Essais & Simulations 151

MESURES
MÉTHODE
Operational replication of strain
responses during MIMO random
control tests
Les essais de contrôle des vibrations aléatoires sont réalisés pour vérifier qu’un système et tous ses
sous-composants peuvent résister à un environnement de vibrations aléatoires pendant la durée de vie
opérationnelle. Ces essais visent à reproduire avec précision, par l’intermédiaire d’une excitation contrôlée,
la réponse structurelle en service d’un dispositif testé (DUT) dans l’axe principal de vibration.
Introduction
Random vibration control tests are
performed to verify that a system and all its
sub-components can withstand a random
vibration environment during the operational
life. These tests aim to accurately replicate
via controlled shaker excitation the inservice
structural response of a device under
test (DUT) in the main axis of vibration and
in all the possible axes where the levels
exceed the acceptance thresholds. In the
recent years great visibility has been given
to the problem of accurately replicating in
the laboratory the operational conditions
that the DUT will eventually experience
in-service. Multiple-Input Multiple-Output
(MIMO) Random Control testing allows
for a close replication of the nature of
the operational loads. Previous work on
aerodynamically excited structures has
shown how increasing the number of control
channels and trying to match the operational
mechanical impedance, on top of a successful
random test, also allows to closely match the
response in locations that are not controlled.
These observations are at the basis of the
so-called IMMAT (Impedance-Matched
Multi-Axial Test). In this context, it was
shown that the environmental replication
further improves by increasing the number
of shakers and adopting rectangular control
strategies. The ultimate goal of these studies
is to converge towards a solution that will
lead to a laboratory test that will eventually
lead to damage mechanisms closer to the
one that the component would experience
in service. The objective of this paper is to
continue the investigations to the physical
quantities that can be actively controlled.
The research question to answer with this
work is: since the failure of the unit under
test is directly related to the stresses and
hence the strains, could MIMO Random
Control techniques applied directly to strain
measurements improve the replication of the
operational strain field?
BACKGROUND AND METHODOLOGYS
To address this question, a set of experiments was carried out on
the setup shown in Figure 1. Figure 1 (a) and (b) show the setup
adopted for definition of the “pseudo-operational” conditions,
highlighting the locations of the sensors for recording strain
and acceleration responses. The inputs for the definition of the
pseudo-operational conditions were white-pink noise uncorrelated
voltages sent from a Siemens Simcenter SCADAS system
to Siemens Simcenter Q-Sources inertial shakers attached to
the frame of the DUT. Lumped calibrated masses were also
attached to the lower side of the DUT allowing for simulating
mass loading differences during the “pseudo-test” conditions.
Figure 1 (c) shows the setup adopted for definition of the “pseudo-test”
conditions, The test complexity was gradually increased
introducing differences between “pseudo-operational” and “pseudo-test”
conditions and changing control strategy.
Figure 1 - Test setup adopted for the “pseudo-operational” conditions:
20 I ESSAIS & SIMULATIONS • N°151 • Novembre - Décembre 2022 - Janvier 2023