Nesting simulation of a container terminal operating with its own simulation model

The paper contains a description of a class of simulation models used to generate data to support decisions on the design or re-structuring of a container yard. The models assume that the designed yard makes use of a simulation model on computer. Therefore, the simulation models contain a tool that enables to include nested simulation models. It is assumed that internal transport in the container yards is executed by ground-moving equipment (e.g. forklifts). Other ground-moving equipment (e.g. trailers) is used to realize the transport interface between the yards and their environment. All transport equipment is allowed to move only over empty places (i.e. on which no containers are placed). When some transport equipment has to move to a certain place a (shortest) path is computed, making use of empty places. But while the path is being applied, the configuration of the empty places may change. Simulation discovered that, in such a case, any adaptation algorithm might lead to a deadlock. Therefore the computer installed in the yard works in such a way that, after having computed the path, it simulates (and therefore anticipates) what can happen during the real (time consuming) use of the path. It can discover potential future barriers and look for other paths.