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COMBI214 Element Description
COMBI214 has longitudinal as well as cross-coupling capability in 2-D applications. It is a tension-compression element with up to two degrees of freedom at each node: translations in any two nodal directions (x, y, or z). COMBI214 has two nodes plus one optional orientation node. No bending or torsion is considered.

The spring-damper element has no mass. Masses can be added by using the appropriate mass element (MASS21). The spring or the damping capability may be removed from the element.

A longitudinal spring/damper with torsion capabilities is available via the COMBIN14 element. A general spring or damper is also available in the stiffness, damping or mass matrix element MATRIX27. Another spring-damper element having its direction of action determined by the nodal coordinate directions is COMBIN40.

For more information about this element, see COMBI214 - 2-D Spring-Damper Bearing in the ANSYS, Inc. Theory Reference.

Figure 214.1 COMBI214 Geometry

COMBI214 Element Description
COMBI214 has longitudinal as well as cross-coupling capability in 2-D applications. It is a tension-compression element with up to two degrees of freedom at each node: translations in any two nodal directions (x, y, or z). COMBI214 has two nodes plus one optional orientation node. No bending or torsion is considered.

The spring-damper element has no mass. Masses can be added by using the appropriate mass element (MASS21). The spring or the damping capability may be removed from the element.

A longitudinal spring/damper with torsion capabilities is available via the COMBIN14 element. A general spring or damper is also available in the stiffness, damping or mass matrix element MATRIX27. Another spring-damper element having its direction of action determined by the nodal coordinate directions is COMBIN40.

For more information about this element, see COMBI214 - 2-D Spring-Damper Bearing in the ANSYS, Inc. Theory Reference.

COMBI214 Input Data
The geometry, node locations, and coordinate system for this element are shown in Figure 214.1: "COMBI214 Geometry". The element is defined by two nodes. It has stiffness characteristics K11, K22, K12 and K21 and damping characteristics C11, C22, C12 and C21. The stiffness coefficients should have units of Force/Length, and the damping coefficient units are Force*Time/Length. (The damping capability is not used for static or undamped modal analyses.)

The third node is for orientation and applies to nonlinear analyses only.

For stiffness and damping real constants, either numerical values or tabular array inputs can be specified. If specifying tabular inputs, enclose the table name within “%” characters (%tabname%). These real constants can vary with the amplitude of the rotational velocity vector (defined via the OMEGA or CMOMEGA command). Use the *DIM command and the primary variable OMEGS to dimension the table and identify the variable. Because the amplitude o

f the rotational velocity vector is an absolute value, only positive values of OMEGS in the table parameter are valid. For more information about using tabular inputs, see Array Parameters in the ANSYS APDL Programmer's Guide, Applying Loads Using TABLE Type Array Parameters in the ANSYS Basic Analysis Guide, and Performing a Thermal Analysis Using Tabular Boundary Conditions in the ANSYS Thermal Analysis Guide.

KEYOPT(2) = 0 through 2 options define the element plane. The element operates in the nodal coordinate system.

The KEYOPT(3) = 0 and 1 options specify whether or not the element is symmetric. When symmetric, cross-coupling terms in stiffness and damping coefficients are equal (that is, K12 = K21 and C12 = C21).

A summary of the element input is given in "COMBI214 Input Summary". A general description of element input is given in Element Input.

COMBI214 Input Summary
Nodes
I, J, K (The K orientation node is optional and for nonlinear analyses only.)

Degrees of Freedom
UX, UY (KEYOPT (2) = 0)
UY, UZ (KEYOPT (2) = 1)
UX, UZ (KEYOPT (2) = 2)

Real Constants
K11, K22, K12, K21 , C11, C22, C12, C21
Kij - (i=1,2 j=1,2) Stiffness coefficients
Cij - (i=1,2 j=1,2) Damping coefficients

Note
Real constants may be defined as table parameters as a function of omega (using primary variable OMEGS).

Material Properties
None

Surface Loads
None

Body Loads
None

Special Features
Stress stiffening

Large deflections

Birth and death

KEYOPT(2)
Degrees of freedom selection:

0 --
Element lies in a plane parallel to the XY plane. The degrees of freedom are UX and UY. This value option is the default.

