Torsional Vibrations, Pressure Pulsations, Package Modal Analysis
Torsional vibration analysis
Compression trains, in most of the cases, are designed for the specific project. They are assembled by combining separate machines: compressor, driver, couplings, flywheel, gearbox. Drivers can be of many different kinds: fixed or variable speed electric motor, reciprocating engine, steam or gas turbine. The process requires operation with variable conditions: suction and discharge pressure, capacity handled, speed etc. All these conditions generate different excitations to the train and one must avoid that any of the excitation harmonics goes into resonance with any of the natural frequencies which would cause the amplification of the torsional stresses to a dangerous level.
CST has developed CSTors which is a proprietary software that enables the company to make API compliant studies covering the entire range of operating conditions.
CST Torsional Vibration Analysis include:
Modal analysis with the equivalent shaft and excitations given by the customer
Modal analysis with the equivalent shaft determined by CST with a dedicated FEM Study
Forced response analysis to determine the amplification factors and the relevant dynamic stress amplitude; exciting torques can be supplied by client or calculated by CST by the proprietary software Reciperf
Coupling and flywheel selection and specification
Definition of any necessary limitation in the operating conditions
The availability of 3D Modeling and Simulation software allows CST engineers to asses the natural frequencies of the compression package including its behavior on the foundation system. This analysis is very helpful to design vibration free systems and to identify root cause of vibration problems and make on site corrective actions.
CST, by means of proprietary tools, has the capability to perform the acoustical analysis of the piping system and reservoirs associated to the reciprocating compressors with the aim to limit pressure pulsations and shaking forces. The computation capability is coupled for the purpose to the extended package design experience of its engineers which enables CST to find the most appropriate and economical solution of any pulsation and vibration problem both for new and existing units.
CST capability covers all Design Approaches of the API 618 5th edition.
Preliminary Dampener design
Designers of compressor packages always face up with pressure pulsations and shaking forces in process plant. A good start is an advantage to reach the best final result. CST has developed Damperf, a dedicated proprietary software that allows to get a correct damper design, minimizing the need to modify them after the acoustic study. This software can considers the most frequent compressor arrangements and load conditions (also with more machines acting in parallel). It evaluates the pulsations generated by each cylinder end on the basis of cylinder valve opening angle and crank phase of the various cylinder insisting on the same volume bottle.