Occurs at frequencies other than the running speed. Sub-synchronous vibrations (less than 1X) are highly dangerous because they often signal fluid-film instabilities or aerodynamic swirl, which can cause self-excited, runaway vibrations. 2. Key Components Affecting Rotor Behavior
Rotors experience resonance when their rotational speed matches a natural frequency. Analysis seeks to ensure these speeds are well outside the operating range. Instability Mechanisms:
The compressor rotor model was updated using FEA to simulate alternative seal architectures. The OEM replaced the labyrinth balance piston seal with a hole-pattern swirl-brake damper seal. This modification reduced the circumferential fluid velocity, shifted the log decrement from -0.12 to +0.35, and successfully stabilized the machine across its entire operational envelope.
A Campbell diagram plots the system's natural frequencies against its rotational speed. Critical speeds occur where the "order lines" (multiples of running speed) intersect these frequency curves. Whirling Modes: These are dominant deformation patterns that split into (rotating with the rotor) and (rotating against it) modes due to gyroscopic effects. Stability Analysis: This identifies self-excited vibrations like turbomachinery rotordynamics with case studies pdf
The cylindrical journal bearings were retrofitted with tilt-pad journal bearings . Tilt-pad bearings inherently eliminate cross-coupled stiffness (
A 45-foot vertical pump used for mixing nuclear waste exhibited high-vibration "whirl" problems. Rotordynamic modeling of the segmented shaft system allowed engineers to identify specific coupling and support stiffness issues, correcting the vibration without decommissioning the unit. Liquid Whirl in Labyrinth Seals:
: Polymer build-up caused imbalances that, at critical speed, led to severe vibration and "wrecks" . Occurs at frequencies other than the running speed
Instability occurs when the forces generated within the machine feed energy into a vibration mode rather than dissipating it. Oil Whirl and Oil Whip
The oil whip phenomenon was completely eliminated, and the turbine resumed reliable, vibration-free operation across its entire speed envelope.
Case Study 1: Subsynchronous Vibration in a High-Pressure Centrifugal Compressor The OEM replaced the labyrinth balance piston seal
Mastering Turbomachinery Rotordynamics: Key Concepts & Lessons from Real-World Case Studies (PDF Guide Inside)
Secondary fractional vibrations were eradicated, and total machine life expectancy doubled. Predictive Maintenance, Diagnostics, and Troubleshooting
When the operational speed equals a critical speed, any inherent unbalance excites the system, leading to high-amplitude vibrations.