3D2 Creating a Hex-Penta Mesh using Surfaces
Creating a Hex-Penta Mesh using
Surfaces - HM-3210
In this tutorial, you will learn how to:
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Create solids using different functions
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Check and fix improper model connectivity
For some analyses, it is desirable to use a mesh of hexahedral and pentahedral
elements. This is especially true for parts, which have a large thickness compared to the element size being used, or for parts that have many features and/or changes in
thickness. Castings or forgings are good examples.
Exercise: Creating a Hex-Penta Mesh using Surfaces
This exercise uses the model file, arm_bracket.hm. This exercise introduces you to a number of HyperMesh functions that are used to create hexa-penta meshes. The model is organized into four IGES layers, consisting of 1) the base, 2) the first section of the arm, with a constant cross section and curvature, 3) the second section of the arm, with a tapered cross section, and 4) the boss.
Step 1: Retrieve and review model file.
Open the arm_bracket.hm file.
Step 2: Mesh the top surface of the base, including the L-shaped surface.
1. Set the active component collector to base in one of the following ways:
?In the status bar click the middle box which is the comp: selection and set the current component in the popup.
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In the Model browser right-click base and select Make Current
2. In the Model browser, hide all components except the base component.
3. Access the automesh panel in one of the following ways
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From the Mesh menu click Create, then 2D Automesh
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From the 2D page enter the automesh panel.
4. Select the surfaces on the top of the base, including the L-shaped surface at the intersection of the base and the arm.
For this part of the exercise it might be easier to view the geometry in a shaded mode by clicking Shaded Geometry and Surface Edges ().
5. Select the size and bias sub-panel.
6. Set the meshing mode to automatic.
7. For element size = specify 10.
8. For element type specify quads.
9. Click mesh to mesh the surfaces.
Resulting quad mesh on base surfaces
10. Click return to return to the main menu.
You can now change back to an unshaded view for the geometry.
Step 3: Create layers of hex elements for the base.
1. Go to the elem offset panel.
2. Select the solid layers sub-panel.
3. With the elems selector active, select the elements on the base.
4. For number of layers = specify
5.
5. For total thickness = specify 25.
6. Click offset+.
The hexa mesh is created.
Hex mesh on base
Step 4: Prepare the display for meshing the arm’s curved segment.
1. Show the arm_curve component in the Model browser.
2. Press the F5 key to go to the mask panel.
3. Select elements >> by config, and select the hex8 configuration.
4. Click select entities.
All of the elements with a configuration of hex8 in the model are selected.
5. Select elements >> by config, and select the penta6 configuration.
6. Click select entities.
All of the elements with a configuration of penta6 in the model are selected.
7. Click mask to mask the elements.
8. Click return to return to the main menu.
Step 5: Create a node at the center of the arm radius.
The first segment of the arm can be meshed using the spin panel. This requires a node to be selected as the center point of rotation. The node you create in this step will be used as that center point. To create the center node, you will use the distance / 3 nodes sub-panel.
1. Press the F4 key to enter the distance panel.
2. Go to the three nodes sub-panel.
3. With the N1 selector active, create the temporary nodes on one of the curved lines of the arm as described following.
4. Press and hold the left mouse button. Move the cursor over a curved line. Once over the
line, the cursor will change to a square with a dot in the center, , and the line will be hightlighed. Release your mouse button.
5. Click three locations along the selected line. The active selector advances from N1 to N2 to N3, and the locations will be selected as though there was a node there.
6. Click circle center to create the node at the center.
Three nodes to create a center node
7. Click return to return to the main menu.
Step 6: Create hexa elements in the curved portion of the arm using spin.
1. Set arm_curve as the current component using the Model browser.
2. Go to the spin panel.
3. Select the spin elems sub-panel.
4. Using elems >> by window, select the plate elements within the L-shaped cross section of the arm.
5. Click select entities.
Elements to select for spin function
6. For angle= specify 90 degrees.
7. For the direction, select the x-axis (Y-Z plane).
8. For the base node (B), click the center node created above.
9. For on spin = specify 24.
24 layers of hex elements will be created when the plate elements are spun.
10. Click spin -.
11. Click return to return to the main menu.
spin panel results
Step 7: Create faces on the hex elements.
1. Go to the faces panel.
2. With the entity selector set to comps, select the arm_curve component.
3. Click find faces.
2-D shell elements are created on the free faces of every 3-D solid element in the
component. They are placed in a new component named ^faces.
The ^faces component is created with its visualization set to wireframe, so you will not be able to see the new elements right away if the arm_curve component is displayed and in shaded mode.
4. On the toolbar click Shaded Elements & Mesh Lines to shade the elements.
You will now see the elements in the ^faces component.
Step 8: Prepare the display for meshing the second arm segment.
1. Turn on the display for the arm_straight and ^faces components.
Step 9: Mesh the L-shaped set of surfaces between the arm_straight and boss components.
1. Set the current component collector to arm_straight.
2. Go to the automesh panel.
3.
Select the three surfaces lying on the intersection between the arm_straight and boss components.
These surfaces are in the arm_straight component.
