Volume Meshing Mesh Controls

Model, local and volume selector mesh controls for volume meshing.

Model

Model mesh controls define boundary layer and/or tetrameshing parameters.

BL + Tetra

BL + Tetra model mesh controls define boundary layer and tetrameshing parameters.
Entity Selection Parameters
In the Entities field, use the entity selector to select the entities that the mesh control applies to.
The following entities can be selected using the entity selector:
  • Components
  • Elements
  • Regions (solid selection only)
  • Solids
Note: If you have changed your selection to solid or region in model volume mesh controls, existing local controls that have elements or components selected will be made inactive. Any new local mesh controls will have surfaces set for their default selection.

If regions are selected, final volume mesh controls will be placed in a component with the same name as the region.

Meshing will only work if surfaces or solids have mesh associated with them.

Boundary Layer Parameters
Available parameters vary depending on the Method you select: Simple, Advanced, User Defined. For Simple and Advance mesh controls, refer to Link to CFD Tetramesh Panel.
Table 1. Parameters
Parameter Description
Basic Surface Mesh Treatment
Fixed
Prohibit selected elements from being modified.
Float
Enable 2D base elements to be modified, if necessary. Generally 2D base elements with NoBL are modified when refinement zones are defined and/or when the BL imprints on them.
BL Definition When enabled, parameters will be editable and will be applied to all selections. When disabled, a BL definition will not be applied at model level.

Local controls will override the BL definition at the model level.

First Layer Thickness Specify the thickness of the first boundary layer.
First Layer Thickness Method (A)
Constant
Enable a constant thickness to be defined for the first boundary layer of the selection.
As Factor of Base 2D Elements
Enable a factor, which will be multiplied by the average element size, to be defined. The first layer height for each element equals the average element size multiplied by the factor. This option is useful when the size of 2D elements varies significantly and a constant first layer height is not needed. With this factor, a smooth BL to tetramesh transition for all elements can be achieved.
Figure 1. First Layer Thickness Method (A)


Growth Rate Determine how rapidly elements can increase in size as they are created further and further away from features.
Figure 2. Growth Rate


Elements further from the features grow larger with each row.
BL Growth Rate Method (A)
Constant
Enable a constant ratio to be defined, which determines how boundary layers grow.
Acceleration
Enable a growth acceleration for boundary layers to be defined beyond the first few layers. This option acts as a growth rate on the growth rate, but only after the first few initial boundary layers. A Start Acceleration from Layer must be defined first, and then from that layer the acceleration will be started. An Acceleration to the initial growth rate and a Maximum Growth Rate must also be defined.
By default, the first two boundary layers grow by the growth rate described above. However, subsequent layers grow by the growth rate multiplied by the acceleration factor. Thus, if d is the initial thickness, r is the initial growth rate, and a is the acceleration rate, then the thicknesses of the successive layers are d, d*r, d*r*(r*a), d*r*(r*a)^2, and so on.
Aspect Ratio Based
Enable the growth rate definition for boundary layers to be based on the defined aspect ratio of the final layer. After the first few initial boundary layers, if this type of growth rate method is selected, the rest of the BL will grow to achieve the user defined Final layer height / base ratio.
BL Thickness Control (UD) Enable this option to enter either the Number of layers or the Total BL thickness.
Second Group (UD) Help to get a smooth transition between BL layers and the tet core more quickly, by defining a higher growth rate.
Final Layer Height/Base Ratio Define the ratio between the total boundary layer thickness and the average element size of the base surface elements.
BL Stopping Criteria (A) Determine what to do when BL has reached the defined criteria for Final Layer Height/Base Ratio.
Chop Off Layers
Chop off the BL if elements reach the aspect ratio criteria.
Keep Growing Gr=1
Allow the BL to grow until the neighboring elements begin to grow, even if elements reach the aspect ratio criteria with GR =1.
Number of Layers (S) Define the total number of layers to be generated using the specified first layer thickness and growth rate.
Hexa Transition Mode
Simple Pyramid
Transition from a BL hexahedral’s quad face to a tetrahedral core mesh using one pyramid element. The height of pyramid elements is controlled by a simple transition ratio parameter, which represents the ratio between the transition pyramid height and the characteristic size of the base quad.
All Prism
Split quad elements in the surface mesh into two trias each so that there will be no need to transition from quad faces to tria faces when transitioning from the last boundary layer to the tetrahedral core. This mode is very important when there are quad elements on areas with (low) distributed BL thickness ratios, because in such areas the thickness of the transition elements, for example simple pyramid, was not taken into account when doing the interference study to assign distributed BL thickness ratio to those elements.
All Tetras
Generate tetra elements only in the boundary layer and splits the quad elements of the surface mesh into tria elements.
Boundary Layer Only Generate only the boundary layer, stopping before the tetrahedral core is generated. Adjacent surface meshes are also modified to reflect changes introduced by the boundary layer thickness. A collector named ^CFD_trias_for_tetramesh is created and is typically used to generate the inner core tetrahedral mesh using the Tetramesh parameters subpanel.

