PSI - Issue 24

4

Vincenzo D’Addio et al. / Procedia Structural Integrity 24 (2019) 510–525 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

513

Fig. 1. Schematic drawing of the pump rotating assembly and size of the rotating components.

The design parameters that can be easily varied and have an impact on the pump rotor dynamics are the axial distance between bearings and the support stiffness. In particular, the present analysis will be focused on the latter aspect. 3. Loads acting on the system Before entering more specifically into the details of the dynamic models and simulations, a review of the main loads that excite the system and their frequency content will be given, ref. Ehrich (1998). This is necessary to establish if the operating condition in terms of rotational speed is acceptable or not. Neglecting the fluctuation of the radial load due to the magnetic field and axial loads transmitted by the frame in which the pump is mounted, the principal sources of transverse vibrations for the system are the following:  unbalance;  fluid-dynamic actions on the impeller;  defects on ball bearings. In a rotating system a certain amount of unbalance is always present. The reduction of unbalance due to balancing operations depends on the accuracy of the procedure, but, in any case, it is impossible to achieve perfect balance. Therefore, inertial loads are introduced in the system related essentially to eccentricity and misalignment, as shown in Fig. 2 for the impeller.

Fig. 2. Unbalance introduced by the impeller: eccentricity e and misalignment 

This type of loads rotates with the structure and consequently the frequency of this excitation corresponds to the