4. Set the meshing mode to interactive.
5. Click mesh to go to the meshing module.
6.
From the density sub-panel, adjust the densities to obtain a mesh that matches the following image.
This mesh pattern matches the mesh pattern at the intersection of the two arm segments. This is necessary for the next step.
Densities to correspond to the mesh on the end face
7. Click mesh to update the mesh density.
8. Click return to create the elements and go back to the automesh panel.
9. Click return to return to the main menu.
Step 10: Use linear solid to build the mesh between the two sets of shell elements.
1. Access the linear solid panel in one of the following ways:
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From the Mesh menu, point to Create, choose 3D Elements, and click Linear 3D
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From the 3D page, go to linear solid
2.
With the from: elems selector active, select the ^faces elements lying on the intersection between the first and second arm segments.
You can select one of the elements and then select elems >> by face to select the rest of the necessary elements.
3. Click the to: elems selector to make it active. Then select the shell elements between the arm and boss, which you created using the automesh panel in the last step.
4. Click the from: alignment: N1 selector to make it active. Then select three nodes on one of the "from elements" you selected in sub-step 10.2.
5. Click the to: alignment: N1 selector to make it active. Then select three nodes on the "to element" corresponding to the "from element" with the three "from nodes" you selected in sub-step 10.4. Refer to the following image.
Example selection for alignment nodes
6. For density = specify 12.
7. Click solids to create the mesh.
Linear solid mesh
8. Click return to the main menu.
Step 11: Prepare the display for meshing the boss.
1. Show the boss component using the Model browser.
Step 12: Create a shell mesh on the bottom of the boss.
1. Set the current component collector to boss.
2. Go to the automesh panel.
3. Select the five surfaces on the bottom face of the boss.
4. Click mesh to go to the meshing module.
5. Adjust the densities to match the following image:
Mesh densities on the bottom of the boss
6. Click mesh to update the mesh density.
7. Click return twice to return to the main menu.
Step 13: Project a node to the bottom face of the boss.
1. Go to the project: panel.
2. Select the to line sub-panel.
3. Select the node on the rightmost top vertex, as per the following image.
4. Click nodes >> duplicate.
5. For the to line select the line on the boss’ top face. Refer to the following image.
Projecting a node to a line
6. Select along vector: x- axis.
7. Click project to project the node to the line.
8. Click return to return to the main menu.
Step 14: Generate hexas for the boss using the solid map panel.
1. Access the solid map panel in one of the following ways:
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From the Mesh menu, point to Create, and click Solid Map Mesh
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From the 3D page, go to solid map
2. Go to the general sub-panel.
3. Select source geom: (none).
4. Select along geom: mixed.
5. Under along geom: mixed, click lines to make it the active selector.
6. Select the line indicated in the following image.
7. Click node path to make it the active selector.
8.
Select nodes to define the exact location of the solid element layers, as indicated in the following image.
A total of 13 nodes should be selected, starting at the boss mesh, and then using all of the nodes along the edge of the arm_straight component, ending with the node projected to the top of the boss.
Along nodes for solid map
9. For elems to drag:, select elems >> by collector and select the boss component.
10. Select destination geom: surf and select the top surface of the boss.
11. Click mesh.
The elements are created and the mesh on this part is completed.
Completed mesh of the arm bracket
Step 15 (optional): Check the connectivity of the model.
1. Go to the faces panel.
2. Click comps to go to a list of components.
3. Select every component from the list, or select comps >> all.
4. Select the components to complete the selection and go back to the faces panel.
5. Click find faces.
6. Turn off the geometry display of all components via the Model browser.
7. Turn off the element display of all components except ^faces.
8. Click return to exit the the panel.
9. On the Post page go to the hidden line panel. (F1 on the keyboard.)
10. Go to the cutting sub-panel.
11. Activate the xz plane and trim plane options.
12. Click fill plot.
The faces are now displayed with a plane cutting the model in half. This is so that the interior of the model can be viewed.
13. Click near the cutting plane. Holding the left mouse button down, move the mouse back and forth.
The cutting plane moves through the model, allowing you to see if any face elements exist on the interior of the model.
You should see that there are face elements interior to the model, between the boss and arm. You need to perform some corrections on the connectivity.
Hidden line view of faces
Step 16 (Optional): Correct the connectivity of the model.
1. Display elements for all components except for the ^faces component.
2. Display the elements of the solidmap component as transparent.
3. Go to the faces panel.
4. Select elems >> displayed.
5. Click preview equiv.
Coincident nodes on the intersection between the arm and the boss are highlighted.
6. Specify a slightly larger value for tolerance =, and click preview equiv to identify more coincident nodes on the intersection.
7. Repeat 16.6 until all 60 coincident nodes have been found.
8. Click equivalence.
The nodes are replaced to the location of the lowest node ID.
9. Switch all the components to the shaded visual mode.
Step 17 (Optional): Recheck the connectivity of the model.
Repeat Step 16 to make sure the model is now equivalenced. If you find errors, repeat Step 16.
Step 18 (Optional): Save your work.
The 3-D solid mesh has now been completed. Save the model if desired.
Go to HyperMesh Tutorials