1. 1 SLAC CW11 Modeling and Meshing with CUBIT CUBIT13.0 full user documentation at http://cubit.sandia.gov/help- version13.0/Cubit_13.0_User_Documentation.pdf

2. 2 SLAC CW11 o CUBIT Basics o Modeling - Pillbox Cavity - Model generation with the GUI - Model generation with journal files o Meshing - Meshing process - Tips for meshing o Mesh Format Convert - acdtool Outlook

3. 3 SLAC CW11 Cubit Basics o CUBIT is a meshing Toolkit for use in a finite element analysis code. o CUBIT can import and create geometries for meshing. o CUBIT can create many analytic geometry types from scratch and in decomposition. o Seven primitive types are available and accessed with the Create button/command syntax. o CUBIT can create Bottom-Up geometries from a collection of lower order entities, such as creating vertices, then curves, then surfaces that can be swept to create volumes.

4. 4 SLAC CW11 Command Panels Drop Down Menus Toolbars Work with the CUBIT GUI Graphics Window Command Line in a terminal, type cubit to start a CUBIT session Entity Tree Properties Page

5. 5 SLAC CW11 File -> Options Import …: import previously created geometry or mesh Export …: export new created CAD model (*.sat) or mesh (*.gen) Set Directory: set your working directory Tools -> Options Journal Editor: write/edit journal files for creating or meshing models Play Journal File: play a journal file to create or mesh a model Help -> Options Drop Down Menus Drop Down Menus provide functions such as file management, edit controls, user preferences, display options, journal file management, and help.

6. 6 SLAC CW11 Zoom in, out, and fit Entity Selection Filter Geometry Mesh Perspective on/offCheck point save/undoToggle scale on/off Toggle between Polygon/Box Select Toolbars Redraw Display modes Tet Elements Toolbars provide the most commonly used features by clicking toolbar icons. When an entity is selected, that entity will become highlighted.

7. 7 SLAC CW11 Command Panels Every command entered with buttons in the GUI version can be available in CUBIT’s command language in the command line workspace. Press an Icon to enter a new mode, each button press takes you to a lower level - Geometry: Create, modify, cleanup… - Meshing: Intervals, schemes, smoothing… - Materials and BCs: sidesets, blocks … - Analysis Setup: Export mesh - Post Processing: Customizable shortcut

8. 8 SLAC CW11 Modeling a Pillbox Cavity with GUI Pillbox: Height = 90 mm Radius = 100 mm Beam pipe: Radius = 35 mm Disk: Radius=12mm TM010: f ~ 2GHz, λ~ 150mm

9. 9 SLAC CW11 4 5 6 1.click Geometry 2.click Volume 3.click Create 4.select Cylinder 5.enter values 6.hit Apply Create a Pillbox Cell 2 1 3 Use smaller units when creating and meshing the model. Later scale to meters for ACE3P calculation.

10. 10 SLAC CW11 The command “create cylinder height 90 radius 100” can be entered in the command window. Partly words OK. Need help? CUBIT> Help create Display the Pillbox Cell

11. 11 SLAC CW11 Left-button t o Pan Mid-button to Rotate Right-button to Zoom Using 3 button mouse Adjust the Graphics Display

12. 12 SLAC CW11 Add Beampipe to the Pillbox Cell Transparency view 1 2 1.values 2.Apply

13. 13 SLAC CW11 subtract intersect Unite Geometry Booleans Geometry Booleans define the shape of a body based on overlapping regions : – Subtract Remove regions of overlap – Intersect Remove regions that don’t overlap – Unite Combine all regions into one body

14. 14 SLAC CW11 1 2 3 4 Good to “compress ids” after “unite” or “delete” entries 1.Boolean 2.Unite 3.Volume IDs {1 2} 4.Apply 5 5. type “compress ids” in command window Combine Beampipe and Pillbox Cell

15. 15 SLAC CW11 Select One or a Group of Curves Selecting Curve Put curser on curve Left button click to pick, the curve ID will be shown in Command Line window. Similarly for selecting a surface or volume

