This chapter describes the volume meshing approach with which you can generate a tetrahedral, hexcore, polyhedral, or hybrid volume mesh, with or without inflation layers, for mesh objects created from the imported geometry. You need to create a conformally connected surface mesh using the object wrapping or join/intersect operations before generating the volume mesh. See Object-Based Surface Meshing for details.
The tools to complete these steps can be found in the context-sensitive menus in the Outline View tree. Instructions are described in the following sections.
Note the following alternatives:
You can use the CutCell mesher to directly create a hex-dominant volume mesh for the geometry based on meshing objects created. See Generating the CutCell Mesh for details.
With the Rapid Octree mesher, you can use meshing objects to directly create a mostly isotropic volume mesh that is designed to scale on clusters that include thousands of cores, as described in Generating Rapid Octree Meshes.
When the conformal, connected surface mesh is ready, use the Outline View tree to navigate the volume meshing workflow as follows:
Set up Volumetric Regions.
Volumetric regions are finite, contiguous domains ready to receive a volume mesh. You use the Compute menu option to initialize the volumetric regions within a mesh object. If you perform operations such as merging or deleting, you should Validate the regions before computing the volume mesh. The Update option will recompute existing volumetric regions while preserving names and types.
Tools to compute, update and validate the volumetric regions, as well as tools to modify selected regions, are accessible via the context-sensitive menus. For a full description of available operations, see Volumetric Region Management.
Fill the volumetric regions collectively or individually, as appropriate.
Right-click on any individual volumetric region and you can access menus to setup Scoped Prism, Tet, or Hexcore volume meshing parameters, as appropriate. Descriptions of meshing parameters are found in Prism Meshing Options for Scoped Prisms, Generating Tetrahedral Meshes, and Generating the Hexcore Mesh.
After setting mesh parameters, you can compute the mesh in an individual volumetric region using the Auto Fill Volume option. See Meshing Regions Selectively Using Auto Fill Volume.
To apply meshing parameters and compute the volume mesh collectively for all volumetric regions of the selected object(s), use the Auto Mesh option in the Volumetric Regions context menu. See Meshing All Regions Collectively Using Auto Mesh.
You can also access the Auto Mesh option from the object level context menu, and access the scoped prism option directly using Setup Scoped Prisms... from the Volumetric Regions menu.
Examine the volume mesh and verify the mesh quality.
The computed volume mesh is placed into Cell Zones. You can use the context menus to draw the cell zones individually or collectively to examine the mesh. Cell zones may be merged or deleted if necessary. Volumetric regions are not affected if cell zones are deleted. Refer to Cell Zone Options.
Improve the mesh quality using the Auto Node Move tool, if needed. See Moving Nodes.
When you are satisfied with the quality of the volume mesh, prepare the mesh for transfer to solution mode. Right click on Model at the top of the tree and select Prepare for Solve from the context menu. Operations such as deleting dead zones, deleting geometry objects, deleting edge zones, removing face/cell zone name prefixes and/or suffixes, and deleting unused faces and nodes are performed during this operation.
Important: In object-based workflows, merging cell zones requires that they be in the same volumetric region.
To merge cell zones that cannot be in the same volumetric region because they are not contiguous, you will need to first delete the object(s) only, and then use the Manage Cell Zones dialog box.
Note: When you generate a poly mesh, node weights for node-based gradients are enabled by
default. For postprocessing, this setting can improve the accuracy of the displayed results
near wall edges when you are displaying contours on the poly mesh. When you transfer the
poly mesh to solution mode, a message will notify you that this interpolation is enabled.
You can disable it by setting the /display/set/nodewt-based-interp?
command to no.
Volumetric regions are finite, contiguous domains that are ready for volume meshing. Volumetric regions are computed from the conformal surface mesh and material points. If a volumetric region is changed, you should validate or update the regions prior to filling with the volume mesh.
You can use the context-sensitive menu available for Volumetric Regions for managing the regions collectively:
Use Compute to initialize the regions; Validate to confirm the finite, contiguous domains after changes; and Update to preserve names and types while recalculating regions.
You can use the Select Regions and External Baffles sub-menus to assist in selecting or visualizing regions based on type.
Object-based meshing parameters are set and the volumetric regions filled using the Auto Mesh tool. The Setup Scoped Prisms... tool is a direct link to the Scoped Prisms dialog box.
You can get surface mesh statistics using the Summary option, and a listing of region composition using the Info option.
