Depending on the amount of damping inherent in the pipe then this determines how far away does the resonant frequency must be from the excitation frequency. An empty pipe has very low material (as opposed to viscous or friction) damping force available. Thus the first two or three natural mode...
When considering running clearance, at a minimum, I would consider sixfold parameters: shaft speed, type of bearing in which the shaft is running, allowable shaft mechanical runout, allowable bearing concentricity, allowable misalignmemt, expected shaft temperatures and expected lube viscosity &...
