*MODAL DAMPING
13.10 *MODAL DAMPING: Specify damping formodal dynamic analysis.
This option is used to specify damping for mode-based procedures. It is usually used in conjunction with
the *SELECT EIGENMODES option for selecting eigenmodes for mo dal superposition. If the *SELECT
EIGENMODES option is not used, all eigenmodes extracted in the prior *FREQUENCYstepwillbeused
with the damping values specified under the *MODAL DAMPING option. If the *MODAL DAMPING
option is not used, zero damping values are assumed.
Product: ABAQUS/Standard
Type: History data
Level: Step
References:
•“Material damping,” Section 20.1.1 of theABA QUS AnalysisUser ’sManual
•“Dynamic analysis procedures: overview,” Section 6.3.1of the ABAQUS Analysis User ’sManual
Optional, mutually exclusiveparameters:
MODAL
SetMODAL=DIRECT to select modal dam pingusing the damping coefficients given in this option.
The data lines after the keyword line specify the modal damping values t ob e used in the analysis.
If the *MODAL DAMPING option is used without parameters, MODAL=DIRECT is assumed.
Set MODAL=COMPOSITE to select composite modal damping using the damping
coefficients that have been calculatedin the *FREQUENCY step (“Natural frequency extraction,”
Section 6.3.5 of the ABAQUS Analysis User’s Manual) from the material damping factors
given on the *DAMPING material definition option (“Material damping,” Section 20.1.1 of
the ABAQUS Analysis User’s Manual). Composite modal damping can be used only with
DEFINITION=MODE NUMBERS.
RAYLEIGH
Include this parameter to select Rayleigh damping. The damping term for a particular mode is
defined as ,where and arefactors defined on the first data line of the
option and is the modal mass and is the modal stiffness for m ode M.
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. Th is option can be used only with the
*STEADYSTATEDYNAMICS (“Mode-based steady-state dynamic analysis,” Section 6.3.8 of the
ABAQUS Analysis User’s Manual) or *RANDOM RESPONSE procedures (“Random response
13.10–1
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