How to simulate damage by reducing tower stiffness?

Meng.He · April 1, 2025, 12:18pm

Dear @jjonkman,
I want to simulate damage by reducing the stiffness of the tower by 30 %, but I 'm not sure how to achieve it. I have the following ideas ( all modified for the ElastoDyn _ tower.dat file ) :

Directly set the two parameters of AdjFASt and AdjSSSt to 0.7.
If it is uniform damage, the TwFAStif and TwSSStif values of all segments are multiplied by 0.7 ;
If it is a local damage, and the first paragraph is selected as a local damage, the TwFAStif and TwSSStif values in the line with HtFract value of 0 are multiplied by 0.7.

---------------------- TOWER ADJUSTMUNT FACTORS --------------------------------
1.0 FAStTunr(1) - Tower fore-aft modal stiffness tuner, 1st mode (-)
1.0 FAStTunr(2) - Tower fore-aft modal stiffness tuner, 2nd mode (-)
1.0 SSStTunr(1) - Tower side-to-side stiffness tuner, 1st mode (-)
1.0 SSStTunr(2) - Tower side-to-side stiffness tuner, 2nd mode (-)
1.0 AdjTwMa - Factor to adjust tower mass density (-)
1.0 AdjFASt - Factor to adjust tower fore-aft stiffness (-)
1.0 AdjSSSt - Factor to adjust tower side-to-side stiffness (-)
---------------------- DISTRIBUTED TOWER PROPERTIES ----------------------------
HtFract TMassDen TwFAStif TwSSStif
(-) (kg/m) (Nm^2) (Nm^2)
0.000000000000000e+00 2.300642131074250e+04 6.770513741893661e+12 6.770513741893661e+12
1.114034260838268e-01 2.038926791017103e+04 6.012509438660999e+12 6.012509438660999e+12
2.228068521676536e-01 1.774601273898164e+04 5.243768263364071e+12 5.243768263364071e+12
3.342102782514804e-01 1.506280308193614e+04 4.460141520157670e+12 4.460141520157670e+12
4.456137043353072e-01 1.234240777801470e+04 3.662296012994249e+12 3.662296012994249e+12
5.570171304191340e-01 9.633099266285813e+03 2.864340844739592e+12 2.864340844739592e+12
6.684205565029608e-01 7.026968999232271e+03 2.093608918221600e+12 2.093608918221600e+12
7.798239825867876e-01 4.645483574127345e+03 1.386599057692824e+12 1.386599057692824e+12
8.912274086706145e-01 2.596093483450980e+03 7.761060822822759e+11 7.761060822822759e+11
1.000000000000000e+00 1.715031343116859e+03 3.489844253733395e+11 3.489844253733395e+11

Or to modify other parameters, or the above three methods are wrong ?

Thank you in advance,

Best wishes,

Jason.Jonkman · April 1, 2025, 12:46pm

Dear @Meng.He,

I generally agree with your points 1-3.

Note that when you change the tower stiffness distribution, you should also update the tower mode shapes accordingly.

Best regards,

Meng.He · April 1, 2025, 2:17pm

Dear @jjonkman,
I still don 't quite understand how to do that. After listening to your answer, I have the following confusion :

I can choose any of the above three ideas for damage simulation, but no matter which idea is selected, the corresponding tower mode shapes should be modified, right ?
If I choose the third idea above for damage simulation and achieve local damage by reducing the stiffness of the first section by 30 %, how should I modify the corresponding mode shapes except multiplying the values of TwFAStif and TwSSStif in the row with HtFract 0 by 0.7 ?
HtFract has 10 values, which divide the tower into 9 sections. If I want to reduce the stiffness of only one section at a time, I will reduce the stiffness of 9 sections respectively ( that is, set local damage according to the third idea above ). When setting the first damage, only two parameters of TwFAStif and TwSSStif in the row of the first HtFract ( that is, the HtFract value is 0 ) are modified ; when setting the second damage, only the two parameters of TwFAStif and TwSSStif in the row of the second HtFract (that is, the HtFract value is 1.114034260838268e-01) are modified. Similarly, the third to eighth sections are modified in turn. When the ninth section is damaged, only the TwFAStif and TwSSStif parameters of the ninth HtFract ( that is, the HtFract value is 8.912274086706145e-01 ) are modified. No matter which segment is set to be damaged, the two parameters of TwFAStif and TwSSStif in the row of the 10th HtFract (that is, the HtFract value is 1 ) can be modified without modification, right ? Of course, at the same time, the mode shape of the tower must be modified accordingly, but I only know that in this ElastoDyn_tower.dat there is the setting of MODE SHAPES (namely TOWER FORE-AFT MODE SHAPES and TOWER SIDE-TO-SIDE MODE SHAPES), and I do not know how to modify it. Can you guide me?

------- ELASTODYN V1.00.* TOWER INPUT FILE -------------------------------------
IEA 15 MW offshore reference model on UMaine VolturnUS-S semi-submersible floating platform
---------------------- TOWER PARAMETERS ----------------------------------------
10 NTwInpSt - Number of input stations to specify tower geometry
1.0 TwrFADmp(1) - Tower 1st fore-aft mode structural damping ratio (%)
1.0 TwrFADmp(2) - Tower 2nd fore-aft mode structural damping ratio (%)
1.0 TwrSSDmp(1) - Tower 1st side-to-side mode structural damping ratio (%)
1.0 TwrSSDmp(2) - Tower 2nd side-to-side mode structural damping ratio (%)
---------------------- TOWER ADJUSTMUNT FACTORS --------------------------------
1.0 FAStTunr(1) - Tower fore-aft modal stiffness tuner, 1st mode (-)
1.0 FAStTunr(2) - Tower fore-aft modal stiffness tuner, 2nd mode (-)
1.0 SSStTunr(1) - Tower side-to-side stiffness tuner, 1st mode (-)
1.0 SSStTunr(2) - Tower side-to-side stiffness tuner, 2nd mode (-)
1.0 AdjTwMa - Factor to adjust tower mass density (-)
1.0 AdjFASt - Factor to adjust tower fore-aft stiffness (-)
1.0 AdjSSSt - Factor to adjust tower side-to-side stiffness (-)
---------------------- DISTRIBUTED TOWER PROPERTIES ----------------------------
HtFract TMassDen TwFAStif TwSSStif
(-) (kg/m) (Nm^2) (Nm^2)
0.000000000000000e+00 2.300642131074250e+04 6.770513741893661e+12 6.770513741893661e+12
1.114034260838268e-01 2.038926791017103e+04 6.012509438660999e+12 6.012509438660999e+12
2.228068521676536e-01 1.774601273898164e+04 5.243768263364071e+12 5.243768263364071e+12
3.342102782514804e-01 1.506280308193614e+04 4.460141520157670e+12 4.460141520157670e+12
4.456137043353072e-01 1.234240777801470e+04 3.662296012994249e+12 3.662296012994249e+12
5.570171304191340e-01 9.633099266285813e+03 2.864340844739592e+12 2.864340844739592e+12
6.684205565029608e-01 7.026968999232271e+03 2.093608918221600e+12 2.093608918221600e+12
7.798239825867876e-01 4.645483574127345e+03 1.386599057692824e+12 1.386599057692824e+12
8.912274086706145e-01 2.596093483450980e+03 7.761060822822759e+11 7.761060822822759e+11
1.000000000000000e+00 1.715031343116859e+03 3.489844253733395e+11 3.489844253733395e+11
---------------------- TOWER FORE-AFT MODE SHAPES ------------------------------
0.9413693374950306 TwFAM1Sh(2) - Mode 1, coefficient of x^2 term
0.3468546636521823 TwFAM1Sh(3) - , coefficient of x^3 term
-1.0732425042270761 TwFAM1Sh(4) - , coefficient of x^4 term
1.3138921365298792 TwFAM1Sh(5) - , coefficient of x^5 term
-0.5288736334500164 TwFAM1Sh(6) - , coefficient of x^6 term
139.39115610617628 TwFAM2Sh(2) - Mode 2, coefficient of x^2 term
111.93048260721132 TwFAM2Sh(3) - , coefficient of x^3 term
-656.9153343478758 TwFAM2Sh(4) - , coefficient of x^4 term
845.7553274809915 TwFAM2Sh(5) - , coefficient of x^5 term
-439.16163184650327 TwFAM2Sh(6) - , coefficient of x^6 term
---------------------- TOWER SIDE-TO-SIDE MODE SHAPES --------------------------
0.928651504815363 TwSSM1Sh(2) - Mode 1, coefficient of x^2 term
0.3183110416167346 TwSSM1Sh(3) - , coefficient of x^3 term
-0.9597593899992671 TwSSM1Sh(4) - , coefficient of x^4 term
1.164027965180537 TwSSM1Sh(5) - , coefficient of x^5 term
-0.4512311216133674 TwSSM1Sh(6) - , coefficient of x^6 term
-1970.3543341226898 TwSSM2Sh(2) - Mode 2, coefficient of x^2 term
-2284.293209902991 TwSSM2Sh(3) - , coefficient of x^3 term
11346.453188064506 TwSSM2Sh(4) - , coefficient of x^4 term
-14750.85609454158 TwSSM2Sh(5) - , coefficient of x^5 term
7660.050450502754 TwSSM2Sh(6) - , coefficient of x^6 term

Thank you in advance,

Best wishes,

Meng.He · April 1, 2025, 3:26pm

Dear @jjonkman,

In addition to the above three questions, I have another question. When I reduce the stiffness of the tower proportionally, is there a range limit on the size of the reduction ?

