2-D Infinite Solid

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INFIN110 Element Description

INFIN110 models an open boundary of a 2-D unbounded field problem. A single layer of elements is used to represent an exterior sub-domain of semi-infinite extent. The layer models the effect of far-field decay in magnetic, electrostatic, thermal, or electric current conduction analyses. For information about enclosed elements and analysis types, see Table 110.1: INFIN110 Analyses. INFIN110 may be used for planar and axisymmetric analyses. See INFIN110 in the Mechanical APDL Theory Reference for more details about this element.

Figure 110.1:  INFIN110 Geometry

INFIN110 Geometry

INFIN110 Input Data

The geometry, node locations, and the coordinate system for the element are shown in Figure 110.1: INFIN110 Geometry. KEYOPT(1) specifies the degree of freedom to be used. KEYOPT(2) specifies whether a 4-node or 8-node element is used.

Only one layer of INFIN110 elements should be used between the finite element model and the exterior (infinite) surface. The nodes may be input starting at any corner node, but the face opposite of the finite element model (the exterior face) must be flagged as an infinite surface. This is usually done by selecting the nodes at the outer surface and issuing the SF,ALL,INF command. The other faces have no meaning. For best results, edges connecting the inner and outer surfaces of the infinite element should be radial from the center of the model.

A summary of the element input is given in "INFIN110 Input Summary". A general description of element input is given in Element Input. For axisymmetric applications see Harmonic Axisymmetric Elements.

INFIN110 Input Summary

I, J, K, L (if KEYOPT(2) = 0)
I, J, K, L, M, N, O, P (if KEYOPT(2) = 1)
Degrees of Freedom

Set by KEYOPT(1). See Table 110.1: INFIN110 Analyses.

Real Constants

THK -- Thickness (plane) or fraction of the 360° basis (axisymmetric)

Material Properties

See Table 110.2: INFIN110 Material Properties.

Surface Loads
Infinite Surface Flags -- 

face 1 (J-I), face 2 (K-J), face 3 (L-K), face 4 (I-L)

Body Loads


Special Features



Element degrees of freedom. See Table 110.1: INFIN110 Analyses.


Element definition:

0 -- 

4-node quadrilateral

1 -- 

8-node quadrilateral


Element behavior:

0 -- 


1 -- 



Electric charge reaction sign:

0 -- 


1 -- 


Analysis categories are shown in the following table. KEYOPT(1) specifies the element degree of freedom.

Table 110.1:  INFIN110 Analyses

Analysis CategoryKEYOPT(1)DOF LabelReaction SolutionEnclosed ElementsAnalysis Type

Magnetic Current Segment

(F label = CSG)







Electric Charge

(F label = CHRG)





Heat Flow

(F label = HEAT)






Electric Current Conduction3VOLT

Electric Current

(F label = AMPS)





INFIN110 material properties are shown in the following table. Nonzero material properties must be defined. Material properties are defined with the MP, MPDATA and EMUNIT commands.

Table 110.2:  INFIN110 Material Properties

Analysis CategoryKEYOPT(1)Material Properties
Electrostatic1PERX, PERY, LSST, RSVX, RSVY
Thermal2KXX, KYY, DENS, C
Electric Current Conduction3RSVX, RSVY, LSST, PERX, PERY

INFIN110 Output Data

The solution output associated with the element is in two forms:

Several items are illustrated in Figure 110.2: INFIN110 Element Output. The element output directions are parallel to the element coordinate system. A general description of solution output is given in Solution Output. See the Basic Analysis Guide for ways to view results.

Figure 110.2:  INFIN110 Element Output

INFIN110 Element Output

The following notation is used in Table 110.3: Element Output Definitions:

The Element Output Definitions table uses the following notation:

A colon (:) in the Name column indicates that the item can be accessed by the Component Name method (ETABLE, ESOL). The O column indicates the availability of the items in the file Jobname.OUT. The R column indicates the availability of the items in the results file.

In either the O or R columns, “Y” indicates that the item is always available, a number refers to a table footnote that describes when the item is conditionally available, and “-” indicates that the item is not available.

