“The significant proportion of vibration troubleshoots I get asked to look at are resonance-related. We have seen an increase in these types of problems over the years as assets are fitted with variable speed drives. So, instead of having, say, a 1X forcing frequency fixed, this can move around depending on process demands, making it more likely to get close to a structural natural frequency.
A classic case here is where a water pump suffered from high vibration levels, 25mm/sec+, with poor reliability. The vibration at 1X occurred within a certain speed range; at high speeds, the vibration levels reduced—a good indicator of a possible resonance problem. The motion amplification video was taken just off the critical speed, and we can see the significant flexing of the suspended floor. Resonance bump tests were performed with the MA camera and traditional analyser and confirmed the natural frequency of the floor was within the operating range of the pump.
The recommended solution was to move the natural frequency away from the operating speed by stiffening the floor with additional supports. We suspect that due to the walkway, these were missed off the design, as the other two pumps had the supports present. MA is a great tool to visualise and measure these types of problems, with the data viewed live or within minutes.” — Stuart Walker
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