Simulation of mixed discrete and continuous systems: An iron ore terminal example

Modeling industrial systems involving discrete and continuous processes is a challenge for practitioners. A simulation approach to handle these situations is based on flow rate discretization (instead of mass discretization): the discrete simulation unfolds as a series of steady-state flows calculation updated when a state variable changes or a random event occurs. Underlying mass balancing problem can be solved with the linear programming simplex algorithm. This paper presents a novel technique based on maximizing flow through a network where nodes are black-box model units. This network-based method is less sensitive to problem size; the computation effort required to solve the mass balance is proportional to O(m+n) instead of O(mn) with linear programming. The approach was implemented in Flexsim^TM software and used to simulate an iron ore port terminal. Processes included in the model were: mine-to-port trains handling, port terminal equipment (processing rate, capacity, operating logic, failures) and ship loading.