Thank you in advance,

Best wishes,

Jason.Jonkman · April 1, 2025, 6:24pm

Dear @Meng.He,

Just a few comments:

Any time you change the tower geometry, its mass or stiffness distribution, or tower-top or tower-base boundary conditions, you should recompute the tower mode shapes.
You can calculate tower mode shapes with BModes, Frame3DD, or other FEA software to compute the tower mode shapes, and then fit a polynomial to those mode shapes as required by ElastoDyn. This topic has been discussed many times in this forum.
The tower mass and stiffness data provided in the DISTRIBUTED TOWER PROPERTIES section of the ElastoDyn tower file is interpolated to the tower structural analysis nodes (split it TwrNodes elements of equal length along the flexible portion of the tower between its base and top). The interpolated data used by ElastoDyn is reported in the ElastoDyn summary (ED.sum) file.
I’m not familiar with tower damage to know what a reasonable stiffness change is.

Best regards,

Meng.He · April 2, 2025, 1:56pm

Dear @jjonkman,
After listening to your answer, I have the following confusion :

As mentioned above, there are 10 HtFract values in my ElastoDyn_ tower.dat file, which divides the tower into 9 segments, but the BModes_tower_ prop.dat file I found in github today seems to have 20 nodes ( as shown below ), so I want to delete it to be consistent with my file, but it involves two parameters, flap _ stff and edge _ stff.Are these two parameters the same as the TwFAStif and TwSSStif parameters in the ElastoDyn _ tower.dat file I mentioned earlier ?
In the BMode file I found there is a BModes_ tower.echo file, in the Finite element discretization section of this file has some parameters, such as nselt value is 61, I do not know how to get 61, whether need to modify the parameters of the Finite element discretization section.
Because my segmentation of the tower is not the same as the BMode file I found, in addition to the parameters mentioned in the first and second points, what else do I need to modify ?( (Attached below I found today in the BMode file of the three sub-files, BMode file source link is GitHub - ptrbortolotti/IEA15_BModes )

====================== BModes v3.00 Main Input File ==================
IEA15 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 (rpm), automatically set to zero for tower modal analysis
1.0 romg_mult: rotor speed muliplicative factor (-)
144.386 radius: rotor tip radius measured along coned blade axis OR tower height (m)
15. 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]
20 modepr: number of modes to be printed (-)
t 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 --------------------------------------------
950057.799 tip_mass blade-tip or tower-top mass (see users’ manual) (kg)
-7.16870 cm_loc tip-mass c.m. offset from the tower axis measured along the tower-tip x reference axis (m)
4.584963 cm_axial tip-mass c.m. offset tower tip measures axially along the z axis (m)
3.7173e+08 ixx_tip blade lag or tower s-s mass moment of inertia about the tip-section x reference axis (kg-m^2)
2.6268e+08 iyy_tip blade flap or tower f-a mass moment of inertia about the tip-section y reference axis (kg-m^2)
3.5877e+08 izz_tip torsion mass moment of inertia about the tip-section z reference axis (kg-m^2)
0.0 ixy_tip cross product of inertia about x and y reference axes(kg-m^2)
1.6418e+07 izx_tip cross product of inertia about z and x reference axes(kg-m^2)
0.0 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]
‘BModes_tower_prop.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 --------------------------------------------------
61 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 0.003481894 0.010445682 0.017409471 0.024373259 0.031337047 0.038300836 0.045264624 0.052228412 0.059192201 0.066155989 0.073119777 0.080083565 0.087047354 0.094011142 0.10097493 0.107938719 0.114902507 0.121866295 0.128830084 0.135793872 0.13990 0.149721448 0.156685237 0.163649025 0.170612813 0.177576602 0.18454039 0.191504178 0.198467967 0.205431755 0.212395543 0.219359331 0.22632312 0.233286908 0.240250696 0.247214485 0.250696379 0.320334262 0.37971 0.424791072 0.45961 0.486635 0.51366 0.54068 0.5677 0.594715 0.62173 0.64875 0.67577 0.70279 0.72981 0.75683 0.78385 0.81087 0.83789 0.864905 0.89192 0.91894 0.94596 0.97298 1.0
--------- Properties of tower support subsystem (read only if beam_type is 2) ------------
0 tow_support: : aditional tower support [0: no additional support; 1: floating-platform or monopile with or without tension wires] (-)
0.0 draft : depth of tower base from the ground or the MSL (mean sea level) (m)
0.0 cm_pform : distance of platform c.m. below the MSL (m)
0.0 mass_pform : platform mass (kg)
Platform mass inertia 3X3 matrix (i_matrix_pform):
0. 0. 0.
0. 0. 0.
0. 0. 0.
0.0 ref_msl : distance of platform reference point below the MSL (m)
Platform-reference-point-referred hydrodynamic 6X6 matrix (hydro_M):
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
Platform-reference-point-referred hydrodynamic 6X6 stiffness matrix (hydro_K):
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
Mooring-system 6X6 stiffness matrix (mooring_K):
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0

Distributed (hydrodynamic) added-mass per unit length along a flexible portion of the tower length:
0 n_secs_m_distr: number of sections at which added mass per unit length is specified (-)
0. 0. : z_distr_m [row array of size n_added_m_pts; section locations wrt the flexible tower base over which distributed mass is specified] (m)
0. 0. : distr_m [row array of size n_added_m_pts; added distributed masses per unit length] (kg/m)

Distributed elastic stiffness per unit length along a flexible portion of the tower length:
0 n_secs_k_distr: number of points at which distributed stiffness per unit length is specified (-)

Tension wires data
0 n_attachments: no of wire-attachment locations on tower [0: no tension wires] (-)
0 n_wires: no of wires attached at each location (must be 3 or higher) (-)
0 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 spring constant in each set (see users’ manual) (N/m)
0. 0. th_wire: angle of tension wires (wrt the horizontal ground plane) at each attachment point (deg)

END of Main Input File Data *********************************************************************

        T  Echo           - Echo input file contents to *.echo file if true
        2  beam_type      - beam type, 1: blade; 2: tower

0.0000E+00 rot_rpm - rotor speed (rpm)
1.0000E+00 rpm_mult - rotor speed multiplicative factor
1.4439E+02 radius - rotor tip radius or tower height above ground (m)
1.5000E+01 rroot - hub radius or tower-base height (m)
0.0000E+00 btp - precone (deg)
0.0000E+00 bl_thp - blade pitch setting (deg)
1 hub_conn - hub-to-blade connectivity identifier
20 modepr - number of modes to be printed
T TabDelim - output format (t: std; f: tab-delimited)
F mid_node_tw - t: output twist at mid nodes; f: do otherwise

--------- Blade-tip or tower-top mass properties --------------------------------------------
9.5006E+05 tip_mass - tip mass
-7.1687E+00 cm_loc - tip-mass c.m. location wrt the reference axis
4.5850E+00 cm_axial - tip-mass c.m. axial offset wrt tip
3.7173E+08 ixx_tip - mass moment of inertia about x axis (wt-specific)
2.6268E+08 iyy_tip - mass moment of inertia about y axis
3.5877E+08 izz_tip - mass moment of inertia about z axis
0.0000E+00 ixy_tip - cross product of inertia
1.6418E+07 izx_tip - cross product of inertia
0.0000E+00 iyz_tip - cross product of inertia

--------- Distributed-property identifiers --------------------------------------------------------
1 id_mat - material isotropy identifier (not used; use later)
sec_props_file - name of beam section properties file (-)
“BModes_tower_prop.dat”

Property scaling factors…
1.0000E+00 sec_mass_mult - mass density multiplier (-)
1.0000E+00 flp_iner_mult - blade flap or tower f-a inertia multiplier (-)
1.0000E+00 lag_iner_mult - blade lag or tower s-s inertia multiplier (-)
1.0000E+00 flp_stff_mult - blade flap or tower f-a bending stiffness multiplier (-)
1.0000E+00 edge_stff_mult - blade lag or tower s-s bending stiffness multiplier (-)
1.0000E+00 tor_stff_mult - torsion stiffness multiplier (-)
1.0000E+00 axial_stff_mul - axial stiffness multiplier (-)
1.0000E+00 cg_offst_mult - cg offset multiplier (-)
1.0000E+00 sc_offst_mult - shear center multiplier (-)
1.0000E+00 tc_offst_mult - tension center multiplier (-)

