DSpace Repository :: Browsing by Author "Zuriguel, Iker"

Browsing by Author "Zuriguel, Iker"

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Active particles with desired orientation flowing through a bottleneck
(2018-12) Parisi, Daniel; Cruz Hidalgo, Raúl; Zuriguel, Iker
"We report extensive numerical simulations of the flow of anisotropic self-propelled particles through a constriction. In particular, we explore the role of the particles’ desired orientation with respect to the moving direction on the system flowability. We observe that when particles propel along the direction of their long axis (longitudinal orientation) the flow-rate notably reduces compared with the case of propulsion along the short axis (transversal orientation). And this is so even when the effective section (measured as the number of particles that are necessary to span the whole outlet) is larger for the case of longitudinal propulsion. This counterintuitive result is explained in terms of the formation of clogging structures at the outlet, which are revealed to have higher stability when the particles align along the long axis. This generic result might be applied to many different systems flowing through bottlenecks such as microbial populations or different kind of cells. Indeed, it has already a straightforward connection with recent results of pedestrian (which self-propel transversally oriented) and mice or sheep (which self-propel longitudinally oriented)."
Clogging transition of vibration-driven vehicles passing through constrictions
(2017-12) Patterson, Germán; Fierens, Pablo Ignacio; Sangiuliano Jimka, Federico; König, Pablo; Garcimartín, Ángel; Zuriguel, Iker; Pugnaloni, Luis Ariel; Parisi, Daniel
"We report experimental results on the competitive passage of elongated self-propelled vehicles rushing through a constriction. For the chosen experimental conditions, we observe the emergence of intermittencies similar to those reported previously for active matter passing through narrow doors. Noteworthy, we find that, when the number of individuals crowding in front of the bottleneck increases, there is a transition from an unclogged to a clogged state characterized by a lack of convergence of the mean clog duration as the measuring time increases. It is demonstrated that this transition—which was reported previously only for externally vibrated systems such as colloids or granulars—appears also for self-propelled agents. This suggests that the transition should also occur for the flow through constrictions of living agents (e.g., humans and sheep), an issue that has been elusive so far in experiments due to safety risks."
Effect of physical distancing on the speed–density relation in pedestrian dynamics
(2021-04) Echeverría Huarte, Iñaki; Garcimartín, Ángel; Parisi, Daniel; Cruz Hidalgo, R.; Martín-Gómez, César; Zuriguel, Iker
"We report experimental results of the speed-density relation emerging in pedestrian dynamics when individuals keep a prescribed safety distance among them. To this end, we characterize the movement of a group of people roaming inside an enclosure varying different experimental parameters: (i) global density, (ii) prescribed walking speed, and (iii) suggested safety distance. Then, by means of the Voronoi diagram we are able to compute the local density associated to each pedestrian, which is afterward correlated with its corresponding velocity at each time. In this way, we discover a strong dependence of the speed-density relation on the experimental conditions, especially with the (prescribed) free speed. We also observe that when pedestrians walk slowly, the speed-density relation depends on the global macroscopic density of the system, and not only on the local one. Finally, we demonstrate that for the same experiment, each pedestrian follows a distinct behavior, thus giving rise to multiple speed-density curves."
Flow of pedestrians through narrow doors with dierent competitiveness
(2016) Garcimartín, Ángel; Parisi, Daniel; Pastor, José Martín; Martín-Gómez, César; Zuriguel, Iker
"We report a thorough analysis of the intermittent flow of pedestrians through a narrow door. The observations include five diferent sets of evacuation drills with which we have investigated the efect of door size and competitiveness on the flow dynamics. Although the outcomes are in general compatible with the existence of the faster-is-slower efect, the temporal evolution of the instantaneous flow rate provides evidence of new features. These stress the crucial role of the number of people performing the tests, which has an influence on the obtained results. Once the transients at the beginning and end of the evacuation are removed, we have found that the time lapses between the passage of two consecutive pedestrians display heavy-tailed distributions in all the scenarios studied. Meanwhile, the distribution of burst sizes decays exponentially; this can be linked to a constant probability of finding a long-lasting clog during the evacuation process. Based on these results, a discussion is presented on the caution that should be exercised when measuring or describing the intermittent flow of pedestrians through narrow doors."
