WAsP engineering flow model for wind over land and sea

This report presents the basic wind flow model of WAsP Engineering. The model consists in principle of three parts: the LINCOM model for neutrally stable flow over terrain with hills and varying surface roughness, a sea surface roughness model, and anobstacle model. To better predict flow over or close to water bodies, the model for the sea surface roughness has been developed and interfaced with the existing LINCOM model. As the water roughness depends on the wind velocity, and the wind velocity onthe roughness, the coupling is iterative. The water rougness model is based on a fit to lots of literature data for the Charnock parameter as function of the so called wave age, the ratio between wave velocity and friction velocity, plus a correlation ofwave age to the geometrically obtainable water fetch. A model for the influence on the wind of multiple, finite size, interacting obstacles with any orientation has been formulated on the basis of the Perera formula for the influence of a singlefence-like obstacle perpendicular to the wind. It is not a flow model but shall work as a postprocessor to the LINCOM model, which itself cannot treat such influence.