Solid-Thin Structure Connection
Add the Solid-Thin Structure Connection multiphysics node () to create transitions between domains modeled using the Solid Mechanics or Multibody Dynamics interfaces and boundaries modeled using the Shell or Membrane interfaces.
The Solid-Thin Structure Connection node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).
Coupled Interfaces
Select Solid mechanics — Solid Mechanics or Multibody Dynamics.
Select Thin structure — Shell or Membrane.
Connection Settings
When Membrane is selected from the Thin structure list, the Connection type is set to Shared boundaries. See settings in Shared Boundaries.
When Shell is selected from the Thin structure list, select the Connection type — Solid boundaries to shell edges, Shared boundaries, or Parallel boundaries.
For the first two options, there is an automatic search for possible adjacent geometrical objects. If you want to modify the selections, select the Manual control of selections check box. If you clear it, the selections will be replaced by the automatic ones.
Solid Boundaries to Shell Edges
If the automatic selection is not sufficient, select the Manual control of selections check box. Then, select the connected solid boundaries in the Boundary Selection, Solid section and the corresponding shell edges in the Edge Selection, Shell section.
Select Connected area defined by — Shell thickness, Selected solid boundaries, or Distance from shell midsurface. This parameter determines how much of the selected solid boundaries that are connected to the shell. The default is that a distance from the shell edge having the size of the half the shell thickness in both perpendicular directions is connected.
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Using Selected solid boundaries connects the selected boundaries in their entirety to the shell.
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If you select Distance from shell midsurface, enter a Distance d. This value is used instead of the half the shell thickness for defining the connection distance.
Select a Method — Rigid or Flexible.
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The Rigid version of the coupling only adds constraints to the boundary of the solid, which in general causes local disturbances of the stress field, since the thickness cannot change.
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When using the Flexible coupling, three extra degrees of freedom are added along the shell edge. This allows for a more accurate description of the transition, but the model can in some cases become unconstrained if the mesh on the solid is very coarse.
When either of the Shell thickness or Distance from shell midsurface options are used, the connected area is slightly extended by the distance Δ. Select how to determine this Connection tolerance — Automatic or User defined. For Automatic, the tolerance Δ is set to 0.5% of the shell thickness, which allows for small inaccuracies on for example a curved geometry. By selecting User defined, you can modify the value of Δ.
Shared Boundaries
If the automatic selection is not sufficient, select the Manual control of selections check box. Then, select the connected boundaries in the Boundary Selection section.
The connected area is slightly extended by a distance Δ. Select how to determine this Connection tolerance — Automatic or User defined. For Automatic, the tolerance Δ is set to 0.5% of the shell thickness, which allows for small inaccuracies on for example a curved geometry. By selecting User defined, you can modify the value of Δ.
Parallel Boundaries
Select the connected solid boundaries in the Boundary Selection, Solid section and the corresponding shell boundaries in the Boundary Selection, Shell section.
Select Distance evaluation — Shell properties, Solid-shell geometrical distance, or User defined. This parameter controls how the coupling determines the connection distance, used when expressing the coupling between translation and rotation.
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When Shell properties is selected, the distance is based on the shell thickness and offset, so that a distance equal to half the shell thickness is used.
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If you select Solid-shell geometrical distance, the connection distance is computed from the geometrical distance between the selected boundaries.
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For User defined, enter a Distance d, which defines the connection distance.
The connected area is slightly extended by a distance Δ. Select how to determine this Connection tolerance — Automatic or User defined. For Automatic, the tolerance Δ is set to 0.5% of the shell thickness, which allows for small inaccuracies on for example a curved geometry. By selecting User defined, you can modify the value of Δ.
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For more information about coupling different element types, see Coupling Techniques.
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For details about the formulation of this coupling, see Connection Between Shells and Solids
These types of couplings will commonly generate many constraints, possibly even conflicting with other constraints coming from ordinary boundary conditions. For methods of resolving potential problems, see
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Elemental and Nodal Constraints
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Suppressing Constraints on Lower Dimensions
When there are many interconnected constraints, it may also be useful to change Null-Space Function to Orthonormal or Explicit — Orthonormal, but doing so may increase the memory consumption significantly.
An example of couplings between shells and solids is shown in Connecting Shells and Solids: Application Library path Structural_Mechanics_Module/Beams_and_Shells/shell_solid_connection