  Due to the multitude of scales present in realistic oceanic conditions,
resolving the surface stress is computationally intensive, motivating modeling
approaches. In this work, a dynamic wave drag model is developed for Large Eddy
Simulation to quantify the effects of multiscale dynamically rough surfaces on
the atmospheric boundary layer. The waves are vertically unresolved, and the
total drag due to the horizontally resolved portion of the wave spectrum is
computed through a superposition of the force from each mode. As LES can only
resolve the horizontal wind-wave interactions to the filter scale $\Delta$, the
effects of the horizontally unresolved, subfilter waves are modeled by
specifying a roughness length scale characterizing the unresolved wave energy
spectrum. This subfilter roughness is set proportional to the subfilter
root-mean-square of the height distribution, and the constant of
proportionality is evaluated dynamically during the simulation based on the
assumption that the total drag force at the wave surface is independent of the
filter scale. The dynamic approach is used to simulate the airflow over a
spectrum of moving waves and the results are validated against high-fidelity
phase-resolved simulations. The dynamic approach combined with the wave
spectrum drag model is then used to study flow through a fixed-bottom offshore
wind farm. The dynamic model accurately adapts to the changing velocity field
and accurately predicts the mean velocity profiles and power produced from the
offshore wind farm. Further, the effect of the wind-wave interactions on the
mean velocity profiles, power production, and kinetic energy budget are
quantified.
