arXiv subjects

Amit Dawadi

Publications and source records attributed to Amit Dawadi.

3 recordsLinked to original sources

arXiv2025

Bundling architecture in elastic filaments with applied twist

We investigate the formation of helical multifilament bundles and the torque required to achieve them as a function of applied twist. Hyperelastic filaments with circular cross sections are mounted parallel in a uniform circle onto end-clamps that can move along the twist axis depending on the applied axial load. With increasing twist, the filaments describe a hyperbolic hyperboloid surface before coming into contact in a circle, and then packing in a tight helical bundle in the center with increasing twist. While the bundle appears ordered for sufficiently small number of filaments, they are disordered for large enough number of filaments and applied twist. We reveal with x-ray tomography, that the packing of the filaments becomes disordered following a radial-instability which leads to a decrease in bundle radius, and migration of filaments relative to each other in the bundle. Nonetheless, the helical angle of the filaments in the bundle are found to be essentially constant, resulting in inclination angles which increase with distance from axis of rotation. We develop energy minimization analysis to capture the observed variations in bundle length and torque as a function of number of filaments considering the neo-Hookean nature of the filaments. We show that the bundle geometry and the applied load can be used to describe the non-linear torque profile measured as a function of twist angle.

cond-mat.soft↗

arXiv2024

Self-Propulsion of floating ice blocks caused by melting in water

We show that floating ice blocks with asymmetric shapes can self-propel with significant speeds due to buoyancy driven currents caused by melting. In water baths with temperatures between $10\,^\circ$C and $30\,^\circ$C, model right-angle ice wedges are found to move in the direction opposite to the gravity current which descends along the longest inclined side. We describe the measured speed as a function of the length and angle of the inclined side, and the temperature of the bath in terms of a propulsion model which incorporates the cooling of the surrounding fluid by the melting of ice. The heat pulled from the surrounding liquid by the melting ice block generates a thermal convection flow, leading to momentum exchange and to a net propulsion force. The translation velocity is explained by balancing the propulsion force by drag. We further show that the ice block moves robustly in a saltwater bath with ocean-like salinity and maintains the same direction of motion as in freshwater. A simplified model is further developed to describe the propulsion of asymmetric ice blocks in saltwater, incorporating the effects of rising meltwater and the sinking of the surrounding bath water due to cooling. For sufficiently large temperature, we find that the cooling-induced sinking flow generates a stronger force than the upward flow from the meltwater. Consequently, the net propulsion force is in the same direction and nearly the same magnitude as that observed in freshwater. These findings suggest that melting-driven propulsion may be relevant to the motion of icebergs in sufficiently warm oceanic environments.

physics.flu-dyn↗

arXiv2024

Memory in cyclically crumpled sheets

We investigate the crumpling of a sheet as it is repeatedly crushed onto itself by rolling it into a cylinder and twisting it axially while allowing the end-to-end length to evolve freely. As deduced from its plastic deformations, the sheet creases and collapses into structures which repeat and sharpen over hundreds of cycles to a remarkable degree before forming new configurations. The observed metastablilty increases with applied cycles leading to recurrent structures over a significant range of loading, but reconfigurations can continue to occur for large enough loading as the creases develop tears. The evolution of the sheet structure as measured by the mean curvature and the total crease length is found to increase logarithmically with cycle number with a rate which increases with degree of compression. We explain the overall extent of creasing using flat folding models, and show the logarithmic growth as being a consequence of individual creases becoming sharper with number of folding cycles, and due to the bifurcation in the curvature field leading to the formation of new creases and folding pathways. Thus, we show that elastoplastic sheets can follow complex folding pathways to form convergent structures after a sufficiently large number of training cycles provided material fatigue remains unimportant.

cond-mat.soft↗