NCI Annual Report 2013/14 - page 54

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Keeping quiet
RESEARCH HIGHLIGHT
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.
It’s not just the automotive industry – this
could aid in the design of everything where
you have friction-induced noise.
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.
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