12
Oct

Tackling tidal energy with these turbine tricks

turbine

Extracting energy from the ocean’s tides is a challenging task. However, the amount of available energy and the predictability of the tides provides many incentives. The tidal energy industry is growing rapidly, especially in regions that possess strong tidal resources, such as the Bay of Fundy in Canada and Orkney in Scotland. In-stream tidal energy converters (TECs) are being developed to harness and withstand the forces in these extreme environments. Structural loads, mooring loads, and structure motions need to be well understood before deploying expensive equipment in such harsh environments. Accurate modelling the loads and motions of the TECs is required for rapid and cost effective design. Dynamic Systems Analysis has developed a turbine feature as part of the ProteusDS time domain dynamic analysis software package to help perform analysis on TEC devices.

Daily, DSA’s engineers, and software users work to create, optimize, and analyze virtual prototypes of equipment from moored barges to complex tidal turbine systems. While these two projects differ in many aspects, fundamentally the reason for performing the analysis is the same: reduce risk and uncertainty.

Virtual prototypes show the dynamic response caused by the effect of the wind, waves, and ocean currents. DSA’s easy to use software, ProteusDS, allows for quicker analysis, design iteration, and optimization, providing an accurate assessment of equipment and vessel behavior under a variety of marine environmental conditions. The analysis reduces the need for physical prototypes and testing, saving both money and time.

TEC developers often complete advanced analysis, such as computation fluid dynamics (CFD) or model scale tests, on the turbine itself. Therefore, the thrust, torque, and power curves are already known before the rest of the TEC structure is fully designed. The turbine feature allows TEC developers to quickly input existing thrust and torque data on their turbines into the dynamic analysis tool. The turbine feature also incorporates the control scheme of the turbine that includes operational effects like feathering power or optimal efficiency. By applying these detailed effects of each turbine in the simulation model, developers can better understand the global response of the entire TEC system.

Triton Turbine side view

During turbine operation, turbine thrust loads can have the most significant effect on the system, so it is important to ensure they are accurate. The turbine feature allows for the thrust and torque coefficient to be dependent on the tip speed ratio (TSR), relative velocity, or both and contains a second order control system to allow for the turbine to accelerate realistically with changes to the relative fluid velocity. This feature pairs perfectly with the turbulence modelling available in ProteusDS. This feature also allows for the accurate effect of power shedding such as with flexible turbine blades or feathering blades so that as relative fluid speed increases, the thrust and torque coefficients decrease accordingly.

The turbine feature allows for several scheduled control modes. The user can set the turbine to apply a brake, freewheel, or return to operating mode at any time in the simulation. The user can also specify cut-in and cut-out speeds that will automatically brake the turbine if relative fluid velocity outside of these set-points is reached. These features allow TEC developers to model extreme cases that may trigger turbine shutdowns that will affect the behavior of the entire structure.

The ability to view and understand how a system will react is a big advantage in any ocean industry, but especially so in fast flowing tidal channels. It allows you to plan ahead and gain insight into how a system will react in a wide range of conditions. Determining areas of potential problems will reduce project risk and provides assurance that the design can withstand the extreme ocean conditions.

Modelling tidal energy devices in unique environments are an important step in designing successful TECs, and few tools specific to the tidal industry are available. The turbine feature in ProteusDS allows for quick set-up of a TEC device or farm to help tidal developers perform a numerical analysis. ProteusDS can provide invaluable insight into structure loads, mooring loads, and system motion in varying environmental and operational conditions.