MLife time to failure outputs for O&M modelling

Hi all,

I have used MLife to determine times to failure, lifetime damage and DELs for various OpenFAST outputs for a baseline and enhanced controller. My next step is to determine the maintenance/O&M cost reductions that could be achieved.

However, it is unclear to me how the time to failures for different OpenFAST load/moment outputs (e.g RootMyc1, TwrBsMyt, LSSGagMya, YawBrMxp) correspond to the actual wind turbine components (e.g generator, hub, blades, tower, pitch actuators, yaw system etc) that would fail and need to be maintained and whether these would require a minor/major repair or replacement.

My question is has this been defined or what would be the best way to match the OpenFAST output to a particular physical component that would need to be maintained?

I hope that’s clear. Many thanks as always.


Dear Andrew,

You say you’ve computed times to failure, lifetime damage, and DELs for various OpenFAST outputs. Presumably you mean you computed these by running many load case simulations across a range of operation and parked/idling conditions and you’ve weighted each simulation using the wind speed probability distribution within MLife. Is that correct?

How did you select the ultimate design load for each component (LUlt in MLife) in this process?

The OpenFAST load outputs are defined at various cross sections of the turbine (e.g,. TwrBsMyt is at the tower base). For structures composes of simple cylindrical shapes and isotropic materials such as the tower and shaft, computing the time to failure at various cross sections of those components should give you a sense of the overall lifetime of those components. (You’d likely also need to confirm ultimate strength and resistance to buckling.)

For noncylindrical components such as the hub, nacelle and composite blades, the process is more complicated because you’ll have to use the loads output from OpenFAST as an input into a detailed FEA analysis of those components to determine the resulting state of stress, from which failure can be predicted.

Best regards,

Hi Jason,

Thank you for your response. Yes thats correct, I ran many load cases according to Design Load Cases defined in IEC standards and ran them through MLife, weighted with a weibull distribution.

For the ultimate loads, i determined this by finding the maximum loading across all the simulated load case and multiplied that by a safety factor.

Your comments make a lot of sense. Is there a FEA software that supports the IEA 15MW model?

Would you be able to provide me with a short list of the loads corresponding to simple geometries that would suitable to use the MLife outputs for analysis (i.e tower, blade roots, shaft)?

Many thanks,


Hi @Andrew.Russell

I’m not aware that FEA models have been built for components of the IEA Wind 15-MW RWT (although they could have been, I’m just not aware).

Here are typical outputs considered in loads post-processing:
Blade (ElastoDyn): RootMxb#, RootMyb#, RootMzb# (root); Spn#MLxb#, Spn#MLyb#, Spn#MLzb#
(50% span)
Hub: RootMxc#, RootMyc#, RootMzc# (pitch bearing); LSShftMxa, LSSTipMya, LSSTipMza (shaft)
Shaft/Bearing: LSSGagMxs, LSSGagMys, LSSGagMzs (main shaft bearing)
Bedplate: YawBrMxn, YawBrMyn, YawBrMzn
Tower: YawBrMxp, YawBrMyp, YawBrMzp (top), TwrBsMxt, TwrBsMyt, TwrBsMzt (bottom), TwHt#MLxt, TwHt#MLyt, TwHt#MLzt (50%)

Best regards,