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Keeping quiet

 The sound pressure signal generated by a disk brake system can take on a variety of dynamics, which may form a (a) limit cycle, a (b) torus or a (c) chaotic attractor.


The sound pressure signal generated by a disk brake system can take on a variety of dynamics, which may form a (a) limit cycle, a (b) torus or a (c) chaotic attractor.

Not much affects the nerves like the high-pitched squealing of car brakes. Fortunately, researchers are using NCI’s computational facilities to help design quieter brakes – and save the car industry time and money.

Car brakes squeal when some of the kinetic energy is transferred into sound instead of heat. The friction causes vibration, which produces sound.   

“To develop a more efficient, less noisy design, we need to know exactly where and why it’s squealing,” says Dr Sebastian Oberst from UNSW Canberra, ADFA.

“We do that by experimental testing and simulating brake systems on computers at NCI.”

The project is led by Professor Joseph Lai and is supported by an ARC Discovery grant.

Conventional computer models used by researchers and car manufacturers don’t predict the squeal itself, explains Dr Oberst.

“Instead they only predict unstable vibrations and assume a linear relationship with squeals, but it’s much more complicated than that,” he says.

Dr Oberst and his colleagues took experimental data, including vibration, friction coefficients, temperature and sound levels, and analysed it to evaluate the degree of nonlinearity contained in squeal.

“Linear vibration-only analyses like those used by the car manufacturing industry often cannot predict all squealing events,” says Dr Oberst.

“Many people thought brake designs were producing squeal because the models weren’t quite right – there are so many different parts and materials to get right. But one key factor usually overlooked is non-linearity.” 

Dr Oberst and his colleagues set out to develop a model that incorporated non-linearity. What they found was surprising.

“Non-linear systems can be predictable, but we found that some systems actually behaved chaotically.

“Chaotic vibrations in brake systems can’t be modelled with conventional linear analysis tools. This imposes enormous costs for brake manufacturers as extensive testing and huge computational resources would be required. So it’s really important to develop predictive tools that are both reliable and affordable.

Even using a very simplistic brake model, it takes eight days of continuous computation to create a two-second simulation, says Dr Oberst.

“It’s very time consuming and you need huge amounts of compute power and memory. We couldn’t have done this without NCI.”

Ultimately, the team’s final goal is to develop an approach that’s reliable and affordable for industry to adopt.

Dr Oberst says the research could be applied to many different areas, including those annoying squeaky door hinges.

“It’s not just the automotive industry – this could aid in the design of everything where you have friction-induced noise,” he says.

 

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