university of florida thesis or dissertation formatting template

Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
TEMPORAL ANALYSIS OF TRANSONIC FLOW-FIELD CHARACTERISTICS
ASSOCIATED WITH LIMIT CYCLE OSCILLATIONS
Chair: Richard C. Lind, Jr.
Major: Aerospace Engineering
By
Crystal Lynn Pasiliao
May 2009
Limit Cycle Oscillation (LCO) is a sustained, non-divergent, periodic motion experienced
by aircraft with certain external store configurations. Flutter, an instability caused by the
aerodynamic forces coupling with the structural dynamics, and LCO are related as evidenced by
the accuracy with which linear flutter models predict LCO frequencies and modal mechanisms.
However, since the characteristics of LCO motion are a result of nonlinear effects, flutter models
do not accurately predict LCO onset speed and amplitude. Current engineering knowledge and
theories are not sufficient to provide an analytical means for direct prediction of LCO; instead
engineers rely heavily on historical experience and interpretation of traditional flutter analyses
and flight tests as they may correlate to the expected LCO characteristics for the configuration of
concern.
There exists a significant need for a detailed understanding of the physical mechanisms
involved in LCO that can lead to a unified theory and analysis methodology. This dissertation
aims for a more thorough comprehension of the nature of the nonlinear aerodynamic effects for
transonic LCO mechanisms, providing a significant building block in the understanding of the
overall aeroelastic effects in the LCO mechanism. Examination of a true fluid-structure
interaction (FSI) LCO case (flexible structure coupled with CFD) is considered quasi-
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