• Blocking the geometry.
• Creating the composite curves. • Projecting the edges to curves. • Moving the vertices.
• Creating the O-Grid.
• Fitting the O-Grid using prescribed points. • Discarding the inner block.
• Generating the mesh. • Viewing the scan planes. • Verifying and saving the mesh.
Prerequisites
This tutorial assumes that you are familiar with the menu structure in ANSYS ICEM CFD and that you have read about this functionality. Some of the steps in setup and the procedure will not be shown explicitly.
Conventions
Some of the basic conventions used in this tutorial are:
• The icon to the left of the text (here, Blocking) suggests that you have to select the option from the display tree.
Blocking
• The arrow mark with the text LMB in the box the suggests that you have to click the left-mouse button to enable or disable an option (here, Vertices).
LMB−→ Vertices
• The arrow mark with the text RMB in the box the suggests that you have to click the right-mouse button to enable or disable an option (here, Numbers).
RMB −→ Numbers
For detailed information about GUI and text conventions, refer to the document, Getting Started with ANSYS ICEM CFD.
Blocking Strategy
The topology for this geometry is quite simple. You will first create an O-Grid around the cube and then fit the inside of the O-Grid to the cube using the prescribed points of the model as shown in Figure 1.
1. Enable Surfaces.
Geometry LMB −→ Surfaces
2. Select Create Part.
RMB −→ Parts LMB−→ Create Part
3. Create a new part (SYMM). (a) Enter SYMM in the Part field.
(b) Retain the selection of (Create Part by Selection) and click (Select entities). The Select geometry selection toolbar will appear.
(c) Disable Toggle selection of points , Toggle selection of curves and Toggle selection of bodies (material region definition) to avoid selecting entities other than surfaces.
(d) Ensure to select Toggle selection of surfaces .
(e) Select the four surfaces on the bottom of the geometry with the left-mouse button and click the middle-mouse button.
(f) Click Apply in the Create Part DEZ.
Figure 2: The Sphere Cube with Labelled Surfaces
Step 2: Creating a Material Point
Geometry > Create Body 1. Enter LIVE for Part.
Figure 3: Selection of Locations for Material Point Creation
4. Click Apply in the Create Body DEZ.
Note: The use of a Material Point is not actually required. However, creating one will fix the volume part name within the tetin file. This will avoid any problems caused by the volume name in the block file not being recognized by the tetin (geometry) file in future sessions.
5. Save the geometry file (sphere-cube-new.tin). File > Geometry > Save Geometry As...
Step 3: Blocking the Geometry
1. Create initial block.
Blocking > Create Block > Initialize Blocks
(a) Ensure that Part is set to the right material (LIVE).
(b) Retain the selection of 3D Bounding Box in the Type drop-down list.
You need not select Entities when creating a bounding box around the entire geometry. (c) Click Apply.
Step 4: Creating the Composite Curves
Even though curves can be automatically grouped while associating edges to curves, sometimes it beneficial to group them first. One such benefit is the ability to group all curves that tangentially meet (smooth transition at the ends of two adjacent curves).
1. Group all tangential curves.
(a) Select All tangential under Group.
(b) Click Apply in the Group/Ungroup curves DEZ.
This feature needs geometry connectivity so it will ask you whether to run build topology. Click Yes.
Note: Build Topology will generate a series of curves along all shared edges of sur-faces. It is meant as a geometry diagnostic tool but is also used to determine logical connectivity between surfaces and to build curves and points to capture sharp features.
(c) Click Apply in the Repair Geometry DEZ. For this tutorial, this is an optional step.
Geometry > Repair Geometry > Build Diagnostic (d) Re-apply in the Blocking Associations DEZ.
Blocking > Associate > Group curves
Figure 4: Grouping of all Tangential Curves
Step 5: Projecting the Edges to the Curves
Blocking > Associate > Associate Edge to Curve
1. Select the required edges.
(a) Click (Select edge(s)).
(b) Select the four bottom edges with the left-mouse button. (c) Click middle-mouse button to accept the selection. 2. Select the appropriate curves.
(a) Click (Select compcurve(s)).
(b) Select grouped circular curve with the left-mouse button. (c) Click the middle-mouse button to accept the selection. 3. Click Apply in the Associate Edge -> Curve DEZ.
The selected edges will turn green. 4. Enable Vertices.
Blocking LMB−→ Vertices
5. Select Numbers.
Blocking RMB−→ Vertices LMB −→ Numbers
6. Verify that the correct associations have been set (Figure5). (a) Enable Surfaces.
Geometry LMB −→ Surfaces
(b) Select Solid.
Geometry RMB −→ Surfaces LMB−→ Solid
(c) Select Show association.
Blocking RMB−→ Edges LMB −→ Show association
Figure 5: Projection of the Curve and Sphere Surface
Step 6: Moving the Vertices
Blocking > Associate > Snap Project Vertices
1. Disable Surfaces to better view the new vertex position. Geometry LMB −→ Surfaces
Figure 6: Moving the Vertices
Step 7: Creating the O-Grid
An O-Grid will be used to capture the cube as well as radially propagate the mesh onto the sphere.
