Beginning with an understanding of the laws of motion, the torsional dynamics of any drivetrain can be analyzed during the equipment design stage to avoid the occurrence of adverse conditions. For equipment which is already installed, modern torque measurement systems can be utilized to verify theoretical models, evaluate changes to drivetrains components, or continuously monitor torque for effective defect identification. The integration of angular, radial, and axial vibrations can provide a comprehensive condition-based monitoring system for critical assets susceptible to these failures modes in numerous industries.


What is


distributed throughout the drivetrain. Drivers such as reciprocating engines and VFD-controlled motors; and driven equipment such as mills, large fans, reciprocating compressors, generators, and various turbomachinery can be susceptible to torsional vibration problems.


Depending on the source, torsional vibration can be present in different forms. Sudden impacting (an example shown in figure 1a) from intermittent loading, equipment start-up, or process upsets can produce vibrations that consist of a sharp peak followed by subsequent oscillations that eventually dampen out. Alternatively, torsional vibrations can be present in a more continuous nature as the result of constant process conditions, motor control fluctuations, or resonant conditions as shown in figure 1b.


torsional vibration?


Torsional vibration describes the angular movement of a shaft(s) in a drivetrain, which is superimposed on the steady-state rotational movement of a rotating or reciprocating machine. More simply, torsional vibration refers to the angular or ‘twisting’ movement of the rotating shafts that connect the various pieces of equipment in a drivetrain. This form of vibration can be induced by the driving equipment, the driven equipment, or simply be the result of how the various inertias (rotating masses) and spring stiffness are


As with any type of vibration, a resonant condition will exist when an excitation frequency is in close proximity to a natural frequency. Generally, torsional resonance is more prevalent in higher-speed (> 600 RPM) applications. An example of torsional resonance during the start-up and coast-down of a motor driven centrifugal compressor train is shown in Figure 1c. In this case the first torsional natural frequency was excited by the rotational speed, creating oscillating torques at a frequency of 16 Hz. These torque measurements can be used to identify potentially harmful operating conditions that need to be avoided.


Figures 1a-c: Torque-time waveforms resulting from various conditions such as impacting (a, top left), continuous oscillations from process conditions (b, top right) and resonant conditions which occurring intermittently during start-up and shut-down (c, bottom).


THE REPORT | SEP 2024 | ISSUE 109 | 63


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