Diagrams Campbell

Of all vibration frequeneies, the most dangerous are the synehronous vibrations, where an externally foreed vibration exeites one of the natural (resonant) frequeneies in the maehine. Campbell diagrams eonstrueted by the manufaeturers will help the operator avoid these frequeneies during run-up or eoimuissioning of tlie maehine in question. 

To ensure that blade stress levels are within the fatigue life requirements of the eompressor, it is usual praetiee to strain-gauge the blading on one or two prototype maehines, measure the stress levels, and generate a Campbell diagram showing the plotted test data. To measure data, an impeller ean also be mounted on a shaker table with a variable frequeney output (0-10,000 Hz). Aeeelerometers ean be mounted at various positions on the... 

A Campbell diagram is frequently used to determine the effect of multiple excitation frequencies in high-speed steam turbines. Figure 7-11 shows a Campbell diagram for a condensing steam turbine. If this partic uiar turbine operates at a speed of 8,750 rpm, the turbine blades would not be excited. But, if the turbine speed is reduced to 7,500 rpm, the turbine blades would be excited at four times running speed. If the turbine were operated at 10,000 rpm, a three-times running speed excitation would be encountered. What this means is that any vibration in the... 

Figure 7-11. Typical Campbell diagram. (Courtesy of Elliott Company)...

Sometimes, because of process requirements, it is impossible to avoid some excitation frequencies. If the Campbell diagram shows this will occur, then the blade in question must be carefully designed to keep stresses low. When properly addressed in design, operation can take place in an area of excitation. The major variables affecting turbine selection may be listed as follows ... 

Whenever a torsional analysis is performed, a Campbell diagram shall be furnished to the purchaser for information only. 

The vertical oscillations are primarily excited by changes in the rope tension caused by acceleration and retardation, changes of rope layer and Lebus kicks. The vibration recordings when displayed on a Campbell diagram, see Figure 25, clearly shows influence from the Lebus kick harmonic frequencies and catenary natural frequencies. 

Figure 25. Campbell diagram. Vibrations in the cage in vertical (z) direction traveling down at 8 m/s, payload 300 kg.

Robust optimization of a flexible rotor-bearing system using the Campbell diagram. Eng Optim 43(l) 77-96... 

---