Noise
Reduction charactersitics of a single expansion chamber muffler model
Exhaust noise of internal
combustion engines is known to be the biggest pollutant of the present
day urban environment. Fortunately, however, this noise can be reduced
sufficiently by means of a well designed muffler.In order to determine
the noise reduction charactersitics a single expansion chamber muffler
model several tests can be conducted and these results can be compared
with the predicted values. In most of the applications where the cross-sectional
dimensions of the duct are much smaller than the wavelength of sound,
plane wave assumption gives fairly good results for relatively lower
frequencies. Figure 1 shows the comparison of the predicted and experimental
results for a single expansion chamber muffler model. The theory behind
these experiments and the results were presented at the refreed 11th
national congress of Machine Theory and Dynamics Symposium in Ankara
in September 2003.
Figure 1
Figure 2 shows the comparison
of the predicted and experimental results for a single expansion chamber
muffler model with a longer outlet duct.
Figure 2
In-duct
transmission loss characteristics of circular thin plates
In today’s competent
industrial world, materials have become one of the most important
key issues in machinery design. Durability, strength and flexibility
are some well known design parameters to consider. With the advent
of technology, consumers and manufacturers demand higher standards
for the goods they buy and sell. Noise is a crucial design parameter
which has an increasing significance.
Noise emitted by machines
confronts engineers with the problem of attenuation of the unwanted
noise to acceptable levels. Governments, international agencies and
also manufacturers set desired noise performance standards for some
products. Attenuation of noise emitted by machines is also dependent
on the materials used in the production. If the attenuation values
of several different materials used in production can be predicted
in the design process, the manufacturers will be able to produce better
products in point of view of noise. In this context, sound transmission
through thin plates has received attention, as plate structures are
often employed in machines and appliances and constitute the principal
sound radiating surfaces.
For the in-duct transmission
loss characteristics of thin plates, an experiment set-up had been
established. And tests were conducted for the determination of the
in-duct transmission loss characteristics of thin plates. The results
were found with a computer program, NoRP
, which is written in C++ programming
language. By use of NoRP,
noise reduction characteristics circular thin plates can be determined
with great ease provided the frequency is below the first cut-off
frequency of the circular duct considered. Figure 3 shows the comparison
of the predicted and experimental results for a circular plate. And
the figure below is a screenshot of NoRP.
Figure 3
Dynamic
Analysis of Mechanisms with Elastic Links and Clearances
Advances in machinery design
frequently mean higher operating speeds and greater positioning accuracy.
In the past, it was often possible to size members solely on the basis
of experience and then rely upon a testing program to discover shortcomings
in the design. However, with the increase in complexity, performance
and cost of modern systems, it becomes more and more desirable to
discover any potential system or component shortcoming on paper rather
than on the test stages. Vibrations in mechanism links are often disregarded
by their complexity and rigid body analysis is preferred for its simplicity.
Omitting consideration of link elasticity under dynamic conditions
may contribute to a machine’s failure to perform adequately
at higher speeds of operation. The effects of mass distribution and
elasticity in mechanisms become significant at high speeds. One interpretation
of this terminology may be speed at which inertial forces become so
large that they can not be ignored.
In addition to the link elasticity,
connection clearances in mechanisms play a vital role in the prediction
of the dynamic behavior of the mechanisms under consideration. The
deteriorating effects of the link elasticity and connection clearances
are familiar phenomena. Prediction of these effects is a critical
point in the design process. While some clearance in mechanism connection
is necessary, often manufacturing tolerances and wear further tend
to increase the clearance to a point where the overall system performance
is seriously affected. Manufacture itself is usually the largest source
of clearance which can not be overcome by a substantial increase in
manufacturing expense.
To achieve optimum performance,
the effects of both link elasticity and connection clearances have
to be considered at the design stage. Since the analytical treatment
of this problem normally requires the solution of large sets of complex
and nonlinear differential equations, the problem may be solved by
numerical approaches on efficient computers. One of the foremost important
numerical techniques is the Finite Element Method. The effects of
both link elasticity and connection clearances can be fit into a form
that numerical techniques can reliably be used with relatively small
errors in the results so that the desired accuracy of computations
is achieved.
In study, the fundamental
concepts pertaining both to elastic mechanisms and clearances in connections
are given and methods of solution techniques are discussed.
Determination
of the damping factors & modulus of elasticity for different materials
for a wide range of applications
The modulus of elasticity and
the damping factors of materials used in the production of household
appliances can be found by using the complex modulus apparatus. Complex
modulus apparatus allows the accurate determination of the damping
factors and the dynamic modulus of elasticity for a wide range of
applications. Sample bars are cut from the plates. Sample bars cut
from the plates were firmly fixed at one end by the clamp on the complex
modulus apparatus. Two transducers were also attached onto the complex
modulus apparatus. One of these transducers is the exciter transducer
and the other is the receiver. Exciter transducer is magnetic transducer
which produces a magnetic force on the sample bars. Receiver transducer
is a capacitive transducer sensitive displacement. Little ferromagnetic
discs were glued to non-magnetic samples in order to produce the magnetic
force. Exciter transducer was placed under the sample bars and the
receiver was placed near the fixed end of the sample bars. Observing
the amplitude of vibration and noting the resonance frequencies reveals
the damping factors for the specific mode considered. And the modulus
of ealsticity can be calculated from the theory of the lateral vibration
of bars.
Commercial
Noise Measurements
Measurement of the noise levels
of the main pump station which is close to a residential district.
Balcova Geothermal Energy Plant in Izmir,
Turkey.
Measurement of the noise levels
of the headphones used by the workers of the department. Turk
Telekom, the central unit of consultancy in Izmir, Turkey.
Measurement of the background
noise of an acoustic test room at the construction stage and the octave
band analysis of the acoustic test room for future provisions. ECA,
a leading manufacturer of armatures in Manisa, Turkey.
Comparative noise reduction
measurements of the ducts used for sewage disposal. Ege
Yildiz Plastik Sanayi A.S., Izmir, Turkey.
Measurement of the sound absorption coefficients of different materials
used for sound isolation in automotive industry. CatSIS
Engineering Consultancy A.S., Istanbul, Turkey.
RESEARCH
& INTERESTS