JOINTG (Connectors)

The various joints identified by the JTYPE field require certain corresponding coordinate system rules.

Note: The OptiStruct joints defined using JOINTG are different from the Multibody Dynamics (OS-MBD) joints which are defined using the JOINT entry with OptiStruct-MotionSolve integration.

Universal Joint

A Universal Joint is a joint which allows rotary motion transmission in multiple shafts which are at an angle to each other (for example, in a powertrain drive shaft). The joint works by allowing free rotation along two mutually perpendicular degrees of freedom of the two grid points associated with the joint. The remaining rotational degrees of freedom are automatically constrained. The translational degrees of freedom can be constrained by defining an additional Ball joint.

On the JOINTG entry, follow these rules to define a universal joint:
  1. JTYPE should be set to UNIVERSA.
  2. The X-axis of the coordinate system (CID1) of Grid Point 1 should be mutually perpendicular to the Z-axis of coordinate system (CID2) of Grid Point 2.
  3. The Y-axes of coordinate systems 1 and 2 should be along the corresponding shaft axes. Additionally, they should point in the same direction (should not point opposite to one another).
  4. The translational degrees of freedom can be constrained by defining an additional Ball joint.


Figure 1.

Revolute Joint

A Revolute Joint is a joint which allows single axis rotation functions (for example, in a door hinge). The joint works by allowing free rotation (or enforced displacement via MOTNJG) about one degree of freedom of the two grid points associated with the joint (the two selected degrees of freedom should be the same). The remaining rotational degrees of freedom are automatically constrained. The translational degrees of freedom can be constrained by defining an additional Ball joint.

On the JOINTG entry, follow these rules to define a revolute joint:
  1. JTYPE should be set to REVOLUTE.
  2. The X-axis of the coordinate system (CID1) of Grid Point 1 should be parallel (and in the same direction) to the X-axis of coordinate system (CID2) of Grid Point 2. The MOTNJG Subcase Information and Bulk Data Entries can be used to define the value of rotation (dof=4) about the X-axis.
  3. The other axes of the coordinate system may point in any direction.
  4. The translational degrees of freedom can be constrained by defining an additional Ball joint.


Figure 2.

Ball Joint

A Ball Joint is a joint which allows free rotation in all three directions and translations are constrained in all three directions (for example, in automobile steering and suspension systems). The joint works by allowing free rotation about all three degrees of freedom of the two grid points associated with the joint. The remaining translational degrees of freedom are constrained. For BALL joint, there is no relative translation between the two degrees of freedom in the basic system. Local systems should not be defined for the BALL joint and will not be used if specified.

On the JOINTG entry, follow these rules to define a ball joint.
  1. JTYPE should be set to BALL.
  2. Only the grid points GID1 and GID2 should be specified. The coordinate systems are not required.
  3. The grid points GID1 and GID2 should be coincident to simulate physical joints. If they are not, then the specified joint may deviate from expected behavior.


    Figure 3.

Axial Joint

An Axial Joint is a joint which allows connection between two grid points by enforcing relative displacement along the line joining them. The relative displacement is enforced only along the line connecting the two grid points, and other degrees of freedom are not constrained by this joint.

On the JOINTG entry, follow these rules to define an axial joint.
  1. JTYPE should be set to AXIAL.
  2. Only the grid points GID1 and GID2 should be specified. The coordinate systems are not required and will be ignored if specified.
  3. The MOTNJG Bulk Data Entry should be used to identify the value of the enforced relative displacement via the VALUE field ( u r e l ). The MOTNJG Subcase Information Entry can then be used to identify the corresponding MOTNJG Bulk Data Entries.
  4. To hold the value of the relative displacement from the previous subcase in the subsequent nonlinear subcase (via CNTNLSUB), the VALUE field can be set to FIXED on the MOTNJG Bulk Data Entry. Alternatively, a different value of relative motion can be specified for the continuing subcase.


Figure 4.

Cartesian Joint

A Cartesian Joint allows connection between two grid points by enforcing relative displacement along three directions (1,2,3) of a local Cartesian coordinate system CID1 defined on GID1. The other degrees of freedom are not constrained by this joint.

On the JOINTG entry, follow these rules to define a Cartesian joint.
  1. JTYPE should be set to CARTES.
  2. The grid points GID1 and GID2 should be specified. The coordinate system CID1 on GID1 is required. CID2 is not required and will be ignored if specified.
  3. The MOTNJG Bulk Data Entry should be used to identify the value of the enforced relative displacement via the VALUE fields corresponding to the 1, 2, and 3 degrees of freedom. The MOTNJG Subcase Information Entry can then be used to identify the corresponding MOTNJG Bulk Data Entries.
  4. To hold the value of the relative displacement from the previous subcase in the subsequent nonlinear subcase (via CNTNLSUB), the VALUE field can be set to FIXED on the MOTNJG Bulk Data Entry. Alternatively, a different value of relative motion can be specified for the continuing subcase.

