Strange oscillation response of openFAST simulation in 'Steady-state' stage

Dear Jason,

I run the simulation with some results that presented strange oscillation in steady-state. An example is attached below.

We can see that after the 50s, the response reaches a ‘steady-state’, but the oscillation is strange. It should be a harmonic oscillation but seems some step-like output. The module timestep is 0.0025 and there are multiple points on a single plateau in these plots. Do you have any suggestions on how to fix this problem? Thank you!

Ct time history
1.jpg

Local view of the Ct time history
2.jpg

Dear Xianping,

The problem you are seeing is related to the precision of your OpenFAST output. A similar question was asked and answered in the following forum topic: http://forums.nrel.gov/t/positive-vs-negative-yaw-error-effect/608/3.

Best regards,

Dear Jason,

That works. Thank you for your help.