Workshop 14 Automatic Hex Meshing of a Bent Bar

Create a Project Choose “Open Project“ Icon Browse to the desired working directory Enter the project name Type in the File name as: BentBar.prj Tips: The pull down next to the file name can be used to quickly locate recently used projects. In Windows, The File browser is a standard Windows file browser offering all the functionality of windows explorer. In Unix or Linux, similar functionality is also available. The Project file will contains information about project settings, the working folder and file associations. Once the geometry, mesh, boundary conditions, parameter files etc. are saved with the project file, simply loading the project file will also load these associated files.

Display Tree Import Geometry Bent Bar Open The Geometry: File -> Geometry -> Open Geometry Or use the “Open Geometry” ICON Select: Bar.tin using File Browser Display: Surfaces by left mouse click on icon Display: Solid & Wire mode by right mouse click on Surfaces in Display Tree Display: Transparent mode by right mouse click on Surfaces in Display Tree Display Tree Bent Bar

Build Topology BUILD TOPOLOGY: #1 BUILD TOPOLOGY: Geometry -> Repair Geometry -> Build Diagnostic Topology Default: Tolerance is auto-calculated as 0.06 Default: New Part Name is set to Inherited Accept all defaults and press Apply Observe: Because the New Part Name is set to Inherited Curves & Points will be in the Part of the associated surfaces Turn Off: Surface display using the display tree or Wire frame Icon #2 #3 #4 Tips: set a reasonable tolerance based on model size By default, tolerance is set to 1/1000th the size of the model bounding box diagonal, rounded Use Part by part option if you are working with an assembly #5 Note: Yellow lines would indicate (single edges) a hole. #6

Subdivide Surface For the auto blocking method to work, surfaces should have 4 sides, the long cylinder only has 3 sides and 360 degrees of curvature. It must be broken up. #1 #2 Adjust Display: Turn on Points Adjust surface display to Solid Wire Create ISO-parametric Curves: Geometry -> Create Curves -> Surface Parameter Select: the long cylindrical Surface Set: Isocurve Methods to Point on Edge Select these 4 points Press Apply #3 Selected Surface #4 #5 #6 #7

Subdivide Surface The curves appear along the cylinder surface. We can use the build diagnostic topology to cut this surface with these curves #1 #2 Create ISO-parametric Curves: Geometry -> Repair Geometry -> Build Diagnostic Topology Accept all Defaults Press Apply The curves change color from green (Unattached) to Red (double edges) to show that they have “Cut in.” #3 #7

Set Mesh Sizes Assign Element Size: #1 Assign Element Size: Use the new Mesh Parameters option to: Mesh -> Set Mesh Params by Parts Adjust the Size and Height of the BAR part to 1 press Apply. Hexa Sizes to view #2 #3 #4 #5 Hexa icons indicate mesh sizes set on each surface RMB on Surfaces

Auto Surface Blocking Blocking is created Auto Blocking: #1 #2 Auto Blocking: From the Blocking Tab, Click on the Create Block icon Select 2D as the Initialize Block Type This will create a 2D blocking structure for each surface These 2D Blocks will all be connected The Default Method is All Mapped, unstructured blocks are also available. Select all surfaces with the “a” hotkey Accept Defaults and Apply Blocking is created Blocks are created and a Blocking branch is added to the model tree. #3 #4 #5 #6 #9

Update Sizes and Pre-mesh #1 #2 Pre-mesh Param: Blocking => Pre-mesh Params Accept Defaults and Apply This will update the blocking parameters with the parameters applied to the surface mesh parameters. Display Pre-Mesh Left Click on Pre-Mesh under the blocking branch of the model tree to display the Pre-mesh Right click on Pre-Mesh to display as Solid #3 #4 #5

Hex Dominant Meshing Pre-mesh does not contain separate element information and can only exist along with blocking. Pre-mesh can be converted to Unstructured mesh. Convert to Unstructured Mesh: Right Click on Pre-Mesh under the blocking branch of the model tree Select Convert to Unstructured Mesh Nodes and Elements are created. A “Mesh” branch will appear in the model tree. #1 #2 Using this Quad Dominant or pure Quad Mesh, you can use the Hex Dominant Mesher For more complicated or merely Hex Dominant models, this may be the best solution, but for this model, better hex mesh is available from the Blocking tab!

Blocking 2D to 3D fill 2D to 3D Fill: #1 #2 2D to 3D Fill: Blocking => Create Block => 2D to 3D Accept Default Part Solid and method Fill Apply This runs the hex dominant mesher on the blocks and results in 3D blocking. Generate Pre-mesh to view the mesh #3 #4 #5 2D to 3D Fill Display Pre-mesh

Ogrid The Pure Hex Mesh is higher quality than the hex dominant mesh, except at the corners. Here the Hexa elements are opened out to almost 180 degrees and quality is poor. However, since we have access to the blocking topology, we can add an OGRID! O-grid Topology No O-grid O-grid

Ogrid O-Grid Creation: Blocking => Split Block => Ogrid Block #1 #2 O-Grid Creation: Blocking => Split Block => Ogrid Block Use the Block(s) Picker to select all the Blocks Use the “v“ hotkey to select all the visible blocks Use the Face(s) Picker to select appropriate faces Generally; the flat surfaces that the Ogrid should pass through. Specifically; The 5 faces highlighted below and the corresponding faces on the other end. Apply Update Sizes: Blocking => Premesh Params => Update sizes Update All To ensure entity parameters are set for the new edges #3 #4 #5 #6

Final Mesh The O-grid block topology is automatically created. #1 The O-grid block topology is automatically created. Mesh is now aligned with the walls and the element quality is greatly improved. Other changes can also be made to the blocking file Edge Mesh Parameters Vertex locations Etc. #2 The Pre-mesh and Mesh can be further improved with the Pre-Mesh smoother and hexahedral mesh smoother respectively. Disp. Premesh Conv. to Unstructured