--------- Finite element discretization --------------------------------------------------
61 nselt - number of blade or tower elements (-)
Distance of element boundary nodes from blade or flexible-tower root (normalized wrt blade or tower length), el_loc()
0.0000E+00 el_loc - array of normalized element locations (-)
3.4819E-03 el_loc - array of normalized element locations (-)
1.0446E-02 el_loc - array of normalized element locations (-)
1.7409E-02 el_loc - array of normalized element locations (-)
2.4373E-02 el_loc - array of normalized element locations (-)
3.1337E-02 el_loc - array of normalized element locations (-)
3.8301E-02 el_loc - array of normalized element locations (-)
4.5265E-02 el_loc - array of normalized element locations (-)
5.2228E-02 el_loc - array of normalized element locations (-)
5.9192E-02 el_loc - array of normalized element locations (-)
6.6156E-02 el_loc - array of normalized element locations (-)
7.3120E-02 el_loc - array of normalized element locations (-)
8.0084E-02 el_loc - array of normalized element locations (-)
8.7047E-02 el_loc - array of normalized element locations (-)
9.4011E-02 el_loc - array of normalized element locations (-)
1.0097E-01 el_loc - array of normalized element locations (-)
1.0794E-01 el_loc - array of normalized element locations (-)
1.1490E-01 el_loc - array of normalized element locations (-)
1.2187E-01 el_loc - array of normalized element locations (-)
1.2883E-01 el_loc - array of normalized element locations (-)
1.3579E-01 el_loc - array of normalized element locations (-)
1.3990E-01 el_loc - array of normalized element locations (-)
1.4972E-01 el_loc - array of normalized element locations (-)
1.5669E-01 el_loc - array of normalized element locations (-)
1.6365E-01 el_loc - array of normalized element locations (-)
1.7061E-01 el_loc - array of normalized element locations (-)
1.7758E-01 el_loc - array of normalized element locations (-)
1.8454E-01 el_loc - array of normalized element locations (-)
1.9150E-01 el_loc - array of normalized element locations (-)
1.9847E-01 el_loc - array of normalized element locations (-)
2.0543E-01 el_loc - array of normalized element locations (-)
2.1240E-01 el_loc - array of normalized element locations (-)
2.1936E-01 el_loc - array of normalized element locations (-)
2.2632E-01 el_loc - array of normalized element locations (-)
2.3329E-01 el_loc - array of normalized element locations (-)
2.4025E-01 el_loc - array of normalized element locations (-)
2.4721E-01 el_loc - array of normalized element locations (-)
2.5070E-01 el_loc - array of normalized element locations (-)
3.2033E-01 el_loc - array of normalized element locations (-)
3.7971E-01 el_loc - array of normalized element locations (-)
4.2479E-01 el_loc - array of normalized element locations (-)
4.5961E-01 el_loc - array of normalized element locations (-)
4.8663E-01 el_loc - array of normalized element locations (-)
5.1366E-01 el_loc - array of normalized element locations (-)
5.4068E-01 el_loc - array of normalized element locations (-)
5.6770E-01 el_loc - array of normalized element locations (-)
5.9471E-01 el_loc - array of normalized element locations (-)
6.2173E-01 el_loc - array of normalized element locations (-)
6.4875E-01 el_loc - array of normalized element locations (-)
6.7577E-01 el_loc - array of normalized element locations (-)
7.0279E-01 el_loc - array of normalized element locations (-)
7.2981E-01 el_loc - array of normalized element locations (-)
7.5683E-01 el_loc - array of normalized element locations (-)
7.8385E-01 el_loc - array of normalized element locations (-)
8.1087E-01 el_loc - array of normalized element locations (-)
8.3789E-01 el_loc - array of normalized element locations (-)
8.6491E-01 el_loc - array of normalized element locations (-)
8.9192E-01 el_loc - array of normalized element locations (-)
9.1894E-01 el_loc - array of normalized element locations (-)
9.4596E-01 el_loc - array of normalized element locations (-)
9.7298E-01 el_loc - array of normalized element locations (-)
1.0000E+00 el_loc - array of normalized element locations (-)
--------- Properties of tower support subsystem (read only if beam_type is 2) ------------
0 tow_support: : aditional tower support [0: no additional support; 1: floating-platform or monopile with or without tension wires] (-)
0 tow_support - aditional tower support (-)
Tower section properties
20 n_secs - number of blade or tower sections (-)

  sec_loc             str_tw              tw_iner            mass_den            flp_iner            edge_iner           flp_stff            edge_stff           tor_stff           axial_stff      
    (-)                (deg)               (deg)              (kg/m)              (kg-m)              (kg-m)              (Nm^2)              (Nm^2)              (Nm^2)                (N)

0.00000 0.10047 0.10048 0.20095 0.20096 0.30142 0.30143 0.40190 0.40191 0.50237 0.50238 0.60285 0.60286 0.70332 0.70333 0.80380 0.80380 0.90427 0.90428 1.00000 0.000 0.000 10314.844 0.000 0.000 3.07E+12 3.07E+12 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 10314.844 0.000 0.000 3.07E+12 3.07E+12 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 9523.819 0.000 0.000 2.83E+12 2.83E+12 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 9453.084 0.000 0.000 2.77E+12 2.77E+12 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 8761.306 0.000 0.000 2.57E+12 2.57E+12 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 8333.524 0.000 0.000 2.21E+12 2.21E+12 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 7943.340 0.000 0.000 2.11E+12 2.11E+12 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 7428.459 0.000 0.000 1.72E+12 1.72E+12 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 7087.214 0.000 0.000 1.64E+12 1.64E+12 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 6538.098 0.000 0.000 1.29E+12 1.29E+12 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 6197.175 0.000 0.000 1.22E+12 1.22E+12 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 5616.516 0.000 0.000 9.12E+11 9.12E+11 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 5253.478 0.000 0.000 8.53E+11 8.53E+11 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 4910.276 0.000 0.000 6.97E+11 6.97E+11 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 4334.168 0.000 0.000 6.15E+11 6.15E+11 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 4232.817 0.000 0.000 5.73E+11 5.73E+11 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 3673.388 0.000 0.000 4.98E+11 4.98E+11 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 3577.283 0.000 0.000 4.60E+11 4.60E+11 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 4120.141 0.000 0.000 5.29E+11 5.29E+11 1.00E+14 1.00E+14 0.000 0.000 0.000
0.000 0.000 4074.837 0.000 0.000 5.12E+11 5.12E+11 1.00E+14 1.00E+14 0.000 0.000 0.000

Tower section properties
20 n_secs: number of blade or tower sections at which properties are specified (-)

  sec_loc             str_tw              tw_iner            mass_den            flp_iner            edge_iner           flp_stff            edge_stff           tor_stff           axial_stff           cg_offst            sc_offst            tc_offst      
    (-)                (deg)               (deg)              (kg/m)              (kg-m)              (kg-m)              (Nm^2)              (Nm^2)              (Nm^2)                (N)                 (m)                 (m)                 (m)

0.000000000000000E+00 0.0000 0.0000 1.031484441173360E+04 1.e-6 1.e-6 3.065446681730710E+12 3.065446681730710E+12 1.e+14 1.e+14 0.0 0.0 0.0
1.004745490238510E-01 0.0000 0.0000 1.031484441173360E+04 1.e-6 1.e-6 3.065446681730710E+12 3.065446681730710E+12 1.e+14 1.e+14 0.0 0.0 0.0
1.004822778353140E-01 0.0000 0.0000 9.523818531177400E+03 1.e-6 1.e-6 2.832084716093430E+12 2.832084716093430E+12 1.e+14 1.e+14 0.0 0.0 0.0
2.009490980477020E-01 0.0000 0.0000 9.453084405718950E+03 1.e-6 1.e-6 2.769450452002750E+12 2.769450452002750E+12 1.e+14 1.e+14 0.0 0.0 0.0
2.009568268591660E-01 0.0000 0.0000 8.761306059261840E+03 1.e-6 1.e-6 2.568166429175230E+12 2.568166429175230E+12 1.e+14 1.e+14 0.0 0.0 0.0
3.014236470715530E-01 0.0000 0.0000 8.333524388530640E+03 1.e-6 1.e-6 2.210055981076240E+12 2.210055981076240E+12 1.e+14 1.e+14 0.0 0.0 0.0
3.014313758830170E-01 0.0000 0.0000 7.943339505959190E+03 1.e-6 1.e-6 2.107286870484590E+12 2.107286870484590E+12 1.e+14 1.e+14 0.0 0.0 0.0
4.018981960954040E-01 0.0000 0.0000 7.428459476674180E+03 1.e-6 1.e-6 1.723500010954970E+12 1.723500010954970E+12 1.e+14 1.e+14 0.0 0.0 0.0
4.019059249068680E-01 0.0000 0.0000 7.087214160266680E+03 1.e-6 1.e-6 1.644879215976750E+12 1.644879215976750E+12 1.e+14 1.e+14 0.0 0.0 0.0
5.023727451192560E-01 0.0000 0.0000 6.538098082624470E+03 1.e-6 1.e-6 1.291405296742770E+12 1.291405296742770E+12 1.e+14 1.e+14 0.0 0.0 0.0
5.023804739307190E-01 0.0000 0.0000 6.197174861548130E+03 1.e-6 1.e-6 1.224548874057190E+12 1.224548874057190E+12 1.e+14 1.e+14 0.0 0.0 0.0
6.028472941431070E-01 0.0000 0.0000 5.616516314866140E+03 1.e-6 1.e-6 9.115849751112290E+11 9.115849751112290E+11 1.e+14 1.e+14 0.0 0.0 0.0
6.028550229545700E-01 0.0000 0.0000 5.253477923437150E+03 1.e-6 1.e-6 8.530980440238870E+11 8.530980440238870E+11 1.e+14 1.e+14 0.0 0.0 0.0
7.033218431669580E-01 0.0000 0.0000 4.910275969995680E+03 1.e-6 1.e-6 6.965892589608760E+11 6.965892589608760E+11 1.e+14 1.e+14 0.0 0.0 0.0
7.033295719784210E-01 0.0000 0.0000 4.334167603205980E+03 1.e-6 1.e-6 6.154309947959970E+11 6.154309947959970E+11 1.e+14 1.e+14 0.0 0.0 0.0
8.037963921908090E-01 0.0000 0.0000 4.232816565257490E+03 1.e-6 1.e-6 5.732589718113060E+11 5.732589718113060E+11 1.e+14 1.e+14 0.0 0.0 0.0
8.038041210022720E-01 0.0000 0.0000 3.673387789838780E+03 1.e-6 1.e-6 4.979639354642210E+11 4.979639354642210E+11 1.e+14 1.e+14 0.0 0.0 0.0
9.042709412146600E-01 0.0000 0.0000 3.577282612388080E+03 1.e-6 1.e-6 4.598937820986930E+11 4.598937820986930E+11 1.e+14 1.e+14 0.0 0.0 0.0
9.042786700261230E-01 0.0000 0.0000 4.120141253172980E+03 1.e-6 1.e-6 5.291723868157960E+11 5.291723868157960E+11 1.e+14 1.e+14 0.0 0.0 0.0
1.000000000000000E+00 0.0000 0.0000 4.074837331422720E+03 1.e-6 1.e-6 5.119078821628500E+11 5.119078821628500E+11 1.e+14 1.e+14 0.0 0.0 0.0

