Deformations in body openings: Correlation between vehicle testing and simulation data

Examensarbete för masterexamen

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Type: Examensarbete för masterexamen
Master Thesis
Title: Deformations in body openings: Correlation between vehicle testing and simulation data
Authors: Zaben, Mohamed
Sarkis Krikor, Nerma
Abstract: A comprehensive complete vehicle test was performed within a thesis work by Alexander Jörud and Carl Jacobsson in order to measure the diagonal deformation in major body openings. Their main focus was on preparing and performing the physical test. They also updated the FE model to emulate the actual physical test. The aim with this thesis work is continue their study and to enable comparison between the simulation and test data. The correlation is performed in both time and frequency domains. The final aim is to identify the capability of the complete vehicle simulation procedure to predict body deformations. A procedure to perform a correlation between simulation and physical test has been developed. This study is performed for three different road conditions: Belgian Pavé (PAV), Washboard in phase (WIP) and Washboard out of phase (WOP). The relative displacement is analysed for the car when driven at 30 km/h and 50 km/h on each road condition. The data is processed in order to perform the actual correlation study. This includes converting the data from acceleration to displacement and applying coordinate transformations. The E-line and Diagonal methods have been implemented in order to evaluate the distortion in all closure openings. This study consider time domain using the statistical evaluation (SEP) approach and also frequency domain analysis. For that reason three comparison filters have been developed. An initial validation study resulted in a cutoff frequency at 5 Hz, as the accelerometers gave impercise data below these frequencies. Secondly, both rigid body and structural modes were identified between 5 and 20 Hz. Three different rigid body motions were clearly identified when analysing the local components of the E-line method. A modal analysis in the simulation code Adams was performed in order to analyse the different rigid body motions of the body, engine and wheel suspension further. To prepare for correlation analysis the load level was compared between the physical test data measured using a wheel force transducer (WFT) and simulation data obtained with a Ftire model. Furthermore, the correlation study included a number of different criteria like influence from velocity, modal damping and road profile. The local and global component correlation pattern were analysed. A clear pattern was identified for all load cases during the correlation investigation. For instance, the rear door was subjected to larger deformations than the front door. This pattern was present for all load cases. A likely explanation is that the structure of the car is stiffer close to the A-pillar, which is a closed section, compared to the open sections at the B and C pillars. Furthermore, the PAV road condition contributed to the highest displacement at all closure openings. Both PAV and WOP give torsional loads, causing a higher distortion at the sunroof and the tailgate compared to the side doors. A clear symmetry between left and right side of the vehicle was observed when evaluating the distortion in the side door openings. This was v also observed for the left and right side of the tailgate opening. The absolute distortion value was compared between physical test and two simulations: one with 2% and one with 15% modal damping. The correlation between physical test and simulation varies clearly for the different openings. It was not possible to find one modal damping value to give a good correlation for all closure openings. Therefore, a deeper analysis is required to understand why certain modes give strong or weak contribution. However, when assessing all openings for all load cases it could be concluded that simulation with 2% modal damping is clearly over-predicting the relative motion, whereas simulation with 15% modal damping is slightly under-predicting as compared to the physical test. Finally the local component pattern was studied. For PAV only the front doors and the tailgate presented a clear pattern for physical test and simulation. The results for WOP solely presented a pattern for the tailgate opening. For WIP no clear no clear pattern was identified for any of the openings. Keywords:Body opening distortion, correlation, modal analysis, E-line method, Adams, Diagonal method, modal damping
Keywords: Transport;Teknisk mekanik;Transport;Applied Mechanics
Issue Date: 2019
Publisher: Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper
Chalmers University of Technology / Department of Mechanics and Maritime Sciences
Series/Report no.: Master's thesis - Department of Mechanics and Maritime Sciences : 2019:06
Collection:Examensarbeten för masterexamen // Master Theses

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