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IMPORTANT: Deadline for registration has been extended to December 16th, 2022 The Statistical Physics and Thermodynamics Division of the Mexican Physical Society invites students, postdocs, researchers and professors to attend to the LI Winter Meeting on Statistical Physics which will be held at
The behavior of granular column collapses is associated with the dynamics of geohazards, such as debris flows, landslides, and pyroclastic flows, yet its underlying physics is still not well understood. In this paper, we explore granular column collapses using the spheropolyhedral discrete element method (DEM), where the system contains two types of particles with different frictional properties. We impose three different mixing ratios and multiple different particle frictional coefficients, which lead to different run-out distances and deposition heights. Based on our previous work and a simple mixture theory, we propose a new effective initial aspect ratio for the bi-frictional granular mixture, which helps unify the description of the relative run-out distances. We analyze the kinematics of bi-frictional granular column collapses and find that deviations from classical power-law scaling in both the dimensionless terminal time and the dimensionless time when the system reaches the maximum kinetic energy may result from differences in the initial solid fraction and initial structures. To clarify the influence of initial states, we further decrease the initial solid fraction of granular column collapses, and propose a trial function to quantitatively describe its influence. Due to the utilization of a simple mixture theory of contact occurrence probability, this study can be associated with the friction-dependent rheology of granular systems and friction-induced granular segregations, and further generalized into applications with multiple species of particles in various natural and engineering mixtures.
Small-volume concentrated pyroclastic currents (CPCs) are often responsible for unpredicted and deadly overspills from channel confines when they encounter an abrupt change in propagation direction. We present the first results obtained with a new experimental facility, PyroCLAST, built to investigate the mechanisms of such overspills. The apparatus consists of a 5-m-long flume with a 45° valley bend at mid-distance from the source, and whose slope angle varies from 3 to 15°. Glass beads of 45–90-µm diameter are initially fluidized in a reservoir and rapidly released into the flume through a vertical sliding gate. Experiments are recorded using video cameras to measure the temporal evolution of both the parent channelized and overbank flow velocity and discharge rate, using particle image velocimetry. Overspills are generated when the flows interact with the bend, at slope angles of 9 to 15°, generating a front splash and an overbank flow. Results demonstrate that the slope angle favors the formation of overspill by increasing the flow discharge rate, causing a local increase of the flow thickness along the bend (i.e., superelevation) that overtops the channel sidewall. Moreover, under constant initial conditions, a high channel slope angle and discharge rate favor the development of discrete, internal flow pulses, and a positive correlation is found between the runout of the channelized flows and that of overbank deposits. Data collected in this study will also constitute a reference dataset for future benchmarking of CPC numerical models.
Gustavo Rodríguez Liñán
Beam Scotch