Pedestrian collective motion in competitive room evacuation
(2017-12) Garcimartín, Ángel; Pastor, José Martín; Martín-Gómez, César; Parisi, Daniel; Zuriguel, Iker
"When a sizable number of people evacuate a room, if the door is not large enough, an accumulation of pedestrians in front of the exit may take place. This is the cause of emerging collective phenomena where the density is believed to be the key variable determining the pedestrian dynamics. Here, we show that when sustained contact among the individuals exists, density is not enough to describe the evacuation, and propose that at least another variable-such as the kinetic stress-is required. We recorded evacuation drills with different degrees of competitiveness where the individuals are allowed to moderately push each other in their way out. We obtain the density, velocity and kinetic stress fields over time, showing that competitiveness strongly affects them and evidencing patterns which have been never observed in previous (low pressure) evacuation experiments. For the highest competitiveness scenario, we detect the development of sudden collective motions. These movements are related to a notable increase of the kinetic stress and a reduction of the velocity towards the door, but do not depend on the density."
Pedestrian dynamics at the running of the bulls evidences an inaccessible region in the fundamental diagram
(2021-09) Parisi, Daniel; Sartorio, Alan G.; Colonnello, Joaquín R.; Garcimartín, Ángel; Pugnaloni, Luis Ariel; Zuriguel, Iker
"We characterize the dynamics of runners in the famous “Running of the Bulls” Festival by computing the individual and global velocities and densities, as well as the crowd pressure. In contrast with all previously studied pedestrian systems, we unveil a unique regime in which speed increases with density that can be understood in terms of a time-dependent desired velocity of the runners. Also, we discover the existence of an inaccessible region in the speed–density state diagram that is explained by falls of runners. With all these ingredients, we propose a generalization of the pedestrian fundamental diagram for a scenario in which people with different desired speeds coexist."
Redefining the role of obstacles in pedestrian evacuation
(2018) Garcimartín, Ángel; Maza, Diego; Pastor, José Martín; Parisi, Daniel; Martín-Gómez, César; Zuriguel, Iker
"The placement of obstacles in front of doors is believed to be an effective strategy to increase the flow of pedestrians, hence improving the evacuation process. Since it was first suggested, this counterintuitive feature is considered a hallmark of pedestrian flows through bottlenecks. Indeed, despite the little experimental evidence, the placement of an obstacle has been hailed as the panacea for solving evacuation problems. In this work, we challenge this idea and experimentally demonstrate that the pedestrians flow rate is not necessarily altered by the presence of an obstacle. This result—which is at odds with recent demonstrations on its suitability for the cases of granular media, sheep and mice differs from the outcomes of most of existing numerical models, and warns about the risks of carelessly extrapolating animal behaviour to humans. Our experimental findings also reveal an unnoticed phenomenon in relation with the crowd movement in front of the exit: in competitive evacuations, an obstacle attenuates the development of collective transversal rushes, which are hazardous as they might cause falls."
Simulating competitive egress of noncircular pedestrians
(2017-04) Cruz Hidalgo, R.; Parisi, Daniel; Zuriguel, Iker
"We present a numerical framework to simulate pedestrian dynamics in highly competitive conditions by means of a force-based model implemented with spherocylindrical particles instead of the traditional, symmetric disks. This modification of the individuals’ shape allows one to naturally reproduce recent experimental findings of room evacuations through narrow doors in situations where the contact pressure among the pedestrians was rather large. In particular, we obtain a power-law tail distribution of the time lapses between the passage of consecutive individuals. In addition, we show that this improvement leads to new features where the particles’ rotation acquires great significance."

Browsing by Author "Zuriguel, Iker"

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