ETD system

Electronic theses and dissertations repository


Tesi etd-05212015-132112

Thesis type
Tesi di laurea magistrale
PrandtlPlane Joined Wing: Body Freedom Flutter, Limit Cycle Oscillation and Freeplay Studies
Corso di studi
relatore Prof. Frediani, Aldo
relatore Prof. Demasi, Luciano
relatore Dott. Cavallaro, Rauno
Parole chiave
  • Structural Equivalence
  • Freeplay
  • Body Freedom Flutter
  • Nastran
  • Aeroelasticity
  • PrandtlPlane
  • LCO
  • DLM
Data inizio appello
Data di rilascio
Riassunto analitico
Dynamic aeroelastic behaviour of a joined-wing PrandtlPlane configuration is here in-
vestigated. The baseline model is a beam model obtained from a configuration previously
designed by partner Universities through several multi disciplinary optimizations and several
ad-hoc analyses, including also detailed studies on the layout of control architecture.
This represented an ideal starting point since, due to the novel design, realistic layout
of the mobile surfaces, stiffness and inertia distributions are not available nor easily deter-
minable. An optimization process is defined to build a plate structural model which resembles
the reference model’s modal properties. The modal equivalence is pursued on the first five
structural modes, in terms of shape and frequencies. The obtained model is considered to
qualitatively retain similar aeroelastic properties with great benefits for the applicability of
Flutter and post-flutter regimes, including limit cycle oscillations (LCOs) are studied.
A detailed analysis of the energy transfer between fluid and structure is carried out and
the areas in which energy is extracted from the fluid are identified, to gain insights on the
mechanism leading to the aeroelastic instability.
Starting from an existing design of mobile surfaces on the baseline configuration, freeplay is
considered and its effects on the aeroelastic stability properties of the system are investigated.
Both cantilever and free flying configurations are analyzed. Fuselage inertial effects are
modeled and the aeroelastic properties studied, considering plunging and pitching rigid body
modes. For this configuration a positive interaction between elastic and rigid body modes
turns the design in a flutter free one (in the range of considered speed).
To understand the sensitivity of the system and gain insight, fuselage mass and moment
of inertia are selectively varied. For a fixed pitching moment of inertia, larger fuselage
mass favours the body freedom flutter. When the moment of inertia is varied, a change
of critical properties is observed. For smaller values the pitching mode becomes unstable,
and coalescence is observed between pitching and first elastic mode. Increasing pitching
inertia, the above criticality is posticipated and, in the meanwhile, second elastic mode
becomes unstable at progressively lower speeds. For larger inertial values “cantilevered”
flutter properties, having coalescence of first and second elastic modes, are recovered.