# HM-3120: 2D Mesh in Curved Surfaces

Chordal deviation is a meshing algorithm that allows HyperMesh to automatically vary node densities and biasing along curved surface edges to gain a more accurate representation of the surface being meshed.

In this tutorial you will learn how to:
• Create a mesh based only on element size
• Mesh a set of surfaces using the maximum deviation parameter
• Reduce the maximum angle perimeter
• Increase the maximum element size parameter
This exercise uses the chordal_dev.hm file, which can be found in the hm.zip file. Copy the file from this directory to your working directory.

## Open the Model File

In this step you will open the model file, chordal_dev.hm.

1. Start HyperMesh Desktop.
2. From the menu bar, click File > Open > Model.
3. In the Open Model dialog, open the chordal_dev.hm model file.
4. Observe the model using the different visual options available (rotation, zooming, etc.).

## Set the Mesh Parameters

In this step you will set the mesh parameters and create the mesh.

1. To open the Mesh panel, click Mesh > Create > 2D AutoMesh from the menu bar, or select automesh from the 2D page.
2. Toggle the mesh mode from interactive to automatic.
3. In the element size= field, type 15.000.
4. Set the mesh type to quads.
5. Set the toggle to elems to surf comp.
6. Select surfs >> by collector >> use size.
7. Click select.
8. Click mesh.
The mesh is created.

## Set the Chordal Deviation Parameters

In this step you will set the chordal deviation parameters and create the mesh.

1. Go to the edge deviation subpanel.
2. In the min elem size= field, type 1.000.
Note: To cycle through the parameter settings, press the Tab key after typing in a value.
3. In the max elem size= field, type 15.000.
4. In the max deviation= field, type 0.500.
5. In the max angle= field, type 90.000 for the maximum angle parameter to be neglected.
6. Set the mesh type to quads.
7. Select surfs >> by collector >> deviation ctrl.
8. Click select.
9. Click mesh.
The mesh is created.

## Set the Chordal Deviation Parameters, Part 2

In this step you will set the chordal deviation parameters and create the mesh.

You will use the same chordal deviation settings from the previous step, but reduce the maximum angle parameter to compare the effects.

1. In the max angle= field, type 20.000.
2. Select surfs >> by collector >> angle ctrl.
3. Click select.
4. Click mesh.
The mesh is created on the surfaces.

## Set the Chordal Deviation Parameters, Part 3

In this step you will set the chordal deviation parameters and create the mesh.

You will use the same chordal deviation parameters from the previous step except for the maximum element size parameter. The maximum element size parameter is increased to allow the algorithm to create larger and fewer elements along planer and less curved surface edges.

1. In the max elem size= field, type 30.000.
2. Select surfs >> by collector >> max size ctrl.
3. Click select.
4. Click mesh. The mesh is created.