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Floating offshore VAWT with NREL 5MW Structure
Good Day,
I have downloaded the structural files for the NREL 5MW turbine from the downloads page. I would like to attach a VAWT to the structural files and wanted to know how this can be done. I have seen previous posts indicating to utilise the SANDIA turbine as reference. Is it possible to attach the NREL semi-sub structure to the SANDIA VAWT or a VAWT of my own design to test in offshore conditions?
What are the requirements / edits required to the semi-sub structural file or main file to execute this so that the turbine can be attached to a floating structure?
regards
DJ
Hi DJ,
doing that is quite simple:
You need to add the following line (filename and keyword pair) to the main structural input file of the VAWT turbine:
OC3_Sparbuoy_Sub_LPMD.str SUBFILE
Where the filename indicates the file that defines the substructure.
Here is an example of connecting the SANDIA 34m VAWT model template to the OC3 Sparbuoy from a different model template. I had to remove the ground-fixing guycables of the SANDIA turbine by removing the keyword CABFILE from the main structural input file, add the above line to the main structural input file and then copy the OC3_Sparbuoy_Sub_LPMD.str floater definition file into the same folder as the main SANDIA structural input file. Obviously the sparbuoy would need some redimentioning…
BR,
David
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Hi Dr. David,
I still don’t know what radiation and excitation files are and how I can create them (see Radiation and excitation files.png).
Next to that, I also don’t know how to create the matrices depicted in Matrices.png and Hydrodynamic coefficients.png (this is explained in the User’s guide, but not how to get the values).
Can you help me?
Kind regards,
Brecht
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Hi Brecht,
there are several ways to model a substructure in QBlade, and each approach has its own advantages and limitations.
If you want to use “linear potential flow theory” to model a floater, you will need to obtain radiation, excitation (and possibly sum and difference-frequency) files using a preprocessor that solves the inviscid flow around the floater in the frequency domain. Some examples of such solvers are WAMIT, Nemoh, or Capytaine.
Another approach to model the hydrodynamic forces on the floater is to use the Morison equation. Unlike the linear potential flow theory, this method doesn’t require any preprocessing but can be inaccurate for certain geometries and generally requires a lot of tuning of the hydrodynamic coefficients it’s based on.
There are also various element types (more to come) and options available to model the substructure itself. It can be composed of rigid elements, flexible elements, or no elements at all, and instead, “lumped” hydrodynamic mass, stiffness, added mass, and damping matrices can be used. In most cases, a substructure is defined using a combination of these approaches.
When modeling a substructure with lumped matrices, the entries of these matrices should be based on the real hydrodynamic structure that was possibly designed in another CAD software.
Designing, tuning, and modeling a substructure for a wind turbine is a complex topic that requires a good understanding of the fundamentals of hydrodynamics. It has a steep learning curve, but with the proper knowledge and techniques, it can be done very effectively.
BR,
David
Oke thanks for your respons!
