arXiv subjects

Timothy A Westwood

Publications and source records attributed to Timothy A Westwood.

3 recordsLinked to original sources

arXiv2026

Emergent coordination and propulsion of a model spherical ciliate

A longstanding challenge in biofluid dynamics research is a mechanistic understanding of the coordinated movement of motile cilia and its resulting ability to facilitate fluid transport. In this study, we develop numerical techniques to simultaneously compute the emergent coordination of and propulsion by filamentous model cilia covering the surface of a sphere. To accomplish this, we develop what we refer to as the filament oscillator model, in which each cilium has two dynamic degrees of freedom: a phase variable that maps to a specific shape in a prescribed sequence, and an angle that describes the overall orientation of the sequence. By varying a parameter related to cilium stiffness, we show that there is bistability between symplectic-like and diaplectic metachronal waves, provided that the stiffness is sufficiently low. Above the critical stiffness, only diaplectic waves emerge. Further, we analyse the propulsive capabilities and flow fields of the two emergent states, showing that diaplectic waves provide more efficient propulsion due to their shorter wavelengths. In addition, we examine how introducing beat-plane tilt leads to ciliate rotation while maintaining nearly identical emergent states and comparable swimming speeds.

physics.flu-dyn↗

arXiv2021

Coordinated motion of active filaments on spherical surfaces

Coordinated cilia are used throughout the natural world for micronscale fluid transport. They are often modelled with regular filament arrays on fixed, planar surfaces. Here, we simulate hundreds of interacting active filaments on spherical surfaces, where defects in the cilia displacement field must be present. We see synchronised beating towards or about two defects for spheres held fixed. Defects alter filament beating which causes the sphere to move once released. This motion feeds back to the filaments resulting in a whirling state with metachronal behaviour along the equator.

physics.flu-dyn↗

arXiv2021

A generalised drift-correcting time integration scheme for Brownian suspensions of rigid particles with arbitrary shape

The efficient computation of the overdamped, random motion of micron and nanometre scale particles in a viscous fluid requires novel methods to obtain the hydrodynamic interactions, random displacements and Brownian drift at minimal cost. Capturing Brownian drift is done most efficiently through a judiciously constructed time-integration scheme that automatically accounts for its contribution to particle motion. In this paper, we present a generalised drift-correcting (gDC) scheme that accounts for Brownian drift for suspensions of rigid particles with arbitrary shape. The scheme seamlessly integrates with fast methods for computing the hydrodynamic interactions and random increments and requires a single full mobility solve per time-step. As a result, the gDC provides increased computational efficiency when used in conjunction with grid-based methods that employ fluctuating hydrodynamics to obtain the random increments. Further, for these methods the additional computations that the scheme requires occur at the level of individual particles, and hence lend themselves naturally to parallel computation. We perform a series of simulations that demonstrate the gDC obtains similar levels of accuracy as compared with the existing state-of-the-art. In addition, these simulations illustrate the gDC's applicability to a wide array of relevant problems involving Brownian suspensions of non-spherical particles, such as the structure of liquid crystals and the rheology of complex fluids.

physics.comp-ph↗