A question on measuring the shaft bending moment in FAST

Greetings everyone,

I have come across a problem when trying to measure the rotor low speed shaft bending moment using FAST.

When measuring the shaft bending moment, I noticed that both the rotating and non-rotating bending moments were available in the output options. In this case if I take the vector sum of shaft bending moments in the ys and zs or ya and za directions, shouldn’t the rotating and non-rotating bending moments be the same? However my testing results showed they weren’t the same. /cry

Could someone please tell me what caused them to be different?

Dear Robert,

Yes, the vector sum should be same and I’m not aware of any problems with these FAST outputs. Of course, there may be small differences due to numerical rounding because the FAST output normally only contains 4 significant digits of precision. I suggest you double check your post-processing.

Best regards,