Dynamics of a free finite-sized object in a confined active nematic suspension

A confined active suspension coupled with a freely suspended finite-sized object is analyzed with numerical simulations. A circular object in a circular container is the principal case studied, though the results generalize. The continuum model of Gao et al. (2017), which is based on a kinetic theory, is used. In many cases, the dynamics settle into either a fixed point (in various locations) or a range of distinct high-amplitude limit cycles, depending on initial conditions, container-wall boundary conditions, and the suspension parameters (diffusivity, activity, etc.). The mechanisms of these are discussed. A multi-time-scale analysis of the governing equations shows how limit cycles and fixed points might be expected based on how it leads to a simplified dynamical system. It is interesting that a simple suspension model can reproduce some observed phenomenology of far more complex biological systems.