Response of wave energy to tidal currents in the western sea of Jeju Island, Korea

This study primarily investigates an optimum energy conversion efficiency of asymmetric wave energy converter (WEC). A power take-off (PTO) system that provides a constant load torque opposite to pitch motion was implemented. Incident wave conditions were selected based on the measured data in the western sea of Jeju Island, South Korea. An optimum torque was calculated by comparing the time-averaged extracted power with various PTO load torque. InterDyMFoam solver based on Reynolds-averaged Navier-Stokes (RANS) equations were used in an OpenFOAM v4.0 framework—an open-source computational fluid dynamics model—against the experimental results derived from the wave flume. The upward pitch excursion was induced by wave force due to the asymmetric WEC characteristics; however, the downward pitch excursion depends on its weight. Numerically, the PTO torque was only loaded in uni-direction against the upward pitch motion. Moreover, the optimum PTO torque was estimated by comparing the time-averaged extracted power. Finally, the optimum PTO torque was evaluated by an irregular wave as a function of significant wave height. The optimum PTO provides design information about the asymmetric wave energy converter to improve energy conversion efficiency.

https://www.mdpi.com/1996-1073/14/5/1449/pdf

Study on Optimum Power Take-Off Torque of an Asymmetric Wave Energy Converter in Western Sea of Jeju Island

In this study, the wave energy potential (WEP) was evaluated using the wave data measured at nine stations along the Korean east coast and compared with the results of previous studies. Along the Korean east coast, seasonal variations in the WEP were around 6.4 kW/m in winter and 1.2 kW/m in summer, greater than spatial variations of 2.5~4.3 kW/m. In most stations, the wave power during June to July were shown to be smallest. The estimated annual average WEP was greatest in the Mukho and Jukbyeon stations located in the middle of the Korean east coast at around 4.3 kW/m, and smallest in the Jinha station at around 2.5 kW/m. The results found using the previous hindcast data showed WEP having a tendency to decrease from south to north. However, in this study, the WEP showed a tendency of being greatest in the middle of the Korean east coast and decreasing in both north and south directions.

/pdf/temporal-and-spatial-variations-in-the-wave-energy-potential-44k77363gh.pdf

Temporal and Spatial Variations in the Wave Energy Potential of the East Coastal Seas of Korea

In this paper, wave energy convertors which convert incident wave energy into electric power using floating light buoy are investigated. One-tenth models of a floating light buoy, straight line and seesaw type electric power plant are manufactured and tested in wave flume. In these systems, we measure the horizontal and vertical slope, generated current and power of buoy with different wave heights and periods. This was confirmed the capability of getting electric power, then we suggest further works to get more efficiency.

/pdf/experimental-study-for-wave-energy-convertor-using-floating-3efco0edjq.pdf

Experimental Study for Wave Energy Convertor using Floating Light Buoy

In order to convert wave energy into large quantities of high-efficiency power, it is necessary to study the optimal converter system appropriate for the environment of a specific open ocean area. A wave energy converter system with a counterweight converts the translation energy induced from the heave motion of a buoy into rotary energy. This experimental study evaluated the primary energy conversion efficiency of the system, which was installed on an ocean generating basin with a power take-off system. Moreover, this study analyzed the energy conversion performance according to the weight condition of the buoy, counter-weight, and flywheel by changing the load torque and wave period. Therefore, these results could be useful as basic data such as for the optimal design of a wave energy converter with a counterweight and improved energy conversion efficiency.

http://koreascience.or.kr:80/article/JAKO201611366293179.pdf

Experimental Study on Performance of Wave Energy Converter System with Counterweight

Wave power distribution is investigated to determine the optimal sites for wave power generation at Jeju sea which has the highest wave energy density in the Korean coastal waters. The spatial and seasonal variation of wave power per unit length is calculated in the Jeju sea area based on the monthly mean wave data from 1979 to 2002 which is produced by the SWAN wave model simulation in prior research. The selected favorable locations for wave power generation are compared in terms of magnitude of wave energy density and distribution characteristics of wave parameters. The results suggest that Chagui-Do is the most optimal site for wave power generation in the Jeju sea. The seasonal distribution of wave energy density reveals that the highest wave energy density occurs in the northwest sea in the winter and it is dominated by wind waves, while the second highest one happens at south sea in the summer and it is dominated by a swell sea. The annual average of wave energy density shows that it gradually increases from east to west of the Jeju sea. At Chagui-Do, the energy density of the sea swell sea is relatively uniform while the energy density of the wind waves is variable and strong in the winter.

