Vibration Analysis - Investigating The Dynamic Behavior Of A Structure

The amount of vibration on a machine is a good indicator of the length of time before maintenance is required. With a higher level of vibration, the resulting forces on the structure are higher, which increases the fatigue-related damage to the structure. This can cause bearings and other components of the machine to fail prematurely.

Excessive vibration can have a multitude of sources. The most common are unbalance, misalignment, eccentricity, and faulty bearings. Other sources can also be present depending upon the configuration of other rotating elements.

Resonance can make any vibration present worse, by greatly increasing the amount of vibration for a given excitation force. In some instances, there can be self-excited vibration present, which can build up quickly or very slowly, sometimes taking many years.

Techniques to determine the source of the problem include:

• measuring the vibration simultaneously with the rotation to determine the source (synchronous time averaging)
• phase and amplitude vibration measurements of machine trains to determine the source of vibration problems
• spectral mapping to relate vibration amplitude and phase to machine speed - a powerful method to determine the critical frequencies of the system
• measuring vibrations and comparing them to recognized standards
• frequency or order display of the mapping results
• operating deflection shape analysis
• modal analysis
• speed sweep analysis
• measuring acoustic intensity and noise path transmission

These measurement techniques are invaluable to determine the source of an excessive vibration problem.