# CONN0

Connector ElementCONN0 lets you rigidify the gradient vectors of a single NLFE grid.

## Format

```
<CONN0
id = "integer"
gid = "integer"
conn = "string"
/>
```

## Attributes

`id`- Unique identification number.
`gid`- Grid identification number.
`conn`- String containing at most six characters that describe the connection between the coordinates. See Comment 2 for more details.

## Example

The example demonstrates the definition of a CONN0 element.

`<CONN0 id="1000" gid="101" conn="TTFTFF"/> `

## Comments

This element is used to rigidify the gradient vectors of a single grid. An NLFE node with the complete set of generalized coordinates has 12 DOF by design. When a marker is attached to such an NLFE node, the node is constrained to move and rotate with the marker thereby arresting 6 of the 12 DOFs (3 for translation and 3 for rotation). However, the node still has 6 additional free DOFs. This element can be used to constrain one or all of the remaining 6 DOFs. Thus, the following constraints can be imposed:

(1) $$\begin{array}{l}r{x}^{T}rx={c}_{1}\\ r{y}^{T}ry={c}_{2}\\ r{z}^{T}rz={c}_{3}\\ r{x}^{T}ry={c}_{4}\\ r{x}^{T}rz={c}_{5}\\ r{y}^{T}rz={c}_{6}\end{array}$$- The coefficients on the right hand side in the equations above are
automatically determined by MotionSolve
based on the initial model configuration. You can use the
`conn`string to selectively impose some of the above constraints. The first three constraints maintain constant magnitude of the 3 gradient vectors. The last three maintain the relative directions of the gradient vectors. The letter 'T' in attribute`conn`indicates the particular kinematic relationship will be imposed by MotionSolve at all times during the simulation. The attribute`conn`can have up to six 'T' (True) or 'F' (False) characters. For example, if`conn`="TTTFFF", the magnitude constraints will be imposed and the rest of the conditions will not be imposed by MotionSolve. - The default for the attribute
`conn`is "FFFFFF". Further,`conn`="TTT" is equivalent to`conn`="TTTFFF". - A grid can have either 9 or full 12 generalized coordinates associated with it. CONN0 should not be applied for grids with only 3 or 6 generalized coordinates.
- If a CONN0 is applied to a grid with only 9
generalized coordinates (for example, grid with only
$r,rx,ry$
), you should not apply any
constraints that involve
${r}_{z}$
. For example,
`conn`="TTFTFF" does not apply any constraints involving ${r}_{z}$ and, therefore, satisfies this requirement.