Torsional Analysis
A torsional study evaluates crankshaft, coupling, and gears to ensure torsional vibration is acceptable.
MODEL DESCRIPTION
A cross-section of the model train developed by Engineered Solutions Group is shown above in first graphic. Geometry was defined by drawings and data sheets supplied by the client. The model was generated and analyzed using the DyRoBeS finite element rotor dynamics program and consisted of 3 shafts with 45 elements and 69 sub-elements. A description of the DyRoBeS Software is included at the end of the report. The model was developed using general procedures outlined in references [1] and [1].
ESG vibration experts use our field-proven proprietary simulation software to:
- Conduct a modal analysis of the mass elastic model to determine Torsional Natural Frequencies (TNFs),
- Assess the torque effort curves for all key operating conditions,
- Perform a forced response analysis to accurately predict torsional vibration and stress, and
- Recommend solutions to ensure a safe torsional system.
Unique features offered exclusively by ESG to ensure a more reliable system include:
- Analysis with DYROBES tool yields advanced analytics and design sensitivity.
- Torsional Vibration Analysis integrated with the Pulsation and Mechanical Vibration Analysis ensures superior study results.
- Determination of risks due to lateral frame forces caused by torsional responses in reciprocating compressors and integration with ESG Mechanical Vibration Analysis results in lower probability of vibration.
BACKGROUND
Excessive torsional vibration and resonance leads to damaged crankshafts, couplings, gears, auxiliary equipment, and more. Examples of damaged couplings and shafts are shown below. Repair costs to such equipment can easily exceed $1,000,000 in parts, labor, and downtime.
Over 80% of all torsional systems we analyze require system modification during the design stage to reduce the risk of failures.
Torsional vibration will vary depending on the system’s characteristics and the specific operating conditions (torque effort curve). Any changes to these factors can result in excessive torsional vibration.
APPLICATIONS AND TIPS
The drive trains in the following applications require a Torsional Vibration Analysis:
- Reciprocating Gas Compressors
- Screw Compressors
- Plunger and Centrifugal Pumps
- Centrifugal compressors
- Engine/Generator Sets
TIPS FOR IMPROVED TORSIONAL SYSTEM DESIGN
A TVA should be performed for:
- Any new combination of driver/driven equipment
- Any change in compressor configuration (different cylinders) or significant changes in operating conditions (pressures, cylinder loading)
- Different motor (same frame rarely means same rotor inside)
- Drive trains experiencing failures
- VFD applications
- Sensitive and critical systems
Note: ESG recommends a field assessment to confirm torsional vibration and dynamic stresses.
SCOPE
The following scope is standard in ESG’s torsional studies. The scope is compliant to API requirements, including but not limited to 610, 613, 618, 671, and 684.
Performance Assessment:
- Assess the overall operating envelope to accurately determine the worst case conditions.
- Include upset and startup cases if applicable.
Modal Analysis:
- Generate the mass elastic model for the entire drive train.
- Calculate the torsional natural frequencies and mode shapes
Forced Response Analysis:
- Calculate the vibratory torque acting on the system
- Perform the forced response analysis to assess torsional vibration and dynamic stress amplitudes
Torsional to Lateral Excitation (Reciprocating Compressors):
- Calculate the lateral frame forces induced by the torsional vibration of the crankshaft
- Assess the risk based on magnitude of lateral forces
- Coordinate with ESG Vibration Analysis to avoid mechanical resonance
Motor Electromagnetic Effects:
- Calculate the stiffness and damping across the motor air gap
- Include the effect on torsional natural frequencies and forced responses
Data Visualization and Quality Checks:
- ME Scope software tools are used to assess the system and compare alternatives and can visualize results across hundreds of operating conditions
- Technical review performed to ensure validity of model and inputs
ESG ADVANTAGES
- Comprehensive evaluation of the entire range of operating conditions plus upset conditions – not just the assumed “worst case.” This improves system reliability and avoids the chance of design errors.
- ESG’s tolerance band analysis improves accuracy and minimizes risk. This technology evaluates the risk and design impact due to the tolerances of key input parameters. ESG’s approach reduces the risk of failures and avoids unnecessarily expensive torsional solutions.
- ESG has an extensive database of engine, motor, compressor and coupling information – resulting in faster and more accurate analysis.
- Our system approach focuses on the entire package including engine, driver, coupling, etc. This approach is more comprehensive and accurate compared to services that focus primarily on the engine (or compressor).
- Full service which includes integrated design of torsional, pulsation, and mechanical systems. This enables effective solutions to torsional/lateral excitation, coordination between pulsation changes, and torsional impacts.
- Technical review for improved quality control. Industry leading technical experts are involved on your project to avoid problems or errors.
- Dedicated torsional support team that can provide fast, efficient, and high-quality designs.
Field engineers can support you to provide onsite testing and verification of torsional vibration & stress.