You must place the INFIN47 elements such that the global origin is located centrally with respect to them. A circular arc of far-field elements at the boundary of the finite element domain usually gives best results.

The infinite elements INFIN110 and INFIN111 give you greater flexibility in modeling far-field effects.

For best results, define INFIN110 and INFIN111 elements with their "poles" (see the Element Reference) coinciding with centers of disturbances, such as loads. There may be multiple poles, which may or may not fall at the coordinate system origin. Element poles should coincide with nearby disturbances, or with the approximate centroid of disturbances. In contrast to INFIN47, INFIN110 and INFIN111 need not be placed such that the global origin is located centrally with respect to them.

When using the INFIN110 or INFIN111 elements, you must flag the exterior surface with the INF surface load. To do so, use the SF family of commands or their equivalent menu paths. (See 2D Transient Magnetic Analysis.)

You can easily define a layer of INFIN111 elements by creating a volume to be meshed, using one of the following:

The INFIN110 and INFIN111 elements are usually much longer in the infinite direction, resulting in skewed meshes. Therefore, contour plots exclude these elements. Element plots, however, include them.

For optimal performance of either INFIN110 or INFIN111, you must meet one or both of the following conditions.

Boundaries Must Describe a Smooth Curvature

INFIN110 and INFIN111 perform best when the boundary between the finite element (FE) domain and the infinite element (IFE) domain describes a smooth curvature. Figure 11.3: Interface between FE and Infinite Element Domains illustrates this point.

If your model construction does not allow a smooth FE to IFE domain interface, you may do so provided the infinite elements "radiate" from any sharp corners in the FE domain. Only one element edge may be "exposed" to the open exterior. Figure 11.4: IFE Constructions for Non-Smooth FE to IFE Domain Interface illustrates this point for both a correct and incorrect IFE construction for a quarter symmetry model.

Figure 11.4: IFE Constructions for Non-Smooth FE to IFE Domain Interface also illustrates that only one face of an infinite element may be exposed to infinity. Be careful to assure that one face of the infinite element is exposed to infinity. You should avoid constructions that lead to infinite element with sides converging from the FE interface to the interface with infinity. Figure 11.5: 2D Infinite Element Structures illustrates this point.

The accuracy of field calculations at sharp edges of the FE/IFE domain interface will be of lower quality than those achieved at a smooth interface.

Length of Elements Should Equal Depth of Domain

The second condition that improves the performance of INFIN110 and INFIN111 is the relative dimensions of the FE and IFE domains. The relative length of the infinite elements should be approximately equal to the depth of your model's FE domain. Figure 11.6: Relative Dimensions of FE and IFE Domains illustrates this relationship for a 2D quarter symmetry example.

When INFIN47 elements enclose higher-order elements in a model, remove the midside nodes of the higher-order elements at the interface with the far-field elements (EMID command). When INFIN110 or INFIN111 elements enclose higher-order elements in a model, use the higher-order setting for the far-field elements (KEYOPT(2) = 1).