Creation of the mechanical mesh in HyperMesh

Introduction

In this part, the steps in HyperMesh to create and export the “mechanical mesh” where the magnetic forces will be computed in Flux are presented. The advantage of this method is that the magnetic forces will be directly used in OptiStruct without any interpolation or projection which can generate errors.

Mechanical mesh

The mesh which will be used for forces computation in Flux must respect the following constraints:

It must be cylindrical, centered on motor axis
At the interface of two regions having different magnetic permeability value (stator/air or rotor/air)

Note: The mesh should not contain superimposed nodes or unused free nodes

Figure 2. Elements not connected detected with the "free edges" tool in HyperMesh

Note: The normal vectors orientation is defined in HyperMesh and Flux respects this orientation. To visualize (and eventually change) the orientation, please use the following commands:

HyperMesh graphic area manipulation

Some tips concerning graphic area manipulation (for first HyperMesh usage) are presented here:

To Translate the geometry: use Ctrl + right click
To rotate the geometry: use Ctrl + left click
To zoom in/out the geometry: use control + roll scroll wheel
To manage the transparency / opacity of geometry or mesh, use the following icons (below the graphic area):
To manage the displaying of the model components geometry and mesh, use :

HyperMesh entities selection

Some tips concerning entities selection (for first HyperMesh usage) are presented here:

To select entities: for example, to select faces:

Click on surfs
Remarks:
allows to change the entity type to select.
allows to reset the selected entities
Option 1: click on the yellow field to open the temporary extended menu to get multiple selection methods. For example: « all / displayed / … »
Option 2: select face by face on the graphic with the mouse left click (without Ctrl button). The selected face is highlighted (in white). To deselect a face, use the mouse right click

Mechanical mesh in HyperMesh

The steps in HyperMesh to create the mechanical mesh are described below. Screen shots of the different steps are available.

Make sure to select the OptiStruct user profile when opening HyperMesh:

You can review this window by clicking on the icon.
Import CAO file of the geometry to consider (stator / rotor / all / …). Here we consider stator part:
- Menu : File > Import > Geometry
- Click on the following icon to select the CAO file
  
  The path of the selected CAO file appears in the window below the icon
- Click on import to confirm the import
  
  The geometry is imported and visible in the graphic area, and the Model tab contains the different geometry components
Mesh the solid components (volume mesh):

In our example case the volume mesh is the best tool to use.

This mesh step should be adapted according to the complexity of the input geometry.
- Check the geometrical distance between two points to define the mesh element size:
- Open the 3D panel and select the solid map tool:
- To mesh, follow the steps below:
  - Select one volume
  - Click on solid (highlighted with blue line)
  - Select the components to mesh on the graphic
  - Fill the element size
  - Click on mesh
  - If the mesh is ok, click on return. Otherwise, click on reject and modify the mesh data.
Create the faces of the solid component(s) containing the surface mesh support:
- Select the Tool panel and the tool faces
- To generate a component containing the external surface mesh:
  - Click on comps
  - select the component(s)
  - click on find faces
    
    The component ^faces has been created. It contains the faces of all the solid component(s)
- Right click on this component and select isolate to display only the surface mesh
In the ^faces component, delete the surface mesh which should not be exported. This step can be fastidious, so the selection by relation and the reverse command can be used. On this example:
- Click on the following icon:
  The following window is opened:
- Follow the below steps described:
  - Select one element by tooth as on the image
  - Click twice on elems to activate the extended menu. At the first click select by face.
    All the meshed teeth faces are selected
  - At the second click on elems select reverse
    All the other meshed faces are selected
- Click on delete entity
  The final face mesh corresponds to:
- Right click on ^faces component, rename and delete ^ to export it.
(optional) Save the HyperMesh model :
Export the displayed mesh :
- Menu : File > export > Solver Deck:
- Ensure to display only the meshed faces of the faces component
- Export the displayed mesh in Optistruct format:

Superimposed nodes problem

HyperMesh, contrary to Flux, allows the creation of superimposed nodes / elements. Consequently, sometimes the exported mesh can be duplicated and superimposed (often because of a user manipulation error, for example by clicking two times on mesh). In Flux, the support creation using this mesh fails.

In this paragraph, the method to merge superimposed nodes is presented.

Attention: this command must be used carefully because some close points (under tolerance value) can be merged.

Open the HyperMesh meshed model
Launch the command Equivalence on nodes :

Following window opens :
- Click on comps :
- Select faces and click on select
Verify the tolerance value and click on preview equiv .

This step helps you to review the nodes that HyperMesh detects within the tolerance.
If you agree click on equivalence.
If not modify the tolerance and repeat the above steps.
Then, click on return

At the bottom left of HyperMesh window, the number of equivalenced nodes is indicated:
Export the mesh by following the step 5 of the previous step/action table.

Free nodes problem

HyperMesh allows free nodes which are not attached to elements. If the mechanical mesh contains such nodes, the mesh import fails in Flux.

2 solutions in HyperMesh are proposed here.

The first solution:

Open the Geom panel below the graphic area and select the temp nodes tool:
Click on nodes and select all.
Click on clear all
Export the mesh by following the step 5 of the previous step/action table

The second solution:

On the window below the graphic area, select Analysis and preserve node:
Click on nodes and select all.
Click on clear all preserved.

The preserved nodes will not be exported
Export the mesh by following the step 5 of the previous step/action table.

Note: Please note that as you export the meshed support, you should not modify the mechanical mesh.

It will be used to setup the NVH analysis.