Thank you in advance,

Best wishes,

Meng.He · April 2, 2025, 2:38pm

Dear @jjonkman,

In addition, when setting local damage to the tower, I mentioned before. HtFract has 10 values, which divide the tower into 9 sections. If I want to reduce the stiffness of only one section at a time, I will reduce the stiffness of 9 sections respectively ( that is, set local damage according to the third idea above ). When setting the first damage, only two parameters of TwFAStif and TwSSStif in the row of the first HtFract ( that is, the HtFract value is 0 ) are modified ; when setting the second damage, only the two parameters of TwFAStif and TwSSStif in the row of the second HtFract (that is, the HtFract value is 1.114034260838268e-01) are modified. Similarly, the third to eighth sections are modified in turn. When the ninth section is damaged, only the TwFAStif and TwSSStif parameters of the ninth HtFract ( that is, the HtFract value is 8.912274086706145e-01 ) are modified. No matter which segment is set to be damaged, the two parameters of TwFAStif and TwSSStif in the row of the 10th HtFract (that is, the HtFract value is 1 ) can be modified without modification, right ? (The content of ElastoDyn_tower.dat is attached below)

Of course, after the stiffness of the TOWER is modified, the corresponding MODE modes are calculated using BMode and input into the above-mentioned ElastoDyn_tower.dat (that is, tower SIDE-TO-SIDE MODE SHAPES).

------- ELASTODYN V1.00.* TOWER INPUT FILE -------------------------------------
IEA 15 MW offshore reference model on UMaine VolturnUS-S semi-submersible floating platform
---------------------- TOWER PARAMETERS ----------------------------------------
10 NTwInpSt - Number of input stations to specify tower geometry
1.0 TwrFADmp(1) - Tower 1st fore-aft mode structural damping ratio (%)
1.0 TwrFADmp(2) - Tower 2nd fore-aft mode structural damping ratio (%)
1.0 TwrSSDmp(1) - Tower 1st side-to-side mode structural damping ratio (%)
1.0 TwrSSDmp(2) - Tower 2nd side-to-side mode structural damping ratio (%)
---------------------- TOWER ADJUSTMUNT FACTORS --------------------------------
1.0 FAStTunr(1) - Tower fore-aft modal stiffness tuner, 1st mode (-)
1.0 FAStTunr(2) - Tower fore-aft modal stiffness tuner, 2nd mode (-)
1.0 SSStTunr(1) - Tower side-to-side stiffness tuner, 1st mode (-)
1.0 SSStTunr(2) - Tower side-to-side stiffness tuner, 2nd mode (-)
1.0 AdjTwMa - Factor to adjust tower mass density (-)
1.0 AdjFASt - Factor to adjust tower fore-aft stiffness (-)
1.0 AdjSSSt - Factor to adjust tower side-to-side stiffness (-)
---------------------- DISTRIBUTED TOWER PROPERTIES ----------------------------
HtFract TMassDen TwFAStif TwSSStif
(-) (kg/m) (Nm^2) (Nm^2)
0.000000000000000e+00 2.300642131074250e+04 6.770513741893661e+12 6.770513741893661e+12
1.114034260838268e-01 2.038926791017103e+04 6.012509438660999e+12 6.012509438660999e+12
2.228068521676536e-01 1.774601273898164e+04 5.243768263364071e+12 5.243768263364071e+12
3.342102782514804e-01 1.506280308193614e+04 4.460141520157670e+12 4.460141520157670e+12
4.456137043353072e-01 1.234240777801470e+04 3.662296012994249e+12 3.662296012994249e+12
5.570171304191340e-01 9.633099266285813e+03 2.864340844739592e+12 2.864340844739592e+12
6.684205565029608e-01 7.026968999232271e+03 2.093608918221600e+12 2.093608918221600e+12
7.798239825867876e-01 4.645483574127345e+03 1.386599057692824e+12 1.386599057692824e+12
8.912274086706145e-01 2.596093483450980e+03 7.761060822822759e+11 7.761060822822759e+11
1.000000000000000e+00 1.715031343116859e+03 3.489844253733395e+11 3.489844253733395e+11
---------------------- TOWER FORE-AFT MODE SHAPES ------------------------------
0.9413693374950306 TwFAM1Sh(2) - Mode 1, coefficient of x^2 term
0.3468546636521823 TwFAM1Sh(3) - , coefficient of x^3 term
-1.0732425042270761 TwFAM1Sh(4) - , coefficient of x^4 term
1.3138921365298792 TwFAM1Sh(5) - , coefficient of x^5 term
-0.5288736334500164 TwFAM1Sh(6) - , coefficient of x^6 term
139.39115610617628 TwFAM2Sh(2) - Mode 2, coefficient of x^2 term
111.93048260721132 TwFAM2Sh(3) - , coefficient of x^3 term
-656.9153343478758 TwFAM2Sh(4) - , coefficient of x^4 term
845.7553274809915 TwFAM2Sh(5) - , coefficient of x^5 term
-439.16163184650327 TwFAM2Sh(6) - , coefficient of x^6 term
---------------------- TOWER SIDE-TO-SIDE MODE SHAPES --------------------------
0.928651504815363 TwSSM1Sh(2) - Mode 1, coefficient of x^2 term
0.3183110416167346 TwSSM1Sh(3) - , coefficient of x^3 term
-0.9597593899992671 TwSSM1Sh(4) - , coefficient of x^4 term
1.164027965180537 TwSSM1Sh(5) - , coefficient of x^5 term
-0.4512311216133674 TwSSM1Sh(6) - , coefficient of x^6 term
-1970.3543341226898 TwSSM2Sh(2) - Mode 2, coefficient of x^2 term
-2284.293209902991 TwSSM2Sh(3) - , coefficient of x^3 term
11346.453188064506 TwSSM2Sh(4) - , coefficient of x^4 term
-14750.85609454158 TwSSM2Sh(5) - , coefficient of x^5 term
7660.050450502754 TwSSM2Sh(6) - , coefficient of x^6 term

Thank you in advance,

Best wishes,

Jason.Jonkman · April 2, 2025, 9:52pm

Dear @Meng.He,

I’m not familiar with the repository that you are grabbing BModes examples from, but here are my responses to your questions:

Yes, for a tower in BModes, flp_stff in BModes should match TwFAStif in ElastoDyn and edge_stff in BModes should match TwFSSStif in ElastoDyn.
nselt in BeamDyn is the number of elements used in the analysis and is specified in the BeamDyn (.bmi) input file. nselt in BeamDyn is similar to TwrNodes in ElastoDyn, except that in ElastoDyn, each segment is equal length and the analysis nodes are located at the segment centers, and in BeamDyn, each element can be different lengths and the analysis nodes are located at the element endpoints, which are user-specified in BModes via el_loc.
n_secs in BeamDyn is the number of tower property sections, corresponding to the number of rows in the table below it. The values specified in this table are interpolated to the analysis nodes of BModes (located via el_loc). This is equivalent to NTwInpSt in ElastoDyn, whose values in the table get interpolated to the analysis nodes of ElastoDyn (located at the centers of TwrNodes equal-length segments).

Best regards,

Meng.He · April 3, 2025, 3:22pm

Dear @jjonkman,

I read the relevant discussion in the forum, I know that we can use ModeShapePolyFitting.xls to learn the modal shape, and it is better to choose Normalized lmproved Direct Method, but I do not know when using the polynomials mentioned in ModeShapePolyFitting.xls for calculation, x, y and Slope ( or Estimated slope atbottom ) are the corresponding data in the BModes.out file ?

Thank you in advance,

Best wishes,

Jason.Jonkman · April 3, 2025, 8:36pm

Dear @Meng.He,

Here are the equivalencies between the outputs of BeamDyn and the inputs to ModeShapePolyFitting.xls:

x = span_loc
y = s-s disp for side-side modes or f-a disp for fore-aft modes
Slope = s-s slope at span_loc = 0.0 for side-side modes or f-a slope at span_loc = 0.0 for fore-aft modes

Best regards,

Meng.He · April 4, 2025, 2:58am

Dear @jjonkman,

I understand, thank you very much for your patience to answer my question.

Thank you in advance,

Best wishes,

Meng.He · April 9, 2025, 9:14am

Dear @jjonkman,

I still have two puzzles :

I did not modify the stiffness of the tower, directly run the BMode, according to the principle of combining it to calculate the.out and ModeShapePolyFitting table to get the modal shape should not be the same as the current ElastoDyn _ tower.dat value ? But I calculate it seems not the same, I use the data of Mode No.7 in the calculated out into the ModeShapePolyFitting table, the value obtained is not the same as that in ElastoDyn _ tower.dat, is it reasonable ? ( The calculation results of the table and the ElastoDyn _ tower.dat file are attached below )
If I modify the stiffness of the tower, is it necessary to modify the values in BModes _ tower _ prop.dat after modifying the values of TwFAStif and TwSSStif in ElastoDyn _ tower.dat, and then run BModes ?

