  Objective Eulerian Coherent Structures (OECSs) and instantaneous Lyapunov
exponents (iLEs) govern short-term material transport in fluid flows as
Lagrangian Coherent Structures and the Finite-Time Lyapunov Exponent do over
longer times. Attracting OECSs and iLEs reveal short-time attractors and are
computable from the Eulerian rate-of-strain tensor. Here we devise an optimal
control strategy to create short-time attractors in viscosity-dominated active
fluids. By modulating the active stress intensity, our framework achieves a
target profile of the minimum eigenvalue of the rate-of-strain tensor,
controlling the location and shape of short-time attractors. We use numerical
simulations to show that our optimal control strategy effectively achieves
desired short-time attractors while rejecting disturbances. Combining optimal
control and recent advances on coherent structures, our work offers a new
perspective to steer material transport in unsteady flows, with applications in
synthetic active nematics and multicellular systems.
