Workflow for Importing Nastran Mesh Directly

Hi,

I'm trying to import a Nastran file directly into Explicit Dynamics. I have read some other posts (https://forum.ansys.com/discussion/14809/i-need-help-please and https://forum.ansys.com/discussion/6685/importing-a-geometry-step-file-and-a-nastran-mesh-into-explicit-dynamics) and have been able to open the nastran file and run a simulation and get results.

However, when I use Explicit Dynamics or Mechanical, a new mesh of tetraheadral elements is generated and doesn't match the volume mesh of prism elements used in the nastran file.

In the past, I believe the Workbench toolbox included a Fine Element Modeler, but it is no longer available. Is there a workflow or tool I should use in order to be able to run a simulation with the original nastran mesh preserved?

Thank you.

Best Answer

  • peteroznewmanpeteroznewman Member Posts: 11,071
    edited January 24 Accepted Answer

    @tartan2020x

    Ah, I didn't read your original post carefully enough.

    The problem is Nastran has a Prism element while Ansys does not.

    The Nastran linear prism element has 6 nodes.

    ANSYS creates a Prism element by using a Hex element and collapses one face to put two nodes at the same corner. There are still 8 nodes.

    When ANSYS reads in a Nastran deck, the way they convert a Prism element is to split it into three Tet elements, keeping the same number of nodes.

    If you have the geometry that was meshed for Nastran, bring that into ANSYS. Meshing in ANSYS (either Hex or Tet elements) is going to create better quality elements than the triple split of a Nastran Prism element into Tets.

Answers

  • peteroznewmanpeteroznewman Member Posts: 11,071

    @tartan2020x

    How many nodes were on each Nastran Hex element? Was it a linear 8-node element or was it a quadratic 20-node element?

    Explicit Dynamics can only use linear elements.

  • tartan2020xtartan2020x Member Posts: 4

    Thank you for your response! It is a linear 6-node penta element.

  • peteroznewmanpeteroznewman Member Posts: 11,071
    edited January 24 Accepted Answer

    @tartan2020x

    Ah, I didn't read your original post carefully enough.

    The problem is Nastran has a Prism element while Ansys does not.

    The Nastran linear prism element has 6 nodes.

    ANSYS creates a Prism element by using a Hex element and collapses one face to put two nodes at the same corner. There are still 8 nodes.

    When ANSYS reads in a Nastran deck, the way they convert a Prism element is to split it into three Tet elements, keeping the same number of nodes.

    If you have the geometry that was meshed for Nastran, bring that into ANSYS. Meshing in ANSYS (either Hex or Tet elements) is going to create better quality elements than the triple split of a Nastran Prism element into Tets.

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