Numerical and experimental investigation of a novel breakwater combining coastal defence and energy generation for near shore environment

1. Introduction In recent years, many different concepts of wave energy devices have been proposed to capture the power from surface waves in marine environment. Majority of them are designed primarily for energy generation only in the deep ocean. In the near shore area, however, such device can also potentially provide coastal defence function which is beneficial to coastal management as well. A novel floating breakwater system, developed by Wave Energy Developments Ltd, is one of such device that has been designed to be able to intercept much of the near shore wave energy as well as work as shore protections. Through a floating beach, the approaching incident waves are directed towards collector tubes and provide energy output using the water hammer principle within these tubes. The present study illustrates the preliminary testing of such concept through both laboratory experiments at Lancaster University and computer simulations at Liverpool University. 2. Methods A 1:10 scale model of the device has been tested in the wave flume at Lancaster University for various incident waves. Head losses and power output were measured on different setting of the device in order to identify the optimal design. CFD computer models were also used at the University of Liverpool for both laboratory model and prototype so that potential power generation at different scales can be obtained. Model testing is currently carried out for wider range of conditions that are expected at designed near shore sites. 3. Results Initial laboratory tests suggest that the efficiency of the device depends on the floating beach used for directing the approaching waves, as well as the design of the water tube for the power generation. The incident wave angle generally has less impact on the total power production, in comparison with the wave length. Computer model results also showed the complex flow structure over the floating beach and inside the tube. Details of the effects from wave non-linearity, incident wave angles and non-return valve on the total energy production are currently under investigation. 4. Conclusions A novel floating breakwater system has been designed for energy generation from near shore waves. Apart from the energy production, the system also aims at providing shore protection. Both laboratory experiments and computer modelling works are currently underway to examine the details of the design and possible optimisation. The computer model results and laboratory tests will also help to improve the system operation under real offshore severe conditions