------- ELASTODYN V1.00.* TOWER INPUT FILE -------------------------------------
IEA 15 MW offshore reference model on UMaine VolturnUS-S semi-submersible floating platform
---------------------- TOWER PARAMETERS ----------------------------------------
20 NTwInpSt - Number of input stations to specify tower geometry
1.0 TwrFADmp(1) - Tower 1st fore-aft mode structural damping ratio (%)
1.0 TwrFADmp(2) - Tower 2nd fore-aft mode structural damping ratio (%)
1.0 TwrSSDmp(1) - Tower 1st side-to-side mode structural damping ratio (%)
1.0 TwrSSDmp(2) - Tower 2nd side-to-side mode structural damping ratio (%)
---------------------- TOWER ADJUSTMUNT FACTORS --------------------------------
1.0 FAStTunr(1) - Tower fore-aft modal stiffness tuner, 1st mode (-)
1.0 FAStTunr(2) - Tower fore-aft modal stiffness tuner, 2nd mode (-)
1.0 SSStTunr(1) - Tower side-to-side stiffness tuner, 1st mode (-)
1.0 SSStTunr(2) - Tower side-to-side stiffness tuner, 2nd mode (-)
1.012 AdjTwMa - Factor to adjust tower mass density (-)
1.0 AdjFASt - Factor to adjust tower fore-aft stiffness (-)
1.0 AdjSSSt - Factor to adjust tower side-to-side stiffness (-)
---------------------- DISTRIBUTED TOWER PROPERTIES ----------------------------
HtFract TMassDen TwFAStif TwSSStif
(-) (kg/m) (Nm^2) (Nm^2)
0.000000000000000e+00 2.029915384490826e+04 6.34237969641029e+12 6.34237969641029e+12
1.003225756663734e-01 2.022546527594423e+04 6.603749839477144e+12 6.603749839477144e+12
1.003302927875785e-01 2.022546527594423e+04 6.603749839477144e+12 6.603749839477144e+12
2.006451513327469e-01 2.023160599002457e+04 6.609766335624008e+12 6.609766335624008e+12
2.006528684539519e-01 2.023160599002457e+04 6.609766335624008e+12 6.609766335624008e+12
3.009677269991203e-01 2.014972980228675e+04 6.529846332759697e+12 6.529846332759697e+12
3.009754441203253e-01 7.322246657002261e+03 2.398364219075645e+12 2.398364219075645e+12
4.012903026654937e-01 7.027048474103984e+03 2.119831120597360e+12 2.119831120597360e+12
4.012980197866988e-01 6.559959619960716e+03 1.979756603965887e+12 1.979756603965887e+12
5.016128783318671e-01 6.298251757227584e+03 1.752139464827495e+12 1.752139464827495e+12
5.016205954530722e-01 5.849659029832589e+03 1.628055029897855e+12 1.628055029897855e+12
6.019354539982406e-01 5.718854421470604e+03 1.521264430029204e+12 1.521264430029204e+12
6.019431711194456e-01 5.060688247269418e+03 1.347089835872890e+12 1.347089835872890e+12
7.022580296646139e-01 4.941573191012188e+03 1.254190895026094e+12 1.254190895026094e+12
7.022657467858191e-01 4.298499856237385e+03 1.091725960511694e+12 1.091725960511694e+12
8.025806053309874e-01 4.135733940854927e+03 9.723460353016257e+11 9.723460353016257e+11
8.025883224521925e-01 3.723048360853340e+03 8.757368303973829e+11 8.757368303973829e+11
9.029031809973608e-01 3.241853127377142e+03 5.781735578187830e+11 5.781735578187830e+11
9.029108981185660e-01 3.780608307293219e+03 6.737063635067307e+11 6.737063635067307e+11
1.000000000000000e+00 3.355419345609961e+03 4.710065834970021e+11 4.710065834970021e+11
---------------------- TOWER FORE-AFT MODE SHAPES -------
0.8652 TwFAM1Sh(2) - Mode 1, coefficient of x^2 term
-2.2378 TwFAM1Sh(3) - , coefficient of x^3 term
6.7891 TwFAM1Sh(4) - , coefficient of x^4 term
-6.5162 TwFAM1Sh(5) - , coefficient of x^5 term
2.0998 TwFAM1Sh(6) - , coefficient of x^6 term
31.3349 TwFAM2Sh(2) - Mode 2, coefficient of x^2 term
-43.4365 TwFAM2Sh(3) - , coefficient of x^3 term
79.7339 TwFAM2Sh(4) - , coefficient of x^4 term
-123.2282 TwFAM2Sh(5) - , coefficient of x^5 term
56.5959 TwFAM2Sh(6) - , coefficient of x^6 term
------------------------ TOWER SIDE-TO-SIDE MODE SHAPES -
0.8676 TwSSM1Sh(2) - Mode 1, coefficient of x^2 term
-2.2540 TwSSM1Sh(3) - , coefficient of x^3 term
6.8267 TwSSM1Sh(4) - , coefficient of x^4 term
-6.5533 TwSSM1Sh(5) - , coefficient of x^5 term
2.1130 TwSSM1Sh(6) - , coefficient of x^6 term
31.3344 TwSSM2Sh(2) - Mode 2, coefficient of x^2 term
-43.4357 TwSSM2Sh(3) - , coefficient of x^3 term
79.7323 TwSSM2Sh(4) - , coefficient of x^4 term
-123.2259 TwSSM2Sh(5) - , coefficient of x^5 term
56.5948 TwSSM2Sh(6) - , coefficient of x^6 term

Thank you in advance,

Best wishes,

Jason.Jonkman · April 9, 2025, 12:43pm

Dear @Meng.He,

Here are my responses:

Are you sure you extracted the correct first tower mode from BModes? Your plot does not look like a first tower-bending mode. Regardless, I suspect you will not get the exact same results for the polynomial coefficients for tower mode shapes of the IEA Wind 15-MW RWT atop the UMaine semisubmersible because I don’t believe these mode shapes were derived from BModes (although I was not the one to make the original OpenFAST model). That said, I would suggest plotting the mode shape directly based on the polynomial coefficients to see how close the mode shapes actually are (mode shapes with different polynomial coefficients can look similar).
Yes.

Best regards,

Meng.He · April 9, 2025, 1:32pm

Dear @jjonkman,

I still have two puzzles :

I mean to say that the value calculated by BModes and ModeShapePolyFitting is different from the value of ElastoDyn _ tower.dat in the first place, let alone the drawing ? I 'm not sure if I have any parameter settings that are not quite right, can you help me see ? ( Attached here are my bmi file, tower _ prop file, BMode 's.out file and some ModeShapePolyFitting input )（Due to word limit,.out file only put Mode No.6 ~ 8 in it.）
By the way, I see a post about BModes on the Internet, which says that in the Bmodes operation result file ( i.e.,.out ), mode 1 ~ 2 corresponds to sway and surge, mode 3 corresponds to heave, mode 4 ~ 5 corresponds to roll and pitch, mode 6 corresponds to yaw, mode 7 and later modes are the modes of the tower, and by judging the values of s-sdisp and f-adisp. To determine whether the current mode is the side-side or fore-aft mode of the tower. Therefore, I choose span _ loc in mode 7 as the x value in ModeShapePolyFitting, f-adisp as the y value in ModeShapePolyFitting, and f-aslope when span _ loc is 0 as the Slope value. Am I right to do this ?
====================== BModes v3.00 Main Input File ==================
IEA-15-240-RWT Offshore Tower (from tip to TP 15 m above MSL). Substructure is computed from Subdyn Summary files.

--------- General parameters ---------------------------------------------------------------------
True 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 (-)
150. radius: rotor tip radius measured along coned blade axis OR tower height (m)
15. 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
3 hub_conn: hub-to-blade connection [1: cantilevered; other options not yet available]
20 modepr: number of modes to be printed (-)
t 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 --------------------------------------------
1639877. tip_mass blade-tip or tower-top mass (see users’ manual) (kg)
-6.476016 cm_loc tip-mass c.m. offset from the tower axis measured along the tower-tip x reference axis (m)
4.2691133 cm_axial tip-mass c.m. offset tower tip measures axially along the z axis (m)
3.89258526e+08 ixx_tip blade lag or tower s-s mass moment of inertia about the tip-section x reference axis (kg-m^2)
2.29364247e+08 iyy_tip blade flap or tower f-a mass moment of inertia about the tip-section y reference axis (kg-m^2)
1.86875391e+08 izz_tip torsion mass moment of inertia about the tip-section z reference axis (kg-m^2)
0. ixy_tip cross product of inertia about x and y reference axes(kg-m^2)
-7199394.0784606 izx_tip cross product of inertia about z and x reference axes(kg-m^2)
0. 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]
‘IEA-15-240-RWT_BModes_tower_prop.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 --------------------------------------------------
61 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 0.003481894 0.010445682 0.017409471 0.024373259 0.031337047 0.038300836 0.045264624 0.052228412 0.059192201 0.066155989 0.073119777 0.080083565 0.087047354 0.094011142 0.10097493 0.107938719 0.114902507 0.121866295 0.128830084 0.135793872 0.13990 0.149721448 0.156685237 0.163649025 0.170612813 0.177576602 0.18454039 0.191504178 0.198467967 0.205431755 0.212395543 0.219359331 0.22632312 0.233286908 0.240250696 0.247214485 0.250696379 0.320334262 0.37971 0.424791072 0.45961 0.486635 0.51366 0.54068 0.5677 0.594715 0.62173 0.64875 0.67577 0.70279 0.72981 0.75683 0.78385 0.81087 0.83789 0.864905 0.89192 0.91894 0.94596 0.97298 1.0

