ODS ANALYSIS BY SALAH KHAIRY.

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ODS ANALYSIS BY SALAH KHAIRY.

  1. 1.  ODS stands for operating deflection shape.  ODS analysis generates a computer model of your machinery that depicts its motion while running at operating speed & load. You literally “see” how your machine is moving as it operates. This modeling can be extremely useful to illuminate an otherwise elusive solution to machinery vibration problems.  First, a CAD model of the machine or mechanical system is created (structure file).  Second, detailed & meticulous vibration measurements are made on the machine typically during normal operation. These measurements consist of both the amplitude & phase of vibration at one or multiple frequencies of interest all referenced to a common point.  Finally, these field measurements are imposed on the model to generate visible animations of the model/machine at the distinct vibration frequencies of interest (typically the “offending frequencies”).
  2. 2.  When standard vibration analysis techniques have failed to determine the exact problem.  When resonance is suspected.  An ODS or Modal job begins best with a determination of the “offending frequencies of vibration” usually made using standard, route vibration spectra
  3. 3.  The Le Tourneau Crane should operate at max running speed 0.025 CPS or 1.5 Rpm, it is observed high vibration levels during operation (jerking) and structure looseness problem which has destructive effect on the long run operation.  Vibration measurement and ODS analysis were carried out by in order to detect the main source of that high vibration, also in order to shows the crane motion while operating & the crane deflection shape due to that vibration.  The crane rotates by large swing gear with 82 teeth which showed by the black arrow in the next image & driven by pinion gear connected to the gear box  The whole structure shows high vibration levels 42 mm/s rms on the column, swing table & Control room base.
  4. 4.  The Machine exhibits unacceptable vibration levels.  The main vibration at the machine bearings spectra is at the high amplitude gear meshing frequency 2 Hz or (82 X) which indicates gear eccentricity and/or improper backlash problem.  Bump test was carried out to the structure and it is found that the column natural frequency is matching the gear meshing frequency which causing resonance in the structure.  It is recommended to make ODS analysis to locate the max deviation point, as the problem should be solved either by adjusting gear backlash and adding stiffen supports to the crane base.
  5. 5. Gear Meshing Frequency
  6. 6. Point Location Amplitude Units Phase Angle Readings Ref. Point 15 mm/s 0.00° Point No.1 15 mm/s 230 Point No.2 7 mm/s 220 Point No.3 12 mm/s 240 Point No.4 11 mm/s 220 Point No.5 10 mm/s 210 Point No.6 4 mm/s 169 Point No.7 15 mm/s 160 Point No.8 14 mm/s 160 Point No.9 4 mm/s 240 Point No.10 12 mm/s 230 Point No.11 14 mm/s 220 Point No.12 2 mm/s 110 Point No.13 4 mm/s 130 Point No.14 5 mm/s 98 Point No.15 8 mm/s 140
  7. 7. Point No.16 12 mm/s 160 Point No.17 15 mm/s 230 Point No.18 16 mm/s 230 Point No.19 22 mm/s 230 Point No.20 23 mm/s 230 Point No.21 25 mm/s 230 Point No.22 12 mm/s 230 Point No.23 17 mm/s 230 Point No.24 18 mm/s 230 Point No.25 19 mm/s 230 Point No.26 20 mm/s 230 Point No.27 22 mm/s 240 Point No.28 15 mm/s 240 Point No.29 17 mm/s 240 Point No.30 18 mm/s 240
  8. 8.  It recommended that we should use 3rd party to check the swing gear teeth profiling and how much back lash between the pinion gear and swing gear.  In addition we should add stiffen supports to the column base at the same arrows locations in the pervious image.
  9. 9.  After gear teeth profiling checking we found that we got 19 mm back lash between the two gears so, we changed the pinion gear with different one ( same number of teeth but larger size)  Also after adding the stiffen supports to the column base the vibration levels shows significant decrease.

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