| Summary: | The active suppression of elastic buckling has the potential to significantly increase
the effective strength of thin-wall structures. Despite all the interest in
smart structures, the active suppression of buckling has received comparatively
little attention. This research further develops analytical and experimental techniques
for the optimal control of columns and plates using piezo-ceramic actuators.
Previous work in this area has included numerous theoretical studies and a
very limited number of experiments.
Numerical models are formulated to simulate both the structure and its active
control system. The inclusion of mixed continuous-discrete control simulations
for active laminate design is unique to this research and provides insight into
issues that arise when trying to implement a continuous control strategy for
this unstable system with a discrete controller subject to sensor and noise error.
Therefore, limitations such as sensor uncertainty and noise, actuator saturation
and control architecture are included in the model. Three active plate strips and
a pneumatic compression loading system are implemented based on simulation
results and optimal controller design, to command the structure to deform in
ways that interfere with the development of buckling mode shapes. Due to the
importance of early detection, the relative effectiveness of active buckling control
is shown to be strongly dependent on the performance of the sensing scheme, as
well as on structure specific characteristics.
Initial experiments highlight the difficulties involved in obtaining ideal buckling behaviour in a practical environment. Correction of initial curvature in laminates
is successfully implemented, resulting in buckling curves closely resembling
finite element results. Active control is combined with the constant actuator
offset required to correct for initial curvature to obtain further gains in effective
strength.
Current experimental results show a 37% increase in the measured buckling
load from 2.1 to 2.9 kN and simulations indicate that the controlled critical
load can be further increased given higher actuator authority. These results are
significant because they stabilise a structure approximately 30 times stiffer than
in any other published results, where this high stiffness has introduced additional
difficulties mainly due to the faster dynamics of the structure. They are also the
first known experimental results to successfully stabilise an active laminate plate
structure.
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