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Fellow: Ivana Horka
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Home
Institute:
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Hosting
Institute:
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Department of
Building testing
Faculty of Civil Engineering,
University of Technology,
Brno,
Czech Republic
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Department of Mechanical
and Manufacturing engineering, T
rinity College Dublin,
Ireland
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Home
Supervisors:
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Hosting
Supervisors:
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Prof. Ing.
Jiri Adamek, CSc.
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Prof Henry Rice
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Figure: Arrangement of measurement
instruments - a laser fixed on an aluminium frame, a vacuum chamber
placed straight under the laser to improve sgnal quality and
repeatability
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The project was
carried out under the European Doctorate in Sound and Vibration Studies
programme by Ivana Horka at the University
of Dublin, Trinity College,
within the Department of Mechanical and Manufacturing Engineering.
The project was
concerned with an experimental study of the vibro-acoustics of porous
materials. The goal was to develop a test system to produce high
quality dynamic data for porous material structural property studies.
It was financed by the European Commission under the Marie Curie
Training Site scheme.
As shown in the pictures on the left hand
side, the measuring system consists of a laser doppler velocimeter
(lens just visible) supported on a spider rig over a vacuum test
chamber. The chamber contained the porous material samples mounted on a
shaker with a reference accelerometer to measure table motion. The
samples (with aluminium loading plate) undergoing preliminary static
tests are shown in the figure series below
The shaker is placed within the vacuum
chamber, upon which a sample of the material to be tested is placed,
that is in turn topped with a aluminium plate.
The natural frequency of the tested porous
material was found from the mechanical properties, and a frequency
range was defined for the measuring system – 30 Hz to 230 Hz.
Frequency responses were measured with the assistance of the laser at
each point of a grid marked on the top of the loading plate to
determine (rigid) mode shapes.
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The
first part of the observation was done with normal laboratory settings.
The next part of the experiment was carried out in vacuum conditionsas
low as .0001 atm.
Subsequently,
a series of tests were carried out to determine the frequency response
and coherence in vacuum conditions. After some work very high quality
FRFs were measured a sample of which is shown in the following figure.
Figure: Comparison of
frequency response measured in the vacuum (red) and without the vacuum
(blue) in the frequency range 30 to 230 Hz .
In
this case the air entrained in the porous sample provides an inertial
loading to the system. The quality of the data is now sufficient in
quality to begin studieson dynamic effects in partial vacuum which
would be a continuation of this project.
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