Papers by Rauno Cavallaro
2019 18th European Control Conference (ECC), Jun 1, 2019
The paper proposes an alternative methodology to build Linear Fractional Transformation (LFT) mod... more The paper proposes an alternative methodology to build Linear Fractional Transformation (LFT) models of uncertain aeroelastic systems described by Fluid-Structure Interaction (FSI) solvers with the aim of studying flutter with the µ analysis technique from robust control. Two main issues can be identified for the fulfillment of this task. On the one hand, there is the difficult reconciliation between sources of physical uncertainty (well distinguishable in the original highorder system) and the abstracted uncertainties (defined in the reduced-order size representation used for the robust analyses). On the other hand, the large size of the resulting LFT model can prevent the application of robust analysis techniques. The solution proposed here consists of a symbolic LFT algorithm applied at FSI solver level, which guarantees the connection between the physical uncertainties and the parameters captured by the LFT. It also alleviates the final size of the LFT by exploiting the modal-oriented approach taken in introducing the uncertainties. Application of the framework using an unconventional aircraft layout as case study is finally discussed.
Aerospace
A hybrid reduced-order model for the aeroelastic analysis of flexible subsonic wings with arbitra... more A hybrid reduced-order model for the aeroelastic analysis of flexible subsonic wings with arbitrary planform is presented within a generalised quasi-analytical formulation, where a slender beam is considered as the linear structural dynamics model. A modified strip theory is proposed for modelling the unsteady aerodynamics of the wing in incompressible flow, where thin aerofoil theory is corrected by a higher-fidelity model in order to account for three-dimensional effects on both distribution and deficiency of the sectional air load. Given a unit angle of attack, approximate expressions for the lift decay and build-up are then adopted within a linear framework, where the two effects are separately calculated and later combined. Finally, a modal approach is employed to write the generalised equations of motion in state-space form. Numerical results were obtained and critically discussed for the aeroelastic stability analysis of a uniform rectangular wing, with respect to the relevan...
Aerotecnica Missili & Spazio
Aerospace Science and Technology
Springer Optimization and Its Applications, 2016
57th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2016
57th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2016
ABSTRACT Last decade trends in aerospace engineering have run in the direction of multidisciplina... more ABSTRACT Last decade trends in aerospace engineering have run in the direction of multidisciplinary preliminary optimization, which requires an integrated framework, where different modules are capable to interact with each other in order to estimate the effects of the configuration modifications undergone. The code presented in this paper is a platform where geometric modeling, grid generation and aerodynamic configuration evaluation are integrated. In the geometric modeling module the aerodynamic configuration is defined, the process of shape definition is easily achieved with the aid of specific features (as, for example, in the case of a wing, airfoils, their position along spanwise, twist angles etc). Useful tools like section sketcher, airfoil manager, NACA airfoil generator and flap sketcher are also available. Once the reference parameters are set a NURBS description is given. Other tools are offered, like configuration export to the IGES format; thus, the generated configuration could be imported in advanced CAD programs. In the meshing module structured or unstructured grids are built on the defined configuration. The structured grid is exported in the LaWGS standard, in order to use it as input grid in PanAir, the panel method code integrated in the aerodynamic module to carry out the aerodynamic configuration evaluation. The unstructured grid can be exported in different standard in order to eventually submit more accurate and time consuming aerodynamic analysis by means of external CFD programs.
Springer Optimization and Its Applications, 2012
56th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2015
An analytical formulation for the induced drag minimization of closed wing systems is presented. ... more An analytical formulation for the induced drag minimization of closed wing systems is presented. The method is based on a variational approach which leads to the Euler-Lagrange integral equation in the unknown circulation distribution. It is formally demonstrated for the first time that the Augmented Munk's Minimum Induced Drag Theorem formulated in the past for open single-wing systems is also applicable to closed systems, Joined Wings, and generic biwings. The Quasi-Closed C-Wing Minimum Induced Drag Conjecture discussed in the literature and regarding the equality of the optimum induced drag of a quasi-closed C-wing with the minimum induced drag of the corresponding closed system, is also addressed. Using the variational procedure presented in this work, it is also shown that in a general biwing under optimal conditions the aerodynamic efficiency of each wing is equal to the aerodynamic efficiency of the entire wing system (Biwing's Minimum Induced Drag Theorem). This theorem holds even if the two wings are not identical and present different shapes and wingspans. A direct consequence is that the optimal aerodynamic lift on each wing cannot be negative. It is then verified (but yet not demonstrated) that when the two wings of a biwing are brought close to each other so that the lifting lines identify a closed path, the minimum induced drag of the biwing is identical to the optimal induced drag of the corresponding closed system (Closed System's Biwing Limit Theorem). Finally, the non-uniqueness of the optimal circulation for a closed wing system is rigorously addressed and it is shown that there is an infinite number of equivalent solutions obtained by adding an arbitrary constant to a reference optimal circulation. This property has direct implication in the design of Joined Wings as far as the wing load repartition is concerned.
