Gian Mario Polli

Shunted piezoelectric patches in elastic and aeroelastic vibrations

Abstract A procedure for a modal-based modeling and analysis of the effectiveness of shunted piezoelectric devices in increasing passive damping of elastic and aeroelastic systems is presented. Dynamical models with different levels of complexity, including both elastic and aeroelastic systems, have been considered in order to show the capability of the proposed approach. The numerical tests presented concern the description of several systems of aeronautical interest with piezoelectric devices to achieve a selective control of different modes. The linear aeroelastic modeling has been reduced to a rational polynomial transfer function, i.e., it has been represented in a linear state–space form which has allowed to extend the proposed piezo modeling to a general linear aeroelastic system. In particular, the aeroelastic application showed a weak capability of improving the stability margin, but a significant performance in the reduction of the gust response level in proximity of the critical condition of the system (e.g., when the flight speed is close to the flutter speed). Thus, a suitable performance of the piezo damper should be designed for any flight speed, altitude and Mach number. An optimal strategy to evaluate the electrical load for the tuning of piezo devices, as function of the flight speed (semi-active control), has been also proposed.

Sensitivity Analysis for the Dynamic Aeroelasticity of a Launch Vehicle

launcherintermsofthe firstnonzeronaturalfrequenciesandmodesofvibrationiscarriedout.Moreover,areducedorder model for the unsteady transonic aerodynamics is obtained, performing several prescribed modal transient boundary conditions by laminar-based computational fluid dynamics. Thus, a modal input/output system identification for the aerodynamics, performed in the frequency domain, allows one to identify the linearized unsteady aerodynamic operator in the neighborhood of the specific transonic flight condition. Both the structural andaerodynamic modelsare finally employedin the aeroelastic coupledmodel given bythe generalized Lagrangian equations of motion. An eigenanalysis, in terms of aeroelastic-system poles and complex eigenvectors on the linearized model, is performed to check the local dynamic stability of the launch vehicle. Finally, the proposed approach also allows one to give an evaluation of the uncertainty in the obtained stability scenario in terms of perturbing flight parameters like angle of attack, Mach number, flight speed, and air density.

Aeroelastic Response of Composite Aircraft Swept Wings Impacted by a Laser Beam

A closed-form solution for the thermoaeroelastic response of an aircraft swept wing made of advanced composite materials and exposed to a thermal impact generated by a laser beam is presented. For the aircraft wing, an advanced one-dimensional structural model that includes a number of nonclassical effects, such as transverse shear, warping inhibition, and thermoelastic anisotropy of constituent materials, is developed. It is supposed that the wing is immersed in an incompressible flowfield whose speed is below the flutter critical speed of the system. The solution of the problem has been obtained analytically in the space-time Laplace transform domain. Within this approach, the problem is reduced to the solution of an algebraic equation system in the transformed kinematical unknowns that is afterward inverted in the physical space. Although confined to the dynamic aeroelastic response, the approach of the dynamic response can provide important information on the conditions yielding the occurrence of the flutter instability.

Aerothermoelastic Stability of Composite Aerovehicle Wings Subjected to Heat Inputs

In this paper, a coupled aerothermoelastic dynamic stability analysis of composite aerovehicle wings featuring nonclassical effects, and immersed in an incompressible gas flow is developed. Specifically, the study concerns the aerothermoelastic stability of swept wings made of advanced composite materials and exposed to a heat flow generated by a laser beam impacting its deformed surface. Because of its exceptional features in thermal insulation of aerospace structures, the pyrolytic graphite is adopted in the actual numerical simulations together with consideration of a rectangular single-layered swept wing. The evaluation of the temperature field on the deformed (actual) configuration of the wing permits the authors to address the problems of the aerothermoelastic response and stability in a coupled framework. As a result, the exact analytical expression of the aerothermoelastic response of the heated wing is obtained in the Laplace space domain and, following it, the static and dynamic aeroelastic instabilities are determined. The obtained results indicate that the aeroelastic stability is substantially affected by the thermoelastic coupling. In the presentation and discussion of the results, special attention is given to the effects played by the flight speed, thermal anisotropy of the material constituent, ratio of the characteristic thermal time to the natural period of vibration, and direction of the external heat flux impacting the wing surface.

