Dear Nicolás,
Normally turbulent wind conditions are simulated about a fixed mean wind speed; i.e. stationarity of the inflow turbulence is assumed. NREL has not provided an engineering tool to calculate the turbulent wind atop a wind ramp. A similar question was discussed fairly recently on this forum–see: Stitch Together TurbSim Timeseries.
HydroDyn computes the wave-elevation time series by performing an inverse FFT. The number of frequency components is determined by the wave time step (WaveDT), which determines the maximum frequency, and periodic length (WaveTMax), which determines the frequency step. This is described in the HydroDyn documentation, as well as in the comments to the right of inputs WaveTMax and WaveDT in the HydroDyn input file.
Best regards,