Dear OpenFAST team,
I´m currently using Modes.exe to obtain Blade Mode Shapes for my Blade files. The linear mass of my first section (x=0, blade root) has decreased, so I changed that value and proceeded to obtain the modes again. Then, I realized that modifying the linear mass density at the first blade station (x = 0.0, start of the flexible portion) produces no change in computed mode shapes or natural frequencies, even with unrealistically large values.
This behavior is independent of the Rigid beam length setting: I varied Rigid beam length over a wide range and the result is the same (mass at x=0 does not affect the solution).
In contrast, changing mass density at the second station (x > 0) or changing Flap and Edge Stiffnesses in the first section (x=0) does affect the results as expected. Having seen this, my question is as follows:
- Is the x=0 station treated as a clamped node such that its mass contribution is effectively excluded from the eigenproblem?
- If one wants to represent root mass change, is the recommended approach to distribute it over a short span with x > 0?
Thank you once again for your time and kind regards,
Kepa