Boundary layer elements are placed in a collector named CFD_boundary_layer; core tetrahedral elements are placed in a collector named CFD_Tetramesh_core. Both collectors are automatically created if they do not exist. However, if these collectors do exist, it is recommended that you empty them before meshing; otherwise there will be more than one set of elements occupying the same physical volume. If you mesh the volume in several steps (multi-volume meshing), it is recommended that you empty the collector before generating the mesh for the next adjacent volume.

Core Mesher Parameters
Available options will direct how the core domain should be meshed. All options will also rely on option in “Tetra Mesh” section.
Table 2. Parameters
Parameter Description
Core Mesh
Tetra Mesh
Will create tetra mesh in core.
Hex Dominant
Will create hex elements in core and create pyramids/tetrahedral in transition region. All elements will have conformal connectivity.
Core Hex elements will be created based on user defined Hexa Size. Height of tetra/pyramid transition region can be controlled using Tet-core Layer Height Factor.
Octree Dominant
Will create octree elements in core and create pyramids/tetrahedral in transition region. All elements except core octree elements will have conformal connectivity.
Core Octree elements will be creates based on user defined Max Octant Size and Min Octant Size. Height of tetra/pyramid transition region can be controlled using Tet-core Layer Height Factor.
Figure 3. Core Octree Element


Hexa Size Size of the hex mesh.
Enable Hexa Transition When checked, allows you to generate a variable size hex mesh with transition.
Minimal Hexa Size The minimum size of the hex generated around the boundary.
Tetra Mesh Parameters
The tetramesher is multi-threaded and will utilize available threads for meshing similar. This behavior is similar to that of boundary layer meshing.
Table 3. Parameters
Parameter Description
Element Size Limits Specify the average, minimum, maximum, or minimum/maximum size of the tetramesh.
None
The maximum element size will be determined by the input 2D elements size and growth rate.
Average Size
Enter the average element size for the tetramesh. If you enter 10, the element sizes will range between 6.6 and 14.
Maximum Size
Tetra element will not be above this size.
Minimum Size
Tetra elements will not be below this size.
Minimum/Maximum Size
Tetra elements will not be below or above this size.
Minimum Height
Generate tetramesh with a minimum height above the value defined. The tetramesh algorithm will try to enforce the user-defined minimum height.
Minimum Height/Maximum Size
Tetra elements will not be below or above this height.
Maximum element size guidelines:
  • When the input shell element size is close to the user defined maximum tetra size, then the maximum tetra size is used in averaged sense (therefore the actual maximum size may be larger than defined). This prevents a large number of elements from being created.
  • When the input shell element size is sufficiently different then the user defined maximum tetra size, the maximum size will be enforced.
Quality
Normal
Use the standard tetra-meshing algorithm.
Optimize Speed
Use an algorithm for faster meshing. Use this option if element quality considerations are less important than mesh generation time.
Optimize Quality
Spend more time optimizing element quality, and employs the volumetric ratio, or CFD skew measurement for tetras as a quality measure. Use this option if your solver is sensitive to element quality.
Tetra Mesh Method Select a tetra mesh method:
Delaunay
Enable a mesher, which is implemented based on the delaunay approach. This method is recommended for improved performance.
Advancing Front
Enables the legacy tetra mesher.
Octree Based
Enable an octree structured based tetrameshing. Smoothing near boundaries will be performed with this method.
Growth Rate The Growth rate parameter works as follows: if d is the initial thickness and r is the initial growth rate, then the thicknesses of the successive layers are d, d*r, d*r^2, d*r^3, d*r^4, and so on.

If element quality is important and you are not concerned with the total number of elements being created, then Interpolate will produce the best results because the element size changes smoothly and therefore the element quality is better.

