Multiscale modeling of rapid granular flow with a hybrid discrete-continuum method

Both discrete and continuum models have been widely used to study rapid granular flow, discrete model is accurate but computationally expensive, whereas continuum model is computationally efficient but its accuracy is doubtful in many situations. Here we propose a hybrid discrete-continuum method to profit from the merits but discard the drawbacks of both discrete and continuum models. Continuum model is used in the regions where it is valid and discrete model is used in the regions where continuum description fails, they are coupled via dynamical exchange of parameters in the overlap regions. Simulation of granular channel flow demonstrates that the proposed hybrid discrete-continuum method is nearly as accurate as discrete model, with much less computational cost

A comparative assessment and unification of bond models in DEM simulations

Bonded contact models have been increasingly used in the discrete element method (DEM) to study cemented and sintered particulate materials in recent years. Several popular DEM bond models have been proposed in the literature; thus it is beneficial to assess the similarities and differences between the different bond models before they are used in simulations. This paper identifies and discusses two fundamental types of bond models: the Spring Bond Model where two bonded particles are joined by a set of uniform elastic springs on the bond’s cross-section, and the Beam Bond Model in which a beam is used to connect the centres of two particles. A series of cantilever beam bending simulation cases were carried out to verify the findings and assess the strength and weakness of the bond models. Despite the numerous bond models described in the literature, they can all be considered as a variation of these two fundamental model types. The comparative evaluation in this paper also shows that all the bond models investigated can be unified to a general form given at a predefined contact point location

On the scaling law of JKR contact model for coarse-grained cohesive particles

The computational cost of using discrete element method (DEM) simulations for particulate processes with fine and cohesive particles is enormously large. To overcome this limitation, various coarse-grain DEM models have been developed which use a smaller number of larger sized particles. Although the computational cost is significantly reduced, the accuracy of the simulations depends on the underlying scaling law. We propose a scaling of the Johnson-Kendall-Roberts (JKR) contact model for adhesive viscoelastic particles. A scaling law using a single Bond number or Cohesion number criterion is insufficient to keep the motion of the coarse-grained particles the same as the original particles. The scaling law in this work is developed based on mass, momentum and energy conservation, which achieves good consistency between the kinematic characteristics of the coarse-grained and original particles. The simulated effective coefficients of restitution were compared for a range of particle-wall impact velocities and validated against experimental data.EPSR

Oblique impact breakage unification of nonspherical particles using discrete element method

Particle breakage commonly occurs during processing of particulate materials, but a mechanistic model of particle impact breakage is not fully established. This article presents oblique impact breakage characteristics of nonspherical particles using discrete element method (DEM) simulations. Three different particle shapes, i.e. spherical, cuboidal and cylindrical, are investigated. Constituent spheres are agglomerated with bridging bonds to model the breakage characteristics under impact conditions. The effect of agglomerate shapes on the breakage pattern, damage ratio, and fragment size distribution is fully investigated. By using a newly proposed oblique impact model, unified breakage master surfaces are theoretically constructed for all the particle shapes under oblique impact conditions. The developed approach can be applied to modelling particulate processes where nonspherical particles and oblique impact breakage are prevailing.</p

Multiscale digital twin for particle breakage in milling: From nanoindentation to population balance model

A multiscale modelling approach to integrate resultful information of particle breakage at distinct scales is presented for quantitative prediction of a milling process. The nanoindentation test of zeolite particles is carried out to provide the deterministic value of mechanical properties, prior to which the Hertz based contact theory is described. The impact pin milling test is made to measure the particle size distribution subject to three rotary speeds. The population balance model composed of selection function and breakage function is developed to predict the varying milling operations based on successful model validation. With the hybrid of theoretical, experimental and numerical avenues, a conceptual multiscale modelling roadmap with complementary strength is proposed. The best available information spanning distinct scales is scoped where the interaction of physical twin and digital twin is highlighted. Global system analysis of the key parameters provides projected confidence in milling performance beyond the existing experimental space

A dumbbell probe-mediated rolling circle amplification strategy for highly sensitive microRNA detection

We herein report the design of a dumbbell-shaped DNA probe that integrates target-binding, amplification and signaling within one multifunctional design. The dumbbell probe can initiate rolling circle amplification (D-RCA) in the presence of specific microRNA (miRNA) targets. This D-RCA-based miRNA strategy allows quantification of miRNA with very low quantity of RNA samples. The femtomolar sensitivity of D-RCA compares favorably with other existing technologies. More significantly, the dynamic range of D-RCA is extremely large, covering eight orders of magnitude. We also demonstrate miRNA quantification with this highly sensitive and inexpensive D-RCA strategy in clinical samples

IGFBPL1 Regulates Axon Growth through IGF-1-mediated Signaling Cascades

Activation of axonal growth program is a critical step in successful optic nerve regeneration following injury. Yet the molecular mechanisms that orchestrate this developmental transition are not fully understood. Here we identified a novel regulator, insulin-like growth factor binding protein-like 1 (IGFBPL1), for the growth of retinal ganglion cell (RGC) axons. Expression of IGFBPL1 correlates with RGC axon growth in development, and acute knockdown of IGFBPL1 with shRNA or IGFBPL1 knockout in vivo impaired RGC axon growth. In contrast, administration of IGFBPL1 promoted axon growth. Moreover, IGFBPL1 bound to insulin-like growth factor 1 (IGF-1) and subsequently induced calcium signaling and mammalian target of rapamycin (mTOR) phosphorylation to stimulate axon elongation. Blockage of IGF-1 signaling abolished IGFBPL1-mediated axon growth, and vice versa, IGF-1 required the presence of IGFBPL1 to promote RGC axon growth. These data reveal a novel element in the control of RGC axon growth and suggest an unknown signaling loop in the regulation of the pleiotropic functions of IGF-1. They suggest new therapeutic target for promoting optic nerve and axon regeneration and repair of the central nervous system

Hybrid discrete-continuum model for granular flow

AbstractWe present a hybrid discrete-continuum model for multi-scale simulation of granular flow. In this method, the domain is decomposed into a discrete sub-domain, where individual particles are tracked using discrete element method, and a continuum sub-domain is solved using the Navier-Stokes equation combined with kinetic theory of granular flow. The spatial coupling between continuum method and discrete method is achieved through an overlap region, in which both methods’ variables are shared with each other. The feasibility of the hybrid discrete-continuum model is demonstrated through the simulation of a velocity-driven granular Poiseuille flow with mono-disperse, smooth (frictionless) particles