14 research outputs found

    Confined flow of suspensions modeled by a frictional rheology

    Full text link
    We investigate in detail the problem of confined pressure-driven laminar flow of neutrally buoyant non-Brownian suspensions using a frictional rheology based on the recent proposal of Boyer et al., 2011. The friction coefficient and solid volume fraction are taken as functions of the dimensionless viscous number I defined as the ratio between the fluid shear stress and the particle normal stress. We clarify the contributions of the contact and hydrodynamic interactions on the evolution of the friction coefficient between the dilute and dense regimes reducing the phenomenological constitutive description to three physical parameters. We also propose an extension of this constitutive law from the flowing regime to the fully jammed state. We obtain an analytical solution of the fully-developed flow in channel and pipe for the frictional suspension rheology. The result can be transposed to dry granular flow upon appropriate redefinition of the dimensionless number I. The predictions are in excellent agreement with available experimental results, when using the values of the constitutive parameters obtained independently from stress-controlled rheological measurements. In particular, the frictional rheology correctly predicts the transition from Poiseuille to plug flow and the associated particles migration with the increase of the entrance solid volume fraction. We numerically solve for the axial development of the flow from the inlet of the channel/pipe toward the fully-developed state. The available experimental data are in good agreement with our predictions. The solution of the axial development of the flow provides a quantitative estimation of the entrance length effect in pipe for suspensions. A analytical expression for development length is shown to encapsulate the numerical solution in the entire range of flow conditions from dilute to dense.Comment: Submitted to J. Fluid Mech. on Dec. 24, 2013, Revised version July 10, 2014, Accepted for publication Sept. 19, 201

    Fault-size dependent fracture energy explains multi-scale seismicity and cascading earthquakes

    Full text link
    Earthquakes vary in size over many orders of magnitude, yet the scaling of the earthquake energy budget remains enigmatic. We propose that fundamentally different "small-slip" and "large-slip" fracture processes govern earthquakes. We combine seismological observations with a physics-based mechanical earthquake model under flash-heating friction. We find that dynamic weakening and restrengthening effects are non-negligible in the energy budget of small earthquakes and establish a simple linear scaling relationship between small-slip fracture energy and fault size. We use supercomputing to apply this scaling and unveil volumetric "Mode-4" earthquake cascades involving >700>700 multi-scale fractures within a fault damage zone, capable of dynamically triggering large earthquakes. Our findings provide an intuitive explanation of seismicity across all scales with important implications for comprehending earthquake nucleation and multi-fault rupture cascades.Comment: 41 pages, 10 figure

    Pressure-Driven Suspension Flow near Jamming

    No full text
    We report here magnetic resonance imaging measurements performed on suspensions with a bulk solid volume fraction (φ0) up to 0.55 flowing in a pipe. We visualize and quantify spatial distributions of φ and velocity across the pipe at different axial positions. For dense suspensions (φ0>0.5), we found a different behavior compared to the known cases of lower φ0. Our experimental results demonstrate compaction within the jammed region (characterized by a zero macroscopic shear rate) from the jamming limit φm≈0.58 at its outer boundary to the random close packing limit φrcp≈0.64 at the center. Additionally, we show that φ and velocity profiles can be fairly well captured by a frictional rheology accounting for both further compaction of jammed regions as well as normal stress differences. © 2015 American Physical Society
    corecore