printing _creating a hexahedral mesh using the solid map function - hm-3200

Creating a Hexahedral Mesh using the Solid Map Function - HM-3200

For this tutorial, it is recommended that you complete the introductory tutorial Getting Started with Hyper Mesh - HM-1000, and the tutorial Creating 2-D Elements from Surfaces using the Automesh Function - HM-3100. Working knowledge of the automeshing secondary panel and the creation of 2-D elements are definite pre-requisites.

In this tutorial you will learn how to model a complex part using solid hexahedral elements, and how to approach a volume by breaking it down into individual portions that can be meshed more easily.

While HyperMesh provides an automatic volume mesher using tetrahedral elements, there is no such engine for the automatic creation of hexahedral (brick) elements. In this tutorial, the standard technique of creating first 2-D elements in preparation for the generation of the 3-D hexahedral elements will be applied. While several panels in HyperMesh allow you to create solid hexahedral elements, this tutorial will put additional focus on the use of the solid map panel for the creation of hexahedral elements. The other main meshing tools used will be the automesh, spin, and linear solid panels.

For more information regarding these panels, please refer to the Panels section of the Hyper Mesh on-line help, or click the Hyper Mesh help button while in the panel to activate its context sensitive help.

This tutorial requires about one hour to complete and uses a file located in the <install_directory>/tutorials/hm/ directory. For detailed instructions on how to locate the installation directory <install_directory> at your site, see Finding the Installation Directory <install_directory>.

To load and review the model file:

In this section, retrieve the HyperMesh model file, and review the organization of the geometry into component collectors.

1. Use the files panel to retrieve the file control_panel_hex.hm from the <install_directory>/tutorials/hm/ directory.

2. From the Disp page of the macro menu, set Vis opts: 3 to shade the surfaces in the model and display surface edges in topology mode.

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Control arm

3. Go to the disp panel to review the component collectors pre-defined in the model.

The mode is organized into several component collectors that have been pre-defined based on the geometry of the control arm. The initial set of surfaces has been broken down into logical areas to facilitate the creation of solid elements. The geometry has also been cleaned up based on the various areas. While this tutorial does not include the steps for dividing up the volume, meshing the various parts will put into light the reasons for these choices.

In the subsequent sections, we will hex mesh the various parts defined by the component collectors in this model except for the surfaces component. This last component has also been cleaned up and broken down into some areas, but will serve as a practice area once the tutorial is completed.

To mesh the neck1 region:

The main difficulty of hex meshing lies in ensuring that groups of solid elements can be joined. While it is often easy to create hex elements in most areas of a part, the challenge comes from creating the transition between the various groups and this is what often requires planning.



In this model, cylinder1, cylinder2 and arm are components that, individually, can be meshed fairly easily. The areas that separate them though, offer some unique challenges in the sense that at the end, all elements have to match up. This, in turn, affects the way the simpler areas should be meshed.

In this section, start by creating hex elements in the neck1 volume that represents the transition between cylinder1 and center_area. Start by creating 2-D elements using the ruled panel, and then create one layer of solid elements into this volume using the solid map panel.

1. Use the disp panel to turn off all the geometry except the neck1 component.

Observe the geometry available to define this volume. This determines the approach to use. The bottom area will be common to the solids for neck1 and center_area. This is where these two portions need to match up and this where you create the 2-D elements.

2. Use the Disp page of the macro menu to set Vis opts: 0.

3. Use the global panel to set the current component to neck1.

4. Use the ruled panel to create an all-quad mesh in the area defined by surface edges and the pre-defined additional lines.

- From the 2D page, go to the ruled panel.

- Set the upper entity selector to line list and select one surface edge defining the longer side of the area (see figure below).

- Set the lower entity selector to line list and select the opposite surface edge (see figure below).



Surfaces edges to select

- Set the switch to mesh, dele surf.

- Verify auto reverse is activated.

- Click create.

- Use the density sub-panel of the automeshing secondary panel to adjust edge to a density of 5 for all edges.

- Click mesh to preview the mesh.



Previewed mesh

- Click return to accept this mesh and go back to the ruled panel.

- With the upper selector set to line list, select the two surface edges and one line as shown in the figure below.

- Set the lower selector to node list and select the nodes shown in the figure below.



Line and node selection

- Click create.

- Use the density sub-panel to adjust the density on the lines to 7 elements.


- Click return to accept the elements.

- Repeat the steps above for the remaining open area and obtain the mesh described in the figure below.

