BeamDyn - Possibility to output for more than 9 nodes


Could you please tell me whether outputting variables for more than 9 nodes in BeamDyn of OpenFAST is possible? As can be seen from the default source code, this is limited with total max 9 nodes. Is there any workaround for, say, 2 beam elements each containing 9 nodes?

Kind regards

Dear Kutalmis,

It is not possible without modification of the source code to output variables from BeamDyn at more than 9 nodes. (Of course you can run OpenFAST with BeamDyn multiple times with different node numbers output, but this would be computationally expensive.) The output of 9 nodes was a deemed a reasonable compromise in terms of ease of implementation and sufficient resolution to capture the variation of response along the blade (and is quite consistent with other OpenFAST modules e.g. ElastoDyn and AeroDyn).

Best regards,

Many thanks Dr. Jonkman.

Dear Dr. Jonkman,

Could you please then advise me an off-the-shelf method, if there is any, to interpolate nodal displacements and rotations onto key-points, if you know?

Many thanks.

Dear Kutalmis,

It may be reasonable to use linear interpolation between the FE nodes and the key points depending on the relative difference between the two and the accuracy you need. A better approach would be to use the underlying shape functions of the FE (in this case Lagrangian Interpolants). Please note that interpolating rotations in 3D is not trivial, unless the rotations are small.

We have a related open issue posted in OpenFAST regarding the need to add motion outputs from BeamDyn based on the quadrature scheme (both internally within the source code and as output quantities to be written to the output file): My intent here would be to use the underlying shape functions.

Best regards,

Many thanks for your help Dr. Jonkman.