Improved visco-plastic models in the flow of granular materials

Theoretical models are presented to represent the flow of granular material s stored in sibs and hoppers by means of fluid flow formulation The present ation follows previous work by Diet and Godoy (1992) using viscoplasticity, and refinement are introduced to improve the convergence of the solution a nd satisfaction of the constitutive equations. First, a model with constrai nts is developed in which the apparent viscosity has upper and lower bounda ries to account for rigid behavior. A second model uses viscoplasticity wit h modified function of discontinuity and a weighting factor on selective te rms of the apparent viscosity. The first model improve convergence but lead s to unsatisfactory values compared with experimental results. The second m odel controls convergence by the weighting factor and shows good agreement with experiments.