# Cylinder

## Setting Up the Environment


First, make sure the SALOME platform is installed and note its path, referred to here as ```$PathToSALOME```. If you don't have SALOME installed, you can download it [here](https://www.salome-platform.org/?page_id=2430). 

Then, create a working directory and launch SALOME:

```bash
mkdir -p TRUST_tutorials/salome/exo1
cd TRUST_tutorials/salome/exo1
$PathToSALOME/salome &
```

## Creating the Geometry

- **Create a new study:** File → New

- **Select the Geometry module** from the SALOME drop-down menu (which lists all available modules)

- **Save your study frequently** in HDF format (SALOME's native format)

- **Create the cylinder:**
  - Go to: New Entity → Primitives → Cylinder
  - Set Radius `R = 100` and Height `H = 300` (default values)
  - Click "Apply and Close"

  ![Cylinder creation dialog](/_static/FIGURES/salome2.jpg)

- **Navigate the view:**
  - Use the "Interaction style switch" (Mouse icon) to rotate, zoom, and pan the geometry

## Defining Boundary Groups

To define boundaries for TRUST, we need to create groups for the top, bottom, and lateral surfaces:

- **Create groups:** New Entity → Group → Create Group

- **Select Shape Type:** Surface

- **Create the "Inlet" group (top):**
  - Group Name: `Inlet`
  - Click the arrow button in the Main Shape field
  - Select "Cylinder_1" from the Object Browser or the visualization window
  - Click on the top surface of the cylinder
  - Click "Add" → "Apply"

  ![Creating boundary groups](/_static/FIGURES/salome3.jpg)

- **Create the "Wall" group (lateral surface):**
  - Repeat the process with Group Name: `Wall`
  - Select the lateral surface

- **Create the "Outlet" group (bottom):**
  - Group Name: `Outlet`
  - Rotate the cylinder to access the bottom surface
  - Select and add it

- **Verify:** Check that all three groups appear in the Object Browser (click the "▷" next to "Cylinder_1")

## Creating the Mesh

- **Switch to the Mesh module** from the SALOME drop-down menu

- **Display the geometry:**
  - Select "Cylinder_1" in the Object Browser
  - Right Click → 'Show' (or click the eye icon)

- **Create the mesh:**
  - Go to: Mesh → Create Mesh
  - Select "Cylinder_1" as the geometry (if not already selected)
  - Choose the "Netgen 1D-2D-3D" algorithm
  - Click "Apply and Close"

- **Compute the mesh:**
  - Select "Mesh_1" in the Object Browser
  - Right Click → Compute (or Mesh → Compute)
  - A table showing the number of triangles, quadrangles, etc. will appear
  - Click "Close"

- **Hide the geometry:**
  - Select "Cylinder_1" in the Object Browser
  - Right Click → Hide (or click the eye icon)

  ![Computed mesh](/_static/FIGURES/salome4.jpg)

## Exporting the Mesh

- **Verify boundary groups:** Check that the three boundaries have been automatically added to the "Group of Faces" of the **Mesh_1** object in the Object Browser

- **Export to MED format:**
  - Select "Mesh_1"
  - Right Click → Export → MED file (or File → Export → MED file)
  - Save as `Mesh_1.med`

## Reading the Mesh with TRUST

Create a TRUST data file named `dom.data`:

```
dimension 3
domaine dom
Read_MED { domain dom file Mesh_1.med }
Postraiter_domaine { domaine dom fichier mesh format lata }
```

Run TRUST and visualize with VisIt:

```bash
trust dom
visit -o mesh.lata
```

**Warning:** A common mistake is forgetting to define boundary groups for the geometry. TRUST will detect this during discretization when building all mesh faces, including boundary faces.

## Refining the Mesh with Viscous Layers

To improve mesh quality near walls, viscous layers can be used:

- **Create a new mesh:** Mesh → Create Mesh
  - Name: `Refined_mesh`
  - Select "Cylinder_1" geometry

- **Select a 3D algorithm:** "Netgen 3D" or "MG-Tetra"

- **Add viscous layers:**
  - Click the wheel icon next to "Add. Hypothesis" → "Viscous Layers"
  - Total thickness: `30`
  - Number of layers: `3`
  - Stretch factor: `1.1`
  - Add the "Inlet" and "Outlet" groups to "Faces without layers"
  - Click "OK"

- **Add a 2D algorithm:** "Netgen 1D-2D" or "MG-CADSurf"

- **Configure 2D parameters:**
  - Click the wheel icon next to "Hypothesis"
  
  **For Netgen 2D parameters:**
  - Change "Fineness" from "Moderate" to "Very Fine"
  
  **For MG-CADSurf parameters:**
  - Set "User size" to `20`

- **Apply and compute:**
  - Click "Apply and Close"
  - Select "Refined_Mesh" in the Object Browser
  - Right Click → Compute

  ![Refined mesh comparison](/_static/FIGURES/salome6a.jpg)

The resulting mesh will contain a mix of tetrahedral, hexahedral, pyramid, and prism elements (for Netgen) or tetrahedral and prism elements (for MG algorithms).

## Converting to Tetrahedral Elements

Since TRUST only accepts tetrahedral elements:

- Select "Refined_Mesh" in the Object Browser
- Go to: Modification → Split Volumes
- Select "Tetrahedron"
- Keep the default parameters
- Click "Apply and Close"

## Final Steps

- **Verify boundaries:** Check that the three boundaries are listed under "Group of Faces" of **Refined_Mesh**

- **Export the mesh:**
  - Select "Refined_mesh"
  - Right Click → Export → MED file
  - Save as `Refined_Mesh.med`

- **Save your work:**
  - HDF format: File → Save/Save As...
  - Python format: File → Dump Study...

```{note}
Solution files (`mesh.py` for the first mesh and `prism.py` for the refined mesh) are available at: `$TRUST_ROOT/doc/TRUST/exercices/salome`
```