Parametric tool for initial estimation of thermal and mechanical stress in high speed rotors

Abstract

Bearingless drives magnetically integrate magnetic bearing and motor function. They offer non-contaminating working environment, are maintenance free and generally have long lifetime. Bearingless drives is a good choice in high speed applications due to the absence of friction losses. Permanent magnets employed at the rotor of bearingless drives suffer from mechanical stresses due to high centrifugal forces. Hence, the yield strength of the rotor materials is the only limiting factor of speed in permanent magnet rotors. The stress analysis in permanent magnet rotors are generally carried out using finite element software such as ansys, abaqus etc. This approach is time consuming which limits them in applications where rapid testing of varying geometries is a requirement. Therefore, an analytical tool to predict the initial mechanical stress in high speed permanent magnet rotors is proposed in this thesis. A parametric tool to predict the peak stress for four basic permanent magnet configurations like cylindrical permanent magnet, surface permanent manet, interior permanent magnet and V-Shaped permanent magnet is developed in matlab 17. The results from matlab code is verified with the help of finite element based software ansys 18. The material properties and geometrical definitions used in the matlab code input is repeated in the ansys model to make a fair comparison of results. Two different test cases like geometry test and speed test were framed to do the testing. The test cases are repeated for all four permanent magnet configurations studied in this paper. Moreover, a correction factor is also introduced in the code from the speed test results to improve the accuracy. The reliability of this factor is ensured by using the same factor for different geometries in geometry test. The analytical tool developed gave faster and moderately accurate results on testing.