Two-Way Radio User Manual

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MODAL DAMPING
13.10
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MODAL DAMPING: Specify damping for modal dynamic analysis.
This option is used to specify damping for mode-ba sed procedures. It is usually used in conjunction with
the
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SELECT EIGENMODES option for selecting eigenm odes for modal superposition. If the
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SELECT
EIGENMODES option is not used, all eigenmodes extracted in the prior
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FREQUENCYstepwillbeused
with the damping values specified under the
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MODAL DAMPING option. If the
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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 the ABAQUS Analysis User’s Manual
•
“Dynamic analysis procedures: overview,” Section 6.3.1 of the ABAQUS Analysis User’s Manual
Optional, mutually exclusive parameters:
MODAL
Set MODAL=DIRECT to select modal damping using the dam ping coefficients given in this option.
The data lines after the keyword line specify the modal damping values to be used in the analysis.
If the
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MODAL DAMPING option is used without parameters, MO DAL=D IRECT is assumed.
Set M ODA L=COMPOSITE to select composite m odal dam ping using the dam ping
coefficients that have been calculated in the
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FREQUENCY step (“Natural frequency extraction,”
Section 6.3.5 of the ABAQUS Analysis User’s Manual) from the material damping factors
given on the
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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 dam ping. The damping term for a particular mode is
defined as
,where and are factors defined on the first data line of the
option and
is the modal mass and is the modal stiffness for mode M.
STRUCTURAL
Include this param eter to select structural damping, which means that the damping is proportional
to the internal forces b ut opposite in direction to the velocity. This option can be used only with the
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STEADY STATE DYNAMICS (“Mode-based steady-state dynamic analysis,” Section 6.3.8 of the
ABAQUS Analysis User’s Manual) or
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RANDOM RESPONSE procedures (“Random response
13.10–1
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