The properties of the Damping Controls category vary based on the type of analysis being performed. Using these properties, you can define the following types of system damping:
See the Damping section of the Mechanical APDLStructural Analysis Guide for more information.
Supported Analysis Types
The Damping category is available for the following analysis types:
Property Descriptions
Mechanical supports the following system-level damping properties.
- Eqv. Damping Ratio From Modal
This Damping Controls property is available for a Harmonic Response analysis when the Solution Method property is set to Mode Superposition (MSUP) and for a Transient Structural analysis linked to a Modal analysis. For these analyses, if the upstream Modal analysis Solver Type is undamped and you define the Damping Ratio in the Material Dependent Damping property grouping of Engineering Data, then this property can control the material-based Damping Ratio effect in your MSUP Harmonic and MSUP Transient solutions for all options of Expand Results From property. The options for this property include:
: The application includes the material-based Damping Ratio (MP,DMPR) effect in your MSUP Harmonic or MSUP Transient solution.
Important: For Reaction Force calculations, results differ when considering material-based Damping Ratio (MP,DMPR) when you have the Expand From property set to either or , compared to when you have it set to . This difference is a result of the way the element damping nodal loads are calculated.
Specifically, when you set the Expand From property to or , the solver considers the Material Damping Coefficient as a Constant Structural Damping Coefficient. If you refer to MAPDL Theory Reference, the element damping matrix of Equation 14-101 is calculated on Equation (14-39) for the setting and Equation 14-37 for setting.
When you set the Expand From property to the setting, the element damping matrix is obtained by combining the element damping nodal loads written to the mode file with coefficients obtained from Equation (14-42). Those results should be considered as the expected ones when any material-based Damping Ratio is defined.
No: The application does not include the material-based Damping Ratio (MP,DMPR) effect in your MSUP Harmonic or MSUP Transient solution.
Important: The application automatically sets this property to and it becomes read-only if you link a Harmonic Response analysis to a downstream Structural Optimization analysis or if the Future Analysis property (Analysis Settings > Analysis Data Management) is set to .
Note:If you define the Damping Ratio in the Material Dependent Damping property grouping, the application automatically sets this property to .
When you have a Mode Superposition Harmonic Response analysis that is linked to an upstream Modal analysis and you set the Damped property in the Modal analysis to , the application automatically hides the Eqv. Damping Ratio From Modal property in the harmonic system.
- Constant Damping
This property is available for Random Vibration analyses. The default setting is . You may also set the property to .
- Damping Define By
For a Harmonic Response analysis when the Solution Method property is set to Mode Superposition, this property enables you to specify damping using a Damping Ratio (default) or a Constant Structural Damping Coefficient. Based on your selection, an associated property of the same name displays. See the descriptions below.
Important: The application automatically makes this property read-only if you link a Harmonic Response analysis to a downstream Structural Optimization analysis or if the Future Analysis property (Analysis Settings > Analysis Data Management) is set to .
- Damping Ratio
This property specifies the amount of damping in the structure as a percentage of critical damping using the DMPRAT command. Note the following conditions:
If you set this property in conjunction with the Stiffness Coefficient and Mass Coefficient, the effects are cumulative.
For a Random Vibration analysis, this property defaults to 0.01 (1%). Set the Constant Damping property to to specify the value.
Note: The Engineering Data workspace also includes a Damping Ratio property that you can specify for a material. Mechanical supports material-based damping in addition to damping specified in the application. See the Material Dependent Damping Definition topic in the Define Engineering Data section for a listing of the analysis types, and their requirements, that support material-based damping.
- Constant Structural Damping Coefficient
This property specifies the amount of constant structural damping data using the DMPSTR command. The property is available for:
Mode Superposition-based Harmonic Response analyses.
Modal analysis when the:
Damped property is set to and the is set to either or .
Damped property is set to , the is set to , and the property is set to .
property is set to and the Solver Type is set to .
property is set to and the Solver Type is set to where the application specified the setting.
Note: If you parameterize the Constant Structural Damping Coefficient property using the option, based on the Solver Type selection, damping is added or removed during the design point solution.
