Moving Mesh Interface

The interface (

), found under the branch (

) when adding a physics interface, can be used to create models where the geometry, here represented by the mesh, changes shape due to some physical phenomena without material being removed or added. The difference between the Deformed Geometry and Moving Mesh interfaces is that the former defines a deformation of the material frame relative to the geometry frame, while the latter defines a displacement of the spatial frame relative to the material frame. The Moving Mesh interface can be used to study both stationary states and time-dependent deformations where the geometry changes its shape due to the dynamics of the problem. For example, it can be used for fluid domain deformations in fluid-structure interaction (FSI) or electrostatic domain deformations in MEMS.

When this interface is added, these default nodes are also added to the : and (the default boundary condition). Then, from the toolbar, add other nodes that implement, for example, boundary conditions. You can also right-click to select features from the context menu.

The Moving Mesh interface includes the following predefined variables for the spatial frame, which can be of interest, for example, to monitor the quality of the mesh and define a stop criterion for remeshing (see Adding a Stop Condition):

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The local relative element volume, spatial.relVol, is a quantity that measures the local volumetric distortion of the elements. When this measure approaches zero in some part of the mesh, frame transformations become singular causing solvers to fail.

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The minimum relative element volume, spatial.relVolMin, must be > 0, otherwise the mesh elements are inverted. A suitable stop criterion using this variable is that the minimum relative element volume must be larger than a small positive number.

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The minimum mesh quality, spatial.minqual, must be > 0; an acceptable mesh quality is typically larger than 0.1 (where the quality measure is a number between 0 and 1).

	Sloshing Tank: Application Library path COMSOL_Multiphysics/Fluid_Dynamics/sloshing_tank

The is the default physics interface name.

The is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the field. The first character must be a letter.

The default (for the first physics interface in the model) is ale.

	You do not need to use a Moving Mesh interface in domains where a Solid Mechanics interface is active. The displacements automatically control the spatial frame when Include geometric nonlinearity is selected in a study step.

Specify the names of the spatial coordinates of the base frame for the physics interface — the material frame — in the fields. The defaults are the coordinates of the spatial frame in uppercase letters (, , and ). You can change the names in the fields for the , , and coordinate. The field labels include the default spatial coordinate names in parentheses.

The setting controls the order of polynomials — (linear), (quadratic; the default), (cubic), (quartic),or (quintic, 2D only) — used for representing the geometry shape in the spatial frame. The same order is used for Lagrange shape functions defining the mesh position in domains where has been activated.

Select the smoothing type for freely deformed domains from the list. Choose between , , , and smoothing. The default is Laplace smoothing. For Yeoh smoothing, also specify a (default: 100).