First of alll, i am so grateful for your quick reply @Pietro.Bortolotti.

Fortunately, now the second side to side and fore aft tower mode shapes (not taking the rna into account, but only the tower) are very similar. However, there is something that makes me confused. I have done four graphs and for every graph i compare the mode shapes between Elastodyn, BModes (for the tower without rna), BModes (for the tower with rna) and Modes. One graph is for the 1st fore-aft tower mode shape, another is for 1st side-to-side tower mode shape, one more is for 2nd fore-aft tower mode shape, and lastly one more for 2nd side-to-side tower mode shape:

As @Jason.Jonkman told me, Modes does not depict the tower mode shape as accurate as BModes does. However, my doubt is why for the second mode shapes (both for fore-aft and side to side), there is a noticable difference between ElastoDyn and BModes with tower_rna_of? Plus, the second fore-aft mode shape for the tower with rna (tower_rna_on) seems very incoherent, right? I am saying this because it is hard to believe there is going to be 5 meters of tower deflectionâ€¦

Surprisingly, for the second side-to-side mode shape, ElastoDyn and BModes (taking the RNA into account) are the same. Maybe the coefficients from the elastodyn input file are taken from BModes (for the tower with RNA)? But i do not know why the polynomic coefficients taken from elastodyn tower input file and the ones i acquired from the excel Modeshapepolyfitting are not the same. Is there an explanation for this? I demonstrate the two ways for the coefficients below:

For elastodyn tower input file, polynomic coefficients are:

-0.5122368127986152 TwSSM2Sh(2) - Mode 2, coefficient of x^2 term

2.236214062644386 TwSSM2Sh(3) - , coefficient of x^3 term

-4.450315822523695 TwSSM2Sh(4) - , coefficient of x^4 term

6.21339621261931 TwSSM2Sh(5) - , coefficient of x^5 term

-2.4870576399413857 TwSSM2Sh(6) - , coefficient of x^6 term

On the other hand, the coefficients using the excel called Modeshapepolyfitting are:

|a2| -0.81565769

|a3| 5.371358112

|a4| -10.92275327

|a5| 11.00488145

|a6| -3.637828603

Lastly, i would like to do a campbell diagram. I have been exploring in many forums, but i do not know how to create the straight lines (by straight lines i mean the ones that if there is one intersection point with the natural frequencies, there is resonance). I have also discovered that if i change the rotor speed, the natural frequency does not change anything (both for the blade and tower). Shouldnâ€™t it change even a bit?

Best regards. Alberto