TORSION V6: Torsional Vibration Analysis Package

The torsional vibration package uses a finite-element based formulation for performing damped and undamped torsional natural frequencies, mode shapes, stability, steady-state response, and time-transient response of mechanical drive trains. TORSION consists of three sub-modules: TORNAT, TORHRM and TORRSP integrated by TORSION's user interface. The user interface controls the sub-modules to provide a complete torsional vibration analysis environment. Click here for our complete brochure.

The release of RBTS’ ARMD Version 6 Torsion is a major milestone in the product’s development history, rolling out a completely new and improved graphical user interface for the package with enhanced numerical capabilities and features. The software’s front end was redesigned with our customers’ and industry’s input to incorporate the most logical, efficient, and productive techniques to model and analyze complex multi-shaft systems for torsional vibrations.

ARMD TORSION users will immediately see the improvements as element, shaft, and system data are presented in a flatter format, with key fields and analysis options readily visible and accessible from the main data entry screens. Engineering productivity to design models is vastly improved as shafts and systems can be easily imported from user-generated component template models. Furthermore, the ability to simultaneously run multiple instances of the program permits rapid side-by-side comparison of results.

By identifying new trends from industry standards, along with RBTS’ involvement in turbomachinery standards revisions, new technical features were added to the software. Addition of equivalent torsional stiffness diameters, better handling of shaft connections, expanded user-defined torques application, and access to temperature dependent properties all combine to provide more accurate modeling and matching of analysis results to actual system empirical results. 

TORSION accepts/imports models generated with the ROTLAT rotor dynamics package and has advanced modeling features and capabilities including the modeling of multi-shaft/multi-branch systems, coupling stiffness and damping, gear tooth flexibility, stiffness/mass/inertia diameter, torsional springs to ground, various types of external excitations, synchronous motor start-up torque, compressor load torque, user specified time varying torques, electrical faults for motor and generator, and many others.

Among the features incorporated in TORSION package are electrically-induced, time-varying exciting torques associated with generator and induction motor operation that include:


  • 3-phase short circuit
  • Line-to-line short circuit
  • False coupling short circuit

Induction Motor

  • Start from standstill
  • 3-phase short circuit at terminals
  • 2-phase short circuit at terminals
  • High-speed automatic reclosing

TORSION results include:


  • Damped and undamped
  • Growth factors and damping ratios
  • Vibration mode shapes
  • Critical speed map (Campbell Diagrams)


  • Vibratory amplitudes (displacement, velocity and acceleration)
  • Dynamic torques
  • Dynamic stresses
  • Dynamic heat dissipation


  • Dynamic shaft-torque time-history
  • Dynamic stresses
  • Fatigue life

Real-time graphics updates of the 2-D image corresponding to numeric data input in data grids provides visual confirmation of model correctness while building system models. 2-D Model auto resizing gives users the option to “fit-to-page” complete models or single branches. Users can automatically view the model with the correct aspect ratio, thereby permitting rapid, visual model review. 

Built-in graphics utilities permits customization of graphics output of all outputs including steady-state and time-transient results as shown. This includes legends, notations, horizontal and vertical markers, fonts, symbols, colors, etc. Graphics are easily exported to other applications for presentation and reporting purposes.