Zuriguel-Ballaz, Í. (Íker)
- Publications
- item.page.relationships.isContributorAdvisorOfPublication
- item.page.relationships.isContributorOfPublication
88 results
Search Results
Now showing 1 - 10 of 88
- Influence of the feeding mechanism on deposits of square particles(2013) Pagonabarraga, I. (Ignacio); Zuriguel-Ballaz, Í. (Íker); Cruz-Hidalgo, R. (Raúl); Acevedo-Escalante, M. (Manuel Francisco); Maza-Ozcoidi, D. (Diego)In a previous paper [Hidalgo et al., Phys. Rev. Lett. 103, 118001 (2009)] it was shown that square particles deposited in a silo tend to align with a diagonal parallel to the gravity, giving rise to a deposit with very particular properties. Here we explore, both experimentally and numerically, the effect on these properties of the filling mechanism. In particular, we modify the volume fraction of the initial configuration from which the grains are deposited. Starting from a very dilute case, increasing the volume fraction results in an enhancement of the disorder in the final deposit characterized by a decrease of the final packing fraction and a reduction of the number of particles oriented with their diagonal in the direction of gravity. However, for very high initial volume fractions, the final packing fraction increases again. This result implies that two deposits with the same final packing fraction can be obtained from very different initial conditions. The structural properties of such deposits are analyzed, revealing that, although the final volume fraction is the same, their micromechanical properties notably differ.
- Clogging and unclogging of many-particle systems passing through a bottleneck(EDP Sciences, 2017) Zuriguel-Ballaz, Í. (Íker); Arevalo, R. (Roberto); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Garcimartín-Montero, Á. (Ángel)When a group of discrete particles pass through a narrowing, the flow may become arrested due to the development of structures that span over the size of the aperture. Then, it is said that the system is clogged. Here, we will discuss about the existence of a phase diagram for the clogged state that has been recently proposed, arguing on its usefulness to describe different systems of discrete bodies ranging from granular materials, to colloidal suspensions and live beings. This diagram is built based on the value of a flowing parameter which characterizes the intermittent flow observed in all these discrete systems provided that there is an external or internal energy supply. Such requirement, which is necessary to destabilize the clogging arches, is absent in a standard static silo, which is therefore examined as a particular case. This view will help to understand some a priori inconsistencies concerning the role of driving force in the clogging process that have been found in the last years.
- Pedestrian collective motion in competitive room evacuation(2017) Parisi, D.R. (D. R.); Zuriguel-Ballaz, Í. (Íker); Gómez, C. (Carlos); Pastor-Gutierrez, J.M. (José Martín); Garcimartín-Montero, Á. (Ángel)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.
- A glossary for research on human crowd dynamics(2019) Ronchi, E. (Enrico); Köster, G. (Gerta); Toschi, F. (Federico); Neville, F. (Fergus); Fu, Z. (Zhijian); Wijermans, N. (Nanda); Michalareas, G. (Georgios); Schadschneider, A. (Andreas); Kneidl, A. (Angelika); Adrian, J. (Juliane); Zuriguel-Ballaz, Í. (Íker); Beermann, M. (Mira); Corbetta, A. (Alessandro); Spearpoint, M. (Michael); Zanlungo, F. (Francesco); Amos, M. (Martyn); Drury, J. (John); Küpper, M. (Mira); Hunt, A. (Aoife); Seyfried, A. (Armind); Boltes, M. (Maik); Sieben, A. (Anna); Dezecache, G. (Guillaume); Sullivan, G.B. (Gavin Brent); Wal, N. (Natalie) van der; Bode, N. (Nikolai); Reicher, S. (Stephen); Kanters, T. (Tinus); Schadewijk, F. (Frank) van; Krüchten, C. (Cornelia) von; Shipman, A. (Alastair); Templeton, A. (Anne); Hofinger, G. (Gesine); Baratchi, M. (Mitra); Geraerts, R. (Roland); Yücel, Z. (Zeynep); Ntontis, E. (Evangelos); Gwynne, S. (Steve); Konya, K. (Krisztina)This article presents a glossary of terms that are frequently used in research on human crowds. This topic is inherently multidisciplinary as it includes work in and across computer science, engineering, mathematics, physics, psychology and social science, for example. We do not view the glossary presented here as a collection of finalised and formal definitions. Instead, we suggest it is a snapshot of current views and the starting point of an ongoing process that we hope will be useful in providing some guidance on the use of terminology to develop a mutual understanding across disciplines. The glossary was developed collaboratively during a multidisciplinary meeting. We deliberately allow several definitions of terms, to reflect the confluence of disciplines in the field. This also reflects the fact not all contributors necessarily agree with all definitions in this glossary.
