MPC184 Genc Joint Element Description

The MPC184 Genc joint is a two-node element. The relative rotations in this element are characterized by the rotation vector. By default, no relative degrees of freedom (DOFs) are fixed. However, you can specify as many relative DOFs to be constrained as needed to simulate different joint behaviors.

If the relative rotations need to be parametrized for joint type behavior, use the other MPC184 joint elements (for example, MPC184-General or MPC184-Genb).

Figure 184genc.1: MPC184 Genc Joint Geometry

By default, both displacement and rotational DOFs are activated at the nodes of the element. If only displacement DOFs are required, such as in a model that has only continuum elements, set KEYOPT(4) = 1.

The rotation vector is defined as the vector that positions the local axes at node J with respect to the local axes at node I under a finite rotation. Let and be the local bases at nodes I and J, respectively. Then, is a rotation vector that positions with respect to as:

for = 1,2,3 and is the skew symmetric matrix of the rotation vector.

MPC184 Genc Joint Input Data

Set KEYOPT(1) = 20 to define a two-node Genc joint element.

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

For this element, you can specify which relative DOFs 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 you must issue the SECJOINT command twice to constrain some DOFs. The first SECJOINT command defines the local coordinate systems for the joint. The second SECJOINT command specifies up to six relative DOFs. The Genc joint element allows you to simulate joint behavior.

When KEYOPT(4) = 1, the local coordinate systems specified at nodes I and J remain fixed in their initial orientation, and any rotation at the nodes 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 Genc 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 components of the rotation axis.

The relative displacements and rotations are suitably constrained when some or all the relative DOFs are fixed.

For an unconstrained Genc joint, the constitutive calculations use the following equations for the relative displacement:

where:

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

The following equations are used to define relative rotations:

where:

, , and are the calculated current rotation angles, and

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

MPC184 Genc Joint Output Data

The solution output associated with the element has 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 Genc joint element.

Table 184genc.3: MPC184 Genc Joint Item and Sequence Numbers - SMISC Items and Table 184genc.4: MPC184 Genc 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 Genc Assumptions and Restrictions

MPC184 Genc Joint Product Restrictions

None.