A generalized model for simulating commodity movements by ship

The paper describes the logic structure and techniques used in a Simscript program for simulating the movement of ships through a network of locks, reaches, lakes, and ports. The program also provides for endogenous route selection between “micro-route” alternatives, i.e., parallel locks or canals, and for the endogenous scheduling of ship movements, given port-to-port commodity movement demand and fleet mix. The model is basically a general network simulation tool based on the concept of a “route map” which describes the sequence of facilities to be traversed between given points in the network. The cardinal mechanism in the model is a Movement Control Module which monitors the route map of each ship during its voyage and sends the vessel to generalized satellite modules where the performance of locks, reaches, lakes, and ports are simulated. Attributes carried by the ship initialize the generalized modules to simulate a specific lock, reach, lake, or port as dictated by the ship's position along its route map. The model is being used to simulate the performance of the Great Lakes System for the Corps of Engineers.