Good afternoon,

I am wondering where I can download Bmodes.

I could not find a working link.

Thanks in advance.

Best regards.

Florence Haudin.

Dear Florence,

As I announced here: http://forums.nrel.gov/t/other-news/846/1, the NWTC Information Portal crashed before the replacement site is available. I’ve now shared the old BModes v3.00 archive, as well as the version known on this forum as BModes_JJ here: drive.google.com/drive/folders/ … sp=sharing.

Best regards,

Thanks Jason,

I am brand new with BMode so sorry in advance if my questions are basic.

I have 2 questions. I want to have the modes for the system considered in OC6 phase 2, tower + monopile considered as a land-based system.

The first one is related to the mooring system stiffness matrix in .bmi file? Is it the way the model the connection with the ground for a land-based system as done in subdyn by introducing a boundary stiffness matrix ?

My second question is related to this section of the .bmi file :

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)"

I am wondering what is the equivalent of that part in Elastodyn ?

Thanks in advance.

Best regards.

Florence.

Dear Florence,

Here are my answers to your questions:

Yes, you can use hydro_K or mooring_K in BModes_JJ to represent the lumped (coupled springs, CS) stiffness of the foundation of the tower + monopile. But please keep in mind that hydro_K and mooring_K are applied at the platform reference point (0,0,0), so, you’ll want to ensure that you don’t set draft > 0 m. For example, for the OC6 Phase II system (DTU 10-MW turbine + monopile), you’ll want to set radius = 145.63 m, draft = 0 m instead of radius = 115.63 m, draft = 30 m.

The distributed elastic stiffness per unit length feature available in BModes_JJ would be useful for modeling the foundation via a distributed springs (DS) representation. FAST v8 and OpenFAST do not currently support such a model. At one point we developed a customized version of FAST v7 that supported DS modeling of the foundation. This is discussed in the following forum topic: http://forums.nrel.gov/t/turbine-soil-interaction-influence-on-the-mode-shapes/481/1, especially my post dated Feb 01, 2013, where I share an example UserTwrLd_DS.f90 file.

Best regards,

##
Thanks Jason,

I calculated the bending modes with Bmodes and the different coefficients of the 6th order polynomial with ModeShapePolyFitting.

I then copied the coefficients in the mode shape section of the Elastodyn Tower file.

But when I tried to run the simulation I got the following error message :

Running ElastoDyn.

FAST_InitializeAll:FAST_Init:ValidateInputData:OutFmt produces a column width of 13 instead of 10

characters.

FAST_InitializeAll:ED_Init:ED_ValidateInput:ValidateTowerData: Mode shape coefficients for tower

fore-aft mode 1 must add to 1.0.

FAST encountered an error during module initialization.

Simulation error level: FATAL ERROR

## Aborting OpenFAST.

Is there any restriction on the coefficients ?

Here are the values I got with ModeShapePolyFitting (I checked the polynomial coefficient of ModeShapePolyFitting : fits here attached )

---------------------- TOWER FORE-AFT MODE SHAPES ------------------------------

0.8777 TwFAM1Sh(2) - Mode 1, coefficient of x^2 term

-1.2037 TwFAM1Sh(3) - , coefficient of x^3 term

3.7952 TwFAM1Sh(4) - , coefficient of x^4 term

-3.7017 TwFAM1Sh(5) - , coefficient of x^5 term

1.2225 TwFAM1Sh(6) - , coefficient of x^6 term

-689.6822 TwFAM2Sh(2) - Mode 2, coefficient of x^2 term

713.3420 TwFAM2Sh(3) - , coefficient of x^3 term

-1026.2863 TwFAM2Sh(4) - , coefficient of x^4 term

1573.5238 TwFAM2Sh(5) - , coefficient of x^5 term

-569.8972 TwFAM2Sh(6) - , coefficient of x^6 term

---------------------- TOWER SIDE-TO-SIDE MODE SHAPES --------------------------

0.9189 TwSSM1Sh(2) - Mode 1, coefficient of x^2 term

-1.3624 TwSSM1Sh(3) - , coefficient of x^3 term

4.0968 TwSSM1Sh(4) - , coefficient of x^4 term

-3.9707 TwSSM1Sh(5) - , coefficient of x^5 term

1.3174 TwSSM1Sh(6) - , coefficient of x^6 term

79.5897 TwSSM2Sh(2) - Mode 2, coefficient of x^2 term

-74.2219 TwSSM2Sh(3) - , coefficient of x^3 term

99.7401 TwSSM2Sh(4) - , coefficient of x^4 term

-145.1723 TwSSM2Sh(5) - , coefficient of x^5 term

41.0643 TwSSM2Sh(6) - , coefficient of x^6 term

Many thanks in advance.

Best regards.

Florence Haudin.

OpenFAST_Prescribing_Loads_at_Tower_Top.pdf (1.01 MB)

mode_shapes.pdf (142 KB)

Hi Florence,

I would guess you just have a numerical round-off problem. Checking the first set of coefficients for the fore the first tower fore-aft mode, the sum of the coefficients is 0.99, not 1.

Best regards,

Hi Jason,

Thanks for sharing these file. I would like to ask you if is there any manual regarding the .bmi file for BModes?

I am trying to you the file OC3Hywind.bmi that you shared but with DTU 10MW RWT replacing the NREL 5MW.

Thank you in advance.

Best regards,

Ioannis.

