Description

The controls in the Tetrahedra frame allow you to establish the criteria by which the solver decides whether and how to modify the isotropic portion of a block.

Tetrahedra Tab
The Tetrahedra frame provides settings to control isotropic tetrahedra sizes and Advanced solver controls.

The Min. Equilateral Edge Length parameter allows you to specify a lower limit on tetrahedral edges. This parameter is used primarily as a safeguard to avoid a potential excessive refinement of the block driven by the combined effects of the other parameters. The unstructured block solver computes the volume of an equilateral tetrahedron with an edge length equal to the target Min. Equilateral Edge Length. The computed equilateral volume is then compared to the volume of actual cells in a block. If the volume of the actual cells in a region of a block are sufficiently smaller than the computed equilateral volume, the actual cells in that region are decimated.

Similarly, the Max. Equilateral Edge Length parameter allows you to specify an upper limit on tetrahedral edges. The unstructured block solver computes the volume of an equilateral tetrahedron with an edge length equal to the target Max. Equilateral Edge Length. The computed equilateral volume is then compared to the volume of actual cells in a block. If the volume of the actual cells in a region of a block are sufficiently larger than the computed equilateral volume, the actual cells in that region are refined.

The Min. Equilateral Edge Length and Max. Equilateral Edge Length pull-down lists contain two identical options each that will determine how the target value for these parameters should be computed:

  • User Specified: Sets the Min. Equilateral Edge Length/Max. Equilateral Edge Length target value to the value entered in the associated text field.
  • Use Boundary: Sets the Min. Equilateral Edge Length/Max. Equilateral Edge Length target value to the minimum/maximum edge length on the boundary.

The Max. Edge Growth Rate option in the Advanced sub-frame is a limiter on lengths of adjacent edges of a given cell. This helps prevent skewing on the interior of the volume, particularly in areas adjacent to poorly distributed bounding surface grids or when local source influence has widely disparate spacing values. If the ratio of adjacent edge lengths is greater than the entered Max. Edge Growth Rate, the longer edge will be split. This control has the effect of producing a smoother mesh for smaller values of Max. Edge Growth Rate at the possible expense of not reproducing the local target distribution. Minimum = 1.0, default = 1.8, maximum = ∞.

Demonstration

Unstructured Block Edge Lengths

Using Unstructured Tetrahedra Solver Algorithm Settings