NREL 5MW wind turbine blade and tower degradation

Problem
➔Track the degradation of one rotor blade and tower base over over as 10 months period under wind inflow and operational uncertainties
Scenario
➔Continuous wind turbine blade and tower stiffness degradation, emulating blade root delamination resulting in dynamic instability, leading to the tower base excess fatigue.
Simulation environment and setup in FAST v8 :
➔In the blade input file: modify flap and edge stiffnesses in damage regions, blade root (only 1 in 3 blades is affected). Assumed equal degradation in both edgewise and flapwise directions
➔In the blade input file: modify mode shapes coefficients (1st flap, 2nd flap and 1st edge modes)
➔In the tower input file: modify FA and SS stiffnesses in damage regions, tower base
➔In the tower input file: modify mode shapes coefficients (1st & 2nd FA and 1st & 2nd SS modes)
➔Note that the tower degradation only "shows up" in the last 2 monitoring periods
➔In the turbulence input file: modify wind speed, tuburlence intensity, shear exponent, horizontal and vertical inflow angles.
➔Further complication by assuming that the average input environmental conditions are not stationary over the monitoring period, emulating seasonal variations.
➔This means 120 environmental samples (and consequenly input wind field time series) are sampled from different distributions each period during the degradation process