MPC184 Spherical Joint Element Description

The MPC184 spherical joint element is a two-node element with the relative displacement degrees of freedom constrained. The relative rotational degrees of freedom are left unconstrained. These rotations cannot be controlled. The kinematic constraints are imposed using the Lagrange multiplier method.

Figure 184sphe.1:  MPC184 Spherical Joint Geometry

MPC184 Spherical Joint Input Data

Set KEYOPT(1) = 15 to define a two-node spherical joint element.

Figure 184sphe.1: MPC184 Spherical Joint Geometry shows the geometry and node locations for this element. Two nodes define the element. The two nodes (I and J) are expected to have identical spatial locations initially. If the two nodes are not coincident, the relative positions of the two nodes are maintained.

A local Cartesian coordinate system should be specified at the first node, I, of the element. The specification of the second local coordinate system at node J is optional. If the local coordinate system is not specified at node J, the local coordinate system at node J is assumed to be the same as that at node I. Use the SECJOINT command to specify the identifiers of the local coordinate systems.

The constraints imposed in a spherical joint element are described below. Referring to Figure 184sphe.1: MPC184 Spherical Joint Geometry, the constraints imposed at any given time are as follows:

For output purposes, the relative rotations between nodes I and J are characterized by the Cardan (or Bryant) angles as follows:

Since the output of relative rotations is characterized by the Cardan (or Bryant) angles, the rotation around the local e₂ axis is limited to between -PI/2 to +PI/2 (see the expression for Φ above). When this rotation value reaches |PI/2|, the other two angles become indeterminate. Therefore, if the accumulated angles around an axis of rotation is greater than |PI/2|, the axis of rotation should typically be specified as the local e₁ or e₃ axis.

Since the relative rotational degrees of freedom cannot be controlled, the spherical joint element does not allow stops and locks or material behavior specifications. Other input data that are common to all joint elements are described in "Joint Input Data" in the MPC184 element description.

MPC184 Spherical Joint Output Data

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

These tables use the following notation:

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 available.

The following table shows additional non-summable miscellaneous (NMISC) output available for the spherical joint element.

Table 184sphe.3: MPC184 Spherical Joint Item and Sequence Numbers -SMISC Items and Table 184sphe.4: MPC184 Spherical Joint Item and Sequence Numbers - NMISC Items list output available via 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 for further information. The table uses the following notation:

MPC184 Spherical Joint Assumptions and Restrictions

MPC184 Spherical Joint 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