Multipoint Constraint Element: Screw Joint
The MPC184 screw joint element is a two-node element which is very similar to the cylindrical joint element in construction. Whereas the cylindrical Joint element has two free relative degrees of freedom, the screw Joint has only one. In a screw joint, the “pitch” of the screw relates the relative rotation angle (around the cylindrical or screw axis) to the relative translational displacement along the axis of the screw. All other relative degrees of freedom are fixed.
Set KEYOPT(1) = 17 to define a two-node screw joint element.
Figure 184scr.1: MPC184 Screw Joint Geometry shows the geometry and node locations for this element. Two nodes (I and J) define the element.
A local Cartesian coordinate system must be specified at the first node, I, of the element. The local coordinate system specification at the second node is optional. The local coordinate systems specified at nodes I and J evolve with the rotations at the respective nodes. Use the SECJOINT command to specify the identifiers of the local coordinate systems. The e3 axes of the local coordinate systems specified at the nodes must align to form the axis of the screw joint.
Note that the SECJOINT command is issued twice for the screw joint element. The first SECJOINT command defines the local coordinate systems for the joint. The second SECJOINT command specifies the screw pitch that relates the relative rotation angle to the relative translational displacement along the axis of the screw.
The basic constraints imposed in a screw joint element are described below:
The constraint relating the relative rotational angle to the relative translational displacement along the axis is given by:
where p is the pitch of the screw defined as the ratio of relative axial displacement (length units) to the relative rotation (in radians) , ϕ is defined as:
and ϕ0 is defined in the reference configuration with the same expression given above.
The change in the relative position of the nodes I and J is given by:
and is computed in the reference configuration using the same expression above.
The relative rotation between nodes I and J is given by:
The change in the relative angular position between the two local coordinate systems is given by:
where ϕ 0 is the initial angular offset between the two coordinate systems and m is an integer accounting for multiple rotations about the screw axis.
The constitutive calculations use the following definition of the joint displacement:
|= reference length specified on SECDATA command.|
The constitutive calculations use the following definition of the joint rotation:
|= reference angle, angle3, specified on the SECDATA command. If this value is not specified, then Φ 0 is used in place of|
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.
This input summary applies to the screw joint element option of MPC184: KEYOPT(1) = 17.
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.
UX, UY, UZ, ROTX, ROTY, ROTZ
Use the JOIN label on the TB command to define stiffness and damping. (See MPC184 Joint in the Material Reference for detailed information on defining joint materials.)
Screw joint element
The solution output associated with the element is in two forms:
Nodal displacements included in the overall nodal solution
Additional element output as shown in Table 184scr.1: MPC184 Screw Joint Element Output Definitions and Table 184scr.2: MPC184 Screw Joint Element - NMISC Output.
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 184scr.1: MPC184 Screw Joint Element Output Definitions
|NODES||Element node numbers (I, J)||-||Y|
|FX||Constraint Force in X direction||-||Y|
|FY||Constraint Force in Y direction||-||Y|
|MX||Constraint Moment in X direction||-||Y|
|MY||Constraint Moment in Y direction||-||Y|
|CSTOP3||Constraint force if stop is specified on DOF 3||-||Y|
|CSTOP6||Constraint moment if stop is specified on DOF 6||-||Y|
|CLOCK3||Constraint force if lock is specified on DOF 3||-||Y|
|CLOCK6||Constraint moment if lock is specified on DOF 6||-||Y|
|CSST3||Constraint stop status on DOF 3||-||Y|
|CLST3||Constraint lock status on DOF 3||-||Y|
|CSST6||Constraint stop status on DOF 6||-||Y|
|CLST6||Constraint lock status on DOF 6||-||Y|
|JRP3||Joint relative position of DOF 3||-||Y|
|JRP6||Joint relative position of DOF 6||-||Y|
|JCD3||Joint constitutive displacement on DOF 3||-||Y|
|JCD6||Joint constitutive rotation on DOF 6||-||Y|
|JEF3||Joint elastic force in direction -3||-||Y|
|JEF6||Joint elastic moment in direction -6||-||Y|
|JDF3||Joint damping force in direction -3||-||Y|
|JDF6||Joint damping moment in direction -6||-||Y|
|JRU3||Joint relative displacement of DOF 3||-||Y|
|JRU6||Joint relative rotation of DOF 6||-||Y|
|JRV3||Joint relative velocity of DOF 3||-||Y|
|JRV6||Joint relative rotational velocity of DOF 6||-||Y|
|JRA3||Joint relative acceleration of DOF 3||-||Y|
|JRA6||Joint relative rotational acceleration of DOF 6||-||Y|
|JTEMP||Average temperature in the element||-||Y|
|0 = stop not active, or deactivated|
|1 = stopped at minimum value|
|2 = stopped at maximum value|
|0 = lock not active|
|1 = locked at minimum value|
|2 = locked at maximum value|
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 screw 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 184scr.2: MPC184 Screw Joint Element - NMISC Output
|The following output is available for all screw joint elements (KEYOPT(4) = 0 and 1)|
|E1X-I, E1Y-I, E1Z-I||X, Y, Z components of the evolved e1 axis at node I||-||Y|
|E2X-I, E2Y-I, E2Z-I||X, Y, Z components of the evolved e2 axis at node I||-||Y|
|E3X-I, E3Y-I, E3Z-I||X, Y, Z components of the evolved e3 axis at node I||-||Y|
|E1X-J, E1Y-J, E1Z-J||X, Y, Z components of the evolved e1 axis at node J||-||Y|
|E2X-J, E2Y-J, E2Z-J||X, Y, Z components of the evolved e2 axis at node J||-||Y|
|E3X-J, E3Y-J, E3Z-J||X, Y, Z components of the evolved e3 axis at node J||-||Y|
|JFX, JFY, JFZ||Constraint forces expressed in the evolved coordinate system specified at node I||-||Y|
|JMX, JMY, JMZ||Constraint moments expressed in the evolved coordinate system specified at node I||-||Y|
Table 184scr.3: MPC184 Screw Joint Item and Sequence Numbers - SMISC Items and Table 184scr.4: MPC184 Screw 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 table uses the following notation:
output quantity as defined in the Element Output Definitions table.
predetermined Item label for ETABLE command
sequence number for single-valued or constant element data
Table 184scr.3: MPC184 Screw Joint Item and Sequence Numbers - SMISC Items
|Output Quantity Name||ETABLE and ESOL Command Input|
Table 184scr.4: MPC184 Screw Joint Item and Sequence Numbers - NMISC Items
|Output Quantity Name||ETABLE and ESOL Command Input|
Boundary conditions cannot be applied on the nodes forming the screw 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 screw 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.
The pitch of the screw joint is defined as the ratio of relative axial displacement (length units) to relative rotation (in radians). Note that the relative rotation is expressed in radians and not as “number of revolutions.” Thus, the ANSYS definition for the pitch of a screw joint differs from some commonly used definitions for pitch.
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 relative rotation and relative translation degrees of freedom for this joint are not independent. Loads or boundary conditions (applied with the FJ or DJ command) can be specified on only one of these two relative degrees of freedom, while the other relative degree of freedom is automatically defined via the constraint equations of the element.
The element currently does not support birth or death options.
The equation solver (EQSLV) must be the sparse solver.
The element coordinate system (/PSYMB,ESYS) is not relevant.