I am offering final-year projects for third-year BSc and fourth-year MMath students at Durham for the upcoming 2021–22 year.

I would be very happy to talk you about the project and possible directions if you would like to get in touch.

### MATH3382 (Project III) 2021–22

#### Project title

Sheepdog trials: collective motion in 2D

#### Overview

Fans of BBC Alba’s Farpaisean Chon-Chaorach will know that sheep herding is a competitive business. It will not surprise you, then, to learn that the motion of individual sheep as a moving herd — collective motion known as flocking or swarming — is mathematically quite well described.

At the local level, each sheep behaves as an individual, but if we zoom out, the herd of sheep behaves as a continuum. And at the continuum level, we can describe the motion of sheep using partial differential equations. How do herds decide where to go? Do they ever end up just going round in circles?

This project offers you to chance to examine this interesting behaviour. We will derive the governing PDEs of some common models, and then numerically solve these equations. At the same time, we can simulate a bunch of individual sheep operating using simple rules. Will these two approaches converge? We will see!

This dichotomy of microscale vs macroscale, and how we move between them, is a key concept in applied mathematics.

#### How we might structure the the project

At the start, we could have something like:

- What is flocking? Where else do we see this behaviour?
- Looking up different models for how sheep behave around other sheep
- Coding up a few sheep in Python and seeing what they do
- Investigating the Vicsek model
- Deriving PDEs for our sheep and beginning to look for ways to solve them

#### Prerequisites

This is an applied maths project and you will have to do a bit of practical coding. You should therefore have some familiarity with Python, but you do not have to be a numerical analysis expert at all! We will learn some numerical differential equation solving techniques together. There will be plenty of support.

#### Courses to take at the same time

Nothing essential. You might enjoy comparing these models to those you see in Mathematical Biology III and Fluid Mechanics III, but this is optional.

#### Resources

### MATH4072 (Project IV) 2021–22

#### Project title

How do microorganisms swim?

#### Overview

If you were a microorganism — say, a bacterium or a sperm cell — the world would feel very different to you. Not just because you are 1µm tall, but also because the physics you experience at this scale is quite different to what we experience as metre-sized humans.

As humans, we are familiar with the notion that everything moves according to Newton’s second law: $F = ma$. But as a microorganism, your mass is so small, that the acceleration term becomes neglible. Instead, you live in an inertialess world, where all forces just balance out, all the time.

Many microorganisms swim, and if you have taken a fluid mechanics course (although this is not required), you will know that fluids move according to the Navier–Stokes equation. A big part of what makes this equation hard is the acceleration term. Not a problem for a microorganism!

So really our governing equations become a lot simpler, and we are able to use techniques you will have learnt over the last three years to start looking at how these microorganisms really swim.

#### How we might structure the the project

At the start, we could have something like:

- Introduction to Stokes flow; derivation as a limit of the Navier–Stokes equations
- Solutions to Stokes flow using Green’s functions
- Looking up different methods of solving the Stokes equations on the shape of a microorganism
- Coding up the simplest model of a microorganism (if you like Python)

#### Prerequisites

This is an applied maths project and there will be an opportunity to do some computational work, as well as some analytical work, so you should have some familiarity with Python, but you do not have to be a numerical analysis expert!

There are no prerequisite models for this project. Possibly useful modules to have taken are Fluid Mechanics III and Mathematical Biology III for the Green’s functions. However, **these are not essential** because, together, we will derive the governing equations and learn an intuition for the physics which is completely new.

#### Resources

- Life at low Reynolds number, , 1976.
- Small particles in a viscous fluid, course notes, , 2014.
- A Physical Introduction to Suspension Dynamics, textbook, , 2012.
- Stokesian Dynamics online game, to get a feel for the physics, .