Design of a Mooring System for Inertial Sea Wave Energy Converter (ISWEC)

Wave energy’s field has been growing up in the last few years, with several power extraction devices. It represents an important part for future energy scenario. ?? ISWEC, among these devices, takes advantage of pitch motion caused by incident wave. This motion, together with flywheel motion, generates the rotation of a gyroscopic unit around the PTO (power generator) axis. It is thereby possible considering a whole set of reasons to explain the importance of a correct design of a mooring system, especially talking about ISWEC. Above all, a mooring system has to ensure the station-keeping of device according to rules. For this reason, it is important to know the regulations. About mooring system, there are different rules, from various institutions, quite similar each other. The analysed one in this work is DNV rules, precisely DNV-OS-E301 “Position Mooring”. There are, moreover, a series of others factors which must be analysed, like influence of mooring system in power loss or cost, like the capability of the mooring system to ensure device weathervaning, like the environmental impact on seabed flora and fauna, like ability to ensure an easily maintenance and monitoring service. The purpose of this work is to find a design process which ensure not only the rules validation but also an optimization to power extraction. The design process developed is made of three part: the first one with a static model which ensures low computational cost with “low fidelity”, the second one is an optimization part with a dynamic approach, and at the end will be another dynamic model with a validation according to rules. The static model and the optimization model will be tested and described in details. A series of software were analysed and, at the end, MoorDyn was chosen for the optimization part and Orcaflex for the validation. MoorDyn is mooring dynamic solver with a Matlab\Simulink interface, therefore, its versatility drove the choice. To validate MoorDyn, it was tested comparing it with experimental data. Two different mooring models have been built following the configurations used in an experimental campaign in Naples. Each validation was done in un-coupled simulation, giving to the software the kinematic input of experimental campaign. ?? A further mooring model in MoorDyn coupled with ISWEC Simulink model was built to study the importance and the influence of mooring system in power loss. ?? The last part of the design process will be the validation part, where Orcaflex will be used.