arXiv subjects

Leonardo Gordillo

Publications and source records attributed to Leonardo Gordillo.

At least 19 recordsLinked to original sources

arXiv2026

Stress network dynamics influence on large particle segregation

A plethora of natural and industrial shear-driven granular flows exhibit particle-size segregation. Its occurrence is commonly attributed to two primary mechanisms: kinetic sieving and squeeze expulsion. While kinetic sieving is relatively well understood, squeeze expulsion lacks a clear mechanical explanation and direct experimental evidence due to difficulties in measuring stresses in granular media. Here, we investigate force networks around a large intruder in a bidimensional granular shear cell. We use transparent, birefringent disks to visualize stress chains via photoelasticity. Experiments were conducted with two different granular media to study force chains over size ratios between the intruder and surrounding particles of 1.25 to 4.0. Particle Tracking Velocimetry and G-square analysis are used to quantify particle trajectories and identify active grains. These methods enable us to measure force-chain lengths and structures around the intruder through the gap factor. Our results confirm that squeeze-expulsion strongly depends on stress transmission. Larger size ratios lead to longer force chains and greater particle participation in the global stress network. In parallel, stress fluctuations predominate in driving or restraining intruder motion by forming anisotropic force chains. These findings advance the understanding of granular segregation by clarifying the link between force-network dynamics and segregation mechanics.

cond-mat.soft↗

arXiv2026

Inertia-Dilatancy Interplay Governs Shear-Thickening Drop Impact

Combining high-speed photography with direct force measurements, we investigate the impact dynamics of drops of cornstarch-water mixtures -- a premier example of shear-thickening fluids -- across a wide range of impact conditions. Our study identifies three distinct impact regimes. In addition to the liquid-like and solid-like behaviors generally expected for the impact-induced response of shear-thickening fluids, we uncover a counterintuitive regime in which high-concentration cornstarch-water mixtures display a liquid-like response at the onset of impact when shear rates are high and only transition to a solid-like behavior at later times as shear rates reduce. By integrating the classic drop-impact theory with the Reynolds-Darcy mechanism for dilatancy, we develop a unified model that quantitatively describes the impact dynamics of shear-thickening drops across all regimes. Our work reveals the unexpected response of shear-thickening fluids to ultra-fast deformation and advances fundamental understanding of drop impact for complex fluids.

physics.flu-dyn↗

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↗

arXiv2024

A synchrotron-like pumped ring resonator for water waves

The wave-like behaviour of matter in quantum physics has spurred insightful analogies between the dynamics of particles and waves in classical systems. In this study, drawing inspiration from synchrotrons that resonate to accelerate ions along a closed path, we introduce the concept of a synchrowave: a waveguide designed to generate and sustain travelling water waves within a closed annular channel. In analogy to unavoidable energy losses in conventional particle accelerators due to electromagnetic radiation and inelastic collisions, the system displays undesired water-wave dampening, which we address through the synchronised action of underwater wavemakers. Our analogies extend the resonance mechanisms of synchrotrons to generate gravity waves in closed waveguides efficiently. A proof-of-concept experiment at a laboratory scale demonstrates the unique capability of this technique to build up anomalously large travelling waves displaying a flat response in the long-wave limit. Besides quantifying the performance of wave generation, our findings offer a framework for both industrial and computational applications, opening up unexplored possibilities in hydraulics, coastal science and engineering. In a broader context, our experimental apparatus and methods highlight the versatility of a simple yet powerful concept: a closed-path continuous-energy-pumping scheme to effectively harvest prominent resonant responses within wave-supporting systems displaying weak dissipation.

physics.flu-dyn↗

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↗

arXiv2022

Mutation and SARS-CoV-2 strain competition under vaccination in a modified SIR model

The crisis caused by the COVID-19 outbreak around the globe raised an increasing concern about the ongoing emergence of variants of SARS-CoV-2 that may evade the immune response provided by vaccines. New variants appear due to mutation, and as the cases accumulate, the probability of the emergence of a variant of concern increases. In this article, we propose a modified SIR model with waning immunity that captures the competition of two strain classes of an infectious disease under the effect of vaccination with a highly contagious and deadly strain class emerging from a prior strain due to mutation. When these strains compete for a limited supply of susceptible individuals, changes in the efficiency of vaccines may affect the behaviour of the disease in a non-trivial way, resulting in complex outcomes. We characterise the parameter space including intrinsic parameters of the disease, and using the vaccine efficiencies as control variables. We find different types of transcritical bifurcations between endemic fixed points and a disease-free equilibrium and identify a region of strain competition where the two strain classes coexist during a transient period. We show that a strain can be extinguished either due to strain competition or vaccination, and we obtain the critical values of the efficiency of vaccines to eradicate the disease. Numerical studies using parameters estimated from publicly reported data agree with our theoretical results. Our mathematical model could be a tool to assess quantitatively the vaccination policies of competing and emerging strains using the dynamics in epidemics of infectious diseases.

