arXiv subjects

Sunghwan Jung

Publications and source records attributed to Sunghwan Jung.

At least 19 recordsLinked to original sources

arXiv2026

Static and Dynamic Estimation of Flexural Rigidity of Soybean

This paper evaluates a cantilever system as a simple method for measuring the mechanical rigidity (bending rigidity EI or Young's modulus E) of plants. Using soybeans as a test sample -- whose E values have rarely been reported -- we conducted static and dynamic experimental measurements alongside numerical modal analysis. Results showed good agreement in EI values between the static and dynamic tests when branches and leaves were removed, provided the stem responded uniformly. However, the added mass of attached foliage causes complex dynamic interactions, which we analyze through both experimental and numerical approaches. Ultimately, our findings suggest that cantilever force-deflection measurements provide a practical, on-site approach, contributing to the development of an affordable and reliable standard for estimating plant mechanical properties.

physics.bio-ph↗

arXiv2026

Deformation and instability of sessile soap bubbles in an electric field

Interfacial deformation under electric fields is a common phenomenon in many industrial processes. Particularly, we are interested in the dynamics of sessile soap bubbles in a parallel-plate electric field which exhibits a stable deformation regime followed by conical instability. Using side-view imaging, we track the equilibrium shapes, the transition to the unstable regime, and the pre-jet apex dynamics within one experimental system. In the stable regime, the meridional profile is well described by a spheroidal fit, and the aspect ratio collapses across initial bubble sizes onto a single steady-state branch when plotted against the dimensionless field $E^\ast = \sqrt{\mathrm{Bo}_e}$ for data acquired within a fixed ambient session where the electric Bond number $\mathrm{Bo}_e$ is defined as $\varepsilon_0 E_0^2 R_0/(2γ)$. The endpoint of this branch marks the transition to the unstable regime. Above onset of instability, the apex sharpens into a cone with half-angle $30.0^{\circ}$ $\pm$ $0.6^{\circ}$, below the classical Taylor value. To quantify the late pre-jet stage, we define the axial distance $b(t)$ from the instantaneous apex to a fixed reference vertex determined from the terminal cone geometry and measure its evolution. The corresponding rate grows as jetting is approached, and a near-tip inertia-capillary model captures the observed logarithmic trend as an approximation. Together, these measurements establish a single-system experimental benchmark in which stable electrocapillary deformation is organized by a single steady-state branch that leads into conical instability and pre-jet dynamics.

physics.flu-dyn↗

arXiv2026

Ground effect on Undulation and pumping near surfaces

Locomotion and fluid pumping near surfaces are ubiquitous in nature, ranging from the slow crawling of snails to the rapid flight of bats. This study categorizes these behaviors based on the Undulation number ($\text{Un}$) and Reynolds number ($Re$). We contrast low $Re$ undulatory propulsion ($\text{Un} > 1$), exemplified by freshwater snails, with high $Re$ flapping propulsion ($\text{Un} < 1$), seen in bats and bees. For snails, we derive lubrication models showing that pumping and swimming speeds scale with $(a/h_0)^2$, a result validated by robotic experiments which also reveal the detrimental effects of surface deformation (high Capillary/Bond ratio). Conversely, for high $Re$ fliers, we examine the ground effect's role in lift enhancement. Biological data from bats (\textit{R. ferrumequinum}) reveal a 2.5-fold increase in lift coefficient during surface-skimming drinking flights, attributed to aerodynamic squeezing effects. Finally, we analyze honeybee fanning, demonstrating how a "jet-vortex" mechanism utilizes ground effect to transport pheromones efficiently against diffusion. These findings provide a unified framework for understanding fluid-structure interactions near boundaries in biological systems.