Different default values are specified for the various growth rate options:
Standard
1.2
Aggressive
1.35
Gradual
1.08
Interpolate
1.08
User Controlled, Octree based, Delaunay
Define your own value when you select this option.
Tetramesh Height Factor Near Boundary The Delaunay method allows options to control the height of tetra mesh near boundary. Tetra transition from boundary layer or surfaces can be controlled using this factor.
Figure 4. Height Factor = 1


Figure 5. Height Factor = .5


Pyramid Transition Ratio Define the relative height of pyramid elements used for the transition from hexa elements in the boundary layer to the tetra elements in the core.
Smoothing Apply an extra stage of calculation to improve overall mesh quality. Additional smoothing and swapping steps will be performed and tetra elements will be split to achieve a smoother mesh transition. If tetra elements are used in the boundary layer, then those elements will be excluded from smoothing to maintain the original distribution.
Use Number of Layers

Define the number of tetrahedral layers to generate.

When enabled, the Tetramesher ensures the tetracore contains, at minimum, the specified number of tetra layers in the model. This functionality ensures a certain mesh resolution in case of close proximity or thin channels.

When generating multiple tetrahedral layers, keep the following restrictions in mind:
  • Do not generate more than three or four layers, unless you refine the surfaces to have a fine mesh at close proximity areas.
  • Layer meshes will not be created near narrow strip surfaces, as the current algorithm does not alter the surface mesh given.
Advanced Parameters
Table 4. Parameters
Parameter Description
Boundary Layer Propagation
Treatment at Sharp Edges
Node collapse
Collapse BL at baffles or sharp corners below the defined angle.
Figure 6. Node Collapse. The baffle is colored yellow.


Multiple normal
Grow multiple normals around baffles or sharp corners below the defined angle. If two adjacent elements enclose an angle smaller than the threshold (sharp edge pointing into the volume), normals will be computed on that edge and the boundary layer will consider those normals.
Figure 7. Multiple Normal. The baffle is colored yellow.


Entities If multiple normal option is selected, select lines or nodes on which the multiple normal BL needs to be created. If there is no selection and multiple normal option is selected, it will consider features defined by "Sharp edge angle". You can define any angle.
Sweep Angle If multiple normal option is selected, sweep angle will define number of BL segments created at defined feature edge. The number of BL segments at the defined edge = 180 / sweep angle. BL is smoother with smaller angles.
Sharp Edge Angle Define the threshold of angles below which the BL should be collapsed.
Auto append neighboring edges If on, automatically append the neighboring selection to avoid early termination of BL.
Minimum Imprint Angle from BL to Non-BL Control which cases to imprint BL entities on without BL components. If the angle between the BL component and the non BL component is high, imprinting will create high aspect ratio elements. If the angle between BL and Non-BL entities (component elements) is less than the imprint angle or greater than (180-imprint angle), then the BL will collapse rather than imprinting on non-BL entities.

Recommended range: 6-10

Max Layer Difference Between Neighbors Control the maximum layer difference between neighboring elements. This parameter helps avoid situations where all BLs collapse at once, and also provides smooth BL transitions in cases of BL truncation. A good value for this parameter is 1/4 of the total BL layers. The value specified also depends on layer height.

Recommended range: Depends on how many layers you are growing.

Proximity
Maximum BL Compression Enable BL compression, or squeezing, when there is not enough space available for the BL to grow. The BL will try to compress by the max BL compression factor first. For example, if the original total BL height is defined as 1, with a 0.4 max BL compression, the BL layers will try to be compressed until 0.6 of the total height is reached. Once the BL is compressed to this value, the mesher will start chopping off layers if there is not enough space.

A value of zero enforces no BL compression, which is useful when you want to maintain the BL height; a value of one enables the maximum possible compression.

Recommended range: 0-0.6

Minimum BL Thickness/Base Ratio Due to close proximity, the BL will sometimes only be able to generate one to two layers (a very small total BL height at that location). At that location, it might be possible that the transition between BL layers and the tetra core is bad. With this factor, if the total BL height is less than the defined factor base size, all of the BL layers will be chopped off.

By default, this value is zero, which disables the effects of this parameter.

Minimum Tetcore/Final Layer Height Ratio Control the minimum height of the tet core as a factor of the final layer height.

After creating the BL in close proximity, there will be a small space available for tetramesh. This results in high aspect ratio tetra elements.

Recommend value: 1.3 (default)

Boundary Layer Quality
Generation Method
Controls the growth of boundary layers.
Optimize Quality
Use a set of meshing parameters, which ensures a good quality boundary layer in most cases.
Optimize Speed
Choose meshing parameters in a way that the meshing time is minimized and an acceptable boundary layer quality is achieved.
Maximum Cell Skewness Chop off BL cells exceeding the defined maximum cell skewness. This parameter prevents the generation of highly skewed elements.

