Matt,
TypeLMF is used to establish a ‘fixed mean’ for the fatigue channel. This fixed mean is used to adjust all the variable mean fatigue cycle ranges to ranges about a single fixed mean.
Lrf = Lr * ( Lult - abs (Lmf) ) / ( Lult - abs(Lm) ), where Lmf = the fixed mean load, Lm = the mean load of the current cycle, Lult = the ultimate load, Lr = the load range for the current cycle, Lrf = adjusted load range about a fixed mean.
These adjusted ranges are used when computing lifetime damage and damage equivalent loads (DELs) in MCrunch.
Originally, TypeLMF was intended to support three options. 1) The fixed mean value, 2) the string ‘AM’ which would tell MCrunch to compute a fixed mean using the aggregate mean of the channel, and 3) ‘WM’ which is the aggregate mean further weighted by the Rayleigh wind distribution. Only option 1 was implemented in the code.
I’m currently implementing a new Matlab-based fatigue analysis package called MLife. The package implements all three of the above options. Additionally, MLife computes damage about both a fixed mean and a zero mean. Short-term DELs are computed using the raw variable mean cycle ranges, a fixed mean, and zero mean. The long-term DELs (computed over the design lifetime) are computed for fixed and zero mean.
Best Regards,
Greg Hayman
NREL subcontractor
Greg.Hayman@nrel.gov