56th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2015
An invariant procedure for the minimization of induced drag of generic biwings and closed systems... more An invariant procedure for the minimization of induced drag of generic biwings and closed systems (Joined Wings) was presented in the companion paper [Minimum Induced Drag Theorems for Joined Wings, Closed Systems, and Generic Biwings: Theory] and is now adopted to study several theoretical open questions regarding these configurations. It is numerically verified that a quasi-closed C-wing presents the same optimal induced drag and circulation of the corresponding closed system. It is also verified that when the two wings of a biwing are brought close to each other so that the lifting lines identify a closed path, the minimum induced drag of the biwing is identical to the optimal induced drag of the corresponding closed system. The optimal circulation of this case differs from the quasi-closed C-wing one by an additive constant. The non-uniqueness of the optimal circulation for a closed wing system is also addressed and it is shown that there is an infinite number of equivalent solutions obtained by adding an arbitrary constant to a reference optimal circulation. This property has direct positive impact in the design of Joined Wings as far as the wing load repartition is concerned: the percentage of aerodynamic lift supported by each wing can be modified to satisfy other design constraints and without induced drag penalty. Finally the theoretical open question regarding the asymptotic induced drag behavior of Joined Wings when the vertical aspect ratio approaches infinity has been resolved. It has been shown that for equally loaded wings indefinitely distant from each other the boxwing minimum induced drag tends to zero. In that condition the upper and lower wings present a constant aerodynamic load. Prandtl's approximated formula for the minimum induced drag of a boxwing (Best Wing System) cannot be used to describe the asymptotic behavior. This work also shows that the optimal distribution over the equally loaded horizontal wings of a boxwing is not the superposition of a constant and an elliptical functions. This is an acceptable approximation only for small vertical aspect ratios (of aeronautical interest).
56th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2015
Diamond Wings, Strut- and Truss-Braced Wings, Box Wings, and PrandtlPlane, the so-called “JoinedW... more Diamond Wings, Strut- and Truss-Braced Wings, Box Wings, and PrandtlPlane, the so-called “JoinedWings”, represent a dramatic departure from traditional configurations. Joined Wings are characterized by a structurally overconstrained layout which significantly increases the design space with multiple load paths and numerous solutions not available in classical wing systems. A tight link between the different disciplines (aerodynamics, flight mechanics, aeroelasticity, etc.) makes a Multidisciplinary Design and Optimization approach a necessity from the early design stages. Researchers showed potential in terms of aerodynamic efficiency, reduction of emissions and superior performances, strongly supporting the technical advantages of Joined Wings. This review will present these studies, with particular focus on the United States joined-wing SensorCraft, Strut- and Truss- Braced Wings, Box Wings and PrandtlPlane.
Springer Optimization and Its Applications, 2012
ABSTRACT Last decade trends in aerospace engineering have run in the direction of multidisciplina... more ABSTRACT Last decade trends in aerospace engineering have run in the direction of multidisciplinary preliminary optimization, which requires an integrated framework, where different modules are capable to interact with each other in order to estimate the effects of the configuration modifications undergone. The code presented in this paper is a platform where geometric modeling, grid generation and aerodynamic configuration evaluation are integrated. In the geometric modeling module the aerodynamic configuration is defined, the process of shape definition is easily achieved with the aid of specific features (as, for example, in the case of a wing, airfoils, their position along spanwise, twist angles etc). Useful tools like section sketcher, airfoil manager, NACA airfoil generator and flap sketcher are also available. Once the reference parameters are set a NURBS description is given. Other tools are offered, like configuration export to the IGES format; thus, the generated configuration could be imported in advanced CAD programs. In the meshing module structured or unstructured grids are built on the defined configuration. The structured grid is exported in the LaWGS standard, in order to use it as input grid in PanAir, the panel method code integrated in the aerodynamic module to carry out the aerodynamic configuration evaluation. The unstructured grid can be exported in different standard in order to eventually submit more accurate and time consuming aerodynamic analysis by means of external CFD programs.
