Goal of this Tutorial
Get to know the Mesh to CAD workflow
Training:
Relevant data for this tutorial:
Step 1: Automatic Workflow
For a Retransition to a NURBS-Geometry a non-intersected optimisation result is needed. Therefore, the Smooth-Geometry from the Post Processing can be selected. The geometry of this file stays always inside the Design Spaces limits except of the Interface areas, they intentionally exceed the Design Space limits to enable an easy and clean Boolean Intersection.
Choose the Transfer Design Candidate Shape to pre process button and select the option Map LBCs and Material. With this option, the transfer of the geometry to the pre processing, the NURBS retransitioning and the intersection with the Design Space are carried out automatically. This automated workflow is not stopping after the intersection but is continuing to map the LBCs and Material information to the Design Candidate e.g. for a verification with MSC Apex (FE-Reanalysis).
Alternative Workflow:
Step 1: Reimport your already optimised geometry
Choose the Transfer Design Candidate Shape to pre process button.
If the default conversion option “NURBS” is activated, the Retransition back to a NURBS-Geometry (CAD) runs automatically. In this case please continue with Step 2.
If the conversion option “Facet” is activated, the Facet-Geometry is transferred to the Pre Processing.
With the Facet to NURBS Tool in the Geometry Edit Tools the STL-file can be transitioned to a NURBS-Geometry. Therefore, the Automatic Size Calculation and the Partition Preview can stay active. The NURBS Face Density influences the number of patches merged together to one bigger patch. A low density value means that fewer, bigger patches and a high density means that more, smaller patches are created.
With the middle mouse button (MMB) the operation is executed.
In a first step a preview of the partitioned quad mesh is shown.
If the partition looks satisfying the NURBS patch creation can be started. If a higher precision is desired the NURBS Face size can be varied manually. To change the size of the patches the NURBS Face Density can be modified.
When the transition is finished, the status bar in the bottom left displays “NURBS is created based on partitioned Facet Body” and a new solid shows up in the model tree.
From time to time and depending on the geometry some NURBS patches might fail. These will be displayed in the status bar as well. If this happens the geometry can be repaired manually. How this works is described here.
Step 2: Geometry Cleanup
We recommend to use the Geometry Cleanup Tools after the NURBS CAD-Geometry is created. The Find and Display Geometry Faults Method on the right side geometry faults can be displayed. With the Geometry Clean and Optimise Method on the left side an automatic repair can be performed.
Step 3: Creation of functional surfaces and sharp edges with Boolean Operations
To create the final NURBS-Geometry all functional surfaces and sharp edges have to be created with Boolean Operations. The best way for this is a Boolean Intersection between the retransitioned optimisation result and the Design Space of the optimisation.
Activate the Retain Original Bodies option to keep the Design Space.
The result is an intersected CAD-Geometry with all functional sharp edges and surfaces. At this point it is also possible to create Machining Allowances on functional surfaces if a geometry was not already created directly during the optimisation.
The finished Geometry can be used in any CAD software and for all further steps like a FE-Reanalysis with MSC Nastran.
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