This is an example of visco-elastic interactions involving fluid dynamics,
rigind body dynamics and elastic membranes.
In the simulation a flexible balloon made of elastic material and filled
with a liquid is hit by a hard ball. The motion of the hard ball is
pre-determined, i.e. directed by an external force and is not responsive
to the reaction forces of the balloon. The liquid motion inside the
balloon is viscous and compressible. The material of the walls has
resistance to stretching and torsion (normal and shear stresses). The
balloon is touching a hard flat surface of the floor. The interaction of
the balloon with the floor is of non-slip type. Initially the pressure
inside the balloon is higher than the ambient pressure, which causes it to
inflate at the beginning of the simulation. After the balloon is hit by
the ball it deforms and gradually changes shape as the fluid inside it
moves, and the pressure forces cause the elastic surface to deform.
Animations: Surface forces, Internal flow-field.