Layered Tetrahedrons mesh method creates unstructured tetrahedral mesh in layers based on a specified layer height and fits it to the geometry.
This method can be used for simulating the printing process in Additive Manufacturing as the build parts must conform to a mesh with fixed step sizes in the global Z direction.
The meshing process involves the following approach:
Generates an initial surface mesh based on the defined settings.
Generates mesh layers based on the specified layer height. The mesher generates the mesh layers starting from the Z-location of the plane.
Projects nodes on the geometry within the specified tolerance (Relative Tolerance) of the layer plane to the plane during the initial layer operation.
Layered Tetrahedron method preserves feature nodes and corner nodes determined based on the Feature Angle and the Corner Angle, respectively.
Identifies problematic sliver faces based on Sliver Triangle Height and collapses or fixes sliver faces to improve quality.
Identifies and inflates the geometry faces overlapping the layer planes based on the Overlapping angle. Additionally, geometry faces close to the layer planes which leads to bad quality tets are identified based on the Layer Height and proximity to the plane. These faces inflate away from the layer planes to create space for better quality tets based on the Inflate Relative Tolerance value specified.
Fills the improved surface mesh with tetrahedral mesh conforming to the mesh layer. Thus, improves the tetrahedral mesh quality.
Note:
Layered Tetrahedrons Mesh Method does not support bodies with shared topology. Conformal mesh is not created even when the bodies have shared interface(s).
This method cannot be used with mesh controls such as Inflation, Refinement, Match Control, Pinch, Face Meshing and Edge Sizing controls.
The mesh is not associated back to geometry. See Association Using Named Selections for more details.
To access the Layered Tetrahedrons Method control,
On the Tree Outline, right-click Mesh and click Insert > Method.
Or
On the Tree Outline, click Mesh and click Method in the Mesh Context tab on the Ribbon.
Select Method as Layered Tetrahedrons Method in the Automatic Method Details view.
When you choose the Layered Tetrahedrons Method option, the Details view expands to include additional settings, many of which are unique to this option. For basic usage, the procedure is to apply a Method Control to the body and set Method to Layered Tetrahedrons. Set the Layer Height and accept the default values of the various settings.
Meshing Recommendations
The Layered Tetrahedrons method is available only when Use Adaptive Sizing is set to No.
Minimum and maximum sizes should be decided based on the model.
The minimum size should be decided based on the features to be resolved and the Layer Height. You should set a value smaller than the Layer Height.
The Element Size should not be greater than 6 times the specified minimum size. The mesh quality reduces as the Element Size to Min Size ratio increases.
The Max Size does not influence the layered tet mesher.
Set the Growth Rate, the recommended range of values is 1.2 to 2.
The recommended range for the Curvature Normal Angle is up to 36 degrees.
The Sliver Triangle Height is based on the minimum size specified. The default value is 10% of the minimum size. You should use a Sliver Triangle Height not more than 50% of min size.
Increasing Relative Tolerance and Inflate Relative Tolerance can avoid generating thin pockets of mesh. The recommended range for Relative Tolerance is between 0.01 to 0.02. The recommended range for Inflate Relative Tolerance is between 0.1 to 0.3.
The Layered Tetrahedrons mesh method includes the following options:
Scope
Scoping Method: Allows you to scope geometry bodies or named selection. The default value is Geometry Selection.
Geometry Selection: Allow you to scope the geometry bodies. When you select Geometry Selection, the Geometry allows you to select the geometry from the Geometry window.
Named Selection: Allow you to scope bodies grouped under a named selection.
Definition
Suppressed: Allows you to suppress the selected control. The default value is No. When Suppressed is set to Yes, Active displays the status of the selected control. Active is read-only.
Method: Allows you to select the method.
Element Order: Allows you to select the element order. The default value is Use Global Setting. For information about the Element Order option, refer Method Controls and Element Order Settings.
Note: Only straight sided mid-nodes are available for quadratic element type.