--------- Properties of tower support subsystem (read only if beam_type is 2) ------------
1 tow_support: : aditional tower support [0: no additional support; 1: floating-platform or monopile with or without tension wires] (-)
-15.0 draft : depth of tower base from the ground or the MSL (mean sea level) (m)
0.0 cm_pform : distance of platform c.m. below the MSL (m)
0.0 mass_pform : platform mass (kg)
Platform mass inertia 3X3 matrix (i_matrix_pform):
0. 0. 0.
0. 0. 0.
0. 0. 0.
-15.0 ref_msl : distance of platform reference point below the MSL (m)
Platform-reference-point-referred hydrodynamic 6X6 matrix (hydro_M):
0.168773E+06 0.000000E+00 0.000000E+00 0.000000E+00 -0.987753E+06 0.000000E+00
0.000000E+00 0.168773E+06 0.000000E+00 0.987753E+06 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.146961E+06 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.987753E+06 0.000000E+00 0.830811E+07 0.000000E+00 0.000000E+00
-0.987753E+06 0.000000E+00 0.000000E+00 0.000000E+00 0.830811E+07 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.364523E+07
Platform-reference-point-referred hydrodynamic 6X6 stiffness matrix (hydro_K):
0.353727E+09 0.000000E+00 0.000000E+00 0.000000E+00 -0.751078E+10 0.000000E+00
0.000000E+00 0.353727E+09 0.000000E+00 0.751078E+10 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 0.656870E+10 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 0.751078E+10 0.000000E+00 0.240814E+12 0.000000E+00 0.000000E+00
-0.751078E+10 0.000000E+00 0.000000E+00 0.000000E+00 0.240814E+12 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.644996E+11
Mooring-system 6X6 stiffness matrix (mooring_K):
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0

Distributed (hydrodynamic) added-mass per unit length along a flexible portion of the tower length:
0 n_secs_m_distr: number of sections at which added mass per unit length is specified (-)
0. 0. : z_distr_m [row array of size n_added_m_pts; section locations wrt the flexible tower base over which distributed mass is specified] (m)
0. 0. : distr_m [row array of size n_added_m_pts; added distributed masses per unit length] (kg/m)

Distributed elastic stiffness per unit length along a flexible portion of the tower length:
0 n_secs_k_distr: number of points at which distributed stiffness per unit length is specified (-)

Tension wires data
0 n_attachments: no of wire-attachment locations on tower [0: no tension wires] (-)
0 n_wires: no of wires attached at each location (must be 3 or higher) (-)
0 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 spring constant in each set (see users’ manual) (N/m)
0. 0. th_wire: angle of tension wires (wrt the horizontal ground plane) at each attachment point (deg)

END of Main Input File Data *********************************************************************

Tower section properties (15 MW reference turbine)
20 n_secs: number of blade or tower sections at which properties are specified (-)

  sec_loc             str_tw              tw_iner            mass_den            flp_iner            edge_iner           flp_stff            edge_stff           tor_stff           axial_stff           cg_offst            sc_offst            tc_offst      
    (-)                (deg)               (deg)              (kg/m)              (kg-m)              (kg-m)              (Nm^2)              (Nm^2)              (Nm^2)                (N)                 (m)                 (m)                 (m)

0.000000E+00 0.000000E+00 0.000000E+00 9.701837E+03 1.302815E+05 1.302815E+05 3.065447E+12 3.065447E+12 2.430899E+12 2.471806E+11 0.000000E+00 0.000000E+00 0.000000E+00
1.003156E-01 0.000000E+00 0.000000E+00 9.701837E+03 1.302815E+05 1.302815E+05 3.065447E+12 3.065447E+12 2.430899E+12 2.471806E+11 0.000000E+00 0.000000E+00 0.000000E+00
1.003233E-01 0.000000E+00 0.000000E+00 8.957821E+03 1.203636E+05 1.203636E+05 2.832085E+12 2.832085E+12 2.245843E+12 2.282247E+11 0.000000E+00 0.000000E+00 0.000000E+00
2.006390E-01 0.000000E+00 0.000000E+00 8.891291E+03 1.177016E+05 1.177016E+05 2.769450E+12 2.769450E+12 2.196174E+12 2.265297E+11 0.000000E+00 0.000000E+00 0.000000E+00
2.006467E-01 0.000000E+00 0.000000E+00 8.240625E+03 1.091471E+05 1.091471E+05 2.568166E+12 2.568166E+12 2.036556E+12 2.099522E+11 0.000000E+00 0.000000E+00 0.000000E+00
3.009623E-01 0.000000E+00 0.000000E+00 7.838266E+03 9.392738E+04 9.392738E+04 2.210056E+12 2.210056E+12 1.752574E+12 1.997010E+11 0.000000E+00 0.000000E+00 0.000000E+00
3.009700E-01 0.000000E+00 0.000000E+00 7.471269E+03 8.955969E+04 8.955969E+04 2.107287E+12 2.107287E+12 1.671078E+12 1.903508E+11 0.000000E+00 0.000000E+00 0.000000E+00
4.012857E-01 0.000000E+00 0.000000E+00 6.986989E+03 7.324875E+04 7.324875E+04 1.723500E+12 1.723500E+12 1.366736E+12 1.780124E+11 0.000000E+00 0.000000E+00 0.000000E+00
4.012934E-01 0.000000E+00 0.000000E+00 6.666023E+03 6.990737E+04 6.990737E+04 1.644879E+12 1.644879E+12 1.304389E+12 1.698350E+11 0.000000E+00 0.000000E+00 0.000000E+00
5.016090E-01 0.000000E+00 0.000000E+00 6.149541E+03 5.488473E+04 5.488473E+04 1.291405E+12 1.291405E+12 1.024084E+12 1.566762E+11 0.000000E+00 0.000000E+00 0.000000E+00
5.016167E-01 0.000000E+00 0.000000E+00 5.828879E+03 5.204333E+04 5.204333E+04 1.224549E+12 1.224549E+12 9.710673E+11 1.485065E+11 0.000000E+00 0.000000E+00 0.000000E+00
6.019324E-01 0.000000E+00 0.000000E+00 5.282729E+03 3.874236E+04 3.874236E+04 9.115850E+11 9.115850E+11 7.228869E+11 1.345918E+11 0.000000E+00 0.000000E+00 0.000000E+00
6.019401E-01 0.000000E+00 0.000000E+00 4.941265E+03 3.625667E+04 3.625667E+04 8.530980E+11 8.530980E+11 6.765067E+11 1.258921E+11 0.000000E+00 0.000000E+00 0.000000E+00
7.022557E-01 0.000000E+00 0.000000E+00 4.618460E+03 2.960504E+04 2.960504E+04 6.965893E+11 6.965893E+11 5.523953E+11 1.176678E+11 0.000000E+00 0.000000E+00 0.000000E+00
7.022634E-01 0.000000E+00 0.000000E+00 4.076589E+03 2.615582E+04 2.615582E+04 6.154310E+11 6.154310E+11 4.880368E+11 1.038622E+11 0.000000E+00 0.000000E+00 0.000000E+00
8.025791E-01 0.000000E+00 0.000000E+00 3.981262E+03 2.436351E+04 2.436351E+04 5.732590E+11 5.732590E+11 4.545944E+11 1.014334E+11 0.000000E+00 0.000000E+00 0.000000E+00
8.025868E-01 0.000000E+00 0.000000E+00 3.455080E+03 2.116347E+04 2.116347E+04 4.979639E+11 4.979639E+11 3.948854E+11 8.802751E+10 0.000000E+00 0.000000E+00 0.000000E+00
9.029024E-01 0.000000E+00 0.000000E+00 3.364686E+03 1.954549E+04 1.954549E+04 4.598938E+11 4.598938E+11 3.646958E+11 8.572448E+10 0.000000E+00 0.000000E+00 0.000000E+00
9.029101E-01 0.000000E+00 0.000000E+00 3.875283E+03 2.248983E+04 2.248983E+04 5.291724E+11 5.291724E+11 4.196337E+11 9.873332E+10 0.000000E+00 0.000000E+00 0.000000E+00
1.000000E+00 0.000000E+00 0.000000E+00 3.832671E+03 2.175608E+04 2.175608E+04 5.119079E+11 5.119079E+11 4.059430E+11 9.764767E+10 0.000000E+00 0.000000E+00 0.000000E+00

