Coupled distinct element method computational fluid dynamics analyses for reservoir landslide modelling

The Vajont landslide involved a large mass of rock splashing at high speed into the reservoir which in turn generated a highimpulse water that overtopped the dam and swept away the downstream village. In several cases of reservoir landslide, albeit the flood defence structures may remain intact, a catastrophe still occur due to the generation of a ‚tsunami‘ wave. Since the features of the tsunami wave strongly depend on the physics of the rock splashing and the subsequent rock –water interaction, a numerical tool accounting for such physics is required for predictions to be reliable. Here, the formulation of a coupled 3D Distinct Element Method (DEM) – Computational Fluid Dynamics (CFD) code used to simulate the rock slide from onset to impact with the reservoir and the subsequent generation of the impulse wave, is presented. To run realistic simulations in an affordable runtime, coarse graining is employed. The main results of quasi 3D analyses in plane strain along two cross-sections representative of the eastern and western slope sectors are presented. The results show to be in broad agreement with the available recorded observations

Influence of Inter-Particle Friction and Damping on the Dynamics of Spherical Projectile Impacting Onto a Soil Bed

This study investigates the dynamics of a spherical projectile impact onto a granular bed via numerical simulations by discrete element method (DEM). The granular bed is modeled as an assembly of polydisperse spherical particles and the projectile is represented by a rigid sphere. The DEM model is used to investigate the cratering process, including the dynamics of the projectile and energy transformation and dissipation. The cratering process is illustrated by tracking the motion of the projectile and granular particles in the bed. The numerical results show that the dynamics of the projectile follows the generalized Poncelet law that the final penetration depth is a power-law function of the falling height. The numerical results can match well the experimental data reported in the literature, demonstrating the reliability of the DEM model in analyzing the impact of a spherical projectile on a granular bed. Further analyses illustrate that the impact process consists of three main stages, namely the impact, penetration and collapse, as characterized by the evolution of projective velocity, strong force chains and crater shape. The initial kinetic and potential energy of the projectile is dissipated mainly by inter-particle friction which governs the projectile dynamics. The stopping time of projectile decreases as the initial impact velocity increases. The final penetration depth scales as one-third the power of total falling height and is inversely proportional to the macroscopic granular friction coefficient.National Natural Science Foundation of China (No. 42107155), the Royal Society, Sino-British Fellowship Trust International Exchanges Award (No. IES\R2\202023), the Fundamental Research Funds for the Central Universities (No. 2682021CX061), the National Key R&D Program of China (No. 2017YFC1502500

On the dynamic fragmentation and lubrication of coseismic landslides

The three-dimensional discrete element method (DEM) has been employed to analyze the dynamic fragmentation and lubrication mechanisms of coseismic Tangjiashan landslide induced by the 2008 Ms 8.0 Wenchuan earthquake. The numerical results show that the internal rock damage occurs and propagates gradually along the basal failure plane due to seismic shaking. At peak ground displacement, a sudden increase of tensile and shear stresses can lead to the complete breakage of basal bonds. This is associated with a sudden relief of overburden stress and rapid decrease of basal stress ratio. Thus, the slope fails as a whole and moves quickly downslope. In this process, several large transversal cracks develop at the middle and upper rear regions, disintegrating the slope into several large blocks. During landslide propagation, the thickness of basal fragmented layer increases progressively due to intense shearing, and the basal stress ratio reduces accordingly from 0.68 to 0.28. The reduction of landslide basal stress ratio occurs when the strong basal resistance is overcome by seismic and gravity induced shear forces together with intense particle rearrangements. It can be quantified by vibrational and rotational granular temperatures of the basal shear layer, with the peak values of 35.2 m2 /s2 and 11.6 m2 /s2, respectively. The widespread internal slope fragmentation and subsequent lubrication have been identified as the key mechanisms governing landslide motion, which appear to be the intrinsic features of landslide irrespective of its triggering mechanism. The earthquake shaking is more relevant to the detachment than to the spreading of landslide mass.National Natural Science Foundation of China, Fundamental Research Funds for the Central Universities and RockHoriZon advanced tools for rockfall hazard and risk zonation at the regional scal

