Dear Boran,
We have recently added linearization functionality in OpenFAST for floating offshore wind turbines, including linearization of MAP++ and HydroDyn, the latter of which includes the ability to include a wave disturbance in state-space form (in addition to the linearization of wind turbine related modules previously available). See our IOWTC 2018 paper for more information: nrel.gov/docs/fy19osti/71865.pdf. We presented the verification results at the DeepWind 2019 conference in January (paper still in the publication process). We are currently finalizing the verification results and documentation before the public release.
Best regards,