HF-0200: Geometry Cleanup

When designers create CAD geometry, their priorities are different from those of analysts trying to use the data. A single smooth surface is typically split into smaller patches, each a separate mathematical face. The juncture between two surfaces often contains gaps, overlaps, or other misalignments.

To make the geometry more appropriate for meshing, analysts need to combine a number of faces into a single smooth surface. A single, smooth surface not only allows the elements to be created on the entire region at once, but also prevents unnecessary artificial or accidental edges from being present in the final mesh.

Sometimes, the gaps, overlaps, and misalignments present when surface data is imported can affect the mesh quality. By eliminating misalignments and holes, and suppressing boundaries between adjacent surfaces and unnecessary details, you can automesh across larger, more logical regions of the model and improve the overall meshing speed and quality.

In this tutorial, you will use a variety of tools to prepare surface geometry for meshing.

Files for this Tutorial

Bpillar_cleanup.hf

Auto Cleanup panel

The Auto Cleanup panel performs automatic geometry cleanup.

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Quick Edit panel (F11 hotkey)

This panel combines many tools for rapid editing of model geometry.

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In this exercise, you will first review a variety of common geometric problems after reading a CAD file. The solutions are discussed in Exercise 2.

Step 1: Load the model file

1.	Select File > Open.

2.	Navigate to the model file Bpillar_cleanup.hf.

Note: The model files for this tutorial are located in the file mfs-1.zip in the subdirectory \hf\1Step\. See Accessing Model Files.

hf-200-1

Step 2: Review the model in Topology color mode

1.	Select View > Toolbars > Visualization to display the Visualization toolbar. The Visualization toolbar will need the panels displayed also in the View menu.

2.	From the toolbar, select Geometry Color Mode and change to By Topo. Notice the color of the model is changed and topology definitions are displayed on screen.

3.	From the toolbar, click Shaded Geometry & Surface Edges icon to shade the surfaces on screen.

The model comes in with several geometric problems after importing. You will first review the problems to have a better understanding of the nature of the model.

In Topology color mode, each color represents different topological modes:

Free edge	(Red color): The edge is owned by one surface. On a clean model, free edges appear only along the outer perimeter of the part and internal holes. Free edges that appear between two adjacent surfaces indicate the existence of a gap between the two surfaces.
Shared edge	(Green color): The edge is owned by two adjacent surfaces. When the edges between two adjacent surfaces are shared (green), there is no gap or overlap between the two surfaces, and they are geometrically continuous. The automesh utility always places seed nodes along their length and will produce a continuous mesh without any gaps along that edge. The automesh utility will not construct any individual elements that cross over a shared edge.
Suppressed edge	(Blue color): The edge is owned and shared by two adjacent surfaces but it is ignored by the automesh utility. They are blue dotted lines by default. Like a shared edge, a suppressed edge indicates geometric continuity between two surfaces but, unlike a shared edge, the automesh utility will mesh across a suppressed edge as if were not even there. The automesh utility does not place seed nodes along their length and, consequently, individual elements will span across it. By suppressing undesirable edges you are effectively combining surfaces into larger logical meshable regions.
Non-manifold edge	(Yellow color): The edge is owned by three or more surfaces. They typically occur at "T" intersections between surfaces or when 2 or more duplicate surfaces exist. The automesh utility always places seed nodes along their length and will produce a continuous mesh without any gaps along that edge. The automesh utility will not construct any individual elements that cross over a nonmanifold edge. These edges cannot be suppressed and can sometimes be indication for duplicated geometry.

Step 3: Review and measure the largest pinhole diameter

1.	From the toolbar, select the Visualization icon .

2.	From the Visualization tab, select the Topology icon and clear the Shared, Suppressed and Non-manifold check boxes. Only the red free edges display.

3.	Click Close to close the Visualization tab.

4.	Press T on your keyboard and input thetax = -101.154, thetay = -59.845 and thetaz = 109.363.

5.	Click set angles to set the true view.

6.	Notice several pinholes, as shown in image below.

Notice the biggest pinhole as indicated in the left side of the image is considered as a part of the feature and will be kept. The smaller holes on the flange area are considered removable.

7.	Press F4 on the keyboard to go to the Distance panel.

8.	Hold the Ctrl key and middle mouse button to draw a circle to zoom in the center bigger pinhole on the flange, as indicated in the image below.

9.	In the Distance panel, select the two nodes option. Notice a halo is surrounding N1.

10.	Hold the left mouse button and move the mouse cursor to the N1 location on top of the hole (location A in the image) until the hole is highlighted. Release the left mouse button and click again to create a temp green node created on top of the hole.

11.	Repeat the same procedure for N2 to create a second blue temp node as shown as location B in the image.

12.	Notice the diameter of the hole (value next to distance = ) is about 3.2.

The approximate diameter of the largest hole is about 3.2. Remember this value so you can apply it when you remove pinholes later.

13.	Press F on the keyboard to fit the model to the screen.

14.	Click return to close the panel.

Step 4: Review free edges

1.	From the toolbar, select the Wireframe Geometry icon .

2.	Notice several red lines as shown as in the image below. An example can be found as indicated where an arrow is pointing.

