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Simulation of collective phenomena in microswimmer suspensions

Bardfalvy, Dora LU (2020)
Abstract
Collective motion is ubiquitous in biological and synthetic systems across many
length- and timescales. On the macroscopic scale, examples include schools of fish, herds of sheep and flocks of birds. On the microscopic scale, bacteria, algae and synthetic self-propelled particles exhibit a range of collective phenomena. In suspensions of swimming bacteria, collective motion is often caused by hydrodynamic interactions between the swimmers, and is manifested as long-ranged chaotic flows, dubbed active turbulence. In this work, we study collective motion in simplified models of bacterial and algal suspensions with particle-resolved lattice Boltzmann simulations. Using an
extended force dipole as a minimal model for a microswimmer, we... (More)
Collective motion is ubiquitous in biological and synthetic systems across many
length- and timescales. On the macroscopic scale, examples include schools of fish, herds of sheep and flocks of birds. On the microscopic scale, bacteria, algae and synthetic self-propelled particles exhibit a range of collective phenomena. In suspensions of swimming bacteria, collective motion is often caused by hydrodynamic interactions between the swimmers, and is manifested as long-ranged chaotic flows, dubbed active turbulence. In this work, we study collective motion in simplified models of bacterial and algal suspensions with particle-resolved lattice Boltzmann simulations. Using an
extended force dipole as a minimal model for a microswimmer, we have been able to study large systems, containing up to 3 × 10^6 particles, and to capture information about large-scale collective behaviours. We have studied four separate aspects of collective motion in microswimmer suspensions. First, we performed unprecedentedly large simulations of 3-dimensional active suspensions to test predictions from kinetic theory about the transition to active turbulence and characterize the ensuing turbulent state. The focus was then turned to the effects of swimming velocity on the transition to active turbulence of pusher suspensions. In nature, front- and rearactuated microswimmers (so called pushers and pullers, respectively) coexist, which motivated us to study how the presence of pullers in the suspension changes the collective behaviour of pushers. Finally, motivated by the fact that most experiments are performed in 2-dimensional geometries, we also investigated and characterized the collective phenomena in a quasi-2-dimensional system, finding important qualitative differences compared to unbounded suspensions. (Less)
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author
supervisor
opponent
  • Professor Gompper, Gerhard, Theoretical Soft Matter and Biophysics at "Institute of Complex Systems" and "Institute for Advanced Simulation" Forschungszentrum Jülich
organization
publishing date
type
Thesis
publication status
published
subject
pages
108 pages
publisher
Lund University, Faculty of Science
defense location
Kemicentrum sal C, Sölvegatan 39, Lund Join via zoom or youtube: https://lu-se.zoom.us/j/61710647813 / https://www.youtube.com/channel/UCnuD6zyuQ4vwg9zSBeTQoQQ/featured
defense date
2020-12-17 09:15:00
ISBN
978-91-7422-770-3
978-91-7422-771-0
language
English
LU publication?
yes
id
337de4f4-c464-4ab1-8dd7-d2271156658a
date added to LUP
2020-11-20 09:43:44
date last changed
2020-12-03 10:53:04
@phdthesis{337de4f4-c464-4ab1-8dd7-d2271156658a,
  abstract     = {{Collective motion is ubiquitous in biological and synthetic systems across many<br/>length- and timescales. On the macroscopic scale, examples include schools of fish, herds of sheep and flocks of birds. On the microscopic scale, bacteria, algae and synthetic self-propelled particles exhibit a range of collective phenomena. In suspensions of swimming bacteria, collective motion is often caused by hydrodynamic interactions between the swimmers, and is manifested as long-ranged chaotic flows, dubbed active turbulence. In this work, we study collective motion in simplified models of bacterial and algal suspensions with particle-resolved lattice Boltzmann simulations. Using an<br/>extended force dipole as a minimal model for a microswimmer, we have been able to study large systems, containing up to 3 × 10^6 particles, and to capture information about large-scale collective behaviours. We have studied four separate aspects of collective motion in microswimmer suspensions. First, we performed unprecedentedly large simulations of 3-dimensional active suspensions to test predictions from kinetic theory about the transition to active turbulence and characterize the ensuing turbulent state. The focus was then turned to the effects of swimming velocity on the transition to active turbulence of pusher suspensions. In nature, front- and rearactuated microswimmers (so called pushers and pullers, respectively) coexist, which motivated us to study how the presence of pullers in the suspension changes the collective behaviour of pushers. Finally, motivated by the fact that most experiments are performed in 2-dimensional geometries, we also investigated and characterized the collective phenomena in a quasi-2-dimensional system, finding important qualitative differences compared to unbounded suspensions.}},
  author       = {{Bardfalvy, Dora}},
  isbn         = {{978-91-7422-770-3}},
  language     = {{eng}},
  publisher    = {{Lund University, Faculty of Science}},
  school       = {{Lund University}},
  title        = {{Simulation of collective phenomena in microswimmer suspensions}},
  url          = {{https://lup.lub.lu.se/search/files/87066002/Dora_kappa_part.pdf}},
  year         = {{2020}},
}