1,721,032 research outputs found
On the relevance of a microslip contact model for under-platform dampers
No full textA crucial part of building reliable models for the design of under-platform dampers for turbine blades resides in the appropriate description of the contact conditions, both in the normal and in the tangential direction. The aim of this paper is to determine to what extent microslip due to the combined non-linearities along the normal and the tangent of non-conforming contact surfaces influence the damper behaviour. The ultimate goal is to determine whether introducing these features in the contact model would improve the performance of numerical routines used at the blade-damper design stage. In order to explore this problem, a purposely developed contact model is tuned on a single-contact test and then included in the numerical model of a curved-flat damper to simulate its cylindrical interface. The damper numerical routine is then validated against the results from an experimental device purposely developed to test the dynamics of a damper loaded between moving platforms. It is shown that the validated numerical routine featuring the newly introduced contact model predicts, in comparison with the standard contact model (where partial slip and normal approach non-linearity are not considered), a lower dissipated energy by an amount that would not be justifiable to neglec
Tools and methods for investigations on underplatform damper inner mechanics
No full textUnderplatform dampers (UPDs) are widely used as a source of friction damping and are frequently incorporated into compressors and turbines for both aircraft and power-plant applications to mitigate the effects of resonant vibrations on fatigue failure.
Due to the nonlinear nature of dry friction, in general dynamic analysis of structures constrained through frictional contacts is difficult, direct time integration with commercial finite element codes may not be a suitable choice given the large computation times. For this reason, ad hoc numerical codes have been developed in the frequency domain.
Some authors prefer a separate routine in order to compute contact forces as a function of input displacements, others include the damper in the FE model of the bladed array. All numerical models, however, require knowledge or information of contact -friction parameters, which are established either through direct frictional measurements, done with the help of single contact test arrangements, or by fine tuning the parameters in the numerical model and comparing the experimental response of damped blade against its computed response. The standard approach is to fine-tune and experimentally validate the UPDs models by comparing measured and calculated vibration response of blade pairs.
To our knowledge, nobody has ever attempted to directly measure the forces transmitted between the platforms through the damper and the relative damper-platform movement.
In the light of recent results from direct measurements on dampers it is evident that a dedicated routine for the damper mechanics is an effective tool to capture those finer details which are essential to an appropriate description of damper behaviour.
This was made possible by the successful effort of the present authors to accurately measure the forces transmitted between the platforms through the damper, to connect them with the relative platforms movement and to use the findings for the validation of the numerical model.
The cross-comparison between numerical and experimental results allows to gain a clear understanding of all contact events (stick, slip, lift) which take place during the cycle, and on how they influence the damping performance
Latest Investigations on Underplatform Damper inner Mechanics
Full text linkUnderplatform dampers (UPDs) are widely used as a source of friction damping and are frequently incorporated into compressors and turbines for both aircraft and power-plant applications to mitigate the effects of resonant vibrations on fatigue failure.
Due to the nonlinear nature of dry friction, in general dynamic analysis of structures constrained through frictional contacts is difficult, direct time integration with commercial finite element codes may not be a suitable choice given the large computation times. For this reason, ad hoc numerical codes have been developed in the frequency domain.
Some authors prefer a separate routine in order to compute contact forces as a function of input displacements, others include the damper in the FE model of the bladed array. All numerical models, however, require knowledge or information of contact -friction parameters, which are established either through direct frictional measurements, done with the help of single contact test arrangements, or by fine tuning the parameters in the numerical model and comparing the experimental response of damped blade against its computed response. The standard approach is to fine-tune and experimentally validate the UPDs models by comparing measured and calculated vibration response of blade pairs.
To our knowledge, nobody has ever attempted to directly measure the forces transmitted between the platforms through the damper and the relative damper-platform movement.
In the light of recent results from direct measurements on dampers it is evident that a dedicated routine for the damper mechanics is an effective tool to capture those finer details which are essential to an appropriate description of damper behaviour.
