|Tipo di tesi||Tesi di dottorato di ricerca|
|Titolo||Metodologie NVH per applicazioni automotive: valutazione delle prestazioni vibroacustiche attraverso l’analisi agli elementi finiti|
|Titolo in inglese||NVH methods for automotive applications: evaluation of vibro-acoustic performance through FE analysis|
|Settore scientifico disciplinare||ING-IND/14 - PROGETTAZIONE MECCANICA E COSTRUZIONE DI MACCHINE|
|Corso di studi||INGEGNERIA INDUSTRIALE E DEL TERRITORIO|
|Data inizio appello||2017-03-20|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
L’attività di ricerca è stata svolta su tematiche NVH per applicazioni automotive e ha lo scopo di definire una metodologia di predizione e valutazione del rumore di rotolamento attraverso l’analisi agli elementi finiti. In particolare, i veicoli sono soggetti a differenti forzanti dinamiche; la vibrazione e il rumore indotti determinano le prestazioni della vettura in termini di integrità strutturale, confort e le performance di handling. Le vibrazioni all’interno di un veicolo coinvolgono un range esteso di frequenze [da 1 Hz fino a circa 10 kHz]. Un aspetto fondamentale da considerare è che la vibrazione indotta non solo dipende dall’intensità della eccitazione, ma anche dal comportamento della struttura che può amplificare tali effetti a causa delle risonanze strutturali e acustiche. Generalmente in una vettura, la trasmissione strutturale del rumore prevale a basse frequenze (<400Hz) mentre la trasmissione aerea è dominante a frequenze più alte. Le linee di trasmissione dei carichi sono individuate dalle VTF e dalle NTF; tali funzioni di trasferimento di vibrazione e rumore sono strettamente legate alla struttura e alla cavità acustica.
The research activity is focused on Noise, Vibration and Harshness (NVH) topics for automotive applications. The PhD thesis aims to the definition of a methodology for the prediction and evaluation of the rolling noise through Finite Element Analysis (FEA). In particular, vehicles are affected by several dynamic excitations and the induced vibration and noise have a number of effects on the vehicle and its passengers such as the integrity of the structure, the perception of comfort and the handling performance. Moreover, the vibrations that occur in a vehicle involve a wide range of frequencies [from below 1 Hz up to about 10 kHz]. A fundamental aspect that has to be noted is that the effect does not only depend just on the nature and the intensity of the excitation, but also on the behavior of the structure that can amplify the effect due to structural and acoustic resonances. Generally in a vehicle, the structure-borne noise transmission path prevails at low frequency (<400 Hz) whereas the air-borne noise transmission path dominates above 500 Hz. The rolling noise depends on the transfer paths from the road to the ears of passengers through the suspension points. Transmission paths are assess by Vibration Transfer Functions (VTFs) and Noise Transfer Functions (NTFs); these transfer functions are strictly related to the structure and to the cavity. A modal correlation activity on a rear subframe and on a front hood has been performed in order to evaluate the influence of the different modeling techniques of connections (e.g. rivets, welded and bonded joints). At first, a comparison between experimental test and FE analysis has been presented to validate the methodology. A good correlation was achieved by monitoring dynamic parameters such as natural frequencies, mode shapes, and frequency response functions (FRFs). Cavity modes were measured and numerically simulated in order to represent the acoustic behavior and resonances that occur in the passenger compartment. The correlation between test and simulation was performed and a comparison of mode shapes is illustrated. The reduction of interior noise and vibration of vehicles can be obtained introducing patches of damping material on the panels. A correlation activity on damping materials was performed in order to identify reliable material properties. A specific FE analysis was performed to reduce the amount of damping pads on the chassis. Evaluating the acoustic participation of each panel to the interior noise, it was possible to rank the contributions. This analysis allows to identify the critical transmission paths and to apply the damping patches only where it was useful to reduce the interior noise. A conclusive structural optimization was also proposed in order to increase the efficiency of the damping pads distribution. It is worth pointing out that the research does not account for the simulation of the road forces transmitted to the suspension points (road inputs) and for the impact of the trims on the transmission paths. These aspects are explained in a detailed section as they represent requirements for a reliable interior noise simulation. The estimation of the rolling noise as further described in the thesis, allows to quickly evaluating the individual noise and vibration contributions to the occupants, bringing the NVH characteristics of the vehicle forward into the design process.