physics.flu-dyn↗

arXiv2026

The physics of crêpes: Elasto-gravity control of soft folding

Like a crêpe resting on a plate, a thin elastic sheet can fold smoothly under its own weight, forming reversible shapes without creases or imposed hinges. Such soft folds arise from a balance between elastic bending and gravity, yet their stability, packing limits, and dynamics remain poorly understood. Here we show that these behaviors are governed by a single physical length scale, the elasto-gravity length $\ell_{eg}$. Using experiments and heavy-elastica theory, we demonstrate that $\ell_{eg}$ sets the characteristic fold geometry, determines when a fold becomes unstable and unfolds, and limits how many reversible folds can be stacked in rectangular and circular sheets. In particular, when lengths are rescaled by $\ell_{eg}$, fold shapes and stability thresholds collapse across materials and thicknesses. We further show that unfolding follows a universal speed scaling $v \sim \sqrt{g\,\ell_{eg}}$, revealing a gravity-controlled time scale for the release of stored bending energy. Together, these results establish a unified physical framework for reversible folding, compact storage, and gravity-assisted deployment of thin elastic sheets.

cond-mat.soft↗

arXiv2025

Peeling-Induced Rolling and Heterogeneous Adhesion in Blistered Films

Blisters, delaminated regions that form in multilayered structures under compressive stresses, are observed across a wide range of length scales, from two-dimensional materials to protective coatings and laminated composites. Far from being passive defects, such interfacial features have emerged as functional motifs for three-dimensional architectures and reconfigurable surfaces. Here we reveal an unusual peel response of a blistered thin film on a soft substrate. When peeled from one end, the advancing peel front triggers reattachment at the blister edge once a critical separation is reached, initiating spontaneous rolling of the film on the substrate. This peel-to-roll transition produces a sharp drop in the measured adhesion force, which then remains constant throughout the rolling phase. Using experiments, scaling analysis, and molecular dynamics simulations, we resolve the contact morphology at the transition and identify the contact length at which rolling initiates. We show that this length arises from interactions between the two contact edges and is independent of the work of adhesion. Once rolling begins, a dynamically imposed dwell time - defined by the rolling length and peel speed - translates contact history into spatial variations in adhesion force, thereby governing the magnitude of the force drop. Together, these results point to a new pathway for generating spatially tunable, heterogeneous adhesion from otherwise homogeneous interfaces.

cond-mat.soft↗

arXiv2025

Mechanics-guided parametric modeling of intranasal spray devices and formulations for targeted drug delivery to the nasopharynx

Improving the efficacy of nasal sprays by enhancing targeted drug delivery to intra-airway tissue sites prone to infection onset is hypothesized to be achievable through an optimization of key device and formulation parameters, such as the sprayed droplet sizes, spray cone angle, and formulation density. This study focuses on the nasopharynx, a primary locus of early viral entry, as the optimal target for intranasal drug delivery. 3D anatomical upper airway geometries reconstructed from high-resolution computed tomography scans were used to numerically evaluate a cone injection approach, with inert particles mimicking the motion of sprayed droplets within an underlying inhaled airflow field. We have considered monodisperse sprayed particles sized between 10 to 50 microns, six densities ranging from 1.0 to 1.5 g/ml for the constituent formulation, and twelve plume angles spanning 1 to 70 degrees subtended by the spray jet at the nozzle position. Large Eddy Simulation-based modeling of the inhaled airflow physics within the anatomical domains was coupled with a Lagrangian particle-tracking framework to derive the drug deposition trend at the nasopharynx. The resulting globally averaged deposition contour map, obtained by interpolating the outcomes for the discrete test parameters, revealed that nasopharyngeal deposition peaked for droplet sizes 25 to 45 microns and plume angles equal to or less than 30 degrees. In addition, the formulation density of 1.0 g/ml yielded the highest mean deposition rate, over the tested range of sprayed particle sizes and plume angles. The findings were experimentally validated through representative physical spray tests conducted in a 3D-printed replica of one of the test geometries and collectively demonstrate that rational optimization of the intranasal spray design is attainable, with substantial enhancement of targeted drug delivery to the nasopharynx.

