arXiv subjects

Jack-William Barotta

Publications and source records attributed to Jack-William Barotta.

10 recordsLinked to original sources

arXiv2026

Vertical motion of a periodically driven floating disc

We present the results of a combined theoretical and experimental investigation into the vertical dynamics of floating discs subjected to an imposed time-periodic forcing. The axisymmetric and inviscid wavefield is governed by a linear elliptic boundary value problem with mixed boundary conditions, wherein the no-penetration boundary condition is satisfied under the disc while the free surface boundary conditions are enforced away from it. The problem is solved by recasting the system of partial differential equations as a second-kind Fredholm integral equation which is then solved numerically. The solution furnishes a prediction for the dependence of the disc's oscillation amplitude on the forcing frequency, which exhibits good agreement with experiments. We interpret our results physically by computing the added mass, wave damping and effective spring coefficients of the disc, both numerically for a range of forcing frequencies and analytically in the low-frequency limit.

physics.flu-dyn↗

arXiv2026

The physics of cranberry bogs

The common New England sight of a cranberry bog presents a rich tapestry of fluid dynamics and soft matter phenomena. Here, we present four connected problems exploring the behavior of cranberries in their stages of harvest: the buoyant rise of a cranberry in a flooded bog, the stable floating configuration of a cranberry on the surface, the aggregation and interaction between many floating cranberries collected with a boom, and the piling of cranberries onto a truck for transportation. We model these phenomena from first principles and develop simple computational simulations of their collective behaviors. Additionally, we describe tabletop experiments to accompany these problems, either as in-class demonstrations or lab activities. Throughout, we draw connections to broader physical principles in soft condensed matter and fluids, allowing the real-world example of the cranberry bog to serve as a bridge between the undergraduate curriculum and topics in soft matter research.

physics.app-ph↗

arXiv2025

Non-equilibrium thermodynamics in driven macroscopic self-assembly

Equilibrium statistical mechanics provides a robust framework for characterizing phase transitions in systems whose microsopic dynamics are time-reversible. Efforts to develop and validate theoretical frameworks for time-irreversible, non-equilibrium systems are constrained by experimental data that capture only partial measurements of the system dynamics. We herein overcome this limitation using a tunable macroscopic platform for non-equilibrium physics: millimetric spheres bound by capillary attractions at the fluid interface and driven out of equilibrium by a field of supercritical Faraday waves. The external driving induces correlated fluctuations in the particle trajectories, which in turn excite structural rearrangements between distinct metastable cluster topologies. By tracking all microstate transitions experimentally, we directly measure a non-zero entropy production rate reflecting broken detailed balance and quantifying the system's departure from equilibrium. The measured stochastic dynamics are in quantitative agreement with a many-body active Ornstein-Uhlenbeck model, thus establishing a bridge to a wider class of athermal, self-propelled systems at the microscale. These results invite parallel studies of non-equilibrium self-assembly kinetics using active colloids or passive particles immersed in bacterial baths whose dynamics and irreversibility are likewise governed by correlated active forces and tunable inter-particle interactions.

cond-mat.soft↗

arXiv2025

Macroscopic Brownian Motion on a Chaotic Fluid Interface

Brownian motion is the erratic motion of an object due to collisions with the fluid in which it is immersed. In this work, we detail a tabletop laboratory demonstration of underdamped Brownian motion wherein a macroscopic particle resting on a driven fluid interface exhibits ballistic motion at short times and diffusive motion at long times. We observe the trajectory of a millimetric disk driven by a field of chaotic Faraday waves excited by a shaker. The crossover from ballistic to diffusive motion occurs at time and length scales experimentally accessible through particle tracking of a video recorded with a standard phone camera. Along with representative data, we provide a complete assembly guide, and operating procedure for students so that the experiment can be readily applied in the classroom. The tabletop setup can also be adapted for other student projects and active research topics relating to particle motion on a vibrating fluid interface.

physics.ed-ph↗

arXiv2025

Propulsion and interaction of wave-propelled interfacial particles

When a floating body is internally or externally vibrated, its self-generated wavefield can lead to steady propulsion along the interface. In this article, we review several related and recently discovered systems that leverage this propulsion mechanism and interact hydrodynamically with one another via these surface waves. Particles with an onboard oscillatory driver may self-propel by virtue of a fore-aft asymmetric wavefield, a phenomenon with demonstrated relevance to biological and artificial systems across scales. Freely floating particles on a vibrated fluid bath can also self-propel along straight paths, but may also rotate in place or move along curved arcs, depending sensitively on the particle asymmetries and driving parameters. Such surfing particles interact at a distance through their mutual capillary wavefield and exhibit a rich array of collective dynamics. Overall, these accessible, tunable, and visually appealing systems motivate future investigations into a number of outstanding questions in fundamental fluid mechanics, while potentially also informing advances in the fields of active matter, hydrodynamic quantum analogs, and robotics.