Table 110.3:  Element Output Definitions

ELElement NumberYY

Nodes - I, J, K, L (KEYOPT(2) = 0)
Nodes - I, J, K, L, M, N, O, P (KEYOPT(2) = 1)

MATMaterial numberYY
XC, YCLocation where results are reportedY4
MUZEROMagnetic permeability of free space11
PERX, PERYElectric relative permittivity (element coordinates)22
KXX, KYYThermal conductivity (element coordinates)33

  1. If KEYOPT(1) = 0

  2. If KEYOPT(1) = 1

  3. If KEYOPT(1) = 2

  4. Available only at centroid as a *GET item.

Table 110.4: INFIN110 Item and Sequence Numbers lists output available through the ETABLE command using the Sequence Number method. See The General Postprocessor (POST1) in the Basic Analysis Guide and The Item and Sequence Number Table in this manual for more information. The following notation is used in Table 110.4: INFIN110 Item and Sequence Numbers:


output quantity as defined in the Table 110.3: Element Output Definitions


predetermined Item label for ETABLE command


sequence number for single-valued or constant element data

Table 110.4:  INFIN110 Item and Sequence Numbers

Output Quantity NameETABLE and ESOL Command Input

INFIN110 Assumptions and Restrictions

  • The area of the quadrilateral infinite element must be nonzero.

  • The element cannot degenerate to a triangle.

  • The exterior surface (for example, KL or KOL in Figure 110.1: INFIN110 Geometry) of the element must be flagged using the INF option on the SF family of commands.

  • Only one layer of infinite elements can be used on the exterior boundary of the finite element model.

  • The lines JK and IL of the infinite element IJKL (in Figure 110.2: INFIN110 Element Output) should either be parallel or divergent from each other. That is, the enclosed surface should be convex and the infinite domain must be represented by one layer of infinite elements without overlap or gap. Ideally, the length OJ should equal JK, and OI should equal IL. The point "O" is the "pole" of mapping for the infinite element. The pole is chosen arbitrarily, and may or may not coincide with the origin of the coordinate system. For best results, the poles should be placed at the centers of disturbances (loads). There can be multiple poles for a problem. See the Mechanical APDL Theory Reference for more about poles.

  • Although this element can have 8 nodes (KEYOPT(2) = 1), for theoretical reasons (see the Mechanical APDL Theory Reference), only 5 nodes are included in the solution.

  • The element assumes that the degree of freedom (DOF) value at infinity is always zero (0.0). That is, the DOF value at infinity is not affected by TUNIF, D, or other load commands.

  • The infinite elements are not included in solution result displays but may be viewed in element displays [EPLOT].

  • There are considerations in the application of INFIN110 that will lead to optimal performance in the analysis of your model. These consideration are covered in detail in the Low-Frequency Electromagnetic Analysis Guide.

  • When used in a model with the higher-order elements PLANE35, PLANE77, PLANE121, and PLANE230, use the higher-order setting for INFIN110 (KEYOPT(2) = 1).

  • This element may not be compatible with other elements with the VOLT degree of freedom. To be compatible, elements must have the same reaction solution for the VOLT DOF. Elements that have an electric charge reaction solution must all have the same electric charge reaction sign. KEYOPT(6) sets the electric charge reaction sign. For more information, see Element Compatibility in the Low-Frequency Electromagnetic Analysis Guide.

INFIN110 Product Restrictions

When used in the product(s) listed below, the stated product-specific restrictions apply to this element in addition to the general assumptions and restrictions given in the previous section.

ANSYS Mechanical Pro 

  • The AZ and VOLT degrees of freedom are not active. KEYOPT(1) defaults to 2 (TEMP) instead of 0 and cannot be changed.

ANSYS Mechanical Premium 

  • The AZ and VOLT degrees of freedom are not active. KEYOPT(1) defaults to 2 (TEMP) instead of 0 and cannot be changed.

Release 18.2 - © ANSYS, Inc. All rights reserved.