Topology Mesh Overview
1)Import Geometry
2)Repair Geometry
3)Create Surface Mesh
4)Create Boundary Layer Mesh
5)Create Volume Mesh
1. Import
Open File Dialog - Import CAD Data Twenty-one CAD formats are supported natively. The available Ennova Servers are listed in the figure below.
2. Topology Generation
Repair Geometry Dialog
Use Repair Geometry tab to process dirty geometry to obtain clean water tight geometry / Topology. The tool can be used in various ways. Firstly the tool can be used in a completely automatic mode where Ennova performs many tasks to clean and find the meshing volumes. Depending on the type of mesh you require and the level of geometry quality sometimes it is more convenient to control this stage of the process and perform the tasks manually . Here the geometry can be checked after each task to verify each stage. The various options from menu are discussed below
List of Commands for Repair Geometry Dialog and their Meanings
Stitch Surfaces – Merges surfaces that are within tolerance together.
Restart from Cad - Resets the model to the original CAD data
Reload from Server – If the Client becomes out of sync with the server, this resets the Client to match the server.
Find Structured Faces Check – Identifies faces that can be mapped in a rectangular fashion.
Defeature Geometry Check – Removes small features.
Combine Edges - Splices tangent edges together.
Repair Setup controls which items will be performed on Repair.
1. Stitch Node /Edge check uses the Merge tolerance to decide which edges and nodes will be merged or joined together.
2. Find Volume Check identifies CFD Volumes for Meshing.
3. Imprint Check finds bodies that are mated together on the same surface.
4. Find Structured Faces interrogates the model and identifies surfaces that can be meshed as structured.
Tolerance Setup
1. Merge tolerance is the maximum distance at which objects are considered the same.
2. Defeature tolerance is the maximum allowed size of objects/geometry that are to be removed.
3. Angle – Not Implemented.
3. Create Surface Mesh
Mesh Parameters Dialog
Ennova uses a hierarchical method to decide which parameters to apply. There are 3 levels of parameter setting. Firstly a parameter can be set for the Entity, the group an Entity is in, or a global setting. Ennova checks the Entity first and if this parameter has been set it uses it. If the parameter has not been set, Ennova next checks the Group the entity is in. Again, if the parameter is set for the Group, Ennova will use this. If the parameter has not been set at the Group level, then Ennova uses the Global parameters to find the Entity. Lastly if the Global parameter has not been set, then Ennova uses local knowledge to decide a value itself.
It is key to note that the same Parameter can be available in the menus at different levels. We will simply discuss each parameter in turn, but please be careful to set the parameter both to its correct value and to the level at which you wish it to be set.
Use the Setup Mesh to initially define Global Meshing Parameters.
The Global Parameters dialog box is a convenient way to set the global parameters
Note that is these parameters have not been set at an edge,face or group level these values will be applied and used. The physical interpretation of these numbers can be found in the next two tutorials. However Booster is a variational smoother for the mesh and the having this ticked on runs booster automatically after volume meshing. The booster can also be run manually from the mesh menu.
But use the View Meshing Parameter Window to gain access to the Group level. The Window has both Global and Local Settings. Notice there are two methods to enter Mesh Parameter settings. The first is a drop down dialog box and the other is a spreadsheet accessed from the “Open Mesh Parameter Settings Button” in the local Mesh Setting Dialog box. Both methods point to the same data and may be used at your convenience. Please note that for the Dialog box entry (not the spreadsheet) you must “Apply” your changes for the database to be updated.
For Entity Control, highlight the entity and use RMB to set the Mesh Parameters.
The last useful place to adjust the mesh parameters can be found by
Opening the “Open Mesh Parameters Settings Spreadsheet”. The command for this is found in the local Settings menu we just discussed above.
Here by now everything should be available in a single spreadsheet. Note these various dialog boxes and spreadsheets are just windows to the same data. So you can use which ever method is the most convenient for you and the data is only stored once. Now we have learnt how to control the parameters by global value or group it is also possible to control the parameters by entity uniquely. This is the finest level of control in Ennova.
To do this select the entity and then RMB will bring up Set Edge Mesh Parameters control (and similar for a face ). Use this to control that particular edge or face
List of Mesh Parameters and their Meanings
F inally now we have learnt to set the parameters here is a short description of what they all mean. Further details are demonstrated in the tutorials.
1. Maximum Size - Maximum allowable size of element
2. Minimum Size - Minimum allowable size of element
3. Sag Number – Ratio of distance to real surface to maximum distance to real distance from linear approximation of element.
4. Refinement Number - Number of elements used to represent an arc for 360 degrees. A refinement number of 8 means a hexagon will be used to mesh a complete circle, an element every 45 degrees
5. Size Ratio - Controls the growth rate of the mesh along Edges of the Topology. This is analogous to the Expansion Factor that does the same for mesh elements on the surface or in the volume.
More parameters are also available for prism meshing and volume meshing . So first the Prism layer mesh.
4. Create Boundary Layer Mesh
Set Up Prism Layer Mesh Prism Layers may be setup in a similar way as Mesh Parameters but are controlled at a Group level. They may, however, pick up Global values.
List of Prism Layer Parameters and their Meanings
1. Prism - On or Off - Controls whether Group has Prisms or not.
2. Height – The height of the first prism, commonly referred to as the y+ value.
3. Height Ratio – The geometric growth of the prism boundary layers in the surface normal direction.
4. Number of Prism Layers - Maximum number of prism layers possible.
5. Minimum Quality - Prism Layers are turned off if their quality is less than this value.
Again these controls are available Global or local and are set as above.
5. Create Tetra Volume Mesh
Set Up Prism Layer Mesh Once the surface mesh and prism layers are complete there is very little work for the user to perform to obtain a volume mesh. The same expansion factor used in the surface meshing is enforced in the volume mesh. So at this point the volume mesh is usually fully defined. Advanced controls such as density boxes can be added but these are discussed in detail in the tutorials. This concludes the overview of Ennova. Specific tutorials follow to demonstrate the meshing techniques and advanced details.
Conclusion – A Final Word
There are a lot of controls and at first these can all be a bit intimidating. But , in practice remember that Ennova is a server application and it is designed to run automatically. It is in the large part able to set all these parameters itself and obtain a very useful mesh. We don’t expect you the user to enter everything manually. We just give you the ability to do so – so the mesh can be refined and optimized anywhere you the engineer see fit. Or the geometry is very dirty and missing many surfaces. With Ennova the meshing process becomes iterative. Within a few hours you can be running a mesh so a quick CFD solution can be used to refine where you wish to study your solution. The next section gives some details on setting up the client / server process.
