Multi-Body Dynamics and Harmonic Analyses of Scroll compressor to predict stress level in piping system

Abstract

In this thesis the dynamic behavior of a scroll compressor with piping system is studied using numerical and experimental tools in order to improve the knowledge in numerical modeling. A multi-body dynamics analysis is firstly performed by completing an existing finite element model to obtain a complete compressor. The model inputs are chosen to best represent the real conditions applied to the compressor. Then, the results of this first model are used to create excitations in a second model which studies the harmonic response of the system. A modal analysis must be done to obtain the different natural frequencies of the system and then determine how it will react to these excitations. A second harmonic analysis is realized using the same excitations but calculated analytically. The comparison of the two harmonic responses leads to similar results which allows to affirm that the analytical calculations are sufficient to have a consistent harmonic response and that a multi-body analysis is not essential in this case. Finally, experimental modal analysis and vibration tests are conducted on an experimental structure in order to measure eigenfrequencies, accelerations and strains at several points of the real system and compare them with numerical results. It appears that the experimental accelerations are up to three times lower than the numerical ones because the multi-body model does not start from a static equilibrium and therefore, under the application of gravity, it is dropped on the grommets and bounces on them. The simulation is too short to dampen this phenomenon which means that the model is not yet in a steady state. These excessive accelerations imply too high displacements and thus lead to high strains which explains the factor 10 between the numerical and experimental strains. Lastly, some points of possible improvement are detailed for future works.