Individually, you can use the context-sensitive menu for a named volumetric region to modify and examine the region, as well as set up regional mesh parameters.
Use Draw, Draw Options, and List Selection to assist in selecting and visualizing the regions.
The tools available in the Diagnostics..., Change Type, Manage, and Remesh Faces menus are used to modify the volumetric region.
You can set up regional mesh parameters using the Scoped Prisms, Tet, and Hexcore menus. The Auto Fill Volume... tool is used to generate the volume mesh for the individual region.
Delete Cells will remove any existing volume mesh while preserving the volumetric region information.
You can get surface mesh statistics using the Summary option and the region's composition using the Info option.
The available options are described in detail in the following sections.
The controls described here are found in the context-sensitive menu accessed by right-clicking on Volumetric Regions.
- Compute
Volumetric regions need to be computed prior to object based volume meshing. The Compute Regions dialog box contains options for computing volumetric regions to produce ready to mesh domains. The computing of regions includes topology checks, re-orienting of normals, and baffle identification and handling before generating the volume mesh.
The volumetric region computation can also handle overlapping zones, so long as they are not multi-connected.
Select Compute... to open the Compute Regions dialog box.
Select the material points in the Material Points selection list and click .
Note: When regions are computed, region names and types will be based on the face zone labels of the mesh object selected. If regions are recomputed, all previous region names and types will be over written.
- Validate
Volumetric regions must be closed, water-tight domains. If individual regions are modified after initially computing volumetric regions, the modified regions need to be validated before proceeding to volume meshing. Regions can be modified using operations such as merging, deleting, or renaming them or changing the region type. Also, the region may also be modified if scoped prism settings are applied.
To manually validate the volumetric regions, select Validate. Also, the regions will be validated when the volume mesh is generated.
- Update
Some of your modifications may involve changing the name or type for the volumetric region. You can recalculate the volumetric region without affecting the region name or type using the Update control.
- Select Regions
Connects to a sub-menu that allows you to select multiple regions based on type (fluid, solid, dead, or all).
- External Baffles
Connects to a sub-menu that allows you to display, select, or remove the baffle(s) from the volumetric regions.
- Setup Scoped Prisms
Provides direct access to Scoped Prisms dialog box in which you can define inflation layers to specific entities in the model.
- Auto Mesh
Use this menu item for setting up volume fill meshing parameters and computing the volume mesh in the full object.
- Summary
From the menu, you can use Summary to obtain an overall summary with counts of face zones, all, free, multi, and duplicate faces, the maximum skewness and number of faces with skewness > 0.85.
- Info
From the menu, you can use Info to obtain a listing of all regions with type, volume, material point, and face zones.
The context-sensitive menus for individual volumetric regions offer several options to select or draw regions. With one or more regions selected in the tree:
Use the menu item to draw the highlighted region(s), replacing what was previously displayed.
Use the submenu to add, remove, highlight, or select the region(s) to (from) the display.
This submenu also provides options to draw, add, remove, highlight, or select regions based on boundary type ( or ), interface type ( interface, interface, or interface), or volume type (Filled Volume or Empty Volume).
Use the submenu to add, remove, or select the region(s) to (from) a selection list in a dialog box.
This submenu also provides options to select, add, or remove regions based on boundary type ( or ), interface type ( interface, interface, or interface), or volume type (Filled Volume or Empty Volume).
Operations to modify the selected volumetric region(s) include the following:
Face connectivity and quality based diagnostic tools are available for fluid volumetric regions. Select Diagnostics... in the menu available for the region selected to open the Diagnostic Tools dialog box.
Use the Change Type option to change the region type in the corresponding drop down list.
Merge multiple regions using the > option in the menu. Enter the New Region Name and select the type for the merged region in the New Region Type drop-down list in the Merge Regions dialog box.
Note: If there are shared face zones, merging regions will delete the shared face zones. However, if there are cell zones associated with the regions, then merging the regions will not delete the shared face zones. In this case, the shared face zones will be deleted when the cell zones are deleted.
Rename individual regions using the > option in the menu. Enter the New Region Name in the Rename Region dialog box.
Delete regions using the > option in the menu.
Tip: Deleting regions may cause face zones to be deleted. It is recommended that the region type be changed to dead instead of deleting the region.
Use the Remesh Faces option in the menu to remesh the face zones based on the existing size field.
