You can export the results of modal analyses and the associated geometry (mesh) to a RecurDyn RFlex Input (RFI) file for use in RecurDyn. The following conditions must be satisfied:
Natural Frequency (Modal). RecurDyn RFI file export is
not
supported for Natural Frequency (Modal) with Load Stiffening or Natural Frequency (Modal) with Nonlinear Material Models. From the Results environment, execute the following command to export an RFI file:

Export
RecurDyn RFI. Unlike the majority of third-party FEA file formats, which are text files, the RFI file is a binary file format.