INFIN257


Structural Infinite Solid

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INFIN257 Element Description

Use INFIN257 with standard 2D or 3D solid elements (the base elements) to model infinite domain.

A single layer of elements represents an exterior subdomain of infinite domain. In a static structural analysis, the layer models the effect of far-field decay. In a harmonic or transient analysis, the layer behaves as an absorbing boundary at the face attached to the base element. Use base elements to model the near-field domain that interacts with the solid structures or applied loads.

Figure 257.1: Near-field vs. Far-field

Near-field vs. Far-field

For more information about this element, see INFIN257 - Structural Infinite Solid in the Theory Reference.

Figure 257.2: INFIN257 Geometry

INFIN257 Geometry

INFIN257 Input Data

The geometry and nodal locations for this element are shown in Figure 257.2: INFIN257 Geometry.

Create INFIN257 elements from the selected nodes on base elements via the EINFIN command. The command determines the stress state and material properties according to the base element. Only linear elastic material properties (except density) are transferred to INFIN257. The real constant of the thickness input for a 2D plane stress element (KEYOPT(3) = 3) is copied to the INFIN257 element.

Valid base elements are: PLANE182, PLANE183, SOLID185, SOLID186, SOLID187, and SOLID285.

INFIN257 does not support element loading. Apply element loading to base elements only.

INFIN257 Input Summary

Nodes

Same as those of the base element, as shown:

Base ElementINFIN257 Nodes
2D 4-Node SolidI, J, K, L
2D 8-Node SolidI, J, K, L, M, N, O, P
3D 8 Node SolidI, J, K, L, M, N, O, P
3D 20-Node SolidI, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z, A, B
3D 4-Node Tetrahedral Structural SolidI,J,K,L,M,N,O,P
3D 10-Node Tetrahedral Structural SolidI,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A,B
Degrees of Freedom

Same as those of the base element, as shown:

Base ElementINFIN257 Degrees of Freedom
2D 4-Node SolidUX, UY
2D 8-Node Solid
3D 8-Node SolidUX, UY, UZ
3D 20-Node Solid
3D 4-Node Tetrahedral Structural Solid
3D 10-Node Tetrahedral Structural Solid
Real Constants

None

Material Properties

None

Surface Loads

None

Body Loads

None

Special Features

None

KEYOPTS

None

INFIN257 Output Data

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

A general description of solution output is given in Solution Output. See the Basic Analysis Guide for ways to view results.

Figure 257.3: INFIN257 Stress Output

INFIN257 Stress Output

Stress directions are in the global directions.

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 letter or number refers to a table footnote that describes when the item is conditionally available, and “-” indicates that the item is not available.

Table 257.1: INFIN257 Element Output Definitions

NameDefinitionOR
ELElement Number-Y
NODES

Nodes - I, J, K, L (2D)

Nodes - I, J, K, L, M, N, O, P (3D)

-Y
MATMaterial number-Y
XC, YC, ZCLocation where results are reported.Y1
S:X, Y, Z, XY, YZ, XZStresses (SZ = 0.0 for plane stress elements)YY
S:1, 2, 3Principal stresses-Y
EPEL:X, Y, Z, XY, YZ, XZElastic strainsYY
LOCI:X, Y, ZIntegration point locations-2

  1. Available only at centroid as a *GET item. For a 2D element, ZC = 0.

  2. Available only if OUTRES,LOCI is used.

For axisymmetric solutions in the global coordinate system, the X, Y, Z, and XY stress and strain outputs correspond to the radial, axial, hoop, and in-plane shear stresses and strains, respectively.

Table 257.2: INFIN257 Item and Sequence Numbers lists output available (ETABLE) using the Sequence Number method. The table is applied only if the base element is 2D and KEYOPT(3) = 3. See Creating an Element Table in the Basic Analysis Guide and The Item and Sequence Number Table in this reference for more information. The following notation is used in the table:

Name

Output quantity as defined in Table 257.1: INFIN257 Element Output Definitions

Item

Predetermined Item label for the ETABLE command

E

Sequence number for single-valued or constant element data

I, J, K, L

Sequence number for data at nodes I, J, K, and L

Table 257.2: INFIN257 Item and Sequence Numbers

Output Quantity NameETABLE and ESOL Command Input
ItemEIJKL
THICKNMISC1----

INFIN257 Assumptions and Restrictions

  • The element supports static, transient, and harmonic analyses.

  • In a transient or harmonic analysis, traction at the interface from a static load step is not transferred to the absorbing boundary.

  • A valid base element must be present for each INFIN257 element.

  • Valid base element types are: PLANE182, PLANE183, SOLID185, SOLID186, SOLID187, and SOLID285.

  • Because the element has no pressure degree of freedom, using it with pressure degree-of-freedom (DOF) base elements may give poor results in the finite domain.

  • In a static analysis, base elements can have anisotropic material properties. It is good practice, however, to limit the finite element domain to a reasonable size so that INFIN257 elements are in a linear elastic state.

  • Layered solid elements (an option available with SOLID185 and SOLID186, for example) are not compatible with INFIN257 elements.

  • The element technology of a base element is not transferred to infinite elements.

  • For 2D models, the element must lie in a global XY plane as shown in Figure 257.2: INFIN257 Geometry, and the Y axis must be the axis of symmetry for axisymmetric analyses. Model an axisymmetric infinite element in the same quadrants in which the base element is modeled.

  • For 2D INFIN257 elements, degeneration is not allowed and generalized plain strain is not supported.

  • 3D INFIN257 elements must have 8 or 20 nodes. You can form a prism-shaped element by using a degenerated base element.

INFIN257 Product Restrictions

There are no product-specific restrictions for this element.