Thin Elastic Layer
The Thin Elastic Layer node to apply elastic and damping conditions between two parts on an interior boundary. The condition can be added from the Porous Matrix Conditions submenu and it can be combined with any of the conditions found in the Fluid Conditions submenu.
The Thin Elastic Layer and Spring Foundation nodes are similar, with the difference that a Spring Foundation connects the structural part on which it is acting to a fixed “ground”.
Coordinate System Selection
The spring and damping constants are given with respect to the selected coordinate system, with the exception that when the stiffness is specified by Use material data, the coordinate system selection is not used.
Spring
Select the Spring type and its associated spring constant or force using Table 3-1 as a guide. The default option is the spring type for the type of geometric entity and space dimension, and there are different combinations available based on this.
When the option is of the type “force as function of extension”, then the built-in variables describing the spring extension must be used in the expression as described in Springs and Dampers. The spring matrix can be entered as Isotropic, Diagonal, Symmetric, or Full. For Isotropic the same spring constant is used in all the diagonal elements of the spring matrix.
When Use material data is selected as Spring type, the spring stiffness values are computed from material data and layer thickness. From the Specify list, select a pair of elastic properties — Young’s modulus and Poisson’s ratio, Young’s modulus and shear modulus, or Bulk modulus and shear modulus. Each of these pairs define the elastic properties and it is possible to convert from one set of properties to another according to Table 3-3. For the chosen properties, select from the applicable list to use the value From material or enter a User defined value or expression. In order to use From material, you must have assigned a material to the selected boundaries.
Enter a Thickness, ds, to specify the physical thickness of the elastic layer.
ktot
kA
N/(mm2)
kL
N/(mm)
Ftot
FA
FL
Added Mass
Enter the added mass of the thin elastic layer. The type of input depends on the selected Spring type; see Table 3-1.
For Total spring constant and Total force as function of extension, enter the Total mass m of the thin elastic layer.
For Spring constant per unit area and Force per area as function of extension, enter the Mass per unit area ρA of the thin elastic layer.
For Spring constant per unit area and Force per area as function of extension, enter the Mass per unit length ρL of the thin elastic layer.
For Use material data, enter the Density ρ of the thin elastic layer. Either use the value From material or enter a User defined value or expression. In order to use From material, you must have assigned a material to the selected boundaries.
Loss Factor Damping
From the Loss factor type list, select Scalar (Same for all components) or Individual components.
For Scalar (Same for all components) enter a single Loss factor for spring ηs, which is used to multiply all values of the spring matrix or spring force vector.
For Individual components select Isotropic, Diagonal, Symmetric, or Full and enter values or expressions in the table for the Loss factor for spring ηk or ηf based on space dimension. The loss factors act on the corresponding components of the spring matrix or spring force vector. If you select Isotropic, the effect is the same as when you select Diagonal and enter the same value for all diagonal elements.
Viscous Damping
Select the Damping type using Table 3-2 as a guide. The default option is the default damping type for the space dimension. The damping matrix can be entered as Isotropic, Diagonal, Symmetric, or Full. For Isotropic the same viscous constant is used in all the diagonal elements of the damping matrix.
dA
Ns/(mm2)
dtot
Ns/m
dL
Ns/(mm)
Energy Dissipation
You can select to compute energy dissipation variables. Select the Calculate dissipated energy check box as needed to compute the energy dissipated by damping.
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box.