M.Sc. Thesis Experiment
Set-up
Representation of the
incident and reflected wave components in the inlet and outlet ducts
Educational Muffler
Test Set-up
Noise reduction characteristics
of muffler models can be measured by use of the travelling microphone
method. This method depends on measuring the maximum SPL values in
the inlet and outlet pipes. The crucial point in the measurements
is the cut-off frequency of the pipes used in the tests. Match between
the predicted and measured values show a fairly good agreement in
the frequency region under the first cut-off frequency. Theoretical
computations can be carried out by use of the plane wave propagation
which gives satisfactory results in most automobile exhaust applications.
FFT Analysis Using
the Educational Four Cylinder Engine and B&K 2148 Signal Analyzer
Complex Modulus Apparatus
and Auxiliary Equipments
The reduction of vibration
resonances is a problem of the greatest importance, in the case of
many simple devices, in which only a few natural resonances are present,
they can be rejected outside the range of the exciting frequencies
by suitably modifiying the stiffness-mass ratios in the design of
the article. Generally, mechanical constructions present an extremely
large number of resonances, and the only practical solution to the
problems caused by their existence, is to reduce the resonance amplitude
by means of damping materials or special absorbents. A direct consequence
of these developments is a great need for objective, internal damping
measuring technique. The internal damping properties of materials
are characterized by means of the loss factor d which is defined as
the inverse of the quality factor of the resonances produced by the
materials.
Measuring techniques, for the
measurement of the loss factor d, should cover the great variety of
modern construction materials and also the ever extending range of
temperature in which modern machinery is used. One of the methods
to measure the internal damping factor is the frequency response method.
In this method a bar shaped sample is excited into vibration with
a variable amplitude periodic force and the vibration amplitude is
plotted as a function of frequency. From such a curve, at a resonance
peak the loss factor is calculated as
where 
is the bandwidth at the half power points (3 dB points ), 
is the resonance frequency and index n is the order of the resonance,
or mode number.
EXPERIMENTAL
SETUPS