MLife Fatigue DEL Calculation

[Jason.Jonkman]

Dear Bruno,

Unfortunately, the NWTC Information Portal has crashed and is no longer available, and there is a bit of gap before the new website becomes live–see the following announcement for more information: Other News.

Regardless, here is what the old FAQ said regarding the question, “What values do I use for TypeLMF and LUlt in my MCrunch and MLife input files?”:

The answer depends on the nature of your analysis/study, and the available information you have about your turbine design.
LUlt is the highest load (in absolute value) that the cross section of the component in question can withstand before failure based on its ultimate strength. TypeLMF is the mean load of the cross section of the component in question. LUlt and TypeLMF are used to define the load range versus cycles to failure (S-N or Whöler) curve, which is used by the damage, lifetime, and Goodman calculations of the fatigue analysis.
Ideally, LUlt would be based on a strength (e.g., FEA) analysis of the cross section of the component in question. If this is not available—for conceptual designs for example—what we’ve done in the past is to see how the fatigue loads vary over a range of LUlt values. We’ve defined a range by taking the overall maximum value of the load in question (e.g., derived from MExtremes), and multiplying by scaling factors of 1.25, 2.5, 5, 10, and 20. The fatigue loads will asymptotically approach a fixed value for large values of LUlt.
Ideally, TypeLMF would be the mean load in question over the time period of interest (e.g., the mean over the time series or the mean over the lifetime). In MLife, you can explicitly define this mean, set TypeLMF to AM to tell MLife to compute the mean using the aggregate mean across all input files, or set TypeLMF to WM to tell MLife to compute the mean by weighting the mean on a per file basis using the specified probability distribution.
Fatigue calculations involve rainflow cycle counting where the time series are sorted into a set of cycles each with different ranges and means. In the fatigue calculation process, MCrunch and MLife can apply the Goodman correction to transform the load ranges with varying means to equivalent load ranges at a fixed-mean load. For generalized design studies, some people choose to perform their fatigue-life analysis without applying the Goodman correction. In MLife this is possible by setting the GoodmanFlag to 0. In this case, MLife uses the load range cycles without applying a correction, and to use a fixed-mean load of zero.
Please refer to the MLife theory manual for additional information.

Until the new website becomes live, I’ve temporarily places the MExtremes (as well as MCrunch and MLife) download(s) here: wind.nrel.gov/public/jjonkman/M … MExtremes/.

Best regards,