Fluid-structure interaction problems involving thin active shells and microswimmers

In this thesis some fluid-structure interaction problems related to swimming are investigated. The broad domain in which the cases can be classified is that of swimming at low-Reynolds numbers, that is in conditions close to the Stokes flow. In the first part, a simpler flow configuration is considered together with an active structure, to identify possible swimming strategies arising from deformations of a multi-stable shell. After a first analysis, based on numerical simulations, an asymptotic approach is employed aiming to confirm the results analytically. In the second part a more complex flow model is considered, in order to analyze a case where the Reynolds number is small but possibly finite. The case considered is that of a robotic swimmer in a viscous fluid, inspired by a celebrated paper of Purcell which is revisited here with more modern tools, from numerical techniques to experiments. Numerical solvers are developed to simulate the related flows: particular care is devoted to the scalability and efficiency of numerical methods in order to solve the Navier-Stokes equations within acceptable time constraints. The validity and accuracy of common models for micro swimmers are assessed by comparison of numerical results with experimental results.