Research On Form And Mechanism Of Sand Particles Initial On Horizontal Sand Bed In The Saltation Of Sand Grains

Desertification is one of the major global environmental problems today. Windproduce a series of geological features, such as soil erosion, sand flow, sanddeposition and dune forward, etc., in the sandy surface. Sand movement on thesurface is the main reason for land desertification and sandstorms. The study of theevolution law of saltation of sand grain initial driving by the multiple factors hasimportant significance on the revealing sand initial form and sand initial mechanicalmechanism. It also provides the theoretical basis for the prevention and control ofland desertification and sand-fixing.This paper is from the National Natural Science Foundation (NO.40975094) andthe National Basic Research Program (NO.2006CB403701).This paper make a indoor simulation of the natural saltation of sand grainphenomena by using the environmental wind tunnel to build a saltation of sand grainflow simulation experiment system. First of all, through the saltation of sand grainsimulation system, the sand motion of the saltation of sand grain in sand two-phasewas simulated, and the clear, intuitive sand instantaneous motion images were gotfrom the image acquisition system. Secondly, image data were processed through thedata processing system by using the Motion Studio image processing software andMATLAB data platform. Instantaneous movement parameters were got in this stage:sand trajectory in the whole moving process; the horizontal speed and vertical speedand the horizontal acceleration and the vertical acceleration in every moment. Finally,all these parameters were analyzed in order to get the sand grain initial forms andmechanism.This paper is different from other papers in the experimental methods and dataprocessing:(1) In the previous experiment studies, experimental conditions and experimentalmeans limit the experimental results. The lacker of the light intensity would cause thevaguer sand grain in the image, and the bigger scope of the light would cause moreinterference factors. All of these restrict the research of the mechanism of sand graininitial. In this experiment, the shoot source was made up by the laser light source andlens group, this laser source system effectively solve the problems mentioned above.(2) In the experiment, macro CCD camera is used to get clear image of sandmovement in the bed surface.(3) In the processing of experiment data, the image data processing method usedin this paper is manual processing and image data post processing. The traditionalimage processing technology often uses the algorithm program to process the images. But the sand initial is random, and the result is that the concentration of the shootedsand was very high. This high concentration would make some problems when it wasused the traditional arithmetic to process the image data. The artificial processing andpost data processing method has two advantages:"flexibility" and "fuzzy".Instantaneous movement parameters, which include sand trajectory in the wholemoving process, speed and acceleration of sand grains and so on, were got from theprocessing of the experimental data. Through the analyzing of the informationcombined with the existing theory, the following conclusions can be got:(1) Based on a large amount of tracking and restoration of the sand trajectory, thesand movement in the air flow accords with a quadratic function and its trajectory islike a parabola;(2) The main form of the sand grain initial is the impact initial, through the largeamount of tracking the sand grain.(3) Through the analysis and processing of the image got from the experiment,sand initial is mainly affected by the turbulence in the process of the sand motion, itsessence lies in the transfer of momentum.