This was made possible by the successful effort of the present authors to accurately measure the forces transmitted between the platforms through the damper, to connect them with the relative platforms movement and to use the findings for the validation of the numerical model.
The cross-comparison between numerical and experimental results allows to gain a clear understanding of all contact events (stick, slip, lift) which take place during the cycle, and on how they influence the damping performance
Numerical and experimental investigations on underplatform damper mechanics
Full text linkSo called under-platform dampers are widely used as a source of friction damping to mitigate resonance in gas turbine blades and avoid service failures.
Due to the high computational cost of performing dynamic analysis of structures constrained through frictional contacts, ad hoc numerical codes have been developed in the frequency domain. Whatever the numerical model, it requires knowledge of contact-friction parameters, which are established either through single contact frictional measurements, or by tuning the damper parameters though comparison of the experimental response of damped blade against its computed response or, else, by fine tuning the damper parameters by comparing the measured v. the calculated hysteresis cycle. The last one is these authors’ choice. Equipment and method are described accordingly
Competitive time marching solution methods for systems with friction-induced nonlinearities
Full text linkFinding efficient and accurate solution methods for nonlinear equilibrium equations is a challenging task. This is the case of systems with friction-induced nonlinearities, e.g., friction-damped turbomachinery assemblies and automotive applications such as brakes. In order to tackle this strategic task, several methods have been developed, both in the time and in the frequency domains.
Time marching methods are regarded as the most accurate option, but their computational cost becomes prohibitive when friction nonlinearities are present. This poses a problem in all those cases where alternative frequency domain methods cannot be applied effectively, e.g., if transients, non-periodic excitation/solution, or highly nonlinear systems are of interest. The purpose of this paper is to propose three independent methods to make time-marching more competitive. Two of these methods can be applied to any existing direct integration scheme with minimal adjustments, but the computational time cut they introduce is significant. The last method is instead tailored for systems where the inertia force contribution is negligible. All methods are thoroughly validated numerically using a standard Newmark-β integration scheme as a reference
Progettazione circolare di un velomobile - LCA della fase d'uso per valutare la potenziale riduzione di emissioni
No full textI trasporti su strada contribuiscono in modo significativo ai problemi ambientali, con i veicoli leggeri nell'Unione Europea responsabili di circa il 10% del consumo totale di energia e delle emissioni atmosferiche. Questo riconoscimento ha suscitato un crescente interesse per i veicoli alternativi per la mobilità a breve e media distanza. Le opzioni a propulsione umana, come le cargo-bike e i velomobili, mostrano un impatto ambientale minimo durante l’uso in quanto una significativa parte della potenza è fornita dall’uomo, anche nel caso di assistenza elettrica alla pedalata.
Il presente lavoro esplora il potenziale dei velomobili, veicoli chiusi a propulsione umana (HPV), come soluzione praticabile verso una transizione ad alternative più sostenibili rispetto ai veicoli convenzionali. Un sondaggio condotto su più di 1200 individui in Italia, con un’attenzione particolare alla regione Piemonte, ha fornito approfondimenti sui modelli di pendolarismo e sulla propensione all’adozione di velomobili. Tramite successiva Valutazione comparativa del Ciclo di Vita (LCA comparativa) sono state stimate le riduzioni delle emissioni di GHG ottenibili tramite il “modal shift”, ovvero la sostituzione dei mezzi di trasporto attualmente utilizzati con il velomobile. Nonostante le ipotesi conservative adottate, lo studio evidenzia risultati promettenti, con riduzione delle emissioni di GHG dal 20% al 30% negli scenari più realistici analizzati.
Dai risultati del lavoro svolto, i velomobili si dimostrano essere strumenti efficaci in grado di guidare la transizione verso un trasporto su strada più sostenibile o, meglio, meno insostenibile. Pur riconoscendo le possibili variazioni regionali, lo studio suggerisce esiti incoraggianti per l’adozione di velomobili in Italia
- …
