Research On The Non-linear Characteristics Of Incipient Motion For Blown Sand

In the two-phase flow of sand blown, the mechanism of particles starting from the surface of bed under the effect of wind field is an important research subject. Particles starting from the earth’s surface indicating the beginning of wind erosion, wind erosion is one of the main powers which causing the land degradation in arid and semiarid areas, while the threshold wind velocities of particles is a key factor which may influences wind erosion. Therefore, threshold wind velocities of particles has been pay high attention by researchers. The main contents of this thesis are as follows:l.This thesis derived mechanical equilibrium equations of particles firstly, according to the mutation characteristics of process of particles starting from the surface of bed, using catastrophe theory in nonlinear science set Cusp Catastrophic Model on that process, through theoretical derivation verified that particles starting with effects of gravity、drag force、saffman force and electric field force can be described by Cusp Catastrophic Model and then verified this conclusion using numerical calculation. After verifying the feasibility of process of particles starting with Cusp Catastrophic Model, we mainly discussed the electric field force effect on that process. The calculated result is in accordance with experiment and other theory model results. It demonstrated that under the conditions of weak electric field, the electric field force has a low effect on process of particles starting, so it can be neglected when computational analysis. While under the conditions of strong electric field, electric field force has a high effect on threshold wind velocities, so it can not be neglected.2. We observed that in the wind field effect before particles starting from the surface of bed,the particles is shaking instead of holding still. This kind of shaking is caused by fluctuating wind field. However, this conclusion is obtained from experimental observation and there is no theory model can support the conclusion. Therefore, we begin from force analysis of particles, established the differential dynamic equation of particles effected by the wind field and imitated the fluctuation as a sine function. Firstly, solving the initial boundary value of differential equation in order to get the threshold wind velocities of particles when there is no fluctuation, and then adjusting fluctuation intensity, getting the influence of different fluctuation intensity to get the threshold wind velocities of particles. The conclusion is that when the fluctuation intensity of wind field is stronger the of main value of threshold wind velocities will become slower. Secondly, aiming at the physical phenomenon that vibration of particles in fluctuating wind field, after setting the Nonlinear non-autonomous system model, we studied the dynamic characteristics of periodic vibration, period-doubling bifurcation, QPO, chaos and so on. And provided different movement form of particles on the bed under different incentive parameters.