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-<br>vestigated. The baseline model is a beam model obtained from a configuration previously<br>designed by partner Universities through several multi disciplinary optimizations and several<br>ad-hoc analyses, including also detailed studies on the layout of control architecture.<br>This represented an ideal starting point since, due to the novel design, realistic layout<br>of the mobile surfaces, stiffness and inertia distributions are not available nor easily deter-<br>minable. An optimization process is defined to build a plate structural model which resembles<br>the reference model’s modal properties. The modal equivalence is pursued on the first five<br>structural modes, in terms of shape and frequencies. The obtained model is considered to<br>qualitatively retain similar aeroelastic properties with great benefits for the applicability of<br>results.<br>Flutter and post-flutter regimes, including limit cycle oscillations (LCOs) are studied.<br>A detailed analysis of the energy transfer between fluid and structure is carried out and<br>the areas in which energy is extracted from the fluid are identified, to gain insights on the<br>mechanism leading to the aeroelastic instability.<br>Starting from an existing design of mobile surfaces on the baseline configuration, freeplay is<br>considered and its effects on the aeroelastic stability properties of the system are investigated.<br>Both cantilever and free flying configurations are analyzed. Fuselage inertial effects are<br>modeled and the aeroelastic properties studied, considering plunging and pitching rigid body<br>modes. For this configuration a positive interaction between elastic and rigid body modes<br>turns the design in a flutter free one (in the range of considered speed).<br>To understand the sensitivity of the system and gain insight, fuselage mass and moment<br>of inertia are selectively varied. For a fixed pitching moment of inertia, larger fuselage<br>mass favours the body freedom flutter. When the moment of inertia is varied, a change<br>of critical properties is observed. For smaller values the pitching mode becomes unstable,<br>and coalescence is observed between pitching and first elastic mode. Increasing pitching<br>inertia, the above criticality is posticipated and, in the meanwhile, second elastic mode<br>becomes unstable at progressively lower speeds. For larger inertial values “cantilevered”<br>flutter properties, having coalescence of first and second elastic modes, are recovered.