spike energy

[shipvibration]

can someone explain spike energy and modes of vibration in simple terms?
thanx.

 

[electricpete]

spike energy is a tool which is very sensitive/effective in identifying the unique types of high frequency energy present in repetitive impacting type events. An increase in spike energy will usually be one of the earliest indicators of a rolling-element bearing defect. Furthermore the distintive fault frequency associated with the defect (BPFO, BPFI, 2xBSF, FTF) will show up in a clearer and easier-to identify pattern in the spike energy spectrum (usually at it's fundamental frequency) as compared to the regular spectrum (usually a haystack of harmonics of fault frequencies in a wide range around 100kcpm)

 

[electricpete]

In my mind a mode refers to the shape that a vibrating part takes.

Best example is a simple beam supported at both ends. It can vibrate like a simple bow (at a given instant in time goes from zero at the ends to max in the middle). Or it can vibrate in a more complex pattern that has two, three etc peaks. Each of these is a different mode shape. Each will have a different resonant frequency.

Someone help me out if there's a better/easier way to explain modes.