Abstract : The minisymposium focuses on computational methods for low (zero)
Reynolds number flows, where viscous effects dominate. Due to the
linearity of the fluid governing equations at zero Reynolds number,
considerable progress in numerical methods has been made to understand
the fluid-structure interactions at this small scale. This minisymposium
will cover recent developments in numerical methods for modeling and
simulating systems involving small immersed structures and suspensions
of rigid and deformable particles, such as cilia, capsules,
microorganisms, actin filaments in the cell cytoskeleton, catalytic
colloids, electrolyte solutions in microfluidics or batteries, and
others.
[04825] Cross-stream migration of vesicles in vortical flows
Format : Online Talk on Zoom
Author(s) :
Gokberk Kabacaoglu (Bilkent University )
Abstract : We use numerical simulations to systematically investigate the vesicle dynamics in two-dimensional (2D) Taylor-Green vortex flow in the absence of inertial forces. We study the effects of two parameters on the vesicle dynamics: the ratio of the interior fluid viscosity to that of the exterior one and the ratio of the shear forces on the vesicle to the membrane stiffness (characterized by the capillary number).
[04962] Confinement effects on a suspension of squirmers
Format : Talk at Waseda University
Author(s) :
Yuan Nan Young (New Jersey Institute of Technology)
Bryan Quaife (Florida State University)
Henry Shum (University of Waterloo)
Sangwoo Shin (University at Buffalo)
Abstract : Using a model recently developed for the many-body hydrodynamics of amphiphilic JPs suspended in a viscous background flow (JFM, 941, 2022), we investigate how various swimming dynamics of squirmers that interact with the solvent through a hydrophobic potential (HP) may vary from tuning the hydrophobicity/hydrophilicity of the squirmers. In the absence of such HP, several configurations of squirmers are known to be stable for squirmers to swim together. We numerically investigate how HP may help stabilize/destabilize these configurations. These results are further compared with the Vicek model for schooling and flocking of swimmers. We further investigate the effects of confinement and how active control of HP may be used for a cluster of swimmers to swim in specific fashions, indicating that the squirmers may actively change their surface properties so the collective of squirmers may swim in certain ways.
[04477] Hydrodynamics and rheology of fluctuating, semiflexible, inextensible, and slender filaments in Stokes flow
Format : Talk at Waseda University
Author(s) :
Aleksandar Donev (Courant Institute, New York University)
Abstract : Every animal cell is filled with a cytoskeleton, a dynamic gel made of inextensible filaments / bio-polymers, such as microtubules, actin filaments, and intermediate filaments, all suspended in a viscous fluid. Similar suspensions of elastic filaments or polymers are widely used in materials processing. Numerical simulation of such gels is challenging because the filament aspect ratios are very large.
We have recently developed new methods for rapidly computing the dynamics of non-Brownian and Brownian inextensible slender filaments in periodically-sheared Stokes flow. We apply our formulation to a permanently and dynamically cross-linked actin mesh in a background oscillatory shear flow. We find that nonlocal hydrodynamics can change the visco-elastic moduli by as much as 40% at certain frequencies, especially in partially bundled networks.
I will focus on accounting for bending thermal fluctuations of the filaments by first establishing a mathematical formulation and numerical methods for simulating the dynamics of stiff but not rigid Brownian fibers in Stokes flow. I will emphasize open questions for the community such as whether there is a continuum limit of the Brownian contribution to the stress tensor from the filaments.
[04813] Numerical simulations of swimming with multiple bacterial flagella
Format : Talk at Waseda University
Author(s) :
Henry Shum (University of Waterloo)
Vahid Nourian (University of Waterloo)
Abstract : To understand some of the consequences of different morphologies of flagellated bacteria, we numerically simulate their swimming motion using a boundary element-regularized Stokeslet method. The flagella are modelled as discretized Kirchhoff rods. We apply our model to: (i) bacteria with a pulling flagellum in front and a pushing flagellum at the rear, and (ii) bacteria with three pushing flagella. Bacterial hook flexibility and flagellar placement are important considerations, especially near a no-slip wall.
