Dear Jason,
My second question means:
The following lines colored in red in the input file for OC3Hywind (wind.nrel.gov/public/jjonkman/BM … Hywind.bmi), i think they are referring to the same distance  from the MSL to Tower base, but the direction is opposite. That means the “tower rigidbase height” should be 10, and the “draft” should be 10.
But in the input file, the “tower rigidbase height” value is 0. So, I’m a little confused, am I misunderstanding the meaning of the two parameters?
Best regards,
Lei
====================== BModes v3.00 Main Input File ==================
NREL 5MW Tower
 General parameters 
true Echo Echo input file contents to *.echo file if true.
2 beam_type 1: blade, 2: tower ()
0. romg: rotor speed, automatically set to zero for tower modal analysis (rpm)

romg_mult: rotor speed muliplicative factor ()
87.6 radius: rotor tip radius measured along coned blade axis, OR tower height above ground level [onshore] or MSL offshore
0.0 hub_rad: hub radius measured along coned blade axis OR tower rigidbase height (m)
0. precone: builtin precone angle, automatically set to zero for a tower (deg)
0. bl_thp: blade pitch setting, automatically set to zero for a tower (deg)
2 hub_conn: hubtoblade or towerbase boundary condition [1: cantilevered; 2: freefree; 3: only axial and torsion constraints] ()
20 modepr: number of modes to be printed ()
t TabDelim (true: tabdelimited output tables; false: spacedelimited tables)
f mid_node_tw (true: output twist at midnode of elements; false: no midnode outputs)
 Bladetip or towertop mass properties 
3.500003109E+005 tip_mass bladetip or towertop mass (kg)
0.4137754432 cm_loc tipmass c.m. offset from the tower axis measured along xtower axis (m)
1.9669893542 cm_axial tipmass c.m. offset tower tip measures axially along the z axis (m)
4.370E7 ixx_tip blade lag mass moment of inertia about the tipsection x reference axis (kgm^2)
2.353E7 iyy_tip blade flap mass moment of inertia about the tipsection y reference axis (kgm^2)
2.542E7 izz_tip torsion mass moment of inertia about the tipsection z reference axis (kgm^2)
0. ixy_tip cross product of inertia about x and y reference axes(kgm^2)
1.169E6 izx_tip cross product of inertia about z and x reference axes(kgm^2)
0. iyz_tip cross product of inertia about y and z reference axes(kgm^2)
 Distributedproperty identifiers 
1 id_mat: material_type [1: isotropic; nonisotropic composites option not yet available]
‘OC3Hywind_tower_secs.dat’ : sec_props_file name of beam section properties file ()
Property scaling factors…
1.0 sec_mass_mult: mass density multiplier ()
1.0 flp_iner_mult: blade flap or tower fa inertia multiplier ()
1.0 lag_iner_mult: blade lag or tower ss inertia multiplier ()
1.0 flp_stff_mult: blade flap or tower fa bending stiffness multiplier ()
1.0 edge_stff_mult: blade lag or tower ss bending stiffness multiplier ()
1.0 tor_stff_mult: torsion stiffness multiplier ()
1.0 axial_stff_mult: axial stiffness multiplier ()
1.0 cg_offst_mult: cg offset multiplier ()
1.0 sc_offst_mult: shear center multiplier ()
1.0 tc_offst_mult: tension center multiplier ()
 Finite element discretization 
50 nselt: no of blade or tower elements ()
Distance of element boundary nodes from blade or flexibletower root (normalized wrt blade or tower length), el_loc()
0.0000 0.0200 0.0400 0.0600 0.0800 0.1000 0.1200 0.1400 0.1600 0.1800 0.2000 0.2200 0.2400 0.2600 0.2800 0.3000 0.3200 0.3400 0.3600 0.3800 0.4000 0.4200 0.4400 0.4600 0.4800 0.5000 0.5200 0.5400 0.5600 0.5800 0.6000 0.6200 0.6400 0.6600 0.6800 0.7000 0.7200 0.7400 0.7600 0.7800 0.8000 0.8200 0.8400 0.8600 0.8800 0.9000 0.9200 0.9400 0.9600 0.9800 1.0000
 Properties of tower support subsystem (read only if beam_type is 2) 
1 tow_support: : aditional tower support [0: no additional support; 1: floatingplatform or monopile with or without tension wires] ()
10.0 draft : depth of tower base from the ground or the MSL (mean sea level) (m)
89.9155 cm_pform : distance of platform c.m. below the MSL (m)
7466.33E3 mass_pform : platform mass (kg)
Platform mass inertia 3X3 matrix (i_matrix_pform):
4229.23E6 0. 0.
0. 4229.23E6 0.
0. 0. 164.23E6
…