Assessment of implicit and explicit algorithms in numerical simulation of granular matter

The objectives of this dissertation are to investigate and demonstrate the potentials of implicit integration methods in predicting the dynamics of granular media and to describe the granular dynamics on forward and backward acting grates by discrete element method.
Traditionally, explicit integration methods are employed within the context of Discrete Element Method. Generally, explicit equations are simpler to solve than the implicit ones but they require a small time step to be utilized. In this study, an implicit Numerov integration scheme is employed to integrate the equations of motion. The implicit method is verified in different test cases starting from simple cases to more complicated cases including hundreds of particles. Comparing the results with the results of the explicit method, it is shown that the implicit method exhibits a distinguished advantage only at very large time steps. Taking into account the overhead of solving non-linear equations at each time step, it is concluded that implicit methods are computationally too expensive for their limited gains.
Addressing the second objective of this study, the residence time distribution of granular particles on forward and backward acting grates are numerically predicted. Very good agreement between the predictions and the available experimental results is achieved. It can be concluded that the Discrete Element Method is highly capable of predicting the dynamics of solid fuel particles on grate systems. Future work shall include coupling of the method with computational fluid dynamics in order to account for thermal conversion of the fuel particles.