arXiv subjects

Pablo Gutiérrez

Publications and source records attributed to Pablo Gutiérrez.

9 recordsLinked to original sources

arXiv2026

Unjamming in a 3D Granular System: The Micromechanical Role of Friction in Force Distributions and Rheological Properties

In this work, we investigate the unjamming transition in a three-dimensional granular system composed of frictional spheres, in which the packing fraction is systematically reduced by random particle extractions. Using Discrete Element Method (DEM) simulations, we analyze the evolution of key micro-mechanical quantities, such as the interparticle forces, the coordination number and the overall packing density as a function of the interparticle friction coefficient. Our results reveal friction-dependent relationships on structural as well as mechanical observables, and exhibit trends that are qualitatively consistent with observations reported in dense granular systems. These trends persist despite the very different driving mechanism considered here. This paper is part of the thematic issue \emph{``Sand, silos and asteroids: clustering challenges in granular materials research''}.

cond-mat.soft↗

arXiv2025

Fluid Motion Makes the Bottle-Flip Challenge Mechanically Unintuitive But Viable

The bottle-flip challenge -- the upright landing of a partially filled bottle after tossing and flipping it in the air -- unexpectedly became a viral mechanics exercise. Through high-speed visualization, we evidence that fluid content strongly affects the challenge mechanics at every stage. First, fluid motion hinders bottle rotation through water redistribution after release and, later, through jet impact during free flight. Water also attenuates the bounce at touchdown, which is crucial for challenge success. The fluid makes the mechanics unintuitive and yet builds up the challenge feasibility.

physics.flu-dyn↗

arXiv2023

Stability of a tilted granular monolayer: How many spheres can we pick before the collapse?

The triggering of avalanches is investigated using discrete element simulations for a process of random extraction of spheres. A monolayer, formed by identical spheres in a hexagonal configuration, is placed on a tilted plane surrounded by a small fence that sustains the spheres, mimicking the disposal of fruits in the market. Then, a random continuous extraction process of spheres is imposed until the collapse. For this simple numerical experiment, a phase diagram was obtained to visualize the occurrence of avalanches triggered by vacancies as a function of the tilting angle, system size, and friction coefficient. More importantly, a sub-zone was found where we can predict the critical number of extractions until the avalanche takes place. The prediction is made from an evolution model of the average coordination number based on statistical considerations. The theoretical prediction also gives a constant critical void fraction of spheres, which implies the system collapses at a critical packing fraction.

cond-mat.soft↗

arXiv2022

Fluid motion for reducing the bounce of partially filled containers

Certain spatial distributions of water inside partially filled containers can significantly reduce the bounce of the container. In experiments with containers filled to a volume fraction $ϕ$, we show that rotation offers control and high efficiency in setting such distributions and, consequently, in altering bounce markedly. High-speed imaging evidences the physics of the phenomenon and reveals a rich sequence of fluid-dynamics processes, which we translate into a model that captures our overall experimental findings.

physics.flu-dyn↗

arXiv2020

Faraday-waves contact-line shear gradient induces streaming flow and tracers' self-organization: from rotating rings to spiral galaxy-like patterns

In this letter we experimentally demonstrate self-organization of small tracers under the action of longitudinal Faraday waves in a narrow container. We observe a steady current formation dividing the interface in small cells given by the symmetries of the Faraday wave. These streaming currents are rotating in each cell and their circulation increases with wave amplitude. This streaming flow drives the tracers to form patterns, whose shapes depend on the Faraday wave's amplitude: from low to high amplitudes we find dispersed tracers, a narrow rotating ring and a spiral galaxy-like pattern. We first describe the main pattern features, and characterize the wave and tracers' motion. We then show experimentally that the main source of the streaming flow comes from the time and spatial dependent shear at the wall contact line, created by the Faraday wave itself. We end by presenting a 2D model that considers the minimal ingredients present in the Faraday experiment, namely the stationary circulation, the stretching component due to the oscillatory wave and a steady converging field, which combined produce the observed self-organized patterns.

physics.flu-dyn↗

arXiv2016

Clustering of floaters on the free surface of a turbulent flow: an experimental study

We present an experimental study of the statistical properties of millimeter-size spheres floating on the surface of a turbulent flow. The flow is generated in a layer of liquid metal by an electromagnetic forcing. By using two magnet arrays, we are able to create one highly fluctuating flow and another, more stationary flow. In both cases, we follow the motion of hundreds of particles floating at the deformed interface of the liquid metal. We evidence the clustering of floaters by a statistical study of the local concentration of particles. Some dynamical properties of clusters are exposed. We perform spatial correlations between particle concentration and hydrodynamical quantities linked with inertial effects; with vortical motion, and with horizontal divergence (corresponding to compressibility in the surface). From comparing these correlations, we propose the so-called surface compressibility as the main clustering mechanism in our system. Hence, although floaters are not passive scalar and move on a deformed surface, the scenario is similar to the one reported for passive scalar on an almost flat free surface of a turbulent flow.

