Transport and deformation of flexible fibers in structured environments

Flexible fibers are encountered in various situations in nature and industrial applications. Examples include microplastics fibers, cellulose fibers, and biofilm streamers. In a wide range of such situations, flexible fibers are often immersed in a fluidic environment with obstacles embedded. For instance, laundry washing machines discharge a large number of microplastics fibers (around 1900 fibers per wash) into wastewaters which contain a significant amount of debris. In such complex media, flexible fibers can exhibit nontrivial conformations and different modes of transport through the surrounding obstacles. These dynamics result from the complex interplay between their elastic response, collisions and hydrodynamic interactions. Understanding of these phenomena is therefore essential to study the physics of biological, environmental and industrial systems, but also to prevent issues such as pollution or clogging. While modeling slender particles in viscous fluids has been a major area of research over the past few decades, methodologies involving surrounding environments are scarce. The resulting complex coupling leads to a constrained formulation of the problem in addition of being stiff. Therefore, modeling fibers in complex media is challenging and can be computationally costly.In this thesis, we will propose a methodology to model flexible fibers in different environments that are made of rigid stationary obstacles. Our implementation enables dynamic simulations of large systems in a reasonable wall times on a single modern Graphics Processing Unit (GPU). Using the capabilities afforded by our method, together with simple experiments, we will investigate the sedimentation of flexible fibers in structured environments. The resulting findings provide physical insight into future experiments and the design of gravity-based sorting devices.