MPC184-General

Multipoint Constraint Element: General Joint

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## 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.

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:

 KEYOPT(4) = 0 (default) - both displacement and rotational degrees of freedom are activated. KEYOPT(4) = 1 - only displacement degrees of freedom are activated.

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 Input Summary

This input summary applies to the general joint element option of MPC184: KEYOPT(1) = 16.

Nodes

I, J

Note:  For a grounded joint element, specify either node I or node J in the element definition and leave the other node (the grounded node) blank.

Degrees of Freedom

UX, UY, UZ, ROTX, ROTY, ROTZ (KEYOPT(4) = 0)

UX, UY, UZ (KEYOPT(4) = 1)

Real Constants

None

Material Properties

Use the JOIN label on the TB command to define stiffness and damping behavior. (See MPC184 Joint in the Material Reference for detailed information on defining joint materials.)

None

Temperatures --

T(I), T(J)

For an unconstrained general joint:

Displacement (KEYOPT(4) = 0 or 1) --

UX, UY, UZ

Rotation (KEYOPT(4) = 0) --

ROTX, ROTY, ROTZ

For a constrained general joint, loads are based on the free relative degrees of freedom in the joint.

Special Features
 Large deflection Linear perturbation
KEYOPT(1)

Element behavior:

16  --

General joint element

KEYOPT(4)

Element configuration:

0  --

General joint with both displacement and rotational degrees of freedom activated.

1  --

General joint with only displacement degrees of freedom activated.

## 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.

Table 184gen.1:  MPC184 General Joint Element Output Definitions

NameDefinitionOR
General joint with displacement and rotation DOF (KEYOPT(4) = 0)
ELElement number-Y
NODESElement node numbers (I, J)-Y
The constraint force and moment output depends on which of the relative DOFs are constrained.
FXConstraint force in X direction-Y
FYConstraint force in Y direction-Y
FZConstraint force in Z direction-Y
MXConstraint moment in X direction-Y
MYConstraint moment in Y direction-Y
MZConstraint moment in Z direction-Y
The following output depends on which of the relative DOFs are unconstrained.
CSTOP1-6Constraint force/moment if stop is specified on DOFs 1-6-Y
CLOCK1-6Constraint force/moment if lock is specified on DOFs 1-6-Y
CSST1-6Constraint stop status on relative DOFs 1-6[1]-Y
CLST1-6Constraint lock status on relative DOFs 1-6[2]-Y
JRP1-6Joint relative position of DOFs 1-6-Y
JCD1-6Joint constitutive displacement/rotation of DOFs 1-6-Y
JEF1-6Joint elastic force/moment 1-6-Y
JDF1-6Joint damping force/moment 1-6-Y
JRU1-6Joint relative displacement/rotation 1-6-Y
JRV1-6Joint relative velocity (or rotational velocity) 1-6-Y
JRA1-6Joint relative acceleration (or rotational acceleration) 1-6-Y
JTEMPAverage temperature in the element[3]-Y
General joint with displacement DOF (KEYOPT(4) =1)
ELElement number-Y
NODESElement node numbers (I, J)-Y
The constraint force and moment output depends on which of the relative DOFs are constrained.
FXConstraint force in X direction-Y
FYConstraint force in Y direction-Y
FZConstraint force in Z direction-Y
The following output depends on which of the relative DOFs are unconstrained.
CSTOP1-3Constraint force if stop is specified on DOFs 1-3-Y
CLOCK1-3Constraint force if lock is specified on DOFs 1-3-Y
CSST1-3Constraint stop status on relative DOFs 1-3[1]-Y
CLST1-3Constraint lock status on relative DOFs 1-3[2]-Y
JRP1-3Joint relative position of DOFs 1-3-Y
JCD1-3Joint constitutive displacement of DOFs 1-3-Y
JEF1-3Joint elastic force 1-3-Y
JDF1-3Joint damping force 1-3-Y
JRU1-3Joint relative displacement 1-3-Y
JRV1-3Joint relative velocity 1-3-Y
JRA1-3Joint relative acceleration 1-3-Y
JTEMPAverage temperature in the element[3]-Y

1. Constraint stop status:

 0 = stop not active, or deactivated 1 = stopped at minimum value 2 = stopped at maximum value
2. Constraint lock status:

 0 = lock not active 1 = locked at minimum value 2 = locked at maximum value
3. Average temperature in the element when temperatures are applied on the nodes of the element using the BF command, or when temperature are applied on the element using the BFE command.

The following table shows additional non-summable miscellaneous (NMISC) output available for all forms of the general joint element.

Note:  This output is intended for use in the ANSYS Workbench program to track the evolution of local coordinate systems specified at the nodes of joint elements.

