SimLab mesh export workflow

Introduction

This section presents the steps to follow in SimLab 2017 to export the mesh in a Nastran file.

Preliminary

Before detailing the workflow to follow, here are some useful information for a first SimLab using:

  • In SimLab, contrary to HyperMesh, all the operations (geometry, verifying …) are applied to the mesh and not to the geometry. The CAD import allows only to visualize the geometry. So the first step is to mesh in surface. The volume mesh is done at the end.
  • To open the help, press the key « F1 ». The help will be opened on the page concerning the active command.

Workflow

In the following table, the steps to follow in SimLab for a nominal scenario are presented (geometry imported from CAD file, air box creation, etc.).

Stage Description Illustration
1 Open SimLab  
2

Import the geometry CAD

Two CAD imports exist :

  • File > Import > CAD:

    It allows using the native format (Parasolid, Step, CATIA, ProE…). But the associated software must be installed

  • File > Import > CAD through translation

    It converts and imports the native formats in Step or Parasolid.

Attention: the conversion can generate geometrical errors.

→ For this import, it is truly advised to choose the conversion in Parasolid . It gives access to automatic assembly option « Imprint solid bodies » which has to be checked at the import.

After the import, the components are visible in the data tree. If each component faces define a volume, then the following icon appears:

CAD through translation :
3

Mesh the geometry faces :

Mesh > Mesh (in « 2D Create »)

  • Select in the data tree the components to mesh
  • Choose the mesh order (Tri3 for the first order and Tri6 for the 2 nd order)
  • Choose the mean element size. The value will be applied to all the entities without « mesh controls »
Attention: if the value is too high, the geometry can be misrepresented
  • In « Advanced Options » check the option « imprint meshing » allowing the management of mesh conformity
  • Click on « ok » to mesh

→ The old geometrical components are made invisible, and new component of mesh type are created and visible in the data tree:

All the operations will be applied on those mesh components
4

Most of the components which have a contact face will be assembled to obtain a conform mesh, thanks to the option presented before.

If there are components which are not assembled, it is possible to do it manually.

  • Use the command « join » :

    Assembly > Join

  • Check the option « general faces » to join all type of faces
  • Click on « show » to visualize the faces to join, and then « join »
  • Make a re-mesh of all the components to re-mesh correctly the contact area (with the same mesh data as the first mesh)

    Mesh > Re-mesh

Note: If it s a componet indoor another component, use the command « Boolean »: Assembly > Boolean
5

Check the mesh:

  • Mesh > Edges

    This command allows verifying if the mesh contains free edges (a free edge is an edge belonging to only one surface element) or non-manifold edges (belonging to more than 3 surface elements. This is authorized only in case of internal/shared faces)

  • Mesh > Intersection

    This command allows verifying the intersections between elements

In case of defaults, several tools can be used to correct:

  • Mesh > Fill to fill holes or cracks
  • Mesh > Create (element) to create missing surface elements
  • Etc.
6

It is possible to create the air box in SimLab or in Flux.

If user wants to create the air box in SimLab:

Geometry > Create (Body) > Bounding body

  • Choose the bounding box shape (Box/Sphere/Cylinder).

Here we choose « box » shape.

  • Click on define > modify box
  • Check « bodies », then select all the components (left click). The box appears: it is possible to move a face directly on the graphic (to extend or reduce the box size)
  • Validate

  • Define element size « mesh size » or elements number « number of elements » of the bounding box

    Attention: choose a value close to the value entered for the device (to allow the mesher connecting the elements)
  • Validate

→ A new mesh component « Bounding_Box1 » is created
7

Prepare the project for volume meshing :

  • Verify in the preferences that the option which allows meshing the holes inside a volume is activated
  • File > Preferences > Mesh : check « fill hollow space in solids when volume meshing »
  • If the bounding box « Bounding_Box1 » is not in the same node (in data tree) as the device component, make a drag&drop to the same node
  • To have a conform mesh, make a merge + of all the components (including bounding box)

    Geometry > Merge+

→ Only one component exists in the data tree :
8

Mesh the component in volume

Mesh > Volume mesh

  • Select the mesh order (TET4 for first order and TET10 for second order)
  • Define the mean element size
  • Choose the volume mesh « internal grading » coefficient (1.2 corresponds to a low grading, 2 to a high grading)
  • Choose the quality criteria

    (Stretch > Aspect > ratio > …)

  • Validate the volume mesh
  • Make a « merge – » on the component

Geometry > Merge-

→ The initial components appear:
9

Export the mesh :

File > Export > Solver input file

  • Select the components
  • Choose the « Nastran » solver
  • A message asking if the user wants to create and assign properties to components appears: click on « yes »

    → That allows distinguishing the volumes in Flux

  • Choose the name of the .bdf file to export
Note: the option « Renumber » can be checked if the file would contain high elements numbers (for example if it is a little part of a large size device)