Blade Spar / Spar Cap Optimisation

I have a question about the aerostructure optimsation caclulations.

I have created 2 turbines, a reference turbine and the same turbine but with an increased stiffness carbon used throughout. I ran the aerostructure optimisation and compared the results - see image.


I would have thought the tip deflection would be maintained and then the spar cap thickness reduced to capitalise on the better material properties to reduce the weight and cost of the blade further. But this is not the case - tip deflection reduces with the better performing material. Is there another criteria that is being used to size the blades instead of deflection/stiffness? Is there a strength criteria that is used? I think this boils down to my main question : what is driving the spar cap thickness?

Hello Connor,
thanks for using WISDEM and contributing to the wind energy research.
You can set the design variables and constraints in the analysis options yaml.
If I understand your problem correctly, I would start by running a blade structural optimization problem. You can do it by calling wisdem with this yaml file

To keep things as simple as possible, you could turn off the design variables controlling the thickness of the TE reinforcement (lines 24 and 31), and the corresponding max strain constraints (lines 54 and 59). At this point, the only two constraints driving your spar cap thickness will be max strains and ultimate tip deflection.
Let us know how this design run goes.
Best regards,


Thanks for your help. That did indeed work. Do you have an explanation for why this happened for my understanding?

I also did a test to increase the power to 6.6MW but the rotor diameter has gone to the minimum - I thought it would have increased. Do you know what might be happening here?


Many thanks,

Hi Connor,
I’m not sure I understand your questions. You’ve increased nameplate power. Are you trying to optimize rotor D? What figure of merit are you using? If it’s blade mass, I’m not surprised that the optimizer will try to minimize it. My general recommendation is to keep a close eye on your openmdao recorder log and check design variables, figure of merit, and constraints during the optimization. You can call this script WISDEM/ at develop · WISDEM/WISDEM · GitHub
to visualize the outputs in the log.
Good luck!