Vibration Suppression in Flexible Structures using Hybrid Active and Semi-active Control

229 Pages·2017·15.23 MB·English

by  Irfan Ullah Khan

Vibration Suppression in Flexible
Structures using Hybrid Active and
Semi-active Control
Irfan Ullah Khan
Supervisor: Prof. D. Wagg and Prof. N. D. Sims
Department of Mechanical Engineering
University of Sheffield
This dissertation is submitted for the degree of
Doctor of Philosophy
June 2017

Iwouldliketodedicatethisworktomyparents.

Declaration
I hereby declare that all the work presented in this thesis is original unless otherwise
stated or referred and has not been submitted anywhere else to attain a degree. The
thesis meets the university requirements and has less than 80,000 words including
appendices, references, footnotes, equations, tables. The work presented here is my
ownworkandhasnotbeendoneincollaborationwithanyinstituteorgroup.
IrfanUllahKhan
June2017

Acknowledgements
Firstofall, Iwouldliketo thank myparentsandfamilyfor theirsupportandbeliefin
me. Without their support, it would not be feasible for me to reach up to this stage. I
wouldliketoexpressmydeepgratitudetomysupervisorsProf. DavidWaggandProf.
Neil Sims for their guidance and help. Weekly discussions with my supervisors and
theircontinuous feedback helpedmea lotineverystep ofmyresearch. I acknowledge
and appreciate Prof. David Wagg, who has provided me with various opportunities
topresentmyworkindifferentconferences. HehasassociatedmewithEngineering
Nonlinearity (ENL) group as well, where I have presented my work in the form of
postersandpresentations. Thisplatformhasalsogivenmeanopportunitytointeract
with people linked with academia and industry. I also want to thank everyone from
the Dynamic Research Group (DRG) for their support. I would like to acknowledge
Mr. Les Morton help during redesigning of rig in the lab and Mr. Richard Kay, who
provided his expertise along with the Oddy hydraulics people for fault identification
inthehydraulicsystem. Iamthankfultoallmyfriendswhosupported,toleratedand
encouraged me throughout this journey. Last but not the least, a special gratitude to
MelanieFitzgeraldandNumairaKhanforthesupportandhelpwiththeproofread.

Abstract
This thesispresents a new hybrid active and semi-active controlmethod for vibration
suppression in flexible structures. The method uses a combination of a semi-active
device and an active control actuator situated elsewhere in the structure to suppress
vibrations. The key novelty is to use the hybrid controller to enable the semi-active
device to achieve a performance as close to a fully active device as possible. This is
accomplishedbyensuringthattheactiveactuatorcanassistthesemi-activedeviceinthe
regionswhereenergyisrequired. Also,thehybridactiveandsemi-activecontrolleris
designedtominimisetheswitchingofthesemi-activecontroller. Thecontrolframework
usedistheimmersionandinvariancecontroltechniqueincombinationwithasliding
modecontrol. Atwodegree-of-freedomsystemwithlightlydampedresonancesisused
asanexamplesystem. Bothnumericalandexperimentalresultsaregeneratedforthis
systemandthencomparedaspartofavalidationstudy.
The experimental system uses hardware-in-the-loop simulation to simulate the
effectofboththedegrees-of-freedom. Theresultsshowthattheconceptisviableboth
numerically and experimentally, and improved vibration suppression results can be
obtainedforthesemi-activedevicethatapproachestheperformanceofanactivedevice.
To illustrate the effectiveness of the proposed hybrid controller, it is implemented to
keepthecontactforceconstantinthepantograph-catenarysystemofhigh-speedtrains.
Adetailedderivationisgivenafterwhichthesimulationresultsarepresented.
Then a method to design a reduced order observer using an invariant manifold
approachisproposed. Themainadvantageofthisapproachisthatitenablesasystematic
design approach, and (unlike most nonlinear observer design methods), it can be
generalisedoveralargerclassofnonlinearsystems. Themethodusesspecificmapping
x
functions in a way that minimises the error dynamics close to zero. Another important
aspectistherobustnesspropertywhichisduetothemanifoldattractivity: animportant
featurewhenanobserverisusedinaclosedloopcontrolsystem. Theobserverdesign
is validated using both numerical simulations and hardware-in-the-loop testing. The
proposedobserveristhencomparedwithaverywellknownnonlinearobserverbasedon
theoff-linesolutionoftheRiccatiequationforsystemswithLipschitztypenonlinearity.
Inallcases,theperformanceoftheproposedobserverisshowntobeexcellent.