“The ability of Coustyx to predict the tuning frequency within 2% error margin helps us retain excellent product quality before production. With the confidence in simulation, we avoid the cost of prototyping parts and accompanying testing is circumvented as well.”
– Karthik Jayakumar
NVH Engineer, Toledo Molding and Die, Inc.
TMD's advanced engineering group provides
simulation support for every product line
employing FEA, CFD or BEM simulation
techniques. Their main objective is to
improve product quality by performing
simulations beforehand to minimize
prototyping and testing costs. The group also
establishes new simulation methodologies
to limit the amount of testing required to meet
design requirements which is achieved by
confirming excellent test-simulation correlations.
The advanced engineering group preforms
transmission loss simulations to identify
the tuning frequency of each side branch
Helmholtz resonator or quarter wave tuner
in an induction system. An induction
system provides air intake for an engine.
Similar to the exhaust system of an engine,
the intake must be properly engineered and
tuned to provide the greatest efficiency and
power while simultaneously meeting noise
requirements. An ideal induction system
should increase the velocity of the air until
it travels into the combustion chamber,
while minimizing turbulence, restriction
of flow and noise at the induction inlet.
Induction noise is caused by the pressure
differential created between the inlet port
and the cylinder cavity when the piston
descends during the intake stroke.
The overall induction noise is a combination
of several sinusoidal components known
as orders. Engine orders are simply the
amplitude of the frequency components
which are the multiples of the rotating
frequency. In order to meet the noise target
at induction inlet, resonators are built into
the induction system targeting particular
frequencies. These frequencies are
dependent on the resonator's dimensions
such as the volume, resonator neck
diameter and length.
The frequencies of the induction system
are chosen based on the dyno testing at
a customer site and are dependent on the
tuner dimensions. The target frequency
needs to be achieved with a high degree
of accuracy in order to meet the acoustic
requirements for the induction system.
Even though the designer packages it
according to provided dimensions based
on theoretical formulae, there have been
circumstances where the theoretical
calculations did not match the test data.
The formulae don't take into consideration
several factors such as the effect of the
shape or dimensional inaccuracies across
the tuner that arise during the CAD process.
TMD turned to CAE to improve tuning
frequency predictions for the resonators
in an effort to more closely match tuning
frequency predictions to the actual
TMD employs computer-aided engineering
when performing transmission loss
simulations. One of the software packages
the engineers use is Altair's HyperWorks
suite, especially HyperMesh for preprocessing, HyperView or HyperGraph
for post-processing and OptiStruct for
optimization tasks. In addition to the
HyperWorks suite, TMD uses Coustyx
by ANSOL via the Altair Partner Alliance
to run acoustic simulations and predict
the tuning frequencies.
Coustyx is a next generation analysis
software that integrates Advanced Boundary
Element formulations with Fast Multipole
Method to yield fast, accurate solutions to
very large problems in acoustics across a
wide frequency range.
For the transmission loss simulation covered
in this story, TMD uses HyperMesh for
pre-processing to create both a fine mesh
meeting the quality requirements for CFD
simulation and a coarser mesh for the
acoustic simulation. A NASTRAN format
output is created in HyperMesh which is
then used as an input for Coustyx. Necessary
skinning of the surface mesh is performed
in Coustyx and with the assignment of
boundary conditions, a transmission loss
simulation is performed.
With the APA, customers can access third
party solutions such as Coustyx via their
HyperWorks licensing pool without additional
charge. This offers great flexibility in software
usage, especially when applying tools that
are not used every day.
Conclusions and Outlook
Coustyx considers both the shape and
size of the cavity inside the resonators
when predicting the tuning frequencies.
“The ability of Coustyx to predict the
tuning frequency within 2% error margin
helps us retain excellent product quality
before production. With the confidence in
simulation, we avoid the cost of prototyping
parts and accompanying testing is circumvented
as well” explained Karthik Jayakumar.
Out of the HyperWorks suite, TMD uses
HyperMesh for modeling as well as
HyperView or HyperGraph for visualization
depending on the simulation output.
OptiStruct is used for optimization purposes
ranging from topology, topography to gauge.
TMD uses Coustyx, nCode DesignLife and
Maple software via the Altair Partner Alliance.
Access to the APA software suite has given
TMD the ability to evaluate software for an
indefinite amount of time without actually
owning the software. They get the most
out of their HyperWorks Units by utilizing
HyperMesh during work hours and running
Coustyx or other partner software over the
weekends or for a quick end of the day run
to help keep costs down. They have been
working with Coustyx support to expand the
transmission loss simulation capability to
other applications. There is currently excellent
test-simulation correlation for tuner frequency
prediction but TMD would like to expand it to
magnitude prediction as well. TMD is always
exploring the APA's software offering to see
what else may be useful to them.