Input Parameters of Tower for Bmodes and Elastodyn (IEA 15 MW)

Wind & Water Structural Analysis
1

Dear All

I noticed differences in the input parameters of IEA 15 MW between the Elastodyn and the Bmodes regards the tower height.

1st: Why the tower height is different?

In Elastodyn the TowerHt = 144.386 m
In Bmodes the radius = 150 m

Noting that the hub_rad = - draft = 15 m

2nd: Why the mass density is different in both input files?
IEA-15-240-RWT-Monopile_ElastoDyn_tower.dat

IEA-15-240-RWT_BModes_tower_prop.dat

The integration of the mass density over the tower height of each input file results in the following total mass of the IEA 15 MW Tower. The reported mass in the definition report is 860 tons

Elastdyn Tower mass = 971.44814893031 tons (Assume TowerHt = 144.386 m)
Bmodes Tower mass = 930.09917997326 tons (Assume radius = 150 m)

The attached figures clarify the differences in tower mass density, fore-aft, and side-by-side stiffness

Thanks for your considerations
Regards
M.Fekry

MassDensityComp
MassDensityComp1920×1479 114 KB

Fore-aftStiffnessComp
Fore-aftStiffnessComp1920×1479 108 KB

Side-by-sideStiffnessComp
Side-by-sideStiffnessComp1920×1479 109 KB

1 Like
2

Hi there,

Thank you for the question and letting me know that the BModes inputs were still posted on the repository. I actually thought they were deleted with the v1.1 release update.

BModes is really deprecated software, although we understand that it is still used in some workflows. The code isn’t truly open-source and the usage of the accompanying mode shape Excel-tool for ElastoDyn is both complex and fragile enough that errors are likely.

The ElastoDyn data is up-to-date, tested, and more representative of the design intent. I will remove the BModes files from the repository in the next minor update (to stay current with changes in the OpenFAST API).

Cheers,
Garrett

3

Dear Dr Garrett

Many thanks for your clarifications.

Could you tell me what is the other alternatives of Bmodes that are used to calculate the mode shapes of the tower and blades of IEA 15 MW?

Regards
M.Fekry

4

If BModes works for you, don’t let my prior message keep you from using it. You would just have to put it a bit more effort to build the input files and ensure their accuracy yourself.

At NREL, we have shifted to using WISDEM, which is also part of WEIS, which calls Frame3DD to do the modal analysis. The ElastoDyn input file for the IEA Wind 15-MW was generated directly with WEIS. This is for both blade and tower modal inputs.

5

Dear Dr. Garrett

Thanks for your reply.
I appreciate it if you guide me to build the Bmodes input file for the tower as below:

1- I changed the radius to 129.386 m which is the flexible length of the tower.

2- I changed the tower tip mass properties to the values of table 5-1, page 26, in [1]

3- The Platform hydrodynamic 6X6 matrix (hydro_M) and Platform hydrodynamic 6X6 stiffness matrix (hydro_K) are obtained from the Subdyn summary file (MBBt and KBBt respectively)

4- The tower distributed properties are calculated based on the Elastodyn input file of the tower, appendix B, and Table 4-2, page 23, in [1]

I found the natural frequency of the tower becomes 0.2575 Hz although it should be 0.17 Hz as reported on page 21 of [1]

Is there anything else that should be considered?

[1] IEA Wind TCP Task 37 Definition of the IEA Wind 15-Megawatt Offshore Reference Wind Turbine Technical Report

