Using a dynamic variant of the Vicsek model, we show that the emergence of disorder from an orderly moving human crowd is a nonequilibrium first-order phase transition. We also show that this transition can be reversed by modifying the dynamics of a few agents, deemed as game changers. Surprisingly, the optimal placement of these game changers is found to be in regions of maximum local crowd speed. The presence of such game changers is effective owing to the discontinuous nature of the underlying phase transition. Thus our generic approach provides strategies to (i) delay crowd crush and (ii) design safe evacuation procedures, two aspects that are of paramount importance in maintaining safety of mass gatherings of people. © 2019 American Physical Society.

Sumesh P. Thampi

Department Of Chemical Engineering

Mahesh V. Panchagnula

Department of Applied Mechanics

Atomic physics

Collective motions

First-order phase transitions

GENERIC APPROACH

HUMAN CROWD

Non equilibrium

OPTIMAL PLACEMENTS

SAFE EVACUATION

VICSEK MODELS

Physics

CROWDING (AREA)

decision making

Emotion

Human

movement (physiology)

theoretical model

Choice Behavior

CROWDING

Emotions

Humans

Models, Theoretical

Movement

Fulltext

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Physical Review Letters

Sparse Game Changers Restore Collective Motion in Panicked Human Crowds

We study the collective motion of a dense suspension of active swimmers in a viscous fluid medium. The swimmers are modeled as soft spheres moving in a highly viscous fluid medium. The magnitude of the propelling thrust exerted by each particle is taken to be a constant and the direction is aligned to its velocity. Depending on the magnitude of the exerted thrust, several nonequilibrium steady states are observed. The transitions between the steady states are characterized using the total dissipation as a function of the magnitude of the thrust. The transitions between the nonequilibrium states are characterized by changes in exponent at low thrust values. At high thrust values, hysteretic transitions between ordered and disordered states are observed. © 2017 American Physical Society.

Physical Review E

Transitions between multiple dynamical states in a confined dense active-particle system

We use a recently developed coupled fluid–particle discrete element model to study mixing of a wet granular material in a two dimensional setting. The particles are modeled as linearly elastic disks and are considered to be immersed in a Newtonian fluid. The fluid–particle interaction is modeled using a linear drag model under the assumption that the fluid inertia is small compared to particle inertia. The granular slurry is driven by a belt moving at constant velocity in a square cavity. In the simulations, we consider three types of size distributions: monodisperse, bidisperse with several particle size ratios, and polydisperse Gaussian distributions with several different standard deviations. Mixing is characterized using both strong and weak measures. Size segregation is observed only in the bidisperse simulations. The energy required for mixing polydisperse slurries decreases with increasing standard deviation of the particle sizes. Finally, we show the benefits of engineering certain polydisperse particle size distributions towards minimizing energy consumption. © 2016, Springer-Verlag Berlin Heidelberg.

Granular Matter

Effect of size distribution on mixing of a polydisperse wet granular material in a belt-driven enclosure

We study two-dimensional flow of a granular slurry in a lid driven cavity using novel coupled fluid–particle discrete element simulations. The particles are assumed to be linearly elastic and fully immersed in a Newtonian fluid. In contrast to previous approaches to coupling fluid particle interactions, the fluid–particle interaction in the present study is modeled purely through Stokes’ drag. This assumption is based on the fluid inertia being small in comparison to particle inertia. Using this model, we study mixing of two initially stratified layers of the granular material in a belt-driven square cavity. We also study the microscopic aspects of the mixing process by monitoring the breakup of representative unit cells. Higher belt velocities are observed to require lower overall energy to achieve a well-mixed state. © 2015, Springer-Verlag Berlin Heidelberg.

A novel coupled fluid–particle DEM for simulating dense granular slurry dynamics

This review summarizes theoretical progress in the field of active matter, placing it in the context of recent experiments. This approach offers a unified framework for the mechanical and statistical properties of living matter: biofilaments and molecular motors in vitro or in vivo, collections of motile microorganisms, animal flocks, and chemical or mechanical imitations. A major goal of this review is to integrate several approaches proposed in the literature, from semimicroscopic to phenomenological. In particular, first considered are &quot;dry&quot; systems, defined as those where momentum is not conserved due to friction with a substrate or an embedding porous medium. The differences and similarities between two types of orientationally ordered states, the nematic and the polar, are clarified. Next, the active hydrodynamics of suspensions or &quot;wet&quot; systems is discussed and the relation with and difference from the dry case, as well as various large-scale instabilities of these nonequilibrium states of matter, are highlighted. Further highlighted are various large-scale instabilities of these nonequilibrium states of matter. Various semimicroscopic derivations of the continuum theory are discussed and connected, highlighting the unifying and generic nature of the continuum model. Throughout the review, the experimental relevance of these theories for describing bacterial swarms and suspensions, the cytoskeleton of living cells, and vibrated granular material is discussed. Promising extensions toward greater realism in specific contexts from cell biology to animal behavior are suggested, and remarks are given on some exotic active-matter analogs. Last, the outlook for a quantitative understanding of active matter, through the interplay of detailed theory with controlled experiments on simplified systems, with living or artificial constituents, is summarized. &copy; 2013 American Physical Society.

Reviews of Modern Physics

Hydrodynamics of soft active matter

Journal	Data powered by TypesetPhysical Review Letters
Publisher	Data powered by TypesetAmerican Physical Society
ISSN	00319007
Open Access	Yes