Calculated vs. WISDEM Output Strains

Wind & Water Systems Engineering Software Tools
1

Hi all,

I have been trying to replicate the strain calculation in WISDEM using the equations listed in RotorSE ComputeStrains

        x, y = rotate(xuu, yuu)
        strainU = M1 / EI11 * y - M2 / EI22 * x - F3in / EA

        x, y = rotate(xll, yll)
        strainL = M1 / EI11 * y - M2 / EI22 * x - F3in / EA

I ran the IEA 15MW turbine as is with no changes in WISDEM. Then from the WISDEM output, I used the following variables to try replicating WISDEM’s output for strain:

rotorse.rs.strains.alpha
rotorse.rs.strains.EI11
rotorse.rs.strains.EI22
rotorse.rs.strains.M1
rotorse.rs.strains.M2
rotorse.rs.strains.F3
rotorse.xu_spar
rotorse.xl_spar
rotorse.yu_spar
rotorse.yl_spar
rotorse.xu_te
rotorse.xl_te
rotorse.yu_te
rotorse.yl_te
All position vectors were rotated to align to the principal axes.

However, my resulting strains did not match WISDEM, and were quite a bit off from one another. I am pretty sure I replicated these equations. This plot just shows the spar caps, but I saw differences in the trailing edge strains as well. Does anyone have any ideas why this would be the case?

image
image824×620 127 KB

Thanks in advance

2

There are some coordinate transformations necessary when computing strains. Take a look at the source code for the calculation here and hopefully that clarifies where the mismatch might be.

3

Hi Garrett,

Thank you for your response. I did rotate the coordinates according to the source code in my calculation. I believe WISDEM’s default used pbeam set to false, so no rotation of M1 or M2 was necessary. I did try rotating them just to check and still got differing results. Is there anything else I could try?

Also, I noticed that the axial component in the source code is negative but the documentation has it as positive as I would expect. This doesn’t change the results much regardless since the axial component is much smaller but I was curious about that as well.

Thanks again,
Max