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silence Simulating Achieving the level of silence we’ve come to expect in a

moving vehicle is no easy task, reports Paul Schreier, but acoustics engineers are taking advantage of sophisticated software to get the job done


he job of an acoustics engineer to reduce noise and improve sound quality is getting more challenging. The industry is ‘downsizing’ with

smaller motors, sometimes with two or three cylinders that produce the same amount of power, and these involve new injectors and multi-stage turbochargers that add annoying noise components, like turbocharger whine. The move to electric and hybrid vehicles has also created some interesting problems. When the noise from an internal combustion engine (ICE) drops out, other sounds become noticeable. Torque variations in transmission systems are increasing, generating gear-rattle- noise issues, while gear tooth whine is becoming more dominant. With no ICE, noise from the HVAC

(heating, ventilation and air conditioning) system, fan, inverter and battery cooling are all more prominent. Some engineers are also designing baffl es for fuel tanks because the sloshing of petrol becomes annoying where there are no other sounds to mask it. Taking the completely opposite approach, designers in some cases are engineering noise into electrical


vehicles because they’re so quiet they present a danger to pedestrians and others on the road. However, the requirement is that the noise must simply alert and not annoy. All these areas present major challenges

that are being addressed to a large extent with vehicle simulations. Koen De Langhe, product line manager for Noise and Vibration in the Simulation Division of LMS International, says: ‘Acoustics engineers today are not only trying to reduce noise levels but, in addition, through simulation, they’re looking to see where and how they can take away material, resulting in lighter cars that achieve better fuel economy yet maintain the same or better noise performance.’

Technology shifts There are some shifts in the application of the underlying simulation technologies. While in the past fi nite-element-based solutions were of limited value for full system simulations and higher frequencies because model sizes were impractical, computing technology has made enormous leaps. De Langhe explains that there are four major technologies – fi nite element method (FEM), boundary element method

(BEM), statistical energy analysis (SEA) and ray-tracing – that have advanced to address more complex, full system problems. For some applications such as injectors, turbochargers and radiation, he sees a shift from BEM to FEM, as the latter can solve larger problems more quickly. However, other applications like full vehicle exterior acoustics up to high frequencies will still rely on BEM. Many people in the industry would argue

that three companies dominate the market for acoustics software in the auto industry: LMS International, The ESI Group and Free Field Technologies (FFT). Auto manufacturers and suppliers have long invested in in-house codes, and it’s important to note that general-purpose codes are often put to work in this sector. LMS started in data acquisition and moved into simulation software with the acquisition of NIT, whose Sysnoise software forms the basis of much of the company’s current product line. De Langhe points out the wide technology portfolio of software that addresses FEM, FEM AML (the company’s version of PML – perfectly matched layers), BEM, ray tracing and SEA. He comments further that LMS does more than just produce simulation software; it is, to a larger extent, a test company that can take a hybrid approach that couples test models with simulation models. The company’s key software is ‘Virtual.

Lab’, an integrated 3D CAE simulation suite that covers acoustics, NVH (noise/vibration/ harshness), durability and multi-body dynamic

Image courtesy of ArchMan/Shutterstock

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