1,721,009 research outputs found
Involucro portante in pannelli costruiti in pallet di legno, soluzioni progettuali e operative
No full textSull'impiego di strati in piezoelettrico nel controllo attivo del comportamento strutturale di elementi in composito
No full textA dry friction model and robust computational algorithm for reversible or irreversible motion transmissions
Full text linkThe motion transmission elements are generally affected by dry friction which may give rise to reversible or irreversible behaviour of the whole system. So, the potential high effect of the dry friction on the dynamic behaviour of the mechanical system requires proper simulation models characterised by high computational accuracy, nevertheless compactness and efficiency. Aims of the work are: - the proposal of a general purpose physical and mathematical dry friction dynamic model and, consequently, the detailed description of two related numerical algorithms, developed in different computational environments (low level language and Matlab-Simulink), able to simulate the behaviour of a general dynamic system affected by dry friction and equipped or not with ends of travel; - the simulation of some representative actuation runs in order to validate the proper accuracy of the mechanical device computational algorithm and the analysis of the results
Progetto di sistemi aeronautici e spaziali: alcune esperienze sviluppate al Politecnico di Torino.
No full textIR study of the acidity of ITQ-2, an "all-surface" zeolitic system
No full textTwo samples of ITQ-2 with different Al content (Si/Al =50 and 25, respectively) and different degree of exfoliation have been characterized by IR spectroscopy and compared to MCM-22 samples with the same Al content, to assess the changes brought about by the development of a large external surface. Brønsted acidity has been measured as the propensity of OH species to either protonate ammonia or engage in H-bonds with suitable molecules (CO, N2, n-heptane, olefins, aromatics). Lewis acidity has been evaluated by measuring the spectra of CO adsorbed at room temperature. Comparison with MCM-22 samples shows that no substantial loss in Brønsted acidity takes place because of exfoliation, although the bridged species Si(OH)Al exposed at the external surface do not basically survive as such and are probably converted into new AlOH acidic species. These are not directly detectable in the IR spectra; indirect evidence, however, suggests their location at the external cups of the surface. Bridged Si(OH)Al species survive instead in the 10-MR channels
Acidity of ITQ-2 zeolite as studied by FT-IR spectroscopy of adsorbed molecules in comparison with that of MCM-22
No full textProposta di velivolo da addestamento avanzato mirato alla sicurezza: valutazione di efficacia, efficienza, e analisi del rischio
No full textPrincipal servocontroller failure modes and effects of active flutter suppression
Full text linkConventional active flutter and vibration control technology relies on the use of aerodynamic control surfaces operated by servo-hydraulic actuators, which can be affected by some specific types of failure. In order to assure a sufficiently high safety degree, it is necessary to verify the dynamic behaviour of the whole system when a defined failure occurs. The purpose of this paper is to analyze the aeroservoelastic behaviour of a typical wing with active flutter suppression performed by a hydraulic servomechanism equipped with a defined proper control law (relating the required surface deflection angle to speeds and acceleration of the main aerofoil surface) and affected by the principal modes of servocontroller failures, as: • servovalve feedback spring failure • hydraulic system pressure drop • whole active flutter control failure • piston seizure • piston internal sealing failure. Active control and its failure modes have been implemented within the model of a representative actuation system acting on a wing structure embedded in a defined aerodynamic field. The results presented in this work are obtained in case of not redundant servosystem; so the failure effects are not limited by the action of the operative portion of an eventually redundant device. However the results are significant mainly for their conceptual aspects and show the possible criticality of a singular failure in a not redundant device. It can be noted that the more critical failures are those concerning the loss of the piston internal sealing, the total supply pressure drop or the total piston seizure. Sealing damage and pressure drop can be efficiently overcome by a proper redundancy; on the contrary, the piston seizure, particularly in case of force summed redundancies, must be considered seriously critical because the operative portion of the system may be incapable of overcoming the failure effect
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