q-bio.PE↗

arXiv2022

Pedal underwater motion triggers highly-peaked resonance on water waves

Pedal wavemakers that generate surface gravity waves through bed orbital motion have been shown to produce particle-excursion patterns that mimic deep-water wave behaviour but in finite-depth channels. In this article, we report that gravity waves in a general viscous fluid can resonate through the action of pedal wavemakers. We analyse the linear response of waves in an infinite channel in terms of the displacement amplitude, frequency, and wavelength of the bottom action. We show that the system behaves as a long-pass filter in space and a high-pass filter in time with a sharp resonance affected by viscosity. Furthermore, we propose a protocol to design deep gravity waves with an on-demand wavelength in a finite-depth water channel. Our theoretical framework agrees with numerical simulations using Smoothed Particle Hydrodynamics. Our results thus quantify the performance of pedal wavemakers and provide essential formulas for industrial and computational applications of the pedal wavemaking technique, useful both in hydraulics and coastal engineering problems.

physics.flu-dyn↗

arXiv2022

Universal wrinkling of supported elastic rings

An exactly solvable family of models describing the wrinkling of substrate-supported inextensible elastic rings under compression is identified. The resulting wrinkle profiles are shown to be related to the buckled states of an unsupported ring and are therefore universal. Closed analytical expressions for the resulting universal shapes are provided, including the one-to-one relations between the pressure and tension at which these emerge. The analytical predictions agree with numerical continuation results to within numerical accuracy, for a large range of parameter values, up to the point of self-contact.

cond-mat.soft↗

arXiv2022

Stress distribution and surface shock wave of drop impact

Drop impact causes severe surface erosion, dictating many important natural, environmental and engineering processes and calling for substantial prevention and preservation efforts. Nevertheless, despite extensive studies on the kinematic features of impacting drops over the last two decades, the dynamic process that leads to the drop-impact erosion is still far from clear. Here, we develop a method of high-speed stress microscopy, which measures the key dynamic properties of drop impact responsible for erosion, i.e., the shear stress and pressure distributions of impacting drops, with unprecedented spatiotemporal resolutions. Our experiments reveal the fast propagation of self-similar noncentral stress maxima underneath impacting drops and quantify the shear force on impacted substrates. Moreover, we examine the deformation of elastic substrates under impact and uncover impact-induced surface shock waves. Our study opens the door for quantitative measurements of the impact stress of liquid drops and sheds light on the origin of low-speed drop-impact erosion.

physics.flu-dyn↗

arXiv2022

Pressure-driven wrinkling of soft inner-lined tubes

Wrinkling of an inextensible elastic lining of an inner-lined tube under imposed pressure is considered. A simple equation modeling the elastic properties of the lining, the pressure, and the soft-substrate forces is derived. This equation aims to capture the wrinkling response of arterial endothelium to blood pressure changes. Numerical continuation is used to construct a bifurcation diagram as a function of the imposed pressure for in-plane deformations, in excellent agreement with weakly nonlinear theory, which we also develop. Our approach explains how the wavelength and amplitude of the wrinkles are selected as a function of the parameters in compressed wrinkling systems and shows how localized folds and mixed-mode states form in secondary bifurcations from wrinkled states.

cond-mat.soft↗

arXiv2021

Generation of gravity waves by pedal-wavemakers

Experimental wave generation in channels is usually achieved through wavemakers (moving paddles) acting on the surface of the water. Although practical for engineering purposes, wavemakers have issues: they perform poorly in the generation of long waves and create evanescent waves in their vicinity. In this article, we introduce a framework for wave generation through the action of an underwater multipoint mechanism: the pedal-wavemaking method. Our multipoint action makes each point of the bottom move with a prescribed pedalling-like motion. We analyse the linear response of waves in a uniform channel in terms of the wavelength of the bottom action. The framework naturally solves the problem of the performance for long waves and replaces evanescent waves by thin boundary layer at the bottom of the channel. We also show that a proper synchronisation of orbital motion on the bottom can produce waves that mimic deep water waves. This last feature has been proved to be useful to study fluid-structure interaction in simulations based on smoothed particle hydrodynamics.

