# Transient behaviour with fixed rotorspeed

Hey everyone,

How can i explain the transient behaviour of the Tower top fore aft displacement with a fixed rotorspeed and GenDof off. How does it correspond with a real wind turbine condition?

I dont quite understand the describtion of Rotspeed in Elastodyn. It says initial or fixed or initial rotational speed. As far as I understand, these two are two different things. The initial speed is the rotational speed of the turbine at initial condition and the fixed speed is the wind turbine rotational speed at a fixed end condition. When I set the initial speed to 0 rpm (i assume this represents the wind turbine at standstill), the wind speed after the transient is completly dependent from the aerodynamics. But when I set a fixed rotational speed with GenDof off there will be a transient like behavior at the beginning of the simulation.

best regards

Dear @Zong.Linyang,

By “initial or fixed rotor speed”, we mean that `RotSpeed` is the initial speed at the start of the simulation if `GenDOF` = TRUE and `RotSpeed` is the fixed speed of the rotor when `GenDOF` = FALSE.

Best regards,