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  1. VibFrank

    Combination of load cases and stress linearization

    Hello, we often have the typical situation of a pressure vessel with a nozzle. At the nozzle there are given 6 max allowable loads (3 forces, 3 moments), but those loads are absolute values, so the direction is not known. The stress distribution in the pressure vessel should be checked with...
  2. VibFrank

    Safety margins for torsional eigenfrequencies of big shaftlines?

    Perhaps I am a little bit late: API 610 (we have 8. edition I think) also gives 10%
  3. VibFrank

    Hertzian Pressure in a Bearing

    P is the load from earthquake: P=mass*acceleration
  4. VibFrank

    Hertzian Pressure in a Bearing

    I also did not realize the "sign-convention" at the beginning. Or perhaps from another point of view: are the formulas valid for r1 nearly equal r2 but with different sign ? frank
  5. VibFrank

    Damped versus undamped critical speed calculations

    You can find references to 1% modal damping in the references of the API Publication 684...but certainly: measurements are the best...
  6. VibFrank

    Damped versus undamped critical speed calculations

    Hi, in the ANSYS help, there are formulas given. You take 2 frequencies and the modal damping (typicaly 1%) at those frequencies. Then you can calculate the alpha and beta. In between the two frequencies you have a lower modal damping, outside it is higher, so you have to chose the frequencies...
  7. VibFrank

    Hertzian Pressure in a Bearing

    Hy, I try to calculate the stress inside a journal bearing, if the shaft gets into contact with the bearing housing during shocks. I calculated with the formulas of Hertz (cylinder inside cylinder) and I found very low values for the pressure. This results from 1/r1+1/r2 (r1=radius of the...
  8. VibFrank

    UBC verification for Pump

    I think, they want a stability analysis from you. UBC (you have to buy the book) you need to get the earthquake acceleration with which to calculate the forces on the foundation. Depending on the pump type, you make a static or dynamic calculation. Normaly for the static one, there is a chapter...
  9. VibFrank

    Damped versus undamped critical speed calculations

    Hy experts, I often have the job to calculate lateral critical speeds for pumps. The one who did the job before me only did undamped calculations whereas I do both damped and undamped. Now the problem: most specifications still have the sentence: the distance to rotational speed must be greater...
  10. VibFrank

    Stiffness/Damping coefficients at nonsynchronous rotational speed

    Hy, the calculated stiffness- and damping values for plain cylindrical journal bearings are valid only for forces with rotational speed. How do they change with much higher frequencies (10x rotational speed) ? Thanks for your comments Frank
  11. VibFrank

    Rotordynamics book

    Hello, I just saw at amazon a book about rotordynamics from Donald Bently. Because I did not find it in libraries for a preview, I wanted to ask here. Is it good ? I need a more practical book (certainly with the typical mathematics, good explained). Thanks for your comments
  12. VibFrank

    Calculating half frequency whirl ?

    Hy, electripete: I read your calculation und I think I understood it :-) (one question: isn't there another squareroot at 180 degrees of "your" roots ? That one would be stable..) I tried to make your calculation with a damped system, but I failed. Have you done such a calculation or do you...
  13. VibFrank

    Calculating half frequency whirl ?

    Hy, a longer question.. We measure the transient bearing loads of a vertical rotor with low bearing load. We also see, that a half frequency whirl occurs. If I take the load and calculate with this load the linear stiffness and damping coefficients of the bearing and then the damped natural...
  14. VibFrank

    rotordynamics software

    Hello, which rotordynamics software do you use ? We are looking for a rotordynamics-software for: -lateral and torsional -undamped and damped -harmonic excitation -journal bearings, seals and gaps -journal bearings: nonlinear (transient) -3 or more rotating shafts, each above each other (similar...
  15. VibFrank

    API 610 1n/2n Torsional Excitation

    Is this independent of the number of blades in the diffuser ?
  16. VibFrank

    API 610 1n/2n Torsional Excitation

    Hy, I have in a torsional analysis an intersection of 2n with a natural frequency (Campbell diagram). It is a (asysnchronous) motor-gear-pump-system. According to API 610 in such a case a harmonic analysis with 2n has to be done to determine the existing stresses. But is there an excitation with...
  17. VibFrank

    Torsional Analysis

    Hy, I try for the first time to do a torsional analysis of a shaft configuration with a hydrodynamic coupling. I have the frequency-dependent stiffness and values of the coupling. some questions: How do you model such a coupling ? tors-spring with damper ? Which stiffness-value do I take for...
  18. VibFrank

    Interaction frequencies of rotor and stator

    ...of centrifugal pumps" of U. Bolleter in "Vibrations", Vol. 4, No. 3, 1988. In his example of m=2 (fig. 6) he says, that the pattern rotates with p2*n/2. I see only p2*n ! In his conclusion on page 10 he writes, that for m=2, no radial forces are expected. But if I use z2=5 and z3=7, I have a...
  19. VibFrank

    Stress Classification

    Hy, I just want to learn something about peak stress, primary stress, primary bending stress, secondary stress etc... and I read an article from W.C. Kroenke "Classification of finite element stress according to asme section III stress categories" (It seems to be an older article and it is a...
  20. VibFrank

    Stiffness of gaps in rotordynamics

    Hy, thanks for your answer. I still have problems to understand: 1.) Where is the difference between Black, Fritz ... with decentrating forces and on the other side the journal bearing theory with centrating forces ? If I have a gap that isn't defined as journal bearing, which theory could be...

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