16. 16 SLAC CW11 1.Curve 2.Modify 3.Blend/Chamfer 4.Curve IDs {5 6} 5.Blend 6.Radius {12} 7.Apply Rounding the Iris of the Pillbox Cavity 6 2 3 4 5 7 1

17. 17 SLAC CW11 Geometry Webcutting slices 1 Body into 2 Bodies - Plane - Cylindrical surface - Extended surface - Intersection with “Tool” body Webcut with yzplane, delete unneeded bodyWebcut with zxplane, delete unneeded body Geometry Webcutting

18. 18 SLAC CW11 Reduce ½ of the Pillbox Cavity 1. Volume; 2. Webcut; 3. Plane; 4. Volume ID {1}; 5. YZ plane; 6. Offset value {0}; 7. Apply 1 2 3 4 5 6 7

19. 19 SLAC CW11 Good to “compress ids” after “unite” or “delete” entries 4. type “compress ids” in command window Delete Unneeded Body 1.Delete 2.Volume IDs {2} 3.Apply 4 2 3 1

20. 20 SLAC CW11 Reduce 1/4 of the Pillbox Cavity 1.Webcut 2.Plane 3.Volume ID {1} 4.ZX plane 5.Offset value {0} 6.Apply 1. Delete; 2. Volume IDs {1}; 3. Apply; 4. Type “compress ids” in command window 1 2 3 4 5 6 1 2 3

21. 21 SLAC CW11 Save the Model in ACIS (.sat) Format 1.File -> options 2.Choose Export 3.Save to “pillbox.sat” 4.Finish choose.sat format

22. 22 SLAC CW11 Tools Tools -> options ->Journal Editor In Journal Editor window -> File -> Import -> Command Tab save to a file (eg. ModelPillbox.jou) Modeling a Pillbox Cavity with Journal Files Journal Editor window Files Every command entered with buttons in the GUI version has been recorded in CUBIT’s command language in command tab.

23. 23 SLAC CW11 Define Variables #{cav_length = 90} ….and Replace numbers with variables in {} Parameters Create & Edit the Journal File Add “reset” at top to clean up the workspace when “play” the ModelPillbox.jou ModelPillbox.jou

24. 24 SLAC CW11 Play the Journal file to Create a Pillbox Cavity Tools Tools options -play journal files: select ModelPillbox.jou Open: will run through commands in ModelPillbox.jou, pillbox model generated

25. 25 SLAC CW11 Meshing Process Import the Solid Model (*.sat) - check and fix bad geometries - imprint and merge body all if there are multi volumes Choose Tet mesh scheme Set element size (~λ/10~λ/15, σ/3) and generate mesh - check mesh quality - smooth surfaces/volumes Apply BCs at interior & exterior surfaces - check BC Set block IDs for material attributes and volume element type Scale units and export the mesh (*.gen) Orders can be exchanged Meshing a Pillbox Cavity with GUI

26. 26 SLAC CW11 Import the Solid Model File options - > Import - > the file name (pillbox.sat) in your working Dir. - > open Select “Separate Multi-Volume Bodies” Files

27. 27 SLAC CW11 Choose Tetmesh Scheme 6 1.Meshing 2.Volume 3.Mesh 4.Type {all} 5.select {Tetmesh} 6.Apply Scheme 3 2 1 4 5

28. 28 SLAC CW11 1.Intervals; 2.enter {all}; 3.Geometry-adaptive; 4.defaults; 5. Apply; 6. Mesh Smaller mesh size around curved surfaces {adaptive} Set Element Size and Generate Mesh can use advanced options to limit the max element size ~λ/10 First try to use defaults option to mesh 1 2 3 4 5 6

29. 29 SLAC CW11 1.Delete; 2.Volumes ID(s) {all}; 3.Apply Delete Unsatisfied Mesh 1 2 3