Volume meshing operations include options to set up meshing parameters, fill the volume based on the parameters set, and manipulate the cell zones in the regions.
Use the > option to open the Scoped Prisms dialog box for setting scoped prism controls.
Use the > option to open the Tet dialog box for setting tetrahedral mesh controls.
Use the > option to open the Hexcore dialog box for setting hexcore mesh controls.
Use the Auto Fill Volume... option to open the Auto Fill Volume dialog box to create the volume mesh for the selected volumetric regions based on the meshing parameters set.
Use the Delete Cells option to delete the cell zones of the volumetric regions.
The Summary and Info options print information to the console about the surface mesh and the region's composition, respectively, for the selected volumetric region(s).
When regions have been computed and verified, you can proceed to generate the volume mesh. Use the process described below that is best suited to your workflow or problem:
Note: The workflow for object-based volume meshing does not support partial meshing within a region. Operations such as prisms generation only, Tet-initialization only, Hexcore only, etc., require a domain-based workflow.
Important: In the object-based volume meshing procedure, by default a backup of the surface mesh is created before volume meshing starts. To restore the surface mesh at any point, select Restore Faces in the context-sensitive menu for the mesh object. When you select the Restore Faces option, the current object face zones and cell zones will be deleted.
To disable the backup, set the
/mesh/auto-mesh-controls/backup-object command to
no. In that case, you will not be able to restore the surface mesh
using the Restore Faces option.
There may be a difference in the initial volume mesh generated for an object and that generated after restoring the object surface mesh due to differences in the order of zones/entities processed during volume meshing.
The Auto Mesh dialog box contains options for generating the volume mesh for all computed volumetric regions of the mesh object.
The volume mesh can be generated as follows:
Open the Auto Mesh dialog box from the context-sensitive menu available by right-clicking on any mesh object or its Volumetric Regions or Cell Zones branch in the tree.
You can also use the > menu item to open the Auto Mesh dialog box.
Ensure that the mesh object is selected in the Object drop-down list.
Note: If you open the Auto Mesh dialog box from the context-sensitive menu in the tree, the mesh object to which the cell zones, or volumetric regions, belong is automatically selected.
Enable/disable Keep Solid Cell Zones and Keep Dead Cell Zones, as required.
Select the appropriate option in the Grow Prisms drop-down list in the Boundary Layer Mesh group box.
Retain the default selection of none if you do not need to grow prism layers for the current meshing approach.
Select scoped if you want to specify object-based prism controls. Click to open the Scoped Prisms dialog box and define the prism controls for the mesh object. Refer to Prism Meshing Options for Scoped Prisms for details.
Tip: You can save your scoped prism controls to a file (*.pzmcontrol) for use in batch mode, or read in a previously saved scoped prism file.
Select zone-specific if you want to specify zone-specific prism parameters. Click to open the Prisms dialog box and specify the zone-specific prism parameters. Refer to Procedure for Creating Zone-based Prisms for details.
Note: Poly meshing does not support zone-specific prisms.
Select the appropriate quad-tet transition elements from the Quad Tet Transition list. Click the button to open the Pyramids dialog box or the Non Conformals dialog box (depending on the selection) and specify the appropriate parameters. Refer to Creating Pyramids and Creating a Non-Conformal Interface for details.
Note: The Quad Tet Transition options are not applicable to poly mesh.
Select the appropriate option from the Volume Fill list. Click the Set... button to open the Tet, Hexcore, or Poly dialog box (depending on the selection). Specify the appropriate parameters. Refer to Initializing the Tetrahedral Mesh, Refining the Tetrahedral Mesh, Controlling Hexcore Parameters, and Generating Polyhedral Meshes for details.
Note:The No Fill option is not available when a mesh object is selected for volume meshing.
Some operations such as prisms generation only, Tet-initialization only, Hexcore only, are not available for object-based volume meshing. Similarly, options under the Zones group in the Tet and Hexcore dialog boxes, that require a zone-based workflow, have no effect for object-based volume meshing.
Specify the appropriate Volume Fill Options.
For the Tet or Poly methods, set the following:
Select the appropriate option for Cell Sizing.
Size Field specifies that the cell size is determined based on the current size-field.
Geometric specifies that the cell size in the interior of the domain is obtained by a geometric growth from the closest boundary according to the growth rate specified.
Set the Growth Rate required.
Specify the Max Cell Length. Click to compute the maximum cell size based on the mesh object.
For the Hexcore method, set the following:
Select the appropriate option for Type.