Free edges that appear between two adjacent surfaces indicate the existence of a gap between the two surfaces.

Step 5: Review a missing surface

1.	From the toolbar, select Shaded geometry and surface edges . The surfaces are shaded on the screen.

2.	From the toolbar, select the Visualization icon .

3.	From the Visualization tab, select the Topology icon and check Shared, Suppressed and Non-manifold to turn on the display of all definitions.

4.	Click v on the keyboard to open the dialog with saved views.

5.	Click restore 1 to display the previously saved missing surf view.

6.	Notice the missing surface as shown in the image below.

Step 6: Review the distorted surface

1.	Click v on the keyboard to open the dialog with saved views.

2.	Click restore 2 to display the previously saved distorted surf view.

Notice the dark shadow on top of the surface as indicated in the image below.

You will use the Automesh panel to verify the quality of the surface in the following procedures.

3.	Click Mesh > Auto Mesh.

4.	Click surfs and select only the surface with dark shadow. Notice two surfaces are selected as shown in the image below. This is a first indication of distorted surface.

5.	Click element size = and input 0.5.

6.	Click mesh. The mesh pattern has poor quality and higher node density at the center area (along the center shared edge). This is a second indication of the distorted surface.

7.	Click abort to abort the meshing operation.

8.	Click return to close the panel.

Step 7: Review the duplicated surface

In this model, you have duplicated surfaces existing in this model.

1.	Click v on the keyboard to open the dialog with saved views.

2.	Click front to review the front view. Notice the yellow lines surrounding the surface as indicated by an arrow below:

3.	Click Geometry > Defeature and then select the duplicates subpanel.

4.	Click the switch and change to faces.

5.	Click find. The two surfaces are highlighted and identified.

Step 8: Review deviated trim line

1.	Click v on the keyboard to open the dialog with saved views.

2.	Click restore 3 to display the previously saved improve share view.

Notice the deviation of one trim line as circled in the image below. The deviation of the trim lines could cause poor mesh quality. An ideal trim line will look like the dash line on the right hand side of the image below. You will correct this problem later.

Step 9: Review incorrect fixed point definition

1.	Click v on the keyboard to open the dialog with saved views.

2.	Click restore 4 to display the previously saved fixed point view.

Notice the incorrect definition for the free boundary. This is due to the incorrect definition of the fixed point, as indicated in the image below.

In this exercise, you will use a variety of tools to fix geometry problems.

Step 1: Remove pinholes using the Auto Cleanup panel

1.	From the Geometry menu, select Autocleanup.

2.	Click edit parameters to launch the Parameters File editor to modify Auto Cleanup settings.

3.	In the Parameters File editor, clear all settings under Other options.

4.	Click the next to Other options and change to . This disables the other options.

5.	Repeat the steps above and disable all options EXCEPT Geometry cleanup and Surface hole recognition.

6.	Click (Delete line) to delete the second row under Surface hole recognition.

7.	In the first row under Surface hole recognition, input 4.0 under R< and check Remove. The final result should look like the image below. Since the largest diameter of the holes on the flange is about 3.2, using the value 4.0 can make sure all the holes on the flange will be removed.

8.	Change Target element size: to 3.0. The target element size is the desired mesh size after geometry cleanup.

9.	Click Apply and Ok to return to the Auto Cleanup panel.

10.	Click surfs >> all from the pop-up window.

11.	Click autocleanup.

Notice the cleanup process is launched. A message is displayed "There is a conflict between the user requested element size of 3 and the quality criteria ideal element size 0.5 used in the optimization, How do you wish to proceed?"

12.	Click Continue.

When the cleanup process is finished, a message "Geometry cleanup process is finished" is displayed in the status bar. After the auto cleanup process, notice that:

•	The four holes on the flange are removed.

•	The number of free edges (red edges) is reduced as shown in the image below. If you wish to see only the free edge definitions, select the Visualization icon and deactivate all topologic definitions EXCEPT Free edges.

•	Duplicate surfaces are removed.

13.	Click return to close the Auto Cleanup panel.

Step 2: Fix the missing surface using the Quick Edit panel

In this step, you will manually clean up geometry using the Quick Edit panel.

1.	From the toolbar, select the Visualization icon and activate all topologic definitions.

2.	From the toolbar, click the Shaded Geometry & Surface edges icon to shade surfaces.

3.	Click v on the keyboard to open the dialog with saved views.

4.	Click restore 1 to withdraw previously saved missing surf view.

5.	Click F11 to access the Quick Edit panel.

6.	Click the line(s) button right next to filler surf:. A blue halo appears and surrounds the line button.

7.	Click any red edge of the missing rectangular surface. A surface is created to fill the missing surface. Notice the previous four free edges are now changed to a green shared edge.

8.	Click return to close the panel.

Step 3: (optional) Delete the distorted surface and recreate it

Using the Auto Cleanup function, most of the time, distorted surfaces are removed automatically. If you do not see distorted surfaces after the Auto Cleanup operation, skip this step.

