Hygroscopic Swelling Coupling
Hygroscopic Swelling
The Hygroscopic Swelling multiphysics coupling node () is for moisture concentration coupling between the Solid Mechanics interface and either the Transport of Diluted Species or Transport of Diluted Species in Porous Media interfaces.
Hygroscopic swelling is an internal strain caused by changes in moisture content. This strain can be written as
where βh is the coefficient of hygroscopic swelling, cmo is the moisture concentration, and cmo,ref is the strain-free reference concentration.
Settings
The Label is the default multiphysics coupling feature name.
The Name is used primarily as a scope prefix for variables defined by the coupling node. Refer to such variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different coupling nodes or physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first multiphysics coupling feature in the model) is hs1.
Hygroscopic Swelling Properties
Enter a Strain reference concentration cmo,ref . This is the concentration at which there are no strains due to hygroscopic swelling.
Enter the Molar mass of the fluid, Mm. The default value is 0.018 kg/mol, which is the molar mass of water.
The default Coefficient of hygroscopic swelling βh uses values From material. For User defined select Isotropic (the default), Diagonal, or Symmetric from the list to enter one or more components for a general coefficient of hygroscopic swelling tensor βh.The default value for the User defined case is 1.5e-4 m3/kg. When a non-isotropic coefficient of hygroscopic swelling is used, the axis orientations are given by the coordinate system selection in the structural mechanics material node to which it contributes.
The Include moisture as added mass check box is selected by default. When selected, the mass of the fluid is included in a dynamic analysis, and when using mass proportional loads. It will also contribute when computing mass properties.
Hygroscopic Swelling
This section defines the physics involved in the Hygroscopic Swelling multiphysics coupling. The Moisture concentration and Structure lists include all applicable physics interfaces.
You can select None from either list to uncouple the coupling node from a physics interface. If the physics interface is removed from the Model Builder, for example Solid Mechanics is deleted, then the list defaults to None as there is nothing to couple to.
If a physics interface is deleted and then added to the model again, then in order to re-establish the coupling, you need to choose the physics interface again from the lists. This is applicable to all multiphysics coupling nodes that would normally default to the once present interface. See Multiphysics Modeling Approaches in the COMSOL Multiphysics Reference Manual.