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Sound and science

Jean-Louis Migeot argues that acoustic simulation needs to be an early part of any product design and that

software is now available to ensure it can be done easily S

ound is oſten an indicator of function and quality. Sometimes it’s silence – like a dishwasher you can run at night without keeping the kids awake.

Sometimes it’s the reassuring ‘thunk’ of a car door closing solidly. Whatever the product, making the expected sound is part of what helps it succeed or fail. With the advent of new materials and design

imperatives, companies can’t take their products’ sound profiles for granted. Tey need to know whether the shutter click of the digital SLR camera will sound enough like a mechanical SLR to satisfy serious photographers. Tey need to know if their hybrid vehicle is so quiet, when it’s running on battery power, that drivers can hear gasoline sloshing in the tank – for they need to mask that noise. Creating the right sound profile is increasingly

complicated. Te current emphasis on energy efficiency and smaller environmental footprints, driven by government mandates and consumer preferences, influences designers. Integrating acoustic simulation soſtware into their design processes gives them insight before their products hit the showroom floor. But few companies have the tools and processes to incorporate new materials and designs into their products without altering their sound profiles for the worse.

Efficiency versus noise Te conflict between efficiency and noise is perhaps most stark in the aerospace industry. Aircraſt manufacturers face strong pressure to make aircraſt quieter and more efficient, even though those two imperatives oſten conflict. Giving one a lower priority won’t work, because they both directly affect the aerospace industry’s economics. Noise probably has a more profound influence

on air travel than on any other industry. Airports restrict take-off and landing hours to protect surrounding areas from excessive noise. At the same time, air travel’s popularity and the world economy’s reliance on air freight are creating


demand for more flights. Unless the aerospace industry responds to the challenge with quieter aircraſt, local authorities will have no choice but to manage airport noise by restricting hours. But fuel costs account for anywhere from 29 to

41 per cent of airline budgets, and the prices keep rising. So, while responding to noise concerns, aircraſt manufacturers also have to keep fuel efficiency high on their priority list. Aerospace engineers have developed methods

for increasing fuel efficiency. Light materials reduce aircraſt weight and fuel consumption. Streamlined new fuselage shapes reduce air friction. Advanced engine designs, such as counter-rotating jet engines, consume less fuel. Each of these measures has noise implications.

For engineers to balance noise and fuel-efficiency, they must be able to predict how the aircraſt


will perform in the physical world, long before it becomes a physical object as a prototype. Tis is the big weak spot in most product design processes. Engineers tend not to be provided with acoustic simulation tools that will help them understand, early in the process, whether a fuel- saving modification will make the aircraſt noisier. Early is critical. Waiting until later in the

process limits engineers’ ability to make substantial changes and adds significant cost and time to the development process.

Integrated acoustic simulation Airbus is the successor to the consortium that developed the noise-plagued Concorde supersonic jet, so it has a long history of managing jet noise. About 15 years ago, Airbus and jet engine maker Rolls-Royce teamed up

with Free Field Technologies to develop Actran – acoustic simulation soſtware that can model entire systems, i.e. the combination of engine noise and airflow around the fuselage. Te earliest acoustic simulation soſtware was

too sophisticated for every engineer in the process to learn, but Airbus has worked over the past 15 years to ‘democratise’ it. Now acoustic simulation is fully integrated into Airbus’ design processes. Any design engineer in Airbus can initiate

an acoustic simulation calculation. Tey change values for parameters such as speed, temperature and altitude in a simulation model and submit it for calculation. Actran runs the simulation and reports the results. Airbus engineers can use the soſtware at the beginning of the process to get a broad idea of which geometry is most promising. As they get closer to a final design, they can

adjust the parameters for optimal performance. Tis system eliminates guesswork and needless iteration. It avoids costly, late-stage errors, through constant simulation that reveals when an idea is going awry. Whatever a company’s sound management challenges, Airbus shows that it is possible to infuse acoustic simulation into design processes from beginning to end. Other companies may not have to simulate

every phase of the process, because their products do not change significantly from one version to the next. Tey might need only occasional acoustic simulation to verify their sound profile. Or they might be able to create one acoustic model of their product, and then use it to create best practices for sound engineering. Companies don’t need to have the resources of

a large aerospace company to embrace acoustic simulation, but they do need to embrace acoustic simulation if they are to deliver function and quality, as well as the sound profile that acts as an indicator of that function and quality.

Dr Jean-Louis Migeot is co-founder and CEO of Free Field Technologies, an MSC Software company.

@scwmagazine l

Jean-Louis Migeot

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