Alessandro Agneni

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.

Damping measurements from truncated signals via Hilbert transform

Abstract The procedure of damping factor measurements by the instantaneous envelope and phase of a system impulse response, derived from the complex signal formed by the impulse response itself and its Hilbert transform, provides good results even when testing lightly damped structures. The damping factor evaluation of these systems, by the half power method in the frequency domain, represents a serious problem because of the truncation at the end of the observation window. The results, obtained from numerical simulations and presented in this paper, reveal the validity of this method even when the signal is highly truncated, wherein the frequency domain approach would lead to unacceptable errors.

Use of finite element codes for structures with passive piezoceramic devices

036Abstract\vspace{2mm} 038Limiting structural response by increasing damping with passive devices it is attractive because these elements, even if they fail to work properly, will never introduce mechanical energy into the structure. Thus although active control results more efficient, nevertheless possible malfunction of the control system or the changed properties of mechanical components, during lifetime, may cause the control system itself to trouble the structure dynamics. That is especially true in space, where external operations are difficult or even impossible and the system must work for lifetimes of years in the space environment (radiations, space debris, etc.). In this paper piezoceramic materials, suitably loaded with either resistors or resistors and inductors, are considered. The similarity of the piezo device complex stiffness with the ones used for viscoelastic material models allows one to simulate, with relative ease, the behaviour of a structure equipped with passive piezo devices by the use of general purpose finite element codes. Finite element models of a beam and one model of a plate are considered as test cases. Estimations of the damping coefficients, introduced by the passive devices, are in excellent agreement in the different models of the beam considered and are consistent in the case of the plate.

Elastic waves propagation in bounded periodic structures

Abstract Large space structures are mostly designed and constructed by repetitive lattice grids. Continuum models have been proposed in the literature as a simple means for the structural analysis of lattices. However continuum models hide some typical properties of the modular structures, such as their filtering effects. This paper investigates the differences between continuum and periodic models of a modular structure from the point of view of the elastic wave propagation. The analysis reveals that only for small wave numbers the models are equivalent, otherwise the dispersive behavior strongly differs and the continuum models become no longer effective.

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

Technological requirements for a passively attitude stabilized solar orbiter

The paper represents an intermediate issue of a research project targeting a possible low cost probe to investigate the Sun. The proposed design involves a passively attitude stabilized, conical shaped spacecraft which continuously keeps its rotation axis directed towards the Sun. The mission analysis is here pursued with particular emphasis to thermal aspects. A simulation code has been arranged especially to solve the thermal field of the problem along the orbit. Equilibrium temperature is obtained as function of the distance from the Sun, and several test cases, including different characteristics for material absorptance and emission as well as for the solar cell distribution on the probe surface, have been investigated