The tetra mesher sometimes creates better quality elements compared to the BL mesher. If your input 2D mesh has bad element quality and topology, it is recommended that you define a higher value.

Recommended range: 0.8 - 0.95

Minimum Normalized Jacobian Chop off BL cells exceeding the defined minimum normalized Jacobian. This parameter prevents the generation of negative elements.

Recommended range: 0.05 - 0.2

Tetra Quality
Element Quality Target Select an element criteria and threshold. After the tetrameshing step, a mesh optimization step will be performed to fulfill the defined threshold for the selected element criteria.

Available quality criteria include: Volume Skew, Tetra Collapse, and Cell Squish.

Volume Setup
Validate 2D Input Check BL elements before tetrameshing to rectify if there is anything wrong with the input (intersecting elements) provided for the tetramesh.
Fix Invalid 2D Element Fix invalid elements (at present only unoffsettable nodes) before volume meshing.

For unoffsettable nodes (where BL collapses if not smooth), the connected elements will be smoothed where the BL will be generated.

Fix Component Boundaries Anchor nodes are maintained during CFD tetrameshing, so that the new mesh adheres to them. 1D elements can be selected instead of nodes if you need a tetra element edge at a certain location. Select this option when certain mesh nodes or edges are required on a certain location, such as for post-processing purposes.
If the Float option is selected for some boundary regions, surface shell edges will be swapped during mesh generation. However, this prevents the swapping of edges between two components.
Figure 8.


Update Input Shells Automatically update the shells on all boundaries after meshing. Updated shell elements are placed in the initial boundary shell components.
Fill Void Mesh all volumes. If your geometry includes volumes inside of another volume, enable this parameter.

For example, if you had a sphere inside of a larger sphere, enabling this parameter would cause the volume of the inner sphere as well as the volume between the two spheres to be meshed.

Other
Anchor Node Node that will remain and be re-used in the new mesh. Anchor nodes are "fixed" so that the automesher cannot move or replace them; in essence, they are exceptions to the re-meshing operation, and the new mesh must utilize them.

Tetra

Tetra mesh controls define tetrameshing parameters.
Entity Selection Parameters
In the Entities field, use the entity selector to select the entities that the mesh control applies to.
The following entities can be selected using the entity selector:
  • Components
  • Elements
  • Regions (solid selection only)
  • Solids
Note:

If you have changed your selection to solid or region in model volume mesh controls, existing local controls that have elements or components selected will be made inactive. Any new local mesh controls will have surfaces set for their default selection.

If regions are selected, final volume mesh controls will be placed in a component with the same name as the region.

Meshing will only work if surfaces or solids have mesh associated with them.

Tetra Mesh Parameters
Table 5. Parameters
Parameter Description
Base Surface Mesh Treatment
Fixed
Prohibit selected elements from being modified.
Float
Modify 2D base elements, if necessary. Generally 2D base elements with NoBL are modified when refinement zones are defined and/or when the BL imprints on them.
Element Size Limits Specify the average, minimum, maximum, or minimum/maximum size of the tetramesh.
None
The maximum element size will be determined by the input 2D elements size and growth rate.
Average Size
Enter the average element size for the tetramesh. If you enter 10, the element sizes will range between 6.6 and 14.
Maximum Size
Tetra element will not be above this size.
Minimum Size
Tetra elements will not be below this size.
Minimum/Maximum Size
Tetra elements will not be below or above this size.
Minimum Height
Generate tetramesh with a minimum height above the value defined. The tetramesh algorithm will try to enforce the user-defined minimum height.
Minimum Height/Maximum Size
Tetra elements will not be below or above this height.
Maximum element size guidelines:
  • When the input shell element size is close to the user defined maximum tetra size, then the maximum tetra size is used in averaged sense (therefore the actual maximum size may be larger than defined). This prevents a large number of elements from being created.
  • When the input shell element size is sufficiently different then the user defined maximum tetra size, the maximum size will be enforced.
Quality
Normal
Use the standard tetra-meshing algorithm.
Optimize Speed
Use an algorithm for faster meshing. Use this option if element quality considerations are less important than mesh generation time.
Optimize Quality
Spend more time optimizing element quality, and employs the volumetric ratio, or CFD skew measurement for tetras as a quality measure. Use this option if your solver is sensitive to element quality.
Tetra Mesh Method Select a tetra mesh method:
Delaunay
Enable a mesher, which is implemented based on the delaunay approach. This method is recommended for improved performance.
Advancing Front
Enables the legacy tetra mesher.
Octree Based
Enable an octree structured based tetrameshing. Smoothing near boundaries will be performed with this method.
Growth Rate The Growth rate parameter works as follows: if d is the initial thickness and r is the initial growth rate, then the thicknesses of the successive layers are d, d*r, d*r^2, d*r^3, d*r^4, and so on.

