Crash and Vibration Analysis of rotors in a Roots Vacuum Booster

The dynamic behaviour of a roots vacuum booster with two rotors is presented. The dynamic response of the structure is, thereby, investigated using an explicit analysis for the crash behaviour and an implicit analysis for the vibration behaviour. Typically the rotors run from 3000rpm to 3600rpm, but because of a desired rise in power density it is necessary to design rotors for operation at 6000rpm. With increasing rotational velocity the dynamic loading and the inertial forces increase as well. To face this challenge a rotor with less weight was devel- oped. To come to a conclusion about impact behaviour, dynamic deformation and bearing-reactions a crash between the two rotors has been simulated. These results are compared with another rotor which show the potential of weight reduction. The rotor and shaft are made from cast iron. For the material model in the crash analysis, a comparison between Mat Piecewise Linear Plasticity and Mat Gurson JC has been accomplished. To consider tri- axiality a vonMises yield locus is used together with the Johnson-Cook failure criterion in Mat Gurson JC, i.e. damage and its accumulation has been neglected, see [4] and [7]. In an implicit eigenvalue analysis the eigenfrequencies are determined. Roots pumps are assembled in industrial installations, where it is necessary to know the appearing natural frequencies to avoid reso- nance vibrations.

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