Dynamic Fragmentation of Jointed Rock Blocks During Rockslide-Avalanches: Insights From Discrete Element Analyses

The dynamic fragmentation of jointed rock blocks during rockslide avalanches has been investigated by discrete element method simulations for a multiple arrangement of a rock block sliding over a simple slope geometry. The rock blocks are released along an inclined sliding plane and subsequently collide onto a flat horizontal plane at a sharp kink point. The contact force chains generated by the impact appear initially at the bottom frontal corner of the rock block and then propagate radially upward to the top rear part of the block. The jointed rock blocks exhibit evident contact force concentration and discontinuity of force wave propagation near the joint, associating with high energy dissipation of granular dynamics. The corresponding force wave propagation velocity can be less than 200 m/s, which is much smaller than that of an intact rock (1,316 m/s). The concentration of contact forces at the bottom leads to high rock fragmentation intensity and momentum boosts, facilitating the spreading of many fine fragments to the distal ends. However, the upper rock block exhibits very low rock fragmentation intensity but high energy dissipation due to intensive friction and damping, resulting in the deposition of large fragments near the slope toe. The size and shape of large fragments are closely related to the orientation and distribution of the block joints. The cumulative fragment size distribution can be well fitted by the Weibull’s distribution function, with very gentle and steep curvatures at the fine and coarse size ranges, respectively. The numerical results of fragment size distribution can match well some experimental and field observations

Spin-Imbalance in a One-Dimensional Fermi Gas

Superconductivity and magnetism generally do not coexist. Changing the relative number of up and down spin electrons disrupts the basic mechanism of superconductivity, where atoms of opposite momentum and spin form Cooper pairs. Nearly forty years ago Fulde and Ferrell and Larkin and Ovchinnikov proposed an exotic pairing mechanism (FFLO) where magnetism is accommodated by formation of pairs with finite momentum. Despite intense theoretical and experimental efforts, however, polarized superconductivity remains largely elusive. Here we report experimental measurements of density profiles of a two spin mixture of ultracold 6Li atoms trapped in an array of one dimensional (1D) tubes, a system analogous to electrons in 1D wires. At finite spin imbalance, the system phase separates with an inverted phase profile in comparison to the three-dimensional case. In 1D we find a partially polarized core surrounded by wings composed of either a completely paired BCS superfluid or a fully polarized Fermi gas, depending on the degree of polarization. Our observations are in quantitative agreement with theoretical calculations in which the partially polarized phase is found to be a 1D analogue of the FFLO state. This study demonstrates how ultracold atomic gases in 1D may be used to create non-trivial new phases of matter, and also paves the way for direct observation and further study of the FFLO phase.Comment: 30 pages, 7 figure

Investigation of rock fragmentation during rockfalls and rock avalanches via 3-D discrete element analyses

This paper investigates the characteristics of dynamic rock fragmentation and its influence on the postfailure fragment trajectory. A series of numerical simulations by discrete element method (DEM) were performed for a simple rock block and slope geometry, where a particle agglomerate of prismatic shape is released along a sliding plane and subsequently collides onto a flat horizontal plane at a sharp kink point. The rock block is modeled as an assembly of bonded spherical particles with fragmentation arising from bond breakages. Bond strength and stiffness were calibrated against available experimental data. We analyzed how dynamic fragmentation occurs at impact, together with the generated fragment size distributions and consequently their runout for different slope topographies. It emerges that after impact, the vertical momentum of the granular system decreases sharply to nil, while the horizontal momentum increases suddenly and then decreases. The sudden boost of horizontal momentum can effectively facilitate the transport of fragments along the bottom floor. The rock fragmentation intensity is associated with the input energy and increases quickly with the slope angle. Gentle slopes normally lead to long spreading distance and large fragments, while steep slopes lead to high momentum boosts and impact forces, with efficient rock fragmentation and fine deposits. The fragment size decreases, while the fracture stress and fragment number both increase with the impact loading strain rate, supporting the experimental observations. The fragment size distributions can be well fitted by the Weibull's distribution function.Wile