physics.med-ph↗

arXiv2025

Marangoni swimmer pushing particle raft under 1D confinement

Active matter systems, due to their spontaneous self-propulsion ability, hold potential for future applications in healthcare and environmental sustainability. Marangoni swimmers, a type of synthetic active matter, are a common model system for understanding the underlying physics. Existing studies of the interactions of active matter with passive particles have mostly focused on the modification of the behavior of the passive particles. In contrast, we analyse here experimentally the impact on the self-propulsion of camphor-infused agarose disks (active) of their interactions with floating hollow glass microspheres (passive) within an annular channel. Two distinct regimes are observed: a steady regime with uni-directional motion of the swimmer at low packing fractions (ϕ_{\textrm{ini}} \lesssim 0.45) and an oscillatory regime with to-and-fro motion at higher packing fractions (ϕ_{\textrm{ini}} \gtrsim 0.45). In the former, the swimmer pushes nearly the entire particle raft together with it, like a towing cargo, causing a decrease in swimmer speed with increasing packing fraction due to the additional drag from the particle raft. A simplified force-balance model is finally proposed that captures the experimental trend in swimmer speed reasonably well.

cond-mat.soft↗

arXiv2025

Leaf-inspired rain-energy harvesting device

We study a rain-powered energy-harvesting device inspired by the natural impact of raindrops on leaves. In nature, a raindrop striking a leaf at high speed causes it to deform and vibrate. Inspired by this, our device uses an elastic beam coupled with a piezoelectric material to convert mechanical vibrations from droplet impacts into electrical energy. We conduct experiments to analyze how beam length, droplet impact location, and residual droplet mass affect energy conversion. Our results, supported by a theoretical model, show strong agreement when the beam length exceeds 5 cm. Beyond this length, the energy conversion becomes independent of further increases, suggesting that 5 cm is optimal for maximizing output. To validate practical applicability, we also test the device under real rain conditions, demonstrating consistent performance. Understanding the interplay between raindrop dynamics and energy conversion can guide the design of efficient, scalable rain-powered energy-harvesting systems for environmental applications.

physics.ins-det↗

arXiv2025

Acoustic-Driven Surface Cleaning with Millimeter-Sized Bubbles at Translational Resonance

Traditional surface cleaning methods often suffer from drawbacks such as chemical harshness, potential for surface damage, and high energy consumption. This study investigates an alternative approach: acoustic-driven surface cleaning using millimeter-sized bubbles excited at low, sub-cavitation frequencies. We identify and characterize a distinct translational resonance of these bubbles, occurring at significantly lower frequencies (e.g., 50 Hz for 1.3 mm diameter bubbles) than the Minnaert resonance for a bubble of the same size. Experiments reveal that at this translational resonance, stationary bubbles exhibit amplified lateral swaying, while bubbles sliding on an inclined surface display pronounced "stop-and-go" dynamics. The theoretical model treats the bubble as a forced, damped harmonic oscillator, where surface tension provides the restoring force and the inertia is dominated by the hydrodynamic added mass of the surrounding fluid. It accurately predicts the observed resonant frequency scaling with bubble size ($\propto R_0^{-3/2}$). Cleaning efficacy, assessed using protein-based artificial soil on glass slides, was improved by approximately 90\% when bubbles were driven at their translational resonant frequency compared to off-resonant frequencies or non-acoustic conditions. These findings demonstrate that leveraging translational resonance enhances bubble-induced shear and agitation, offering an effective and sustainable mechanism for surface cleaning.

cond-mat.soft↗

arXiv2025

Droplet Outbursts from Onion Cutting

Cutting onions often leads to tear-inducing aerosol release in kitchen, yet the underlying mechanics of droplet generation remain poorly understood. In this work, we combine custom-developed high-speed particle tracking velocimetry (PTV) and digital image correlation (DIC) to visualize and quantify droplet ejection during onion cutting. We show that droplet formation occurs via a two-stage process: an initial high-speed ejection driven by internal pressurization of the onion first-layer, followed by slower ligament fragmentation in air. By systematically varying blade sharpness and cutting speed, we find that faster or blunter blades significantly increase both the number and energy of ejected droplets. Strain mapping via DIC reveals that the onion's tough epidermis acts as a barrier to fracture, enabling the underlying mesophyll to undergo significant compression before rupture, thereby increasing both the quantity and velocity of the resulting splashed droplets. Developing a scaling model and a simplified bi-layer model with a spring foundation, we experimentally and theoretically demonstrated how sharpened blades lead to not only fewer but also slower droplets. Numerical calculations accurately explain the onion critical fracture force obtained from independent Instron tests. The work highlights the importance of blade sharpening routines to limiting ejected droplets infected with pathogens in the kitchen, which pack additional outburst energy due to vegetables' outer strong casings.

