A numerical study of contact force in competitive evacuation

Abstract

Crowd force by the pushing or crushing of people has resulted in a number of accidents in recent decades. The aftermath investigations have shown that the physical interaction of a highly competitive crowd could produce dangerous pressure up to 4500 N/m, which leads to compressive asphyxia or even death. In this paper, a numerical model based on discrete element method (DEM) as referenced from granular flow was proposed to model the evacuation process of a group of highly competitive people, in which the movement of people follows Newton's second law and the body deformation due to compression follows Hertz contact model. The study shows that the clogs occur periodically and flow rate fluctuates greatly if all people strive to pass through a narrow exit at high enough desired velocity. Two types of contact forces acting on people are studied. The first one, i.e., vector contact force, accounts for the movement of the people following Newton's second law. The second one, i.e., scale contact force, accounts for the physical deformation of the human body following the contact law. Simulation shows that the forces chain in crowd flow is turbulent and fragile. A few narrow zones with intense forces are observed in the force field, which is similar to the strain localization observed in granular flow. The force acting on a person could be as high as 4500 N due to force localization, which may be the root cause of compressive asphyxia of people in many crowd incidents.

Study on the collision dynamics and the transmission pattern between pedestrians along the queue

“…Many experiments were conducted to collect parameters including velocity, location, density, evacuation time, and flow [47][48][49][50], but only a few were concentrated on the interactions between pedestrians while empirical data of the contact forces was scarce. In most of the current models, contact force models can be divided into two types: the customized model and the elastic force model [51][52][53]. However, their definitions are too simple to reflect the features of the interaction process.…”

Effects of Ticket-Checking Failure on Dynamics of Pedestrians at Multi-Exit Inspection Points with Various Layouts

“…In reality, when two or several pedestrians compete for the same position, there would be a collision between the pedestrians, increasing the risk of injury or crowd disturbances. In the previous work of Lin et al [ 38 ], it was found that the competitive behavior of pedestrians at the exit may cause force localization and compressive asphyxia of people. In the CA simulation, such behavior is associated with two or three pedestrians completing for one cell when updating their positions.…”

Modelling physical contacts to evaluate the individual risk in a dense crowd

“…However, individuals involved in physical contacts may experience extremely high accelerations exceeding physiological limits due to simplified kinetic equations and idealized numerical calculations. This can be called "acceleration error during individual physical contacts", objectively requiring excessive contact forces as a guarantee 24 . During collisions, individuals are forced to experience high acceleration in order to avoid overlap and to quickly separate from others, and the contact force and penetration distance will be significantly abnormal if the acceleration is constrained by the physiological reality 25,26 .…”