arXiv subjects

L. Mahadevan

Publications and source records attributed to L. Mahadevan.

170 records · Page 10Linked to original sources

arXiv2004

Soft lubrication

We consider some basic principles of fluid-induced lubrication at soft interfaces. In particular, we show how the presence of a soft substrate leads to an increase in the physical separation between surfaces sliding past each other. By considering the model problem of a symmetric non-conforming contact moving tangentially to a thin elastic layer, we determine the normal force in the small and large deflection limit, and show that there is an optimal combination of material and geometric properties which maximizes the normal force. Our results can be generalized to a variety of other geometries which show the same qualitative behavior. Thus they are relevant in the elastohydrodynamic lubrication of soft elastic and poroelastic gels and shells, and in the context of bio-lubrication in cartilaginous joints.

cond-mat.soft↗

arXiv2004

Dynamics of poroelastic filaments

We investigate the stability and geometrically non-linear dynamics of slender rods made of a linear isotropic poroelastic material. Dimensional reduction leads to the evolution equation for the shape of the poroelastica where, in addition to the usual terms for the bending of an elastic rod, we find a term that arises from fluid-solid interaction. Using the poroelastica equation as a starting point, we consider the load controlled and displacement controlled planar buckling of a slender rod, as well as the closely related instabilities of a rod subject to twisting moments and compression when embedded in an elastic medium. This work has applications to the active and passive mechanics of thin filaments and sheets made from gels, plant organs such as stems, roots and leaves, sponges, cartilage layers and bones.

cond-mat.soft↗

arXiv2004

Peeling from a patterned thin elastic film

Inspired by the observation that many naturally occurring adhesives arise as textured thin films, we consider the displacement controlled peeling of a flexible plate from an incision-patterned thin adhesive elastic layer. We find that crack initiation from an incision on the film occurs at a load much higher than that required to propagate it on a smooth adhesive surface; multiple incisions thus cause the crack to propagate intermittently. Microscopically, this mode of crack initiation and propagation in geometrically confined thin adhesive films is related to the nucleation of cavitation bubbles behind the incision which must grow and coalesce before a viable crack propagates. Our theoretical analysis allows us to rationalize these experimental observations qualitatively and quantitatively and suggests a simple design criterion for increasing the interfacial fracture toughness of adhesive films.

cond-mat.soft↗

arXiv2004

Kinks, rings, and rackets in filamentous structures

Carbon nanotubes and biological filaments each spontaneously assemble into kinked helices, rings, and "tennis racket" shapes due to competition between elastic and interfacial effects. We show that the slender geometry is a more important determinant of the morphology than any molecular details. Our mesoscopic continuum theory is capable of quantifying observations of these structures, and is suggestive of their occurrence in other filamentous assemblies as well.

cond-mat.soft↗

arXiv2004

Flutter of a Flag

We give an explanation for the onset of wind-induced flutter in a flag. Our theory accounts for the various physical mechanisms at work: the finite length and the small but finite bending stiffness of the flag, the unsteadiness of the flow, the added mass effect and vortex shedding from the trailing edge. Our analysis allows us to predict a critical speed for the onset of flapping as well as the frequency of flapping. We find that in a particular limit corresponding to a low density fluid flowing over a soft high density flag, the flapping instability is akin to a resonance between the mode of oscillation of a rigid pivoted airfoil in a flow and a hinged-free elastic filament vibrating in its lowest mode.

physics.flu-dyn↗

arXiv2003

Modeling DNA loops using the theory of elasticity

A versatile approach to modeling the conformations and energetics of DNA loops is presented. The model is based on the classical theory of elasticity, modified to describe the intrinsic twist and curvature of DNA, the DNA bending anisotropy, and electrostatic properties. All the model parameters are considered to be functions of the loop arclength, so that the DNA sequence-specific properties can be modeled. The model is applied to the test case study of a DNA loop clamped by the lac repressor protein. Several topologically different conformations are predicted for various lengths of the loop. The dependence of the predicted conformations on the parameters of the problem is systematically investigated. Extensions of the presented model and the scope of the model's applicability, including multi-scale simulations of protein-DNA complexes and building all-atom structures on the basis of the model, are discussed.

physics.bio-ph↗

arXiv2001

Shocks in sand flowing in a silo

We study the formation of shocks on the surface of a granular material draining through an orifice at the bottom of a quasi-two dimensional silo. At high flow rates, the surface is observed to deviate strongly from a smooth linear inclined profile giving way to a sharp discontinuity in the height of the surface near the bottom of the incline, the typical response of a choking flow such as encountered in a hydraulic jump in a Newtonian fluid like water. We present experimental results that characterize the conditions for the existence of such a jump, describe its structure and give an explanation for its occurrence.

cond-mat.soft↗

arXiv2000

Rippling Instability of a Collapsing Bubble

When a bubble of air rises to the top of a highly viscous liquid, it forms a dome-shaped protuberance on the free surface. Unlike a soap bubble, it bursts so slowly as to collapse under its own weight simultaneously, and folds into a striking wavy structure. This rippling effect occurs in fact for both elastic and viscous sheets, and a theory for its onset is formulated. The growth of the corrugation is governed by the competition between gravitational and bending (shearing) forces and is exhibited for a range of densities, stiffnesses (viscosities), and sizes -- a result which arises less from dynamics than from geometry, suggesting a wide validity. A quantitative expression for the number of ripples is presented, together with experimental results which are in agreement with the theoretical predictions.

cond-mat.soft↗