Retain the default selection of Cartesian or select the Octree type.
Set the number of Buffer Layers and Peel Layers.
Specify the Max Cell Length for the Cartesian approach. Click to compute the maximum cell size based on the mesh object.
Specify the Min Cell Length for the Octree approach.
Enable or disable additional Options as desired.
Enable Merge Cell Zones within Regions to create a single cell zone within a region, or disable to keep the cell zones separate.
Click in the Auto Mesh dialog box.
Alternatively, you can use the command /mesh/auto-mesh to
generate the mesh automatically. Specify a mesh object name for object-based auto mesh; if
no name is given, face zone based auto mesh is performed. Specify the mesh elements to be
used when prompted. Specify whether to merge the cells into a single zone or keep the cell
zones separate. For face zone based meshing, specify whether to automatically identify the
domain to be meshed based on the topology information.
Note: You can specify the meshing parameters for the mesh elements (prisms, pyramids or
non-conformals, tet, or hex) using either the respective dialog boxes or the associated
text commands prior to using the auto-mesh command. Commands
for poly meshes are located under the mesh/poly menu.
The Auto Fill Volume dialog box contains options for generating the volume mesh in selected volumetric regions for mesh objects.
The volume mesh can be generated as follows:
In the tree, expand Volumetric Regions and select the regions to be meshed.
Set up the regional meshing parameters for the selected regions.
Specify scoped prism controls for the boundary layer mesh, if applicable. Select > in the context-sensitive menu to open the Scoped Prisms dialog box. Refer to Prism Meshing Options for Scoped Prisms for details.
Specify tetrahedral mesh or hexcore mesh parameters, as applicable.
Select > to open the Tet dialog box. Refer to Initializing the Tetrahedral Mesh, and Refining the Tetrahedral Mesh for details.
Select > to open the Hexcore dialog box. Refer to Controlling Hexcore Parameters for details.
Note: When you click the button in the Tet or Hexcore dialog box, you will be asked if the maximum cell size is to be computed based on the mesh object selected. Click Yes to recompute the cell sizes based on the mesh object.
Alternatively, open the Auto Fill Volume dialog box from the menu for the selected regions. Click the button in the Boundary Layer Mesh and Volume Fill group box to set the scoped prism and tetrahedral/hexcore mesh parameters, respectively.
Set the boundary layer mesh and volume fill options in the Auto Fill Volume dialog box.
Enable Grow Scoped Prisms if scoped prism controls have been set up.
Select Tet or Hexcore in the Volume Fill list.
Click in the Auto Fill Volume dialog box.
Repeat this procedure for any empty volumetric regions until all regions are filled.
The context-sensitive menu for Cell Zones contains options for visualizing and manipulating all cell zones collectively:
Use Draw All Boundaries to draw all the cell zone boundaries or Draw All Cells in Range to draw all the cells within a specified range (for either unreferenced or referenced zones). The range can be set in the Bounds group in the ribbon.
Use Auto Mesh... to access the Auto Mesh tool for volume meshing.
Use Auto Node Move... to access the Auto Node Move tool for improving the mesh quality by moving nodes.
Use the Select Cell Zones sub-menu for selection of all cell zones as well as selection by type (fluid, solid, or dead).
Use Delete All to delete all cell zones, if needed.
Use Summary to obtain an overall summary of cell count and quality or Info to obtain individual cell zone type and cell zone count by type.
The context-sensitive menu for individual cell zones offers several options to select or draw cell zones.
Use Draw Boundaries to draw the boundaries of the selected zones, or Draw Cells in Range to draw the cells within a specified range.
Use the submenu to add, remove, highlight, or select the cell zone(s) to (from) the display.
Use the submenu to add, remove, or select the cell zone(s) to (from) a selection list in a dialog box.
Use Auto Node Move... to access the Auto Node Move tool for improving the mesh quality of the selected zone by moving nodes.
Use Merge to combine two or more selected cell zones into a single zone.
Important: In object-based workflows, merging cell zones requires that they be in the same volumetric region.
To merge cell zones that cannot be in the same volumetric region because they are not contiguous, you will need to first delete the object(s) only, and then use the Manage Cell Zones dialog box.
Use Delete to delete the cell zones, if needed. Volumetric regions are not affected if cell zones are deleted.
Use Summary to obtain a summary of cell count and quality or Info to obtain individual cell zone type and cell zone count by type.