AIR COMPRESSOR FOUNDATION     OXYGEN COMPRESSOR FOUNDATION       Total of these installations analyzed and designed so far: (including concrete construction drawings) 1981 - Elevated table top Sulzer Oxygen Compressor Barstow, CA. 1981 - Elevated table top Sulzer Air Compressor near Barstow, CA. 1988 - Elevated table top Sulzer Oxygen Compressor Cominco, Trail, BC. 1988 - Elevated table top Sulzer Air Compressor for Cominco, Trail, BC. 1997 - Demag Delaval Oxygen Compressor USX at Braddock, PA. 1997 - Demag Delaval Air Compressor for USX at Braddock, PA. 1999 - Demag Delaval Oxygen Compressor Coffeyville, KS. 1999 - Demag Delaval Air Compressor near Coffeyville, KS. 70 hours required for Static & Dynamic Analysis 60 hours required for drafting Foundation Dwg's   REFERENCES - above shown Oxygen Compressor near Coffeyville, KS. Demag Delaval dwg. PJ50040B sht. 1-3 BOC log 7760-414425-CP-14/53-42A, 58, 59 Demag Delaval foundation loading diag. sht 1-5 BOC log 7760-414425-CP-14/53-53 Synchronous motor outline drawing - - - - - - - - - -BOC log 7760-414425-CP-14/53-4F KOP-Flex coupling (shaft) - BOC log 7760-414425-CP-14/53-98 Motor rotor detail - BOC log 7760-414425-CP-14/53-43   Above 6-column structure is standing on a 4ft thick concrete mat supported by end bearing piles. The computer model consists of ANSYS Rev 5.2 SOLID45 & BEAM4 & PIPE16 elements as shown. The BEAM4 elements are used for modeling the compressor & motor axis with bull-gear, motor rotor, and for making a rigid connection to the concrete structure. The coupling is hollow and is therefore modeled with the PIPE16 element. Unbalance forces are applied at joint 3207 (bull-gear), joint 3211 (motor), joint 3225 (1st/2nd stage rotor) & joint 3223 (3rd/4th stage rotor) & joint 3231 (5th/6th stage rotor). For computation of these forces see sheet-5. For additional comments see computer input file in this package (sheet-7).         The picture to the left is a simplified representation of the shaft of any of the rotating components of the compressor (including motor) for which unbalance forces need  to be considered (65-steps/cycle). The main shaft with bull-gear and motor rotor turn at  an operating speed of 1792 rpm which is the same as 29.866 cps. One could also say that the time it takes for the shaft to make a full 360 deg. turn or one revolution is 0.03348 seconds. For the concrete frames supporting compressor and motor to experience the unbalance forces computed on sheet-5 the following needs to be considered for the mathematical model: The computed unbalance force must be applied at the center of gravity of the rotating component under consideration. These unbalance forces must also be applied so as to be acting in a plane perpendicular to the rotating axis of the shaft. Forces must point into the direction which is consistent with the time-step sequence. Each time-step is measured in degrees and fractions of a second (time). The time-steps chosen for this installation correspond to an angle of 5.53846 deg and have a duration of (5.5385/360)*0.03348 = 0.00051511 seconds. For each time-step the applied force generates a response (or reaction) of the structure the character of which depends on the magnitude and direction of the applied force and the stiffness & inertia of the structure along with the effect of damping. A sufficient number of time-step responses must be computed so that after several revolutions the displacement amplitudes remain more or less constant cycle after cycle. In order to implement all of this a time-history dynamic analysis needs to be performed. The radial unbalance forces need to be resolved into vertical & horizontal components and then assigned to the relevant time interval. Instead of computing these components one could also specify the phase angle - either way - the input of these forces becomes very tedious when dealing with 100 (or more) time-steps, so that it will be expedient to take advantage of the ANSYS parametric design language which is similar to FORTRAN. Please note that the 1st/2nd & 3rd/4th & 5th/6th stage rotor operating speeds are not the same as the operating speed of bull-gear & motor. The corresponding time-step (alpha)-angles are assigned to the parameters ARG6, ARG8, AR10 & AR12 - see statements near the end of the input file (sheet-13). Range of natural frequencies (eigenvalues) chosen so that the frequency band is widened by 10 cyc/sec beyond the upper & lower operating speeds of the rotating machinery parts. The required minimum rang would be from 30 -10 = 20  cyc/sec based on the 30 cyc/sec operating speed of bull-gear and motor rotor (the lowest natural frequency for the foundation arrangement is 27.089 cyc/sec according to the modal analysis ) and up to  486 +10 = 496 cyc/sec for the 1st/2nd stage rotor. This would take care of the interfering frequencies as stated on the DEMAG foundation loading diagram sheets. The actual frequency range chosen goes from 27.089 (1625.rpm) to 638 cyc/sec (38280.rpm) as can be seen from the computer generated values (modes 1-99). On the following 6-sheets the displacement response is plotted showing the amplitudes based on the dynamic forces from sheet-5. These displacement amplitudes determine if the structure is acceptable or not depending on if a certain limiting value is exceeded or not. Readings were taken at joint 3207 for the  bull-gear bearing and at joint 3211 for the front motor bearing and at joint-3225 for the 1st/2nd stage rotor. Limiting displacement for bearing of rotating parts at speed of 1800.rpm is 0.00115 in.  For rotor speeds above 10000.rpm there are no relevant guides, also, the unbalance energy of these small rotors would  not be sufficient to excite such higher level modes of the structure. Maximum horizontal displacement for bull-gear and motor rotor = 0.00060 < 0.00115 in (sheet-17) OK. The compressor rotors all undergo the same basic vibrational displacement as the bull-gear despite their extremely high rotational speeds which exceed 20000.rpm. All amplitudes are within the allowable limits.     Additional links for this web site:   [Sample Calculation] [Compressor Foundation Dynamics] [Large Deflection Plate Panel] [Sample Structure] [Pressure Vessel] [Reference Letter] [Resume] [Efficiency Drawings Calculations] [Home]   accuracy air analysis assembled ansys applications autocad boxes cold compressor computer concentration consultant creep cryogenic cylindrical deflection design details diagonals dynamics efficiency efficient element elevated enercalc engineering excellent execution field finite foundation gtstrudl highly insulation job large licenses mat members membrane mesh mobilized models performance perlite piles pipe plants plates pressure professional real reinforcing seismic separation services silo shrinkage skids speed staad stainless steel storage stresses Strucalc structural tanks tension theory timber time toronto university without zones