physics.flu-dyn↗

arXiv2025

Fringe around a Beet Slice: Wetting-induced Dimple in a Thin Liquid Film

When a slice of beet is placed on a plate with a thin layer of beet juice, one can observe a clear fringe around the beet, where the color is more translucent than the rest of the juice. The hypotheses in literature were inconsistent and limited, which motivated us to revisit this phenomenon. Using a motorized confocal displacement sensor, we measured the temporal evolution of the liquid surface profile across the fringe. Our findings suggest that a suction flow, induced by the capillary rise of the contact line, causes a dimple - a small concave depression - to form on the liquid surface. While surface tension and gravity tends to smooth out the dimple, viscous drag acts against them if the liquid film is sufficiently thin. Our scaling analysis correctly estimates the dependence of dimple lifetime on liquid properties and film thickness. We also capture the dimple formation dynamics by numerically solving the lubrication equation with the Young-Laplace equation. This work provides a new interpretation for a common phenomenon.

cond-mat.soft↗

arXiv2025

Vortex transition and thermal mixing by pitching a perforated flexible panel

The effective transport of heat and mass is crucial to both industrial applications and physiological processes. Recent research has evaluated the benefit of using flexible reeds for triggering the vortex induced vibration to enhance mixing, as opposed to traditional techniques like rigid blender or static meshes. Inspired by the soft, porous, and moving fish gill lamellae, we proposed a new concept of thermal dispenser that prescribes active pitching motion to the leading edge of an otherwise passively flapping perforated panel. Experimental measurements revealed drastic differences between the steady leaky flow wake behind a statically deflected perforated panel and the periodic shedding wakes with complex vortex structure transitions behind an actuated perforated panel with or without chord-wise flexibility. A semi-empirical simulation of the thermal convection and diffusion takes the experimentally obtained velocity as input and yields the temperature results. Vortex dynamics, Lagrangian coherent structures, and thermal mixing behaviors were analyzed and compared to elucidate the effects of kinematics, perforation, and flexibility on the wake mode transitions, lateral entrainment mixing, and overall heating. Our work provides a foundational understanding of the fluid-structure interactions of perforated bendable panels under active control which has not been described before in the intermediate Reynolds number range. It provides insights for developing an innovative bio-inspired heat or mass dispenser potentially suitable for subtle and small scale applications.

physics.flu-dyn↗

arXiv2024

Resonance and Damping in Drop-Cantilever Interactions

In this study, we investigated the dynamics of a droplet impacting and oscillating a polycarbonate cantilever beam of nine varying lengths. We analyzed the cantilever's damping and vibration frequency in relation to a resonance length, where the frequencies of the droplet and the cantilever are equal. In the pre-resonance length, the beam vibrates at a frequency higher than that of the droplet. Upon reaching resonance, the frequencies of both the droplet and the cantilever align, and the cantilever is out of phase with the oscillation of the droplet's apex. This leads to increased damping rates. At this resonance length, the droplet's force and the direction of the cantilever oppose each other. When the cantilever length exceeds the resonance length, it synchronize more with the droplet apex. This alignment allows the droplet force and the cantilever to work in phase. Our findings provide fundamental insights into the damping effect of droplet impacts on elastic surfaces around resonance.

physics.flu-dyn↗

arXiv2024

Effect of Feathers on Drag in Plunge Diving Birds

This study explores the impact of feathers on the hydrodynamic drag experienced by diving birds, which is critical to their foraging efficiency and survival. Employing a novel experimental approach, we analyzed the kinematics of both feathered and non-feathered projectiles during their transition from air to water using high-speed imaging and an onboard accelerometer. The drag coefficients were determined through two methods: a direct calculation from the acceleration data and a theoretical approach fitted to the observed velocity profiles. Our results indicate that feathers significantly increase the drag force during water entry, with feathered projectiles exhibiting approximately double the drag coefficient of their smooth counterparts. These findings provide new insights into the role of avian feather morphology in diving mechanics and have potential implications for the design of bio-inspired aquatic vehicles in engineering. The study also discusses the biological implications of increased drag due to feathers and suggests that factors such as body shape might play a more critical role in the diving capabilities of birds than previously understood.

