The Research On The Criteria Of Incipient Motion Of Sand Particles In Windblown Sand

The evolution process of windblown sand has always been of concern to many scholars. Due to the particularity of windblown sand, the observations in experimental study are often affected by the experimental equipment and the surrounding environment, thus limiting the awareness of windblown sand. So it is difficult to get some quantitative results in predicting the evolution process of windblown sand only through experiment. The numerical simulation and theoretical analysis are often combined with experiment to predict the evolution process. The incipient motion of sand particle from sand bed plays a very important role in the prediction of evolution process of windblown sand. The comparison between average or instantaneous wind speed and critical wind speed is usually used to determine whether the criteria of incipient motion of sand particle can be satisfied. Based on existing work, this paper proposes a new method for the prediction of incipient motion of sand particle based on wind speed fluctuation, i.e., in duration when the wind speed is larger than the critical wind speed, if the total impulse on sand particle is larger than the critical impulse, incipient motion of sand particle occurs, or incipient motion of sand particle cannot occur. This paper also theoretically compares the effect of the new method with existing methods in judging the incipient motion of sand particle. Moreover, from the analysis of entrainment in the rolling and lifting modes, we find that when the average wind speed is smaller than the critical wind speed, average wind speed is used to judge the incipient motion of sand particle, it will underestimate the number of sand particles jumping from the bed, and instantaneous wind speed is used to judge incipient motion of sand particle, it will overestimate the number of sand particles jumping from the bed; when the average wind speed is larger than the critical wind speed, average wind speed and instantaneous wind speed were used to judge the incipient motion of sand particle, it will overestimate the number of sand particles jumping from the bed. Finally, this paper applies this method to the simulation program of windblown sand for the estimation of sand transport rate. Through the comparison between the results of sand transport rate calculated by this new method and the previous methods, it is concluded that the results are consistent with theoretical analysis. Meanwhile, this paper shows the comparison among the results calculated by different methods quantitatively and discusses the response time lag problem of transport rate to wind speed through the comparison, which provides a new train of thought for the further study of this problem.