Damping vibration of 15 MW wind turbine blade in beamdyn

I want to simulate the steady-state response of the IEA 15 MW wind turbine using Beamdyn to compare the thrust between the rigidbody assumption and the geometrically exact beam theory assumption.
I used the K and M matrix for beamdyn derived from VABS and provided by default in the original folder on Github. the time step is 0.0005 s (the minimum time step required for not crushing the simulation). I set the damping coefficient for each degree of freedom of the blade to 8%, the gravity is null and the wind speed is set to 8 m/s and it is constant without shear.
The issue is that the blade root moments keep oscillating without any damping. I wonder if there is a possibility to eliminate the oscillations after a limited transient to a steady-state.
all degrees of freedom are disabled (rotor speed set to 7 RPM, bladepitch set to 0 deg). I tried to set the damping coefficient to 50 or 100 % but without any success.
Any tips.
thanks for your time
here the plots of the bladeroot moments got by beamdyn.

Dear @Massimo.Sirigu,

Have you eliminated shaft tilt? Otherwise, even though you have no other DOFs enabled, no gravity, and no shear, the shaft tilt will result skewed flow that will cause oscillatory aerodynamic loads and a periodic response.

Best regards,

Dear Mr Jonkman,
Yes, it was the problem. There is still some vibration in the structure, but much less than in previous results. Thank you for being so supportive.
Best regards