One-dimensional transitional behaviour in saltation

One-dimensional simulations of the unsteady saltation process show that the transport rare's response depends on the amplitude and frequency of the wi nd fluctuations. At frequencies higher than f approximate to 0.5 Hz the tra nsport rate was found not to respond to the wind changes. The initial overs hoot reported by previous investigators was found not to appear for simulat ion heights smaller than 50 to 60 cm. This is due to the fast propagation o f the grains' influence upward in the flow and the immediate deceleration o f the wind. Confirmation of these findings comes from reports of experiment s conducted in wind tunnels of different sizes. Further test calculations show that the discretization time step size Delta t has an influence on the model's temporal behaviour. The reason for this is the better coupling of the wind-sand system when a smaller Delta t is us ed. The implications of bed area choice on the statistical accuracy of pred icted transport rate is also demonstrated. In the one-dimensional case the grain cloud's total forward momentum equals transport rate, which is indepe ndent of model geometry. Copyright (C) 2000 John Wiley & Sons, Ltd.