arXiv subjects

P. R. Onck

Publications and source records attributed to P. R. Onck.

5 recordsLinked to original sources

arXiv2024

Emergent dynamics and spatiotemporal patterns in soft robotic swarms

The collective swimming of soft robots in an infinite viscous fluid is an emergent phenomenon due to the non-reciprocal hydrodynamic interactions between individual swimmers. These physical interactions give rise to unique spatiotemporal patterns and unusual swimming trajectories that are often difficult to predict due to the two-way fully coupled nature of the strong fluid-structure interaction at a thermodynamic state that is far from equilibrium. Until now, robotic swarms have mostly been studied for rigid swimmers in two-dimensional settings. Here we study the emergence of three-dimensional spatiotemporal patterns of helical magnetically actuated soft-robotic swimmers by systematically studying the effect of different initial configurations. Our results show that swimmers with variations in initial positions in the swimming direction are attracted to each other, while swimmers with variations in lateral positions repel each other, eventually converging to a state in which all swimmers concentrate in one lateral plane drifting radially outward.

physics.flu-dyn↗

arXiv2009

Nature-inspired microfluidic propulsion using magnetic actuation

In this work we mimic the efficient propulsion mechanism of natural cilia by magnetically actuating thin films in a cyclic but non-reciprocating manner. By simultaneously solving the elasto-dynamic, magnetostatic and fluid mechanics equations, we show that the amount of fluid propelled is proportional to the area swept by the cilia. By using the intricate interplay between film magnetization and applied field we are able to generate a pronounced asymmetry and associated flow. We delineate the functional response of the system in terms of three dimensionless parameters that capture the relative contribution of elastic, inertial, viscous and magnetic forces.

physics.flu-dyn↗

arXiv2009

Magnetically-actuated artificial cilia for microfluidic propulsion

Natural cilia are hair-like microtubule-based structures that are able to move fluid at low Reynolds number through asymmetric motion. In this paper we follow a biomimetic approach to design artificial cilia lining the inner surface of microfluidic channels with the goal to propel fluid. The artificial cilia consist of polymer films filled with magnetic nanoparticles. The asymmetric, non-reciprocating motion is generated by tuning an external magnetic field. To obtain the magnetic field and associated magnetization local to the cilia we solve the Maxwell equations, from which the magnetic torques can be deduced. To obtain the ciliary motion we solve the dynamic equations of motion which are then fully coupled to the fluid dynamic equations that describe fluid flow around the cilia. By doing so we show that by properly tuning the applied magnetic field, asymmetric ciliary motion can be generated that is able to propel fluid in a microchannel. The results are presented in terms of three dimensionless parameters that fully delineate the asymmetry and cycle time as a function of the relative contribution of elastic, inertial, magnetic and viscous fluid forces.

physics.flu-dyn↗

arXiv2006

Stiffening of semiflexible biopolymers and cross-linked networks

We study the mechanical stiffening behavior in two-dimensional (2D) cross-linked networks of semiflexible biopolymer filaments under simple shear. Filamental constituents immersed in a fluid undergo thermally excited bending motions. Pulling out these undulations results in an increase in the axial stiffness. We analyze this stiffening behavior of 2D semiflexible filaments in detail: we first investigate the average, {static} force-extension relation by considering the initially present undulated configuration that is pulled straight under a tensile force, and compare this result with the average response in which undulation dynamics is allowed during pulling, as derived earlier by MacKintosh and coworkers. We will show that the resulting mechanical behavior is rather similar, but with the axial stiffness being a factor 2 to 4 larger in the dynamic model. Furthermore, we study the stretching contribution in case of extensible filaments and show that, for 2D filaments, the mechanical response is dominated by {enthalpic} stretching. Based on the single-filament mechanics, we develop a 2D analytical model describing the mechanical behavior of biopolymer networks under simple shear, adopting the affine deformation assumption. These results are compared with discrete, finite-element (FE) calculations of a network consisting of semiflexible filaments. The FE calculations show that local, nonaffine filament reorientations occur that induce a transition from a bending-dominated response at small strains to a stretching-dominated response at larger strains. Stiffening in biopolymer networks thus results from a combination of stiffening in individual filaments and changes in the network topography.

physics.bio-ph↗

arXiv2005

The origin of stiffening in cross-linked semiflexible networks

Strain stiffening of protein networks is explored by means of a finite strain analysis of a two-dimensional network model of cross-linked semiflexible filaments. The results show that stiffening is caused by non-affine network rearrangements that govern a transition from a bending dominated response at small strains to a stretching dominated response at large strains. Thermally-induced filament undulations only have a minor effect; they merely postpone the transition.

cond-mat.soft↗