Vibration is one of the major drawbacks of helicopters. Active and passive control techniques aimed at reducing helicopter vibrations have been extensively studied in the last few decades. Combinations of these techniques have led to what are known as tunable passive devices, where actuators adjust the passive mechanical properties to changes in the excitation frequency. The Active Control of Structural Response (ACSR) is an active control technique that aims to reduce vibrations in the fuselage and as other active approaches it makes use of the so-called T-matrix algorithm, which is a frequency-domain method based on the linear relationship between the control input and the output measurements at the disturbance frequency. The presence of a rotor head resonator, like the Mast Vibration Absorber (MVA), could interfere with the ACSR. This interaction results in an active control that either is too slow to adapt to changes in the disturbance or is likely to drive the closed-loop response unstable as a result of the coupling with the passive device. The purpose of the thesis is to design a novel modified control algorithm that makes the ACSR system able to coexist with the Mast Vibration Absorber. The major difficulty arises from the constraint condition of the problem; indeed, both the number and the locations of actuators and sensors are fixed. The proposed solution aims to design an active control system that is decoupled from the MVA. The consequent approach is based on the assumption that the T-matrices with and without the MVA are known. This assumption is perfectly reasonable since both the actuators and the accelerometers are placed on the fuselage. This implies that the T-matrix is slightly affected by changes in flight condition and off-line or past on-line measurements are therefore available. Once the novel decoupled controller has been designed, an eigenvalue analysis is performed to evaluate the effectiveness of the technique developed. As a consequence of the constraints imposed on the control action, the performances of the active vibration control are highly affected. Therefore, different solutions to enhance the performances are proposed.
Le elevate vibrazioni presenti nell’elicottero ne rappresentano una delle principali limitazioni. La loro riduzione, con tecniche di controllo attivo e passivo, è stata oggetto di una notevole attenzione negli ultimi decenni. L’impiego coordinato di queste tecniche ha dato luogo a quelli che vengono identificati come dispositivi semi-attivi, dove gli attuatori adattano le proprietà meccaniche del sistema passivo in corrispondenza di variazioni della frequenza del disturbo. L’ Active Control of the Structural Response (ACSR), tecnica che tende a ridurre le vibrazioni nella fusoliera, così come altri approcci di controllo attivo, fa uso di quello che viene usualmente chiamato algoritmo T-matrix. Questo è un metodo nel dominio della frequenza fondato sulla relazione lineare tra l’ingresso del sistema di controllo e le misure di opportuni sensori, alla frequenza del disturbo. La presenza di un risonatore posto sul rotore, come ad esempio l’MVA, può interferire con l’azione dell’ACSR. Questa interazione degrada le prestazioni del controllore, fino a rendere possibile il sorgere di instabilità. L’obiettivo della tesi è la progettazione di un nuovo algoritmo di controllo, che consenta la coesistenza dell’ACSR con l’MVA. La soluzione proposta rende possibile il disaccoppiamento del progetto del sistema di controllo attivo dall’MVA. Di conseguenza, si assume che la T-matrix sia nota con e senza MVA, essendo sia gli attuatori che gli accelerometri posizionati sulla fusoliera. Questo implica che la T-matrix sia solo marginalmente influenzata dalle condizioni di volo, e che quindi sia nota attraverso misure off-line. L’algoritmo di controllo così progettato è quindi stato oggetto di un’approfondita analisi in cui si è messa in evidenza l’efficacia di questo nuovo sistema di controllo. Nella tesi viene inoltre evidenziato come in questo caso le limitazioni imposte al controllo attivo ne degradino le potenziali prestazioni e sono conseguentemente delineate possibili soluzioni per migliorarle.
Integrated active and passive rotorcraft vibration control
Rubinacci, Roberto
2019/2020
Abstract
Vibration is one of the major drawbacks of helicopters. Active and passive control techniques aimed at reducing helicopter vibrations have been extensively studied in the last few decades. Combinations of these techniques have led to what are known as tunable passive devices, where actuators adjust the passive mechanical properties to changes in the excitation frequency. The Active Control of Structural Response (ACSR) is an active control technique that aims to reduce vibrations in the fuselage and as other active approaches it makes use of the so-called T-matrix algorithm, which is a frequency-domain method based on the linear relationship between the control input and the output measurements at the disturbance frequency. The presence of a rotor head resonator, like the Mast Vibration Absorber (MVA), could interfere with the ACSR. This interaction results in an active control that either is too slow to adapt to changes in the disturbance or is likely to drive the closed-loop response unstable as a result of the coupling with the passive device. The purpose of the thesis is to design a novel modified control algorithm that makes the ACSR system able to coexist with the Mast Vibration Absorber. The major difficulty arises from the constraint condition of the problem; indeed, both the number and the locations of actuators and sensors are fixed. The proposed solution aims to design an active control system that is decoupled from the MVA. The consequent approach is based on the assumption that the T-matrices with and without the MVA are known. This assumption is perfectly reasonable since both the actuators and the accelerometers are placed on the fuselage. This implies that the T-matrix is slightly affected by changes in flight condition and off-line or past on-line measurements are therefore available. Once the novel decoupled controller has been designed, an eigenvalue analysis is performed to evaluate the effectiveness of the technique developed. As a consequence of the constraints imposed on the control action, the performances of the active vibration control are highly affected. Therefore, different solutions to enhance the performances are proposed.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/173506