The plant installed a new motor that was about 2000 lb lighter than the old one and has a lower profile. This is a vertical pump.

With out the motor running the structure now vibrates at .25 ips and goes to about .4 ips with it in service. A dynamic absorber reduced the vibration to .2 ips with the motor running.

My question is how many other nuclear plants have or are using dynamic absorbers to resolve a structural resonance problems?

This message has been edited. Last edited by: Ron Stiemsma,

We are a nuke plant using a dynamic absorber to control resonant vibration on our vertical well water pump/motors.

We chose this method over a brace because there is not much to brace off of in the area.

Our attachment is a collar which clamps around the motor. A vertical bar is attached to the collar with an adjustable weight at the top. It seems to require periodic tuning but has helped us cope with the resonance.

This system (well water) is less important and requires a lower level of design/configuraiton control than most plant systems at our plant. I don't know whether everyone at our plant would agree to using a dynamic absorber as a long-term solution in a critical application.

I can speak for a few of the nuke plants in Sweden. The active dynamic absorber has been tested a few times, and as soon as time has permitted, it has been replaced with a permanent maintenance free solution. Such as stiffening and adding mass, a fixed detuning. I am not aware of any still running. Mind you, I do not know by far all what happens over here, there are still 11 reactors left from the attacks from the politicians. I could get you more detailed contact paths if you like to know more facts. The plants are Ringhals (3xPWR,1xBWR), Oskarshamn and Forsmark (3xBWR each)

I will say in agreement with Arne that I do not know of dynamic absorbers classified as a permanent fix. I have never seen them recommended as a 'real' fix; only a fix until a permanent solution can be accomplished or run until an outage and then make a permanent fix. But in every case on a temperory solution. I have a software program that can help calculate and design.

The downside of a dynamic absorber:

- may require tuning – if so you will see it in increased vib measurement and be alerted to tune it – no risk to equipment
- may eventually fail by fatigue – if so you will see it in increased vib measurement and be alerted to replace it – no risk to equipment
Did I miss any disadvantages?

So, it’s better than nothing, not as good as bracing, but also in some cases not as expensive as bracing in terms of initial cost (although higher in ongoing costs)

It seems to me this has a niche in non-critical equipment where there is nothing convenient to brace to, and in business environments where initial cost investments are evaluated with a payback period of 2 years. That’s kind of how we got here.

Comments?

The failure by fatigue could cause injury, too. The design should include a fatigue analysis and possible means to restrain or capture a failure. I've seen cages around the absorber or chains used to prevent one from going too far if it failed.

Industrial or nuke systems are not the only source for vibrations problems. There are many systems that can't be braced or modified; please remember a very few special things like wheels for citroen cars, washing machines or some special buildings can,t be braced and dynamic absorbers are the only way to control vibrations.

I like very much that system and have used it for some special tools, instruments and centrifuges ¿where can I get that software?

Regards

Iván Pérez G.

Iván, the earlier VW Passat has a 6 lb weight on a dual flat beam spring on the front axle. Take it away and you immediately feel the difference. It must be well engineered since I never saw one along the roads here and we have many such cars around :-).