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SubDyn is a time-domain structural-dynamics module for multi-member fixed-bottom substructures.

It has been coupled into the FAST aero-hydro-servo-elastic engineering tool. Substructure types supported by SubDyn include monopiles, tripods, jackets, and other lattice-type substructures common for offshore wind installations in shallow and transitional water depths. SubDyn can also be used to model lattice support structures for land-based wind turbines.

SubDyn follows the requirements of the FAST Modularization Framework, couples to FAST version 8, and provides new capabilities (relative to prior versions) for modeling the substructure dynamic loading on multi-member substructures. SubDyn can also be driven as a stand-alone code to compute the mode shapes, natural frequencies, and time-domain responses of substructures, uncoupled from FAST and in the absence of external loading other than gravity and interface motion.

SubDyn relies on two main engineering schematizations:

  1. A linear frame finite-element beam model (LFEB)
  2. A dynamics system reduction via Craig-Bampton's (C-B) method, together with a Static-Improvement method, greatly reducing the number of modes needed to obtain an accurate solution.

This software was developed by Rick Damiani, Huimin Song, and Emmanuel Branlard of NREL.

Newer versions and ongoing development now take place in GitHub in the OpenFAST repository.