Vibration analysis of an idealized vertical pump model

Vertical pumps have intrinsically weak structures for vibration resonance because of their long slender shapes. Therefore, it is important to estimate the vibration characteristics of a vertical pump analytically and/or experimentally before its final installation. Sometimes, however, unexpected resonances arise after the installation. The unexpected resonance is found to be due to the difference between the boundary condition of a vertical pump for rigid-foundation test operation and for flexible-foundation real operation. In order to examine this problem and quantify the effect of the foundation condition on the natural frequencies and mode shapes of the entire pump assembly, a mathematical model using a Euler-Bernoulli beam with a flexible foundation is presented. This model combines the lower and upper parts of a vertical pump, distinguishing it from previous analytical models. Experiments and simulations have been performed to validate this mathematical model and to evaluate the effect of foundation stiffness on vibration behaviour. Parametric studies have also been carried out to investigate the effects of other design variables on the dynamic characteristics of the pumps and to propose design strategies for improvement in the dynamics.