Results generated by BModes (v1.03.01, 25-Sept-2007, compiled using double precision) on 03-Apr-2025 at 18:45:20.
IEA-15-240-RWT Offshore Tower (from tip to TP 15 m above MSL). Substructure is computed from Subdyn

        tower frequencies & mode shapes
        --- only first  20 modes printed

-------- Mode No. 6 (freq = 0.213657E+01 Hz)

span_loc s-s disp s-s slope f-a disp f-a slope twist

0.0000 -0.038562 -0.110050 0.000000 0.000000 0.000000
0.0035 -0.038902 -0.109376 0.000000 0.000000 0.000087
0.0104 -0.039575 -0.107972 0.000000 0.000000 0.000260
0.0174 -0.040239 -0.106492 0.000000 0.000000 0.000433
0.0244 -0.040893 -0.104939 0.000000 0.000000 0.000606
0.0313 -0.041538 -0.103313 0.000000 0.000000 0.000779
0.0383 -0.042172 -0.101618 0.000000 0.000000 0.000952
0.0453 -0.042795 -0.099855 0.000000 0.000000 0.001125
0.0522 -0.043408 -0.098026 0.000000 0.000000 0.001299
0.0592 -0.044009 -0.096132 0.000000 0.000000 0.001472
0.0662 -0.044598 -0.094177 0.000000 0.000000 0.001645
0.0731 -0.045175 -0.092161 0.000000 0.000000 0.001818
0.0801 -0.045739 -0.090087 0.000000 0.000000 0.001991
0.0870 -0.046290 -0.087956 0.000000 0.000000 0.002164
0.0940 -0.046828 -0.085772 0.000000 0.000000 0.002337
0.1010 -0.047352 -0.083536 0.000000 0.000000 0.002510
0.1079 -0.047861 -0.081059 0.000000 0.000000 0.002697
0.1149 -0.048355 -0.078526 0.000000 0.000000 0.002885
0.1219 -0.048833 -0.075939 0.000000 0.000000 0.003072
0.1288 -0.049295 -0.073301 0.000000 0.000000 0.003261
0.1358 -0.049740 -0.070613 0.000000 0.000000 0.003449
0.1399 -0.049995 -0.069005 0.000000 0.000000 0.003560
0.1497 -0.050581 -0.065096 0.000000 0.000000 0.003826
0.1567 -0.050975 -0.062271 0.000000 0.000000 0.004015
0.1636 -0.051351 -0.059405 0.000000 0.000000 0.004205
0.1706 -0.051710 -0.056500 0.000000 0.000000 0.004394
0.1776 -0.052051 -0.053558 0.000000 0.000000 0.004584
0.1845 -0.052373 -0.050582 0.000000 0.000000 0.004774
0.1915 -0.052677 -0.047573 0.000000 0.000000 0.004964
0.1985 -0.052962 -0.044534 0.000000 0.000000 0.005155
0.2054 -0.053228 -0.041223 0.000000 0.000000 0.005361
0.2124 -0.053472 -0.037856 0.000000 0.000000 0.005568
0.2194 -0.053696 -0.034436 0.000000 0.000000 0.005778
0.2263 -0.053898 -0.030963 0.000000 0.000000 0.005990
0.2333 -0.054079 -0.027440 0.000000 0.000000 0.006204
0.2403 -0.054238 -0.023867 0.000000 0.000000 0.006420
0.2472 -0.054375 -0.020247 0.000000 0.000000 0.006638
0.2507 -0.054434 -0.018420 0.000000 0.000000 0.006748
0.3203 -0.054377 0.020174 0.000000 0.000000 0.009068
0.3797 -0.052320 0.057332 0.000000 0.000000 0.011391
0.4248 -0.049404 0.087750 0.000000 0.000000 0.013446
0.4596 -0.046321 0.111154 0.000000 0.000000 0.015176
0.4866 -0.043433 0.128975 0.000000 0.000000 0.016621
0.5137 -0.040123 0.146248 0.000000 0.000000 0.018168
0.5407 -0.036399 0.163518 0.000000 0.000000 0.019917
0.5677 -0.032274 0.179520 0.000000 0.000000 0.021799
0.5947 -0.027784 0.193871 0.000000 0.000000 0.023840
0.6217 -0.022966 0.206818 0.000000 0.000000 0.026197
0.6488 -0.017875 0.216457 0.000000 0.000000 0.028673
0.6758 -0.012597 0.222312 0.000000 0.000000 0.031280
0.7028 -0.007230 0.223852 0.000000 0.000000 0.034034
0.7298 -0.001887 0.220121 0.000000 0.000000 0.037266
0.7568 0.003298 0.210646 0.000000 0.000000 0.040551
0.7839 0.008183 0.195209 0.000000 0.000000 0.043892
0.8109 0.012624 0.173607 0.000000 0.000000 0.047290
0.8379 0.016420 0.141403 0.000000 0.000000 0.051272
0.8649 0.019352 0.101643 0.000000 0.000000 0.055328
0.8919 0.021236 0.054098 0.000000 0.000000 0.059461
0.9189 0.021968 0.005870 0.000000 0.000000 0.063118
0.9460 0.021465 -0.048754 0.000000 0.000000 0.066796
0.9730 0.019573 -0.109759 0.000000 0.000000 0.070494
1.0000 0.016139 -0.177137 0.000000 0.000000 0.074213

-------- Mode No. 7 (freq = 0.218057E+01 Hz)

span_loc s-s disp s-s slope f-a disp f-a slope twist

0.0000 0.000000 0.000000 -0.040104 -0.113737 0.000000
0.0035 0.000000 0.000000 -0.040455 -0.112995 0.000000
0.0104 0.000000 0.000000 -0.041150 -0.111452 0.000000
0.0174 0.000000 0.000000 -0.041835 -0.109828 0.000000
0.0244 0.000000 0.000000 -0.042510 -0.108128 0.000000
0.0313 0.000000 0.000000 -0.043173 -0.106351 0.000000
0.0383 0.000000 0.000000 -0.043826 -0.104502 0.000000
0.0453 0.000000 0.000000 -0.044467 -0.102581 0.000000
0.0522 0.000000 0.000000 -0.045096 -0.100590 0.000000
0.0592 0.000000 0.000000 -0.045712 -0.098532 0.000000
0.0662 0.000000 0.000000 -0.046316 -0.096410 0.000000
0.0731 0.000000 0.000000 -0.046906 -0.094224 0.000000
0.0801 0.000000 0.000000 -0.047482 -0.091977 0.000000
0.0870 0.000000 0.000000 -0.048044 -0.089672 0.000000
0.0940 0.000000 0.000000 -0.048592 -0.087310 0.000000
0.1010 0.000000 0.000000 -0.049125 -0.084895 0.000000
0.1079 0.000000 0.000000 -0.049642 -0.082222 0.000000
0.1149 0.000000 0.000000 -0.050143 -0.079490 0.000000
0.1219 0.000000 0.000000 -0.050626 -0.076703 0.000000
0.1288 0.000000 0.000000 -0.051092 -0.073862 0.000000
0.1358 0.000000 0.000000 -0.051540 -0.070970 0.000000
0.1399 0.000000 0.000000 -0.051796 -0.069242 0.000000
0.1497 0.000000 0.000000 -0.052383 -0.065040 0.000000
0.1567 0.000000 0.000000 -0.052776 -0.062008 0.000000
0.1636 0.000000 0.000000 -0.053150 -0.058932 0.000000
0.1706 0.000000 0.000000 -0.053505 -0.055818 0.000000
0.1776 0.000000 0.000000 -0.053841 -0.052665 0.000000
0.1845 0.000000 0.000000 -0.054157 -0.049478 0.000000
0.1915 0.000000 0.000000 -0.054454 -0.046258 0.000000
0.1985 0.000000 0.000000 -0.054730 -0.043007 0.000000
0.2054 0.000000 0.000000 -0.054985 -0.039467 0.000000
0.2124 0.000000 0.000000 -0.055218 -0.035871 0.000000
0.2194 0.000000 0.000000 -0.055429 -0.032219 0.000000
0.2263 0.000000 0.000000 -0.055617 -0.028514 0.000000
0.2333 0.000000 0.000000 -0.055782 -0.024757 0.000000
0.2403 0.000000 0.000000 -0.055923 -0.020950 0.000000
0.2472 0.000000 0.000000 -0.056041 -0.017094 0.000000
0.2507 0.000000 0.000000 -0.056091 -0.015149 0.000000
0.3203 0.000000 0.000000 -0.055757 0.025800 0.000000
0.3797 0.000000 0.000000 -0.053348 0.064968 0.000000
0.4248 0.000000 0.000000 -0.050096 0.096823 0.000000
0.4596 0.000000 0.000000 -0.046716 0.121179 0.000000
0.4866 0.000000 0.000000 -0.043580 0.139610 0.000000
0.5137 0.000000 0.000000 -0.040009 0.157355 0.000000
0.5407 0.000000 0.000000 -0.036014 0.174945 0.000000
0.5677 0.000000 0.000000 -0.031612 0.191052 0.000000
0.5947 0.000000 0.000000 -0.026847 0.205253 0.000000
0.6217 0.000000 0.000000 -0.021761 0.217721 0.000000
0.6488 0.000000 0.000000 -0.016417 0.226532 0.000000
0.6758 0.000000 0.000000 -0.010911 0.231174 0.000000
0.7028 0.000000 0.000000 -0.005350 0.231076 0.000000
0.7298 0.000000 0.000000 0.000139 0.225015 0.000000
0.7568 0.000000 0.000000 0.005409 0.212762 0.000000
0.7839 0.000000 0.000000 0.010307 0.194094 0.000000
0.8109 0.000000 0.000000 0.014677 0.168805 0.000000
0.8379 0.000000 0.000000 0.018302 0.131826 0.000000
0.8649 0.000000 0.000000 0.020941 0.086751 0.000000
0.8919 0.000000 0.000000 0.022397 0.033345 0.000000
0.9189 0.000000 0.000000 0.022565 -0.020455 0.000000
0.9460 0.000000 0.000000 0.021358 -0.081065 0.000000
0.9730 0.000000 0.000000 0.018614 -0.148471 0.000000
1.0000 0.000000 0.000000 0.014169 -0.222670 0.000000

