The phenomenon of vibrations is one of the most critical aspects of any mechanism, as it’s the cause of mechanical stress, wear, noises and less comfort felt during the use. This latter criticality is particularly accentuated in powered paraglider, in which the engine used, a two-stroke engine, is mounted on the frame in close contact with the pilot, a few centimeters away. The objective of this study is the reduction, as far as possible, of the vibrations felt during the flight, identifying the components and mechanisms where they are originated, modeling and simulating dynamic equivalent systems that describe the behavior of the engine in term of accelerations and then characterize and optimize the engine currently in production. The fields on which the analysis focuses concern the optimization of the balance of the rotary thrust crank, the analysis of the engine’s accelerations and the dampers’ vibration transmissibility according to their type and arrangement, all of this in function of the engine and propeller’s geometric and inertial parameters. The work is divided into three parts. In the first it’s carried out a dynamic study of the forces and moments generated by the piston-connecting rod-crank system, with the aim to optimize and reduce the stresses transmitted, working both on the shaft counterweight and evaluating the introduction of a balancing countershaft. The second part describes, in a more complete way, the engine’s functioning, developing detailed mathematical models that reproduce the engine and chassis’ dynamic behavior to directly evaluate their accelerations. In these systems it’s introduced the contribution of the forces generated by the propeller, by the crank mechanism and the balance used and also the inertial properties such as the motor and propeller’s inertia and position of the center of mass. They also make it possible to compare the results by changing arrangement and type of dampers. Finally, in the third and last part are described the experimental tests for the measurement of engine’s vibration, illustrating the instruments used, the set-up of the tests, the problems encountered, their solutions and the first results used for the characterization and alignment of the mathematical systems.
Il fenomeno delle vibrazioni è uno degli aspetti più critici di qualsiasi meccanismo, in quanto causa di stress-meccanico, usura, oltre che rumorosità e un minor confort avvertito durante l’utilizzo. Quest’ultima criticità è particolarmente accentuata nel parapendio a motore, in cui il propulsore utilizzato, un motore a combustione interna a due tempi, viene montato sul telaio a stretto contatto con il pilota, a pochi centimetri di distanza. L’obiettivo di questo studio è proprio quello di ridurre, per quanto possibile, le vibrazioni avvertite durante il volo, identificando i componenti ed i meccanismi da cui si originano, modellare e simulare dei sistemi equivalenti dinamici che permettano di descrivere il comportamento del motore, infine caratterizzare e ottimizzare il motore attualmente in produzione. I campi su cui pertanto verte l’analisi riguardano l’ottimizzazione del bilanciamento del manovellismo rotativo di spinta, l’analisi delle accelerazioni sviluppate dal motore e la trasmissibilità degli antivibranti in funzione della loro tipologia e disposizione, oltre che dei parametri geometrici e inerziali di motore ed elica. Il lavoro proposto si articola in tre parti. Nella prima si effettua uno studio dinamico delle forze e momenti generati dal sistema pistone-biella-manovella, finalizzato all’ottimizzazione e riduzione delle sollecitazioni trasmesse, lavorando sia sul contrappeso dell’albero sia valutando anche l’introduzione di un contro-albero di bilanciamento. Nella seconda parte si descrive in modo più completo il funzionamento del motore, sviluppando dei modelli matematici dettagliati che riproducono il comportamento dinamico di motore e telaio allo scopo di valutare direttamente le accelerazioni, cioè le vibrazioni sviluppate. In questi sistemi si introduce il contributo delle forzanti generate dall’elica, oltre che dal manovellismo, il suo bilanciamento, le proprietà inerziali quali inerzia e posizione del centro di massa di motore ed elica. Esse permettono inoltre di confrontare i risultati al variare della disposizione e tipologia degli antivibranti. Infine, nella terza e ultima parte vengono descritte le prove sperimentali per la misura delle vibrazioni del motore, illustrando la strumentazione utilizzata, il set-up delle prove, le problematiche incorse e la loro soluzione insieme ai primi risultati, utilizzati per la caratterizzazione ed allineamento dei sistemi matematici.
Modellazione e analisi dinamica per la riduzione delle vibrazioni di un motore a due tempi per paramotore
CONCETTI, FILIPPO
2021/2022
Abstract
The phenomenon of vibrations is one of the most critical aspects of any mechanism, as it’s the cause of mechanical stress, wear, noises and less comfort felt during the use. This latter criticality is particularly accentuated in powered paraglider, in which the engine used, a two-stroke engine, is mounted on the frame in close contact with the pilot, a few centimeters away. The objective of this study is the reduction, as far as possible, of the vibrations felt during the flight, identifying the components and mechanisms where they are originated, modeling and simulating dynamic equivalent systems that describe the behavior of the engine in term of accelerations and then characterize and optimize the engine currently in production. The fields on which the analysis focuses concern the optimization of the balance of the rotary thrust crank, the analysis of the engine’s accelerations and the dampers’ vibration transmissibility according to their type and arrangement, all of this in function of the engine and propeller’s geometric and inertial parameters. The work is divided into three parts. In the first it’s carried out a dynamic study of the forces and moments generated by the piston-connecting rod-crank system, with the aim to optimize and reduce the stresses transmitted, working both on the shaft counterweight and evaluating the introduction of a balancing countershaft. The second part describes, in a more complete way, the engine’s functioning, developing detailed mathematical models that reproduce the engine and chassis’ dynamic behavior to directly evaluate their accelerations. In these systems it’s introduced the contribution of the forces generated by the propeller, by the crank mechanism and the balance used and also the inertial properties such as the motor and propeller’s inertia and position of the center of mass. They also make it possible to compare the results by changing arrangement and type of dampers. Finally, in the third and last part are described the experimental tests for the measurement of engine’s vibration, illustrating the instruments used, the set-up of the tests, the problems encountered, their solutions and the first results used for the characterization and alignment of the mathematical systems.File | Dimensione | Formato | |
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TESI_Filippo_Concetti.pdf
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Descrizione: Tesi Filippo Concetti
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https://hdl.handle.net/20.500.12075/10707