characteristics of wave transformation in the shallow water of the Nakdong River estuary due to variations in air pressure, air temperature, wind speed, and wind direction. We analyzed the correlation between weather factors and wind waves in offshore regions near Geoje Island and the Nakdong River estuary in April and May 2007. The weather and wind wave data were obtained from the automatic ocean observation buoy near Geoje Island operated by the Korean Meteorological Administration (KMA). For the estuary region, the wind wave information was the result of field observations, and weather data were obtained from the Busan Meteorological Station. Field observations of water waves in April and May showed that the maximum wave height decreased by about 2.2 m. M oreover, wave height decreased significantly by about 1.3 m due to the reduction in wave energy caused by the water waves propagating from Geoje buoy to the Nakdong River estuary. We conclude that offshore or wind waves coming into the Nakdong River estuary showed considerable height variation due to the prevailing weather conditions, especially wind speed and direction. In particular, headwinds tended to decrease the wave size in inverse proportion to the wind speed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.335-349
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• 2017

Submerged breakwaters installed under the water surface are a representative coastal structure to prevent coastal erosion, and various types of submerged breakwaters have been proposed and discussed so far. Generally, submerged breakwaters make the complex wave fields due to abrupt change in water depth at the crown of the breakwater. In this study, wave heights and mean water level formed around a breakwater are examined numerically for three-dimensional permeable submerged breakwaters. OLAFOAM, CFD open source code, is applied in the numerical analysis, and the comparisons are made with available experimental results on the permeable upright wall and the impermeable submerged breakwater to verify its applicability to the three-dimensional numerical analysis. Based on the applicability of OLAFOAM numerical code, the wave height and mean water level distribution formed around the permeable submerged breakwaters are investigated under the formation condition of salient. The numerical results show that as the gap width between breakwaters decreases, the wave height in the center of the gap increases, while it decreases behind the gap, and the installing position of the breakwater from the shoreline has little influence on the change of the wave height. Furthermore, it is found that the decrease of the mean water level near the gap between breakwaters increases with decreasing of the gap width.

• Journal of the Korean Society for Marine Environment & Energy
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• v.7 no.3
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• pp.131-136
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• 2004

The transmission coefficients of impermeable submerged breakwater on permeable bottom are computed numerically using a boundary element method. The analysis method is based on the wave pressure function with the continuity in the analytical region including fluid and structures. Wave motion over permeable bottom is simulated by introducing a linear dissipation coefficient and an added mass coefficient. The results indicate that the wave over permeable bottom travels being damped, and that transmission coefficients for permeable bottom are smaller than those for impermeable bottom, and result from the change of width and height of submerged breakwater.

• Journal of the Korean Society for Marine Environment & Energy
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• v.9 no.3
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• pp.141-147
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• 2006

A newly designed floating breakwater made of Polyethylene with considering the introduction of new material for being harmony with environment and stability of the floater is developed for a marine ranching. In this study, the new concept in which incident wave dissipates its energy due to the vortex shedding by passing through the pipes and sheets is selected for wave breaking mechanism. Model experiment in order to te st its capability is performed for the regular and irregular waves in ocean engineering basin. Good capability to break the incident wave within the 6 seconds of period and 1 m of height is shown. Breaking efficiency for long period wave is not so good in regular and irregular wave. The results of this study will contribute to the design and construction of the floating breakwater.