physics.flu-dyn↗

arXiv2023

Coherent spore dispersion via drop-leaf interactions

The dispersion of plant pathogens, such as rust spores, is responsible for more than 20% of global yield loss annually, and poses a significant threat to human health. However, the release mechanics of pathogens from flexible plant surfaces into the canopy is not well understood. In this study, we investigated the interplay between leaf elasticity and raindrop momentum, revealing how it induces flow coherence and enhances spore transport with 2-10 times greater energy compared to impacts on stationary surfaces. We observed that a flexible leaf generates vortex dipoles, leading to a super-diffusive stream flow. We then developed a theoretical model that accurately predicted the average air flux from leaf edges and the vortex strength to be proportional the vibration speed of the leaves. With Lagrangian diagnostics, we further revealed the presence of hyperbolic and elliptical coherent structures around fluttering leaves, providing the dynamical description of spore transport. Our model demonstrated that a leaf aspect ratio (length/width) negatively correlates with dispersion, indicating that shorter and wider leaves promote greater pathogen spread. Additionally, we found that leaf rigidity positively correlates with dispersion due to damping effects. These mechanistic insights would help the construction of physically informed analytical models for improve local crop disease management.

physics.flu-dyn↗

arXiv2023

Toroidal cavitation by a snapping popper

Cavitation is a phenomenon in which bubbles form and collapse in liquids due to pressure or temperature changes. Even common tools like a rubber popper can be used to create cavitation at home. As a rubber popper toy slams a solid wall underwater, toroidal cavitation forms. As part of this project, we aim to explain how an elastic shell causes cavitation and to describe the bubble morphology. High-speed imaging reveals that a fast fluid flow between a snapping popper and a solid glass reduces the fluid pressure to cavitate. Cavitation occurs on the popper surface in the form of sheet cavitation. Our study uses two-dimensional Rayleigh-Plesset equations and the energy balance to capture the relationship between the bubble lifetime and the popper deformability. The initial distance between the popper and the wall is an important parameter for determining the cavitation dynamics. Presented results provide a deeper understanding of cavitation mechanics, which involves the interaction between fluid and elastic structure.

physics.flu-dyn↗

arXiv2023

Optimal free-surface pumping by an undulating carpet

Examples of fluid flows driven by undulating boundaries are found in nature across many different length scales. Even though different driving mechanisms have evolved in distinct environments, they perform essentially the same function: directional transport of liquid. Nature-inspired strategies have been adopted in engineered devices to manipulate and direct flow. Here, we demonstrate how an undulating boundary generates large-scale pumping of a thin liquid near the liquid-air interface. Two dimensional traveling waves on the undulator, a canonical strategy to transport fluid at low Reynolds numbers, surprisingly lead to flow rates that depend non-monotonically on the wave speed. Through an asymptotic analysis of the thin-film equations that account for gravity and surface tension, we predict the observed optimal speed that maximizes pumping. Our findings reveal a novel mode of pumping with less energy dissipation near a free surface compared to a rigid boundary.

physics.flu-dyn↗

arXiv2022

Backflipping motion of air bubbles colliding with a tilted wall

Oblique collision of solid particles with surfaces has been a topic of extensive study in Newtonian mechanics, which also explains the motion of bubbles and droplets to some extent. Here, we observe that air bubbles exhibit a backflipping behavior when they collide with a tilted surface. Our experiments reveal that bubbles with radii 0.6-0.7 mm undergo backflipping when they collide with surfaces at an angle of up to 15^o with the strongest backflipping at 3^o. Particle image velocimetry reveals that the backflipping behavior is caused by wake-induced circulation around the bubble, which applies a lift force on the bubble. We develop a theoretical model that incorporates potential flow theory to characterize the circulation caused by the interaction between the bouncing bubble and its wake. The theoretical results are in good agreement with the experiments confirming the key role of the wake-induced lift force in backflipping. Finally, we show that the backflipping behavior of air bubbles can be leveraged for sustainable cleaning of a biological surface coated with a protein solution.

physics.flu-dyn↗