MPC184 Genb Joint Element Description

The MPC184 Genb joint is a two-node element. This element's relative rotations are defined by the 3-1-3 Euler angles. 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.

Figure 184genb.1: MPC184 Genb 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 3-1-3 Euler angles rotate the local coordinate system given at node I to the local coordinate system at node J through a series of rotations around the local axes. An initial rotation of around local coordinate gives rise to an intermediate coordinate system. In this intermediate system, a rotation of is imposed on the local X axis of this intermediate system. Lastly, a final rotation of is imposed on the axis yielding the final local coordinate system at node J. These local coordinate axes in the initial, intermediate, and the final system are referred to as the first local Z direction, intermediate X direction and final Z direction.

MPC184 Genb Joint Input Data

Set KEYOPT(1) = 19 to define a two-node Genb 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.

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 Genb 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 3-1-3 Euler angles as follows (only if KEYOPT(4) = 0):

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

Note that the relative angular positions for the Genb joint are characterized by the 3-1-3 Euler angles. This requires that the rotations about the local axis be restricted between –π to +π. Thus, the local axis should not be used to simulate the axis of rotation. When defining the local coordinate systems in the joint, ensure that the and axes do not align.

For an unconstrained Genb joint, the calculations use the following constitutive 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 = reference angle specifications, angle1, angle2, angle3 on the SECDATA command.

MPC184 Genb Joint Output Data

The solution output associated with the element has two forms:

Genb joint rotational output quantities are always represented in the following sequence: 4 = first local Z direction, 5 = intermediate X direction, 6 = final Z direction.

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 Genb joint element.

Table 184genb.3: MPC184 Genb Joint Item and Sequence Numbers - SMISC Items and Table 184genb.2: MPC184 Genb Joint Element - NMISC Output 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:

Table 184genb.3: MPC184 Genb Joint Item and Sequence Numbers - SMISC Items lists 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 Genb Assumptions and Restrictions

MPC184 Rigid Link/Beam Product Restrictions

None.