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Shurafa

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How much of your job is in rotor dynamics?

Hello everyone,

Because of my limited exposure to large machinery and rotating equipment projects, I rarely deal with vibration problems requiring rotor dynamic background, despite my interest in this field.

Maybe from the entire daily activies, I'm involved in (which cover non-vibration problems), I image the rotor dynamic problems are less than 5 %. I work for an Oil & Gas facility.

How about you?

Regards- Ali M. Al-Shurafa

MarkL

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Reply with quote  #2 
Zero thankfully,
Honestly, rotor dynamics gives me the heeby-jeebies...white metal bearings are black magic/voodoo to me, and orbit plots make me woosey[frown]........lest to say I dont have anything to do with them and that suits me fine.
[biggrin]...I seen a Bentley nevada rack once and got cold sweats.
Shurafa

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Hey Mark!

That is really hilarious! [biggrin]

I assume many of us here don't do much of that stuff but some do. They are smart and able to take responsibility. Many factors are involved in analyzing these machines/problems and many of these factors are assumed as it is not always easy to verify them when the machine is running.

Let's hear from the others.

Regards- Ali M. Al-Shurafa
 
Noknroll

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0% involvement

However, I once worked for Alstom who merged with GE and subsequently attended a compulsory one month solid of classroom GE field engineers boot camp where we were educated in everything Bentley Nevada such as setting up prox probes,alarms, trips, 3500 racks etc
fburgos

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Reply with quote  #5 
not as much as I would like to be involved
spciesla

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Reply with quote  #6 
I think that you need to define the question a little bit better.  I work for Bently Nevada doing machinery diagnostics on turbo-machinery with fluid film bearings every day.  However, I wouldn't say that I do much of any "rotor dynamics".

Steve
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Reply with quote  #7 

MarkL I did feel the same but I have a prehistoric couple of Bently probes that I use when really needed. However on customer demand I spent a number of random occasions in later years even balancing with eddy probes and there is nothing to it just treat it as any other input. In those cases I was not involved in procuring the data however..... use compensated data regardless of what end user say.....
So that is far from actual rotor dynamics it is very rare that I pull out the old software to see a rotor resonance and predict influence of a modification these days, designers are getting better I think.
I just got (last evening) invited to balance a 40+ year old counter rotating radial 3000RPM about 40MW steamturbine those my father worked on and balanced every day of his working days and I never balanced one of those so the ranks of special people or stupid people that take a job like that are getting thinner so that may be as close to rotor dynamics I get this year. Balancing planes are accessed by entering the condenser, I try to stay out of that..... I don't feel that I got that specific info on machine level specifics like test weight selection thru the gene pool, just the general balancing know how maybe.

 


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Shurafa

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Quote:
Originally Posted by spciesla
I think that you need to define the question a little bit better.  I work for Bently Nevada doing machinery diagnostics on turbo-machinery with fluid film bearings every day.  However, I wouldn't say that I do much of any "rotor dynamics".

Steve


Well, I'm not referring to collecting data from online racks for turbomachinery mounted on fluid film bearings.

I'm referring to the involvement in the evaluation and modifications of stiffness and damping of bearings, controlling the effect of seals on the vibration, predicting and tuning the critical speeds, balancing variable speed machines on multiple planes or between critical speeds etc.

As you might already know, these cases require a good understanding of the structural physics or tribology of bearings, in addition to the general understanding of machinery vibration.

Models of lateral and torsional vibration are reviewed during projects of large machines. They involve theory, math, computer modeling and compliance with standards.

Regards- Ali M. Al-Shurafa



Danny Harvey

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Reply with quote  #9 
I have almost none because I am not qualified in rotor dynamics other than a little balancing. 

In one location, there is a corporate guy who looks after all the big stuff for a large power generating company. I leave all that to him and wish he would do the same when it comes to Predictive Maintenance because while he certainly knows his rotor dynamics, he's never even run a route and his efforts are allowing defects to go undetected in the areas where his responsibilities require such knowledge as how to determine proper data collection parameters.




electricpete

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Reply with quote  #10 

I'd say my job responsibilities (plant electric motor engineer) do not require rotor dynamics.

I have gravitated towards studying rotor dynamnics either at home or stealing some time on the job, mostly because it seemed mysterious and interesting.

I have tried to model some of our motors/machines a few times to help understand a specific problem (example: understanding role of rotor dynamic flexibility in a rotor/stator rub that we had). In retrospect, I don't think any actions have been changed as a result.

Since we don't have any rotor dynamic-savvy engineers on site, I have been asked to comment on vendor proposals a few times, for coupling changeout on high speed machine, for bearing changeout on high speed machine, and proposals related to concerns about turbine 2nd critical too close to running speed. Most of the time it is just a few questions that I ask. Again I don't think my comments have ever changed what we did.

In the end, I have probably spent 1% of my job time on these types of things. And there has been zero payback in terms of affecting decisions. Maybe I just did it to make myself feel smarter ;-)

Shurafa

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Reply with quote  #11 
Danny,

I always thought that these are two different sets of skills though the overlap in the basics.

Peter,

You shared some of your models and I think they are very interesting and require advanced knowledge in physics, math and the programming. MS Excel is what most of us have but you made of it a great analysis tool for the critical speeds and mode shapes.

Regards- Ali M. Al-Shurafa
Danny Harvey

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Reply with quote  #12 
"I always thought that these are two different sets of skills though the overlap in the basics."

I agree.

But I add further that expertise in one does not convey expertise in the other.
Rang

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Reply with quote  #13 
Quote:
Originally Posted by Noknroll
0% involvement

However, I once worked for Alstom who merged with GE and subsequently attended a compulsory one month solid of classroom GE field engineers boot camp where we were educated in everything Bentley Nevada such as setting up prox probes,alarms, trips, 3500 racks etc


Hmmm, can you send me the course notes Nok?
RustyCas

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Reply with quote  #14 
“expertise in one does not convey expertise in the other”.... I completely agree with Danny on this. I am a really good run-of-the-mill analyst and comfortable balancing any rigid-rotor machine. I spent the first 14 years of my career in large fossil power plants and assisted on numerous large turbine balance jobs, but if called today for such a job, I wouldn’t even consider it. That’s not the kind of job for less than an expert, and I’m no rotor-dynamics expert.

We had a guy on the old board however, who was, and said as much quite often. He thought it made him an expert in all things vibration-related, but he wasn’t... and I said as much quite often.

My favorite version of Danny’s quote (which I probably use once a week):




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Barry

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Reply with quote  #15 
As Danny has said before sometimes it more important to know what you don’t know.
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