Tower elasticity


I am currently working on my bachelor thesis and I have stumbled upon an interesting problem where it is required to simulate and draw the loads on the tower of a 3-blade 1.5 MW turbine while considering two cases and to compare between them.
The 1st case is considering the tower as a rigid body i.e. neglecting its elasticity.
The 2nd case is considering the tower as a normal elastic body.
I have found that I will need to change some parameters in the input file Baseline_tower to account for neglecting the elasticity of the tower.
If someone can help in aiding me to know what specific parameters to change to achieve that.

Kind regards.

Dear Hisham,

You don’t need to change the Baseline_Tower.dat file to make the tower rigid. Instead, the flexibility of the tower is enabled/disabled in the ElastoDyn module of FAST v8 or OpenFAST by setting the tower degrees of freedom (DOF) flags in the ElastoDyn primary input file to True/False (TwFADOF1, TwFADOF2, TwSSDOF1, TwSSDOF2).

Best regards,

Thank you so much for your reply.

If I may ask another question, in this very same simulation when the total run time is increased to more than 43 seconds, I get the following error: “FF wind array was exhausted at 43 seconds”. I would like to know what does that mean and also what are the factors that limit the maximum run time that can be specified.

Thank you,

Dear Hisham,

An error regarding the “FF wind array was exhausted” has been discussed many times on this forum e.g.:

I hope that helps.

Best regards,

Thank you for your prompt reply, if I may ask one final question.

I would like to know what are the profound differences between Aerodyn v14 and the updates that are found in v15 in terms of functionality and accuracy, I am more interested with changes that may affect the accuracy of the results which are mainly: Shear forces on LSS and Tower top and base.

Thank you so much for all your help.

Dear Hisham,

Appendix G from the draft AeroDyn v15 User’s Guide and Theory Manual provides a nice summary of how AeroDyn v15 differs from earlier versions: … 15.04a.pdf.

Best regards,

Hello all ,
I am currently running a 600s simulation with the 5MW OC3 Hywind wind turbine (I have changed the geometry of the turbine), and i am facing the ‘‘FF wind array was exhausted’’ problem 62,88s into my simulation.
I read in other topics that the problem may be that the simulation is numerically unstable .Due to that , I turned off all the DOF’s of the Elastodyn input file ,so i could gradually turn them on one by one in order to find where the problem is. However, as odd as it may seem i still get the same error .
After that , i installed again the OpenFast files and i get the FF wind array error 65,638s into the simulation.
I would also like to emphasize , that when i was changing the geometry of my turbine , i was running the simulation at the default time of 60s so the problem never occured.
I would deeply appreciate any help .
Best regards

Dear Nikos,

Sounds like the wind data file you are using is not long enough for the simulation you are trying to run. Did you generate your wind data using TurbSim for 600 s or longer? Did you set UsableTime = “ALL” in TurbSim?

Best regards,