Wave Energy Distribution at Jeju Sea and Investigation of Optimal Sites for Wave Power Generation

Long-term wave distribution at Jeju sea is investigated by a numerical simulation based on the thirdgeneration wave model SWAN (Simulating WAves Nearshore) The Jeju sea which retains relatively high wave energy density among Korean coastal regions is considered to be a suitable site for wave power generation and the efficiency of wave power generation is closely related to local wave characteristics The monthly mean of a large-scale long-term wave data from 1979 to 2002, which is provided by Korea Ocean Research & Development Institute is used as the boundary condition of SWAN model simulation with 1km grid An analysis of wave distribution concentrates on the seasonal variation and spatial distribution of significant wave heights, mean wave directions and mean wave periods Significant wave heights are higher in winter and summer and the west sea of Jeju appears relatively higher than east's The highest significant wave height occurs at the northeast sea in winter and the second highest significant wave height appears at the southeast sea in summer, while the significant wave heights in spring and autumn are relatively low but homogeneous The distribution of wave directions reveals that except the rear region influenced by wave refraction, the northwest wave direction is dominant in summer and the southeast in winter Wave periods are longer in summer and winter and the west sea of Jeju appears relatively longer than east's The longest wave period occurs at the west sea in winter, and in summer it appears relatively homogeneous with a little longer period at the south sea

Analysis of Long-Term Wave Distribution at Jeju Sea Based on SWAN Model Simulation

Recently, securing a vast land in the land region becomes more difficult and efforts to seek its alternation in the sea area have been increased. As a consequence, the coastal region has been faced to extensive beach erosion problems. In planning offshore structures such as artificial islands, it is necessary to forecast the influence of the structure construction exerting on the beach erosion of the adjacent coast. In the present study, the sediment movement pattern behind offshore structure was examined through a series of three dimensional movable bed experiments, so as to develop the numerical model which forecasts morphological change including beach erosions. The experimental results reveal that the sediment movement patterns of the beach line side and the depth region are separated at a certain boundary line. In details, at the beach side including swash zone the sediment movement becomes dominant, which is governed by a relation between depth contours and incident wave directions, while at the depth region the bed load and suspended load due to the orbit motion of waves are carried by nearshore currents, and both movements are clearly separated at a specified boundary that is related to partial standing wave from the beach. It is expected that these results can be effectively used for verification of a numerical model on morphological change of the coast.

An Experimental Study of Sediment Transport Patterns behind Offshore Structure

In the wave spectrum distribution based on linear wave theory, the appearance of a giant wave whose wave height reaches to 30m has been considered next to almost impossible in a real sea However since more than 10 giant waves were observed in a recent investigation of global wave distribution which was carried out by the analysis of SAR imagines for three weeks, the existence of the giant waves is being recognized and it is considered the cause of many unknown marine disasters. The change of wave height distribution concerning a formation of wave train, nonlinear wave to wave interaction and so on were raised as the causes of the appearance of the giant waves, but the occurrence mechanism of the giant waves hasn`t been cleared yet. In present study, we investigated appearance circumstances of the giant waves in real sea and its occurrence mechanism was analyzed based on linear and nonlinear wave focusing theories. Also, through a development of numerical model of the nonlinear equation, the formations of the giant wave from progressive wave train were reproduced.

/pdf/a-study-of-the-appearance-characteristics-and-generation-4ih351ha73.pdf

Hong Keyyong

Papers

Wave Energy Distribution at Jeju Sea and Investigation of Optimal Sites for Wave Power Generation

Analysis of Long-Term Wave Distribution at Jeju Sea Based on SWAN Model Simulation

An Experimental Study of Sediment Transport Patterns behind Offshore Structure

A Study of the Appearance Characteristics and Generation Mechanism of Giant Waves