On Modeling of Piezoelectric Patches in Aeroelastic Vibrations

A procedure for the analysis of the effectiveness of shunted piezoelectric devices in increasing passive damping on aeroelastic systems is presented. The proposed methodology is based on the description of aeroelastic systems composed by a flexible fixed-wing in a linear potential flow bonded with several piezo-electric devices in order to achieve a selective control of critical aeroelastic modes. The aeroelastic application has shown the capability of improving the stability margin and reducing the response amplitude in the parametric operative range of the system assigned in term of flight speed, air density, and Mach number. Indeed, a relevant issue emphasizing the complexity of the aeroelastic vibrations is represented by the explicit parametric dependency of the system to such parameters. Thus, a suitable performance of the piezo damper should be designed for any flight speed, altitude and Mach number. Moreover, a control law has been used for the optimal tuning of piezo devices within the parameters ranges by means of a resistive-inductive shunt of such devices. The modal model, the stiffness matrices of piezo elements and also the aerodynamic model have been calculated by a commercial finite element code. The use of a finite-state form for the aerodynamics allows to get the solution of the problem by a standard first-order state-space representation.© 2002 ASME

Aerothermoelastic Response of a Functionally-Graded Aircraft Wing to Heat Loads

In this paper, a coupled aerothermoelastic dynamic stability analysis of a functionallygraded composite wing featuring non-classical effects, and immersed in an incompressible gas flow is developed. Specifically, the study concerns the aerothermoelastic stability of aircraft swept wing made of advanced functionally-graded composite materials and exposed to a heat flow generated by a laser beam impacting its deformed surface. The structural model is specialized in the computations to the case of a rectangular, single-layered, swept wing made of functionally graded material (FGM) with a ceramic-metallic-ceramic phase gradient. In particular, aluminun and alumina have been chosen as metallic and ceramic phases respectively. The evaluation of the temperature field on the deformed (actual) configuration of the wing permits to address the problems of the aerothermoelastic response and stability in a coupled framework. As a result, the exact analytical expression of the aerothermoelastic response of the heated wing is obtained in the Laplace space domain and, following this, the static and dynamic aeroelastic instabilities of the wing model are determined. The obtained results indicate that the aeroelastic stability is substantially affected by the thermo-elastic coupling and that the presence of FGM can also significantly influence the aerothermoelastic behavior.

Dynamics of Microstructured Shells with Thickness Extension

The analysis of the natural frequencies of a plate model is carried out in this paper starting from a model of shells which incorporates the eect of thickness extension and that is derived from the Virtual Work Theorem using material coordinates in the deformed configuration. Moreover, the shell is regarded as a micro-structured body whose fibers are free to rotate and distend. Finally, introducing proper internal constraints, and suitable stress resultant definitions, the equilibrium equations are reduced, in the framework of properly modified Reissner-Mindlin kinematical assumptions, to ones formally equivalent to that that can be obtained in the framework of properly modified Kirchho-Love hypotheses, but with additional equations describing the equilibrium in the fiber direction. Using a numerical approach based on a finite dierence scheme, it is shown how the natural frequencies of the Reissner-Mindlin model reduce when the Kirchho-Love constraints are retained. In particular, results indicate that, in the limit in which the Kirchho-Love hypotheses tend to become valid, the numerical frequencies of the pure Reissner-Mindlin model are aected by some round-o error, whereas in the case corresponding to the formulation adopted, where the solution is sought in terms of transversal displacement and dierence between the RM and the KL rotation of the fiber, the numerical solution reproduces exactly the analytical solution, and, notably, this behavior is emphasized at the highest frequencies. Therefore, in the case in which the transverse shear is treated independently one obtains good results, whereas, in the case in which the transverse shear has to be obtained as the dierence of the derivative of the transverse displacement and of the fiber rotation, the numerical solution introduces numerical errors due to the closeness of the present model to the KL kinematical hypotheses.

Aerothermoelastic Stability of Composite Aircraft Wings Subjected to Heat Inputs

In this paper, a coupled aerothermoelastic dynamic stability analysis of composite aircraft wings featuring non-classical efiects, and immersed in an incompressible gas ∞ow is developed. Speciflcally, the study concerns the aerothermoelastic stability of aircraft swept wings made of advanced composite materials and exposed to a heat ∞ow generated by a laser beam impacting its deformed surface. The structural model is specialized in the computations to the case of a rectangular single-layered swept wing composed of a transversely isotropic material. Due to its exceptional features in thermal insulation of aerospace structures, the pyrolytic graphite is adopted in the actual numerical simulations. The evaluation of the temperature fleld on the deformed (actual) conflguration of the wing permits to address the problems of the aerothermoelastic response and stability in a coupled framework. As a result, the exact analytical expression of the aerothermoelastic response of the heated wing is obtained in the Laplace space domain and, following this, the static and dynamic aeroelastic instabilities of the wing model are determined. The obtained results indicate that the aeroelastic stability is substantially afiected by the thermo-elastic coupling. In the presentation and discussion of the results, special attention is given to the efiects played by the ∞ight speed, thermal anisotropy of the material constituent, ratio of the characteristic thermal time to the natural period of vibration, and direction of the external heat ∞ux impacting the wing surface.