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↗

arXiv2019

Shape of a recoiling liquid filament

We study the capillary retraction of a Newtonian semi-infinite liquid filament through analytical methods. We derive a long-time asymptotic-state expansion for the filament profile using a one-dimensional free-surface slender cylindrical flow model based on the three-dimensional axisymmetric Navier-Stokes equations. The analysis identifies three distinct length and time scale regions in the retraction domain: a steady filament section, a growing spherical blob, and an intermediate matching zone. We show that liquid filaments naturally develop travelling capillary waves along their surface and a neck behind the blob. We analytically prove that the wavelength of the capillary waves is approximately 3.63 times the filament's radius at the inviscid limit. Additionally, the waves' asymptotic wavelength, decay length, and the minimum neck size are analysed in terms of the Ohnesorge number. Finally, our findings are compared with previous results from the literature and numerical simulations in Basilisk obtaining a good agreement. This analysis provides a full picture of the recoiling process going beyond the classic result of the velocity of retraction found by Taylor and Culick.

physics.flu-dyn↗

arXiv2019

Localized Faraday patterns under heterogeneous parametric excitation

Faraday waves are a classic example of a system in which an extended pattern emerges under spatially uniform forcing. Motivated by systems in which uniform excitation is not plausible, we study both experimentally and theoretically the effect of heterogeneous forcing on Faraday waves. Our experiments show that vibrations restricted to finite regions lead to the formation of localized subharmonic wave patterns and change the onset of the instability. The prototype model used for the theoretical calculations is the parametrically driven and damped nonlinear Schrödinger equation, which is known to describe well Faraday-instability regimes. For an energy injection with a Gaussian spatial profile, we show that the evolution of the envelope of the wave pattern can be reduced to a Weber-equation eigenvalue problem. Our theoretical results provide very good predictions of our experimental observations provided that the decay length scale of the Gaussian profile is much larger than the pattern wavelength.

nlin.PS↗

arXiv2018

Fluid-supported elastic sheet under compression: Multifold solutions

The properties of a hinged floating elastic sheet of finite length under compression are considered. Numerical continuation is used to compute spatially localized buckled states with many spatially localized folds. Both symmetric and antisymmetric states are computed and the corresponding bifurcation diagrams determined. Weakly nonlinear analysis is used to analyze the transition from periodic wrinkles to single fold and multifold states and to compute their energy. States with the same number of folds have energies that barely differ from each other and the energy gap decreases exponentially as localization increases. The stability properties of the different competing states are established and provide a basis for the study of fold interactions.

nlin.PS↗

arXiv2017

Dynamics of drop impact on solid surfaces: evolution of impact force and self-similar spreading

We investigate the dynamics of drop impacts on dry solid surfaces. By synchronising high-speed photography with fast force sensing, we simultaneously measure the temporal evolution of the shape and impact force of impacting drops over a wide range of Reynolds numbers (Re). At high Re, when inertia dominates the impact processes, we show that the early-time evolution of impact force follows a square-root scaling, quantitatively agreeing with a recent self-similar theory. This observation provides direct experimental evidence on the existence of upward propagating self-similar pressure fields during the initial impact of liquid drops at high Re. When viscous forces gradually set in with decreasing Re, we analyse the early-time scaling of the impact force of viscous drops using a perturbation method. The analysis quantitatively matches our experiments and successfully predicts the trends of the maximum impact force and the associated peak time with decreasing Re. Furthermore, we discuss the influence of viscoelasticity on the temporal signature of impact forces. Last but not least, we also investigate the spreading of liquid drops at high Re following the initial impact. Particularly, we find an exact parameter-free self-similar solution for the inertia-driven drop spreading, which quantitatively predicts the height of spreading drops at high Re. The limit of the self-similar approach for drop spreading is also discussed. As such, our study provides a quantitative understanding of the temporal evolution of impact forces across the inertial, viscous and viscoelastic regimes and sheds new light on the self-similar dynamics of drop impact processes.

physics.flu-dyn↗

arXiv2017

Dynamic self-assembly of charged colloidal strings and walls in simple fluid flows

Colloidal particles can self-assemble into various ordered structures in fluid flows that have potential applications in biomedicine, materials synthesis and encryption. These dynamic processes are also of fundamental interest for probing the general principles of self-assembly in non-equilibrium conditions. Here, we report a simple microfluidic experiment, where charged colloidal particles self-assemble into flow-aligned 1D strings with regular particle spacing near a solid boundary. Using high-speed confocal microscopy, we systematically investigate the influence of flow rates, electrostatics and particle polydispersity on the observed string structures. By studying the detailed dynamics of stable flow-driven particle pairs, we quantitatively characterize interparticle interactions. Based on the results, we construct a simple model that explains the intriguing non-equilibrium self-assembly process. Our study shows that the colloidal strings arise from a delicate balance between attractive hydrodynamic coupling and repulsive electrostatic interaction between particles. Finally, we demonstrate that, with the assistance of transverse electric fields, a similar mechanism also leads to the formation of 2D colloidal walls.

cond-mat.soft↗

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↗