Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: An experimental investigation was conducted usmg a cantilever beam to illustrate an
understanding of vibration techniques and phenomena. The [Tee and forced vibration of the
cantilever beam was investigated using various modelling strategies. Theoretical models such
as the Lumped parameter, Myklestad, Distributed Parameter and Finite Element Methods
were analysed and compared with experimental measurements. Excellent agreement of the
natural frequencies, mode shapes and the harmonic transfer functions were found.
To investigate tail boom vibration, a Finite Element Model of a simplified helicopter tail
boom design was tested against experimentally measured data. The results correlated
accurately and the model was used to evaluate the effectiveness of a vibration suppression
system designed for the tail boom.
The vibration suppression system was designed using two, parallel dynamic absorbers to
reduce tail boom vibrations at its two dominant frequencies. For the purposes of this thesis,
the dynamic absorbers were tuned to reduce the resonant peaks at the dominant excitation
frequencies of the excitation force in-line with the thrust of the tail rotor only. This excitation
force was estimated using a simplified tail rotor dynamic model, which when compared with
actual vibration data was assumed to predict the basic frequency trends of the force, reliably.
Incorporating the designed components into an accurate Lumped Parameter model of a
cantilever beam structure and simulating the response of the structure at the dominant
excitation frequencies of the calculated excitation force, tested the vibration suppression
system. The results of this investigation proved the effectiveness of the design procedure and
optimisation process of the design parameters. A similarly designed suppression system was
incorporated into the Finite Element tail boom model and from the analytical results obtained
it was shown to cause a fair reduction in the vibration response at the two dominant
frequencies of the excitation force.
Finally, two possible applications were suggested from the research presented in this thesis.
The first application was the simplified configuration of a vibration monitoring system for the
tail boom. The second application was the possible development of a system using the
response of vibration suppression absorbers to predict the magnitudes of the excitation forces
on the tail boom. / AFRIKAANSE OPSOMMING: 'n Experimentele ondersoek is ondemeem deur gebruik te maak van 'n ingeklemde balk om
vibrasie tegnieke te illustreer. Die vrye en geforseerde vibrasie van die ingeklemde balk is
ondersoek deur verskillende model tegnieke te gebruik. Teoretiese modelle soos die Lumped
parameter, Myklestad, Distributed Parameter en Eindige Element Metodes was geanaliseer
en vergelyk met die eksperimentele waardes. Uitstekende ooreenstemmings was gevind
tussen die natuurlike frekwensies, die eievektore en die harmoniese oordragsfunk:sie.
Om stert vibrasie te ondersoek, was'n eindige element model van 'n helikopter stert getoets
teenoor die eksperimentele data. Die resultate het akuraat gekorreleer en dus was die model
gebruik om die effektiwiteit van 'n vibrasie supressie sisteem te evalueer.
Die vibrasie supressie sisteem was ontwerp deur gebruik te maak van twee parallele
dinamiese absorbeerders om die helikopter stert se eerste twee dominante vibrasie
frekwensies te minimeer. Vir die doel van hierdie tesis was die dinamiese absorbeerders
ingestel om net die resonante pieke van die opgewende krag wat in lyn is met die drykrag van
die stert rotor te minimeer Hierdie opgewende krag was, deur gebruik te maak van 'n basiese
stert rotor dinamiese model, aanvaar om die basiese frekwensie tendense van die krag te
voorspel. Die supressie sisteem wat ontwerp was, was getoets op die lumped parameter balk
en het veroorsaak dat die voorspelde opgewende krag by al twee van sy dominante .
frekwensies baie geminirneer was. Die effektiwiteit van die sisteem was dus bewys en die
sisteem was gebruik om die respons van die eindige element model van die stert te verbeter.
Die resultate het 'n aanvaarbare reduksie in die respons by die twee dominante frekwensies
van die opgewende krag, gewys.
Laastens, deur gebruik te maak van die resultate in hierdie tesis. was twee moontlikhede
voorgestel. Die eerste een was die konfigurasie van 'n vibrasie moniterings sisteem vir die
helikopter stert. Die tweede mmontlikheid was die moontlike ontwikkeling van 'n sisteem
wat die grootte van die opgewende krag by die stert rotor kon voorspel, deur gebruik te maak
van die vibrasie suppressie absorbeerders.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52873 |
| Date | 04 1900 |
| Creators | Funnell, M. E. (Marc Edwin) |
| Contributors | Pienaar, D., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 1 v. (various foliations) : ill. |
| Rights | Stellenbosch University |
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