Cardan Joint

A Cardan Joint allows connection between two grid points by enforcing relative rotation along three directions (4,5,6). Three successive rotations are performed based on the Cardan angles that correspond to the local coordinate system directions at GID1 and GID2. The other degrees of freedom are not constrained by this joint.

On the JOINTG entry, follow these rules to define a Cardan joint.
  1. JTYPE should be set to CARDAN.
  2. The grid points GID1 and GID2 should be specified. The coordinate system CID1 is required. CID2 is not required and will be ignored if specified.
  3. The MOTNJG Bulk Data Entry should be used to identify the value of the Cardan angles via the VALUE fields corresponding to the 4, 5, and 6 degrees of freedom. The MOTNJG Subcase Information Entry can then be used to identify the corresponding MOTNJG Bulk Data Entries.
  4. To hold the value of the relative displacement from the previous subcase in the subsequent nonlinear subcase (via CNTNLSUB), the VALUE field can be set to FIXED on the MOTNJG Bulk Data Entry. Alternatively, a different value of relative motion can be specified for the continuing subcase.

In-Plane Joint

An in-plane joint allows connection between two grid points by enforcing zero relative displacement along direction 1 of a local Cartesian coordinate system CID1 defined on GID1. Additionally, enforced relative displacement is applied in the 2 and 3 directions of CID1. The other degrees of freedom are not constrained by this joint.

On the JOINTG entry, follow these rules to define a In-Plane joint.
  1. JTYPE should be set to INPLANE.
  2. The grid points GID1 and GID2 should be specified. The coordinate system CID1 on GID1 is required. CID2 is not required and will be ignored if specified.
  3. The MOTNJG Bulk Data Entry should be used to identify the value of the enforced relative displacement via the VALUE fields corresponding to the 2, and 3 degrees of freedom. The MOTNJG Subcase Information Entry can then be used to identify the corresponding MOTNJG Bulk Data Entries.
  4. To hold the value of the relative displacement from the previous subcase in the subsequent nonlinear subcase (via CNTNLSUB), the VALUE field can be set to FIXED on the MOTNJG Bulk Data Entry. Alternatively, a different value of relative motion can be specified for the continuing subcase.

In-Line Joint

An in-line joint allows connection between two grid points by enforcing zero relative displacement along directions 2 and 3 of a local Cartesian coordinate system CID1 defined on GID1. Additionally, enforced relative displacement is applied in the 1 direction of CID1. The other degrees of freedom are not constrained by this joint.

On the JOINTG entry, follow these rules to define a In-Line joint.
  1. JTYPE should be set to INLINE.
  2. The grid points GID1 and GID2 should be specified. The coordinate system CID1 on GID1 is required. CID2 is not required and will be ignored if specified.
  3. The MOTNJG Bulk Data Entry should be used to identify the value of the enforced relative displacement via the VALUE field corresponding to the 1 degree of freedom. The MOTNJG Subcase Information Entry can then be used to identify the corresponding MOTNJG Bulk Data Entries.
  4. To hold the value of the relative displacement from the previous subcase in the subsequent nonlinear subcase (via CNTNLSUB), the VALUE field can be set to FIXED on the MOTNJG Bulk Data Entry. Alternatively, a different value of relative motion can be specified for the continuing subcase.

Orient Joint

An Orient joint allows connection between two grid points by enforcing zero relative rotations along directions 4, 5, and 6 of two local Cartesian coordinate systems CID1 and CID2. The other degrees of freedom are not constrained by this joint.

On the JOINTG entry, follow these rules to define an Orient joint.
  1. JTYPE should be set to ORIENT.
  2. The grid points GID1 and GID2 should be specified. The coordinate systems CID1 and CID2 are required.

Hinge Joint

A Hinge joint allows connection between two grid points by enforcing zero relative translations along directions 1, 2, and 3 of two local Cartesian coordinate systems CID1 and CID2. Additionally, the relative rotations in 5 and 6 are also constrained. Only degree of freedom 4 is not constrained by this joint. The joint works by allowing free rotation in degree of freedom 4 of the two grid points associated with the joint (the two X axes of both CID1 and CID2 should match for this joint).

Therefore, on the JOINTG entry, the following rules should be followed to define a Hinge joint:
  1. JTYPE should be set to HINGE.
  2. The grid points GID1 and GID2 should be specified. The coordinate systems CID1 and CID2 are required.
  3. The X-axes of both CID1 and CID2 should match.
  4. The Hinge joint is equivalent to a combination of Revolute joint and Rigid Pin joint.

Rigid Pin Joint

A Rigid Pin joint allows connection between two grid points by enforcing zero relative translations along directions 1, 2, and 3 of a local Cartesian coordinate system CID1 defined on grid GID1. The joint works by allowing free rotation in degrees of freedom 4, 5 and 6 of the two grid points associated with the joint. For RPIN joint, there is no relative translation between the grids in the local system defined on CID1 (this is where RPIN differs from BALL joint). Note that for any local system defined on a grid for the joints, the local systems move/rotate along with the grids on which they are defined. Therefore, even though from the perspective of the basic system, there may seem to be relative translation between the grids in RPIN joint, there will not be any relative translation between the grids in the local CID1 which moves/rotates with grid GID1.

