Common Properties: Damping

Description

Damping properties commonly found in beam, plate and brick property sets.

Properties

Damping Ratio (NFA)

This is used only by the Natural Frequency Solver to compute an effective modal damping ratio for each mode. These modal damping ratios can then be used in the mode superposition dynamic analysis solvers such as Harmonic Response Analysis and Spectral Response Analysis.

In the case where every property in a model contains the same Damping Ratio (NFA) value, the calculated modal damping ratio will be that same value, and the same for every calculated natural frequency mode. But in the case where different properties in a model have different Damping Ratio (NFA) values, the calculated modal damping ratio will be a different value that depends on the modal displacement contribution of each property in the model, for each mode.

The Damping Ratio (NFA) value has no effect on the results of the natural frequency solution itself. The computed natural frequency modes are always undamped.

Dimensionless.

Viscous Damping

Coefficient of viscous damping as a volume density. The value is used to produce a damping matrix, similar to a mass matrix, for an element. This is used in the Linear Transient Dynamic and Nonlinear Transient Dynamic solvers.

Units are (Force×Time/Length)/Volume (e.g., (N.s/m)/m³, (lbf.s/in)/in³).

Rayleigh Damping

Method by which Rayleigh damping factors (a, b) are specified. These are used to construct the Rayleigh damping element matrix, which is used in the Linear Transient Dynamic and Nonlinear Transient Dynamic solvers.

Frequencies

Damping factors are calculated from two specified damping ratios occurring at the corresponding frequencies.
Alpha, Beta

Damping factors are specified directly.

Edit Graphically

Opens the Rayleigh Damping dialog, which allows for the editing and visual inspection of the damping ratios over a frequency range.

See SOLVERS Home: Rayleigh Damping.

Frequency 1 / 2

Two frequencies used to specify the Rayleigh damping factors.

Applicable only when Frequencies is selected under Rayleigh Damping.

Units are Hz.

Damping Ratio 1 / 2

Two damping ratios used to specify the Rayleigh damping factors.

Applicable only when Frequencies is selected for Rayleigh Damping.

Dimensionless.

Alpha / Beta

Rayleigh damping factors.

Applicable only when Alpha, Beta is selected for Rayleigh Damping.

Units are 1/s and s, respectively.