*SUBSTRUCTURE MODAL DAMPING

Specify damping for a substructure property.

This option is used to specify diagonal modal damping coefficients associated with the substructure eigenmodes. Substructure modal damping contributes to the substructure damping matrices at the substructure usage stage. This option is used in conjunction with the SUBSTRUCTURE PROPERTY option. If this option is omitted, the element set containing the substructures for which the properties are being defined will exclude modal damping.

This page discusses:

See Also
In Other Guides
Using Substructures
Generating Substructures

ProductsAbaqus/Standard

TypeModel data

LevelModel

Optional, mutually exclusive parameters (if no parameter is specified, Abaqus assumes that the modal damping coefficients are provided on the data lines)

STRUCTURAL

Include this parameter to select structural damping, which means that the damping is proportional to the internal forces but opposite in direction to the velocity.

This parameter can be used only with the STEADY STATE DYNAMICS, RANDOM RESPONSE, SIM-based MODAL DYNAMIC, or COMPLEX FREQUENCY procedures (see Mode-Based Steady-State Dynamic Analysis, Random Response Analysis, Transient Modal Dynamic Analysis, and Complex Eigenvalue Extraction).

The value of the damping coefficient, γ, that multiplies the internal forces is entered on the data line.

VISCOUS

Set VISCOUS=FRACTION OF CRITICAL DAMPING to select modal damping using the damping coefficients given in this option. The data lines specify the modal damping values to be used in the analysis.

Set VISCOUS=RAYLEIGH to indicate that the damping for a particular mode is defined as αM⁢mM+βM⁢kM, where αM and βM are coefficients defined on the first data line of the option and mM is the modal mass and kM is the modal stiffness for mode M.

Optional parameters

DEFINITION

Set DEFINITION=MODE NUMBERS (default) to indicate that the damping values are given for the specified mode numbers.

Set DEFINITION=FREQUENCY RANGE to indicate that the damping values are given for the specified frequency ranges. Frequency ranges can be discontinuous.

Data lines to define a fraction of critical damping by specifying mode numbers (if no parameters are specified or if VISCOUS=FRACTION OF CRITICAL DAMPING and DEFINITION=MODE NUMBERS)

First line

  1. Mode number of the lowest mode of a range.

  2. Mode number of the highest mode of a range. (If this entry is left blank, it is assumed to be the same as the previous entry so that values are being given for one mode only.)

  3. Fraction of critical damping, ξ.

Repeat this data line as often as necessary to define modal damping for different modes.

Data lines to define Rayleigh damping by specifying mode numbers (VISCOUS=RAYLEIGH and DEFINITION=MODE NUMBERS)

First line

  1. Mode number of the lowest mode of a range.

  2. Mode number of the highest mode of a range. (If this entry is left blank, it is assumed to be the same as the previous entry so that values are being given for one mode only.)

  3. Mass proportional damping, αM.

  4. Stiffness proportional damping, βM.

Repeat this data line as often as necessary to define modal damping for different modes.

Data lines to define structural damping by specifying mode numbers (STRUCTURAL and DEFINITION=MODE NUMBERS)

First line

  1. Mode number of the lowest mode of a range.

  2. Mode number of the highest mode of a range. (If this entry is left blank, it is assumed to be the same as the previous entry so that values are being given for one mode only.)

  3. Damping coefficient, γ.

Repeat this data line as often as necessary to define modal damping for different modes.

Data lines to define a fraction of critical damping by specifying frequency ranges (VISCOUS=FRACTION OF CRITICAL DAMPING and DEFINITION=FREQUENCY RANGE)

First line

  1. Frequency value (in cycles/time).

  2. Fraction of critical damping, ξ.

Repeat this data line as often as necessary to define modal damping for different frequencies. Abaqus interpolates linearly between frequencies and keeps the damping value constant and equal to the closest specified value outside the frequency range.

Data lines to define Rayleigh damping by specifying frequency ranges (VISCOUS=RAYLEIGH and DEFINITION=FREQUENCY RANGE)

First line

  1. Frequency value (in cycles/time).

  2. Mass proportional damping, αM.

  3. Stiffness proportional damping, βM.

Repeat this data line as often as necessary to define modal damping for different frequencies. Abaqus interpolates linearly between frequencies and keeps the damping value constant and equal to the closest specified value outside the frequency range.

Data lines to define structural damping by specifying frequency ranges (STRUCTURAL and DEFINITION=FREQUENCY RANGE)

First line

  1. Frequency value (in cycles/time).

  2. Damping coefficient, γ.

Repeat this data line as often as necessary to define modal damping for different frequencies. Abaqus interpolates linearly between frequencies and keeps the damping value constant and equal to the closest specified value outside the frequency range.