Hi,
I am trying to use, for modelling an offhsore wind turbine substructure, SubDyn, and in particular I have structural members other than circular, and therefore need to use the MEMBER COSINE MATRICES COSM(i,j).
Is anyone aware of an example of how this part is used? Is there an example of SubDyn.dat file that I can look at?
I hav egone through the readthedocs section here, but the explanation is not very extensive.
Any material you can point me to would be good!
Many thanks
Dear @Maurizio.Collu,
I’m not fully up to speed, but my understanding is that support for arbitrary cross-sectional properties, including specification of the direction matrices, is not fully supported by SubDyn. There was a placeholder for future functionality in SubDyn for a while, until an external developer updated the code in OpenFAST v3.5 to provide basic support: SD: Implementing directional cosine matrices and section properties for rectangular members by samuel-ramsahoye · Pull Request #1413 · OpenFAST/openfast · GitHub. I’m not aware of any public tests that have been developed to test this recently merged capability and it doesn’t look like the documentation was updated when the source code was implemented by the external contributor.
NREL has recently kicked-off a project to add direct support for members with rectangular cross sections to HydroDyn and SubDyn. With this development, we will likely be changing how rectangular cross sections are defined in SubDyn. This project is being worked on now, but completion is not expected until later this summer.
Best regards,
In case this is useful, a spring element was developed in SubDyn and this element makes use of the member cosine matrices to define its orientation in the space. This element will be released in OpenFAST v4.0.0. You can find a description here: New spring element in SubDyn: 6 by 6 stiffness matrix by RBergua · Pull Request #1889 · OpenFAST/openfast · GitHub
In addition, the documentation about the member cosine matrices was a bit misleading and I tried to clarify it here: SubDyn documentation: Member Cosine Matrices by RBergua · Pull Request #2374 · OpenFAST/openfast · GitHub
I agree with Jason about the rectangular cross sections. I believe at this moment only the spring element in SubDyn makes use of the member cosine matrices provided by the user as input.
I hope that helps!
Thanks a lot, @Jason.Jonkman and @Roger.Bergua for the quick answer.
The reason I thought the capability to model rectangular members was implemented is because in the OpenFAST releases notes here is mentioned, under the SubDyn notes “#1413 Implementing directional cosine matrices and section properties for rectangular members”, as you mentioned, Jason.
I suppose the safer approach is to model any member as a cylindrical beam for the time being…
Many thanks! And wishing you relaxing and enjoyable holidays!