Pyramid element transitions

When you are working with Simcenter Nastran, ANSYS, Simcenter 3D Thermal/Flow, Simcenter 3D Electronic Systems Cooling, Simcenter 3D Space Systems Thermal, or Simcenter Samcef as your specified solver, you can use the Transition with Pyramid Elements option in the 3D Tetrahedral Mesh dialog box to create transitional pyramid elements between the tetrahedral mesh and an adjacent hexahedral mesh. Pyramid elements offer several advantages over using rigid elements or multi-point constraint equations to connect dissimilar meshes. Pyramid elements:

• Provide a direct transition from hexahedral elements to tetrahedral elements, thus ensuring a conforming mesh.

• Result in greater solution accuracy and reduced solution time.

You can:

• Have the software automatically create pyramid elements at the interface between hexahedral and tetrahedral meshes.

• Import existing Simcenter Nastran, ANSYS, Thermal/Flow, Electronic Systems Cooling, Space Systems Thermal, or Simcenter Samcef models that contain pyramid elements and work with those elements in Pre/Post. For details on the types of ANSYS elements supported, see Importing ANSYS models that contain pyramid elements.

The following example shows the use of transitional pyramid elements at the interface of hexahedral and tetrahedral meshes on a simple, partitioned block. (A) shows a side view of the interface between the two different meshes, while (B) shows only the pyramid elements with the tetrahedral elements.

Pyramid element requirements

For the software to create transitional pyramid elements at hexahedral-tetrahedral interfaces:

• You must be working in a FEM file in which Simcenter Nastran, ANSYS, Thermal/Flow, Electronic Systems Cooling, Space Systems Thermal, or Simcenter Samcef is the specified solver language.

• The adjacent body must have an existing mesh of hexahedral elements.

• A Glue Coincident type of mesh mating condition must be defined at the interface between the two bodies to ensure that the nodes on the adjacent hexahedral and tetrahedral meshes match exactly.

Boundary layer meshes can contain pyramid elements to transition between the boundary layer region and the tetrahedral mesh. When the software generates boundary layer meshes, transitional pyramid elements at hexahedral-tetrahedral interfaces outside of boundary layer regions are never created. The Transition with Pyramid Elements check box is inactive.

Mixed order elements supported

You can use Transition with Pyramid Elements to create transitions between:

• Elements of the same order.

• Elements of different orders.Note: With Simcenter Nastran SOL 601 and SOL 701 analyses, you can only use pyramid elements to create transitions between elements of the same order. See Using pyramid transitions with Simcenter Nastran for more information.

If you create a pyramid transition between elements of different orders, the software creates “mixed order” pyramid and tetrahedral elements where necessary. A mixed order element has a mix of linear and parabolic edges:

• The parabolic edges have midside nodes.

• The linear edges do not have midside nodes.

With a mixed order pyramid element, typically the edges of its base are linear while its other edges are parabolic. However, it is possible to have pyramid and tetrahedral elements with any number of missing midside nodes. For details, see Using pyramid transitions with Simcenter Nastran and Supported element types for ANSYS pyramid transitions.

Pyramid and tetrahedral elements with missing midside nodes function very similarly to other 3D elements. For example, you can:

• Select and display pyramid and tetrahedral elements with missing midside nodes.

• Apply loads and boundary conditions to pyramid and tetrahedral elements with missing midside nodes.

However, you cannot use the commands on the Nodes and Elements tab to create new 2D or 3D elements from the faces of elements that are missing midside nodes.

Note:

Mixed order elements are not supported for Thermal/Flow, Electronic Systems Cooling, and Space Systems Thermal solvers.

Pyramid elements stored in same collector with tetrahedral elements

Typically, the software creates separate mesh collectors depending upon the element type. When you either create or import pyramid elements, the software creates two separate meshes within a single mesh collector—one for the pyramid elements and one for the tetrahedral elements.

• If you delete the pyramid mesh, the software automatically deletes the associated tetrahedral mesh.

• If you delete the tetrahedral mesh, the software automatically deletes the associated pyramid mesh.

Where do I find it?

With the FEM file displayed and the solver set to either Simcenter Nastran, ANSYS, Simcenter 3D Thermal/Flow, Simcenter 3D Electronic Systems Cooling, or Simcenter 3D Space Systems Thermal:

• Choose Home tab→Mesh group→3D Tetrahedral Mesh .

• Choose Insert→Mesh→3D Mesh.

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Pyramid element transitions, Simcenter 3D 2021.1 Series

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