  We address the fluid-structure interaction of flexible fin models oscillated
in a water flow. Here, we investigate in particular the dependence of
hydrodynamic force distributions on fin geometry and flapping frequency. For
this purpose, we employ state-of-the-art techniques in pressure evaluation to
describe fluid force maps with high temporal and spatial resolution on the
deforming surfaces of the hydrofoils. Particle tracking velocimetry (PTV) is
used to measure the 3D fluid velocity field, and the hydrodynamic stress tensor
is subsequently calculated based on the Navier-Stokes equation. The shape and
kinematics of the fin-like foils are linked to their ability to generate
propulsive thrust efficiently, as well as the accumulation of external contact
forces and the resulting internal tension throughout a flapping cycle.
