Group Damping: Element Mass & Stiffness Proportional

Group Damping is used to assign different damping ratios resulting from time history analysis to different element and boundary

 groups.

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.

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.

From the Main Menu select Model > Properties > Group Damping: Element Mass & Stiffness Proportional

Select Geometry > Properties > Group Damping: Element Mass & Stiffness Proportional in the Menu tab of the Tree Menu.

Group Damping : Element Mass & Stiffness Proportional dialog box

Revision of Gen 2011

Default Value for Unspecified Elements and Boundaries

Apply the default damping ratio to the elements and boundaries to which damping ratios are not assigned by groups or materials.

Damping Type

Check whether or not the damping matrix type is proportional to mass and/or stiffness.

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’.

Coefficients 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 : Specify the damping ratios corresponding to the specified Frequencies or Periods.

Note

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.

Coefficients 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.

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.

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 Coefficients for Specified Elements and Boundaries

 Damping Coefficients defined by Groups or Material Data

Priority of Damping Damping Ratio

Priority Damping Ratio dialog box

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

Small Value : Apply the small damping ratio.

Large Value : Apply the large damping ratio.

Note

When Element Mass & Stiffness Proportional damping type is selected, only Lanczos method will be supported for the Eigenvalue analysis.