Abstract
Active fluids are suspensions of self-driven agents that convert local energy into large-scale flows. Some examples include bacterial suspensions, cellular cytoskeleton, kinesin–microtubule suspensions, Janus colloids, and ciliary carpets. They give rise to distinctive phenomena not observed in passive complex fluids. Active fluids can be categorized based on the symmetry of their constituent agents. Among these, active nematics – composed of rod-like particles – are the most widely studied. In the bulk, they exhibit spontaneous instabilities, defect-driven flows, and novel distributions of vortical structures and energy. Beyond the bulk, the behavior of active nematics is strongly influenced by boundaries. When interacting with a fluid interface, active nematics show enhanced wetting, traveling surface waves, and asymmetric height fluctuations. In many biological systems, active fluids interact with elastic boundaries rather than with fluid–fluid interfaces. To date, studies of active nematics interacting with elastic boundaries remain relatively sparse. In this thesis, we simulate the dynamics of an elastically deformable filament immersed in a two-dimensional active nematic fluid using the Immersed Boundary Method (IBM). This numerical framework allows us to investigate two distinct physical scenarios. First, we examine the interactions of an elastic inclusion with an active nematic fluid. The organization of curvature fluctuations and flow structures around the membrane depends on whether it is initially taut or deflated. Sharply curved regions arise from localized pulling forces that drive the fluid normal to the membrane, with the resulting dynamics strongly influenced by the membrane’s initial tension state. This manifests as a tension dependent asymmetry in the curvature fluctuations. In the second scenario, we consider an active isotropic fluid confined between two walls, where one wall is elastically deformable and the other remains rigidly fixed. Below a critical channel width, we observe co-existence of a quiescent, nematically aligned region and a chaotic, bulging active pocket. Both studies share a common theme. There is a of separation of features influenced by topology and mechanics. Topology influences the azimuthally averaged defect distributions, while other features like local force distribution, membrane fluctuations are influenced by mechanics. The work in this thesis constitutes a first step in uncovering dynamics of elastic objects interacting with active fluids. The findings here can be used to engineer systems that extract work from otherwise turbulent complex fluid systems.