Possibility modeling ocean tidal turbine using NWTC wind turbine tools

Dear all, dear Dr. Jason,

I would like to ask for your advice on modeling ocean tidal turbine using FAST and other related NTWC_released tools.
The tidal turbine consists of a floater (but completed submerged in water), and a mooring system (see below picture).

In such case, it is possible to model it using NWTC open-public tools? for example, FAST v8.
In this modeling, what are the differences between modelling of wind and tidal turbine, that I should pay attention to?
Thank you for your kind advice.

Yingyi Liu

Dear Yingyi,

Here are a few comments:

  • Your system configuration is quite different from that of FAST v8, which assumes a floater + tower + nacelle + rotor, with hydrodynamic loads only applied to the floater.
  • It is unclear from your picture, but it appears your system may have a fairing that may restrict the conventional wake expansion, perhaps requiring a modification to the blade-element/momentum theory within FAST v8.
  • Buoyancy and hydrodynamic added mass are important sources of loading not yet included in FAST v8; that said, I know the water power team at NREL is working to add these effects, which will be released in a future version.
  • The inflow to the rotor may require specialized turbulence consistent with tidal flows, and perhaps including contributions from wave kinematics.

My guess is modifications would be required to the FAST v8 source code to model your system.

Best regards,

Hi Yingyi,

It sounds like OPENFOAM may be more suited to your needs than FAST. There is an example of a floating tidal turbine analysis in OPENFOAM by researchers in Plymouth University (slideplayer.com/slide/10266973/) that seems to be similar on concept to your design. OPENFOAM is a much more demanding software than FAST in both computing requirements and learning curve so it is possible that it may be more than you are looking for.

Issues to consider for tidal turbines are discussed in all-energy.co.uk/__novadocuments/14949. HARP_OPT is mentioned as a possible solution for tidal turbines but I dont know enough about the software to say if it would be suitable for a floating structure.

Your design is also similar to the reference model 4 of the Sandia Labs reference project (energy.sandia.gov/energy/renewab … oject-rmp/). The model was designed using HARP_OPT for the turbine and Orcaflex for the other sections. If Orcaflex is not available, then maybe the Openwarp-Nemoh software and FAST/Moordyn could substitute.