Regards
M.Fekry

IEA-15-240-RWT_BModes_Tower_M.bmi

======================   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 (-)
129.386      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
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 --------------------------------------------
820888     tip_mass    blade-tip or tower-top mass (see users' manual) (kg)
5.486       cm_loc      tip-mass c.m. offset from the tower axis measured along the tower-tip x reference axis (m)
3.978       cm_axial    tip-mass c.m. offset tower tip measures axially along the z axis (m)
12607277    ixx_tip     blade lag or tower s-s mass moment of inertia about the tip-section x reference axis (kg-m^2)
21433958    iyy_tip     blade flap or tower f-a mass moment of inertia about the tip-section y reference axis (kg-m^2)
18682468    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)
0           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) ------------
2          tow_support: : aditional tower support [0: no additional support 1: Tension guy wires for the land-based tower 2: offshore turbine support: floating platform or monopile] (-)
-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):
     2.687731E+05,   0.000000E+00,   0.000000E+00,   0.000000E+00,  -9.877533E+05,   0.000000E+00
     0.000000E+00,   2.687731E+05,   0.000000E+00,   9.877533E+05,   0.000000E+00,   0.000000E+00
    0.000000E+00,   0.000000E+00,   2.469607E+05,   0.000000E+00,   0.000000E+00,   0.000000E+00
    0.000000E+00,   9.877533E+05,   0.000000E+00,   9.558109E+06,   0.000000E+00,   0.000000E+00
   -9.877533E+05,   0.000000E+00,   0.000000E+00,   0.000000E+00,   9.558109E+06,   0.000000E+00
   0.000000E+00,   0.000000E+00,   0.000000E+00,   0.000000E+00,   0.000000E+00,   6.145229E+06
Platform-reference-point-referred hydrodynamic 6X6 stiffness matrix (hydro_K):
     3.537275E+08,   0.000000E+00,   0.000000E+00,   0.000000E+00,  -7.510777E+09,   0.000000E+00
    0.000000E+00,   3.537275E+08,   0.000000E+00,   7.510777E+09,   0.000000E+00,   0.000000E+00
     0.000000E+00,   0.000000E+00,   6.568704E+09,   0.000000E+00,   0.000000E+00,   0.000000E+00
     0.000000E+00,   7.510777E+09,   0.000000E+00,   2.408142E+11,   0.000000E+00,   0.000000E+00
    -7.510777E+09,   0.000000E+00,   0.000000E+00,   0.000000E+00,   2.408142E+11,   0.000000E+00
     0.000000E+00,   0.000000E+00,   0.000000E+00,   0.000000E+00,   0.000000E+00,   6.449958E+10
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 *********************************************************************
*************************************************************************************************

IEA-15-240-RWT_BModes_tower_prop.dat

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)        
0.0	0.0	0.0	10517.987	344127.1177989468	344127.1177989468	3526376830986.6265	3526376830986.6265	3526376830986.6265	284689996998.3259	0.0	0.0	0.0
0.05276273814258928	0.0	0.0	10314.8444	319808.6014073988	319808.6014073988	3275871604639.355	3275871604639.355	3275871604639.355	264293150601.7534	0.0	0.0	0.0
0.1055254762851786	0.0	0.0	9919.392	299365.6919538348	299365.6919538348	3065446681730.708	3065446681730.708	3065446681730.708	247180551443.41275	0.0	0.0	0.0
0.1582882144277679	0.0	0.0	9488.4515	299365.6919538348	299365.6919538348	3065446681730.708	3065446681730.708	3065446681730.708	247180551443.41275	0.0	0.0	0.0
0.2110509525703571	0.0	0.0	9107.2422	270550.2234846103	270550.2234846103	2769450452002.746	2769450452002.746	2769450452002.746	226529700592.35434	0.0	0.0	0.0
0.2638136907129464	0.0	0.0	8547.4152	270550.2234846103	270550.2234846103	2769450452002.746	2769450452002.746	2769450452002.746	226529700592.35434	0.0	0.0	0.0
0.3165764288555357	0.0	0.0	8138.4485	215927.5176534576	215927.5176534576	2210055981076.2383	2210055981076.2383	2210055981076.2383	199701039744.324	0.0	0.0	0.0
0.369339166998125	0.0	0.0	7685.8995	215927.5176534576	215927.5176534576	2210055981076.2383	2210055981076.2383	2210055981076.2383	199701039744.324	0.0	0.0	0.0
0.4221019051407142	0.0	0.0	7257.8513	168376.11747004036	168376.11747004036	1723500010954.9673	1723500010954.9673	1723500010954.9673	178012448518.4323	0.0	0.0	0.0
0.4748646432833035	0.0	0.0	6812.6561	126144.10593653902	126144.10593653902	1291405296742.7688	1291405296742.7688	1291405296742.7688	156676206149.63974	0.0	0.0	0.0
0.5276273814258928	0.0	0.0	6367.6534	126144.10593653902	126144.10593653902	1291405296742.7688	1291405296742.7688	1291405296742.7688	156676206149.63974	0.0	0.0	0.0
0.5803901195684821	0.0	0.0	5906.8456	89024.92164339477	89024.92164339477	911584975111.2295	911584975111.2295	911584975111.2295	134591812002.54358	0.0	0.0	0.0
0.6331528577110713	0.0	0.0	5435.0205	89024.92164339477	89024.92164339477	911584975111.2295	911584975111.2295	911584975111.2295	134591812002.54358	0.0	0.0	0.0
0.6859155958536606	0.0	0.0	5081.8769	68028.4768673688	68028.4768673688	696589258960.8757	696589258960.8757	696589258960.8757	117667768272.1226	0.0	0.0	0.0
0.7386783339962499	0.0	0.0	4622.2891	56010.01655059259	56010.01655059259	573258971811.3063	573258971811.3063	573258971811.3063	101433418769.64978	0.0	0.0	0.0
0.7914410721388392	0.0	0.0	4283.4921	56010.01655059259	56010.01655059259	573258971811.3063	573258971811.3063	573258971811.3063	101433418769.64978	0.0	0.0	0.0
0.8442038102814284	0.0	0.0	3953.1686	44954.92983902112	44954.92983902112	459893782098.69336	459893782098.69336	459893782098.69336	85724481485.45592	0.0	0.0	0.0
0.8969665484240177	0.0	0.0	3625.3352	44954.92983902112	44954.92983902112	459893782098.69336	459893782098.69336	459893782098.69336	85724481485.45592	0.0	0.0	0.0
0.949729286566607	0.0	0.0	3848.7779	50007.59608078196	50007.59608078196	511907882162.8501	511907882162.8501	511907882162.8501	97647671493.47519	0.0	0.0	0.0
1.0	0.0	0.0	4097.4893	50007.59608078196	50007.59608078196	511907882162.8501	511907882162.8501	511907882162.8501	97647671493.47519	0.0	0.0	0.0
6

