# Normal and Tangent Vectors#

```Normal and Tangent Vectors = {yes | no}
```

## Description / Usage#

This option allows one to write the values of the normal and tangent vectors used in rotating the mesh and momentum equations as nodal variables to the output EXODUS II file. In two-dimensional problems, the normal and tangent vectors are saved as N1, N2, N3 and T1, T2, T3 in the output EXODUS II file; in two dimensions these vectors are calculated at all the nodes. In three-dimensional problems, the normal and tangent vectors are saved as N1, N2, N3, TA1, TA2, TA3, and TB1, TB2, TB3; in three dimensions, these vectors only exist at nodes with rotation specifications, and the vectors correspond to the rotation vectors chosen by the ROT Specifications for the given node (see description for ROT cards). Thus in three-dimensional problems, vectors are not necessarily saved for every node, nor do the vectors necessarily correspond to the normal, first tangent, and second tangent, respectively.

The permissible values for this postprocessing option are:

 yes Calculate the vectors and store as nodal variables in the output EXODUS II file. no Do not calculate the vectors.

## Examples#

The following sample card produces no output to the EXODUS II file:

```Normal and Tangent vectors = no
```

## Technical Discussion#

This option is mostly used to debug three-dimensional meshes for full threedimensional ALE mesh motion. The tangent fields in 3D should be smooth across the surfaces, and Goma takes many steps to make them so. The surface normal crossed into any vector that is different will produce one tangent vector. Then the normal crossed (viz. cross product of two vectors) with the first tangent will produce a second tangent vector. Because the surface tangent basis fields are not unique, they must be uniform over a surface when the rotated Galerkin weighted residuals are formed (see description for ROT cards). Imperfections or defects in the mesh can lead to nonsmooth fields.