# GRID

Model ElementGRID defines an NLFE node in 3D space.

## Description

- Current location in space (X, Y, and Z coordinates)
- Relaxed location in space (X, Y, and Z coordinates)
- Current gradient vectors in space (X, Y, and Z gradient vectors)
- Relaxed gradient vectors in space (X, Y, and Z gradient vectors)

These are called the nodal co-ordinates for this GRID.

## Format

```
<GRID
id = "integer"
x = "real"
y = "real"
z = "real"
rx = "string"
ry = "string"
rz = "string"
x0 = "real"
y0 = "real"
z0 = "real"
rx0 = "string"
ry0 = "string"
rz0 = "string"
xd = "real"
yd = "real"
zd = "real"
rxd = "real"
ryd = "real"
rzd = "real"
/>
```

## Attributes

`id`- Unique GRID identification number.
`x`,`y`,`z`- The current X, Y, and Z position of the GRID.
`x0`,`y0`,`z0`- The relaxed X, Y, and Z positions of the GRID.
`rx`,`ry`,`rz`- The X, Y, and Z gradient vectors for the GRID. Each vector is specified as a string of three space separated values that represent the vector components.
`rx0`,`ry0`,`rz0`- The X, Y, and Z relaxed position gradient vectors for the GRID. Each vector is specified as a string of three space separated values that represent the vector components.
`xd`,`yd`,`zd`- The X, Y, and Z velocity of the grid.
`rxd`,`ryd`,`rzd`- The time of the X, Y and Z gradient vector.

## Example

The following is an example of a GRID defined at the origin:

`<GRID id="303001" x="0.000000" y="0.000000" z="0.000000" rx="1.000000 0.000000 0.000000" ry="0.000000 1.000000 0.000000" rz="0.000000 0.000000 1.000000" />`

## Comments

- Each GRID has a unique identification number with respect to other GRIDs.
- The number of nodal coordinates depends on the element type. For instance, a CABLE element can be specified using only one gradient vector, however other elements such as the BEAM element require two gradient vectors.
- The nodal positions are required to be defined for each NLFE body.
- You may define the relaxed nodal coordinates
(
`x0`,`y0`,`z0`,`rx0`,`ry0`and`rz0`) for the NLFE body. If these are different than the model configuration (`x`,`y`,`z`,`rx`,`ry`and`rz`), then the NLFE body will try to regain its relaxed configuration which will produce internal stresses. This may be used to model preload in the NLFE body. If the relaxed nodal coordinates are not defined, MotionSolve assumes the relaxed configuration of the component to be the same as the model configuration of the component and no internal stresses are generated.