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.