Piezoelectric shunt damping of rotationally periodic structures

structures with extremely low damping which may be responsible for severe vibrations

and possible high-cycle fatigue problems. To solve this, various techniques

of damping enhancement are under investigation. The present work is focused on

piezoelectric shunt damping.

This thesis considers the RL shunt damping of rotationally periodic structures using

an array of piezoelectric patches, with an application to a bladed drum representative

of those used in turbomachinery. Due to the periodicity and the cyclic symmetry of

the structure, the blade modes occur by families with very close resonance frequencies,

and harmonic shape in the circumferential direction; the proposed RL shunt

approaches take advantage of these two features.

When a family of modes is targeted for damping, the piezoelectric patches are

shunted independently on identical RL circuits, and tuned roughly on the average

value of the resonance frequencies of the targeted modes. This independent

configuration offers a damping solution effective on the whole family of modes, but

it requires the use of synthetic inductors, which is a serious drawback for rotating

machines.

When a specific mode with n nodal diameters has been identified as critical and

is targeted for damping, one can take advantage of its harmonic shape to organize

the piezoelectric patches in two parallel loops. This parallel approach reduces considerably

the demand on the inductors of the tuned inductive shunt, as compared

to independent loops, and offers a practical solution for a fully passive integration

of the inductive shunt in a rotating structure.

Various methods are investigated numerically and experimentally on a cantilever

beam, a bladed rail, a circular plate, and a bladed drum. The influence of blade

mistuning is also investigated.