Simulation of wind-blown sand movement and probability density function of liftoff velocities of sand particles

[ 1] Accurately describing the probability density function (PDF) of liftoff or initial velocities of wind-blown sand ejecting from a sand bed is fundamental to understanding the mechanisms of wind-blown sand movement. Our objective was to investigate the efficacy of developing the PDF of liftoff velocities based on wind tunnel measurements of sand flux and wind speed profile. On the basis of experimental results an optimization algorithm to numerically search for the PDF was developed by multiobjective optimization associated with the saltation model. Through fitting all sets of the PDF numerical results of optimization with the least squares method an empirical formula of the PDF was obtained. To show the efficacy and accuracy of the formula of the PDF obtained using this approach, simulations of the sand flux and wind speed profile using selected PDFs of liftoff velocities were performed with the developed function and functions previously proposed by other researchers. By comparing the suite of predicted PDFs with the experimental measurements we found that although all the predictions agree reasonably well with the measured data, the method proposed herein for obtaining the PDF in this paper results in a more accurate PDF for predicting sand flux and wind speed profile than other tested functions. These results validate the approach of obtaining the PDF of liftoff velocities based on wind tunnel measurements.