Mesh Controls

Mesh > Controls > Mesh Controls

Introduction

Global and Local Mesh Control

Mesh controls can be a Global or a Local control. Global control is assigned to bodies or assemblies and all underlying geometry entities like faces, edges will inherit this global mesh controls. Suppose a local geometry, like a body, face, edge, are assigned a local mesh control, then the local mesh control will determine the mesh on these entities while the global mesh control will determine the mesh on rest.

CAD and Mesh Models

The mesh control can be assigned to CAD models that are imported into SimLab or to Mesh models created inside of SimLab. The mesh controls are also respected when meshing an assembly or a single body as well as when "Local Re-meshing" is called on a portion of the mesh body.

Almost all CAD models imported are manifold. In other words, there are no shared faces between 2 bodies. So meshing of a CAD assembly is the same as meshing individual bodies in the assembly. This is not the case when meshing an assembled mesh body. A mesh body can be a non-manifold, in other words faces and edges of a body can be shared by adjacent mesh bodies. In traditional FEM terms there are shared nodes between the 2 solids. When meshing mesh bodies with shared face, it is desired to a mesh that also has shared faces after meshing. The toggle "Assembly" in the global mesh control dialog box can be used to instruct the system to retain the non-manifold nature of the assembly during meshing.

Managing Mesh Control

When a mesh control is created with a given name, an entry with this name is added to the tree in "Mesh Control" tab in the "Model Browser". When creating a mesh control the geometry on which it is assigned has to be selected. Otherwise a mesh control cannot be created. Existing mesh control can be modified by double clicking the mesh controls in the tree view. A mesh control can be deleted by highlighting the mesh control in the tree view following by pressing the delete key on the key board.

When a mesh control is assigned on a face, the face changes color to indicate that a mesh control is assigned. The color for a mesh control can selected when creating or editing. Visual display of the mesh control can be turned ON/OFF by checking/un-checking the "Mesh Control" menu item under "Visibility". Mesh control visual display is disabled if View Toolbar > Render Mode > Color options is turned ON.

Mesh Specification File

Mesh control created can be saved in an external file, called "Mesh Specification" and saved file can be imported back into SimLab. This is very useful when meshing models of similar types when the mesh control created for one can be reused for the others. For example, the meshing requirements for modelling most engine heads are similar. So if a mesh control is created for one engine head model, then it is most likely that this can be reused for other engine head as well. This option also helps standardize the meshing process.

When creating mesh controls, geometry has to be selected. The selected geometry ids are stored with the mesh control. When a mesh control is exported the specification file can have the geometry ids. It is not necessary for two different CAD models to have the same ids for the geometry. So a mesh specification file that refers to ids for one CAD model will not be useful for another CAD model. So when exporting a mesh specification file one can choose to export with no geometry ids (Template option), with geometry ids (Body option), face color (Face color option) or group name (Group option).

When importing a mesh specification file that was exported with "Template" option, it will create mesh control objects in the "Mesh Control" tree view but with empty icons in the second column of the Model Browser. The empty icons indicates that these mesh controls have not been assigned to geometry. User can double click to open these mesh control and assign them to geometry and this will turn the mesh control object on the tree view to become bright.

Unit support

The mesh specification file will be exported in same unit system as that of the database.

If the exported mesh specification file has units, it should be imported only into a database where unit system is set ON. When the unit system of mesh specification and database is different, then the values in mesh specification file will be automatically converted to database unit system.

If the exported mesh specification file does not have unit system, it should be imported only into the database which does not have unit system.

Priority

When many "Mesh Controls" are assigned, it is possible that multiple "Mesh Controls" can have an influence on one geometry. For example, a face can have a local mesh size assigned as 5, while the body might have a mesh size of 10. What will be the mesh on the face? Another example will be 2 faces sharing an edge can have different mesh sizes. What will be the mesh size on the edge? The meshing code looks at all the mesh control and determines what size it should use for a geometric entity. For each geometry type the mesh size is determined as follows.

Edge

Face

Body

It is important to understand that the mesh size on geometry inside of a region as defined in "Region Mesh Control" ignores all geometry based mesh sizes other than the mesh seed.

Large Model Meshing

Meshing large CAD models can take time. On a machine with 2GB memory, 1.58GHz Pentium processor it can roughly take 20 minutes to mesh an engine head model. After meshing and inspecting a mesh a re-mesh might be required. Meshing the body again can take 20 more minutes. Every mesh size modification makes it more expensive. Once satisfied, the mesh specification file can be saved and reused for meshing similar models and this can save time.

The option is to assign the mesh controls and only mesh the surfaces of interest. This will take less time. Once satisfied with the mesh in the local regions of interest, then mesh the entire body.

Meshing Faceted Geometry

Facet geometry is created when STL, VRML and IDI files are imported. Facet geometry is based on piecewise flat triangles grouped together as faces with edges and vertices. When importing, features like planes, cylinders, fillets are identified and flagged. This is not an exact process but works for most cases. In case a feature is not identified, it can be forced by using the Assembly | Align command.

A CAD model when imported will be displayed with smooth surfaces. But a facet geometry will appear like a mesh, typically with large skinny triangles. Otherwise the creation of mesh control and meshing are the same as that for a CAD model.

Note that the graphics performance, operations like rotation, picking, etc, can be slower than that for a CAD model. This is yet to be optimized.

Global Mesh Control

Global mesh control is assigned when meshing the surface, ( Mesh | 2D Create | Mesh) or the volume of a body (Mesh | 3D Create | Solid Mesh). The specifications are used to mesh all geometry entities selected for meshing, that do not have a local mesh control.

Local Mesh Control

1. Body Mesh Control
2. Face Mesh Control
3. Edge Mesh Control
4. Fillet Mesh Control
5. Circle and Washer Mesh Control
6. Cylinder Mesh Control
7. Washer Mesh Control
8. Valve Seat Pocket Mesh Control
9. Logo and Details
10. Holes
11. Region Mesh Control
    1. Cuboid
    2. Cylinder
    3. Plane
    4. Sphere
    5. Cone
12. Include Mesh Control
13. Imprint Circle Mesh Control
14. Iso-Line Mesh Control
15. Volume Layer Mesh Control
16. Symmetry Mesh
17. Proximity
18. Cartesian Refinement Mesh Control
19. Immersed Refinement Mesh Control
20. Hard Points Mesh Control
21. Preserve Entities
    1. Face Shape
    2. Face Edges
    3. Edges
    4. Mesh
22. Mesh Patterns
    1. Iso Mesh
    2. Free Mesh
    3. Union Jack
    4. Aligned Mesh
23. Boundary Layer