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Frequency-domain modal analysis with aeroelastic applications

maandag, 14 december, 2009 - 16:00
Campus: Brussels Humanities, Sciences & Engineering campus
K
auditorium P. Janssens
Tim De Troyer
doctoraatsverdediging

The vibration of a mechanical structure is usually stable, i.e. the
oscillatory motion dies out if no excitation is present. If a structure is
exposed to a fluid flow, its vibration characteristics will change depending
on the speed of the flow. There exists a critical speed (the flutter speed)
above which the vibration amplitude starts to increase indefinitely. The
flutter speed is an important design parameter for an aircraft’s wing and
tail surfaces, the blades of a wind turbine or a compressor, etc. All newly
developed aircraft must for instance be tested in flight to verify that its
vibration is stable for all combinations of altitude and speed it is designed
for. Since the vibration’s amplitude grows violently when flutter occurs,
these tests are very dangerous, time-consuming, and costly.

In this dissertation we improve existing methods to deal with the
requirements posed by ground and flight flutter testing. On the one hand,
the computational speed is important since flutter can occur suddenly. On
the other hand, the vibration parameters must be estimated accurately,
even though the measurements are perturbed by turbulence and other
noise sources. We provide a compromise between computational speed
and accuracy, derive uncertainty intervals, and show how one can use the
effect of turbulence to advantage. Finally, we introduce a new method to
predict the flutter speed based on measurements at lower speed.