1.	Click v on the keyboard to open the dialog with saved views.

2.	Click restore 2 to display the previously saved distorted surf view.

3.	Press F2 on the keyboard to go to the Delete panel.

4.	Click the entity selector and change it to surfs.

5.	Click surfs and select the distorted surface (the surface with dark shadow) from the screen.

6.	Click delete entity. This action deletes the distorted surface.

7.	From the menu bar, click Geometry > Create > Surfaces > Ruled.

8.	If necessary, click the switch to set the selection to line list. Click the upper line list selector and select the three red edges, as shown in the image below.

9.	Click the lower line list selector and select the one red edge, as shown in the image below.

10.	Verify that Auto reverse is activated.

11.	Click create.

12.	Click return.

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Notice a new surface is created at the same location. The new surface has three shared (green) edges and one free (red) edge as indicated in the image below.

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13.	Press the F11 key to open the Quick Edit panel.

14.	Click the line(s) button right next to toggle edge:.

15.	Change the tolerance to 0.1. This is the geometric cleanup tolerance.

16.	Use the left mouse button to click the red free edge to turn it into a shared green edge.

17.	Click return to close the panel.

Step 4: (optional) Delete the duplicated surfaces

Using the Auto Cleanup function, most of the time, duplicated surfaces are removed automatically. This step is optional if you wish to remove duplicated surfaces manually without Auto Cleanup. If you don’t see duplicated surfaces after the Auto Cleanup operation, skip this step.

1.	Click Geometry > Defeature.

2.	Select the duplicates subpanel.

3.	Change the entity selector from surfs to faces.

4.	Click faces and select all from the pop-up window.

5.	Click find. Notice two duplicated surfaces are highlighted and identified.

6.	Click delete to remove the duplicated surfaces.

7.	From the toolbar, select the Visualization icon .

8.	From the Visualization tab, select the Topology icon and uncheck Shared, Suppressed and Non-manifold to turn off the display of all definitions EXCEPT free edge (red line).

9.	From the toolbar, select the Wireframe Geometry icon .

Notice a red circular line indicating free edge. Since there is no hole existing, it indicates a problem with redundant surface.

10.	From the toolbar, click the Shaded Geometry & Surface edges icon to shade surfaces.

11.	Press F2 on the keyboard to go to the Delete panel.

12.	Change the entity selector to surfs.

13.	Hold the left mouse button and move the cursor to the red circular line until the circular surface edge is highlighted. Let go of the left mouse button and click delete entity to delete the surface. Refer to the image below.

14.	Click return to close the panel.

15.	From the toolbar, select the Visualization icon .

16.	Check Shared, Suppressed and Non-manifold to turn on the display of all definitions.

Step 5: (optional) Relocate a shared edge

Using the Auto Cleanup function should have relocated this edge. If you do not see this edge after the Auto Cleanup operation, skip this step.

1.	Click v on the keyboard to open the dialog with saved views.

2.	Click restore 3 to display the previously saved improve share view.

3.	Click F11 to access the Quick Edit panel.

4.	Click the Points panel right next to replace points:. The function is activated.

5.	Click points and click the fixed point B as shown in the image below

6.	Click retain and click the fixed point A as shown in the image below.

Notice the two fixed points are now merged. Point B is moved to point A.

7.	Repeat steps 5 and 6 to merge point C and point D by moving point D to the location of point C.

Step 6: Fix the incorrect fixed point

1.	Click v on the keyboard to open the dialog with saved views.

2.	Click restore 4 to display the previously saved fixed point view.

3.	Click point(s) for release point to activate this feature.

4.	Click the fixed point, as indicated in the image below.

Notice the fixed point is released and some free edges are generated.

5.	Click return to close the panel.

Step 7: Merge the two free edges

In the following steps, you will switch two free edges by replacing one free edge with the other free edge.

1.	Click Geometry > Edit > Surface Edges > Replace.

2.	Click line under moved edge: and select the line shown as B in the image.

3.	Click line under retained edge: and select the line shown as A in the image.

4.	Click cleanup tol = and input 1.0.

5.	Click replace. Notice the gap is closed and a new share edge is generated.

Step 8: Toggle the remaining red edges into shared edges and un-suppress two blue edges

You are still in the Edit Surface Edges panel.

1.	Click toggle subpanel.

2.	With a blue halo surrounding the edge button, click the two free edges as indicated in the image below.

3.	Notice the two red free edges are now converted into shared edges.

4.	Press the t key and input thetax = 145.968, thetay = -79.495 and thetaz = 30.150.

5.	Click set angles to set the true view.

Notice three blue suppressed edges are indicated in the image below. You will toggle the blue suppressed edges and turn these two suppressed edges to green shared edges.

6.	Click return to go back to the Edit Surface Edges panel.

7.	With the edge button activated, right-click the two suppressed edges to change them to green shared edges.

Step 9: Save the cleanup result

1.	From the File menu, click Save As.

2.	Use the file browser to save the file as Bpillar_cleanup_complete.hf.

3.	Click save.

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