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NVH applications at Advanced Analysis Ltd


Study of the potential sound quality of a component based on predicted sound files. ... An SAE paper was written describing the work and it is available on request. ... – PowerPoint PPT presentation

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Title: NVH applications at Advanced Analysis Ltd

NVH applications at Advanced Analysis Ltd
  • Measurements Prediction

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.

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

Louvres transmission
Incident wave
Structural transmission
Direct transmission
Sound Pressure on foam-structure layout
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
Intake/Exhaust Noise Simulations. Applications
  • Intake / Exhaust snorkel noise prediction.
  • Noise reduction of intake system snorkel
  • Noise reduction of exhaust system snorkel
  • 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.

Exterior Noise Radiation from Structural
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.
Exterior Radiation from Structural Vibration.
  • 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

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
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.
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
  • 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

Sound Quality Predictions Why and How ?
  • WHY?
  • The sound of a motorbike or car interior feels
  • The interior sound of a vehicle is not sporty
  • 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.

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
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.
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
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
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