arXiv subjects

Eli Silver

Publications and source records attributed to Eli Silver.

8 recordsLinked to original sources

arXiv2026

Surface Waves Alter Air Entrainment During Water Entry

When a sphere crosses an air-water interface it can entrain a significant volume of air, a process relevant to numerous naval, industrial, and environmental settings. While air entrainment through sphere impact onto quiescent baths has been extensively studied, real-world interfaces are inherently unsteady, and the influence of surface waves is less understood. In this Letter, we systematically investigate the effect of interfacial geometry on the air entrained by impacting hydrophobic spheres onto an axisymmetric wavefield. By analyzing the resulting cavity across a wide parameter space, including wave phase, driving amplitude, and frequency, we reveal that local interface deformation dramatically alters air entrainment. This effect is driven by a geometric modulation of the splash curtain, which shifts the transition between cavity closure modes. We demonstrate that the influence of the waves is fully described by the local wave slope at the radius of the sphere, which alongside the Weber number We and Bond number Bo, establishes a foundational parametric framework for predicting air entrainment and cavity metrics across highly dynamic, real-world surfaces like the open ocean.

physics.flu-dyn↗

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 excellent 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↗

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

Bouncing to coalescence transition for droplet impact onto moving liquid pools

A droplet impacting a deep fluid bath is as common as rain over the ocean. If the impact is sufficiently gentle, the mediating air layer remains intact, and the droplet may rebound completely from the interface. In this work, we experimentally investigate the role of translational bath motion on the bouncing to coalescence transition. Over a range of parameters, we find that the relative bath motion systematically decreases the normal Weber number required to transition from bouncing to merging. Direct numerical simulations demonstrate that the depression created during impact combined with the translational motion of the bath enhances the air layer drainage on the upstream side of the droplet, ultimately favoring coalescence. A simple geometric argument is presented that rationalizes the collapse of the experimental threshold data, extending what is known for the case of axisymmetric normal impacts to the more general 3D scenario of interest herein.

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↗

arXiv2024

FIEVel: A Fast InExpensive Velocimeter based on an optical mouse sensor

Fluid velocimetry is fundamental to a breadth of applications spanning academia and industry, however velocimetry at high temporal resolution is often prohibitively costly. Here, we introduce a Fast and InExpensive Velocimeter (FIEVel) based on an optical mouse sensor. At its core, the optical mouse sensor consists of a small pixel array that acquires image data at high rates, with onboard hardware to compute and output motion in two orthogonal axes directly. By adapting this widely available integrated circuit to fluid velocimetry, we demonstrate that FIEVel is capable of resolving two components of velocity non-intrusively in the bulk of a flowing fluid at rates up to 6.4 kHz, at orders of magnitude lower cost than traditional velocimetry devices. We demonstrate and validate the velocimeter across a range of flows, operating conditions, and illumination strategies. As a sample application, we measure the temporal spectrum of a grid-generated turbulent flow and show excellent agreement with traditional Particle Image Velocimetry (PIV) using a high-speed camera.

physics.flu-dyn↗

arXiv2024

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↗

arXiv2023

Drag on a partially immersed sphere at the capillary scale

We study the drag on a centimetric sphere in a uniform flow in the presence of a free surface as a function of submergence depth. Through direct force measurements in a custom benchtop recirculating flume, we demonstrate that the drag can significantly exceed the corresponding drag in a single-phase flow and achieves a peak at submergence depths just prior to complete immersion. The additional drag in the partially immersed state is rationalized by considering hydrostatic effects associated with the asymmetric surface height profile induced by the obstacle in the flow direction which persists for flow speeds below the minimum capillary-gravity wave speed. At these scales, the sphere's wettability plays a pronounced role in determining the maximum possible drag and results in hysteretic behaviors near touchdown and complete immersion. The influence of flow speed, sphere size, and surface tension on the drag characteristics are additionally explored through a combination of experiments and numerical simulations.

physics.flu-dyn↗