The couple stress of a three-dimensional vertical granular flow is investigated by means of a combined approach of discrete element method and averaging method. The velocity, mass density and couple stress are quantif...
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The couple stress of a three-dimensional vertical granular flow is investigated by means of a combined approach of discrete element method and averaging method. The velocity, mass density and couple stress are quantified under various flow conditions. The velocity and mass density profiles are illustrated to be consistent with those obtained by the previous experiments and numerical simulations, confirming the validity of the proposed approach. The couple stress profiles are shown to be significantly affected by the wall supporting the vertical flow, and be contributed by the rolling resistance due to the asymmetrical normal traction distributions in the contact areas between particles and between particle and wall. For mono-sized particles, the couple stress far from the wall can be ignored although it may vary slightly causing the fluctuation of flow behavior;however, the couple stress in the region close to a wall must be taken into account to properly describe the flow behavior of particles. For multi-sized particle, the couple stress is mainly contributed by the sliding resistance and to a less degree by the rolling resistance;the transport of particle plays a limited role. Implication of the present numerical results to continuum modeling is also discussed. (C) 2003 Elsevier Science B.V. All rights reserved.
The flow of granular nickel particles moving down a vertical pipe from a hopper in the presence of a local, horizontal ac electric field is studied. It is found that the flow can be retarded by the electric field, and...
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The flow of granular nickel particles moving down a vertical pipe from a hopper in the presence of a local, horizontal ac electric field is studied. It is found that the flow can be retarded by the electric field, and the retardation depends upon the initial conditions of the flow. If the flow is dilute when passing through the field, there exists a critical voltageV(1), the flow transition from dilute to dense occurs and flow rate is retarded when V is greater than V-1. For V < V-1, the steady-state flow rate is practically unaffected. The flow rate decreases abruptly at V-1. particle aggregations near the top end of the electrodes are observed. A two-dimensional moleculardynamics (MD) simulation is performed. It confirms the aggregation and intermittence of the flow, and the abrupt change in flow rate at the dilute-dense transition. The MD simulation results agree qualitatively well with the experimental observations. (C) 2003 Elsevier B.V. All rights reserved.
The method of dissipative particledynamics (DPD) was introduced by Hoogerbrugge and Koelman (Europhys. Lett., 19 ( 1992) 155) to study meso-scale material processes. The theoretical investigation of the DPD method wa...
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The method of dissipative particledynamics (DPD) was introduced by Hoogerbrugge and Koelman (Europhys. Lett., 19 ( 1992) 155) to study meso-scale material processes. The theoretical investigation of the DPD method was initiated by Espanol (Phys. Rev. E, 52 ( 1995) 1734) who used a Fokker-Planck formulation of the DPD method and applied the Mori-Zwanzig projection operator calculus to obtain the equations of hydrodynamics for DPD. A current limitation of DPD is that it requires a clear separation of scales between the resolved and unresolved processes. In this letter, we suggest a simple extension of DPD that allows for inclusion of unresolved stochastic processes with exponentially decaying variance for any value of the decay rate, and give an application of this algorithm to the simulation of the shallow-water equations using the Hamiltonian particle-mesh method. The proposed extension is as easy to implement as the standard DPD methods.
The dynamics of polymer collapse with a fixed distance between endpoints is studied analytically and numerically by the Nose-Hoover algorithm. We find that at the pearling stage of the collapse the number of pearls de...
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The dynamics of polymer collapse with a fixed distance between endpoints is studied analytically and numerically by the Nose-Hoover algorithm. We find that at the pearling stage of the collapse the number of pearls decays as t(-1/2) leading to anomalously long collapse time. To understand the effect of Stokes drag we reduced the problem of long-polymer-chain collapse to the one-dimensional diffusion-limited coalescence of particles with the mass-dependent mobility. In this case the number of pearls decays slower, as t(-3/7).
We present a new multi-chain Brownian dynamicssimulation of a polymeric network containing both crosslinks and slip-links (entanglements). We coarse-grain at the level of chain segments connecting consecutive nodes (...
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We present a new multi-chain Brownian dynamicssimulation of a polymeric network containing both crosslinks and slip-links (entanglements). We coarse-grain at the level of chain segments connecting consecutive nodes (cross- or slip-links). A ne displacement of nodes is not imposed;rather, their displacement as well as sliding of monomers through slip-links is governed by force balances. The stress-strain response in uniaxial extension is compared with the slip-link theories of Ball et al. (Polymer, 22 (1981) 1010) and Edwards and Vilgis (Polymer, 27 (1986) 483), and with the molecular-dynamicssimulations of Grest et al. (J. Non-Cryst. Solids, 274 (2000) 139). Qualitative agreement both with the Mooney-Rivlin expression and with the stress upturn at large strains confirms the role of entanglements in explaining departure from the classical theory of phantom chain networks. However, quantitative agreement with data is satisfactory at low strains only, and the observed discrepancy at larger strains suggests possible refinements of the model. Additivity of free energy contributions of crosslinks and entanglements used in several molecular theories of rubber elasticity is confirmed by the simulation results.
We present a scaling theory describing the collapse of a homopolymer chain in poor solvent. At time t after the beginning of the collapse, the original Gaussian chain of length N is streamlined to form N/g segments of...
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We present a scaling theory describing the collapse of a homopolymer chain in poor solvent. At time t after the beginning of the collapse, the original Gaussian chain of length N is streamlined to form N/g segments of length R (t), each containing g similar to t monomers. These segments are statistical quantities representing cylinders of length Rsimilar tot(1/2) and diameter d similar to t(1/4), but structured out of stretched arrays of spherical globules. This prescription incorporates the capillary instability. We compare the time-dependent structure factor derived for our theory with that obtained from ultra-large-scale molecular-dynamicssimulation with explicit solvent. This is the first time such a detailed comparison of theoretical and simulation predictions of collapsing chain structure has been attempted. The favorable agreement between the theoretical and computed structure factors supports the picture of the coarse-graining process during polymer collapse.
We report and analyze the results of numerical studies of dense granular flows on an incline with a rough bottom in two and three dimensions, using linear damped spring or Hertzian force laws between particles with a ...
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We report and analyze the results of numerical studies of dense granular flows on an incline with a rough bottom in two and three dimensions, using linear damped spring or Hertzian force laws between particles with a Coulomb failure criterion. This ow geometry produces a constant density pro le that satis es scaling relations of the Bagnold, rather than viscous, kind. The type of force law has little impact on the behavior of the system. The bulk and the surface layer di er in their rheology, as evidenced by the change in principal stress directions near the surface. Surface-only flows are not observed for the cases studied.
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