Discrete Element Analyses of a Realistic-shaped Rock Block Impacting Against a Soil Buffering Layer

The final authenticated version is available online at https://doi.org/10.1007/s00603-020-02116-0National Natural Science Foundation of China (grant 51779164, 41602289 and 41877260), the open funding of the State Key Laboratory of Hydraulics and Mountain River Engineering (Sichuan University) (No. Skhl1808) and the @RockHoriZon advanced tools for rockfall hazard and risk zonation at the regional scale (Grant 2016–0756), Fondazione CARIPLO

Fabrication and characterization of novel multilayered structures by stereocomplexion of poly(D-lactic acid)/poly(L-lactic acid) and self-assembly of polyelectrolytes

The enantiomers poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) were alternately adsorbed directly on calcium carbonate (CaCO3) templates and on poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) multilayer precursors in order to fabricate a novel layer-by-layer (LBL) assembly. A single layer of poly(L-lysine) (PLL) was used as a linker between the (PDLA/PLLA)n stereocomplex and the cores with and without the polymeric (PSS/PAH)n/PLL multilayer precursor (PEM). Nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) were used to characterize the chemical composition and molecular weight of poly(lactic acid) polymers. Both multilayer structures, with and without polymeric precursor, were firstly fabricated and characterized on planar supports. A quartz crystal microbalance (QCM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and ellipsometry were used to evaluate the thickness and mass of the multilayers. Then, hollow, spherical microcapsules were obtained by the removal of the CaCO3 sacrificial template. The chemical composition of the obtained microcapsules was confirmed by differential scanning calorimetry (DSC) and wide X-ray diffraction (WXRD) analyses. The microcapsule morphology was evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The experimental results confirm the successful fabrication of this innovative system, and its full biocompatibility makes it worthy of further characterization as a promising drug carrier for sustained release

Slope erosion induced by surges of debris flow: insights from field experiments

Data availability: All data generated during the study are available from the corre- sponding author by request.Copyright © The Author(s) 2022. We conducted field observations and experiments to explore debris flow dynamics, sediment transportation and slope erosion at an active natural debris flow gully in the headwaters of Jiangjia Ravine (Dongchuan region, Southwest China). In this region, the hillslopes were heavily jointed, weathered and sparsely vegetated, providing continuous and rich sediment supplies for initiating debris flows. The debris flow propagated in the channel as a sequence of surges, with periodical changes of flow flux, velocity, water content, and viscosity as controlled mainly by the conditions of erodible sediments and water supplies from the upstream. The water content of bank sediments ranged from 5 to 8%, while it was 16 to 26% for debris surges in the channel. The particle size distribution of sediments on the alluvial fan followed the Weibull’s cumulative distribution and the mean size was in the range of 2 ~ 4 mm. The coarse particles were primarily elongated or prismoidal and aspect ratios followed well a normal distribution with the mean value of 0.4. The angular particles entrained in dense viscous debris flow surges could effectively abrade and groove the channel bed and banks, increasing the intensity of slope erosion. The incised slope had a sequence of terraced depositional layers on both banks. The layer thickness decreased as the erosion depth moved deeper into the stratum where hard bed soil/rock layers existed. The water-soil mixture of debris flow exhibited a clear shear-thinning behavior with its viscosity decreasing gradually with the increase of shear rate following the widely accepted power-law model. The dense viscous debris flow can facilitate the transportation of coarse gravels in channel and contribute to slope erosion.Royal Society, Sino-British Fellow- ship Trust International Exchanges Award (No. IES\R2\202023); open funding of the State Key Laboratory of Geomechanics and Geotechnical Engineering (No. Z019004)