Note It is very important to ensure that only quad elements are created. In the subsequent steps we will add a dimension to the shell elements to obtain the hexahedral elements. With this approach, any tria shell elements would produce penta elements. If the densities mentioned above do not produce only quad elements, modify them to obtain only quads.

Final shell mesh in shaded mode

5. Use the edges panel to ensure continuity of the shell mesh.

- From the Tool page, go to the edges panel.

- Set the entity selector to elems, click elems and select displayed.

- Set tolerance = to 0.2.



- Click preview equivalence to review the nodes to equivalence.

- Click equivalence to ensure continuity of the mesh.

Note This step was required because we meshed this area in multiple steps. You can look for free edges to verify that the mesh is now continuous.

6. Use the solid map panel to generate one layer of hexa elements in the volume defined by the neck1 geometry.

- From the 3D page, go to the solid map panel.

- Use the switch to set source geom: to lines.

- In the graphics region, select the 8 lines that enclose the 2-D mesh.

- Set destination geom: to lines.

- In the graphics region, select the 8 lines that define where the neck ends.

- Set along geom: to (none).

- Set along parameters: to density= and type in 1.

- Verify intensity= is set to 0.

- Under elems to drag:, click elems and select displayed.



Solid map selections

- Click mesh.

One layer of solid elements is created in the volume and is placed in a component collector called solidmap.

Solid elements

- Click equiv/faces.

This equivalences all the elements in the solidmap component and also directly create faces elements on them in a ^faces component that can be used to generate solid elements in neighboring volumes. It also automatically turns off the elements in the solidmap component.

In this section we started by creating a 2-D mesh at the boundary between two regions and then used the solid map panel to fill the neck volume with solid elements. We also generated some face elements in preparation for meshing the next region.

To mesh the cylinder1 region:

In this section, generate hexahedral elements for the cylinder region attached to the neck that was meshed in the previous section. Start by creating the solid elements that will attach directly to the neck using the linear solid panel. Since the linear solid panel requires two sets of elements to build solids in between, use the project panel to obtain this configuration. Then complete the circular mesh using the spin panel. Spin face elements around the axis of the cylinder to form solid elements. Finally add the missing layer of hexa elements at the ends of the cylinder using the solid map panel.



1. Use the disp panel to turn off all the geometry except the cylinder1 component.

2. Use the project panel to project duplicate elements of the faces elements at the boundary between the neck and cylinder onto the interior cylinder surface.

- From the Tool page, go to the project panel.

- Select the to surface sub-panel.

- Set the left most entity selector to elems.

- In the graphics area, select one element at the center of the faces elements at the boundary neck/cylinder.

- Click elems and select by face.

Elements by face

Verify that only the elements at the boundary between the two regions have been selected (see figure above).

- Click elems and select duplicate.

- Select original comp from the pop-up dialog.

- With the surf selector active, select the surface defining the interior of the cylinder.

- Set along vector: to surface normal.



- Click project.

Projected duplicate elements.

3. Use the global panel to set the current component to solidmap.

4. Use the linear solid panel to create layers of solid elements between the shell elements.

- From the 3D page, go to the linear solid panel.

- With the upper elems selector active, pick one of the elements from the boundary neck/cylinder as done earlier.


This highlights the remaining elements defining the set of elements the linear solid function will start from to build the layers of solid elements.

- Click the lower elems selector to make it active.

- Select one of the elements on the interior cylinder.

- Click elems and select by attached.

This highlights all the elements to which the function will map the first set.

- Click the upper N1 selector to make it active and select up to three nodes to define uniquely one



shell element from the from: set.

Hint Depending on which element you try to define uniquely, the number of nodes you will need may be different. For this example, if you select a corner element, the node located at the "free" corner is not shared with any other element from the selection, and it alone defines the element. Therefore, in such a case, one alignment node is sufficient.

- Click the lower N1 selector to make it active and select the corresponding nodes from the corresponding element as alignment nodes.

Elements and alignment nodes selection

- Verify the toggle is set to distribute layers.

- Set density = to 2.

- Verify that bias intensity = is set to 0.

- Click solids.

This generates solid elements and places them in the solidmap component. Since you have turned this component off in the previous section, the elements do not appear at this time.

5. Use the solid map panel to turn on the solid elements, equivalence them and obtain faces elements.

- From the 3D page, go to the solid map panel.



- Click 3d mesh: on to turn back on the display of the elements in the solidmap component.


This equivalences the solid elements from the two groups that were created up to this point, and generate faces elements on them that can be used for subsequent operations.

