Hygroscopic Swelling

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, Mm is the molar mass, cmo is the moisture concentration, and cmo,ref is the strain-free reference concentration.

The subnode is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).

Shell Properties

This section is only present when is used as a subnode to:

•

in the Layered Shell interface. See the documentation for the Hygroscopic Swelling node in the Layered Shell chapter.

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in the Membrane interface. See the documentation for the Hygroscopic Swelling node in the Membrane chapter.

Model Inputs

From the c list, select an existing concentration variable from another physics interface, if any concentration variables exist. For enter a value or expression for the concentration. The unit for the input depends on the setting of in the Hygroscopic Swelling Properties section. Only concentration variables having the chosen physical dimension are available in the list.


	Hygroscopic strains are proportional to the concentration, while structural strains are computed from the gradient of the displacement field. It is a good practice to match the discretization order of hygroscopic and structural strains. When adding a Hygroscopic swelling subnode in a Layered Shell or Membrane interface, and the concentration field is computed by another physics interface; use a discretization one order lower for the concentration field than what is used for the displacement field. A consistent strain discretization is automatically set up for the Solid Mechanics interface.

Hygroscopic Swelling Properties

In the list, select or , depending on the units used for the concentration.

Enter a cref . This is the concentration at which there are no strains due to hygroscopic swelling.

If is selected as the , enter also the of the fluid, Mm. The default value is 0.018 kg/mol, which is the molar mass of water.

The default βh uses values . For , select , , or from the list to enter one or more components for a general coefficient of hygroscopic swelling tensor βh. The default value for the case is 1.5e-4 m3/kg. When a nonisotropic coefficient of hygroscopic swelling is used, the axis orientations are given by the coordinate system selection in the parent node.

The 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.

Location in User Interface

Context Menus

Ribbon

Physics tab with , , , or node selected in the model tree: