Torsional Analysis

A torsional analysis is required to provide a properly engineered system to the end user free of any possible torsional concerns. Ariel does not conduct torsional analyses. The Packager or a third party conducts the analysis for all unproven drive components, such as:

• Electric motors with rotor shafts smaller than the compressor crankshaft drive stub diameter.

• Steam or gas turbines.

• Gearboxes.

• Engines or motors not previously coupled to a specific compressor frame.

• High torque reversals.

• Variable speed electric motor drives.

Contact Ariel Application Engineering for unit specific information or a list of possible engineering firms that can perform the analysis, but there is no restriction to only these companies. A torsional analysis should include: 1. A comprehensive report, including an executive summary, introduction and purpose, analysis

limitations, reference documents, computation results, discussion, conclusions, and appendices

(tables, figures, and other data).

2. A complete dynamic model of the electric motor shaft, coupling, and compressor formulated in

terms of lumped inertia and massless springs based on normal engineering practice and judgement

to determine motor shaft flexibility from manufacturer supplied information - all included in a

report appendix. Data should also include computed significant natural frequencies of torsional

vibration, along with their modal deflected shapes and a speed-frequency interference diagram.

3. Governing torque-effort curves identified from expected compression service and rank-ordered

for excitation potential with each curve harmonic content specified in terms of Fourier Coefficients.

Consider high volume clearance devices and single acting cylinder operation when analyzing

torsional responses. Single acting cylinders can present a worst case scenario due to a

more dynamic torque effort curve.

4. A written assessment of natural frequency placements acceptability relative to their excitation

potentials.

5. If required, a forced, damped dynamic model assembly that includes estimates of damping at

various locations in the motor and compressor.

6. The dynamic model with appropriate excitations of all governing torque curves applied.

7. Dynamic deflections, torques, and shear stresses determined for the entire dynamic model.

8. An industry-recognized fatigue analysis of Ariel's compressor crankshaft utilizing a modified

Goodman Diagram.

9. An industry-recognized fatigue analysis of the major portion of the electric motor shaft utilizing a

modified Goodman Diagram.

10. An auxiliary equipment check for sensitivity to the anticipated torsional activity.

11. An on-site torsional vibration measurement at equipment start up to confirm the analysis.