Quieter lining

German researchers are using computer simulations to perfect the acoustics inside cars without having to perform extensive tests on prototype interiors.

The roof lining has a decisive effect on the acoustics inside a car, because it reflects and amplifies noise. Linings made of porous absorbent materials such as felt or natural and synthetic fibres help to improve acoustics by resisting the propagation of sound waves. Their porous structure damps noise by creating a frictional barrier that stops air molecules from bouncing back into the car’s interior. The problem is that this roof lining is usually made up of several different types of material, making it difficult to recycle.

Scientists at the Fraunhofer Institute for Industrial Mathematics (ITWM) in Kaiserslautern have succeeded in resolving this dual challenge.

Using an acoustics simulator, they have developed a roof lining that is not only better at absorbing noise inside a car than the commonly used methods but is also made of a single type of material, and thus easily recycled.

‘Our simulation program enabled us to perform numerous virtual experiments to determine whether a recyclable PET fabric would be suitable as a noise absorber,’  says ITWM project manager Dr. Volker Schulz. ‘Previous solutions involved the time-consuming, cost-intensive task of building prototypes to test the materials. Simulation allows to reduce this stage to a minimum number of tests.’

The researchers start by recording an image of the material using a 3-D X-ray scanner. The next step is to run a software program called Geo-Dict to obtain a mathematical model of the porous absorber’s micro-structure.

Sitting at their computers, the researchers can ‘tweak’ various parameters, such as the orientation and diameter of the fibres, or the degree to which the material is compressed. They then run the simulation program to verify whether or not the virtual structure that they have designed possesses the desired acoustic properties.

‘We can keep on modifying the microstructure of the absorber until we arrive at the optimum noise-damping result, without ever having to build a single prototype,’ Schulz explained.

The same simulation method can be applied to any type of situation where noise has a detrimental effect on comfort. It provides a low-cost means of perfecting the design of many materials, including floor carpets and wall coverings.