Exploration of probability distribution of velocities of saltating sand particles based on the stochastic particle–bed collisions

Sci. China Ser. G-Phys. Mech. Astron.

Zhu

Xie

2008

Self Cite

With the discrete element method (DEM), employing the diameter distribution of natural sands sampled from the Tengger Desert, a mixed-size sand bed was produced and the particle-bed collision was simulated in the mixed-size wind sand movement. In the simulation, the shear wind velocity, particle diameter, incident velocity and incident angle of the impact sand particle were given the same values as the experimental results. After the particle-bed collision, we collected all the initial velocities of rising sand particles, including the liftoff angular velocities, liftoff linear velocities and their horizontal and vertical components. By the statistical analysis on the velocity sample for each velocity component, its probability density functions were obtained, and they are the functions of the shear wind velocity. The liftoff velocities and their horizontal and vertical components are distributed as an exponential density function, while the angular velocities are distributed as a normal density function.wind sand flux, mixed-size particle diameter, liftoff velocity, probability density function (PDF), discrete element method (DEM) It is obvious that the liftoff velocities of sand particles with different diameters are of crucial importance for the prediction of wind sand flux. Therefore, a key issue in the research of wind erosion is to clarify the dynamical characteristic of sand particles lifting from the natural sand bed surface due to particle-bed collision [1] , that is, with a given wind shear velocity, to obtain the probability density function (PDF) of liftoff velocities of sand particles rising from the mixed-size sand bed.There have already been many studies on the PDF of liftoff velocities of sand particles since the mid and later 1980s, e.g., deducing from the experimental photographs of 100 glass grains' trajectories with diameters ranging from 0.35 mm to 0.71 mm. Anderson and Hallet [2] thought that the probability densities of liftoff velocities are subject to an exponential function or a Gamma function with regard to shear wind velocity; Willetts and Rice [3] had direct observations on particle-bed collisions with 100 spherical and planar sand particles using a cine-camera. The diameters of sand

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confidence: 99%

A probability density function of liftoff velocities in mixed-size wind sand flux

Sci. China Ser. G-Phys. Mech. Astron.

Zhu

Xie

2008

Self Cite

“…Applying the 2D particle-bed collision model presented in our pervious works [21,22], we take incident angle, impact position and direction of resultant action of sand particles in sand bed on the impacted sand particle into consideration, and calculate the rebound and eject coefficient and angle. Accordance between our numerical results and current experimental results is encouraging.…”

Section: Discussionmentioning

confidence: 99%

“…Anderson and Haff proposed another particle-bed collision model [12,19,20], and obtained, based on their model, lift-off velocities and locations of the sand particles by discrete element method under the assumption that sand particles be represented by uniform discs. However, the theoretical collision models mentioned above describe the natural particle-bed collision without considering randomness inherent in the particle-bed collision process [21,22], and thus cannot reflect the randomness of rebound and eject of the sand particle.…”

mentioning

confidence: 99%

“…In this paper, we take incident angle, impact position and direction of resultant action of sand particles in sand bed on the impacted sand particle as random variables, and apply the 2D particle-bed stochastic collision model presented in our pervious works [21,22] to calculate the rebound and ejected velocities, angles and coefficients and predict the rebound and ejected lift-off probability.…”

mentioning

confidence: 99%

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Probability of rebound and eject of sand particles in wind-blown sand movement

Xie

2007

Acta Mech Sin

Self Cite

When incident particles impact into a sand bed in wind-blown sand movement, rebound of the incident particles and eject of the sand particles by the incident particles affect directly the development of wind sand flux. In order to obtain rebound and eject lift-off probability of the sand particles, we apply the particle-bed stochastic collision model presented in our pervious works to derive analytic solutions of velocities of the incident and impacted particles in the postcollision bed. In order to describe randomness inherent in the real particle-bed collision, we take the incident angle, the impact position and the direction of resultant action of sand particles in sand bed on the impacted sand particle as random variables, and calculate the rebound and eject velocities, angles and coefficients (ratio of rebound and eject velocity to incident velocity). Numerical results are found in accordance with current experimental results. The rebound and eject liftoff probabilities versus the incident and creeping velocities are predicted.

“…Namely, due to the actions of both wind and falling sand particles, sand particles on the bed surface will take off. They then obtain energy from wind field during flying in the air, and the energy is finally transferred to the sand bed by sandbed collision [4][5][6][7]. In the process, the incident and lift-off velocities of saltating sand particles and their distributions are significant quantity bridging the sand particle's movement and the development of windblown sand flux, and are key factors to determine the influence of sand-bed collision on the development of windblown sand flux [8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Analysis of sand particles’ lift-off and incident velocities in wind-blown sand flux

Duan

et al. 2013

Acta Mech Sin

In the research of windblown sand movement, the lift-off and incident velocities of saltating sand particles play a significant role in bridging the spatial and temporal scales from single sand particle's motion to windblown sand flux. In this paper, we achieved wind tunnel measurements of the movement of sand particles near sand bed through improving the wind tunnel experimental scheme of paticle image velocimetry (PIV) and data processing method. And then the influence of observation height on the probability distributions of lift-off and incident velocities of sand particles was analyzed. The results demonstrate that the observation height has no obvious influence on the distribution pattern of the lift-off and incident velocities of sand particles, i.e., the probability distribution of horizontal and vertical velocities of lift-off and incident sand particles follow a Gaussian distribution and a negative exponential distribution, respectively. However, it influences the center of the Gaussian distribution, the decay constant and the amplitude of the negative exponential distribution.