چكيده به لاتين
Magnetic bearings offer many technical advantages compared to mechanical bearings such as oil-free operation, negligible friction loss, low acoustic noise, and extending a limit of rotational speed. Passive magnetic bearings (PMBs) have very simple, robust, and efficient structure compared to common active magnetic bearings (AMBs). PMBs with opposing magnetic rings are one of the well-known configurations in this category. The force between magnets may be repulsive or attractive for radial or axial bearings, respectively. The main disadvantage of such bearings is that they produce positive stiffness and stabilizing effect only in one direction and have negative stiffness and destabilizing effect in other directions. However, their simple structure makes them ideal for stabilizing of one direction in a situation where the instabilities in other directions are compensated with other types of bearings.
These bearings have low stiffness and approximately no any damping and so, despite their very advantages, they have not been given Special attentions. In this thesis, we deal with the methods to improve the performance of such bearings to make them a useful bearing in special applications. The stiffness of such bearings are improved by using rotating magnetization (Halbach stacking) or alternately radially or axially magnetization (standard stacking). Furthermore, we used ferromagnetic materials and air intervals for more improving the stiffness. For producing the required damping, we added a thin layer of conductor in Halbach stacking and also proposed the configuration of reduced Halbach stacking.
The stiffness and damping of the proposed configurations are calculated through a 2D dynamic analytical method. We solve the Laplace equations in each region and after applying the boundry conditions, we determined the magnetic field distributions in the space. After calculating the magnetic fields, the forces, stiffness, and damping are calculated by using classical Maxwell tensor. Then, we validated our analytical results with the finite element method simulation.
The stiffness, damping, and sizes of the magnets and conductors are normalized for giving a general solution. The sizes of the magnets are optimized for maximum stiffness and damping per magnet volume ratio. The procedure of designing of PMBs for maximum of both stiffness and damping was presented. We could achieve the best configurations of PMBs for each special application.
