Manipulating structured materials: paper making and mud swimming

A vast array of materials in the natural world, industry and everyday life are characterised by some form of internal structure, from granular or colloidal suspensions to sponges and foams. In this talk I will briefly consider the dynamics of flow and deformation in two contrasting settings involving such structured materials.  The first involves deformation of a fibrous suspensions, motivated by ‘dewatering’ of pulp suspensions in the paper-making industry. I will present a theoretical model and experimental results, and compare and discuss the solutions and implications. The second involves motion through the broad class of materials that are characterised by a plastic yield stress: I will explore classical models of viscous locomotion (cf. Taylor 1951) when the ambient fluid has a yield stress, both theoretically and with the aid of high-resolution numerical simulations. I will describe the corresponding flow structures and resulting swimming speeds and efficiencies for different basic swimming gaits.