In this paper we propose a two-buoy wave energy converter composed of a heaving semi-submerged cylindrical buoy, a fixed submerged cylindrical buoy and a power take-off(PTO) system, and investigate the effect of the fixed submerged buoy on the hydrodynamics of the heaving semi-submerged buoy based on the three-dimensional potential theory. And the dynamic response of the semi-submerged buoy and the wave energy conversion efficiency of the converter are analyzed. The difference of the hydrodynamics and the wave energy conversion efficiency of a semi-submerged buoy converter with and without a fixed submerged buoy is discussed. It is revealed that the influence of the fixed submerged buoy on the exciting wave force, the added mass, the radiation damping coefficient and the wave energy conversion efficiency can be significant with a considerable variation, depending on the vertical distance between the heaving semi-submerged buoy and the fixed submerged buoy, the diameter ratio of the fixed submerged buoy to the heaving semi-submerged buoy and the water depth.
Based on a general review of marine renewable energy in China, an assessment of the development status and amount of various marine renewable energy resources, including tidal energy, tidal current energy, wave energy, ocean thermal energy, and salinity gradient energy in China's coastal seas, such as the Bohai Sea, the Yellow Sea, the East China Sea, and the South China Sea, is presented. We have found that these kinds of marine renewable energy resources will play an important role in meeting China's future energy needs. Additionally, considering the uneven distribution of China's marine renewable energy and the influences of its exploitation on the environment, we have suggested several sites with great potential for each kind of marine energy. Furthermore, perspectives on and challenges related with marine renewable energy in China are addressed.
An experimental study has been carried out to investigate effects of four flow-altering scour countermeasures placed around a foundation pile under currents only as well as under coexisting waves and currents. The countermeasures are sacrificial piles, downstream bed sill, sleeve and slot in the pile. Their arrangements follow the suggested optimal configurations, with some of them slightly modified. In terms of the evolution of scour depth and bed topography around the pile, the scour countermeasures are evaluated, subjected to steady currents with or without irregular waves. A comparison between maximum scour depth with the countermeasures and one without the countermeasures demonstrates the efficiency of countermeasures. All the tested scour measures reduce the scour depth by 17.6%–42.6% under the action of currents only and 5.8%–24.0% under the combined action of both currents and waves. The results also show that it takes a shorter time for the scour depth to reach its equilibrium with the measures under either coexisting currents and waves or currents only than ones without the measures.
