Dear Jason

Finally, I run BModes and use ModeShapePolyFitting.xls to calculate the mode shapes of NREL-5MW Baseline wind trubine. However, I found that the coefficients of mode shapes provided by “NRELOffsheBsline5MW_Tower_ITIBarge4” are different from what I calculated.

I used the values shown below in BModes main input file:

False Echo Echo input file contents to *.echo file if true.

2 beam_type 1: blade, 2: tower (-)

0. romg: rotor speed (rpm), automatically set to zero for tower modal analysis

1.0 romg_mult: rotor speed muliplicative factor (-)

87.6 radius: rotor tip radius measured along coned blade axis OR tower height (m)

0. hub_rad: hub radius measured along coned blade axis OR tower rigid-base height (m)

0. precone: built-in precone angle (deg), automatically set to zero for a tower

0. bl_thp: blade pitch setting (deg), automatically set to zero for a tower

1 hub_conn: hub-to-blade connection [1: cantilevered; other options not yet available]

10 modepr: number of modes to be printed (-)

f TabDelim (true: tab-delimited output tables; false: space-delimited tables)

f mid_node_tw (true: output twist at mid-node of elements; false: no mid-node outputs)

--------- Blade-tip or tower-top mass properties --------------------------------------------

350000 tip_mass blade-tip or tower-top mass (see users’ manual) (kg)

0.413 cm_loc tip-mass c.m. offset from the tower axis measured along the tower-tip x reference axis (m)

4.370E7 ixx_tip blade lag or tower s-s mass moment of inertia about the tip-section x reference axis (kg-m^2)

2.353E7 iyy_tip blade flap or tower f-a mass moment of inertia about the tip-section y reference axis (kg-m^2)

2.542E7 izz_tip torsion mass moment of inertia about the tip-section z reference axis (kg-m^2)

0.201 ixy_tip cross product of inertia about x and y reference axes(kg-m^2)

1.169E6 izx_tip cross product of inertia about z and x reference axes(kg-m^2)

2.88 iyz_tip cross product of inertia about y and z reference axes(kg-m^2)

--------- Distributed-property identifiers --------------------------------------------------------

1 id_mat: material_type [1: isotropic; non-isotropic composites option not yet available]

‘NRELOffshrBsline5MW_Tower_ITIBarge4_Properties.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 f-a inertia multiplier (-)

1.0 lag_iner_mult: blade lag or tower s-s inertia multiplier (-)

1.0 flp_stff_mult: blade flap or tower f-a bending stiffness multiplier (-)

1.0 edge_stff_mult: blade lag or tower s-s 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 --------------------------------------------------

12 nselt: no of blade or tower elements (-)

Distance of element boundary nodes from blade or flexible-tower root (normalized wrt blade or tower length), el_loc()

0. 0.08 0.16 0.24 0.32 0.40 0.48 0.56 0.64 0.72 0.80 0.90 1.0

--------- Properties of tension wires suporting the tower --------------------------------

0 n_attachments: no of wire-attachment locations on tower, maxm allowable is 2; 0: no tension-wire support (-)

3 3 n_wires: no of wires attached at each location (must be 3 or higher) (-)

6 9 node_attach: node numbers of attacments location (node number must be more than 1 and less than nselt+2) (-)

0.e0 0.e0 wire_stfness: wire sifnness in each set (see users’ manual) (N/m)

0. 0. th_wire: angle of tension wires wrt the tower axis at each attachment point (deg)

The red lines are the modification to original input file because I want to use the properties of NREL-5MW Baseline wind turbine and could you please help me to check if it is right. The values of “ixx_tip”, “iyy_tip”, “izz_tip”, “ixy_tip”, “ixz_tip”, “iyz_tip” are copied from my last post. Is it right to do so?

The section properties of ITI Barge 4 tower is attached and I believe it is correct. (I modified the file type from .dat to .txt so that it could be attached).

The outputs I got from BModes are shown below.

I am wondering why the f-a disp are all zero for mode 1? Because I can not get any result if I put zeros into ModeShapePolyFitting.xls to calculate mode shape coefficients.

By the way, I tried to modify “ixy_tip” and “iyz_tip” to some number similar to “ixx_tip” and then, I got some values for both s-s disp and f-a disp for all modes in output file. Why is that?

Best

XING WEI

NRELOffshrBsline5MW_Tower_ITIBarge4_Properties.txt (2.13 KB)