Dear all,

I’m trying to simulate a 20m blade turbine which is pre bended and sweep. First I defined the pre bending and sweep in ADBlFile using BlCrvAC and BlSwpAC. So lets assume that at the tip we have -1m of prebending and -0.5m of sweep so it should be:

BlSpn BlCrvAC BlSwpAC

19.99 -1 -0.5

Afterwards in the Beamdyn input file I also defined for each node the distribution of prebending and sweep using kp_xb and kp_yb , so it should be

kp_xb kp_yb kp_zb initial_twist

-1 0.5 19.99 0.16

if this is right then, this will crash

sometimes with the below error, although I used very small time step for fast and beamdyn

FAST_AdvanceStates:BD_GA2:BD_DynamicSolutionGA2:Solution does not converge after the maximum number of iterations

sometimes gives this one:

FAST_Solution:FAST_AdvanceStates:AD_UpdateStates:BEMT_UnCoupledSolve:DeterminePhiBounds:

There is no valid value of phi for these operating conditions!

psi = 2.4139, Vx = -1.04651E-02, Vy = 168.79, rlocal = 5.7841, theta = 0.15593

if I put every where for kp_xb and kp_yb 0.0 then this will work however I think thats wrong. I also tried that with a very small prebending value and still will crash.

So I would like to know if the definition of kp_xb and kp_yb is different with what I got or the beamdyn is reading the prebeding directly from areodynfile?

Many Thanks for your answer.

Dear Hamid,

The curved blade geometry is set independently in BeamDyn and AeroDyn. Your approach sounds correct, except that I would expect kp_yb at the tip to equal -0.5 (to match BlSwpAC at the tip); I suspect this was just a typo in your post.

You say that sometimes you receive errors; how often do you mean by “sometimes”? Do the solutions look physically correct up until you the time that you receive the errors?

Best regards,

Dear Jason,

Thanks for your reply. You are right it was a typo for the post. Actually I tried alot and with different combination, it didnt work at all. If I put the correct prebending and sweep, the code will not run at all and the error is

[i] Timestep: 0 of 60 seconds.

FAST_Solution:FAST_AdvanceStates:BD_GA2:BD_DynamicSolutionGA2:Solution does not converge after

the maximum number of iterations

FAST_AdvanceStates:BD_GA2:BD_DynamicSolutionGA2:Solution does not converge after the maximum

number of iterations

FAST_AdvanceStates:BD_GA2:BD_DynamicSolutionGA2:Solution does not converge after the maximum

number of iterations

FAST encountered an error at simulation time 0 of 60 seconds.

Simulation error level: FATAL ERROR[/i]

if I remove the prebending and sweep from beamdyn will work. with this condition I compared the result with our CFD code which uses the same method, the x and y deflection and rotation looks correct. but the Z deflection for the CFD is positive since it has a prebending and for me since I dont have is negative.

if I play abit with the prebending numbers make them abit smaller and bigger or the DT for beamdyn I will get:

[i] Timestep: 0 of 60 seconds.

FAST_Solution:FAST_AdvanceStates:AD_UpdateStates:BEMT_UnCoupledSolve:DeterminePhiBounds:There is

no valid value of phi for these operating conditions! psi = 2.3912, Vx = -32.89, Vy = 511.16,

rlocal = 4.7727, theta = 7.00019E-02

FAST encountered an error at simulation time 0.211 of 60 seconds.

Simulation error level: FATAL ERROR

Aborting FAST.[/i]

I tried to use the Static method it says:

Load may be too large, BeamDyn will attempt to solve with additional steps.(even with many itr same error).

I used 0 gravity and smaller wind velocity same problem.

I also tried to give a small prebending to TEST26 something like 0.1m, that’s give the same first error as above post.

So to conclude, with even a small prebending or sweep value (eg. 0.1) I’m not able to run the code.

Best Regards,

Hamid

Dear Hamid,

I’m not exactly sure why you are running into trouble. One thing that can cause problems is if the pre-curve and pre-sweep are not defined smoothly in BeamDyn, the local curvature can be very large, which may lead to numerical problems and result in either of the two errors you’ve reported. Just so you know, the initial local curvature of the blade (before loading is applied) is derived by fitting cubic splines through the key points. So, if the key points do not form a smooth curve, the splines could introduce “kinks” that would increase the curvature dramatically, and likely cause numerical problems.

To check for any problems with the NREL 5-MW model, I took Test26 and added a small upwind precurve to the blade. Basically, I changed kp_xb in BeamDyn from zeros to a quadratic function from 0 m at the root to -1 m at the tip, likewise for BlCrvAC in AeroDyn. Please find the updated BeamDyn primary and AeroDyn blade input files attached, if you want to run the model yourself. Rerunning Test26 with these change runs as expected.

Just FYI: the static analysis option of BeamDyn is not available when BeamDyn is coupled to FAST. I don’t believe this is currently checked, but in the next release, we’ll add a check to trigger an error if static analysis is selected in a coupled FAST-BeamDyn simulation.

Best regards,

NRELOffshrBsline5MW_BeamDyn_WithUpwindPrecurve.dat.txt (7.42 KB)

NRELOffshrBsline5MW_AeroDyn_blade_WithUpwindPrecurve.dat.txt (4.17 KB)