In addition, I built the input files of the blades of the Bmodes from the available data in the Beamdyn input file and Elastodyn input file of the blades. The radius, hub_rad, precone, romg, and blades’ inertia are given in the definition report of IEA 15 MW.

According to the report page 8 in Table 2-1:
First flapwise natural frequency 0.555 Hz
First edgewise natural frequency 0.642 Hz

According to the Bmodes
First flapwise natural frequency 0.290601E-02 Hz
First edgewise natural frequency 0.429279E-01 Hz

If there anything should I consider please inform me

The input files are shown below:

======================   BModes v3.00 Main Input File  ==================
IEA-15-240-RWT Offshore Blades

--------- General parameters ---------------------------------------------------------------------
True      Echo        Echo input file contents to *.echo file if true.
1         beam_type   1: blade, 2: tower (-)
7.56        romg:       rotor speed (rpm), automatically set to zero for tower modal analysis
1.0       romg_mult:  rotor speed muliplicative factor (-)
117.      radius:     rotor tip radius measured along coned blade axis OR tower height (m)
3.79      hub_rad:    hub radius measured along coned blade axis OR tower rigid-base height (m)
4.        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 --------------------------------------------
0.         tip_mass    blade-tip or tower-top mass (see users' manual) (kg)
-4.71033E-02        cm_loc      tip-mass c.m. offset from the tower axis measured along the tower-tip x reference axis (m)
2.73087E+01        cm_axial    tip-mass c.m. offset tower tip measures axially along the z axis (m)
9.73258E+07   ixx_tip     blade lag or tower s-s mass moment of inertia about the tip-section x reference axis (kg-m^2)
9.73258E+07   iyy_tip     blade flap or tower f-a mass moment of inertia about the tip-section y reference axis (kg-m^2)
1.84290E+04   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)
7.33323E+05 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_blade_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

