22 results found
Mingarelli L, Keaveny EE, Barnett R, 2018, Vortex lattices in binary mixtures of repulsive superfluids, Physical Review A, Vol: 97, ISSN: 2469-9926
© 2018 American Physical Society. We present an extension of the framework introduced in previous work [L. Mingarelli, E. E. Keaveny, and R. Barnett, J. Phys.: Condens. Matter 28, 285201 (2016)JCOMEL0953-898410.1088/0953-8984/28/28/285201] to treat multicomponent systems, showing that new degrees of freedom are necessary in order to obtain the desired boundary conditions. We then apply this extended framework to the coupled Gross-Pitaevskii equations to investigate the ground states of two-component systems with equal masses, thereby extending previous work in the lowest Landau limit [E. J. Mueller and T.-L. Ho, Phys. Rev. Lett. 88, 180403 (2002)PRLTAO0031-900710.1103/PhysRevLett.88.180403] to arbitrary interactions within Gross-Pitaevskii theory. We show that away from the lowest Landau level limit, the predominant vortex lattice consists of two interlaced triangular lattices. Finally, we derive a linear relation which accurately describes the phase boundaries in the strong interacting regimes.
Schoeller SF, Keaveny EE, 2018, From flagellar undulations to collective motion: predicting the dynamics of sperm suspensions, JOURNAL OF THE ROYAL SOCIETY INTERFACE, Vol: 15, ISSN: 1742-5689
Game SE, Hodes M, Keaveny EE, et al., 2017, Physical mechanisms relevant to flow resistance in textured microchannels, PHYSICAL REVIEW FLUIDS, Vol: 2, ISSN: 2469-990X
Keaveny EE, Brown AEX, 2017, Predicting path from undulations for C. elegans using linear and nonlinear resistive force theory, PHYSICAL BIOLOGY, Vol: 14, ISSN: 1478-3967
Mingarelli L, Keaveny EE, Barnett R, 2016, Simulating infinite vortex lattices in superfluids, Journal of Physics Condensed Matter, Vol: 28, ISSN: 0953-8984
© 2016 IOP Publishing Ltd. We present an efficient framework to numerically treat infinite periodic vortex lattices in rotating superfluids described by the Gross-Pitaevskii theory. The commonly used split-step Fourier (SSF) spectral methods are inapplicable to such systems as the standard Fourier transform does not respect the boundary conditions mandated by the magnetic translation group. We present a generalisation of the SSF method which incorporates the correct boundary conditions by employing the so-called magnetic Fourier transform. We test the method and show that it reduces to known results in the lowest-Landau-level regime. While we focus on rotating scalar superfluids for simplicity, the framework can be naturally extended to treat multicomponent systems and systems under more general 'synthetic' gauge fields.
Delmotte B, Keaveny EE, 2015, Simulating Brownian suspensions with fluctuating hydrodynamics
© 2015 AIP Publishing LLC. Fluctuating hydrodynamics has been successfully combined with several computational methods to rapidly compute the correlated random velocities of Brownian particles. In the overdamped limit where both particle and fluid inertia are ignored, one must also account for a Brownian drift term in order to successfully update the particle positions. In this paper, we present an efficient computational method for the dynamic simulation of Brownian suspensions with fluctuating hydrodynamics that handles both computations and provides a similar approximation as Stokesian Dynamics for dilute and semidilute suspensions. This advancement relies on combining the fluctuating force-coupling method (FCM) with a new midpoint time-integration scheme we refer to as the drifter-corrector (DC). The DC resolves the drift term for fluctuating hydrodynamics-based methods at a minimal computational cost when constraints are imposed on the fluid flow to obtain the stresslet corrections to the particle hydrodynamic interactions. With the DC, this constraint needs only to be imposed once per time step, reducing the simulation cost to nearly that of a completely deterministic simulation. By performing a series of simulations, we show that the DC with fluctuating FCM is an effective and versatile approach as it reproduces both the equilibrium distribution and the evolution of particulate suspensions in periodic as well as bounded domains. In addition, we demonstrate that fluctuating FCM coupled with the DC provides an efficient and accurate method for large-scale dynamic simulation of colloidal dispersions and the study of processes such as colloidal gelation.