physics.flu-dyn↗

arXiv2016

Streaming patterns in Faraday waves

Waves patterns in the Faraday instability have been studied for decades. Besides the rich dynamics that can be observed on the waves at the interface, Faraday waves hide beneath them an elusive range of flow patterns --or streaming patterns-- which have not been studied in detail until now. The streaming patterns are responsible for a net circulation in the flow which are reminiscent of convection cells. In this article, we analyse these streaming flows by conducting experiments in a Faraday-wave setup. To visualize the flows, tracers are used to generate both trajectory maps and to probe the streaming velocity field via Particle Image Velocimetry (PIV). We identify three types of patterns and experimentally show that identical Faraday waves can mask streaming patterns that are qualitatively very different. Next we propose a three-dimensional model that explains streaming flows in quasi-inviscid fluids. We show that the streaming inside the fluid arises from a complex coupling between the bulk and the boundary layers. This coupling can be taken into account by applying modified boundary conditions in a three-dimensional Navier-Stokes formulation for the streaming in the bulk. Numerical simulations based on this theoretical framework show good qualitative and quantitative agreement with experimental results. They also highlight the relevance of three-dimensional effects in the streaming patterns. Our simulations reveal that the variety of experimental patterns is deeply linked to the boundary condition at the top interface, which may be strongly affected by the presence of contaminants along the surface.

physics.flu-dyn↗

arXiv2015

Surface waves propagation on a turbulent flow forced electromagnetically

We study the propagation of monochromatic surface waves on a turbulent flow. The flow is generated in a layer of liquid metal by an electromagnetic forcing. This forcing creates a quasi two-dimensional (2D) turbulence with strong vertical vorticity. The turbulent flow contains much more energy than the surface waves. In order to focus on the surface wave, the deformations induced by the turbulent flow are removed. This is done by performing a coherent phase averaging. For wavelengths smaller than the forcing lengthscale, we observe a significant increase of the wavelength of the propagating wave that has not been reported before. We suggest that it can be explained by the random deflection of the wave induced by the velocity gradient of the turbulent flow. Under this assumption, the wavelength shift is an estimate of the fluctuations of deflection angle. The local measurements of the wave frequency far from the wavemaker do not reveal such systematic behavior, although a small shift is measured. Finally we quantify the damping enhancement induced by the turbulent flow. We review various theoretical scaling laws proposed previously. Most of them propose a damping that increases as the square of Froude number. In contrast, our experimental results show a turbulent damping increasing linearly with the Froude number. We interpret this linear behaviour as a balance between the time spent by a wave to cross a turbulent structure with the turbulent mixing time. The larger is the ratio of these 2 times, the more energy is extracted from the progressive wave. Finally, mechanisms of energy exchange and open issues are discussed and further studies are proposed.

physics.flu-dyn↗

arXiv2012

Phase Transition in a Out-of-equilibrium Monolayer of Dipolar Vibrated Grains

We report an experimental study on the transition between a disordered liquid-like state and a ordered solid-like one, in a collection of magnetically interacting macroscopic grains. A monolayer of magnetized particles is vibrated vertically at a moderate density. At high excitation a disordered, liquid-like state is observed. When the driving dimensionless acceleration $Γ$ is quasi-statically reduced, clusters of ordered grains grow below a critical value $Γ_{\rm c}$. These clusters have a well defined hexagonal and compact structure. If the driving is subsequently increased, these clusters remain stable up to a higher critical value $Γ_{\rm l}$. Thus, the solid-liquid transition exhibits an hysteresis cycle. However, the lower onset $Γ_c$ is not well defined as it depends strongly on the acceleration ramp speed and also on the magnetic interaction strength. Metastability is observed when the driving is rapidly quenched from high acceleration, $Γ> Γ_{\rm l}$, to a low final excitation $Γ_q$. After this quench, solid clusters nucleate after a time lag $τ_o$, either immediately ($τ_o = 0$) or after some time lag ($τ_o>0$) that can vary from seconds up to several hundreds of seconds. The immediate growth occurs below a particular acceleration value $Γ_s$ ($\lesssim Γ_c$). In all cases, for $t \geq τ_o$ solid cluster's temporal growth can be phenomenologically described by a stretched exponential law. Finally, by taking into account the finite size of our system and by using simple assumptions we propose an alternative tractable theoretical model that reproduces cluster's growth, but which analytical form is not a stretched exponential law.

cond-mat.stat-mech↗