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

Blades section properties (15 MW reference turbine)
26        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)        
0.0	0.0	15.59455301971172	3127.4021155424143	10166.284427210068	10167.976322208997	149729095916.4146	149629012637.96594	87489183048.03288	46051081603.60474	0.0	0.0	0.0
0.01	0.0	15.58773861176889	2964.7325318133635	9677.506658278193	9670.817488009772	143137826352.7965	142328864112.50156	83285587642.82161	43751344063.19816	0.0	0.0	0.0
0.02	0.0	15.58773861176889	2805.1273323852683	9189.979166446146	9183.723741815673	137008541712.70964	135212838311.38753	79106159653.83638	41569662567.47037	0.0	0.0	0.0
0.03	0.0	15.41083467878359	2591.136783508792	7913.55513775584	8366.670547933158	119514275124.89417	123284345388.39745	69973323042.1117	38669982721.7398	0.0	0.0	0.0
0.04	0.0	15.41083467878359	2389.115405916269	6778.707874270462	7605.999205249704	104365370041.97543	112223397786.614	61533150488.50106	36038990116.73735	0.0	0.0	0.0
0.05	0.0	14.94855563474368	2203.52246956623	5816.730513104689	6947.021691181144	91978034767.20616	102686583994.11134	54135840079.7236	33746441410.19616	0.0	0.0	0.0
0.075	0.0	14.25845480678574	1793.5621800535478	3914.596828171232	5542.22198919525	68686121530.687454	82456226297.96957	38418612295.439545	29212071034.730743	0.0	0.0	0.0
0.1	0.0	13.39714163725627	1694.5071226473444	2785.9557474336307	4883.611585776836	52263394041.37466	72781368868.39719	25428346793.258488	27339201435.297398	0.0	0.0	0.0
0.15	0.0	10.37097608496841	1050.5041617289855	956.3088698304845	3320.8865204968247	27988353518.859665	54125167812.039314	8076640558.8585	22665764106.851646	0.0	0.0	0.0
0.2	0.0	8.55152220118208	668.8389205216013	476.3636681718671	2253.558667409682	21820483410.15772	39196915729.85904	2768066330.973254	20450235425.96102	0.0	0.0	0.0
0.25	0.0	6.551629060916145	531.0612749513001	268.55950272107657	1848.5783850624327	15615256841.10636	35299428705.26732	1026128471.8607168	20473859852.028965	0.0	0.0	0.0
0.3	0.0	5.346089613189348	483.9851580947508	204.06774305708595	1564.7359685439142	13362814423.387625	31051165577.557343	627053086.269001	21366371296.473003	0.0	0.0	0.0
0.35	0.0	3.846955194686785	458.08388673358047	154.74717074687635	1286.7175819089484	10663481378.13921	26088284004.54947	461211585.49078345	21785402237.03918	0.0	0.0	0.0
0.4	0.0	3.07691390977302	433.8716017058155	120.1630106896849	1076.1432859614897	8537806429.681531	22217425410.95908	364794590.1572093	21621041012.04207	0.0	0.0	0.0
0.45	0.0	2.111690772172129	404.9178066535816	90.50849177530833	895.7513821150329	6549534664.533833	18717308525.793583	285660364.09887934	20779461548.755814	0.0	0.0	0.0
0.5	0.0	1.558783420877334	377.731233030784	66.51587194758397	735.407926823897	4893346064.323091	15586807919.093891	220544333.37495336	19923519424.805744	0.0	0.0	0.0
0.55	0.0	1.064427371073839	350.48434003585845	48.3879168461972	593.1078000418055	3604017503.6991744	12739863625.74516	168037150.44173867	18925122694.71336	0.0	0.0	0.0
0.6	0.0	0.4370289000217617	307.3478250743852	35.22217015645534	389.1096748456316	2655217532.05773	8379809772.736286	128226839.00696014	17539655765.235256	0.0	0.0	0.0
0.65	0.0	0.0396776881472392	260.2653356372791	25.215546621059765	215.46936888932268	1917970315.4393296	4637021573.468788	95377930.58201039	15853197990.946262	0.0	0.0	0.0
0.7	0.0	-0.680377614461304	223.94256194555769	17.745330077956677	131.65454148509653	1351951128.6929338	2889083609.8505797	71456369.55600888	14061229868.525568	0.0	0.0	0.0
0.75	0.0	-1.320525255517711	179.58407067190126	11.271194923324614	84.64962149907886	838106592.74152	1877272361.936434	52519301.176315226	11003024089.793188	0.0	0.0	0.0
0.8	0.0	-2.086230093232373	129.3080054809469	6.684580575763557	51.45480233093064	466233432.88131785	1099701983.6863494	38106482.51374478	7310260724.863415	0.0	0.0	0.0
0.85	0.0	-2.175841166085	84.45573745266202	3.616337664050583	31.507539581364625	243066553.4404725	683571619.6771157	23330158.861795776	4521289678.947009	0.0	0.0	0.0
0.9	0.0	-2.018403421317624	54.70473032506861	1.78333715736047	19.319856079506433	113253467.97005808	420297066.7672982	13417874.462175902	2675615584.1350894	0.0	0.0	0.0
0.95	0.0	-1.724325762660474	34.44992885232661	0.7573836161406937	12.262821999907851	36395660.02090348	231512293.70712495	6805118.090718728	1203040036.154266	0.0	0.0	0.0
1.0	0.0	-1.24238770627297	5.394970691335722	0.007180810431802968	0.09373427692288798	186239.91293931668	1384839.7699354952	71452.33631373737	118283403.93224278	0.0	0.0	0.0

Regards
M.Fekry

7

Dear @Mohamed.Fekry,

Regarding your BModes inputs for the tower:

  • radius should be equal the tower height of 144.386 m.

