Dear Kok,
The theory of TurbSim is built around the assumption that the wind is stationary over the course of the TurbSim simulation. By “stationary,” I mean that the wind is assumed to be of a fixed mean speed and turbulence intensity. TurbSim should be run separately for each mean wind speed and turbulence intensity desired. Please see the following forum topic for related information: Lifetime calculations for wind turbines.
Best regards,