Treatment of residual half-cycles in rainflow count./fatigue

Dear all,

I am currently researching approaches for reducing the cost-of-energy of the Upwind 5.0 MW turbine by implementation of (higher harmonic) Individual Pitch Control. An important part of the work is assessment of relative fatigue damage, calculated through equivalent load formulations (no structural data is available for the conceptual turbine, therefore conversion to stresses is not possible). Using a Matlab based rainflow counting algorithm, I transform load sequences to cycles. However, I noticed a lot of residual half-cycles remain, which make a significant difference in the final relative fatigue damage assessment. Looking through the documentation of MCrunch I noticed that the program has the ability to discard them, treat them as full cycles and anything in between those two options (weighing parameter from 0 to 1). What is a generally accepted view of dealing with these residuals? I hope someone can give me some pointers. Thank you for your consideration.

Kind regards,
Bob Prinsen


I’m not an expert in fatigue, but Herb Sutherland is. Here’s what he said in Section of his 1999 report (

Dear Marshall,

Thank you for taking the time in quoting this report. It answers my question perfectly and I will use this approach for my fatigue calculations.

Kind regards,