Linear Actuator
LINK11 Element Description
LINK11 may be used to model hydraulic cylinders and other applications undergoing large rotations. The element is a uniaxial tension-compression element with three degrees of freedom at each node: translations in the nodal x, y, and z directions. No bending or twist loads are considered. See LINK11 in the Mechanical APDL Theory Reference for more details about this element.
LINK11 Input Data
The geometry and node locations for the element are shown in Figure 11.1: LINK11 Geometry. The element is defined by two nodes, a stiffness, viscous damping, and mass. The element initial length Lo and orientation are determined from the node locations.
Element loads are described in Nodal Loading. The stroke (length) is defined through the surface load input using the PRES label. The stroke is relative to the zero force position of the element. A force may be defined in the same manner as an alternate to the stroke.
A summary of the element input is given below. A general description of element input is given in Element Input.
LINK11 Input Summary
- Nodes
I, J
- Degrees of Freedom
UX, UY, UZ
- Real Constants
K - Stiffness (force/length) C - Viscous damping coefficient (force*time/length) M - Mass (force*time2/length) - Material Properties
MP command: BETD, ALPD
- Surface Loads
- Pressures --
face 1 - Stroke face 2 - Axial Force
- Body Loads
None
- Special Features
Birth and death Large deflection Stress stiffening - KEYOPTs
None
LINK11 Output Data
The solution output associated with the element is in two forms:
Nodal displacements included in the overall nodal displacement solution
Additional element output as shown in Table 11.1: LINK11 Element Output Definitions.
A general description of solution output is given in Solution Output. See the Basic Analysis Guide for ways to view results.
The Element Output Definitions table uses the following notation:
A colon (:) in the Name column indicates that 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 “-” indicates that the item is not available.
Table 11.1: LINK11 Element Output Definitions
| Name | Definition | O | R |
|---|---|---|---|
| EL | Element Number | Y | Y |
| NODES | Nodes - I, J | Y | Y |
| ILEN | Initial element length | Y | Y |
| CLEN | Current element length (this time step) | Y | Y |
| FORCE | Axial force (spring force) | Y | Y |
| DFORCE | Damping force | Y | Y |
| STROKE | Applied stroke (element load) | Y | Y |
| MSTROKE | Measured stroke | Y | Y |
Table 11.2: LINK11 Item and Sequence Numbers lists output available through the ETABLE command using the Sequence Number method. The following notation is used in Table 11.2: LINK11 Item and Sequence Numbers:
- Name
output quantity as defined in Table 11.1: LINK11 Element Output Definitions
- Item
predetermined Item label for ETABLE command
- E
sequence number for single-valued or constant element data
LINK11 Assumptions and Restrictions
The element must not have a zero length.
The element assumes a straight line, axially loaded at the ends.
A twist (torsion) about the element x-axis (defined from node I to node J) has no effect.
No bending of the element is considered, as in a pin-jointed structure.
The mass is equally divided between the nodes.
Only the lumped mass matrix is available.
Surface load pressure indicators are not displayed for element or node plots.