Coupled Spring Monopile Analysis

NRELOffshrBsline5MW_Platform_Monopile_RF.txt (6.14 KB)UserPtfmLd_CS.txt (6.35 KB)Hello,

I am reproducing the simulation of the NREL 5MW baseline wind turbine with a monopile support.

In other forums, I could find the source code named “UserPtfmLd_CS” which allows to input the additional platform stiffness.
So, I have complied FAST v7.02 with this code without any errors and run the program, but results can not be presented due to the divergence of platform motions.
After the 0.138 sec, the results were not able to be presented.

In this simulation, all input files are the same with “NRELOffshrBsline5MW_Monopile_RF.zip” from wind.nrel.gov/public/jjonkman/NR … Bsline5MW/.

The modifications that I made are that ;

  1. FAST v7.02 is complied with the source code named “UserPtfmLd_CS”.
  2. I turned on the Platform DOF in surge, sway, roll and pitch directions in FAST PLATFORM FILE.
  3. I changed PtfmLdMod to 1 for a user-defined from routine UserPtfmLd in FAST PLATFORM FILE.

I tried to change the mode shapes of tower obtained from BMODES with inputs from "http://wind.nrel.gov/public/jjonkman/BModes/ ". But the results are still not available.

My question is
Is there any other modifications required to simulation of Coupled Spring foundation model?

Best regards,
Hakun Jang

Dear Hakun,

Your approach sounds correct. In addition to changing the tower mode shapes (which it sounds like you’re working on), the other input that needs to change is the time step (DT) in the primary FAST input file. The introduction of the CS foundation will introduce higher natural frequencies in the FAST model, which will require the use of a smaller time step. My guess is your results are “blowing up” because you didn’t reduce the time step. See my post dated Nov 4, 2010 in the forum topic found here for rules of thumb on how to choose proper time steps: http://forums.nrel.gov/t/error-in-fast-working-in-adams/298/1.

Best regards,

Dear Jason,

Thanks for your prompt reply. As you recommended, I made the smaller DT and the program runs well.
I appreciate your help.

Best regards,
Hakun Jang