Response and Structural Analysis of a Flap-type Wave Energy Converter in a Combined Wind and Wave Concept

Abstract

In this thesis, the novel combined wind turbine and wave energy device, named Semi-submersible Flap Combination (SFC), is studied in terms of supporting arm strength of Wave Energy Converters (WECs) and produced power by WECs.Currently most offshore wind turbines are installed in shallow water up to 50-meter's water depth. However more steady and higher density winds are found in far offshores. In this case, floating platforms have to be used. But there are a lot of problems in designing, constructions and installations. More importantly, the cost is very high for commercialization. On the other hand, projects of WECs have been carried out around the world in the last decade in order to make use of wave energy. The combined concept is come up with in order to produce more power in one single production tool, or multi-use platform to be more cost effective. So the SFC concept has been developed under this background.The SFC consists of one Semi-submersible and three WECs. A comprehensive time domain simulations considering representative stochastic wind-sea states are carried out for both the SFC model and the Bottom-Fixed Wave Energy Converters (BFWEC) in the state-of-art simulation tool SIMO/RIFLEX/AeroDyn. Some theories behind the simulation tool are reviewed before going into simulations. The pitching natural period of BFWEC is estimated by mathematical calculation and decay curve simulation in SIMO/RIFLEX. Natural periods between 14s and 15s are got. The Ultimate Limite States (ULS) strength check is made for the supporting arms of WECs in both operational condition and survival condition according to the NORSOK Standard N004. Utility Factor (UF) is introduced to give a consistent and intuitive result. Comparisons between BFWEC and WECs of SFC are made in terms of UFs. The design for supporting arms are safe and reliable in terms of the design given in this thesis. The last part is calculating produced power by WECs. There are some differences between the BFWEC and WECs of SFC in producing power. Some conclusions are made in the end.