Appendix F. Major Changes in SubDyn

When first released, SubDyn (v0.4) was included as an undocumented feature of FAST v8 and packaged as a stand-alone archive. Since v0.4, SubDyn has been well integrated into FAST v8 and OpenFast, and the stand-alone form is also available. This appendix outlines significant modifications to SubDyn made since v0.4. Following are the main changes that the user may notice, but for more information, refer to the changelog.txt text file within the official archive and the GitHub log. V1.05.00 (October 2021)

  • Version 1.05.00 integrates with OpenFAST version 3.1+

  • SubDyn driver supports loads at given nodes

  • Outputs of Craig-Bampton/Guyan and FEM Modes to JSON format for visualization

  • Streamlined yaml file output, with rigid body mass matrix at different points

  • Bug fix for rigid assemblies.

  • Bug fix for mass reported in summary file V1.04.00 (September 2020)

  • Version 1.04.00 integrates with OpenFAST version 2.4

  • Member types: beam, rigid link, pretension cable

  • Joint types: cantilever, universal, pin, ball

  • Input of all terms for concentrated mass

  • Guyan damping matrix

  • Extra lever arm

  • Coupling sith SoilDyn

  • Inclusion of soil-structure interaction (SSI) via flexible degrees of fixity at the restrained nodes and a new input file that allows for 6x6 stiffness and mass matrices that simulate boundary conditions at those nodes.

  • Controllable pretension cable elements V1.03.00a-rrd (September 2017) V1.01.01a-rrd (September 2014)

Version 1.01.01a-rrd integrates with the FAST v8 software v8.09.00a-bjj.

  • Finite-element eigenvalue bug fixes: the full system eigenvalues were incorrectly reported in the summary file, although with no further consequences on the results. This bug is now fixed.

  • Shear area correction factor improvement: the shear area correction factor in the Timoshenko treatment is now aligned with Steinboeck et al. (2013).

  • The formulation for the TP reaction has been rearranged to adhere to the theory manual, with no consequences on the output results. V1.01.00a-rrd (June 2014)

Version 1.00.01a-rrd integrates with the FAST v8 software v8.08.00c-bjj.

The new implementation has well-defined data exchange interfaces (following the FAST modularization framework) that should make integration of SubDyn into other multiphysics software packages much simpler.

Several improvements and bug fixes have been implemented since version v0.4 and the module has undergone an extensive verification effort with good results.

  • Eigensolver bug fixes: the LAPACK solver proved to be unstable in single precision, and now it is solely run in double precision, regardless of the precision used in other parts of the code.

  • The input file format has changed. Please refer to the sample input file in Appendix A and the following notes:

    • First header line has been removed.

    • Simulation Control Section:

      • SDeltaT: The “DEFAULT” keyword (in place of 0.0) is now used to indicate that the glue-code time step will be used for time integration by SubDyn.

      • IntMethod: Allowed values are now 1-4 (in place of 0-3).

      • SttcSolve: New flag introduced. If set to TRUE, the static-improvement method (SIM) will be used.

    • FEA and Craig-Bampton Parameters Section:

      • In v0.4, the damping coefficients had to be specified for all retained Craig-Bampton modes, or just once for all the modes (if CBMod = FALSE). In this version, the user can input any number of damping coefficients. In case the number of retained C-B modes (NModes) is larger than the input number of damping coefficients (JDampings), the last damping value will be replicated for all the remaining modes.

    • Base Reaction Joints, Interface Joints, Member, and Member Cosine Matrices Sections:

      • One line with units, below the headers, is expected in all the tables of the input file.

    • Output: Summary and Outfile Section:

      • This section now also contains the parameters previously assigned under the Section titled “Output: Fast/Subdyn Output-File Variables”

  • Some of the quantities in the summary file have been fixed. Some of the output matrices were, in fact, being output with wrong values because of an index mismatch. The new summary file is shorter and does not contain some of the CB method matrices, unless the compiler directive, DEBUG, is set.

  • SIM. This new implementation helps minimize the number of needed modes to capture the contribution of certain loads (such as static gravity and buoyancy loads or high-frequency loads transferred from the turbine). In the previous version, a large number of internal modes were needed to engage substructural modes excited by static and high-frequency forces. These modes are no longer needed and fewer modes can be retained while still achieving accurate results (see also Section With SIM enabled, all modes that are not considered by the Craig-Bampton reduction are treated quasi-statically.

  • There is now the possibility of retaining no internal C-B modes, thus relying solely only on SIM, in those cases where the substructure`s first eigenfrequencies are much higher than the expected energy-containing modes of the entire system.

  • The coupling of SubDyn within FAST now includes full hydro-elastic coupling with the HydroDyn hydrodynamics module.