Campbell diagrams are over rated ?

[rQuestionEngineering]

Customer copied OEM shaft and replaced it on their unit without complicated diagrams like Goodman and Campbell .
At most , I saw it was dynamically balanced .
At startup , they just accelerate it pass the critical speed and and load it.
Are these diagrams over rated by OEM for their own design verification purpose ?
Most users don't use these diagrams and it is not required to understand them .

What are your experiences with these diagrams and how you apply it in your work ?

 

[GregLocock]

The completely useless link you gave is not a good example of a campbell diagram. Your question is incomprehensible.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[jimkinney]

For a shaft or a system with a single load (disk, blade, etc.) they're not useful.

If you have a gas turbine engine with lots of disks, each with a different number of blades they're very useful. Trying to navigate shaft speed through multiple blade passing frequencies can be a pain.

Jim

Jim Kinney
Kennedy Space Center, FL

 

[snoopnoon]

As a ST Engineer, in my opinion, they are required. Campbell diagrams at least allow you to know the frequency of the blades. If designing around the operation speed is unavoidable, then the buckets need to be robust enough to operate in resonance. Here they become critical, as you want to know which resonance they are in as there are certain modes more dangerous than others (1TO tangential mode).
You are not always concerned about shaft speed directly, but in a ST the nozzle count/360 at the shaft speed. Typically 1X and 2X would be looked at.
Do you need a diagram to show you this? NO- but like all charts, it is a nice way to present data without calculating numbers on the fly.

 

[geesaman.d]

I don't work in steam turbines; I work in industrial agitators. Our agitators operate below first critical speed and do not behave as flexible rotors.

Yet I have had some customers require full flexible rotordynamic calculations and campbell diagrams. In my case it's completely unnecessary and stupid. When the customer insists, I subcontract the entire exercise and make the calculation, submittal, and approval a hold point on the critical path of the order because I want nothing to do with it. I also make sure it's a cost and lead time adder on the base contract because I want the customer to ask themselves 'why so much' and prompt an actual conversation with someone who understands the specs and value of such exercises.

For steam turbines and other flexible rotor structures with an array of resonances, having the campbell diagrams seems pretty obviously important.