[Question]How to perform seismic load analysis

Wind & Water Computer-Aided Engineering Software Tools
1

I downloaded OpenFASTv4.0.1 today.

I believe that with an onshore wind turbine, the seismic forces are input and the output is the load on the tower, etc.

Could you please tell me how to perform an analysis by inputting seismic forces?

2

Dear @Kazuya.Nishiyama,

Similar questions have been asked and answered in other forum topics, e.g.:
Question about Seismic.
Seismic Motions in OpenFAST

FYI: I have now forwarded you the Seismic archive of FAST v7 via WeTransfer as you requested via e-mail.

Best regards,

4

Thank you for sending.

5

Dear Jason

Do you have a file of an seismic analysis example with WP1.5MW?

6

Dear @Kazuya.Nishiyama,

The Seismic archive of FAST v7 uses examples based on the NREL 5-MW baseline wind turbine. I don’t have similar Seismic examples using the WindPACT 1.5-MW baseline wind turbine. That said, you can find FAST v7 models of the WindPACT 1.5-MW baseline wind turbine in the CertTest directory of the archive of FAST v7: https://www.nrel.gov/wind/nwtc/assets/downloads/FAST/FASTv7.02/FAST_v7.02.00d-bjj.exe. I would recommend starting with Test13 from the FAST v7 CertTest and enable Seismic functionality from that by setting PtfmModel = 1 and using the platform and seismic files from the NREL 5-MW baseline wind turbine examples from the Seismic archive.

Best regards,

7

Dear Jason.

Thank you for your response.

I was able to analyze it.

However, we are planning to do seismic analysis with openfast as we are told that visualization is not available.

Do you have any examples of seismic analysis with openfast?

8

Dear @Kazuya.Nishiyama,

I don’t have an example OpenFAST model with seismic functionality demonstrated, but the forum posts linked above explain how to set up OpenFAST with seismic excitation.

Best regards,

9

Dear Jason

Thank you for your response.
I will refer to it.

10

Dear Jason.

I learned that there are two ways to do seismic load analysis: using the external platform or using the SoilDyn module.

Can you please tell me which one is better to use for analysis?

Also, could you please tell me how to install the SoilDyn module?
(Is there a file like SoilDyn.dat?)

12

Supplement to my question.

The analysis model is an onshore wind turbine of WP 1.5MW.

I would like to input the time history (time and acceleration) of seismic and perform an seismic load analysis.

13

Dear @Kazuya.Nishiyama,

I would suggest using the method based on external platform (ExtPtfm, CompSub = 2). SoilDyn has not yet been publicly released, but will be included in OpenFAST v5 later this year.

You can use your desired acceleration time history to compute the external force needed in ExtPtfm based on the method described in the forum posts linked above.

Best regards,

14

Dear Jason

Thank you for your response.

I checked the other answer.
I have three question.
(I use 5MW_OCJckt_ExtPtfm as an example)

(1) The answer is as follows: am I correct in understanding that the time history of earthquake acceleration cannot be used and that the time history of forces and moments is required?

Answer↓
Yes, you can enable aerodynamics, etc. in an OpenFAST model with CompSub = 2.

The r-test example with CompSub = 2 that you are referencing has 6 Guyan modes + 25 Craig-Bampton modes, for a total of 31 DOFs, which is why the matrices are size 31. To model seismic loading following the approach in the old Seismic functionality of OpenFAST, you can disable all Craig-Bampton modes. In this case, CombSub = 2 should provide the 6x6 mass, damping, and stiffness matrices and 6x1 load vector for the Guyan modes. I would following the documentation from the Seismic functionality (https://www.nrel.gov/wind/nwtc/assets/pdfs/sr-5000-53872.pdf) to derive these matrices and load vector.

(2) What exactly does ExtPtfm indicate?
(Tower? Soil?).

(3) OpenFast-v5 going to add seismic function as well?

15

Dear @Kazuya.Nishiyama,

Here are my responses:

  1. As explained in the NREL report NREL/SR-5000-53872 you linked above, you can use your desired acceleration time history to derive a force time history that will cause the platform in OpenFAST to follow that acceleration time history. The suggested mass, stiffness, and damping terms to enable this are explained in the report, which you can use to define the mass, stiffness, and damping matrices, and force vector in ExtPtfm. This approach would work for the 3 translation degrees of freedom (DOFs) of the floater (surge, sway, heave), assuming you disable the rotation DOFs (roll, pitch, yaw) in ElastoDyn.

  1. ExtPtfm can be thought of as a super-element representing the portion of the support structure not directly modeled in other parts of OpenFAST like ElastoDyn. For seismic excitation, ExtPtfm can be used to represent the mass, stiffness, damping, and force needed to impose an acceleration time history of the platform as explained in (1).

  2. NREL is not currently funded to add seismic functionality to OpenFAST. NREL is certainly capable of adding such functionality, but would need funding to do it.

Best regards,

16

Dear Jason

Thank you for your response.