physics.flu-dyn↗

arXiv2025

Drop rebound at low Weber number

We study the rebound of drops impacting non-wetting substrates at low Weber number $We$ through experiment, direct numerical simulation, and reduced-order modeling. Submillimeter-sized drops are normally impacted onto glass slides coated with a thin viscous film that allows them to rebound without contact line formation. Experiments are performed with various drop viscosities, sizes, and impact velocities, and we directly measure metrics pertinent to spreading, retraction, and rebound using high-speed imaging. We complement experiments with direct numerical simulation and a fully predictive reduced-order model that applies natural geometric and kinematic constraints to simulate the drop shape and dynamics using a spectral method. At low $We$, drop rebound is characterized by a weaker dependence of the coefficient of restitution on $We$ than in the more commonly studied high-$We$ regime, with nearly $We$-independent rebound in the inertio-capillary limit, and an increasing contact time as $We$ decreases. Drops with higher viscosity or size interact with the substrate longer, have a lower coefficient of restitution, and stop bouncing sooner, in good quantitative agreement with our reduced-order model. In the inertio-capillary limit, low $We$ rebound has nearly symmetric spreading and retraction phases and a coefficient of restitution near unity. Increasing $We$ or viscosity breaks this symmetry, coinciding with a drop in the coefficient of restitution and an increased dependence on $We$. Lastly, the maximum drop deformation and spreading are related through energy arguments, providing a comprehensive framework for drop impact and rebound at low $We$.

physics.flu-dyn↗

arXiv2025

Synchronization of wave-propelled capillary spinners

When a millimetric body is placed atop a vibrating liquid bath, the relative motion between the object and interface generates outward propagating waves with an associated momentum flux. Prior work has shown that isolated chiral objects, referred to as spinners, can thus rotate steadily in response to their self-generated wavefield. Here, we consider the case of two co-chiral spinners held at a fixed spacing from one another but otherwise free to interact hydrodynamically through their shared fluid substrate. Two identical spinners are able to synchronize their rotation, with their equilibrium phase difference sensitive to their spacing and initial conditions, and even cease to rotate when the coupling becomes sufficiently strong. Non-identical spinners can also find synchrony provided their intrinsic differences are not too disparate. A hydrodynamic wave model of the spinner interaction is proposed, recovering all salient features of the experiment. In all cases, the spatially periodic nature of the capillary wave coupling is directly reflected in the emergent equilibrium behaviors.

cond-mat.soft↗

arXiv2025

Synchronization and self-assembly of free capillary spinners

Chiral active particles are able to draw energy from the environment to self-propel in the form of rotation. We describe an experimental arrangement wherein chiral objects, spinners, floating on the surface of a vibrated fluid rotate due to emitted capillary waves. We observe that pairs of spinners can assemble at quantized distances via the mutually generated wavefield, phase synchronize and, in some circumstances, globally rotate about a point midway between them. A mathematical model based on wave-mediated interactions captures the salient features of the assembly and synchronization while a qualitative argument is able to rationalize global rotations based on interference and radiation stress associated with the wavefield. Extensions to larger collections are demonstrated, highlighting the potential for this tabletop system to be used as an experimental system capable of synchronizing and swarming.

cond-mat.soft↗

arXiv2024

Mermaid Cereal: Interactions and Pattern Formation in a Macroscopic Magnetocapillary SALR System

When particles are deposited at a fluid interface they tend to aggregate by capillary attraction to minimize the overall potential energy of the system. In this work, we embed floating millimetric disks with permanent magnets to introduce a competing repulsion effect and study their pattern formation in equilibrium. The pairwise energy landscape of two disks is described by a short-range attraction and long-range repulsion (SALR) interaction potential, previously documented in a number of microscopic systems. Such competing interactions enable a variety of pairwise equilibrium states, including the possibility of a local minimum energy corresponding to a finite disk spacing. Two-dimensional (2D) experiments and simulations in confined geometries demonstrate that as the areal packing fraction is increased, the dilute repulsion-dominated lattice state becomes unstable to the spontaneous formation of localized clusters, which eventually merge into a system-spanning striped pattern. Finally, we demonstrate that the equilibrium pattern can be externally manipulated by the application of a supplemental vertical magnetic force that remotely enhances the effective capillary attraction.

cond-mat.soft↗

arXiv2023

Bidirectional Wave-Propelled Capillary Spinners

When a solid body floats at the interface of a vibrating liquid bath, the relative motion between the object and interface generates outwardly propagating surface waves. It has recently been demonstrated that millimetric objects with fore-aft mass asymmetry generate an associated asymmetric wavefield and consequently self-propel in unidirectional motion. Harnessing this wave-powered mechanism of propulsion, we here demonstrate that chiral objects placed on a vibrating fluid interface are set into steady, yet reversible, rotation, with the angular speed and direction of rotation controlled by the interplay between object geometry and driving parameters. Scaling laws and a simplified model of the wavefield reveal the underlying physical mechanism of rotation, while collapsing experimental measurements of the angular velocity across parameters. Leveraging the control over the chiral object's direction of rotation, we then demonstrate that a floating body with an asymmetric mass distribution and chirality can be remotely steered along two-dimensional trajectories via modulation of the driving frequency alone. This accessible and tunable macroscopic system serves as a potential platform for future explorations of chiral active and driven matter, and demonstrates a mechanism by which wave-mediated fluid forces can be manipulated for directed propulsion.

physics.flu-dyn↗