DAGA 2010 - Deutsche Gesellschaft für Akustik eV

Programm DAGA 2010 49
Mo. 16:10 Gauß B 554 Vorkolloquium Körperschall
Stop and pass bands in cross-stiffened plates, a two-dimensional
model of structure-borne sound propagation in stiffened plates
R. Tschakert
TU Berlin, Institut für Strömungsmechanik und Techn. Akustik
Extensive research has been directed towards the propagation of
structure-borne sound in stiffened plates and shells using onedimensional
theoretical models and introducing the effects of periodicity.
In cross-stiffened plates, however, the situation is not the same. A
two-dimensional, analytic model is presented to calculate the structureborne
sound propagation in stiffened, infinite plates. The continuous force
and moment distribution at the beam-like stiffeners are discretised.
The response is obtained by means of a superposition of the excitation
force and all substitution forces and moments. The spatial attenuation of
sound is calculated with respect to the angle of incidence and the ordering
of the stiffeners. The results are validated by measurements on a
perspex plate with several fashions of parallel and crosswise stiffeners.
In cross-stiffened plates distinct stop and pass bands can only be found
in the mid frequency range if the propagation path is parallel to the crossstiffeners.
If not the stop and pass bands diminish. The additional propagation
paths and wave types lead to a non-smooth progression of the
transfer mobility curve over frequency. Due to additional reflections the
attenuation of cross-stiffened plates is partly lower than the attenuation
of parallel stiffened ones.
Mo. 16:35 Gauß B 554 Vorkolloquium Körperschall
Bending waves and spatially varying structural properties
B.A.T. Petersson
TU Berlin, Institut für Strömungsmechanik und Techn. Akustik
The implications of spatially varying structural properties for flexural vibrations
is addressed for one-dimensional waveguides. A solution to the
governing differential equation, based on Bessel functions, enables closed
form expressions for the point and transfer dynamic characteristics
of finite length, tapered beams. Also, under the assumption of pure bending,
a closed form expression has been derived for the semi-infinite
wedge, valid under the same conditions as the finite case solution and
which can be simply extended to encompass spatial variations obeying
non-integer power laws. The influence of tapering on the energy flow is
analysed for the flexural wave counterpart to the acoustic horn, constituted
by a finite length taper attached to a semi-infinite, uniform beam. It
is found that the main distinction to the uniform case is a comparatively
broad-banded transition from flexural vibrations governed by the properties
of the deep part of the system to vibrations governed by those of the
slender part.