  • hub_conn should be 2 to account for the full 6x6 mass and stiffness matrices from SubDyn

  • The-top mass properties should be the full rotor + nacelle, not just the nacelle

  • tow_support should be 1 if you are using BModes_JJ as recommended for towers

  • Your distributed mass and stiffness don’t fully agree with what is in the ElastoDyn tower file. And we generally recommend to set the distributed inertias to near zero to match the assumptions in ElastoDyn.

Regarding your BModes inputs for the blade:

  • radius should be equal the blade radius of 120.97 m

  • hub_conn should be 1 for a cantilevered connection

  • I would expect the blade-tip masses and inertias to be zero

  • Your distributed mass and stiffness don’t fully agree with what is in the ElastoDyn blade file (which has 50 input stations). And we generally recommend to set the distributed twist and inertias to near zero to match the assumptions in ElastoDyn.

FYI: The following forum topic provides further guidance: Consistency between Bmodes and MBC.

Best regards,

8

Dear all,

I am trying to use BModes to obtain the coefficients for the 15 MW reference wind turbine and I would like to confirm if these values (message 5 of the current topic) are correct.

If you already have these data and could share them would be really helpful.

Thanks in advance.

Ivan Fernandez

--------- Blade-tip or tower-top mass properties --------------------------------------------
820888     tip_mass    blade-tip or tower-top mass (see users' manual) (kg)
5.486       cm_loc      tip-mass c.m. offset from the tower axis measured along the tower-tip x reference axis (m)
3.978       cm_axial    tip-mass c.m. offset tower tip measures axially along the z axis (m)
12607277    ixx_tip     blade lag or tower s-s mass moment of inertia about the tip-section x reference axis (kg-m^2)
21433958    iyy_tip     blade flap or tower f-a mass moment of inertia about the tip-section y reference axis (kg-m^2)
18682468    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)
0           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)
9

Dear @Ivan.Fernandez,

As I relayed in my post dated Nov 28, 2022 above, the tower-top mass properties in the post by @Mohamed.Fekry only include contributions from the nacelle (they match the values reported in Table 5-1 of the IEA Wind 15-MW reference wind turbine specifications report referenced in the post). However, the tower-top inputs to BModes should refer to the total combined nacelle + rotor mass, center of mass, and inertia. I have not personally calculated these for the IEA Wind 15-MW reference wind turbine.

Best regards,

10

Dear @Jason.Jonkman , why do you say tower height is 144,386 m? I suppose you take the transition piece as part of the tower height, right?

Plus in the tower sectional properties file in BModes, for the torsional stiffness column, i suppose we could get these values doing interpolation for the 20 nodes for our tower (15 MW Wind turbine) from the tabular excel, right?

BR

11

Dear @Alberto.Utrera,

I agree with your response regarding the tower height.

I’m not sure I understand your second question.

Best regards,

12

Dear @Jason.Jonkman and @Garrett.Barter , about the second question i finally solved it, thank you.

I am still doubting about the BModes_tower_prop.dat input file:

image
image1761×440 261 KB

How can it be possible that the tower has to take the transition piece into account? I am saying this because the previous image (taken from BModes_tower_prop.dat) has the data related to the data in the elastodyn tower input file from the tower start to the tower top (I have highlighted the values in bright yellow in order to confirm that the data from BModes_tower_prop.dat does not take the transition piece into account).

image
image1544×603 26.4 KB

So, in brief, my question would be why the elastodyn_tower input file takes only the tower propeties into account and not the transition piece properties? I am asking this because in BModes we select 144,386 m, but for the properties, we just only select the tower properties and not the transition piece ones…

Thank you. ALberto

13

Dear @Alberto.Utrera,

I’m not sure I fully understand your question. The distributed tower properties you set in BModes should match what you set in ElastoDyn, and be consistent with where you set the tower-top and tower-base locations in BModes and ElastoDyn. Whether or not flexibility within the transition piece is included in the distributed tower properties will depend on how you choose to model the transition piece (whether as flexible or rigid and in ElastoDyn or SubDyn) where you place the tower-base relative to the transition piece.

