Unbalance Force Analysis of Primary Pump Shaft in PGSFR

In this paper, rotor-dynamic characteristics for the primary pump shaft were obtained. On the basis of the results, we decided to almost double the shaft diameter. By virtue of this design change, the revised design can be satisfied with the critical speed design criteria as well as can decrease a number of support bearings. In the results of unbalance analysis, it was figured that the maximum bearing deflections and loads are within the design criteria. All rotating shafts, even in the absence of external loads, have always eccentric distance due to the manufacturing deviations, material defects, and installation error. This unbalance mass resulting in the eccentric distance of the rotating structure causes resonance at critical speeds. The resonance is the state at which the harmonic loads are excited at their natural frequencies causing shafts to vibrate excessively. This vibration of large amplitude causes shafts to bend and twists significantly and leads to permanent failure. Hence, the determination of these rotor-dynamic characteristics of rotating shaft in the mechanical design stage is much important. In this paper following issues are addressed: - Describe how to calculate the unbalance force. - Predict the natural frequency variations and identify critical speeds within or near the operating speed range of a shaft for consideration of the unbalance bearing stiffness and damping. - Determine the available support positions of a pump shaft to avoid resonance within operating speed. - Perform an unbalance response analysis of a shaft in order to calculate shaft displacement and quantify the forces acting on the shaft support that are caused due to shaft unbalance