HydroDyn is a time-domain hydrodynamics module.

It has been coupled into the FAST wind turbine engineering tool to enable aero-hydro-servo-elastic simulation of offshore wind turbines. HydroDyn can also be driven as a standalone code to compute hydrodynamic loading uncoupled from FAST.

HydroDyn is applicable to both fixed-bottom and floating offshore substructures.

HydroDyn allows for multiple approaches for calculating the hydrodynamic loads on a structure: a potential-flow theory solution, a strip-theory solution, or a combination of the two.

Waves in HydroDyn can be regular (periodic) or irregular (stochastic) and long-crested (unidirectional) or short-crested (with wave energy spread across a range of directions). HydroDyn treats waves using first-order (linear Airy) or first- plus second-order wave theory with the option to include directional spreading, but no wave stretching or higher order wave theories are included. To minimize computational expense, Fast Fourier Transforms are applied in the summation of all wave frequency components.

This software was developed by Jason Jonkman of NREL. The source code is supported by Greg Hayman of Hayman Consulting LLC.

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