-------- Mode No. 8 (freq = 0.455262E+01 Hz)

span_loc s-s disp s-s slope f-a disp f-a slope twist

0.0000 0.000000 0.000000 0.027600 0.044729 0.000000
0.0035 0.000000 0.000000 0.027735 0.042621 0.000000
0.0104 0.000000 0.000000 0.027985 0.038346 0.000000
0.0174 0.000000 0.000000 0.028209 0.033998 0.000000
0.0244 0.000000 0.000000 0.028406 0.029582 0.000000
0.0313 0.000000 0.000000 0.028575 0.025104 0.000000
0.0383 0.000000 0.000000 0.028717 0.020571 0.000000
0.0453 0.000000 0.000000 0.028830 0.015987 0.000000
0.0522 0.000000 0.000000 0.028915 0.011359 0.000000
0.0592 0.000000 0.000000 0.028971 0.006693 0.000000
0.0662 0.000000 0.000000 0.028997 0.001995 0.000000
0.0731 0.000000 0.000000 0.028995 -0.002730 0.000000
0.0801 0.000000 0.000000 0.028964 -0.007476 0.000000
0.0870 0.000000 0.000000 0.028903 -0.012236 0.000000
0.0940 0.000000 0.000000 0.028812 -0.017006 0.000000
0.1010 0.000000 0.000000 0.028692 -0.021778 0.000000
0.1079 0.000000 0.000000 0.028541 -0.026945 0.000000
0.1149 0.000000 0.000000 0.028358 -0.032110 0.000000
0.1219 0.000000 0.000000 0.028144 -0.037269 0.000000
0.1288 0.000000 0.000000 0.027897 -0.042415 0.000000
0.1358 0.000000 0.000000 0.027619 -0.047543 0.000000
0.1399 0.000000 0.000000 0.027440 -0.050555 0.000000
0.1497 0.000000 0.000000 0.026967 -0.057719 0.000000
0.1567 0.000000 0.000000 0.026594 -0.062757 0.000000
0.1636 0.000000 0.000000 0.026190 -0.067753 0.000000
0.1706 0.000000 0.000000 0.025755 -0.072703 0.000000
0.1776 0.000000 0.000000 0.025290 -0.077600 0.000000
0.1845 0.000000 0.000000 0.024795 -0.082439 0.000000
0.1915 0.000000 0.000000 0.024270 -0.087215 0.000000
0.1985 0.000000 0.000000 0.023715 -0.091923 0.000000
0.2054 0.000000 0.000000 0.023131 -0.096928 0.000000
0.2124 0.000000 0.000000 0.022515 -0.101889 0.000000
0.2194 0.000000 0.000000 0.021869 -0.106800 0.000000
0.2263 0.000000 0.000000 0.021193 -0.111655 0.000000
0.2333 0.000000 0.000000 0.020487 -0.116449 0.000000
0.2403 0.000000 0.000000 0.019752 -0.121176 0.000000
0.2472 0.000000 0.000000 0.018987 -0.125830 0.000000
0.2507 0.000000 0.000000 0.018594 -0.128128 0.000000
0.3203 0.000000 0.000000 0.009319 -0.168979 0.000000
0.3797 0.000000 0.000000 -0.000344 -0.194702 0.000000
0.4248 0.000000 0.000000 -0.008402 -0.205827 0.000000
0.4596 0.000000 0.000000 -0.014820 -0.207832 0.000000
0.4866 0.000000 0.000000 -0.019786 -0.205004 0.000000
0.5137 0.000000 0.000000 -0.024635 -0.198081 0.000000
0.5407 0.000000 0.000000 -0.029258 -0.186287 0.000000
0.5677 0.000000 0.000000 -0.033542 -0.169833 0.000000
0.5947 0.000000 0.000000 -0.037371 -0.148590 0.000000
0.6217 0.000000 0.000000 -0.040612 -0.120939 0.000000
0.6488 0.000000 0.000000 -0.043143 -0.089519 0.000000
0.6758 0.000000 0.000000 -0.044880 -0.054921 0.000000
0.7028 0.000000 0.000000 -0.045754 -0.017868 0.000000
0.7298 0.000000 0.000000 -0.045666 0.024920 0.000000
0.7568 0.000000 0.000000 -0.044563 0.066524 0.000000
0.7839 0.000000 0.000000 -0.042487 0.105727 0.000000
0.8109 0.000000 0.000000 -0.039510 0.141293 0.000000
0.8379 0.000000 0.000000 -0.035678 0.176672 0.000000
0.8649 0.000000 0.000000 -0.031077 0.205209 0.000000
0.8919 0.000000 0.000000 -0.025885 0.225698 0.000000
0.9189 0.000000 0.000000 -0.020329 0.235485 0.000000
0.9460 0.000000 0.000000 -0.014645 0.236258 0.000000
0.9730 0.000000 0.000000 -0.009058 0.227361 0.000000
1.0000 0.000000 0.000000 -0.003806 0.208277 0.000000

=================================================================================

Thank you in advance,

Best wishes,

Blockquote[appendix](https://appendix)Preformatted text

Jason.Jonkman · April 9, 2025, 6:02pm

Dear @Meng.He,

Just a few comments:

I’m not familiar with all of the mass and stiffness properties of the IEA Wind 15-MW RWT, but can you clarify how you obtained some of the properties you are using in BModes, such as the tower-top mass/inertia, the platform mass/stiffness, and distributed mass and stiffness of the tower?
I would expect hub_conn = 2 for a floating system, not 3, which constrains the heave and yaw modes of the floater.
Are you platform mass and stiffness matrices really computed about the tower-base location at 15-m above MSL, as you have indicated?
Mode shapes 6-8 appear to be quite high frequency (21-45 Hz), which are far too high for the first tower-bending modes of the IEA Wind 15-MW RWT, so, I doubt these are the modes you are expecting.
It does not have to be that modes 1-2 correspond to surge/sway, mode 3 corresponds to heave, modes 4-5 correspond to roll/pitch, and mode 6 correspond to yaw. (And in your case, you’ve constrained the heave and yaw modes anyway.) Rather, which modes numbers correspond to which physical mode will be system dependent.

Best regards,

Meng.He · April 10, 2025, 12:57pm

Dear @jjonkman,

I still have two puzzles :

About the parameters of the Blade-tip or tower-top mass properties part, I directly follow the GitHub above an IEA15 _ BModes ( its source is : ptrbortolotti / IEA15 _ BModes ) subfolder RNAon inside the subfolder bmi file to modify this content, and use the BModes to recalculate it. The frequency of Mode No.6 and Mode No.7 calculated by it is almost the same as that before the modification ( this situation is also wrong according to your statement ).
It may be that my platform mass and stiffness matrix calculations are also incorrect. Maybe you can guide me on how to calculate this part of the value ?
If the pattern correspondence is not what I said before, then how do I determine which pattern values correspond to the TOWER FORE-AFT MODE SHAPES and TOWER SIDE-TO-SIDE MODE SHAPES in the ElastoDyn _ tower.dat file ?
In addition, I am not sure whether the value of tower _ prop.dat involved in BMode is correct. Can you guide me how to calculate this part of the value ?

Thank you in advance,

Best wishes,

Jason.Jonkman · April 10, 2025, 2:56pm

Dear @Meng.He,

Here are my responses:

Looking at Pietro Bortolotti’s GitHub repository for the BModes model of the IEA Wind 15-MW RWT: IEA15_BModes/RNAon at master · ptrbortolotti/IEA15_BModes · GitHub, I see that his tower top-properties differ from yours, so, how did you obtain your values? Pietro’s model is for a cantilevered tower (hub_conn = 1), so, Modes 1 and 2 are the first side-side and fore-aft bending modes shapes and are a reasonable natural frequency (not Modes 6 and 7, which are higher modes).
When calculate the tower mode shapes in BModes for a floating system, hydro_M should be the added mass matrix, hydro_K should be the hydrostatic stiffness weight (accounting both for buoyancy and full-system weight), and mooring_K should be the mooring system stiffness.
You should be able to interpret the modes by plotting the shapes and by their natural frequencies, assuming that you have a reasonable idea what modes to expect (surge, sway, heave, roll, pitch, yaw, tower-bending, etc.)
sec_loc, mass_den, flp_stff, and edge_stff in BModes should match HtFract, TMassDen, TwFAStif, and TwSSStif in the ElastoDyn tower file. The other values in the BModes tower file (str_tw, etc.) should be set to to ensure they don’t have an effect on the solution, e.g., as I describe in the following forum topic: Consistency between Bmodes and MBC.

Best regards,

Topic		Replies	Views
Question about tower stuffiness and BModes Computer-Aided Engineering Software Tools	21	7457	August 4, 2022
Tower first FA mode Structural Analysis	3	3945	December 10, 2017
Ansys model tower Structural Analysis	12	9550	May 9, 2018
Structural control (TMD) effect on the tower fore-aft vibration very insignificant Computer-Aided Engineering Software Tools	6	419	May 21, 2024
fore-aft and side-to-side accelerations at mid-tower Computer-Aided Engineering Software Tools	7	4992	September 17, 2019

How to simulate damage by reducing tower stiffness?

Results generated by BModes (v1.03.01, 25-Sept-2007, compiled using double precision) on 03-Apr-2025 at 18:45:20. IEA-15-240-RWT Offshore Tower (from tip to TP 15 m above MSL). Substructure is computed from Subdyn

Related topics

Results generated by BModes (v1.03.01, 25-Sept-2007, compiled using double precision) on 03-Apr-2025 at 18:45:20.
IEA-15-240-RWT Offshore Tower (from tip to TP 15 m above MSL). Substructure is computed from Subdyn