If element quality is important and you are not concerned with the total number of elements being created, then Interpolate will produce the best results because the element size changes smoothly and therefore the element quality is better.

Different default values are specified for the various growth rate options:
Standard
1.2
Aggressive
1.35
Gradual
1.08
Interpolate
1.08
User Controlled, Octree based, Delaunay
Define your own value when you select this option.
Tetramesh Height Factor Near Boundary Delaunay method allow option to control height of tetra mesh near boundary. Tetra transition from boundary layer or surfaces can be controlled using this factor.
Figure 9. Height Factor = 1


Figure 10. Height Factor = 0.5


Pyramid Transition Ratio Define the relative height of pyramid elements used for the transition from hexa elements in the boundary layer to the tetra elements in the core.
Smoothing Apply an extra stage of calculation to improve overall mesh quality. Additional smoothing and swapping steps will be performed and tetra elements will be split to achieve a smoother mesh transition. If tetra elements are used in the boundary layer, then those elements will be excluded from smoothing to maintain the original distribution.
Use Number of Layers

Define the number of tetrahedral layers to generate.

When enabled, the Tetramesher ensures the tetracore contains, at minimum, the specified number of tetra layers in the model. This functionality ensures a certain mesh resolution in case of close proximity or thin channels.

When generating multiple tetrahedral layers, keep the following restrictions in mind:
  • Do not generate more than three or four layers, unless you refine the surfaces to have a fine mesh at close proximity areas.
  • Layer meshes will not be created near narrow strip surfaces, as the current algorithm does not alter the surface mesh given.
Hexa Size Size of the hex mesh.
Enable Hexa Transition When checked, allows you to generate a variable size hex mesh with transition.
Minimal Hexa Size The minimum size of the hex generated around the boundary.
Advanced Parameters
Table 6. Parameters
Parameter Description
Tetra Quality
Element Quality Target Select an element criteria and threshold. After the tetrameshing step, a mesh optimization step will be performed to fulfill the defined threshold for the selected element criteria.

Available quality criteria include: Volume Skew, Tetra Collapse, and Cell Squish.

Volume Setup
Validate 2D Input Check BL elements before tetrameshing to rectify if there is anything wrong with the input (intersecting elements) provided for the tetramesh.
Fix Invalid 2D Element Fix invalid elements (at present only unoffsettable nodes) before volume meshing.

For unoffsettable nodes (where BL collapses if not smooth), the connected elements will be smoothed where the BL will be generated.

Fix Component Boundaries Anchor nodes are maintained during CFD tetrameshing, so that the new mesh adheres to them. 1D elements can be selected instead of nodes if you need a tetra element edge at a certain location. Select this option when certain mesh nodes or edges are required on a certain location, such as for post-processing purposes.
If the Float option is selected for some boundary regions, surface shell edges will be swapped during mesh generation. However, this prevents the swapping of edges between two components.
Figure 11.


Update Input Shells Automatically update the shells on all boundaries after meshing. Updated shell elements are placed in the initial boundary shell components.
Fill Void Mesh all volumes. If your geometry includes volumes inside of another volume, enable this parameter.

For example, if you had a sphere inside of a larger sphere, enabling this parameter would cause the volume of the inner sphere as well as the volume between the two spheres to be meshed.

Other
Anchor Node Node that will remain and be re-used in the new mesh. Anchor nodes are "fixed" so that the automesher cannot move or replace them; in essence, they are exceptions to the re-meshing operation, and the new mesh must utilize them.

Local

Local mesh controls define regions where boundary layers are desired, or are not desired.

No BL

No BL local mesh controls define components/elements on which boundary layers mesh is not required.
Entity Selection Parameters
In the Entities field, use the entity selector to select the entities that the mesh control applies to.
The following entities can be selected using the entity selector:
  • Components
  • Elements
  • Regions (solid selection only)
  • Solids
Note:

If you have changed your selection to solid or region in model volume mesh controls, existing local controls that have elements or components selected will be made inactive. Any new local mesh controls will have surfaces set for their default selection.

