Jouni Ritvanen

Intermittency of energy in rapid granular shear flows

Hard-disk simulations are used for two-dimensional rapid granular shear flows of circular disks between two rotating cylinders. The intermittency effects associated with the rate of the energy dissipation of collisions are studied. The statistics of intermittent signals of energy dissipation reveals that a power law governs the dynamics of rapid shear granular flows. A dynamical system approach based on the Gledzer-Ohkitani-Yamada shell model of turbulence is employed to reproduce signals for energy dissipation that are statistically consistent with those from simulations. The results suggest that rapid granular flows can be analyzed by appropriate turbulent models.

Analysis and tuning of a CFB model using particle filtering

Abstract Analysis and tuning of a circulating fluidized bed (CFB) hot-loop model are considered. Selected model outputs are fitted to measured data by allowing a set of constant-valued parameters to be considered as time-varying. These include the reaction rate, several heat transfer coefficients, and fuel moisture. Estimates of parameter distributions are created using particle filters (PF). PF provide a Bayesian approach utilizing both the system model and measured data. An illustrative example is given using data and model for a full scale plant.

Experimental and Numerical Investigation of Annular Granular Shear Flows

Shear flows of granular materials represent unique type of flow and deformation in complex systems. When a pack of granular material is subject to shearing the strain field is non‐uniform. A shear‐zone is developed in the vicinity of the shearing wall in which grains are rapidly flowing. However, the regime of deformation varies exponentially with the distance from the shearing wall. In other words, sheared granular materials display both fluid‐ and solid‐like behaviors across the sheared gap.