Dynamics of a droplet driven by an internal active device

A liquid droplet, immersed into a Newtonian fluid, can be propelled solely by internal flow. In simple model, this flow is generated collection of point forces, which represent externally actuated devices or model autonomous swimmers. We work out the general framework to compute self-propulsion droplet as function actuating forces and their positions within droplet. single force, F with orientation position, r_0, gives rise both, translational rotational motion show that mobility anisotropic nonmonotonic | r_0|, depending on viscosity contrast. Due linearity Stokes equation, superposition used discuss more complex arrays forces. analyse force dipoles, such stresslet, biflagellate swimmer rotlet, representing helical swimmer, driven an external magnetic field. For distribution arbitrary high multipole moments propulsion properties depend only few low order multipoles: up quadrupole for special octopole motion. The coupled device discussed exemplary cases. in particular modeled achieves steady comoving state, where position relative remains fixed. fact there are two fixpoints, symmetric respect center tiny selects one them allows switch between forward backward