Nowadays it is possible to design rotating machinery in such a way that operation at a critical speed is possible for a limited period of time, but it is, in any case, necessary that the normal operating range is either below the first critical speed or between two critical speeds and that sustained operation in critical condition is avoided. The present thesis deals with the development of a software for the study of dynamic characteristics and whirl speeds of rotating shafts with high speed, placed into test stand for helicopter gearboxes. In particular, the vibrational problem due to flexural critical speeds was treated, which could be close to operating speed on the bench. The main mechanical system studied in this work, consists of the high-speed driveline, which connects the test stand to the helicopter main gear box (MGB) input. The software based on (FE) modelling, using the eigenvalues/eigenverctors analysis, is a useful tool for rotating machines design. The program helps to determinate normal modes, to estimate response due to asynchronous or mass unbalance forces and to predict the stability of the rotating system in the linear field. Dynamic modelling was developed to describe the test stand speed increaser (shaft, gear wheel, and hydrodynamic bearings), high-speed shafts (including disk couplings or membrane couplings), connecting flanges and helicopter gearbox first reduction stage (gear shaft, roller bearings). Stability studies of rotating systems were conducted, the frequency response functions were extracted, Campbell diagram were drawn and simulated for different design studies. The influence of the journal bearings on the stability of the rotor-bearing system was investigated, for several case studies. The results have been compared with experimental data to establish the accuracy of the model.
La presente tesi è incentrata sulla creazione di un programma di calcolo, per lo studio delle caratteristiche dinamiche e delle velocità critiche flessionali di linee d’alberi rotanti ad alta velocità, presenti su banchi prova, per l’esecuzione di test sulle trasmissioni di velivoli elicottero. Il sistema meccanico studiato in questo lavoro è rappresentato dalla linea d’input che collega il banco prova (moltiplicatore/riduttore di giri), alla scatola principale di trasmissione elicottero (MGB, main gear box). Il programma di calcolo basato sulla modellazione a elementi finiti e sull’analisi agli autovalori/autovettori vuole essere uno strumento utile per lo studio di queste linee ad alta velocità e per l’identificazione di velocità critiche nel range di funzionamento. Il codice implementato in ambiente Matlab, aiuta a calcolare modi di vibrare, a stimare la risposta a forzanti asincrone o di squilibrio di massa e a studiare la stabilità del sistema rotante, nel campo lineare. Per descrivere il sistema reale costituito dal moltiplicatore di giri del banco (in particolare l’albero-pignone d’uscita e i cuscinetti di supporto a film d’olio), l’albero di collegamento (inclusi giunti flessibili a lamelle o a membrana), flange d’attacco e il primo stadio di riduzione della trasmissione elicottero (pignone d’ingresso e cuscinetti volventi), si è creato un modello dinamico dell’intero assieme. Tramite il programma sono stati condotti analisi di stabilità su macchine rotanti, sono state simulate funzioni di risposta in frequenza e sono stati calcolati i diagrammi di Campbell per diversi casi di studio. È stata valutata l’influenza dei cuscinetti a lubrificazione (Journal bearings), sulla stabilità del sistema rotore-cuscinetti. I risultati forniti dal programma sono stati confrontati con i dati sperimentali provenienti da prove condotte su alcune linee ad alta velocità presenti sui banchi, per stabilire l’accuratezza del modello.
Aspetti di dinamica strutturale nella progettazione dei banchi prova trasmissioni MGB
PAGANI, FEDERICO
2013/2014
Abstract
Nowadays it is possible to design rotating machinery in such a way that operation at a critical speed is possible for a limited period of time, but it is, in any case, necessary that the normal operating range is either below the first critical speed or between two critical speeds and that sustained operation in critical condition is avoided. The present thesis deals with the development of a software for the study of dynamic characteristics and whirl speeds of rotating shafts with high speed, placed into test stand for helicopter gearboxes. In particular, the vibrational problem due to flexural critical speeds was treated, which could be close to operating speed on the bench. The main mechanical system studied in this work, consists of the high-speed driveline, which connects the test stand to the helicopter main gear box (MGB) input. The software based on (FE) modelling, using the eigenvalues/eigenverctors analysis, is a useful tool for rotating machines design. The program helps to determinate normal modes, to estimate response due to asynchronous or mass unbalance forces and to predict the stability of the rotating system in the linear field. Dynamic modelling was developed to describe the test stand speed increaser (shaft, gear wheel, and hydrodynamic bearings), high-speed shafts (including disk couplings or membrane couplings), connecting flanges and helicopter gearbox first reduction stage (gear shaft, roller bearings). Stability studies of rotating systems were conducted, the frequency response functions were extracted, Campbell diagram were drawn and simulated for different design studies. The influence of the journal bearings on the stability of the rotor-bearing system was investigated, for several case studies. The results have been compared with experimental data to establish the accuracy of the model.| File | Dimensione | Formato | |
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2014_07_Pagani.pdf
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Descrizione: Testo della tesi
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https://hdl.handle.net/10589/93704