Counterflow In Computational Evacuation Modelling - The Hydraulic Model, Modelling Tools And Trials

The hydraulic model calculates the flow through a door constriction for a unidirectional flow of people primarily based on physical constraints. The method requires the physical door opening width to be reduced by a boundary layer adjustment to determine the effective width. However, the hydraulic model does not provide any guidance on what the flow might be when there is a counterflow condition. One option might be to simply represent counterflow with an equivalent half-door opening effective width.

This paper compares the results from two agent-based, computational evacuation tools to assess counterflow against the hydraulic model and data collected from people movement trials. The trials consisted of around 90 people travelling through an open doorway to generate unidirectional and counterflow scenarios. The trials also investigated how group identity might affect the counterflow measurements by gathering data when such identity was present or absent. Results suggest that the flow through the doorway in a given direction under counterflow conditions is greater than assuming half of the unidirectional flow. There appears to be an effect when in-group psychological behaviour is introduced such that the flow can show an overall increase when compared to having random groups. However, should participants interact then the in-group counterflow also exhibits a greater variability.

The two computational tools are used to generate movement scenarios equivalent to the trials. One tool (Evacuationz) uses a network representation of the geometry while the second tool (Pathfinder) is a continuous model. The paper briefly discusses how these tools simulate agents and their movement in the context of counterflow. The default 'steering' mode in Pathfinder, results in single direction counterflow rates of approximately half of that observed in the trials. However, the 'SFPE' mode in Pathfinder gives results that are similar to those observed in the trials and calculated using Evacuationz.