Damping Options

The tables below describe the input data required to define modal damping for a harmonic response step or modal dynamic step.

For convenience you can specify constant global damping factors for all selected eigenmodes for mass and stiffness-proportional viscous factors, as well as stiffness-proportional structural damping.

You provide modal damping values at specific frequencies. The damping coefficient is automatically interpolated for a mode linearly between the specified frequencies. The damping coefficients are assumed to be constant outside the range of specified frequencies.

This page discusses:

See Also
Applying Damping
In Other Guides
Entering Tabular Data

General Options

Global mass proportional dampingαglobal factor used to apply Rayleigh mass proportional damping to the entire model. (Units of time-1.)
Global stiffness proportional dampingβglobal factor used to apply Rayleigh stiffness proportional damping to the entire model. (Units of time.)
Global structural dampingsglobal factor used to apply frequency-independent stiffness-proportional structural damping to the entire model.
Damping type

Fraction: Specify the fraction of critical damping for a particular frequency range.

Rayleigh: A general damping technique that provides a convenient way to damp lower (mass-dependent) and higher (stiffness-dependent) frequency range behavior.

Structural: Define damping that is proportional to the internal forces but opposite in direction to the velocity.

Fraction Damping Data Table

FrequencyFrequency value in cycles/time.
Damping fractionFraction of critical damping.

Rayleigh Damping Data Table

FrequencyFrequency value in cycles/time.
Mass proportional damping

Mass proportional Rayleigh damping factor, αM.

Stiffness proportional damping

Stiffness proportional Rayleigh damping factor, βM.

Structural Damping Data Table

FrequencyFrequency value in cycles/time.
Damping factor

Damping factor, s, that multiplies the internal forces.