IF WE ARE NOT ABLE TO REDUCE VIBRATION OF A MACHINE, WHAT IS THE PREFERRED METHOD? TO INCREASE MOBILITY OR STIFFNESS?
REGARDS
IRSHAD

The preferred method would be to find and reduce the source of vibration, but this is not always easy to do or possible, as you state.

Depending on the size and type of machine, raising the natural frequency of a machine structure to above the forcing frequency (i.e. increasing stiffness) may be possible. For smaller machines, a hydraulic jack may be able to be tried. Once I used some pieces of wood lying nearby. The vibration dropped from 45 mm/s rms to only 5 mm/s. A permanent fix was installed.

The other way is to add mass.

I have seen both methods used successfully. It is of course important to measure vibration before/during/after making changes.

Mr. Ray,
Suppose we hang one motor in space ad run it. It's stiffness will be very small and mobility will be very high. I want to say that the motor will run for a lomg long time without any defect since no damaging force will be produced. Now, if we constrain it on all sides making it's vibration zero on ground. O.K., vibration will be zero but force on bearing will be tremendously high and cause frequent failures.Am I right?
Regards
Irshad Akhtar