If regions are selected, final volume mesh controls will be placed in a component with the same name as the region.

Meshing will only work if surfaces or solids have mesh associated with them.

Boundary Layer Parameters
Table 7. Parameters
Parameter Description
Basic Surface Mesh Treatment
Fixed
Prohibit selected elements from being modified.
Float
Enable 2D base elements to be modified, if necessary. Generally 2D base elements with NoBL are modified when refinement zones are defined and/or when the BL imprints on them.

Local BL

Local BL local mesh controls define local boundary layer settings. Any settings defined in the model mesh controls will be overridden with the BL settings defined in local mesh controls.
Entity Selection Parameters
In the Entities field, use the entity selector to select the entities that the mesh control applies to.
The following entities can be selected using the entity selector:
  • Components
  • Elements
  • Regions (solid selection only)
  • Solids
Note:

If you have changed your selection to solid or region in model volume mesh controls, existing local controls that have elements or components selected will be made inactive. Any new local mesh controls will have surfaces set for their default selection.

If regions are selected, final volume mesh controls will be placed in a component with the same name as the region.

Meshing will only work if surfaces or solids have mesh associated with them.

Use these general steps to generate boundary layers:
  1. Select the appropriate mesh control and set to Local BL.
  2. Select the surfaces, shared between the solids, in the Entities section of the Entity Editor.
  3. Select the parent solid where you want to generate the boundary layer. If no parent is selected, the BL engine will generate a boundary layer on both sides of the surface interface.
  4. Define boundary layer parameters.
  5. Right-click on the volume mesh folder and run the mesh.
    Figure 12. Bottom Solid as Parent
Boundary Layer Parameters
Available parameters vary depending on the Method you select: Simple, Advanced, User Defined.
Table 8. Parameters
Parameter Description
Base Surface Mesh Treatment
Fixed
Prohibit selected elements from being modified.
Float
Modify 2D base elements, if necessary. Generally 2D base elements with NoBL are modified when refinement zones are defined and/or when the BL imprints on them.
First Layer Thickness Specify the thickness of the first boundary layer.
First Layer Thickness Method
Constant
Define a constant thickness for the first boundary layer of the selection.
As Factor of Base 2D Elements
Enable a factor, which will be multiplied by the average element size, to be defined. The first layer height for each element equals the average element size multiplied by the factor. This option is useful when the size of 2D elements varies significantly and a constant first layer height is not needed. With this factor, a smooth BL to tetramesh transition for all elements can be achieved.
Figure 13. First Layer Thickness Method


Growth Rate Determines how rapidly elements can increase in size as they are created further and further away from features.
Figure 14. Growth Rate


Elements further from the features grow larger with each row.
BL Growth Rate Method
Constant
Define a constant ratio, which determines how boundary layers grow.
Acceleration
Define a growth acceleration for boundary layers beyond the first few layers. This option acts as a growth rate on the growth rate, but only after the first few initial boundary layers. A Start Acceleration from Layer must be defined first, and then from that layer the acceleration will be started. An Acceleration to the initial growth rate and a Maximum Growth Rate must also be defined.
By default, the first two boundary layers grow by the growth rate described above. However, subsequent layers grow by the growth rate multiplied by the acceleration factor. Thus, if d is the initial thickness, r is the initial growth rate, and a is the acceleration rate, then the thicknesses of the successive layers are d, d*r, d*r*(r*a), d*r*(r*a)^2, and so on.
Aspect Ratio Based
Define the growth rate definition for boundary layers based on the defined aspect ratio of the final layer. After the first few initial boundary layers, if this type of growth rate method is selected, the rest of the BL will grow to achieve the user defined Final layer height / base ratio.
BL Thickness Control Enables this option to enter either the Number of layers or the Total BL thickness.
Second Group Help to get a smooth transition between BL layers and the tet core more quickly, by defining a higher growth rate.
Final Layer Height / Base Ratio Define the ratio between the total boundary layer thickness and the average element size of the base surface elements.
Number of Layers Define the total number of layers to be generated using the specified first layer thickness and growth rate.
BL Stopping Criteria Determine what to do when BL has reached the defined criteria for Final Layer Height/Base Ratio.
Chop Off Layers
Chop off the BL if elements reach the aspect ratio criteria.
Keep Growing Gr=1
Grow BL until the neighboring elements begin to grow, even if elements reach the aspect ratio criteria with GR =1.
Advanced Parameters
Table 9. Parameters
Parameter Description
Use Global Values Values defined for advanced parameters will be taken from the advanced parameters defined for the model mesh control.
Maximum BL Compression Enable BL compression, or squeezing, when there is not enough space available for the BL to grow. The BL will try to compress by the max BL compression factor first. For example, if the original total BL height is defined as 1, with a 0.4 max BL compression, the BL layers will try to be compressed until 0.6 of the total height is reached. Once the BL is compressed to this value, the mesher will start chopping off layers if there is not enough space.

