Damping
Use the Damping subnode to add several types of damping to the material model. Damping can be used in Time Dependent, Eigenfrequency, and Frequency Domain studies; for other study types the settings in the Damping subnode are ignored.
You can add the Damping subnode to the Linear Elastic Material, the Nonlinear Elastic Material, and the Hyperelastic Material.
The following types of damping are available:
The available damping models differs between various COMSOL products (see http://www.comsol.com/products/specifications/).
The applicability of the different types of damping are summarized in Table 4-4.
Rayleigh damping
Isotropic loss factor
Anisotropic loss factor
Orthotropic loss factor
Viscous damping
Layer Selection
This section is only present when working with layered shells.
Damping in the documentation for the Layered Shell interface
Damping in the documentation for the Shell interface
Damping Settings
Select a Damping type, and enter settings depending on the type.
Rayleigh Damping
In this damping model, the damping parameter ξ is expressed in terms of the mass m and the stiffness k as
That is, Rayleigh damping is proportional to a linear combination of the stiffness and mass; there is no direct physical interpretation of the mass damping parameter αdM and the stiffness damping parameter βdM.
Select Input parameters Alpha and beta — to enter the damping parameters explicitly, or Damping ratios to derive the damping parameters from the relative damping at two frequencies.
When Alpha and beta is selected, the Mass damping parameter αdM and the Stiffness damping parameter βdK.
When Damping ratios is selected, enter two pairs of frequencies, f1 and f2, and the corresponding damping ratios ζ1 and ζ2 at these frequencies. The Rayleigh damping parameters are computed as
Isotropic Loss Factor Damping
The isotropic loss factor damping is described by the single isotropic loss factor ηs, which acts on all entries in the elastic constitutive matrix. It can be used for isotropic, orthotropic, and anisotropic materials.
When Isotropic loss factor is selected, use the Isotropic structural loss factor list to select the way to enter ηs. The default is to take the value From material. For User defined, enter another value or expression.
Anisotropic Loss Factor Damping
An elastic material is in general described by a symmetric 6-by-6 elasticity matrix D. The loss can be isotropic or anisotropic, and is described by either the isotropic loss factor ηs or by a symmetric anisotropic 6-by-6 loss factor matrix ηD or ηDVo. The orientations are the same as in the parent node.
When Anisotropic loss factor is selected, use the Loss factor for elasticity matrix D list to select the way to enter ηD or ηDVo. The default is to take the values From material. For User defined enter the components of ηD or ηDVo in the upper-triangular part of a symmetric 6-by-6 matrix.
The values for the loss factors are ordered in two different ways, consistent with the selection of either Standard (XX, YY, ZZ, XY, YZ, XZ) or Voigt (XX, YY, ZZ, YZ, XZ, XY) notation in the corresponding Linear Elastic Model. If the values are taken from the material, these loss factors are found in the Anisotropic or Anisotropic, Voigt notation property group for the material. For an isotropic material, the anisotropic loss factor is always given as ηD using the standard notation.
Orthotropic Loss Factor Damping
This option is only available when Orthotropic is selected as the Linear Elastic Material Solid model.
An orthotropic material is described by three Young’s modulus components (Ex, Ey, and Ez) and three shear modulus components (Gxy, Gyz, and Gxz). For an orthotropic material, loss factors can be specified in three different ways:
When Orthotropic loss factor is selected, use the Loss factor for orthotropic Young’s modulus list to select the way to enter ηE. The default is to take the values From material. For User defined enter other values or expressions.
Use the Loss factor for orthotropic shear modulus list to select the way to enter ηG or ηGVo. The default is to take the values From material. For User defined, enter other values or expressions.
The values for the shear modulus loss factors are ordered in two different ways, consistent with the selection of either Standard (XX, YY, ZZ, XY, YZ, XZ) or Voigt (XX, YY, ZZ, YZ, XZ, XY) notation in the corresponding Linear Elastic Model. If the values are taken from the material, these loss factors are found in the Orthotropic or Orthotropic, Voigt notation property group for the material.
Viscous Damping
With viscous damping, the material will get additional stresses proportional to the strain rate. Enter Bulk viscosity ηb and Shear viscosity ηv to model damping caused by volume change and deformation, respectively.
For an example of Damping, see Heat Generation in a Vibrating Structure: Application Library path Structural_Mechanics_Module/Thermal-Structure_Interaction/vibrating_beam
Location in User Interface
Context Menus
Solid Mechanics>Linear Elastic Material>Damping
Solid Mechanics>Nonlinear Elastic Material>Damping
Solid Mechanics>Hyperelastic Material>Damping
Layered Shell>Linear Elastic Material>Damping
Membrane>Linear Elastic Material>Damping
Membrane>Nonlinear Elastic Material>Damping
Membrane>Hyperelastic Material>Damping
Truss>Linear Elastic Material>Damping
Multibody Dynamics>Linear Elastic Material>Damping
Ribbon
Physics tab with Linear Elastic Material, Hyperelastic Material, or Nonlinear Elastic Material node selected in the model tree:
Attributes>Damping