Search

A thorough understanding of the effects of sloshing on aircraft dynamic loadscan be exploited for the future design of aircraft to be able to reduce their structural mass. Indeed, the high vertical accelerations caused by the vibrations of the structure can lead to the fragmentation of the fuel free surface. Fluid impacts on the tank roof are potentially a new source of damping for the structure that have hardly been considered before when computing the dynamic loads of the wings. This work aims at applying recently developed reduced-ordermodels for vertical sloshing to a representative aeroelastic testbed, to investigate their effects on the wing’s response under pre-critical and post-critical conditions. The vertical sloshing dynamics is considered comparing three different reduced order models based, respectively, on neural networks, equivalent mechanical model, and surrogate model then integrated into theaeroelastic system.

For the Aerospace Industry the dynamic identification of a Launch Vehicle under its actual operative conditions is of great importance for assessing the numerical model of the structure and for improving the structural design. Therefore, the development of Operational Modal Analysis procedures able to track the time-dependency of the modal parameters of time-varying systems is of great interest for the aerospace applications. In this paper a method for the estimate of modal parameters of a time-dependent dynamic system that uses the Hilbert-Huang transform is proposed. First, the global time-trend of the natural frequencies is obtained by applying the Hilbert-Huang transform to subsequent time subintervals of the whole observation time. Finally, the damping ratios corresponding to the natural frequencies estimated for each time subinterval are estimated by using a standard method in operational modal analysis working in the frequency domain. The proposed method is assessed considering the numerically evaluated vibrations of a booster of a space launcher system.

The poly-reference Least Squares Complex Frequency-domain (pLSCF) estimator –commercially known as the LMS PolyMAX method- has introduced an improvement in the field of modal analysis. The main advantages are its computational speed and the very clear stabilization diagrams it yields even in the case of highly damped systems and noisy FRF measurements. Moreover, the numerical stability of the algorithm allows for a large-bandwidth and high-model order analysis and makes it suitable both for lowly- and highly-damped structures. Regardless of the very clear stabilization diagrams, it has been observed that the damping estimates are not always reliable for highly damped modes when the FRFs are very noisy. In this paper, a two-step procedure is introduced to improve the damping estimates while maintaining the very clear stabilization diagrams. In the first step, a kind of smoothing is used to remove the noise from the data and in the second step; the pLSCF estimator is applied to the smoothed data resulting in improved (damping) estimates. In addition, the proposed procedure properly deals with uncertainty: the data variance due to measurement noise is taken into account to compute confidence bounds on the modal parameter estimates. The procedure is validated by means of simulated as well as experimental data. The presented procedure to process highly damped noisy vibration data leads to very accurate estimates in comparison to the traditional pLSCF approach.