Hydrodynamic Optimization of a Float-type Wave Energy Converting Device

A shoreline Wave Energy Converter (WEC) was installed (Fig. 1) and tested in the sea near Sanya, China, with the financial support from the Chinese government. However, the performance of the energy device was relatively unsatisfactory though it was designed to make use of the standing wave in front of a seawall. Therefore, the objective of this study is to promote the hydrodynamic performance of the float applied in the WEC and increase the wave energy extraction ratio. A numerical model is built based on the Navier-Stokes solver coupled with immersed boundary method, volume of fluid method and the mechanics model of float. Making use of the laboratory measurements, the numerical model has been proved to be a reliable tool in reproducing wave deformations and the dynamics of the float. Then, the numerical model is employed to simulate the interactions between water waves and the floats of various shapes (see Fig. 2). Note that these floats are designed to have nearly the same volume to guarantee the same weight and draft, and rounded corners are introduced for the type-D. The water particle velocity field and pressure field around the float can be reproduced well, as shown in Fig. 3, which may provide valuable insight into the effect of water flow pattern on the energy capture for different floats. Comparisons can be carried out among the numerical results for the floats in Fig. 2 and the mechanism of the fluid-WEC interaction can be concluded with the help of these snapshots. More importantly, the wave energy conversion efficiency is estimated in a numerical manner for regular waves. Some results are plotted in Fig. 4 with different wave depths. Next, the model will be employed to test the sensibility of float performance to changes in some variables under various waves: wave steepness, water depth, wave period and the shape of float. Meaningful discussions and conclusions are expected to be reported in the full paper.

Figure 1 Side view of the wave energy converting device.

Figure 2 Four designed floats in the WEC.

Figure 3 Water particle velocity field and pressure field around the WEC

Figure 4 Energy conversion efficiency of the WEC with different water depths.