Best regards,

1 Like
14

Understood, thank u very much

15

Dear @Jason.Jonkman and @Garrett.Barter, I am trying to reproduce (or get something close to) the 6th degree polynomial coefficients with the help of BModes_JJ for the IEA 15MW Monopile found here. With your help on your pevious posts I have managed to construct the following .bmi and properties files:

1) .bmi file

======================   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 (-)
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
2         hub_conn:   hub-to-blade connection [1: cantilevered; other options not yet available]
20        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 --------------------------------------------
??????    tip_mass    blade-tip or tower-top mass (see users' manual) (kg)
??????    cm_loc      tip-mass c.m. offset from the tower axis measured along the tower-tip x reference axis (m)
??????    cm_axial    tip-mass c.m. offset tower tip measures axially along the z axis (m)
??????    ixx_tip     blade lag or tower s-s mass moment of inertia about the tip-section x reference axis (kg-m^2)
??????    iyy_tip     blade flap or tower f-a mass moment of inertia about the tip-section y reference axis (kg-m^2)
??????    izz_tip     torsion mass moment of inertia about the tip-section z reference axis (kg-m^2)
??????    ixy_tip     cross product of inertia about x and y reference axes(kg-m^2)
??????    izx_tip     cross product of inertia about z and x reference axes(kg-m^2)
??????    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]
"15MW IEA Tower Section 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 --------------------------------------------------
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):
 2.676988E+05,   0.000000E+00,   0.000000E+00,   0.000000E+00,  -9.814659E+05,   0.000000E+00
 0.000000E+00,   2.676988E+05,   0.000000E+00,   9.814659E+05,   0.000000E+00,   0.000000E+00
 0.000000E+00,   0.000000E+00,   2.460253E+05,   0.000000E+00,   0.000000E+00,   0.000000E+00
 0.000000E+00,   9.814659E+05,   0.000000E+00,   9.505228E+06,   0.000000E+00,   0.000000E+00
-9.814659E+05,   0.000000E+00,   0.000000E+00,   0.000000E+00,   9.505228E+06,   0.000000E+00
 0.000000E+00,   0.000000E+00,   0.000000E+00,   0.000000E+00,   0.000000E+00,   6.122027E+06
Platform-reference-point-referred hydrodynamic 6X6 stiffness matrix (hydro_K):
 3.537284E+08,   0.000000E+00,   0.000000E+00,   0.000000E+00,  -7.510800E+09,   0.000000E+00
 0.000000E+00,   3.537284E+08,   0.000000E+00,   7.510800E+09,   0.000000E+00,   0.000000E+00
 0.000000E+00,   0.000000E+00,   6.568727E+09,   0.000000E+00,   0.000000E+00,   0.000000E+00
 0.000000E+00,   7.510800E+09,   0.000000E+00,   2.408151E+11,   0.000000E+00,   0.000000E+00
-7.510800E+09,   0.000000E+00,   0.000000E+00,   0.000000E+00,   2.408151E+11,   0.000000E+00
 0.000000E+00,   0.000000E+00,   0.000000E+00,   0.000000E+00,   0.000000E+00,   6.449982E+10
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 *********************************************************************
*************************************************************************************************

