Tuned Resonant Absorbers - Practical Experience

[butelja]

We have a couple of 3600 RPM blowers that are installed on elevated structural steel platforms and naturally exhibit high vibration readings. The correct fix in my mind would be to install inertia bases with spring isolators and expansion joints in the piping, along with ensuring proper balancing and alignment of the blowers. The balancing and alignment are no problem, but the $$ are not available to install the inertia bases.

It has been suggested that we try installing a tuned resonant vibration absorber. This would be a dumbell shaped piece of steel rigidly clamped in the center and mounted to the blower. It would be tuned to have its natural frequency tuned to the blowers operating frequency. Since there is a 180° phase shift at resonance, it should in theory exactly cancel out the blower vibration due to imbalance. DOES ANYONE HAVE PRACTICAL EXPERIENCE WITH TRYING THIS APPROACH? Some of the potential pitfalls that might happen include fatigue failure of the absorber and difficulty in tuning it properly. It seems that they should be mounted symmetrically in pairs in the plane of the impeller to avoid inducing moments into the system. ANY THOUGHTS BASED UPON PRACTICAL EXPERIENCE?

 

[svanels]

It is a very common solution, and since your blowers run at a constant velocity of 3600 RPM, it is ideal.
In our vibration lab (years ago) we had a workbench to test absorbers, consisting of a rectangular bar, fixed at both ends, and in the middle a small electric motor with an unbalanced disk.

You can use a metal strip with one mass, which is easier to tune. Fatigue will play a role when the amplitude of the absorber is high.
Allmost all high voltage transmission lines have these small devices atached near the suspension tower, and I never saw someone doing maintenance or replacing.

Regards Steven van Els
SAvanEls@cq-link.sr

 

[wroberts]

I'm in agreement with the above comment. While I haven't done this in an industrial environment, we worked on the same project for vibrations, in school. The bigest thing you need to do is to be able to tune the thing. A metal rod with an movable weight along it's length should work very well. Use some type of Spring steel, and keep it's motion in the elastic range.

Will Roberts
Yazaki-NA