AIAA Journal, 2013
ABSTRACT The postbuckling behavior of joined-wing configurations has not been fully addressed in ... more ABSTRACT The postbuckling behavior of joined-wing configurations has not been fully addressed in the past. This topic is extensively discussed in this work. Starting from a baseline configuration, geometrical parameters as well as wings' load repartition are varied to assess their influence on buckling occurrence. The snap-buckling phenomenon and postcritical pattern are investigated with the adoption of the arc-length technique. The complex load transferring through the joint induces a deformation shape that can no longer carry additional load after a critical point is reached. An abrupt snap to a configuration that is not continuously adjacent to the previous one is then observed. Comparison with the instability state obtained via eigenvalue analysis demonstrates that buckling prediction through linear-buckling analysis is inadequate, and often, the actual critical load is overestimated. This study shows that, for PrandtlPlane joined-wing configurations, increasing the height-to-wingspan ratio is beneficial as far as structural response is concerned. This provides an important design guideline because it is well known from previous studies that high height-to-wingspan ratio decreases the induced drag and fuel consumption. The lift repartition and its effects on buckling show that an improvement of the structural stability of the joined-wing airplane can then be achieved by increasing the amount of aerodynamic load on the upper wing while reducing the lift on the lower wing. The strong bending torsion coupling typical of highly swept joined wings and its influence on the postcritical response are also investigated and discussed.
Dynamic aeroelastic behavior of a joined-wing PrandtlPlane configuration is
investigated herein. ... more Dynamic aeroelastic behavior of a joined-wing PrandtlPlane configuration is
investigated herein. The baseline model is obtained from a configuration previously
designed by partner universities through several multidisciplinary optimizations
and ad-hoc analyses, including detailed studies on the layout of
control architecture. An equivalent structural model has then been adopted to
qualitatively retain similar aeroelastic properties.
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; 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 control surfaces on the baseline configuration, freeplay
is also considered and its effects on the aeroelastic stability properties of the
joined-wing system are investigated for the first time.
Both cantilever and free flying configurations are analyzed. Fuselage inertial
effects are modeled and the aeroelastic properties are studied considering plunging
and pitching rigid body modes. For this configuration a positive interaction
between elastic and rigid body modes yields a flutter-free design (within the
range of considered airspeeds).
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 favors 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 the first elastic mode. Increasing pitching inertia, the above criticality
is postponed; meanwhile, the second elastic mode becomes unstable at progressively
lower speeds. For larger inertial values “cantilever” flutter properties,
having coalescence of first and second elastic modes, are recovered.
Uploads
Papers by Rauno Cavallaro
investigated herein. The baseline model is obtained from a configuration previously
designed by partner universities through several multidisciplinary optimizations
and ad-hoc analyses, including detailed studies on the layout of
control architecture. An equivalent structural model has then been adopted to
qualitatively retain similar aeroelastic properties.
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; 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 control surfaces on the baseline configuration, freeplay
is also considered and its effects on the aeroelastic stability properties of the
joined-wing system are investigated for the first time.
Both cantilever and free flying configurations are analyzed. Fuselage inertial
effects are modeled and the aeroelastic properties are studied considering plunging
and pitching rigid body modes. For this configuration a positive interaction
between elastic and rigid body modes yields a flutter-free design (within the
range of considered airspeeds).
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 favors 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 the first elastic mode. Increasing pitching inertia, the above criticality
is postponed; meanwhile, the second elastic mode becomes unstable at progressively
lower speeds. For larger inertial values “cantilever” flutter properties,
having coalescence of first and second elastic modes, are recovered.
investigated herein. The baseline model is obtained from a configuration previously
designed by partner universities through several multidisciplinary optimizations
and ad-hoc analyses, including detailed studies on the layout of
control architecture. An equivalent structural model has then been adopted to
qualitatively retain similar aeroelastic properties.
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; 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 control surfaces on the baseline configuration, freeplay
is also considered and its effects on the aeroelastic stability properties of the
joined-wing system are investigated for the first time.
Both cantilever and free flying configurations are analyzed. Fuselage inertial
effects are modeled and the aeroelastic properties are studied considering plunging
and pitching rigid body modes. For this configuration a positive interaction
between elastic and rigid body modes yields a flutter-free design (within the
range of considered airspeeds).
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 favors 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 the first elastic mode. Increasing pitching inertia, the above criticality
is postponed; meanwhile, the second elastic mode becomes unstable at progressively
lower speeds. For larger inertial values “cantilever” flutter properties,
having coalescence of first and second elastic modes, are recovered.