> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ntop.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Parametric Shell Domain

## About this Block

The **Parametric Shell Domain** block creates a Parametric FE Domain, which has been parameterized for variable shell thickness. The block uses a FE Volume Mesh as an input Mesh to define the design space. After field optimization, the optimized values for the shell thickness will apply to the design space.

**Common uses:**
This block is an input to the **Parametric FE Model** block.

Once the **Parametric Lattice Domain** is generated, a HUD appears in the Viewport with several options for visualizing the results.

* Implicit View - allows you to view the resulting geometry.
* Property Fields - allows a user to view the mechanical properties of the structure across the design space before performing field optimization.
* State Fields - allows a user to view values of the design parameters across the design space before performing the field optimization.

**Tips:**

* Determining the proper mesh size can be difficult for the FE mesh provided to the Parametric Shell Domain.
  * The input mesh must be very fine from the surface through the maximum shell thickness.
  * However, to increase the speed/efficiency of the optimization algorithm, elements outside of the "shell boundary" should be much larger.
  * The goal is for the total possible design region to contain as many elements as possible (giving up time for accuracy) and for all other areas to contain fewer elements.
  * As such, you should use a **Ramp** block in the Edge Length input to generate the FE Mesh. An example of meshing for shell optimization is below:
  * Taking advantage of the SDF of an implicit, we can ramp our mesh edge length using our ramp function. Some hints for appropriate inputs are below:
    * Scalar Field: Implicit body which we are meshing. The implicit body will allow us to use the signed distance field of the implicit in driving our mesh size.
    * In Min: Maximum shell thickness multiplied by -1. This input will create a divider between the maximum design space of the shell optimization and the void on the inside.
    * In Max: Maximum shell thickness multiplied by -1. Having the same input as "In Min," we can set up the field as a step function.
    * Out Min: Mesh size of shell design space (should be smaller than "Out Max"). The edge size should capture all the detail of the object and be suitable for running simulation.
    * Out Max: Mesh size of the inner void (should be more significant than "Out Min").
      ![Ramp](https://storage.googleapis.com/files-learn/static/ExtendedBlockDocs/ramp_tip.jpg)
* Adjust the *Initial Shell Thickness* to view the geometry generated for the upper/lower bounds to ensure printability before running a field optimization.

## Example File

Download Example: [Parametric Shell Domain](https://storage.googleapis.com/files-learn/static/ExtendedBlockDocs/Variable_Shell.ntop)
![Field Optimization Result](https://storage.googleapis.com/files-learn/static/ExtendedBlockDocs/variable_shell.jpg)

***

Create a Parametric FE Domain for a variable shell structure with the following design parameters: shell thickness (inward direction).

### Inputs

| Name                    | Type                                                                           | Description                                                                                                                                                                                |
| ----------------------- | ------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| Mesh                    | [FE Mesh](../../../../block-documentation/types/fe-mesh)                       | The finite element mesh that defines the design space.                                                                                                                                     |
| Material                | [Isotropic Material](../../../../block-documentation/types/isotropic-material) | The material definition of the shell domain.                                                                                                                                               |
| Min shell thickness     | [Scalar Field](../../../../block-documentation/types/scalar-field)             | The minimum allowable thickness for the shell.                                                                                                                                             |
| Max shell thickness     | [Scalar Field](../../../../block-documentation/types/scalar-field)             | The maximum allowable thickness for the shell.                                                                                                                                             |
| Initial shell thickness | [Scalar Field](../../../../block-documentation/types/scalar-field)             | The initial shell thickness. This defines the starting point of the optimization. Values exceeding the min/max bounds will be clamped.                                                     |
| Filter size             | [Scalar Field](../../../../block-documentation/types/scalar-field)             | A length measure used to control the smoothness of the design parameter field. A lower bound of 0 will be enforced. If not specified, a default will be estimated based on the model size. |

### Outputs

| Type                                                                               |
| ---------------------------------------------------------------------------------- |
| [Parametric FE Domain](../../../../block-documentation/types/parametric-fe-domain) |