Dear @Yosuke.Matsumoto,
The frequencies of the first few of your Craig-Bampton modes are quite low, but I suppose that is because your floater is quite massive relative to the tower stiffness.
Capturing 9P for a rotor speed of 7.56 goes is 1.1.34 Hz, which rises to 1.512 Hz for 12P. So, Roger’s recommendation of 2 Hz sounds sufficient, which limit you to needing at most 6 Craig-Bampton modes.
Best regards,