Function
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Group Damping is used to assign different damping ratios, which results from time history analysis, to element and boundary groups.
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When the materials, vibration control devices or vibration isolators in a structure have different damping ratios, elements with different damping ratios can be assigned to different Element Groups.
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It is common to assign structural members such as beams and columns to a Structural Group and assign boundary conditions (including structures assigned with vibration isolators or vibration control devices) to a Boundary Group in order to define different damping ratios.
Call
From the main menu Select [Properties] tab > [Damping] group > [Group Damping] > [Element Mass Stiffness Proportional]
Input
Group Damping : Element Mass & Stiffness Proportional dialog box
Default Values for Unspecified Elements and Boundaries
Sets the damping ratio to be applied to areas not specified as attenuation by group or material.
Damping Type
Apply the default damping ratio to the elements and boundaries to which damping ratios are not assigned by groups or materials.
Direct Specification : Enter the proportional coefficients for the Damping Types checked on.
Calculate from Modal Damping : The proportional coefficients are automatically determined from the modal damping ratios specified in the ’r;Coefficients Calculation’.
Coefficient Calculation
Depending on the checked Type of Proportional Damping, one or two damping ratios can be defined. If it is proportional to either mass or stiffness, one modal damping coefficient can be defined, and if it is proportional to both, two modal damping coefficients can be defined.
Frequency [Hz] : Specify modal frequencies for which the damping ratios will be defined, which will be used to calculate the proportional coefficients.
Period [sec] : Specify modal periods for which the damping ratios will be defined, which will be used to calculate the proportional coefficients.
Damping Ratio (0.00~1.00) : Specify the damping ratios corresponding to the specified Frequencies or Periods.
When the default damping ratio is set up, there is no need to apply frequencies/periods by groups or materials.
Specified Elements And Boundaries
Enter the damping ratio by materials or groups.
Type
Material : Enter the damping ratio by materials. The damping ratio will be applied to the elements assigned with the Material Data.
Structure : Enter the damping ratio by element groups.
Boundary : Enter the damping ratio by boundary groups. This option is applicable to Elastic Link, General Link and Point Spring boundary conditions.
Name of Material / Group
1. Material : Select the name of the Material Data.
2. Select a group name, which was defined in Model>Group>Structural Group or Boundary Group.
Coefficient Calculation
Depending on the checked Type of Proportional Damping, mass or stiffness modal damping coefficients can be defined. If it is proportional to either mass or stiffness, one modal damping coefficient can be defined, and if it is proportional to both, two modal damping coefficients can be defined.
Damping Type
Choose whether the attenuation matrix is Mass Professional or Stiffness Professional.
Direct Specification : Enter the proportional coefficients for the Damping Types checked on.
Calculate from Modal Damping : The proportional coefficients are automatically determined from the modal damping ratios specified in the ’Coefficients Calculation’.
Frequency / Period
Specify modal frequencies/periods for which the damping ratios will be defined, which will be used to calculate the proportional coefficients. Mass coefficient (alpha) and stiffness coefficient (beta) will be calculated automatically.
Frequency [Hz]: Enter the frequency of the mode in which you want to specify the attenuation ratio for the calculation of the proportional coefficient.
Period [sec]: Enter the period of the mode in which you want to specify the attenuation ratio for the calculation of the proportional coefficient.
Set Default Data: Set the default frequencies/periods for the Unspecified Elements and Boundaries.
Damping Ratio
Define the damping ratio.
Use Material Data : Use the damping ratio defined in the Material Data.
Direct Define : Directly define the damping ratio (It will be disabled when Type>Material>All Material Data is selected).
Damping Coefficient for Specified Elements and Boundaries
Damping Coefficients defined by Groups or Material Data
Priority of Damping Ratio dialog
Priority of Damping Ratio
Selects the priority when more than one attenuation is set to duplicate for an element.
Priority between Material Data and Structure Group
When multi damping ratios from Material Data and Structure Group are assigned to one element, select the option to apply.
Material Data : Apply the damping ratio defined in the Material Data to the analysis.
Structure Group : Apply the damping ratio defined by Structure Group to the analysis.
Priority between Structure Groups
Selects the priority when attenuation of two or more Structure Groups is set to duplicate for one element.
Smallest Damping Ratio : Apply the small damping ratio.
Largest Damping Ratio : Apply the large damping ratio.
When Element Mass & Stiffness Proportional damping type is selected, only Lanczos method will be supported for the Eigenvalue analysis.