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  1. GregLocock

    Seeking Guidance on Learning to Use ACOEM ONEPROD Vibration Analyzer

    B&K produce an excellent series of manuals and technical notes on signal analysis in general and vibration monitoring. The HP/Agilent intro is also fine...
  2. GregLocock

    Balancing large 8600hp electric motor with fluid film bearings

    I have done the non indexed method as an exercise but since all of my data is triggered the index method is more robust and easier.
  3. GregLocock

    Balancing large 8600hp electric motor with fluid film bearings

    In theory it doesn't matter where the trial weights are located on each plane relative to the other plane, I think. But i haven't done this in a long time(25 years). I'd have thought so long as all measurements and locations were referenced to a single shaft reference marker it would be OK.
  4. GregLocock

    Balancing large 8600hp electric motor with fluid film bearings

    You do the 2 single plane balances by record the vibration or velocity at both planes. Same number of runs just more data. Maths is here https://www.eng-tips.com/threads/diy-crankshaft-balancing-with-an-oscilloscope.511892/#post-8933361
  5. GregLocock

    Balancing large 8600hp electric motor with fluid film bearings

    2 plane balancing is more complex than 2 1 plane balances, as you need to consider the influence coefficients from plane1 to plane 2 and vice versa.
  6. GregLocock

    Balancing large 8600hp electric motor with fluid film bearings

    Frankly I'd be calling in a large motor balancing guy. Did you 2 plane balance? Since automotive crankshafts are oil bearings I don't remember any problems balancing them. Depending on the natural frequencies of the rotor you may be operating above the whirl speed. Certainly possible...
  7. GregLocock

    critical speed/natural frequency confusion

    If you are messing about with running close to or above the natural frequency (here there be dragons, but it is common with big turbines) then the other thing to watch for is half speed whirl.
  8. GregLocock

    critical speed/natural frequency confusion

    Yes the first critical speed of the shaft is the first bending mode of the non rotating shaft. Am I right in thinking that gyroscopic and centrifugal forces seem to influence the lateral natural frequencies of the shaft in the rotating reference, as they essentially provide a "stiffening"...
  9. GregLocock

    Root cause of harmonic oscillation in telescopic column

    I have seen successful estimates of stick slip problems, you need to know the axial and radial compliance of the blocks and of course the coefficients of friction, as well as all the other obvious properties of the system
  10. GregLocock

    Root cause of harmonic oscillation in telescopic column

    Shrugs. Without details of the payload, geometry of the tubes etc then it's all going to be handwavium but at a guess you have a non linear kitchen drawer sticking type problem if you only have one set of acetal blocks. 92 Hz is irrelevant.
  11. GregLocock

    Sensor Selection for Measuring Timing

    Knock sensors work 5-10 kHz, they are detecting high frequency modes in the cylinder head. Finding where to put them is a bit of a project on an automotive engine because we are cheap and only want to use one sensor to detect knock in all the cylinders. Since you've got single cylinder heads you...
  12. GregLocock

    Sensor Selection for Measuring Timing

    If you are confident with the timing you can use a gated time window to get rid of the noise. That is you zero out everything but the few degrees of crank sensor around that event. et voila https://www.bkvibro.com/wp-content/uploads/2020/12/BAN0062EN11_MS_Gated_vibrations_recips.pdf
  13. GregLocock

    Sensor Selection for Measuring Timing

    You might find an accelerometer on the head is more useful. It's a tricky project, all those events are at the same fundamental frequency, they'll just have different phases and harmonics. A stethoscope or a screwdriver might be a good place to start.
  14. GregLocock

    Tuned Mass Damper - quick guide to tuning them

    Here's the guts of it everything else is just eye candy %build some matrices K=[k1+k2 -k2;-k2 k2]; M=[m1 0;0 m2]; M_baseline=[m1 0;0 0]; %baseline case, ie main mass only C=[c1+c2 -c2;-c2 c2]; F=[1;0];%excite the main mass, ie engine case %runs happier x1=zeros(1000,1); x2=zeros(1000,1)...
  15. GregLocock

    Tuned Mass Damper - quick guide to tuning them

    Your calculator has an error in it. If you set m2 to a very small value the TL should be the same as the 1dof system. Where is the force being applied, ie do you have a subframe (m2 is excited) or a conventional harmonic damper (M1 is excited)?
  16. GregLocock

    Vibration excitation with electromagnet

    Ah, yes I thought the thickness was a bit exotic. Sorry, i literally have no idea how to spec an electromagnet for that job. It rather depends on what you need it to do.
  17. GregLocock

    Vibration excitation with electromagnet

    Hmm, in the reverse case we use capacitance not magnetism. It'll be very easy to damage your foil.
  18. GregLocock

    Vibration spectrum analysis

    1st order is 28 hz, 2nd at 56, 3rd at 84 hz Now see if you can work out 4th order
  19. GregLocock

    Vibration spectrum analysis

    1689 rpm is 28.15 Hz. You may have some 2nd order at twice that Something doesn't add up, you'd expect to see at least some content at tooth mesh frequency.
  20. GregLocock

    Vibration spectrum analysis

    Not without a much better description of the gearbox, input rpm, number of teeth on each gear etc.

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