Show simple item record

dc.contributor.advisorVan Niekerk, J. L.
dc.contributor.authorEckert, Bernden_ZA
dc.contributor.otherUniversity of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
dc.date.accessioned2007-11-16T08:54:15Zen_ZA
dc.date.accessioned2010-06-01T08:51:11Z
dc.date.available2007-11-16T08:54:15Zen_ZA
dc.date.available2010-06-01T08:51:11Z
dc.date.issued2007-03en_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/2522
dc.descriptionThesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007.
dc.description.abstractThe helicopter is a prime example of a nonlinear multi-body dynamic system that is subjected to numerous forces and motions to which the system must react. When a helicopter, with a conventionally articulated rotor head, is resting on the ground with its rotor spinning, a condition called ground resonance can develop. Ground resonance is a specific self-excited oscillation of the helicopter and is caused by the interaction between the main rotor blades and the fuselage structure. Inertia forces of the blades perform an out-of-phase lagging motion, which reacts with the elastic landing gear of the helicopter. For certain values of the main rotor angular velocity, the frequency of these inertia forces coincides with a natural vibration frequency of the fuselage structure. If this occurs, the inertia forces of the lagging blades produce oscillations of the fuselage, which then further excite the lagging motion of the blades. This interaction is responsible for an instability of conventionally articulated main rotor helicopters, which is called ground resonance. The ground resonance phenomenon is investigated by means of a classical analytical approach in which the ground resonance equations are derived from Euler-Bernoulli beam theory and verified with results in literature. These equations are required to discuss ground resonance stability in further detail and determine the specific regions in which the phenomenon occurs. These results are incorporated in a simplified numerical model using an elastic multiple-body dynamics analysis program called DYMORE to simulate the South African Rooivalk Combat Support Helicopter. DYMORE is a program that offers nonlinear multi-body dynamic analysis code, using the finite element method, which was specifically developed for helicopter modelling. The complexity of helicopter modelling generally requires large amounts of computing power to ensure reasonable processing time. In order to prevent excessive computational time, the numerical model will be simplified in terms of aerodynamic and structural aspects. The scope of the numerical investigation is, therefore, limited to the ground resonance phenomenon without the effect of aerodynamic forces and representing the fuselage as multi-body beam structures of specified stiffness.en_ZA
dc.format.extent4137428 bytesen_ZA
dc.format.mimetypeapplication/pdfen_ZA
dc.language.isoenen_ZA
dc.publisherStellenbosch : University of Stellenbosch
dc.subjectDissertations -- Mechanical engineeringen
dc.subjectTheses -- Mechanical engineeringen
dc.subjectResonant vibrationen
dc.subjectRotors (Helicopters)en
dc.titleAnalytical and a numerical ground resonance analysis of a conventionally articulated main rotor helicopteren_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of Stellenbosch


Files in this item

Thumbnail
Thumbnail

This item appears in the following Collection(s)

Show simple item record