Mitigation of undesirable vibrations during operation of rotating machines is unthinkable without the detailed assessment of their vibrational characteristics. For tasks solved in this field is characteristic a close cooperation with the manufacturer in the design stage and also numerous modifications of the initial design based on analyses results.


Fig.1 Calculation model, electromotor, two stage compressor and auxiliary systems on common frame

The basis of our offer in this field is torsional and lateral vibration analyses of rotating machines. Methodology of analyses is based on the most common set of standards API. For complexity are important our additional services as well: strength analyses of frame including anchoring to basement, assessment of resistance to seismic and environmental loading and also elaboration of drawing documentation of parts and connected systems.


Fig.2 Calculation model, detail of fan on frame

Torsional Vibration Analysis

The result of operation of rotating machines near the torsional eigenfrequencies is usually fatigue of shafts, coupling or gearboxes. The critical hazard of torsional vibration, in contrast to lateral vibrations, that common sensors don’t indicating operation in resonance frequencies.


Fig.3   Significant torsional eigenfrequencies of rotor

By the torsional vibration analysis (TVA) are typically determined torsional eigenfrequencies in relation to the potential excitation frequencies (derived from the shaft rotational speed). The result is the Campbell diagram, which is used for design of the parts of rotor system (usually couplings). In case of complicated rotating machines, if elimination of operation in resonance regions is not possible, it is necessary to confirm suitability of the design by fatigue calculation. Except continuous operation response of system to excitation by transient regimes is analysed as well (start-up, short circuit, etc.). Critical cross-sections are assessed usually for static strength and/or fatigue.


Fig.4   Analysis of potential resonance regions, Campbell diagram


Fig.5   Response torque in coupling, excitation from 3 phase short circuit of electromotor

Lateral Vibration Analysis

Aim of lateral vibration analysis (LVA) is comprehensive assessment of vibration resistance of rotating machines. Calculations are primary focused on calculation of critical shaft speeds in relation to the operating speeds and on elimination of potential operation in resonance regions.

Analyses taking into account imbalances are focused on vibration transfer from the rotor system to frame, constructions, auxiliary and connected systems. Based on results vibrations risk mitigation is possible (suitable frame design and support, changes in stiffness and damping of connected systems).


Fig.6   Amplitude - frequency characteristic of rotating machine vibrations from unbalances

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