Layer Height: Allows you to set the height of steps in elements along the global Z direction.
Control Messages: Provides a message when Use Adaptive Sizing is set to Yes and when layered tetrahedron mesh fails. You can click Control Messages to view the message.
Advanced
Generate Layers Using Facets: Generates layered tetrahedron mesh for the given model using facets. When Generate Layers Using Facets is Yes this allows you to skip the surface mesh generation before slicing. Thus, slicing operation is performed directly on CAD. The default value is No.
Repair Facets: Enables you to repair CAD facets. When set to Yes, Repair Facets allows you to fix Sliver facets and facet intersections aggressively. The default value is No.
Layer Start: Generates the mesh layers from the Z-location of the plane. The default value is the min Z-coordinate of the bounding box enclosing the scoped bodies. For Additive Manufacturing simulations, more specifically, when the AM Process object is available in the Project tree, it automatically sets the value to the Z-coordinate of the top of the baseplate by default.
Relative Tolerance: During the initial layer operation, projects nodes within the specified tolerance (relative tolerance) to the layer plane to the plane on the geometry plane. The default value is 0.01 (1%) which can be used for most cases. The recommended range of values is 0.01 to 0.02 (1-2%). For extreme cases, you may use a value of up to 0.05.
Inflate Relative Tolerance: Improve the surface mesh in the thin layer regions after performing the layering operation. This tolerance moves nodes away to the specified value to improve the quality. The default value is 0.1 (10% of the layer height). The tolerance range of 0.1 and 0.3 help you to achieve good results. The largest acceptable value is 0.5, use this value carefully.
Overlapping Angle: Identify and inflate the geometry faces overlapping the layer planes based on the provided angle. The default is 155 degrees. The acceptable range is an angle greater than the Feature Angle and less than 180 degrees.
Defeature Layer Volume: Specifies the threshold volume for defeaturing a thin end layer of cells. Defeature Layer Volume is used only if a very thin end layer is expected since such layers may cause mesh quality issues.
Aggressive Inflate Option: Enables inflation of faces in the proximity of the layer planes to improve mesh quality in addition to inflation to resolve overlapping faces. This default value is Yes. In some cases, the aggressive inflation may cause some intersections in the surface mesh, in which case you can set the Aggressive Inflate Option to No.
Aggressive Tetrahedrons Improvement: Activates the tetrahedron mesh improvement routines. It allows you to remove the thin tetrahedrons formed during meshing. The default value is No. When set to Yes, allows the mesh to do aggressive tetrahedron improvements.
Sliver Triangle Height: Identifiy and collpases or fixed to improve based on the provided height. The Sliver Triangle Height is based on the specified minimum size. The default value is 10% of the minimum size. Based on the model, you may need to increase the value, however, it is recommended that the value should not be greater than 50% of the min size.
Feature Angle: Determines feature nodes based on Feature Angle and are preserved during meshing. The default feature angle is 40 degrees. The acceptable range is from 0 degrees to an angle less than the specified Overlapping Angle.
Corner Angle: Determines corner nodes based on Corner Angle and are preserved during meshing. The default is 90 degrees. The acceptable range is from 0 to 180 degrees.
Association Using Named Selections
The Layered Tetrahedrons method does not fully associate the mesh to the geometry. To have mesh associated to the geometry, define Named Selections on the faces on which association is required prior to meshing.
Note: Edge and vertex named selections are not considered for mesh association.
Limitations
The Layered Tetrahedrons method has the following limitations:
Multi-body parts with and without shared topology are not supported. You should separate them into individual parts in CAD.
The model should not have other suppressed bodies.
The mesh is not associated back to geometry. See Association Using Named Selections for more details.
Only straight sided mid-nodes are available for quadratic element type.
Contact must be used between two bodies even if they have a shared interface.
Note: Layered Tetrahedron method does not generate conformal mesh when there is a shared interface between bodies.