Therefore, on the JOINTG entry, the following rules should be followed to define a Rigid Pin joint:
  1. JTYPE should be set to RPIN.
  2. The grid points GID1 and GID2 should be specified. The coordinate systems CID1 is required and CID2 should not be specified. CID2 will be ignored if defined.

Rigid Link Joint

A Rigid Link joint allows connection between two grid points by enforcing zero relative translations along direction 1 of the basic coordinate system. The joint does not constrain degrees of freedom 2, 3, 4, 5 and 6 of the two grid points associated with the joint. For RLINK joint, there is no relative translation between the grids in direction 1 in the basic system.
Note: No local coordinate systems are required for the Rigid Link joint.
Therefore, on the JOINTG entry, the following rules should be followed to define a Rigid Link joint.
  1. JTYPE should be set to RLINK.
  2. The grid points GID1 and GID2 should be specified. The coordinate systems CID1 and CID2 should not be specified and will be ignored if defined.

Rigid Beam Joint

A Rigid Beam joint allows connection between two grid points by enforcing zero relative translations along directions 1, 2, and 3 of a local default basic coordinate system on grid GID1. Additionally, zero relative rotations along directions 4, 5, and 6 of two local basic coordinate systems on GID1 and GID2.
Note: No local coordinate systems are required for the Rigid Beam joint, and default local basic systems are used at the two grid points.
Therefore, on the JOINTG entry, the following rules should be followed to define a Rigid Beam joint.
  1. JTYPE should be set to RBEAM.
  2. The grid points GID1 and GID2 should be specified.
  3. By default, CID1 and CID2 are defined as the basic coordinate system and the results are output in the basic coordinate system.

    If a local coordinate system is assigned to these fields, the results are output in the local coordinate system.

  4. The Rigid Beam joint is equivalent to a combination of Rigid Pin joint and Orient joint.

Universal Connection with Rigid Pin Joint

A Universal connection with Rigid Pin Joint allows connection between two grid points by allowing free rotation along two mutually perpendicular degrees of freedom of the two grid points associated with the joint. The remaining rotational degrees of freedom are automatically constrained by enforcing zero relative translations along directions 1, 2, and 3 of a local default basic coordinate system on grid GID1. Additionally, zero relative rotations along directions 4, 5, and 6 of two local coordinate systems, CID1 and CID2, on GID1 and GID2.
Note: Both local coordinate systems are required for this joint.
Therefore, on the JOINTG entry, the following rules should be followed to define a UJOINT joint:
  1. JTYPE should be set to UJOINT.
  2. The X-axis of the coordinate system (CID1) of Grid Point 1 should be mutually perpendicular to the Z-axis of coordinate system (CID2) of Grid Point 2.
  3. The Y-axes of coordinate systems 1 and 2 should be along the corresponding shaft axes. Additionally, they should point in the same direction (should not point opposite to one another).
  4. The grid points GID1 and GID2 should be specified. The coordinate systems CID1 and CID2 should not be specified and will be ignored if defined.

The UJOINT joint is equivalent to a combination of Rigid Pin joint and Universal joint.

Cylindrical Joint

A Cylindrical joint allows connection between two grid points by enforcing zero relative displacement along directions 2 and 3 of a local Cartesian coordinate system CID1 defined on GID1. Additionally, free translation (or enforced relative displacement via MOTNJG) is allowed in the 1 direction of CID1, and free rotation (or enforced displacement via MOTNJG) is allowed about degree of freedom 4 of both CID1 and CID2.
Note: Both local coordinate systems are required for the Cylindrical joint and the degree of freedom 1 should match for both systems.
Therefore, on the JOINTG entry, the following rules should be followed to define a Cylindrical joint:
  1. JTYPE should be set to CYLINDRI.
  2. The grid points GID1 and GID2 should be specified. The coordinate systems CID1 and CID2 should not be specified and will be ignored if defined.

The Cylindrical joint is equivalent to a combination of In-Line joint and Revolute joint.

Translator Joint

A Translator joint allows connection between two grid points by enforcing zero relative displacement along directions 2 and 3 of a local Cartesian coordinate system CID1 defined on GID1. Additionally, free translation (or enforced relative displacement via MOTNJG) is allowed in the 1 direction of CID1, and, zero relative rotations along directions 4, 5, and 6 of two local coordinate systems CID1 and CID2 on GID1 and GID2.
Note: Both local coordinate systems are required for the Translator joint.
Therefore, on the JOINTG entry, the following rules should be followed to define a Translator joint:
  1. JTYPE should be set to TRANSLAT.
  2. The grid points GID1 and GID2 should be specified. The coordinate systems CID1 and CID2 should not be specified and will be ignored if defined.

The Translator joint is equivalent to a combination of In-Line joint and Orient joint.