LiftWEC - Development of a novel wave energy converter based on hydrodynamic lift forces
To date, the vast majority of wave energy converters that have been developed have attempted to exploit buoyancy or diffraction forces in the extraction of wave energy; however, the LiftWEC concept is designed to exploit the lift forces generated using a rotating hydrofoil. This radically different approach to the design of wave energy converters, provided by the LiftWEC concept, offers the opportunity of making a step-change in the potential of wave energy and thus leading the way for its commercialisation. This step-change in the design of wave energy converters could be likened to the step-change in wind turbine performance that occurred with the introduction of high-performance aerofoils to generate lift, when compared to sails and buckets that had previously been used.
In waves of limited steepness, the trajectory of a single particle of water (a drop) forms closed ellipsoidal loops. This is synonymous with a rotating velocity vector of constant magnitude for that one particle.
If we now insert a hydrofoil into the water beneath the waves, the relative velocity of the particles passing the hydrofoil can be used, in combination with a suitable pitch setting of the foil, to generate lift. As the direction of the particle velocity changes over the wave period, the pitch of the foil is adjusted accordingly. Using a carefully tuned system, a constant lift can be generated. By attaching the foil to a lever, a continuous rotary motion is induced which can be harnessed using a power-take-off system to generate electricity. Following this approach, lift-to-drag ratios of up to 10 can be reached, allowing a higher power-capture of the available wave energy.
Within the 36 months duration of the project, the initial concept of the lift-based wave energy converter shall be further developed to demonstrate its feasibility in realistic conditions. While the hydrodynamic principle is straightforward for harmonic, long-crested wave excitation, certain challenges arise when exposing the concept to irregular, short-crested seas. Furthermore, as for most devices designed for deployment in offshore locations, the extreme environmental conditions have to be taken into account to ensure a reasonable life expectancy.
Finally, the environmental impact of the concept has to be assessed in order to ensure the compatibility of an operating device and marine life.
Role of FDS
A key factor to the success of the LiftWEC concept is its economic viability. In order to assess the Levelized Cost of Energy (LCoE) throughout the life-time of the device, reliable numerical models are needed to predict performance and loads, and design each component accordingly.
The Institute of Fluid Dynamics and Ship Theory leads the Numerical Modelling work package within the LiftWEC consortium. As leader of this work package, FDS guides the development of hydrodynamic tools to allow real-time computation of the foils in waves, in coupling with the control algorithm developed by our partners from the National University of Ireland Maynooth, as well as high-fidelity simulations to allow a detailed analysis of the flow dynamics in regular operation and in extreme weather condition.The work is conducted in close collaboration with Innosea, working on the development and integration of the control algorithm in a real-time flow simulation tool and the Ecole Centrale de Nantes, responsible for the physical model testing needed to validate the numerical tools.
Our partners in the joint research project FernSAMS are Queen's University Belfast (coordinator), National University of Ireland Maynooth, Innosea, Aalborg University, University College Cork, Ecole Centrale de Nantes, Julia F. Chozas, WAVEC and University of Strathclyde.