A value of zero enforces no BL compression, which is useful when you want to maintain the BL height; a value of one enables the maximum possible compression.

Recommended range: 0-0.6

Minimum BL Thickness / Base Ratio Due to close proximity, the BL will sometimes only be able to generate one to two layers (a very small total BL height at that location). At that location, it might be possible that the transition between BL layers and the tetra core is bad. With this factor, if the total BL height is less than the defined factor base size, all of the BL layers will be chopped off.

By default, this value is zero, which disables the effects of this parameter.

Local Tetra

A mesh control that allows you to define controls for local tetra capabilities.

Entity Selection Parameters
In the Entities field, use the entity selector to select the entities that the mesh control applies to.
The following entities can be selected using the entity selector:
  • Regions (solid selection only)
  • Solids
Tetra Mesh Parameters
Item Description
Base Surface Mesh Treatment
Fixed
Prohibit selected elements from being modified.
Float
Modify 2D base elements, if necessary. Generally 2D base elements with NoBL are modified when refinement zones are defined and/or when the BL imprints on them.
Element Size Limits Specify the average, minimum, maximum, or minimum/maximum size of the tetramesh.
None
The maximum element size will be determined by the input 2D elements size and growth rate.
Average Size
Enter the average element size for the tetramesh. If you enter 10, the element sizes will range between 6.6 and 14.
Maximum Size
Tetra element will not be above this size.
Minimum Size
Tetra elements will not be below this size.
Minimum/Maximum Size
Tetra elements will not be below or above this size.
Minimum Height
Generate tetramesh with a minimum height above the value defined. The tetramesh algorithm will try to enforce the user-defined minimum height.
Minimum Height/Maximum Size
Tetra elements will not be below or above this height.
Maximum element size guidelines:
  • When the input shell element size is close to the user defined maximum tetra size, then the maximum tetra size is used in averaged sense (therefore the actual maximum size may be larger than defined). This prevents a large number of elements from being created.
  • When the input shell element size is sufficiently different then the user defined maximum tetra size, the maximum size will be enforced.
Quality
Normal
Use the standard tetra-meshing algorithm.
Optimize Speed
Use an algorithm for faster meshing. Use this option if element quality considerations are less important than mesh generation time.
Optimize Quality
Spend more time optimizing element quality, and employs the volumetric ratio, or CFD skew measurement for tetras as a quality measure. Use this option if your solver is sensitive to element quality.
Tetra Mesh Method Select a tetra mesh method:
Delaunay
Enable a mesher, which is implemented based on the delaunay approach. This method is recommended for improved performance.
Advancing Front
Enables the legacy tetra mesher.
Octree Based
Enable an octree structured based tetrameshing. Smoothing near boundaries will be performed with this method.
Growth Rate The Growth rate parameter works as follows: if d is the initial thickness and r is the initial growth rate, then the thicknesses of the successive layers are d, d*r, d*r^2, d*r^3, d*r^4, and so on.

If element quality is important and you are not concerned with the total number of elements being created, then Interpolate will produce the best results because the element size changes smoothly and therefore the element quality is better.

Different default values are specified for the various growth rate options:
Standard
1.2
Aggressive
1.35
Gradual
1.08
Interpolate
1.08
User Controlled, Octree based, Delaunay
Define your own value when you select this option.
Tetramesh Height Factor Near Boundary The Delaunay method allows options to control the height of tetra mesh near boundary. Tetra transition from boundary layer or surfaces can be controlled using this factor.
Figure 15. Height Factor = 1


Figure 16. Height Factor = .5


Use Number of Layers

Define the number of tetrahedral layers to generate.

When enabled, the Tetramesher ensures the tetracore contains, at minimum, the specified number of tetra layers in the model. This functionality ensures a certain mesh resolution in case of close proximity or thin channels.

When generating multiple tetrahedral layers, keep the following restrictions in mind:
  • Do not generate more than three or four layers, unless you refine the surfaces to have a fine mesh at close proximity areas.
  • Layer meshes will not be created near narrow strip surfaces, as the current algorithm does not alter the surface mesh given.
Advanced Parameters
Item Description
Element Quality Target Select an element criteria and threshold. After the tetrameshing step, a mesh optimization step will be performed to fulfill the defined threshold for the selected element criteria.

