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.
Coordinate System Selection
Specify the coordinate system to use for specifying the spring properties. The coordinate system selection is based on the geometric entity level.
Domains (Plate interface)
From the Coordinate system list select from:
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Global coordinate system (the default)
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Shell Local System
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Any additional user-defined coordinate system
Boundaries (Shell and Plate interfaces)
From the Coordinate system list select from:
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Global coordinate system (the default)
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Boundary System (a predefined normal-tangential coordinate system)
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Shell Local System
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Any additional user-defined coordinate system
Edges (Shell interface)
From the Coordinate system list select from:
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Global coordinate system (the standard global coordinate system).
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Local edge system (the default).
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Shell Local System
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Any additional user-defined coordinate system.
Points (Shell and Plate interfaces)
From the Coordinate system list select from:
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Global coordinate system (the default)
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Shell Local System
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Any additional user-defined coordinate system
For details about the definition of local edge systems, see Local edge system.
Spring
Select the Spring type and its associated spring constant or force using Table 5-2 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 Anisotropic. For Isotropic the same spring constant is used in all the diagonal elements of the spring matrix.
Table 5-2: Spring Types For the Spring Foundation Feature
Spring Type
variable
SI units
Geometric Entity Level
Spring constant per unit volume
kV
N/(m⋅m3)
domains (Plate), boundaries (Shell)
Total spring constant
ktot
N/m
domains (Plate), boundaries (Shell, Plate), edges (Shell)
Spring constant per unit area
kA
N/(m⋅m)2
domains (Plate), boundaries (Shell, Plate), edges (Shell)
Spring constant per unit length
kL
N/(m⋅m)
boundaries (Plate), edges (Shell)
Spring constant
kP
N/m
points (Shell, Plate)
Force per volume as function of extension
FV
N/m3
domains (Plate), boundaries (Shell)
Total force as function of extension
Ftot
N
domains (Plate), boundaries (Shell, Plate), edges (Shell)
Force per area as function of extension
FA
N/m2
domains (Plate), boundaries (Shell, Plate), edges (Shell)
Force per length as function of extension
FL
N/m
boundaries (Plate), edges (Shell)
Force as function of extension
FP
N
points (Shell, Plate)
Loss Factor Damping
From the Loss factor type list, select Scalar (Same for all components) or Individual components.
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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.
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For Individual components select Isotropic, Diagonal, Symmetric, or Anisotropic, 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.
Viscous Damping
Select the Damping type using Table 5-3 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 Anisotropic. For Isotropic the same viscous constant is used in all the diagonal elements of the damping matrix
Table 5-3: Damping Types For the Spring Foundation Feature
Damping Type
variable
SI units
Geometric Entity Level
Damping constant per unit volume
dV
N⋅s/(m⋅m3)
domains (Plate), boundaries (Shell)
Damping constant per unit area
dA
N⋅s/(m⋅m2)
domains (Plate), boundaries (Shell, Plate), edges (Shell)
Total damping constant
dtot
N⋅s/m
domains (Plate), boundaries (Shell, Plate), edges (Shell)
Damping constant per unit length
dL
N⋅s/(m⋅m)
boundaries (Plate), edges (Shell)
You can activate and deactivate this boundary condition by assigning it to a constraint group. See Load Cases in the Structural Mechanics Modeling chapter.
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Springs and Dampers in the Structural Mechanics Modeling chapter.
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Spring Foundation and Thin Elastic Layer in the Structural Mechanics Theory chapter.
Location in User Interface
Context Menus
 Shell>Mass, Spring, and Damper>Spring Foundation (Boundary, Edge)
Shell>Points>Spring Foundation
Plate>Mass, Spring, and Damper>Spring Foundation (Domain, Boundary)
Plate>Points>Spring Foundation
Ribbon
Physics tab with Shell selected:
Boundaries>Mass, Spring, and Damper>Spring Foundation
Edges>Mass, Spring, and Damper>Spring Foundation
Points>Shell>Spring Foundation
Points>Membrane>Spring Foundation
Physics tab with Plate selected:
Domains>Mass, Spring, and Damper>Spring Foundation
Boundaries>Mass, Spring, and Damper>Spring Foundation
Points>Plate>Spring Foundation