gbarter
commented
1 month ago The mismatch between your "reverse" calculations and the "forward" calculations in ElastoDyn may be due to neglecting the tower outfitting mass. This is all of the innards in a tower from the cabling, lighting, ladders/elevator, platforms, etc. We have an outfitting multiplier of 7% on top of the total mass here. You can see how that impacts the calculation of the mass density and stiffness properties here. We have made a modeling assumption that this outfitting mass impacts the mass properties, but not the stiffness because those extra components are not load bearing.
I haven't done the calculation myself to determine is this is indeed the source of the discrepancy.
Description
Looking at the tower properties in IEA-15-240-RWT_VolturnUS-S.yaml-file, the outer diameter of the tower top should be 6.5 m. However, calculating the tower diameter using the ElastoDyn tower input file, I find this diameter to be 8.25 m. Moreover, when calculating the inner diameter based on the ElastoDyn tower file, the thicknesses also seem to differ.
Steps to reproduce issue
The outer diameter of the tower sections can be calculated by means of $D_o = 2\sqrt{\frac{TMassDen}{2\pi\hat{\rho}}+2\frac{\hat{\rho}TwFAStif}{ETMassDen}}$, where $TMassDen$ and $TwFAStif$ are distributed tower properties found in the ElastoDyn tower file for this turbine. $\hat{\rho}$ is the material density multiplied by the outfitting factor ($\hat{\rho}=1.07\times 7800 = 8346 \text{kg/m}^3$) and $E$ is the E-modulus ($E=200.e+009 \text{N/m}^2$), both found from IEA-15-240-RWT_VolturnUS-S.yaml. The inner diameter can be calculated as $D_i = \sqrt{D_o^2-\frac{4TMassDen}{\hat{\rho}\pi}}$.
Current behavior
$D{o{TT}} = 6.5\text{m}$ in IEA-15-240-RWTVolturnUS-S.yaml, but is calculated as $D{o{TT}} = 8.25\text{m}$ based on the ElastoDyn-tower file. Similarly, the thickness of the bottom and top section of the tower are listed as $t{TowBas} = 0.09\text{m}$ and $t{TowTop} = 0.00593\text{m}$ in the yaml-file from Wisdem, but I calculate them to be $t{TowBas} = 0.0885\text{m}$ and $t_{TowTop} = 0.0079\text{m}$ based on the ElastoDyn tower input file.
Expected behavior
The properties specified in the wisdem-file and ElastoDyn input file should be the same.