Delmotte B, Keaveny EE, Plouraboué F, et al., 2015, Large-scale simulation of steady and time-dependent active suspensions with the force-coupling method, Journal of Computational Physics, Vol: 302, Pages: 524-547, ISSN: 0021-9991
© 2015 Elsevier Inc. We present a new development of the force-coupling method (FCM) to address the accurate simulation of a large number of interacting micro-swimmers. Our approach is based on the squirmer model, which we adapt to the FCM framework, resulting in a method that is suitable for simulating semi-dilute squirmer suspensions. Other effects, such as steric interactions, are considered with our model. We test our method by comparing the velocity field around a single squirmer and the pairwise interactions between two squirmers with exact solutions to the Stokes equations and results given by other numerical methods. We also illustrate our method's ability to describe spheroidal swimmer shapes and biologically-relevant time-dependent swimming gaits. We detail the numerical algorithm used to compute the hydrodynamic coupling between a large collection (104-105) of micro-swimmers. Using this methodology, we investigate the emergence of polar order in a suspension of squirmers and show that for large domains, both the steady-state polar order parameter and the growth rate of instability are independent of system size. These results demonstrate the effectiveness of our approach to achieve near continuum-level results, allowing for better comparison with experimental measurements while complementing and informing continuum models.
Kalogirou A, Keaveny EE, Papageorgiou DT, 2015, An in-depth numerical study of the two-dimensional Kuramoto–Sivashinsky equation, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, Vol: 471, Pages: 20140932-20140932, ISSN: 1364-5021
Keaveny EE, 2014, Fluctuating force-coupling method for simulations of colloidal suspensions, Journal of Computational Physics, Vol: 269, Pages: 61-79, ISSN: 0021-9991
Keaveny EE, Walker SW, Shelley MJ, 2013, Optimization of Chiral Structures for Microscale Propulsion, NANO LETTERS, Vol: 13, Pages: 531-537, ISSN: 1530-6984
Walker SW, Keaveny EE, 2013, Analysis of Shape Optimization for Magnetic Microswimmers, SIAM Journal on Control and Optimization, Vol: 51, Pages: 3093-3126, ISSN: 0363-0129
Majmudar T, Keaveny EE, Zhang J, et al., 2012, Experiments and theory of undulatory locomotion in a simple structured medium., J R Soc Interface, Vol: 9, Pages: 1809-1823
Undulatory locomotion of micro-organisms through geometrically complex, fluidic environments is ubiquitous in nature and requires the organism to negotiate both hydrodynamic effects and geometrical constraints. To understand locomotion through such media, we experimentally investigate swimming of the nematode Caenorhabditis elegans through fluid-filled arrays of micro-pillars and conduct numerical simulations based on a mechanical model of the worm that incorporates hydrodynamic and contact interactions with the lattice. We show that the nematode's path, speed and gait are significantly altered by the presence of the obstacles and depend strongly on lattice spacing. These changes and their dependence on lattice spacing are captured, both qualitatively and quantitatively, by our purely mechanical model. Using the model, we demonstrate that purely mechanical interactions between the swimmer and obstacles can produce complex trajectories, gait changes and velocity fluctuations, yielding some of the life-like dynamics exhibited by the real nematode. Our results show that mechanics, rather than biological sensing and behaviour, can explain some of the observed changes in the worm's locomotory dynamics.
