Investigation of the structural dynamics in an automotive A/C system

Examensarbete för masterexamen

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Type: Examensarbete för masterexamen
Master Thesis
Title: Investigation of the structural dynamics in an automotive A/C system
Authors: Agnesson, Mårten
Karlsson, Niklas
Abstract: In the range of detectable sounds inside a car coupe interior noise and vibration induced by the A/C system is present. As engines become more efficient and hybrid cars more common this source gets more prominent. The current study has investigated unwanted resonance in the A/C-system. Previous studies has shown that the noise inside the coupe correlates to measured vibrations at the end of the A/C system. Based on these studies a section for the vibration the transfer path, between the compressor and the thermal expansion valve, was considered during this project. The objective of the study was to numerically simulate the structural vibration behavior in the structure. To do so a FE model was built, validated and calibrated to experimental data obtained from modal analysis on the physical system. The procedure of testing with methods of both pre-test planning and post analysis of the measurement is presented. FE modelling was done in ANSA and a normal modes analysis was conducted using Nastran. Post processing of test results was done in Matlab. Validation of results obtained from numerical simulation and experimental modal analysis was performed. The percental deviation between the corresponding eigenfrequencies were calculated and the eigenmodes were evaluated using the modal assurance criterion. A parametrization of the FE model was performed for material- and part properties. The model was then calibrated, using FEMcali, to fit better to the experimental test data. The results showed that the numerical model could predict the eigenmodes with better accuracy after the calibration. Numerical results had a mean deviation to the test of less than ten percent for eigenmodes below 500 Hz. Finally, an investigation was conducted on how two different added mounting points to the car chassis could influence the resonance in the system. The methodology of correlating numerical results to physical testing introduces sources of error during the validation process and the signification of performing it in an iterative manner is discussed.
Keywords: Transport;Teknisk mekanik;Farkostteknik;Transport;Applied Mechanics;Vehicle Engineering
Issue Date: 2016
Publisher: Chalmers tekniska högskola / Institutionen för tillämpad mekanik
Chalmers University of Technology / Department of Applied Mechanics
Series/Report no.: Diploma work - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden : 2017:03
Collection:Examensarbeten för masterexamen // Master Theses

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