30. 30 SLAC CW11 Regenerate Mesh 1 2 3 Remesh using advanced option 4. Advanced; 5. Interpolation; 6. maximum size {12}; 7. Apply; 8. Mesh 4 5 6 7 8 1. Intervals; 2. enter {all}; 3. Geometry-adaptive;

31. 31 SLAC CW11 Apply BCs at Interior & Exterior Surfaces 1. Materials and BCs; 2. Sidesets; 3. Add; 4. SideSet ID {1}; 5. Surface; 6. IDs {1} (one symmetry plane); 7. Apply Select One or a Group of Surfaces 1 2 3 4 5 6 7

32. 32 SLAC CW11 Define symmetry plane 1 Sideset 1 surface 1 Define symmetry plane 2 Sideset 2 surface 7 Define exterior surfaces Sideset 6 surface all except 1 7

33. 33 SLAC CW11 Set Block ID for Material Attributes and Element Type 1.Blocks; 2.Add; 3.Block ID {1}; 4.Volume; 5.IDs {all}; 6.Apply 1 2 3 4 5 6 1 2 3 4 5 1.Element Type; 2.Block ID(s) {1} 3.Volume; 4.Tetra10; 5.Apply Use 10-point Tet for curved elements

34. 34 SLAC CW11 Scale Units and Export the Mesh 1.Geometry 2.Volume 3.Transform 4.Scale 5.“all” 6.Uniform Scaling 7.“0.001” 8.Apply Set the file export type to Genesis files Enter a file name, eg. pillbox.gen Save Finish 1 2 3 4 5 6 7 8 File->Export Scale Units Export Mesh choose.gen format

35. 35 SLAC CW11 Tools -> options ->Journal Editor In Journal Editor window -> File -> Import -> Command Tab save to a file (eg. MeshPillbox.jou) Create and Edit the Mesh Journal File MeshPillbox.jou Reset ##import model import acis "pillbox.sat" ##choose Tet mesh vol all scheme tetmesh volume 1 sizing function type skeleton max_size 12 mesh volume 1 ##apply BC ##sym. planes sideset 1 surface 1 sideset 2 surface 7 #exterial surfaces sideset 6 surface all except 1 7 ##set block ID block 1 volume all ##set block element type block all element type tetra10 ##scale units and export mesh volume all scale 0.001 export genesis "pillbox.gen" overwrite Now you can play the mesh journal file to run through commands in MeshPillbox.jou, pillbox.gen generated Add “reset” at top to clean up the workspace when “play” the MeshPillbox.jou

36. 36 SLAC CW11  Imprint and merge body all before meshing for a multivolume model.  Mesh smaller surfaces first. Small features have good mesh representation.  Sometimes it is good to separate one volume into multi-volumes and mesh them with different mesh element sizes and sizing functions (skeleton, constant).  Smooth transition from coarse to dense regions and smooth mesh on curved surfaces.  Start with a reasonable coarse mesh (element size ~ λ/10 - λ/15 or ~ σ/3) and refine the mesh to check accuracy.  Check mesh quality every time using “ quality vol all distortion”.  Use “Draw sideset #” to check boundary setup. Tips for Meshing  Check and clean models first using clean up, composite… such as: Auto_clean volume all small_surfaces small_curve_size 0.1 Composite create surface

37. 37 SLAC CW11 acdtool is a collection of tools to do prep/post processing. Mesh Format Convert - acdtool convert cubit mesh in GENESIS format to SALC ncdf format mesh examine mesh statistics, quality, and correctness check and remove invalid second order tetrahedral elements For preprocessing, in a terminal, Type acdtool meshconvert pillbox.gen pillbox.ncdf generated

38. 38 SLAC CW11 Acdtool Meshconvert Output If Euler Char is not OK, do not use it for ACE3P simulation. The mesh has some problems. For example, sidesets are incomplete or overlap each other. If aspect ratio > 20, shape measure <0.01, it might take longer time to get the results from ACE3P.

39. 39 SLAC CW11 Working Flow Before Running ACE3P ModelPillbox.jou pillbox.sat MeshPillbox.jou pillbox.gen GUI pillbox.ncdf ACE3P