The concept of an underwater turbine, called tidal current turbine, designates the device which allows the conversion of kinetic energy produced by marine currents into electric energy. This study shows that the world of marine propellers presents an interesting avenue of research with regard to the hydrodynamic behaviour of tidal current turbines. As a marine propeller has to be adapted to a specific ship, a tidal current turbine has to be adapted to a specific site. We chose the most promising site on the French coasts, the race of Alderney. The main numerical tool is a propeller code based on the potential flow model. Putting aside the structure constraints, the design of tidal turbines is restricted by the hydrodynamic efficiency which means that flow separation and cavitation occurrence have to be avoided. An optimization procedure has allowed us to obtain a bare turbine geometry presenting a power coefficient (Cp) reaching 88% of the Betz and avoiding cavitation.

It has been suggested in our previous investigation that the addition of a duct can significantly increase the power output of the turbine when the power coefficient is computed using the rotor diameter. We suggest that adding a duct will not only increase the total weight but also the manufacturing cost. However, the authors show that to properly assess the hydrodynamic benefits of a ducted design, an overall cross-section area has to be considered. A new definition of the power coefficient applied to the ducted configuration was proposed (Cp*). The optimization of the duct leads to an additional power output of 20% compared to the bare turbine and respecting an overall cross-section of the ducted configuration using Cp* definition.

The second part deals with the design of the duct to find a balance between hydrodynamic performance and structural integrity using composite materials. However several iterations of material distribution have been performed to satisfy two main criteria. These criteria are the maximum deflection ( 2% maximum deflexion of the chord) and the onset damage based on Hashin failure criteria. The approach led to introduce the ducted configuration presenting the best ration ‹‹power/mass».

The third part of this work presents a numerical study of the dynamic behaviour of an all-composite ducted tidal turbine. The numerical analysis has been performed by means of advanced numerical models implemented into Abaqus/Explicit. The modelling procedure in term of intralaminar damage was implemented using a 3D damage model including damage onset and propagation implemented into a VUMAT subroutine using various 3D failure criteria. In the other hand, the interlaminar damage (delamination) was modelled using the cohesive zone model (CZM) available in Abaqus/Explicit and well described in the works published by Alfano and further by Camanho. The numerical procedure involving inter/intralaminar damage combination using an uncoupled methodology was validated through comparison with experimental impact test on glass-epoxy tubular samples intended for marine application.

Once the damage methodology has been validated, the objective of the third part deals mainly with the impact damage safety and the design certification to improve the design safety and reduce the certification cost of the proposed ducted turbine, keeping in mind commercial scalability of the MJM design concept. The proposed approach reveals some interesting points concerning the severity of the impact-induced damage and the safety of the composite duct. The computations performed concern only the degradation of the zone in contact with the impactor and the region in front of it but the certification procedure could be applied to other zones of the duct regardless of the impact event in terms of impact energy and incidence.