If you set this in conjunction with the Stiffness Coefficient and Mass Coefficient, the effects are cumulative.
Note: The Engineering Data workspace also includes a Constant Structural Damping Coefficient property that you can specify for a material. Mechanical supports material-based damping in addition to damping specified in the application. See the Material Dependent Damping Definition topic in the Define Engineering Data section for a listing of the analysis types, and their requirements, that support material-based damping.
- Stiffness Coefficient Defined By
Define the Stiffness Coefficient by entering a value, , or by entering a Frequency and a Damping Ratio, .
- Stiffness Coefficient (Beta Damping, β)
A coefficient value that is used to define a Beta damping by multiplying it with stiffness. You can enter the value directly or the value can be computed from a damping ratio at a specified frequency. You define a Stiffness Coefficient in the Details view of the Analysis Settings object.
Beta Damping can also be specified in Engineering Data. Refer to the BETAD command section in the Mechanical APDL Command Reference for more information about the Beta Damping Factor.
Note: The unit for the Stiffness Coefficient (Beta Damping) property is seconds. However, the interface in Mechanical as well as Engineering Data displays the value without a unit.
Frequency: This property is visible when Stiffness Coefficient Defined By is set to . Enter a desired value. Damping Ratio: This property is visible when Stiffness Coefficient Defined By is set to . Enter a desired value. The value of β is not generally known directly, but is calculated from the modal damping ratio, ξi. ξi is the ratio of actual damping to critical damping for a particular mode of vibration, i. If ωi is the natural circular frequency, then the beta damping is related to the damping ratio as β = 2 ξi/ωi. Only one value of β can be input in a step, so choose the most dominant frequency active in that step to calculate β. - Mass Coefficient (Alpha Damping Factor, α)
A coefficient that is used to define an Alpha damping by multiplying it with mass. Beta and Alpha damping factors are collectively called Rayleigh damping.
The Alpha Damping can also be specified in Engineering Data. Refer to the ALPHAD command in the Mechanical APDL Command Reference for more information about the Alpha Damping Factor.
Note: The unit for the Mass Coefficient (Alpha Damping Factor) property is 1/seconds. However, the interface in Mechanical as well as Engineering Data displays the value without a unit.
- Numerical Damping
This option is available for a Transient Structural analysis using a linked Modal analysis system. Numerical Damping is also referred to as amplitude decay factor (γ). This property controls the numerical noise produced by the higher frequencies of a structure. Usually the contributions of these high frequency modes are not accurate and some numerical damping is preferable. Options for this property include (default) and .
The property is accompanied by the Numerical Damping Value property. The default value for this property is 0.005 and is read-only when the Numerical Damping Value is set to setting and can be modified when you use the option.
Note: For Full Transient Structural analysis, you can specify Numerical Damping manually using the option of the App. Based Settings property. The option provides the associated property Amplitude Decay Factor. You use this property to specify a Numerical Damping Value.
- Material Damping
There are two types of material-based damping, Material Dependent Damping and Constant Damping Coefficient. Material Dependent Damping consists of beta damping and alpha damping. These are defined as material properties in Engineering Data.
- Element Damping
Spring damping and Bearing damping are defined in the Details view of the Spring object and Bearing object.
- Rigid Dynamics Analysis Damping
Numerical Damping Control: (Only available with Implicit Generalized-α time integration.) This option allows you to control the noise produced by high frequencies. When the numerical damping control is enabled, you can directly input the value of the
\rho_infcoefficient (refer to Implicit Generalized-α Method). The value must be between 0 and 1. The default value is 0.99, meaning no numerical damping. A smaller value reduces the noise produced by high frequencies.
You can specify more than one form of damping in a model. In addition to structural damping and material damping, the model can have damping from spring and bearing connection, namely Element Damping (see above). The application formulates the damping matrix as the sum of all the specified forms of damping.
You can specify a Material for the spring that includes a constant damping coefficient. Based on the analysis type, the application applies damping as structural damping for damped Modal and Full Harmonic Response systems and as viscous damping for MSUP systems.
Note: Restrictions of applying damping in each analysis type can be found in Damping section of the Mechanical APDL Structural Analysis Guide.