Modal Analysis- the study of how different areas of a structure move at different frequencies. Usually frequency response data is collected by a spectrum analyzer and imported into a modal analysis software program, which then can calculate and animate a structure's dynamic behavior. If the proper and sufficient data is collected, the software can also predict how modifications will change the response of the structure. These techniques are very useful in testing production prototypes and in troubleshooting industrial machines and structures that are found to have vibration problems.
A modal study does not have to be complicated; in some cases, a minimum study can be performed on an industrial part in a few hours that can fully answer the questions on how to modify a design to correct a resonance problem.
Operating Deflection Shapes (ODS)- Often a subset of a modal analysis program in which the primary interest is how a machine is moving while it is in normal operation. ODS will show deflections caused by machine operation that may not be resonant and may not show resonances. Often machinery may operate without interruption during the study.
Examples of Modal Analysis studies Hankinson performed in client's facilities:
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The animation of the first two modes of the bracket can be seen in the following links: |
The picture above is the coordinate structure of the undistorted shape of a bracket exposed to severe vibration. The attachment points are on the 90-degree ears at the back of the bracket.
The following is an example of an Operating Deflection Shape analysis:
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| A 350 HP water pump and its concrete base.
The red is the motor on the left and the pump on the right; the blue is the support structure between the motor and the base and the steel and concrete base are the 3 parallel lines at the bottom.
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The animation of the second deflection shape of the water pump shown above can be seen in the following link: |