campbell_diagram_data.m Needs to be Updated for Recent Linearization Upgrades to OpenFAST

[jjonkman]

The campbell_diagram_data.m script provides a useful representation of the eigensolution so as to enable users to interpret the eigenvectors and eigenvalues resulting from the MBC3 analysis in terms of the full system natural frequencies, damping ratios, and mode shapes. However, the script has not been updated to reflect recent improvements to OpenFAST involving linearization of SubDyn, MoorDyn, AeroDyn, and the structural control (StC) submodel of ServoDyn. A few improvements are warranted:

• For the ElastoDyn and BeamDyn states, only the displacement states are included in the eigenvectors because the velocity states contain redundant information. However, both the displacement and velocity states from MoorDyn are currently included. These velocity states should be removed from the reported eigenvectors.

• The script applies scaling to the blade and tower translation states of ElastoDyn and BeamDyn so as to ensure all states represented in the eigenvector have similar units (radians). That is, the blade translation states are scaled by one over the blade length and the tower translation states are scaled by one of the tower length, effectively converting the translation in meters to an equivalent slope in radians. Similar scaling should be added for the platform transnational displacements in ElastoDyn (based on the tower length) and the mooring line translational states in MoorDyn (based on the water depth). Likewise, a scaling of the C-B mode states in SubDyn and the StC states in ServoDyn should be developed.

• Aerodynamic states from the DBEMT and UA submodels of AeroDyn can now be included in the linearized state-space matrices derived from OpenFAST. It is desired to account for the effect of these aerodynamic states on the frequencies and damping of the structure, but not to have aerodynamic modes themselves show up in the eigensolution. A way to eliminate the aerodynamic modes from showing up in the eigensolution should be developed.

[andrew-platt]

Regarding MD: The velocity states in the model we were looking at may be due to that particular OF code that was run. That branch was missing the updates to MD and the glue code to fix the ordering of the MD states.