- Stability of clogging arches in a silo submitted to vertical vibrations(2015) Zuriguel-Ballaz, Í. (Íker); Lozano, C. (Celia); Garcimartín-Montero, Á. (Ángel)We present experimental results on the endurance of arches that block the outlet of a two-dimensional silo when subjected to vertical vibration. In a recent paper [C. Lozano et al., Phys. Rev. Lett. 109, 068001 (2012)], it was shown that the arch resistance against vibrations is determined by the maximum angle among those formed between each particle in the bridge and its two neighbors: the larger the maximum angle is, the weaker the bridge. It has also been reported that the breaking time distribution shows a power-law tail with an exponent that depends on the outlet size, the vibration intensity, and the load [I. Zuriguel et al., Sci. Rep. 4, 7324 (2014)]. Here we connect these previous works, demonstrating the importance of the maximum angle in the arch on the exponent of the breaking time distribution. Besides, we find that the acceleration needed to break an arch does not depend on the ramp rate of the applied acceleration, but it does depend on the outlet size above which the arch is formed. We also show that high frequencies of vibration reveal a change in the behavior of the arches that endure very long times. These arches have been identified as a subset with special geometrical features. Therefore, arches that cannot be broken by means of a given external excitation might exist.
- Stress transmission in systems of faceted particles in a silo: the roles of filling rate and particle aspect ratio(Springer, 2014) Pagonabarraga, I. (Ignacio); Zuriguel-Ballaz, Í. (Íker); Cruz-Hidalgo, R. (Raúl); Alonso-Marroquin, F. (F.); Acevedo-Escalante, M. (Manuel Francisco); Maza-Ozcoidi, D. (Diego)We present experimental and numerical results for particle alignment and stress distribution in packings of faceted particles deposited in a small-scale bi-dimensional silo. First, we experimentally characterize the deposits’ morphology in terms of the particles’ aspect ratio and feeding rate. Then we use the experimental results to validate our discrete element method (DEM) based on spheropolygons. After achieving excellent agreement, we use contact forces and fabric provided by the simulations to calculate the coarse-grained stress tensor. For low feeding rates, square particles display a strong tendency to align downwards, i.e., with a diagonal parallel to gravity. This morphology leads to stress transmission towards the walls, implying a quick development of pressure saturation, in agreement with the Janssen effect. When the feed rate is increased, both the disorder and the number of horizontal squares in the silo increase, hindering the Janssen effect. Conversely, for elongated particles the feed rate has a weak effect on the final deposit properties. Indeed, we always observe highly ordered structures of horizontal rods where the stress is transmitted mainly in the vertical direction.
- Twisting, an alternative strategy to compact granular materials(EDP Sciences, 2017) Zuriguel-Ballaz, Í. (Íker); Maza-Ozcoidi, D. (Diego); Asencio, K. (Karol)Nowadays, the common method to pack granular materials is to tap the ensemble against the gravity. Despite the apparent simplicity of that method, the asymptotic states reached by the tapped systems have strongly dependences on parameters like the shape of the tapping pulse, the container geometry or the ratio between lateral and axial dimensions. Beyond the restrictions imposed by the system boundaries, the particle shape (like rods or tetrahedrons) plays a central role in the evolution and the final state of the ensemble. In this work, we introduce an unconventional method for compacting granular ensembles by applying a sequence of alternating counterrotating pulses or ¿twists¿. By using spherical particles we analyze the efficiency of this method to achieve highly packed configurations.
- Contact network topology in tapped granular media(2013) Pugnaloni, L.A. (Luis A.); Zuriguel-Ballaz, Í. (Íker); Arevalo, R. (Roberto); Maza-Ozcoidi, D. (Diego)We analyze the contact network of simulated two-dimensional granular packings in different states of mechanical equilibrium obtained by tapping. We show that topological descriptors of the contact network allow one to distinguish steady states of the same mean density obtained with different tap intensities. These equal-density states were recently proven to be distinguishable through the mean force moment tensor. In contrast, geometrical descriptors, such as radial distribution functions, bond order parameters, and Voronoi cell distributions, can hardly discriminate among these states. We find that small-order loops of contacts—the polygons of the network—are especially sensitive probes for the contact structure.
- Multifractal Intermittency in Granular Flow through Bottlenecks(American Physical Society (APS), 2019) Ortín, J. (J.); Zuriguel-Ballaz, Í. (Íker); Gella, D. (Diego)We experimentally analyze the intermittent nature of granular silo flow when the discharge is controlled by an extracting belt at the bottom. We discover the existence of four different scenarios. For low extraction rates, the system is characterized by an on-off intermittency. When the extraction rate is increased the structure functions of the grains velocity increments, calculated for different lag times, reveal the emergence of multifractal intermittency. Finally, for very high extraction rates that approach the purely gravitational discharge, we observe that the dynamics become dependent on the outlet size. For large orifices the behavior is monofractal, whereas for small ones, the fluctuations of the velocity increments deviate from Gaussianity even for very large time lags.
- Experimental evidence of the ‘Faster Is Slower’ effect(Elsevier, 2014) Parisi, D.R. (D. R.); Zuriguel-Ballaz, Í. (Íker); Martín-Gómez, C. (César); Pastor-Gutierrez, J.M. (José Martín); Garcimartín-Montero, Á. (Ángel)The Faster-Is-Slower effect (Helbing et al (2000)) is an important instance of self-organized phenomenon in pedestrian dynamics. Despite this, an experimental demonstration is still lacking. We present controlled tests where a group of students are asked to exit a room through a door. Instead of just measuring the evacuation times, we have analyzed the probability distribution of the time lapses between consecutive individuals. We show how it displays a power-law tail. This method displays clearly the Faster Is Slower effect, and also allows to assess the impact of several tactics that can be put in place to alleviate the problem.