2) distributed properties file

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	1.031484441173360E+04	1.302815E+00	1.302815E+00	3.065447E+12	3.065447E+12	2.430899E+19	2.471806E+19	0.000000E+00	0.000000E+00	0.000000E+00
1.003156E-01	0.000000E+00	0.000000E+00	1.031484441173360E+04	1.302815E+00	1.302815E+00	3.065447E+12	3.065447E+12	2.430899E+19	2.471806E+19	0.000000E+00	0.000000E+00	0.000000E+00
1.003233E-01	0.000000E+00	0.000000E+00	9.523818531177400E+03	1.203636E+00	1.203636E+00	2.832085E+12	2.832085E+12	2.245843E+19	2.282247E+19	0.000000E+00	0.000000E+00	0.000000E+00
2.006390E-01	0.000000E+00	0.000000E+00	9.453084405718950E+03	1.177016E+00	1.177016E+00	2.769450E+12	2.769450E+12	2.196174E+19	2.265297E+19	0.000000E+00	0.000000E+00	0.000000E+00
2.006467E-01	0.000000E+00	0.000000E+00	8.761306059261840E+03	1.091471E+00	1.091471E+00	2.568166E+12	2.568166E+12	2.036556E+19	2.099522E+19	0.000000E+00	0.000000E+00	0.000000E+00
3.009623E-01	0.000000E+00	0.000000E+00	8.333524388530640E+03	9.392738E+00	9.392738E+00	2.210056E+12	2.210056E+12	1.752574E+19	1.997010E+19	0.000000E+00	0.000000E+00	0.000000E+00
3.009700E-01	0.000000E+00	0.000000E+00	7.943339505959190E+03	8.955969E+00	8.955969E+00	2.107287E+12	2.107287E+12	1.671078E+19	1.903508E+19	0.000000E+00	0.000000E+00	0.000000E+00
4.012857E-01	0.000000E+00	0.000000E+00	7.428459476674180E+03	7.324875E+00	7.324875E+00	1.723500E+12	1.723500E+12	1.366736E+19	1.780124E+19	0.000000E+00	0.000000E+00	0.000000E+00
4.012934E-01	0.000000E+00	0.000000E+00	7.087214160266680E+03	6.990737E+00	6.990737E+00	1.644879E+12	1.644879E+12	1.304389E+19	1.698350E+19	0.000000E+00	0.000000E+00	0.000000E+00
5.016090E-01	0.000000E+00	0.000000E+00	6.538098082624470E+03	5.488473E+00	5.488473E+00	1.291405E+12	1.291405E+12	1.024084E+19	1.566762E+19	0.000000E+00	0.000000E+00	0.000000E+00
5.016167E-01	0.000000E+00	0.000000E+00	6.197174861548130E+03	5.204333E+00	5.204333E+00	1.224549E+12	1.224549E+12	9.710673E+19	1.485065E+19	0.000000E+00	0.000000E+00	0.000000E+00
6.019324E-01	0.000000E+00	0.000000E+00	5.616516314866140E+03	3.874236E+00	3.874236E+00	9.115850E+11	9.115850E+11	7.228869E+19	1.345918E+19	0.000000E+00	0.000000E+00	0.000000E+00
6.019401E-01	0.000000E+00	0.000000E+00	5.253477923437150E+03	3.625667E+00	3.625667E+00	8.530980E+11	8.530980E+11	6.765067E+19	1.258921E+19	0.000000E+00	0.000000E+00	0.000000E+00
7.022557E-01	0.000000E+00	0.000000E+00	4.910275969995680E+03	2.960504E+00	2.960504E+00	6.965893E+11	6.965893E+11	5.523953E+19	1.176678E+19	0.000000E+00	0.000000E+00	0.000000E+00
7.022634E-01	0.000000E+00	0.000000E+00	4.334167603205980E+03	2.615582E+00	2.615582E+00	6.154310E+11	6.154310E+11	4.880368E+19	1.038622E+19	0.000000E+00	0.000000E+00	0.000000E+00
8.025791E-01	0.000000E+00	0.000000E+00	4.232816565257490E+03	2.436351E+00	2.436351E+00	5.732590E+11	5.732590E+11	4.545944E+19	1.014334E+19	0.000000E+00	0.000000E+00	0.000000E+00
8.025868E-01	0.000000E+00	0.000000E+00	3.673387789838780E+03	2.116347E+00	2.116347E+00	4.979639E+11	4.979639E+11	3.948854E+19	8.802751E+19	0.000000E+00	0.000000E+00	0.000000E+00
9.029024E-01	0.000000E+00	0.000000E+00	3.577282612388080E+03	1.954549E+00	1.954549E+00	4.598938E+11	4.598938E+11	3.646958E+19	8.572448E+19	0.000000E+00	0.000000E+00	0.000000E+00
9.029101E-01	0.000000E+00	0.000000E+00	4.120141253172980E+03	2.248983E+00	2.248983E+00	5.291724E+11	5.291724E+11	4.196337E+19	9.873332E+19	0.000000E+00	0.000000E+00	0.000000E+00
1.000000E+00	0.000000E+00	0.000000E+00	4.074837331422720E+03	2.175608E+00	2.175608E+00	5.119079E+11	5.119079E+11	4.059430E+19	9.764767E+19	0.000000E+00	0.000000E+00	0.000000E+00

In the files above

  • The hydro_M and hydro_K were taken from the SubDyn summary file (SubDyn Inputs) (MBBt and KBBt respectively)

  • The distributed properties for the flexible part (15 to 144.386m above MSL) were taken from the ElastoDyn_Tower Input file, while flp_iner and edge_iner have been set to small numbers and tor_stff and axial_stff to very high.

The only problem I have is how to calculate the tower-top mass properties (feal free to correct me if I have made any mistake).

