We performed a modal analysis to monitor the potential vibrations of the disks. The excitations known are the residual imbalance and the shaft's longitudinal active magnetic bearing.
Experience on similar choppers has shown that any excitation is predominantly due to the longitudinal active magnetic bearing. The modal analysis therefore focussed on the eigenmodes along the z axis.
Method
The mesh of the model is specific: mapped mesh, 20-node tetrahedral elements SOLID186.
However the disk presents cyclic symmetry, and the modal analysis must be performed on the entire disk, although only a small part of the spectrum to be searched is to be calculated.
We will study the eigenfrequencies whose modal mass is significant compared with the total mass of the disk.
The boundary conditions are:
All degrees of freedom are fixed for 0 £ r £ 28.5 mm.