Dear Jason,

I am performing a batch of aeroelastic simulations under turbulent winds at several hub height average velocities, starting from 5 m/s (5 m/s, 7, 9,11…). With the lower ones, such us 5 m/s I suffer a crash in the simulations when Vx (at hub height) reaches minimum peaks, of about 2 m/s. The given error is this one:

“FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD_CalcOutput:BEMT_CalcOutput(node 9,

blade 2):Compute_UA_AirfoilCoefs:UA_CalcOutput:Mach number exceeds 1.0. Equations cannot be

evaluated.”

Or this one if I set unesteady aerodynamics off:

“FAST_Solution:FAST_AdvanceStates:AD_UpdateStates:BEMT_UpdateStates(node 9, blade

2):BEMT_UnCoupledSolve:DeterminePhiBounds:There is no valid value of phi for these operating

conditions! Vx = -6.63006E-03, Vy = 5.8556, rlocal = 1.438, theta = 0.12822”

This error occurs either if I set the yaw DOF to True or to False.

From the output time series (which are attached in this post) I see that when the failure occurs the rotational speed (around 50 rpm) is too high for the incoming wind velocity (2 m/s more or less). This leads to high TSR and phi angles, and FAST crashes. Initially I have tried a Simple VS control from ServoDyn module of FAST v8 (VSContrl=1), reproducing a fixed pitch passive stall turbine as we discussed in previous topics, line blue in the figure corresponds to this implementation. I have also tried to model the torque control system with a user defined routine (VSContrl=3) (line orange in the figure) setting the generator torque to zero for wind velocities lower than the cut-in velocity (which is 3 m/s, and omega=51 rpm, more or less), and the same curve shape than in the simple VS torque control implementation but the error remains.

I hope that with your experience you could give me advice on this topic.

Thank you very much in advance,

Best regards,

Alvaro Olcoz Alonso

Student at Public University of Navarre

TEST_1_1_1_NTM.rar (1.75 MB)