Showing papers by "Italian Aerospace Research Centre published in 2010"

A shape memory alloys based tuneable dynamic vibration absorber for vibration tonal control

Abstract: This paper examines a novel model of an Adaptive Tuneable Dynamic Vibration Absorber (ATDVA), based on the use of Shape Memory Alloy materials (SMA). Being adaptive, the absorber is able to track variation of the structural dynamic response. The absorber architecture is extremely simple: it consists of a clamped SMA wire and a concentrated mass. Two reference structures have been considered: a typical aeronautical aluminium panel and a fibreglass panel. In the first part, the investigated concept is introduced with a short presentation about the SMA main properties. The realisation and experimental characterisation of the device are then presented. Its implementation, a report on the experimental campaign and the presentation of the attained results conclude the work, together with a discussion on the achieved results and the next investigation steps.

Numerical/Experimental Correlation of a Plasma Wind Tunnel Test on a UHTC-Made Nose Cap of a Reentry Vehicle

Abstract: The nose cap demonstrator named Nose_2 has been tested for the second time in the plasma wind tunnel (PWT) facility which is part of the sharp hot structure (SHS) technology project, focused on the assessment of the applicability of ultrahigh temperature ceramics (UHTC) to the fabrication of high performance vehicles and SHS for reusable launch vehicles. In this paper the FEM based thermal analyses, carried out for the rebuilding of this PWT test, are presented. Experimental data measured in the PWT have been compared with numerical ones in order to validate the FEM model and to help in interpreting the experimental test itself. The knowledge on the physical phenomenon under investigation has been greatly improved, thanks to the synergy between numerical and experimental activities. In particular, a qualitative study of the modeling of the tip-dome interface has been performed in order to estimate the thermal contact resistance that heat flux encounters in passing through the demonstrator. The correlation...

A new approach for the computation of harmonics and interharmonics produced by AC/DC/AC conversion systems with PWM inverters

Abstract: The computation of harmonics and interharmonics produced by AC/DC/AC conversion systems with PWM inverters is considered, and a new approach is presented. Basically, a new inverter model is introduced that is based on the modulation function theory and is able to take into account the voltage ripple at the inverter input terminals. A rectifier model that was previously proposed and the new inverter model are first used in the framework of a direct injection procedure and, then, in an iterative harmonic and interharmonic analysis. The proposed model can be applied successfully to adjustable speed drives for asynchronous motors, achieving better modeling accuracy with respect to approaches based on simplified inverter modeling. They also allow a sensible reduction of computational burden with respect to the time-domain models. For this reason, they constitute an attractive tool inside Monte Carlo simulations for probabilistic analyses of harmonic and interharmonic distortion. Numerical experiments demonstrate the good performance of the proposed models and the need to account for the presence of interharmonics for high-power PWM drives. Copyright © 2009 John Wiley & Sons, Ltd.

Fully Structured Aerodynamic Model for Parameter Identification of a Reentry Experimental Vehicle

Abstract: Vehicle preflight aerodynamic databases are frequently validated and improved using system identification techniques that require the availability of flight data and the definition of suitable aerodynamic models. In this framework, the paper presents a novel theoretical aerodynamic model to be used for the aerodynamic identification of a lifting body in subsonic, transonic, and supersonic regimes. The proposed model is based on the general properties of the continuity equation in the von Karman form. Each aerodynamic coefficient incorporates free parameterstobeestimatedfromthe flightdataanalysisandtakesintoaccountthesimultaneouseffectsoftheseveral vehicle state variables. The proposed model was applied to the identification from the flight data of an experimental vehicle of the Italian Aerospace Research Centre. Identification results show that the model is able to perform an excellent fitting of the aerodynamic coefficients experimented in flight by the vehicle.

Finite Element Implementation of a Multivariant Shape Memory Alloy Model

Abstract: In this article a finite element implementation of a multivariant constitutive model of shape memory alloys for a mono-dimensional element is presented. The model has been implemented by writing the kinetic law and the equilibrium equation in the rate form and integrating this equation along the thermomechanical load path. The implemented model allows to simulate both the operation in isothermal condition, in full or partial pseudoelastic recover and the behavior of shape memory alloy’s wire in mixed thermal and mechanical load application such as in cyclic activations of a wire against a structure. The developed model is suitable for integration in structural finite element program allowing to simulate the action of SMA wires in integrated in complex structure. A number of numerical cases for the developed model are showed in order to verify the ability to reproduce expected typical SMA behaviors.

Multi-tone Switching Shunt Control by a PZT Network Embedded into a Fiberglass Panel: Design, Manufacture, and Test:

Abstract: Research in noise and vibration control has partially focused on semi-active attenuation techniques such as switching shunt control (SSC) systems. Among the various methods, SSC architectures exhibit several interesting advantages such as low power absorption and intrinsic adaptive capabilities. This approach may represent an acceptable compromise between passive and active solutions. In previous work the authors implemented and validated 1D and 2D numerical models, addressed to describe continuous simple isotropic structures under tonal excitations controlled by single-element SSC system. Further efforts were then directed to extend the applicability of those models to non-isotropic structures and to multi-tone control devices. In this article, a 6-PZT network multi-tone SSC system is presented, and embedded into a balanced fiberglass laminate. The network geometry is defined according to an optimization process following modal information. The former 1-channel control circuit was extended to drive up to...

Fourier expansion solution for a switched shunt control applied to a duct

Abstract: In the present work, a semi analytic approach aimed at estimating the effects on reduction of the pressure sound level by synchronised switched shunt logic is described. The displacement field within a 1D longitudinal air column through a Fourier series expansion has been formalised by assigning a sinusoidal perturbation and fluid-structure interface condition on the left and right boundaries, respectively. To simulate the no control operative condition, the solution has been computed for the entire time domain, keeping invariant all circuitry properties; then for the switch working modality, the solution has been computed by splitting the entire time domain into partitions; for any partition, specific circuitry properties (e.g. piezo voltage, electrical field...) have been selected. Based on the displacement information, the related sound pressure level has been compared for no controlled and controlled operative conditions, with and without signal amplification.

Structural design and test capability of an integrated stiffened CFRP panel

Abstract: Purpose – This paper's aim is to focus on the design, manufacture and test of a stiffened panel in composite material with integrated longitudinal foam‐filled stiffeners, spar and rib caps, using one‐shot liquid infusion (LI) process, reducing weight and number of subparts respect to metallic reference baseline P180 Avanti vertical fin.Design/methodology/approach – Extensive activities in computational applications in order to improve the efficiency of the design process finite element analysis/structural sizing codes have led to an optimised engineering design process that resulted in a successful stiffened carbon fibre reinforced polymer panel design in terms of weight and number of parts with respect to the metallic baseline.Findings – The composite panel has fulfilled all the design requirements (reduction of mass and number of parts with respect to the metallic reference baseline) overcoming the certification static test, and confirming the reliability of the theoretical analyses.Research limitations...