NVH applications at Advanced Analysis Ltd

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NVH applications at Advanced Analysis Ltd

• Measurements Prediction

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Noise Measurements

• Typical output from recordings
• Time domain sound file
• Frequency spectra narrow, 1/8 1/3 bands
  Linear A-weighted
• Basic source ranking exercise covered component
  vs. uncovered
• In and out enclosure measurements. Basic
  transmission loss assessment.

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Analysis of Enclosures

• Measurements and analysis of enclosure layout
• Study of direct vs. structural noise transmission
• Detailed analysis of sandwich type of wall
  arrangements. 2D 3D simulations.
• Advanced simulation tools to study absorptive
  components.

air-gap
Louvres transmission
Incident wave
Structural transmission
Direct transmission
panel
foam
foam
Sound Pressure on foam-structure layout
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Intake/Exhaust Noise Reduction
Visualisation of pressure phase distributions
aids design of internal chambers and transfer
tubes for minimum noise transmission
Sound pressure distribution of radiated noise
from intake system
Sound pressure distribution inside exhaust system
Noise intensity vectors in Intake system
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Intake/Exhaust Noise Simulations. Applications

• Intake / Exhaust snorkel noise prediction.
  Applications
• Noise reduction of intake system snorkel
  noise.
• Noise reduction of exhaust system snorkel
  noise.
• Optimisation process to achieve optimal
  dimensions and position of internal baffles and
  transfer pipes. When possible this may also lead
  to weight reduction.
• Study of the potential sound quality of a
  component based on predicted sound files.
• Optimisation for noise attenuation plus sound
  quality within the same process.

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Exterior Noise Radiation from Structural
Vibrations
Dynamic fatigue prediction The movie below shows
a typical example of the vibrations on an
alternator bracket for a fatigue study. The
contours correspond to Von Mises stresses at a
particular engine speed.
Intake manifold skin noise Rapid studies of
basic concepts to minimise or shift vibration
modes, and hence to obtain minimum radiated noise.
Tyre noise prediction Contribution to radiated
noise from vibrations of the tyre surfaces
Noise radiation from engine assembly Rapid
studies of basic changes to the structure to
minimise noise levels. Also sound quality
assessment from predictions.
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Exterior Radiation from Structural Vibration.
Applications

• Prediction of structural vibration. Applications
• Noise reduction of intake system skin noise,
  e.g. plastic intake manifolds.
• Noise reduction of engine covers, e.g. cam and
  timing belt covers.
• Noise reduction and sound quality assessment on
  full engine assemblies.
• Rapid concept studies on changes in geometry
  and/or materials of the structure.
• Prediction of the radiated noise from tyres.
• Optimisation of ancillary components for dynamic
  fatigue.

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Car Interior, NVH Analysis
Structural displacements on dash panel at 80Hz
SPL distribution at 80 Hz
Cavity modes of interior volume
Sound level predicted at drivers ear
Panel Contribution
Magnitude of Normal Velocity
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Car Interior, Acoustic Materials
Study of sandwich type configuration Prediction
of the absorption coefficient and transmission
loss for foam type acoustic materials when
coupled to structures. Rapid optimisation tools
predict the best foam thickness or other
parameter defining the foam acoustic properties.
Perforated metal sheet 0.9mm-thick. Open
area37 Hole radius1.5mm
Glass fibre Thickness1mm Density95kg/m3
Study of dash panels Prediction of the
sensitivities of the dash panel sandwich
configuration with regards to absorption
coefficient and transmission loss.
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Car Interior NVH Analysis. Applications

• Prediction of interior acoustics. Applications
• Study of the effect of dash panels on interior
  sound quality and noise levels.
• Study of natural frequencies of the interior
  volume.
• Panel contribution analysis identifies surfaces
  where weight can be reduced, vibrations need to
  be reduced or absorptive materials need to be
  incorporated to improve the acoustics in the
  interior of the vehicle.
• Rapid optimisation of foam type acoustic
  materials to modify specific frequency ranges for
  sound attenuation and/or improvement of sound
  quality.

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Sound Quality Predictions Why and How ?

• WHY?
• The sound of a motorbike or car interior feels
  harsh.
• The interior sound of a vehicle is not sporty
  enough.
• The overall sound of a motorbike is not boomy,
  i.e. low frequencies are not heard loud enough.
• HOW?
• Noise source ranking tests identify main noise
  contributors. Noise prediction helps to identify
  frequency bands affected by the individual
  components. Hence, predictions help to shape
  the quality of the sound.
• Given that measured pressure data is available,
  predictions allow for rapid study of different
  models and for the generation of audio files for
  sound quality assessment.

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Case Study Motorcycle Sound Quality Targets
Sound quality target generation AAL can generate
the frequency spectra of any recording. This
helps to identify the important frequencies
giving character to a particular sound.
Furthermore, it proves a very helpful information
when optimising a design using numerical
simulations.
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Case Study Exhaust Sound Quality Analysis
Predicted results The graph shows predicted SWL
for the baseline and AAL design. The predicted
audio files indicate the reduction achieve above
800Hz and the enhancement at low frequency (below
300Hz) achieved with the AAL design.
Acoustic model Figure on the left shows a typical
boundary element model (BEM or acoustic model)
for noise prediction.
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Case Study Final Results
Baseline recording
Note that the recordings on the left contain
frequencies up to 3000Hz only and corresponds to
short duration for fair comparison with
predictions. Furthermore, the recordings were
obtained from the whole motorbike not only the
exhaust.
AAL design recording
CONCLUSIONS The trends predicted in the analysis
can be heard, and correlated well with the actual
prototypes. Furthermore, the overall noise levels
of the motorbike were kept within legal noise
limits. This type of work was performed for the
development of the Triumph Bonneville silencers.
An SAE paper was written describing the work and
it is available on request. See below comments
extracted from the BIKE magazine in November
2000 regarding the sound quality of the new
Bonneville Getting the exhaust note right was
vital and a deep drone from the two pipes is as
throaty as youd expect given todays silencing
regs.