Hi Florence,
I’m glad you figured out the problem with the SubDyn output.
NTwInpSt is independent from the number of tower nodes (TwrNodes), as discussed, e.g., in the following forum topic: ElastoDyn handeling of Input TMassDen - #2 by Jason.Jonkman.
The tower analysis nodes are located at the centers of the tower elements, all of which have the same length. The tower nodes locations are also written to the ElastoDyn summary file. The definitions of TwrGagNd, etc. have been discussed several times on this forum, e.g., see: fore-aft and side-to-side accelerations at mid-tower - #4 by Jason.Jonkman.
Best regards,