Benjamin J. Walker

University College London
1851 Research Fellow, Department of Mathematics
benjamin.walker@ucl.ac.uk

Multiscale methods and microswimmer models

The effects of rapid yawing on simple swimmer models and planar Jeffery's orbits.
Physical Review Fluids

If we take a minimal model of a microswimmer and include the effects of rapid side-to-side yawing, does the prediction of the model change? Here, we find out through a simple multiple-scales analysis. Image: the effective hydrodynamic shapes of yawing spheroids.

Canonical orbits for rapidly deforming planar microswimmers in shear flow.
Physical Review Fluids

Suppose we have a swimmer that moves by rapidly changing its shape in the plane of a shear flow. Here, we show that, on average, the shape-deforming swimmer undergoes the classical orbit dynamics studied by G. B. Jeffery a century ago. Image: an example shape-changing swimmer being rotated by a background flow.

Emergent rheotaxis of shape-changing swimmers in Poiseuille flow.
JFM Rapids and Focus on Fluids

Given a simple model of a swimmer being carried by the flow in a pipe, can we deduce its long-term behaviour? Here, we avoid numerical simulation and analytically determine the eventual behaviour of the swimmer through the computation of a single swimmer-dependent constant. Image: closed trajectories in semi-periodic phase-space (angle-position).

Systematic parameterisations of minimal models of microswimming.
arXiv

When we use the simplest microswimmer models to develop intuition for complex, rapidly evolving swimmers, do we have to be careful with our choice of effective parameters? Here, through minimally complex examples and simple multi-timescale analysis, we see that we must be careful even when only seeking qualitative agreement. Image: phase portrait of the interaction of two freely rotating dipoles (angle-angle).

Research interests

Solid mechanics and biological growth

Exploration of the role of solid mechanics in biology, from influencing the growth of tumours to controlling the development of vascular networks.

Filament mechanics

Efficient simulation of elastohydrodynamics in 2D and 3D, exploring the role and regulation of active moments in eukaryotic flagella, in addition to the responses of filaments to flow.

Microscale swimming

Investigation into the low Reynolds number swimming of flagellates, such as the boundary response of large-bodied Leishmania and the interactions between nearby spermatozoa.

Flagellar analysis

Automated processing and identification of flagella from videomicroscopy, enabling population-level waveform analysis without requiring costly researcher input. Publication and ImageJ code for flagella capture freely available here.

Slender-body theory

Incorporation of non-uniform body shapes and curvatures into slender-body theories via asymptotic methods, enabling simple and rapid flow field computation and further theoretical study using regularised singularities.

Publications

Google Scholar

  1. B. J. Walker, K. Ishimoto, E. A. Gaffney. Multi-timescale averaging for minimal microswimmer models: boundaries and interactions. arXiv.
  2. B. J. Walker, G. L. Celora, A. Goriely, D. E. Moulton, H. M. Byrne. Towards a minimal admissible model of solid tumour spheroid growth. arXiv.
  3. A. L. Krause, E. A. Gaffney, B. J. Walker. Concentration-dependent domain evolution in reaction-diffusion systems. arXiv.
  4. B. J. Walker, K. Ishimoto, E. A. Gaffney. A hydrodynamic slender-body theory for local rotation at zero Reynolds number. arXiv.
  5. B. J. Walker, A. T. Dawes (2022). Modelling mechanically dominated vasculature development. Frontiers in Systems Biology. Full text.
  6. B. J. Walker, K. Ishimoto, C. Moreau, E. A. Gaffney, M. P. Dalwadi (2022). Emergent rheotaxis of shape-changing swimmers in Poiseuille flow. Journal of Fluid Mechanics. Full text.
  7. B. J. Walker, K. Ishimoto, E. A. Gaffney, C. Moreau (2022). The control of particles in the Stokes limit. Journal of Fluid Mechanics. Full text.
  8. E. A. Gaffney, M. P. Dalwadi, C. Moreau, K. Ishimoto, B. J. Walker (2022). Canonical orbits for rapidly deforming planar microswimmers in shear flow. Physical Review Fluids. Full text.
  9. B. J. Walker, K. Ishimoto, E. A. Gaffney, C. Moreau, M. P. Dalwadi (2022). The effects of rapid yawing on simple swimmer models and planar Jeffery's orbits. Physical Review Fluids. Full text.
  10. C. Moreau, K. Ishimoto, E. A. Gaffney, B. J. Walker (2021). Control and controllability of microswimmers by a shearing flow. Royal Society Open Science.
  11. E. A. Gaffney, K. Ishimoto, B. J. Walker (2021). Modelling motility: the mathematics of spermatozoa. Frontiers in Cell and Developmental Biology. Full text.
  12. B. J. Walker, E. A. Gaffney (2021). Regularised non-uniform segments and efficient no-slip elastohydrodynamics. Journal of Fluid Mechanics. Full text.
  13. L. S. Kimpton, B. J. Walker, C. L. Hall, B. Bintu, D. Crosby, H. M. Byrne, A. Goriely (2021). A morphoelastic shell model of the eye. Journal of Elasticity.
  14. B. J. Walker, K. Ishimoto, E. A. Gaffney (2020). Efficient simulation of filament elastohydrodynamics in three dimensions. Physical Review Fluids. Full text.
  15. K. Ishimoto, E. A. Gaffney, B. J. Walker (2020). Regularized representation of bacterial hydrodynamics. Physical Review Fluids. Full text.
  16. B. J. Walker, M. P. Curtis, K. Ishimoto, E. A. Gaffney (2020). A regularised slender-body theory of non-uniform filaments. Journal of Fluid Mechanics. Full text.
  17. B. J. Walker, S. Phuyal, K. Ishimoto, C. Tung, E. A. Gaffney (2020). Computer-assisted beat-pattern analysis and the flagellar waveforms of bovine spermatozoa. Royal Society Open Science. Full text.
  18. B. J. Walker, K. Ishimoto, H. Gadêlha, E. A. Gaffney (2019). Filament mechanics in a half-space via regularised Stokeslet segments. Journal of Fluid Mechanics. Full text.
  19. B. J. Walker, K. Ishimoto, E. A. Gaffney (2019). The pairwise hydrodynamic interactions of synchronized spermatozoa. Physical Review Fluids. Full text.
  20. B. J. Walker, R. J. Wheeler (2019). High-speed multifocal plane fluorescence microscopy for three-dimensional visualisation of beating flagella. Journal of Cell Science. Full text.
  21. B. J. Walker, K. Ishimoto, R. J. Wheeler (2019). Automated identification of flagella from videomicroscopy via the medial axis transform. Scientific Reports. Full text.
  22. B. J. Walker, R. J. Wheeler, K. Ishimoto, E. A. Gaffney (2019). Boundary behaviours of Leishmania mexicana: A hydrodynamic simulation study. Journal of Theoretical Biology. Full text.
  23. B. J. Walker, R. J. Wheeler, K. Ishimoto, E. A. Gaffney (2018). Response of monoflagellate pullers to a shearing flow: A simulation study of microswimmer guidance. Physical Review E. Full text.