| dc.description.abstract | Granular flows always play an important role on the flow dynamics and application for both natural phenomena such as stony debris flows, slope avalanches, and rock falls in field and industrial manufactory. In order to understand the physical characteristics and dynamic mechanism in granular flows, this study explores the macroscopic flow characteristic of uniform granular material, size segregation of binary mixture, falling processing induced by gravity, and slope angle decay under horizontal shaking by experimental investigations. Both experimental analyses with digital imaging techniques based on Voronoi velocimetry algorithm and theoretical description are employed in the study.
With regard to the granular flow composed of uniform grains in a rotating drum, a new dimensionless flow rate combining the effects of Froude number, relative particle size and volume filling is proposed in this study, which controls the flow characteristics in a rational drum such as dynamic angle of repose, thickness of the flowing layer, relative free surface velocity, and the shear rates in the flowing layer. For a binary mixture of granular material, the experiments demonstrate the enhancement of side-wall friction will cause a new pattern: the asymmetrical banding stripe. The onset of axial segregation in connection with the variations of size ratio of mixtures, drum geometry, and wall friction are also verified. From trajectory reconstructions and velocity field, one can conclude that the lateral convective cell will expand gradually while Froude number increases for a constant wall friction case. By means of the corresponding scaling law combining the terms of Péclet number and wall roughness, the same axial segregation can be obtained by changing the different control factors.
On the other hand, the falling processes associated with rock avalanches and the sliding of slopes is closely related to the granular physics. With respect to a given size of particles and bottom slope, the retreating upper granular surface follows the presented theoretical curve, and dimensionless mobile length decreases as the dimensionless time parameter increases. Measurements of transient velocity profiles exhibit an exponential-like tail close to the static region at the quasi-static bottom and obey SSH rheology instead of Bagnold’s rheology. As for the slope angle decay in the confined and unconfined boundary under shaking process, the proposed scaling law can be well described the evolution of surface slope angle and reflects the variation among the relative shaking acceleration, surface roughness of grains, and sill height. In addition, the corresponding thickness of internal fluidized layer and final stable slope angle show the important relationship linking to the existence of side-wall effect. Finally, the different types of slope failure mechanisms of these two experiments are also examined and discussed further.
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