Dear Dhaneesh,
I’m not sure what you mean when you say that “it didn’t work”.
Using CompAero = 0 will eliminate all aerodynamic loads from the model.
I have not done this myself, but you should be able to run Seismic in an offshore monopile configuration, with combined wind, wave, and seismic excitation. In this case, you would use PtfmModel = 2 in the FAST v7 primary (*.fst) input file and use FAST tower and platform input files that are similar to the ones for the couple springs (CS) model (found in my post dated Nov 27, 2018 in the following forum topic: Simulating OC3 phase II coupled springs in FAST v7 - #2 by Jason.Jonkman), but with PtfmSgDOF and PtfmSwDOF (and perhaps PtfmHvDOF) enabled; PtfmRDOF, PtfmPDOF, and PtfmYDOF disabled; and PtfmMass set to be a value much larger than combined mass of the turbine + monopile.
Best regards,