1 --
Element lies in a plane parallel to the YZ plane. The degrees of freedom are UY and UZ.

2 --
Element lies in a plane parallel to the XZ plane. The degrees of freedom are UX and UZ.

KEYOPT(3)
Symmetry:

0 --
Element is symmetric: K12 = K21 and C12 = C21. This option is the default.

1 --
Element is not symmetric.

COMBI214 Output Data
The solution output associated with the element is in two forms:

Nodal displacements included in the overall nodal solution

Additional element output as shown in Table 214.1: "COMBI214 Element Output Definitions".

The Element Output Definitions table uses the following notation:

(1) and (2) indicate the first and second axis of the element plane defined by KEYOPT(2). For example, if KEYOPT(2) equals 0, then (1) is the X axis and (2) is the Y axis.

A colon (:) in the Name column indicates 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 a - indicates that the item is not avail

able.

Table 214.1 COMBI214 Element Output Definitions

Name Definition O R
EL Element Number Y Y
NODES Nodes - I, J Y Y
XC, YC, ZC Location where results are reported Y 1
FORC1 Spring force along (1) Y Y
FORC2 Spring force along (2) Y Y
STRETCH1 Stretch of spring along (1) Y Y
STRETCH2 Stretch of spring along (2) Y Y
VELOCITY1 Velocity along (1) - Y
VELOCITY2 Velocity along (2) - Y
DAMPING FORCE1 Damping force along (1) -- Zero unless this is a transient analysis (ANTYPE,TRANS) and damping is present Y Y
DAMPING FORCE2 Damping force along (2) -- Zero unless this is a transient analysis (ANTYPE,TRANS) and damping is present Y Y

Available only at centroid as a *GET item.

Table 214.2: "COMBI214 Item and Sequence Numbers" lists output available via the ETABLE command using the Sequence Number method. See Chapter 5: "The General Postprocessor (POST1)" in the ANSYS Basic Analysis Guide and The Item and Sequence Number Table in this document for more information. The following notation is used in Table 214.2: "COMBI214 Item and Sequence Numbers":

Name
Output quantity as defined in Table 214.1: "COMBI214 Element Output Definitions"

Item
Predetermined Item label for the ETABLE command

E
Sequence number for single-valued or constant element data


Output data for COMBI214 consists of the following:

Table 214.2 COMBI214 Item and Sequence Numbers

Output Quantity Name ETABLE and ESOL Command Input
Item E
FORC1 SMISC 1
FORC2 SMISC 2
STRETCH1 NMISC 1
STRETCH2 NMISC 2
VELOCITY1 NMISC 3
VELOCITY2 NMISC 4
DAMPING FORCE1 NMISC 5
DAMPING FORCE2 NMISC 6

COMBI214 Assumptions and Restrictions
Nodes must lie in the plane defined by KEYOPT(2).

The following applies to a nonlinear analysis:

-- The orientation node K is required.

-- The length of the spring-damper element must not be zero (that is, nodes I, J and K should not be coincident because the node locations determine the spring orientation).

Line (IJ) must be parallel to (1). Line (JK) must be parallel to (2).

The element allows only a uniform stress in the springs.

The following applies when KEYOPT(3) = 0 (symmetric):

-- If K12 is non-zero and K21 is zero, then K21 is set to K12.

-- If C12 is non-zero and C21 is zero, then C21 is set to C12.

The spring or the damping capability may be deleted from the element by setting all Kij (i=1,2 j=1,2) or all Cij (i=1,2 j=1,2) equal to zero, respectively.

The degrees of freedom are specified in the nodal coordinate system and are the same for both nodes. (For more information, see Elements that Operate in the Nodal Coordinate System.) If the nodal coordinate systems are rotated relative to each other, the same degree of freedom may be in different directions (thereby giving possibly unexpected results).

No moment effects are included; that is, if the nodes are offset from the lines of action, moment equilibrium may not be satisfied.

The element is defi

ned such that a positive displacement of node J relative to node I tends to stretch the spring. If, for a given set of conditions, nodes I and J are interchanged, a positive displacement of node J relative to node I tends to compress the spring.

COMBI214 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 Professional. Structural Analysis:


No damping capability; Cij (i=1,2 j=1,2) are not allowed.

Only stress stiffening and large deflections are allowed.