Hi Ioannis,

The draft User’s Guide to BModes included in the BModes v3.00 archive is the most up-to-date documentation I’m aware of. While not fully up to date with BModes_JJ, hopefully it provides enough information. I’ve also placed this document separately in the BModes directory on my Google Drive (drive.google.com/drive/folders/ … sp=sharing).

Best regards,

Dear All,

I am using BModes (version v3.00 on Mac OS version 10.13.3) for calculating the natural frequencies and modes shapes of tower on a floating substructure. I have downloaded the BModes input files from the drive shared by Jason (drive.google.com/drive/folders/ … zksGRnrqxJ). I tried to run both ‘CS_Monopile.bmi’ and ‘OC3Hywind.bmi’ input files and I am getting the following error message.

[attachment=0]Figure 1.png[/attachment]

Can anyone help me how to resolve this issue?

Regards

Ramya

Dear Ramya,

I don’t see that the error Figure is showing up properly.

Best regards,

Dear Ramya,

Instead of using BModes v3.00.00, I would recommend using the BModes.exe available on that link to Google drive. This executable is known as BModes_JJ on this forum, and is the version I recommend that you use.

Best regards,

Dear Jason,

Thanks for the clarification. I understand the BModes_JJ source code shared in the google drive (drive.google.com/drive/folders/ … zksGRnrqxJ) is for windows. Can you be able to share the source code so I can compile and use it on Linux machine?

Regards

Ramya

Dear Ramya,

Unfortunately, the source code used to compile BModes_JJ is not available and the developer no longer works at NREL. Can you run the precompiled executable on a Windows emulator or virtual machine?

Best regards,

Dear Jason,

Thanks for the reply. I have run the executables as you suggested and it is working fine.

Regards

Ramya

Dear All,

Again, my question is to consider the modes of the system in OC6 phase 2.I want to calculate the mode shape and frequency of the system，in particular, the tower and the monopile are considered as a whole.The mode shapes and frequencies of SS and FA of the first bending mode are consistent with the expected results（Mode No.1 and Mode No.2 of the.out file）.However, the SS and FA mode shapes and frequencies of the second bending mode are unsatisfactory.Can you check an input file for me？

Thanks in advance.

Best regards.

Bmodes.zip (7.24 KB)

Dear Monge.Low,

I haven’t checked all of your BModes inputs, e.g., the distributed tower/monopile mass and stiffness, but I see that your BModes mode assumes a rigid/cantilevered foundation, whereas OC6 Phase 2 considers a flexible foundation; the flexible foundation will likely impact the modal frequencies a bit.

I would also suggest reaching out to Roger Bergua of NREL, who is leading OC6 Phase 2 and can likely provide more specific guidance on the model set up and various load case simulations.

Best regards,

Dear Jason,

It’s my pleasure to receive your reply so soon. I will try to contact Roger Bergua.

Anyway, thank you very much for your help.

Best regards，

Hi Jason,

I asked some questions about Bmodes some time ago.

At some point you wrote me this answer :

“Yes, you can use hydro_K or mooring_K in BModes_JJ to represent the lumped (coupled springs, CS) stiffness of the foundation of the tower + monopile. But please keep in mind that hydro_K and mooring_K are applied at the platform reference point (0,0,0), so, you’ll want to ensure that you don’t set draft > 0 m. For example, for the OC6 Phase II system (DTU 10-MW turbine + monopile), you’ll want to set radius = 145.63 m, draft = 0 m instead of radius = 115.63 m, draft = 30 m.”

I am right now interested in the case where there is water and I want to put a stiffness matrix at the seabed. I am not sure wether I should parametrize the system (radius, draft) and if the stiffness matrix has to implemented in K_mooring ? Also I guess that hub_conn should be set to free-free ?

By comparison in Elastodyn when adding water parameters should be (with adequate parameters in Subdyn z going from -30 to 10 m) :

115.63 TowerHt - Height of tower above ground level [onshore] or MSL [offshore] (meters)

10 TowerBsHt - Height of tower base above ground level [onshore] or MSL [offshore] (meters)

0 PtfmCMxt - Downwind distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)

0 PtfmCMyt - Lateral distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)

10 PtfmCMzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)

10 PtfmRefzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform reference point (meters)

But when we consider the system without water that means equivalent to an onshore structure made of tower+substructure, the reference is at sea bed ? So in Elastodyn the parameters should be set to (with adequate compatible parameters in Subdyn z going from 0 to 40 m)

145.63 TowerHt - Height of tower above ground level [onshore] or MSL [offshore] (meters)

40 TowerBsHt - Height of tower base above ground level [onshore] or MSL [offshore] (meters)

0 PtfmCMxt - Downwind distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)

0 PtfmCMyt - Lateral distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)

40 PtfmCMzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)

40 PtfmRefzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform reference point (meters)

Many thanks in advance for any answer.

Best regards.

Florence Haudin.

Dear Florence,

I don’t recall the nature of my original comment where you quoted me, but in BModes_JJ you can shift the platform reference point to be offset from (0,0,0) via BModes input ref_msl. In our example of the NREL 5-MW baseline turbine atop the OC3-monopile with coupled springs (drive.google.com/drive/folders/ … sp=sharing), draft = ref_msl = 20 m.

In FAST / OpenFAST with ElastoDyn and BeamDyn, you can also shift the platform reference point to be offset from (0,0,0) using ElastoDyn input PtfmRefzt.

I hope that helps.

Best regards,