# Different Structure Modes¶

In addition to a unit cell, a structure has a *Structure Mode* which makes up the general geometry of the structure. Currently, only one *Structure Mode* is available:

## Planar Shell Structure¶

### Overview¶

A planar shell structure is a 2D structure which is meshed with 2D elements. When exported, it is extruded in the third direction by a given amount (see Requesting Output). A sample is shown below:

### Bounday Conditions¶

In this structure, *RP-1* is a reference point tied to the the first loading edge (*LD-Edge-1*). This point is fixed in space. The second reference point (*RP-2*) is tied to the second loading edge (*LD-Edge-2*) and recieves the loading. A schematic of loading on planar shell structures is shown below:

### Special Outputs¶

For this structure, two transverse edges *TD-Edge-1* and *TD-Edge-2* are defined and used for processing outputs. Afterwards, two special outputs are calculated:

Poisson’s Ratio at the Midpoint: Two nodes named ‘TD-Midpoint-1’ and ‘TD-Midpoint-2’ are always defined in the model using partitioning. The relative displacement of these nodes and the reference pointsRP-1andRP-2are then used to define the Poisson’s Ratio at the Midpoint.

Mean Poisson’s Ratio: For each ofTD-Edge-1andTD-Edge-2, average values of the displacement in that edge is calculated. The difference between the two displacements is the relative displacement at the transverse direction which along with the relative displacement of the reference pointsRP-1andRP-2are used to define the Mean Poisson’s Ratio.

These geometries are shown in the following figure: