This study aims at developing a procedure to identify and modelling the behaviour of structural elements that show a non-linear behaviour during tests. The structural element taken into account is part of the Intermediate eXperimental Vehicle, that successfully completed its 100-minute mission on 11 February 2015. The element under investigation is the flap developed under the responsibility of Thales Alenia Space Italia, the major contractor, which provided the experimental data needed to accomplish the investigation. In this study the application of the Restoring Force Surface method (or equivalently, the Force State Mapping Technique) as a strategy to characterize and identify localized non-linearities has been investigated. This method, which works in the time-domain, has been chosen because it has 'built-in' characterization capabilities, it allows a direct non-parametric identification of non-linear systems (in so far as Single-Degree-of-Freedom systems are considered) and it can easily deal with sine-sweep excitations. Firstly, the method implementation was validated by means of several numerical simulations. Then it was applied to a simple experimental case prepared on purpose: a clamped beam which showed a non-linear behaviour characterized by a piecewise linear stiffness. Having obtained satisfactory results in the previous steps, the identification of the non-linearity present in a real structure, the IXV flap, was attempted. Once the non-linear parameters were identified, they were used to update the finite element model in order to prove its capability of predicting the flap behaviour for different load levels. The novelty of this work lies in the application of the method to experimental data coming from tests which, in addition, were not meant for this purpose.
Questo lavoro di tesi nasce con lo scopo di mettere a punto una procedura che permetta di identificare e modellare il comportamento di componenti strutturali che mostrano un comportamento non-lineare durante i test. L'elemento strutturale preso in considerazione fa parte del dimostratore IXV (Intermediate eXperimental Vehicle), che ha completato con successo la missione il giorno 11 Febbraio 2015. L'elemento di studio è rappresentato dal flap sviluppato sotto la responsabilità di Thales Alenia Space Italia, prime contractor, la quale ha fornito i dati sperimentali che hanno permesso di completare l'analisi. La tesi esamina l'applicazione del Restoring Force Surface method (o dell'equivalente Force State Mapping Technique) come strategia per caratterizzare e identificare non-linearità localizzate. Questo metodo, definito nel dominio del tempo, è stato scelto per la sua intrinseca capacità di caratterizzazione, perchè permette l'identificazione non-parametrica di sistemi non-lineari (limitandosi a sistemi ad un solo grado di libertà) e perchè permette di gestire facilmente eccitazioni di tipo sine-sweep. Inizialmente, l'implementazione del metodo è stata convalidata attraverso diverse simulazioni numeriche. Successivamente, esso è stato applicato ad un semplice caso sperimentale preparato appositamente: una trave incastrata caratterizzata da una curva di rigidezza lineare a tratti. Avendo ottenuto risultati soddisfacenti nei passaggi precedenti, è stata tentata l'identificazone della non-linearità presente in una struttura reale: il flap del modulo IXV sviluppato da Thales Alenia Space. Una volta che i parametri della non-linearità sono stati identificati, essi vengono usati per aggiornare il modello ad elementi finiti in modo da verificarne la capacità di predire il comportamento del flap per diversi liveli di carico. La novità di questo lavoro risiede nell'applicazione del metodo a dati sperimentali ottenuti da test che inoltre non erano intesi per questo scopo.
Nonlinear spacecraft component parameters identification based on experimental results and finite element model updating
VISMARA, SERENA OLGA
2013/2014
Abstract
This study aims at developing a procedure to identify and modelling the behaviour of structural elements that show a non-linear behaviour during tests. The structural element taken into account is part of the Intermediate eXperimental Vehicle, that successfully completed its 100-minute mission on 11 February 2015. The element under investigation is the flap developed under the responsibility of Thales Alenia Space Italia, the major contractor, which provided the experimental data needed to accomplish the investigation. In this study the application of the Restoring Force Surface method (or equivalently, the Force State Mapping Technique) as a strategy to characterize and identify localized non-linearities has been investigated. This method, which works in the time-domain, has been chosen because it has 'built-in' characterization capabilities, it allows a direct non-parametric identification of non-linear systems (in so far as Single-Degree-of-Freedom systems are considered) and it can easily deal with sine-sweep excitations. Firstly, the method implementation was validated by means of several numerical simulations. Then it was applied to a simple experimental case prepared on purpose: a clamped beam which showed a non-linear behaviour characterized by a piecewise linear stiffness. Having obtained satisfactory results in the previous steps, the identification of the non-linearity present in a real structure, the IXV flap, was attempted. Once the non-linear parameters were identified, they were used to update the finite element model in order to prove its capability of predicting the flap behaviour for different load levels. The novelty of this work lies in the application of the method to experimental data coming from tests which, in addition, were not meant for this purpose.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/107756