Spring Foundation
Use the Spring Foundation node to apply elastic and damping boundary conditions for domains, boundaries, edges, and points.
By adding the Predeformation subnode, you can prescribe that the spring force is zero at a nonzero spring extension.
The Spring Foundation and Thin Layer nodes are similar, with the difference that a Spring Foundation connects the structural part on which it is acting to a fixed “ground”, while a Thin Layer acts between two parts, either on an interior boundary or between two boundaries forming a pair.
The Spring Foundation node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).
Shell Properties

Interface Selection

Pair Selection
If this node is selected from the Pairs menu, choose the pair on which to apply this condition. An identity pair has to be created first.
Coordinate System Selection
The spring and damping constants are given with respect to the selected coordinate system.
Spring
Select the Spring type and its associated spring constant or force using Table 4-9 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 the given material data and a 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 4-10. 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.
kV
N/(mm3)
ktot
kA
N/(mm2)
kL
N/(mm)
kP
FV
Ftot
FA
FL
FP
D(E,ν)
D(E,G)
D(K,G)
E =
ν =
K =
G =
Rotational Spring


Loss Factor Damping
From the Loss factor type list, select Scalar (Same for all components) or Individual components. The latter option is not available for 1D or 1D axisymmetry.
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, then 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.
Rotational Loss Factor Damping


Viscous Damping
Select the Damping type using Table 4-11 as a guide. The default option is the default damping type for the type of geometric entity and space dimension, and there are different combinations available based on this. 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
dV
Ns/(mm3)
dA
Ns/(mm2)
dtot
Ns/m
dL
Ns/(mm)
Rotational Viscous Damping


Energy Dissipation
You can select to compute and store energy dissipation variables in a time-dependent analysis. Doing so will add extra degrees of freedom to the model.
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.
You can activate and deactivate Spring Foundation by assigning it to a constraint group. See Load Cases in the Structural Mechanics Modeling chapter.
Springs and Dampers in the Structural Mechanics Modeling chapter.
Spring Foundation and Thin Elastic Layer in the Structural Mechanics Theory chapter.
Location in User Interface
Context Menus
Ribbon
Physics tab with Solid Mechanics selected:
Physics tab with Shell or Membrane selected:
Physics tab with Plate selected:
Physics tab with Layered Shell selected:
Physics tab with Beam, Pipe Mechanics, or Truss selected:
Physics tab with Multibody Dynamics selected: