When currents influence structures

Inflated, stretched, burst!

Every child loves them...
Balloons: Elastic hollow bodies filled with gas that can increase in size many times over. But most people hate the unpleasant sound of friction and bursting. Do you?

An experiment turns into fun for kids - The story behind the balloons

The story behind balloons is an old one: In 1824, Michael Faraday discovered the first rubber balloon with the help of experiments on hydrogen. Two raw rubber surfaces were pressed together at the edges and dusted with flour on the inside. The balloon expanded greatly, became transparent and floated to the ceiling.

By 1825, the balloon was being marketed and sold as a set by a resourceful and well-known businessman named Thomas Hancock. At that time, people still had to make the balloons themselves using a syringe and raw rubber compound.
A balloon from that time was not particularly durable or stable due to the unvulcanized material and the associated stickiness. Nowadays, plastics technology offers more possibilities with various processes.

A tireless demand - balloons in all imaginable colors and shapes.

At parties, festivals or for play, the requirement for material and durability increased proportionally to the demand. New more stable balloons can now even take on a wide variety of shapes. The pioneer of so-called shaped balloons was Harry Rose Gill from Ohio, who produced the first balloon in the shape of a zeppelin. Different air chambers characterize larger shaped balloons today. Tensile loads, especially at the transitions between the chambers, require a high technical standard in production.

Whether balloons or other gas-filled objects: Can the stability and behavior of such products be calculated?

Fluid-Structure-Interaction - Calculation on variable bodies

Gas-filled bodies can be calculated for a wide variety of concerns. Computational fluid dynamics (CFD) allows for example pressure calculations, gas distribution, as well as inflation and flow velocities of the object. In our first video you can see a typical visualization of the flow velocities in a balloon during the inflation process.

The change in pressure inside the balloon changes the size and therefore the actual fluid area...The balloon expands. This mutual influence and is called "Fluid Structure Interaction". It occurs on elastic, easily deformable, vibrating, rotatably or displaceably mounted, flowed around or through structures.

The detachment of vortices can cause structures flowing around them to vibrate noticeably. Flow-induced oscillations occur, for example, on aircraft wings, on propeller blades, but also in the flow around structures. If the vibrations are large enough, they influence the flow in return*. Damage caused by vibration can be calculated using the FEM method.