Table 184gen.2:  MPC184 General Joint Element - NMISC Output

NameDefinitionOR
The following output is available for all general joint elements (KEYOPT(4) = 0 and 1)
E1X-I, E1Y-I, E1Z-IX, Y, Z components of the evolved e1 axis at node I-Y
E2X-I, E2Y-I, E2Z-IX, Y, Z components of the evolved e2 axis at node I-Y
E3X-I, E3Y-I, E3Z-IX, Y, Z components of the evolved e3 axis at node I-Y
E1X-J, E1Y-J, E1Z-JX, Y, Z components of the evolved e1 axis at node J-Y
E2X-J, E2Y-J, E2Z-JX, Y, Z components of the evolved e2 axis at node J-Y
E3X-J, E3Y-J, E3Z-JX, Y, Z components of the evolved e3 axis at node J-Y
JFX, JFY, JFZConstraint forces expressed in the evolved coordinate system specified at node I-Y
JMX, JMY, JMZConstraint moments expressed in the evolved coordinate system specified at node I-Y

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:

Name

output quantity as defined in the Element Output Definitions table.

Item

predetermined Item label for ETABLE command

E

sequence number for single-valued or constant element data

Table 184gen.3:  MPC184 General Joint Item and Sequence Numbers - SMISC Items

Output Quantity Name ETABLE and ESOL Command Input
ItemE

General joint with displacement and rotation DOF (KEYOPT(4) = 0)
(Some of these values may be zero depending on which relative degrees of freedom are constrained.)

FXSMISC1
FYSMISC2
FZSMISC3
MXSMISC4
MYSMISC5
MZSMISC6
CSTOP1-6SMISC7-12
CLOCK1-6SMISC13-18
CSST1-6SMISC19-24
CLST1-6SMISC25-30
JRP1-6SMISC31-36
JCD1-6SMISC37-42
JEF1-6SMISC43-48
JDF1-6SMISC49-54
JRU1-6SMISC61-66
JRV1-6SMISC67-72
JRA1-6SMISC73-78
JTEMPSMISC79

General joint with displacement DOF (KEYOPT(4) = 1)
(Some of these values may be zero depending on which relative degrees of freedom are constrained.)

FXSMISC1
FYSMISC2
FZSMISC3
CSTOP1-3SMISC7-9
CLOCK1-3SMISC13-15
CSST1-3SMISC19–21
CLST1-3SMISC25-27
JRP1-3SMISC31-33
JCD1-3SMISC37-39
JEF1-3SMISC43-45
JDF1-3SMISC49-51
JRU1-3SMISC61-63
JRV1-3SMISC67-69
JRA1-3SMISC73-78
JTEMPSMISC79

Table 184gen.4:  MPC184 General Joint Item and Sequence Numbers - NMISC Items

Output Quantity Name ETABLE and ESOL Command Input
ItemE
The following output is available for all general joint elements (KEYOPT(4) = 0 and 1)
E1X-INMISC1
E1Y-INMISC2
E1Z-INMISC3
E2X-INMISC4
E2Y-INMISC5
E2Z-INMISC6
E3X-INMISC7
E3Y-INMISC8
E3Z-INMISC9
E1X-JNMISC10
E1Y-JNMISC11
E1Z-JNMISC12
E2X-JNMISC13
E2Y-JNMISC14
E2Z-JNMISC15
E3X-JNMISC16
E3Y-JNMISC17
E3Z-JNMISC18
JFXNMISC19
JFYNMISC20
JFZNMISC21
JMXNMISC22
JMYNMISC23
JMZNMISC24

## MPC184 General Joint Assumptions and Restrictions

• Boundary conditions cannot be applied on the nodes forming the general joint.

• Rotational degrees of freedom are activated at the nodes forming the element. When these elements are used in conjunction with solid elements, the rotational degrees of freedom must be suitably constrained. Since boundary conditions cannot be applied to the nodes of the general joint, a beam or shell element with very weak stiffness may be used with the underlying solid elements at the nodes forming the joint element to avoid any rigid body modes.

• If both stops and locks are specified, then lock specification takes precedence. That is, if the degree of freedom is locked at a given value, then it will remain locked for the rest of the analysis.

• In a nonlinear analysis, the components of relative motion are accumulated over all the substeps. It is essential that the substep size be restricted such that these rotations in a given substep are less than π for the values to be accumulated correctly.

• The element currently does not support birth or death options.

• The equation solver (EQSLV) must be the sparse solver or the PCG solver. The command PCGOPT,,,,,,,ON is also required in order to use the PCG solver.

• The element coordinate system (/PSYMB,ESYS) is not relevant.

## MPC184 General 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

• Linear perturbation is not available.