Known Issues When Modeling Using Infinite Elements

Be aware of the following when modeling with infinite elements:

Use of One Single Infinite Elements Node

Use a separate Infinite Elements node for each isolated infinite element domain. That is, to use one and the same Infinite Elements node, all infinite element domains must be in contact with each other. Otherwise the infinite elements do not work properly.

Element Quality

The coordinate scaling resulting from infinite elements also yields an equivalent stretching or scaling of the mesh that effectively results in a poor element quality. (The element quality displayed by the mesh statistics does not account for this effect.)

The poor element quality causes poor or slow convergence for iterative solvers and makes the problem ill-conditioned in general. The vector element formulations (the ones using two or more components of a vector field variable) in the AC/DC Module are particularly sensitive to low element quality.

For this reason, it is strongly recommended to use swept meshing in the infinite element domains. Select the sweep direction to be the same as the direction of scaling. For Cartesian infinite elements in regions with more than one direction of scaling it is recommended to first sweep the mesh in the domains with only one direction of scaling, then sweep the domains with scaling in two directions, and finally sweep the mesh in the domains with infinite element scaling in all three directions.

Complicated Expressions

The expressions resulting from the stretching get quite complicated for spherical infinite elements in 3D. This increases the time for the assembly stage in the solution process. After the assembly, the computation time and memory consumption is comparable to a problem without infinite elements. The number of iterations for iterative solvers might increase if the infinite element regions have a coarse mesh.

Erroneous Results

Infinite element regions deviating significantly from the typical configurations shown in the beginning of this section can cause the automatic calculation of the infinite element parameter to give erroneous results.

Use the Same Material Parameters or Boundary Conditions

The infinite element region is designed to model uniform regions extended toward infinity. Avoid using objects with different material parameters or boundary conditions that influence the solution inside an infinite element region.