This work presents the experimental investigations of wave
propagation in two-dimensional (2D) periodic lattice structures.
Periodic structures in general feature unique wave propagation
characteristics, whereby waves are allowed to propagate only in
specific frequency bands, while they are attenuated at frequencies
belonging to the so-called "band gap". This behavior makes
periodic structures attractive candidates as passive vibration
isolators. The band-gap characteristics of a rectangular lattice are
here investigated. An optimized configuration is found through a
numerical model previously developed and presented. An aluminum
specimen is manufactured by machining, and tested for validation and
demonstration purposes. The wave field in the lattice is generated
by a point harmonic excitation at various frequencies, and it is
measured through a Scanning Laser Vibrometer. The objective of the
tests is the validation of the numerical model and the demonstration
of the unique filtering properties of the considered structural
assembly.
This paper investigates the wave propagation characteristics of
two-dimensional periodic lattice structures. Periodic structures
in general feature unique wave propagation characteristics,
whereby waves are allowed to propagate only in specific frequency
bands. Two-dimensional periodic structures complement this feature
with a low frequency directional behavior. The combination of
these unique characteristics makes two-dimensional periodic
structures ideal candidates for the design of pass-band
directional mechanical filters. A rectangular lattice
configuration is here considered. The wave attenuation properties
of the lattice are demonstrated and their sensitivity with respect
to geometry changes is explored. An optimization problem is
formulated by considering a set of geometric features as design
variables, and where the width of the attenuation zones and
angular range of propagation at low frequencies are the objective
functions. The identified optimal configuration show the combined
properties of the considered assembly and the effectiveness of the
analysis procedure. The experimental validation of the presented
results represents a natural development of the current effort.
The vibration and the sound radiation of cylindrical shells with cellular core is here analyzed. The considered
structure is composed of a repeated unit cell and can be classified as a Linear Cellular Alloy (LCA) core. The unit
cells are of a tetrahedral configuration, arranged according to a honeycomb lay-out. The considered configuration
has previously been proposed for core designs of sandwich beams with superior structural properties. In here, the
effects of the core configuration on the structural-acoustic behavior of the considered sandwich shell is investigated
through a FE model. The FE model is created with ANSYS, a commercially available Finite Element Analysis
(FEA) package. The sensitivity of the shell's dynamic characteristics to changes in the geometric properties
of the core is investigated. An optimization problem is formulated to determine the core configuration which
minimizes, within a target frequency range, the sound radiation of the shell in an unbounded fluid environment.
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