Keaveny EE, Shelley MJ, 2011, Applying a second-kind boundary integral equation for surface tractions in Stokes flow, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 230, Pages: 2141-2159, ISSN: 0021-9991
Keaveny EE, Shelley MJ, 2009, Hydrodynamic mobility of chiral colloidal aggregates, PHYSICAL REVIEW E, Vol: 79, ISSN: 1539-3755
Liu D, Keaveny EE, Maxey MR, et al., 2009, Force-coupling method for flows with ellipsoidal particles, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 228, Pages: 3559-3581, ISSN: 0021-9991
Keaveny EE, Maxey MR, 2008, Modeling the magnetic interactions between paramagnetic beads in magnetorheological fluids, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 227, Pages: 9554-9571, ISSN: 0021-9991
Keaveny EE, Maxey MR, 2008, Interactions between comoving magnetic microswimmers, PHYSICAL REVIEW E, Vol: 77, ISSN: 1539-3755
Keaveny EE, Maxey MR, 2008, Spiral swimming of an artificial micro-swimmer, JOURNAL OF FLUID MECHANICS, Vol: 598, Pages: 293-319, ISSN: 0022-1120
Keaveny EE, Pivkin IV, Maxey M, et al., 2005, A comparative study between dissipative particle dynamics and molecular dynamics for simple- and complex-geometry flows, JOURNAL OF CHEMICAL PHYSICS, Vol: 123, ISSN: 0021-9606
Bao Y, Rachh M, Keaveny E, et al., A fluctuating boundary integral method for Brownian suspensions
We present a fluctuating boundary integral method (FBIM) for overdampedBrownian Dynamics (BD) of two-dimensional periodic suspensions of rigidparticles of complex shape immersed in a Stokes fluid. We develop a novelapproach for generating Brownian displacements that arise in response to thethermal fluctuations in the fluid. Our approach relies on a first-kind boundaryintegral formulation of a mobility problem in which a random surface velocityis prescribed on the particle surface, with zero mean and covarianceproportional to the Green's function for Stokes flow (Stokeslet). This approachyields an algorithm that scales linearly in the number of particles for bothdeterministic and stochastic dynamics, handles particles of complex shape,achieves high order of accuracy, and can be generalized to three dimensions andother boundary conditions. We show that Brownian displacements generated by ourmethod obey the discrete fluctuation-dissipation balance relation (DFDB). Basedon a recently-developed Positively Split Ewald method [A. M. Fiore, F. BalboaUsabiaga, A. Donev and J. W. Swan, J. Chem. Phys., 146, 124116, 2017],near-field contributions to the Brownian displacements are efficientlyapproximated by iterative methods in real space, while far-field contributionsare rapidly generated by fast Fourier-space methods based on fluctuatinghydrodynamics. FBIM provides the key ingredient for time integration of theoverdamped Langevin equations for Brownian suspensions of rigid particles. Wedemonstrate that FBIM obeys DFDB by performing equilibrium BD simulations ofsuspensions of starfish-shaped bodies using a random finite difference temporalintegrator.
Delmotte B, Keaveny EE, Climent E, et al., Simulations of Brownian tracer transport in squirmer suspensions
In addition to enabling movement towards environments with favourable livingconditions, swimming by microorganisms has also been linked to enhanced mixingand improved nutrient uptake by their populations. Experimental studies haveshown that Brownian tracer particles exhibit enhanced diffusion due to theswimmers, while theoretical models have linked this increase in diffusion tothe flows generated by the swimming microorganisms, as well as collisions withthe swimmers. In this study, we perform detailed simulations based on theforce-coupling method and its recent extensions to the swimming and Brownianparticles to examine tracer displacements and effective tracer diffusivity insquirmer suspensions. By isolating effects such as hydrodynamic or stericinteractions, we provide physical insight into experimental measurements of thetracer displacement distribution. In addition, we extend results to thesemi-dilute regime where the swimmer-swimmer interactions affect tracertransport and the effective tracer diffusivity no longer scales linearly withthe swimmer volume fraction.
Kamal A, Keaveny EE, Enhanced locomotion, effective diffusion, and trapping of undulatory micro-swimmers in heterogeneous environments
Swimming cells and microorganisms must often move though complex fluids thatcontain an immersed microstructure such as polymer molecules, or filaments. Inmany important biological processes, such as mammalian reproduction andbacterial infection, the size of the immersed microstructure is comparable tothat of the swimming cells. This leads to discrete swimmer-microstructureinteractions that alter the swimmer's path and speed. In this paper, we use acombination of detailed simulation and data-driven stochastic models to examinethe motion of a planar undulatory swimmer in an environment of sphericalobstacles tethered via linear springs to random points in the plane oflocomotion. We find that depending on environmental parameters, theinteractions with the obstacles can both enhance swimming speeds, as well asprevent the swimmer from moving at all. We also show how the discreteinteractions produce translational and angular velocity fluctuations that overtime lead to diffusive behaviour primarily due to the coupling of swimming androtational diffusion. Our results demonstrate that directswimmer-microstructure interactions can produce changes in swimmer motion thatmay have important implications to the spreading of cell populations in, or thetrapping of harmful pathogens by complex fluids.
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