Available quality criteria include: Volume Skew, Tetra Collapse, and Cell Squish.

Local Solid Map

A mesh control that allows you to define controls for solid map capabilities. With this control, you can create a hex mesh or hybrid mesh (hex + tet).

Use these steps to create the mesh:
  1. Create a global mesh control with solid selection.
  2. Create a solid map mesh control.
  3. Select mappable solid, source, and target surfaces to mappable solids.
  4. Define surface mesh size, element type, and extrusion size.
  5. Define optional biasing parameters.
  6. Right-click on volume mesh folder and select mesh.
Entity Selection Parameters
Entity Description
Solids for Solid Map Mappable solid where mapped hex mesh needs to be generated. Selection should be mappable solid.
Source Surfaces Select surfaces that define the source face of the volume/solid. Source and target will be auto detected if not selected.
Target Surfaces Select surfaces that define the destination face of the volume/solid. Source and target will be auto detected if not selected.
Elements Size
Item Description
Size on Source Mesh size for source surface. If source surfaces are already meshed, solid map will keep the mesh as is during meshing.
First Layer Height First hex cell size along the direction of source to target. Determines the number of elements along the depth of the mapping. If size or density is set to zero, the element size/density is calculated based on the average element source elements (elems to drag).
Type on Source Mesh type for source surface. If source surfaces are already meshed, solid map will keep the mesh as is during meshing.
Advanced Parameters
Parameter Description
Enable Biasing Choose whether to enable biasing.
Biasing Method Type of biasing to use while creating nodes in the along direction. Biasing style works in conjunction with growth rate.
Growth Rate Increase or decrease hex cell width along the depth of the mapping. A growth rate of 1 will generate a constant size hex along the direction of source to target.
Apply Orthogonality Along Extrusion Attempts to improve orthogonality of the hex along the direction of source to target.
Create Boundary Faces Option to create 2D shell faces on the boundaries that match the generated hex mesh.

Volume Selector

Volume Selector mesh controls define which volumes should be meshed and how mesh should be generated. Only one instance of a volume selector mesh control is allowed.

The parameters defined for Volume Selector mesh controls are applicable to both BL + Tetra and Tetra model mesh controls.
Table 10. Parameters
Parameter Description
Select Volumes Defines which volumes to mesh.
All Volumes
Mesh all of the volumes in the model. This option is also affected by the parameter Fill Void, which fills of the voids (volume completely enclosed in another volume) when enabled.
Example: When this option is enabled, and there is a sphere inside of a larger sphere, the volume of the inner sphere as well as the volume between the two spheres will be meshed.
Exclude Enclosed
Mesh all of the volume except for the volumes enclosed by the defined seed node. The seed node should be enclosed in the volume.
Nth Largest
Select volumes to mesh based on size. Specify whether to select the 1st largest, 2nd largest, ... using the volume index "N", which is volume number. If you do not specify N, the smallest volume will be meshed by default.
By Seed Nodes/Elems
Select volumes to be meshed by either specifying a seed node (the seed node should be enclosed in the volume) or touching elements or geometric solids (if input is solid). All can be defined at same time. If there is a conflict between fluid and solid volumes, the fluid volume will take precedence.
Mesh to File Store the generated mesh in a .nas or .hmx file after meshing is finished. When enabled, specify a location to export the mesh.
BL and Tetras in One Component Store BL elements and tetra elements in one component. When disabled, BL elements and tetra elements will be stored in separate components, which is useful when you need to define morphing constraints on BL elements.
Generate BL Contours Generate a .res file in your working directory of BL result contours (Number of layers, first layer height, total BL thickness) for each input element after volume meshing is finished. This file will automatically be assigned the same name as the HyperMesh model file, but it will have a .resextension. BL contours help you visualize how BLs are generated.

View this file in the Contour panel, or by clicking File > Load > Results from the menu bar. Scroll through the available results.

Only applicable to BL + Tetra model mesh controls.

Volume Mesh Organization Choose where to store the mesh.
Default
For component input – creates a new component for each meshed volume.
For solid input – volume mesh is stored in the solid component.
For region input – volume mesh is stored in the same component name as the region.
Per volume
Creates a new component for each volume.
Per mesh
Creates a new component to store all meshes created in a single run.
Current
Volume mesh is stored in the current component.