Observations of collisions of saltating grains with a granular bed from high‐speed cine‐film

Rice, Michael A; Willetts, B. B.; McEwan, Ian

doi:10.1111/j.1365-3091.1996.tb01456.x

Cited by 136 publications

(153 citation statements)

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“…Most observations of sand movement on a bed surface are from high-speed photography in a wind tunnel (e.g., Mitha et al, 1986;Willetts and Rice, 1986;Rice et al, 1995Rice et al, , 1996Nalpanis et al, 1993). In general, the grain-bed collision process is difficult to measure directly from the high-speed photography because the grains are crowded at the very low height (e.g., Nalpanis et al, 1993;Zou et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

“…White and Schulz, 1977;Willetts and Rice, 1986;Anderson and Hallet, 1986;Werner and Haff, 1988;Anderson and Haff, 1988;Sørensen, 1991;Haff and Anderson, 1993;Nalpanis et al, 1993;Rice et al, 1995Rice et al, , 1996Dong et al, 2002a;Namikas, 2003). If the probability distributions of the horizontal and vertical lift-off velocities or the resultant lift-off velocity and angle of saltating grains are known, the proportion of the number of grains with a given resultant lift-off velocity and lift-off angle will be acquired, then the macroscopic statistic of particles can be deduced from the representative trajectories of saltating grains.…”

Section: Introductionmentioning

confidence: 99%

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Reconstructing the vertical distribution of the aeolian saltation mass flux based on the probability distribution of lift-off velocity

2008

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The probability distribution of lift-off velocity of the saltating grains is a bridge to linking microscopic and macroscopic research of aeolian sand transport. The lift-off parameters of saltating grains (i.e., the horizontal and vertical lift-off velocities, resultant lift-off velocity, and lift-off angle) in a wind tunnel are measured by using a Phase Doppler Particle Analyzer (PDPA). The experimental results show that the probability distribution of horizontal lift-off velocity of saltating particles on a bed surface is a normal function, and that of vertical lift-off velocity is an exponential function. The probability distribution of resultant lift-off velocity of saltating grains can be expressed as a log-normal function, and that of lift-off angle complies with an exponential function. A numerical model for the vertical distribution of aeolian mass flux based on the probability distribution of lift-off velocity is established. The simulation gives a sand mass flux distribution which is consistent with the field data of Namikas (Namikas, S.L., 2003. Field measurement and numerical modelling of aeolian mass flux distributions on a sandy beach, Sedimentology 50, 303-326). Therefore, these findings are helpful to further understand the probability characteristics of lift-off grains in aeolian sand transport.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Reconstructing the vertical distribution of the aeolian saltation mass flux based on the probability distribution of lift-off velocity

2008

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“…Velocities are nondimensionalized by dividing by D/ M/K n . This dimensionless approach lets us model either large bead collisions such as in Rioual et al [5] experiments (6 mm) or sand grains (200 μm) [7,8,9].…”

Section: Numerical Simulationmentioning

confidence: 99%

“…Image analysis treatments [7,8,9] [10]. In addition to the experimental studies, some simulations of the collision process have been performed [11,2,12,13,14].…”

Section: State Of the Artmentioning

confidence: 99%

2D DEM model of sand transport with wind interaction

Oger¹,

Valance²

2013

AIP Conference Proceedings

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Abstract.The advance of the dunes in the desert is a threat to the life of the local people. The dunes invade houses, agricultural land and perturb the circulation on the roads. It is therefore very important to understand the mechanism of sand transport in order to ¿ght against deserti¿cation. Saltation in which sand grains are propelled by the wind along the surface in short hops, is the primary mode of blown sand movement [1]. The saltating grains are very energetic and when impact a sand surface, they rebound and consequently eject other particles from the sand bed. The ejected grains, called reptating grains, contribute to the augmentation of the sand Àux. Some of them can be promoted to the saltation motion.We use a mechanical model based on the Discrete Element Method to study successive collisions of incident energetic beads with granular packing in the context of Aeolian saltation transport. We investigate the collision process for the case where the incident bead and those from the packing have identical mechanical properties. We analyze the features of the consecutive collision processes made by the transport of the saltating disks by a wind in which its pro¿le is obtained from the counter-interaction between air Àow and grain Àows. We used a molecular dynamics method known as DEM (soft Discrete Element Method) with a initial static packing of 20000 2D particles. The dilation of the upper surface due to the consecutive collisions is responsible for maintaining the Àow at a given energy input due to the wind

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“…1) dimensionless amplitude of the sinusoidal wind variation dimensionless angular frequeney stretched angular position of the zero moment line limit valué of 6 0 for stable evolution density of air, of stone, respectively angle between the centre of mass line and the horizontal plañe homogeneous solution angle between the zero moment line and the horizontal plañe ( initial valué (unless otherwise defined) long gust limit short gust limit reference valué exceeding non exceeding One of the erosión mechanisms of relevance here is the saltation process, which has received a large attention over the years. The research performed in this field includes, among others, wind tunnel testing (Ciccone et al, 1990;Rice et al, 1995), 2D numerical simulation (Werner and Haff, 1998) and studying it as a simulation of the cascade colusión and ejection of ions (Ta and Dong, 2007), and the sand-bed impact (Willets andRice, 1985, 1986;Mitha et al, 1986;Rice et al, 1995Rice et al, , 1996Werner and Haff, 1998). The cascade colusión can help to explain the maintenance of saltation, but not the starting process, which is the aim of this paper.…”

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confidence: 99%

The initiation of rotational motion of a lying object caused by wind gusts

Sanz-Andrés

Navarro-Medina

2010

Journal of Wind Engineering and Industrial Aerodynamics

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Keywords:Non-steady loads Train Ballast Erosión DebrisIn this paper, the initiation of motion of an object lying on a horizontal ñoor due to the aerodynamic forcé produced by a time-dependent wind is considered. It is assumed in this paper that when the aerodynamic forcé is large enough, the body starts to rotate around the most rearward supporting contact point, or pivoting point. This motion is analyzed by studying the dynamics of the rotation of the body around a pivoting point fixed to the ñoor, and placed in a gravity field under time-dependent aerodynamic loads produced by a non-steady incoming ñow. This rotation initiation phase, which is relevant in the case of a time-varying gusty ñow, is an intermedíate phase between the two stages generally considered, namely, the initial static equilibrium without motion, and the final flight. In this intermedíate phase, which is studied here, the rotational dynamics of the body should be taken into account and the gust characteristics as well, in order to determine whether once initiated the motion it leads to either a frustrated motion or to a successful one. A non-linear mathematical model has been developed, and a linear approximation is deduced, which allows us to obtain the condition for a successful flight. This condition shows two limits, valid for either long or short duration gusts, respectively. Some experiments have been performed in a gust wind tunnel, and results show a satisfactory agreement. To take into account the intrinsic random character of the phenomena in practical situations, expressions for the probability of exceeding the condition for successful flight under short duration gusts are obtained, assuming common probability density functions for the random parameters involved.

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Observations of collisions of saltating grains with a granular bed from high‐speed cine‐film

Cited by 136 publications

References 16 publications

Reconstructing the vertical distribution of the aeolian saltation mass flux based on the probability distribution of lift-off velocity

Reconstructing the vertical distribution of the aeolian saltation mass flux based on the probability distribution of lift-off velocity

2D DEM model of sand transport with wind interaction

The initiation of rotational motion of a lying object caused by wind gusts

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