Title page for ETD etd-06062008-171425
|Type of Document
||Guigou, Catherine R. J.
||Active control of sound radiation due to subsonic wave scattering from discontinuities on thin elastic beams
|Fuller, Christopher R.
|Singh, Mahendra P.
|Burdisso, Ricardo A.
|Mahan, James Robert
|Wicks, Alfred L.
|Date of Defense
Much progress has been made in recent years in active control of sound radiation
from vibrating structures. Reduction of the far-field acoustic radiation can be
obtained by directly modifying the response of the structure by applying structural
inputs rather than by adding acoustic sources. Discontinuities, which are present
in many structures are often important in terms of sound radiation due to wave
scattering behavior at their location. In this thesis, an edge or boundary type discontinuity
(clamped edge) and a point discontinuity (blocking mass) are analytically
studied in terms of sound radiation. When subsonic vibrational waves impinge on
these discontinuities, large scattered sound levels are radiated. Active control is then
achieved by applying either control forces, which approximate shakers, or pairs of
control moments, which approximate piezoelectric actuators, near the discontinuity.
Active control of sound radiation from a simply-supported beam is also examined.
For a single frequency, the flexural response of the beam subject to an incident
wave or an input force (disturbance) and to control forces or control moments is
expressed in terms of waves of both propagating and near-field types. The far-field
is then evaluated in terms of the structural response, using
Rayleigh's formula or a stationary phase approach, depending upon the application.
The control force and control moment magnitudes are determined by optimizing a
quadratic cost function, which is directly related to the control performance. On
determining the optimal control complex amplitudes, these can be resubstituted in
the constitutive equations for the system under study and the minimized radiated
fields can be evaluated.
|| Approximate Download Time
| 28.8 Modem
|| 56K Modem
|| ISDN (64 Kb)
|| ISDN (128 Kb)
|| Higher-speed Access
next to an author's name indicates that all
files or directories associated with their ETD
are accessible from the Virginia Tech campus network only.
If you have questions or technical
problems, please Contact DLA.