1. For the tip_mass: Can I use the value of Tower-top Mass (almost equal to HubMass(from ElastoDyn Input)+NacMass(from ElastoDyn Input)+YawBrMass(from ElastoDyn Input)+3*blade mass(from ElastoDyn Summary)) found in the summary file of ElastoDyn?

2. For the center of mass and the second moments of inertia: I have seen in other older posts that one can calculate these parameters by using FAST’s linearization. Can OpenFAST be used for the same job or should these parameters be calculated by other means?

For my questions above the only BModes input files I could find was this, and I do not even understand what RNA on means.

I am sorry for the long text, any help would be greatly appreciated and thank you very much in advance!

16

Hi @Achilleas.Kazerakis,
I believe this is the correct file If you saw any wrong parameter in this file, let me know please @Jason.Jonkman:

====================== 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, automatically set to zero for tower modal analysis (rpm)

  1.    romg_mult:  rotor speed muliplicative factor (-)

144.386 radius: rotor tip radius measured along coned blade axis, OR tower height above ground level [onshore] or MSL offshore
15. hub_rad: hub radius measured along coned blade axis OR tower rigid-base height (m)
0. precone: built-in 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: hub-to-blade or tower-base boundary condition [1: cantilevered; 2: free-free; 3: only axial and torsion constraints] (-)
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) ------------
1 tow_support: : aditional tower support [0: no additional support; 1: floating-platform or monopile with or without tension wires] (-)
-15 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. 100000000.
-15 ref_msl : distance of platform reference point below the MSL (m)
Platform-reference-point-referred hydrodynamic 6X6 matrix (hydro_M):
2.676988E+05 0.000000E+00 0.000000E+00 0.000000E+00 -9.814659E+05 0.000000E+00
0.000000E+00 2.676988E+05 0.000000E+00 9.814659E+05 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 2.460253E+05 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 9.814659E+05 0.000000E+00 9.505228E+06 0.000000E+00 0.000000E+00
-9.814659E+05 0.000000E+00 0.000000E+00 0.000000E+00 9.505228E+06 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 6.122027E+06
Platform-reference-point-referred hydrodynamic 6X6 stiffness matrix (hydro_K):
3.537284E+08 0.000000E+00 0.000000E+00 0.000000E+00 -7.510800E+09 0.000000E+00
0.000000E+00 3.537284E+08 0.000000E+00 7.510800E+09 0.000000E+00 0.000000E+00
0.000000E+00 0.000000E+00 6.568727E+09 0.000000E+00 0.000000E+00 0.000000E+00
0.000000E+00 7.510800E+09 0.000000E+00 2.408151E+11 0.000000E+00 0.000000E+00
-7.510800E+09 0.000000E+00 0.000000E+00 0.000000E+00 2.408151E+11 0.000000E+00
0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 0.000000E+00 6.449982E+10
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 (-)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 : z_distr_k [row array of size n_added_m_pts; section locations wrt the flexible tower base over which distributed stiffness is specified] (m)
595318000.0 1165208000 1129400000 1095553000 1059931000 1024493000 989209000 953643000 918718000 883287000 847803000 812541000 777187000 741870000 706616000 671440000 636229000 600957000 565919000 530470000 495081000 459574000 385327000 305479000 280059000 254125000 227500000 200112000 171927000 143115000 114173000 80184000 52237000 35561000 20912000 9000000 1156000 : distr_k [row array of size n_added_m_pts; distributed stiffness per unit length] (N/m^2)

Tension wires data
0 n_attachments: no of wire-attachment locations on tower [0: no tension wires] (-)
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 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 *********************************************************************

17

Thanks, @Alberto.Utrera, for answering @Achilleas.Kazerakis questions!

RNA refers to the rotor-nacelle assembly.

The OpenFAST linearizations do not show the mass matrix directly, but this matrix can often be inferred from other matrices generated through the linearization process. A similar question was asked and answered in the following forum topic: http://forums.nrel.gov/t/openfast-2nd-order-linearization/2249/2 . To get only the RNA mass matrix, set the tower and platform masses to zero.

Best regards,

18

Dear @Alberto.Utrera,
I am so greatful for the help you have given me! I compared the coefficients from your input file with those of the Elastodyn tower file and I got somewhat of a close match:

Comparison

alut
alut777×465 18.7 KB

I have a question though, how did the following matrix occur?

Platform mass inertia 3X3 matrix (i_matrix_pform):
0. 0. 0.
0. 0. 0.
0. 0. 100000000.

Best regards,

19

Dear @Jason.Jonkman,
Thank you so much for your help on the RNA mass matrix!

Best regards,