Two-dimensional kinematic elements can be isoparametric quadrilaterals or triangular elements. The quadrilateral elements have 4 nodes or 8 nodes if midside nodes are included. The triangular elements have 3 or 6 nodes if midside nodes are included. Mid-side nodes are rarely needed but may be useful when these elements share boundaries with 2D or 2D hydrodynamic elements that have midside nodes. Thus free nodes on such boundaries are avoided.
These elements do not experience strains, and thus do not report stresses. Otherwise, these elements behave just like 2D elements. They can have mass, have loads applied on their nodes and faces and experience motion. Their advantage over 2D elements is that they barely contribute to the size of the global stiffness matrix.
These elements are confined to the global YZ plane.
2D Kinematic Element Parameters
When using 2D elements, you must define the thickness of the part in the Thickness field of the Element Definition dialog.
Advanced 2D Kinematic Element Parameters
Next, select the integration order that will be used for the 2D kinematic elements in this part in the Integration Order drop-down box. For rectangular shaped elements, select the 2nd Order option. For moderately distorted elements, select the 3rd Order option. For extremely distorted elements, select the 4th Order option. The computation time for element stiffness formulation increases as the third power of the integration order. Consequently, the lowest integration order which produces acceptable results should be used to reduce processing time.
For the 2D kinematic elements in this part to have the midside nodes activated, select the Included option in the Midside Nodes drop-down box. If this option is selected, the 2D kinematic elements will have additional nodes defined at the midpoints of each edge. This will change a 4-node 2D kinematic element into an 8-node 2D kinematic element. An element with midside nodes will result in more accurately calculated gradients. Elements with midside nodes increase processing time. If the mesh is sufficiently small, then midside nodes may not provide any significant increase in accuracy.
If the Allow for overlapping elements check box is activated, overlapping elements will be allowed to be created when the lines are decoded into elements. Overlapping may be necessary when modeling elements. This is especially true for problems confined to planar motion.
Basic Steps for Use of 2D Kinematic Elements
- Be sure that a unit system is defined.
- Be sure that the model is using a nonlinear analysis type.
- Right-click the Element Type heading for the part that you want to be 2D kinematic elements. Tip: Useful commands for converting 3D models to 2D models are Draw
Pattern Relocate & Scale, Draw Pattern Rotate or Copy, and Draw Modify Project to Plane. For example, you may accidentally create a mesh in the XY plane. You can rotate the mesh to the YZ plane using either the Relocate & Scale or Rotate command. Due to round-off, some nodes may have a small X coordinate value that prevents the element type from being set to 2D. In this case, use Project to Plane to snap the nodes exactly to the YZ plane. - Select the 2D Kinematic command.
- Right-click the Element Definition heading.
- Select the Edit Element Definition command.
- In the General tab, specify the thickness of the 2D kinematic elements in the Thickness field.
- Press the OK button.