Tower top loads

Hello all

I ran a simulation of a FOWT using OpenFAST and have some questions about the results regarding the tower-top loads. I obtained the time-domain responses for shear and moment at both the tower top and tower base(YawBrFxp, YawBrMyp, TwrBsFxt, TwrBsMyt) within a wind speed range of 4m/s to 22m/s (Turbulent Wind). After removing the initial 100 seconds of simulation to obtain the load averages, I plotted the curves normalized to the peak values as shown in the graph. However, I noticed an unusual trend in the average moment at the tower top(YawBrMyp), which doesn’t decrease after the rated wind speed like other loads. Instead, it continues to increase, initially displaying negative values. I’m curious if anyone has a reasonable explanation for this phenomenon.

Thanks in advance for your help!

Dear @Teng.Long,

The shear forces along x at the tower top and tower base, as well as the bending moment about y at the tower base, are driven by thrust loading. However, the bending moment about y at the tower top has a short moment arm for the thrust force to apply. So, the tower-top bending moment can be sensitive to other loading, such as asymmetric loading of the rotor (e.g., from shear).

Best regards,