1. Create the half O-Grid.
Blocking > Split Block > Ogrid Block
(a) Click (Select face(s)).
(b) Select the bottom face of the block.
(c) Click the middle-mouse button to accept the selection.
The block will also be selected. When you select the face, both blocks on either side get selected. The VORFN block beneath the face is not active, so a flat icon is shown instead of the block underneath.
Figure 7: Selecting the Face for the O-Grid
Step 8: Fitting the O-Grid Using Prescribed Points
Use the central block of the O-Grid to represent the cube. 1. Enable Points.
Geometry LMB −→ Points
2. Enable Vertices.
Blocking LMB−→ Vertices
3. Select Show Point Names.
Geometry RMB −→ Points LMB−→ Show Point Names
4. Associate the vertices to the points.
Blocking > Associate > Associate Vertex
(a) Ensure that Entity selected is Point in the Blocking Associations DEZ. (b) Click Select vert(s).
(c) Select a corner vertex (69) of the central block. (d) Click Select point(s).
(e) Select the nearest corner point (GEOM/9) to that vertex on the cube geometry. (f) Click middle-mouse button to accept the selection.
(g) Click Apply.
• Vertex 72 to point GEOM/10. • Vertex 71 to point GEOM/1.
Figure 8: Fitting the Inner Block to the Cube with Prescribed Points
Step 9: Discarding the Inner block
Remove the central block because the mesh will only be generated in the volume between the SPHERE and CUBE. Very often, when multiple blocks are displayed, it is difficult to select the icon representing the block(s). An alternative method is to select the block by selecting a pair of diagonally opposing corners.
1. Delete unnecessary central block.
(a) Select in the selection toolbar. You can type Shft-D on the keyboard.
(b) Select two corner vertices (69 and 71) as shown in Figure9. (c) Click middle-mouse button to accept the selection.
(d) Click Apply to delete the block.
Figure 9: Removing the Central Block
Step 10: Generating the Mesh
1. Disable Edges.
Blocking LMB−→ Edges
2. Select Wire Frame.
Geometry RMB −→ Surfaces LMB−→ Wireframe
3. Set the part parameters. Mesh > Part Mesh Setup
(c) Enter 0.01 and 0.02 for height for CUBE and SPHERE respectively. (d) Enter 1.2 for height ratio for CUBE and SPHERE.
(e) Click Apply and Dismiss the Part Mesh Setup dialog box. 5. Verify the Hexa Sizes (see Figure 10).
Geometry RMB −→ Surfaces LMB−→ Hexa Sizes
Figure 10: Verifying Hexa Sizes
6. Update the mesh.
(c) Enable Pre-Mesh.
Blocking LMB−→ Pre-Mesh
The Mesh dialog box will appear, asking if you want to recompute the mesh. Click Yes.
(d) Disable Edges, Surfaces and other types under Geometry in the Model display control tree.
(e) Select Solid & Wire.
Blocking RMB−→ Pre-Mesh LMB−→ Solid & Wire
The initial mesh is shown in Figure 11.
Figure 11: Mesh After Recompute Operation
Step 11: Viewing the Scan Planes
Viewing the volume mesh can provide another good visual diagnostic. Within blocking, this is done by means of a scan plane, where an I, J, K or radial O-Grid index plane is scrolled through the volume.
Figure 12: The Scan Plane Control Window
(a) Enable On for the index plane, # 0.
# 0, # 1, # 2 represents I, J, K respectively. # 3 represents the radial (O-Grid) direction. In this model, I, J, K is more or less lined up with the global X, Y, Z co-ordinates respectively.
(b) Increase Grid Index for the # 0 index plane.
Keep increasing until the scan plane appears about half way through the model. Note: When you increase the Grid Index, two planes will be visible at the same time.
Along the radial (O-Grid) block, I is equal to 1 throughout the entire block. (c) Click Select in the scan plane control window.
(d) Select one of the edges parallel to the current scan plane (an edge lined up along Y). See Figure 13.
Select enables the index plane perpendicular to any selected edge.
Note: This will select a J edge and the resulting scan plane will be perpendicular to that edge and will display constant J nodes. The index plane, # 1, is automati-cally enabled in the window.
Figure 13: Scan Planes of the Final Mesh
Step 12: Verifying and Saving the Mesh
1. Check the mesh quality.
Blocking > Pre-Mesh Quality Histograms
If you are satisfied with the mesh quality, convert the existing mesh to an unstructured mesh.
2. Select Convert to Unstruct Mesh.
Blocking RMB−→ Pre-Mesh LMB−→ Convert to Unstruct Mesh
3. Save the blocking file (sphere-cube-final.blk). File > Blocking > Save Blocking As...
4. Save the project file (sphere-cube-final.prj). File > Save Project As...