6. Observe closely the elements that were created up to this point for the cylinder region.

The layers at the ends of the cylinder form narrower bands. This is a result from the 2-D mesh we started from and that was created in an area with round corners. This will affect the result of the next operation. We choose here not to perform any operation on these elements.

7. Use the spin panel to add layers of elements in the cylinder.

- From the 3D page, go to the spin panel.

- Go to the spin elems sub-panel.

- With the elems selector active, pick one of the face elements to spin around the axis of the cylinder.


- Set the direction to y-axis.

A base node is needed to position in space the axis the elements will spin around. Use the distance panel to create a node at the center of the cylinder.

- Use the F4 function key to jump to the distance panel.

- Select the three nodes sub-panel.

- Hold the left mouse button down on top of one of the circular lines defining the cylinder.

- Release the left mouse button when the line highlights.

- Click any three locations on the highlighted line for nodes N1, N2, and N3.

- Click circle center.

- Click return to go back to the spin panel.

- With the base selector active, pick the node that was just created.

- Set angle = to .



- Set angle = to 269.0.

An approximate value of the angle of spin to use can be obtained using the distance panel, three nodes sub-panel.

- Set on spin = to 16.

- Verify bias intensity = is set to 0.

- Use the disp panel to turn back on the display of the elements in the solidmap component.

- Spin the faces elements.

If the elements are spun in the wrong direction, reject the operation and spin them in the opposite direction

- Observe the elements obtained and how the situation described earlier affected the solid mesh.

Hexas from spinning shell elements

8. Use the edges panel to restore continuity in the mesh.




- Select the elements displayed.


- Click preview equivalence and review the nodes that are highlighted.

- Click equivalence.

- Verify that the mesh is now continuous and no elements were collapsed. Reject the equivalence if needed, and use the lower tolerance.

Hint For larger gaps that were not closed, use the replace panel from the 2D page to manually equivalence nodes across these gaps. Review the replace panel help for complete details.

9. Use the solid map panel to add the missing layer of solid elements at both ends of the cylinder.

- Go to the solid map panel.

- Click 3d mesh: on if needed to display the solid elements.

- Click equiv/faces to obtain the faces elements on the solid elements.

- Set source geom: to nodes.

- Set the selector to node path.

- Select the nodes around the inside of the cylinder from one end (see figure below).

- Increment the nodelist using the forward arrow under node path.

- Select the nodes on the outside periphery of the cylinder for the same end as a second nodelist (see image below).




- Set destination geom: to surf and select the surface at the end of the cylinder.

- Leave along geom: set to (none).

- Select by face the face elements between the node lists as the elems to drag:.

- Set density= to 1.

- Click mesh.


- Repeat all these steps for the other end of the cylinder.



Neck and cylinder

10. Repeat the steps described in this section and the previous one to mesh the neck2 and cylinder2 components.

11. Use the disp panel to turn on the display of all the geometry and all the elements except the ones in the ^faces component.



Meshed necks and cylinders

In this section, you started by creating the elements in the cylinder that would attach to the neck using the linear solid panel. You then completed the mesh to fill the geometry of the cylinder by using the spin and solid map panels taking advantage of the faces elements that were generated on the solid elements. Finally, you repeated the process of the last two sections to mesh another neck and cylinder volume.

To mesh the arm:

The arm component is broken down into two volumes to limit the influence of some of its features to only one portion of the arm. In this section, use the solid map panel to mesh this arm, starting with the smaller portion that presents the most curvature. Use the same approach to mesh the longer portion aferwards.

1. Use the disp panel to turn off all the geometry except the arm component.

2. Use the disp panel to turn off all the elements except the ̂ faces component.



Note If you do not currently have faces elements created on the solid elements representing neck2, create them using the equiv/faces function from the solid map panel. This only works provided the solid elements are part of the solidmap panel.

3. Use the solid map panel to create solid elements in the portion of the arm attached to neck2.


- Set source geom: to nodes and select the nodes delineating the end of the neck2 (see figure below).

- Set destination geom: to lines and select the lines that breaks the arm into two volumes (see figure below).

- Set along geom: to lines and select all the side lines that define the path from the source to the destination.





- Set bias style: to exponential, and set intensity= to 2.

This helps ensure that the number of elements in the curved areas is sufficient.

- Select the elements by face for elems to drag:.

- Click mesh.


First portion of the arm

4. Repeat step 3 to mesh the second portion of the arm. Do not use biasing and create 30 layers of solid elements.



Completed arm

In this section, you use the solid map panel twice to mesh the arm volume. The volume was broken down into two regions, and biasing was used for the solid elements in one region to capture the curvature properly.

