  The move to high performance applications greatly increases the demand to
produce large instantaneous fluid forces for high-speed maneuvering and
improved power efficiency for sustained propulsion. Animals achieve remarkable
feats of maneuvering and efficiency by changing their body shape to generate
unsteady fluid forces. Inspired by this, we have studied a range of immersed
bodies which drastically change their shape to produce fluid forces. These
include relatively simple shape- changes, such as quickly changing the angle of
attack of a foil to induce emergency stops and the use of tandem flapping foils
to generate three times the average propulsive force of a single flapping foil.
They also include more unconventional shape-changes such as high-speed
retracting foil sections to power roll and dive maneuvers and the use of soft
robotics to rapidly shrink the frontal area of an ellipsoid to power 68%
efficient fast-start maneuvers or even completely cancel the drag force with
91% quasi-propulsive efficiency. These systems have been investigated with
analytics, experimental measurements and immersed-boundary numerical
simulations.