[05143] Accurate close interactions in Stokes flow using coarse grids
Format : Talk at Waseda University
Author(s) :
Anna Broms (KTH Royal Institute of Technology)
Alex Barnett
Anna-Karin Tornberg (KTH Royal Institute of Technology)
Abstract : With the aim of controlling the accuracy in near-contacts of rigid particles in viscous flows with a computationally cheap method, we introduce a singularity-free technique that combines the method of fundamental solutions and the method of images. Sources on inner proxi boundaries are complemented as needed by a small set of extra singularities at locations obtained by considering an image system. Results are compared to a well-resolved boundary integral equation method.
[04881] Bounds on particle configurations in an active suspension
Format : Talk at Waseda University
Author(s) :
Scott Weady (Flatiron Institute)
Abstract : We present bounds on orientational order parameters in the Doi-Saintillan-Shelley kinetic theory of active suspensions. Using the energy method, we show isotropic suspensions are nonlinearly stable for sufficiently low activity. A similar approach admits nontrivial bounds on time averages of order parameters for all levels of activity that are consistent with nonlinear simulations. This work highlights the organizing role of activity in particle suspensions and places precise limits on how organized such systems can be.
[04858] Drag force on spherical particles trapped at a liquid interface
Format : Talk at Waseda University
Author(s) :
Zhi Zhou (Northwestern University)
Petia M Vlahovska (Northwestern University)
Michael J Miksis (Northwestern University)
Abstract : Here we present a combined asymptotic and numerical investigation of the fluid motion past spherical particles attached
to a deformable interface undergoing uniform creeping flows in the limit of small Capillary number and small
deviation of the contact angle from 90 degrees. The drag and torque coefficients are computed as
a function of the contact angle, the viscosity ratio, the Bond number, the slip coefficient along the particle surface, and the distance between two particles.
[05148] Bacterial collective motion and spread in porous media
Format : Online Talk on Zoom
Author(s) :
Yasser Almoteri (New Jersey Institute of Technology)
Enkeleida Lushi (New Jersey Institute of Technology)
Abstract : We investigate through modeling, analysis and nonlinear simulations, the motion of micro-swimmers in fluids with resistance, which approximates porous wet media. We use a continuum model to describe the dynamics of bacteria each performing run-and-tumble motions, coupled to the dynamics of the immersing fluid modeled by the Stokes-Brinkman equation with an added active stress. The linear stability of the uniform isotropic state reveals that the Brinkman resistance weakens or fully suppresses the chaotic motion of the bacterial suspension. Simulations of the full nonlinear PDE system confirm the analytical results. We discuss how the fluid resistance inhibits the spread of bacteria, and its interplay with auto-chemotactic interactions and food chasing give rise to non-trivial dynamics. Last, we discuss simulations of the coupled motion of many individually-traced micro-swimmers in Brinkman flows.
[02866] Soft magnetic microrobots move more efficiently with a flat tire
Format : Talk at Waseda University
Author(s) :
Brennan Sprinkle (Colorado School of Mines)
Yan Gao (Colorado School of Mines)
David Marr (Colorado School of Mines)
Ning Wu (Colorado School of Mines)
Abstract : I'll discuss the rolling of active Pickering emulsions - small droplets (~10-100 um) covered in smaller (~1um) active particles that can be rolled along a surface by an external, AC magnetic field. Curiously, these droplets roll much faster and more efficiently when they have a larger area of contact with the confining surface. I'll describe experiments done by collaborators to validate this behavior and numerical simulations that I developed to quantify it.
[05297] Bacterial swarming above surfaces with friction
Format : Talk at Waseda University
Author(s) :
Enkeleida Lushi (New Jersey Institute of Technology)
Abstract : We present a mathematical model and numerical simulations for the collective dynamics of swimming bacteria above surfaces with and without friction. The bacteria are modeled as self-propelling force-dipole ellipsoids that interact with each-other and the surface through hydrodynamics and direct collisions. The conditions for when the surface friction is sufficient to render an individual swimmer immobile are determined, as well as the swimmer density needed to collectively generate fluid flow disturbances that are strong enough to help regain mobility. Analysis of the characteristics of the emerging collective dynamics reveals a phase diagram of qualitatively distinct regimes for varying swimmer shape and population densities. Lastly, we compare our findings with recent experimental results of swarming Bacillus subtilis mutants.