To mesh the center area:

The last volume you mesh in this tutorial is the center area that connects the arm and the first neck that was worked on. This area also connects to the remainder of the model that you can mesh for additional practice purposes.

To mesh the center area, start by mapping out the solid elements that are involved in the fillets of the part. Use the solid map panel to achieve this. The geometry of this volume has already been edited to facilitate this process. Then, use the spline panel to generate a shell mesh in the central portion, and use the solid map panel to fill the remainder of this volume.

1. Use the disp panel to turn off all the geometry except the center_area component.

2. Use the solid map panel to create solid elements in the fillet areas.


- Set source geom: to nodes and select the nodes delineating the elements to map (see figure



below).

- Set destination geom: to lines and select the lines that define the end area (see figure below).

- Set along geom: to lines and select the four side lines that define the path from the source to the destination.



- Verify intensity= 0.

- Select the elements enclosed by the nodes defining the source for elems to drag:.

- Click mesh.




- Repeat these steps for the second filet area between the meshed neck1 and the unmeshed remainder of the model.

Meshed fillet regions

3. Use the solid map panel to create solid elements in the fillet area between neck1 and arm.


- Set source geom: to nodes and select the nodes delineating the elements to map from the arm component (see figure below).

- Set destination geom: to nodes and select the nodes that surround the corresponding elements from the neck1 component.

- Set along geom: to lines and select the four side lines that define the path from the source to the destination.






- Select the elements enclosed by the nodes defining the source area for elems to drag:.

- Click mesh.

The new elements do not line up completely with the existing elements.

- Click equiv/faces to equivalence some of the solid elements in the solidmap component.

HyperMesh may post a message telling how many nodes can be equivalenced for a given tolerance. Click Yes to accept and continue to click equiv/faces to see if additional elements get equivalenced as each time you try the tolerance is increased, up to 10% of the element size. When no more nodes are equivalenced, it means that the distance between nodes that should be shared, if any remain, is larger than the maximum tolerance.

4. Use the edges panel to equivalence any remaining elements.


- Select the elements displayed.




- Click preview equivalence to review the nodes detected.

- If nodes are missing from the selection, increase the tolerance until they are found.

- Click equivalence.

This equivalences the nodes. Although the elements in the solidmap component were not displayed (an selected), working with the faces elements that share nodes with them ensured that solid elements would be fixed as well.

5. Use the global panel to set the current component to center_area.

6. Use the disp panel to turn on the display of the elements in the center_area component.

7. Use the spline panel to create 2-D elements in the open area.

- From the 2D page, go to the spline panel.

- Set the entity selector to nodes and select the nodes on one side of the control arm surrounding the open area (see figure below).

Hint Use the selection by path to speed up this process.

- Set the switch to mesh, dele surf.

- Click create.

- Use the density sub-panel to adjust the element densities such that they match the neighbor faces elements (see image below).


- As needed, use the type sub-panel to ensure that quad elements are being used to mesh the area.



Previewed mesh

- Click return to accept the quad only mesh.

8. Use the solid map panel to complete the solid mesh in the center_area component.


- Set source geom: to surf and select the surface the elements previously created lay onto.

- Set destination geom: to surf and select the corresponding surface on the other side of the control arm.

- Set along geom: to (none).





- Select by collector the elements created in the previous step for elems to drag:.

- Click mesh.

- Click equiv/faces several times as needed to equivalence the solid elements in the solidmap component.

Completed mesh

9. Use the edges panel to equivalence any nodes that were not equivalenced in the solid map panel, working with the elements displayed and a tolerance of 0.1.

10. Use the disp panel to turn off all the geometry, and turn off all the elements except the ones in the solidmap component.

11. Optionally complete the solid mesh for this control arm using similar techniques as the ones presented in this tutorial.

This concludes this tutorial. You may discard this model or save it to your working directory for your own reference.



In this tutorial, you used the solid map panel in various situations to quickly and effectively create a hexahedral mesh for a control arm. You especially took advantage of built in functions allowing you to quickly equivalence nodes and obtain faces elements from the solid elements, limiting the needs produce shell elements in other panels.

For additional techniques and panels pertaining to the creation of hexahedral elements, refer to the tutorial Meshing a Part with Hexahedral Elements - HM-3220.

See HyperMesh Tutorials for a complete list of tutorials.



printing _creating a hexahedral mesh using the solid map function - hm-3200

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