Dear Cheng ZHANG,
Yes, h is the height along the tower; at the tower-top, h = TowerHt, so, h/H = 1. Likewise, phi(h = TowerHt) = 1 (because SUM(C_i,i=2,3,4,5,6) = 1). q_TwFADOF1 is the displacement of the first tower-bending fore-aft mode DOF.
Please see the following forum topic for more information on the theory basis of the ElastoDyn module of FAST: Coupled blade modes in FAST.
Best regards,