MPC184 General Joint Element Description

The MPC184 general joint is a two-node element. By default, no relative degrees of freedom are fixed. However, you can specify which relative degrees of freedom need to be constrained. By specifying as many relative degrees of freedom to be constrained as needed, you can simulate different joint elements.

Figure 184gen.1: MPC184 General Joint Geometry

By default, a general joint has both displacement and rotational degrees of freedom activated at the nodes of the element. In some cases only displacement degrees of freedom are needed (as in a model consisting of only continuum elements). In such cases, you can specify a general joint with only displacement degrees of freedom activated by setting KEYOPT(4) = 1.

MPC184 General Joint Input Data

Set KEYOPT(1) = 16 to define a two-node general joint element.

Use KEYOPT(4) to specify the active degree-of-freedom set:

For this element, you can specify which relative degrees of freedom need to be constrained. First, define the section type (SECTYPE command) for this joint. Then define the SECJOINT command as follows:

SECJ,LSYS,local cs1,local cs2  ! Defines the local coordinate systems for the joints.
SECJ,RDOF,dof1,dof2,…,dof6   ! Defines the relative DOFs to be constrained.

Note that the SECJOINT command is issued twice when the general joint is used with some degrees of freedom constrained. The first SECJOINT command defines the local coordinate systems for the joint. In the second SECJOINT command, specify as many relative degrees of freedom as needed (a maximum of 6 may be specified). The general joint element allows you to simulate different joint elements by specifying different relative degrees of freedom to be constrained. The following examples highlight the different joint elements that can be simulated:

SECJ,RDOF,dof1,dof2,dof3,dof5,dof6  ! Simulates a revolute joint with local e_1 axis as the axis of revolute.

SECJ,RDOF,dof2,dof3,dof5,dof6   ! Simulates a cylindrical joint with local e_1 axis as the axis of rotation.

SECJ,RDOF,dof1,dof2,dof3,dof4,dof5,dof6   ! Simulates a weld joint.

When KEYOPT(4) = 1, the local coordinate systems specified at nodes I and J remain fixed in their initial orientation. The rotation at the nodes, if any, is ignored.

When KEYOPT(4) = 0, the local coordinate systems specified at nodes I and J are assumed to evolve with the rotations at the nodes.

For an unconstrained general joint (KEYOPT(4) = 0 or 1), the relative displacements between nodes I and J are as follows:

The relative rotations between nodes I and J are characterized by the Cardan (or Bryant) angles as follows (only if KEYOPT(4) = 0):

The relative displacements and rotations are suitably constrained when some or all of the relative degrees of freedom are fixed.

Note that the relative angular positions for the general joint are characterized by the Cardan (or Bryant) angles. This requires that the rotations about the local e₂ axis be restricted between –PI/2 to +PI/2. Thus, the local e₂ axis should not be used to simulate the axis of rotation.

For an unconstrained general joint, the constitutive calculations use the following definitions for relative displacement:

where:

, , and = reference lengths, length1, length2, and length3, specified on the SECDATA command.

The following definitions are for relative rotations:

where:

, , and = reference angle specifications, angle1, angle2, and angle3 on the SECDATA command.

Other input data that are common to all joint elements (material behavior, stops and limits, locks, etc.) are described in "Joint Input Data" in the MPC184 element description.

MPC184 General 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 all forms of the general joint element.

Table 184gen.3: MPC184 General Joint Item and Sequence Numbers - SMISC Items and Table 184gen.4: MPC184 General 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 tables use the following notation:

MPC184 General Joint Assumptions and Restrictions

MPC184 General Joint Product Restrictions

None.