Gravitational instabilities in binary granular materials

P., McLaren, Christopher; Kovar, Thomas; Penn, Alexander; Müller, Christoph R.; Boyce, Christopher M.

doi:10.1073/pnas.1820820116

Cited by 26 publications

(40 citation statements)

References 40 publications

(40 reference statements)

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“…The grain‐grain skeleton is augmented by an EPS skeleton with grains embedded in an EPS matrix (Figure 3g). A Rayleigh‐Taylor instability may also arise, where an upward drag force can increase locally due to a buoyancy effect, which causes channeling of EPS (lighter fluid) to push through denser sands (McLaren et al., 2019). Previous studies have shown the formation of volcano‐like “water escape structures” (McLaren et al., 2019; Nichols et al., 1994), in which the upwelling pore EPS fluid can be squeezed out from the bottom sand structure, along with gas bubbles (Figure ), creating a “vacuum effect” for the pore water, which explains the occurrence of negative pore pressure (Figure 2a).…”

Section: Resultsmentioning

confidence: 99%

Biological Cohesion as the Architect of Bed Movement Under Wave Action

Chen

Zhang

Townend

et al. 2021

Geophysical Research Letters

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Cohesive extracellular polymeric substances (EPS) generated by microorganisms abundant on Earth are regarded as bed “stabilizers” increasing the erosion threshold in sedimentary systems. However, most observations of this phenomenon have been taken under steady flow conditions. In contrast, we present how EPS affect the bed movement under wave action, showing a destabilization of the system. We demonstrate a complex behavior of the biosedimentary deposits, which encompasses liquefaction, mass motion, varying bed formations and erosion, depending on the amount of EPS present. Small quantities of EPS induce higher mobility of the sediments, liquefying an otherwise stable bed. Bed with larger quantities of EPS undergoes a synchronized mechanical oscillation. Our analysis clarifies how biological cohesion can potentially put coastal wetlands at risk by increasing their vulnerability to waves. These findings lead to a revised understanding of the different roles played by microbial life, and their importance as mediators of seabed mobility.

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Section: Resultsmentioning

confidence: 99%

Biological Cohesion as the Architect of Bed Movement Under Wave Action

Chen

Zhang

Townend

et al. 2021

Geophysical Research Letters

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“…Segregation is commonly observed in granular materials that contain a mixture of particles that differ in size [1][2][3][4], density [5,6], shape [7] or mechanical properties (friction, elasticity) [8,9]. A fundamental understanding of the physics behind segregation in granular materials is not only a scientific curiosity [10][11][12], but also of high relevance for practice. In practical applications such as the mixing of pharmaceutical ingredients [13], the filling (and discharge) of hoppers [14]or the transport of granular media through agitation (e.g.…”

Section: Introductionmentioning

confidence: 99%

Accurate buoyancy and drag force models to predict particle segregation in vibrofluidized beds

2021

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The segregation of large intruders in an agitated granular system is of high practical relevance, yet the accurate modelling of the segregation (lift) force is challenging as a general formulation of a granular equivalent of a buoyancy force remains elusive. Here, we critically assess the validity of a granular buoyancy model using a generalization of the Archimedean formulation that has been proposed very recently for chute flows. The first model system studied is a convection-free vibrated system, allowing us to calculate the buoyancy force through three different approaches, i.e. a generalization of the Archimedean formulation, the spring force of a virtual spring and through the granular pressure field. The buoyancy force obtained through these three approaches agree very well, providing strong evidence for the validity of the generalization of the Archimedean formulation of the buoyancy force which only requires an expression for the solid fraction of the intruder, hence allowing for a computationally less demanding calculation of the buoyancy force as coarse-graining is avoided. In a second step, convection is introduced as a further complication to the granular system. In such a system, the lift force is composed of granular buoyancy and a drag force. Using a drag model for the slow velocity regime, the lift force, directly measured through a virtual spring, can be predicted accurately by adding a granular drag force to the generalization of the Archimedean formulation of the granular buoyancy. The developed lift force model allowed us to rationalize the dependence of the lift force on the density of the bed particles and the intruder diameter, and the independence of the lift force on the the intruder diameter, and the independence of the lift force on the intruder density and the vibration strength (once a critical value is exceeded).

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“…Low viscosity suspensions replace high concentration, and high viscosity suspensions and are unstable because of the instability mechanism [4]. The instability in interactions between fluids can develop in several forms [5]. The granular movement process is started with internal fluidization.…”

Section: Introductionmentioning

confidence: 99%

An investigation of granular material movement due to instability post impinging upward fluid

Yudiyanto

Wardana

Widhiyanuriyawan

et al. 2020

EEJET

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Granular is a form of material that is widely used in the industry. To move the granular material, energy is needed to form a flow of granular. Granular instability can be utilized to move granular material. Prevention of jamming and clogging is done by breaking down the parts of the granular, which are locking. Impinging fluid in the granular is used to create granular instability. An observation was made using the experimental method. The granular in the Hele-Shaw cell is shot with fluid in the granular body and results in instability motion. Fluid impinging breaks granular bonds and forms fluid cavities. Furthermore, the fluid cavity moves upward due to unstable conditions. Granular with a strong bond is loose in the form of the agglomerate. Agglomerate is destroyed in the process of moving because there is a drag force. Granular with weak bonds tries to maintain individually form fingering. Granular moves down in the settling process to find a stable position. Instability is affected by the bonds between the grains. A comparison between the cohesion force and the mass weight of the particles is expressed as a granular Bond number B og. In glass sand material, strong granular bonds occur at granular sizes below 100 µm. Granular bonds affect the movement of instability in groups. The value of the granular Bond number is greater than 1. At sizes of 100 to 230 µm, the granular bond still affects the granular instability with the fingering pattern in the granular motion. The value of the granular Bond number is close to 1. Granular sizes above 230 µm indicate the presence of non-dominant bonds between the grains. The individual granular mass is higher than the cohesion force that occurs at the interface between the granular, and the granular Bond number value is less than 1

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Gravitational instabilities in binary granular materials

Cited by 26 publications

References 40 publications

Biological Cohesion as the Architect of Bed Movement Under Wave Action

Biological Cohesion as the Architect of Bed Movement Under Wave Action

Accurate buoyancy and drag force models to predict particle segregation in vibrofluidized beds

An investigation of granular material movement due to instability post impinging upward fluid

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