Hypermesh Quality Tutorials
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HyperMesh 8.0 Tutorials Quality
HyperWorks
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HyperMesh 8.0 Tutorials Quality Checking and Editing Mesh - HM-3300 .......................................................................... 1 Measuring and Improving 2-D Quality using Quality Index - HM-3310................19 Penetration - HM-3320.......................................................................................................34
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Checking and Editing Mesh - HM-3300 In this tutorial, you will learn how to: •
Identify shell element connectivity problems
•
Correct shell element connectivity problems
•
Review the model’s shell elements to ensure connectivity problems were corrected
Re-mesh the elements along the rib
Tools The edges panel can be accessed: •
On the Checks menu, select Edges
•
On the Tool page, click edges
The edges panel allows you to find the free edges in a group of elements, find "T" or discontinuous connections in a group of elements (any edges connected to three or more elements), display duplicate nodes, and equivalence duplicate nodes. Free edges found in your model are displayed in red. You can use equivalence to remove the duplicate nodes, based on a tolerance which you specify. The preview equiv function is available to allow you to see which nodes are removed when the equivalence function is selected.
The normals panel can be accessed: •
Press the Shift + F10 key
•
On the Checks menu, select Normals
The normals panel allows you to display the normal of an element or surface, adjust the orientation of element normals, and reverse the normal of an element or surface. The normal of an element is determined by following the nodes of the element, in order, using the right-hand rule.
The check elems panel can be accessed: •
Press F10
•
On the Mesh menu, select Check Elements
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The check elems panels allow you to verify the basic quality of your elements and to verify the geometric qualities of those elements.
The automesh panel can be accessed: •
Press F12
•
On the Mesh menu, select AutoMesh
The automesh panel allows you to create meshes or re-mesh existing meshing interactively or automatically on surfaces or groups of elements. You can use the sub-panels to provide specific meshing parameters and manipulate surface edges and meshing fixed points (locations where the mesher is required to place a node).
Exercise This exercise uses the model file, cover.hm.
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Step 1: Retrieve and view the HyperMesh model file, cover.hm. Step 2: Review the model’s free edges to identify shell element connectivity problems. 1.
Go to the edges panel.
2.
With the comps selector active, select any element from the graphics area. The component containing the element is selected.
3.
Click find edges. Red, 1-D elements are displayed. They are organized into the new component named ^edges. A red 1-D element is created along each shell element edge that is free; one or more of the element edge’s nodes is not shared by the adjacent elements. Note:
For a component name whose first character is ^, the component and its contents is not written to the input file when the model is exported.
4.
On the View menu, click Utility Menu.
5.
Click the Shaded Elements and Mesh Lines icon
6.
Observe the red, 1-D elements (free edges).
7.
Try to identify gaps in the continuity of the mesh. Hint:
8.
Look closely at free edges interior to the model.
In the Model Browser, turn the display on and off for the component, shells, to continue to identify which red, free edges do not belong.
All red, free edges 9.
.
Red, free edges which belong
Turn on the display for the component, shells.
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Step 3: Correct the shell element connectivity problems using the edges panel. 1.
In the tolerance= field, type 0.01.
2.
Click preview equiv. The header bar displays the following message, "81 nodes were found". A sphere, is created on nodes having a distance between each other equal to or less than the specified tolerance.
3.
Notice that for this exercise’s model, a sphere is not created on every node along all of the red, free edges, which do not belong. A larger tolerance must be specified to identify the rest of the nodes.
4.
For tolerance =, increase its value until all 96 nodes are identified as shown in the image below. Be careful not to increase the tolerance value to too much. Although the 96 nodes will be identified, an excessively large tolerance value may collapse elements when the identified nodes are equivalenced.
The nodes identified with preview equivalence 5.
Click equivalence. The 96 coincident nodes are equivalenced.
6.
Rotate and observe the model to see that the mesh still looks as it should and no elements are collapsed.
7.
Click delete edges. The red, free edges and their component ^edges are deleted.
8.
Remain in the edges panel.
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Step 4: Review the model’s free edges again to confirm that all of the shell element connectivity problems have been corrected. 1.
Click find edges. Observe the red, 1-D elements (free edges). Are there any red, free edges that should not belong if the mesh were continuous or if all of the elements were connected? Hint:
2.
Only red, free edges should exist on the perimeter of the part.
Use the Model Browser, to turn the display off and on for the component shells to observe that all of the free, red edges belong.
Red, free edges which belong
Step 5: Display the element normals and adjust them to point in the same direction. 1.
Go to the normals panel.
2.
With the comps selector active, select one element from the graphics area. The element is highlighted briefly to indicate that the component to which it belongs is selected.
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3.
Click display normals. Arrows (vectors) are drawn from the element centroids and show the direction of the element normals. Notice the arrows do not all point from the same side of the part. For some analyses, the element normals should point from the same side.
4.
Click size = and type the size which the normal should be in model units and select display normals again. When size = is set to zero, the vector will be 10% of the screen.
5.
Toggle vector display normals to color display normals.
6.
Click display normals. The element normals are displayed using colors. The red side of the elements is the positive normal direction, while the blue side is the negative normal direction.
7.
Notice each side of the part shows red and blue.
8.
Click the orientation: elem selector to make it active.
9.
Select an element from the graphics area.
10. Click adjust normals. All elements on either side of the part are the same color, red or blue. The header bar displays the following message, "[X] elements have been adjusted." 11. Click return.
Step 6: Review the quality of the elements using the check elems panel. 1.
Go to the check elems panel.
2.
Go to the 2-d sub-panel.
3.
Verify that jacobian < field is set to 0.7.
4.
Click jacobian to determine if any elements have a jacobian of less than 0.7. Elements having a jacobian of less than 0.7 are highlighted.
5.
Notice that several elements on the triangular rib and around the smaller of the two holes have a jacobian of less than 0.7. The header bar displays a message indicating how many elements failed this check.
6.
In the graphics area, click on an element. A window displays that lists each quality check result for the element.
7.
Click any mouse button to close the pop-up window.
8.
On the right side of the panel menu, switch from standard to assign plot.
9.
Click jacobian to review again. A legend for jacobian values appears and each element is colored accordingly. The red elements have a jacobian less than the threshold, 0.7.
10. Verify that quads: min angle < is set to 45. 11. Click min angle to determine if any quad elements have an angle of less than 45.
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12. Notice that a couple of elements on the rib have an angle of less than 45. 13. Verify that the max angle >field is set to 135. 14. Click max angle to determine if any quad elements have an angle greater than 135. 15. Notice that several elements on the rib have an angle greater than 135. 16. Click return.
Step 7: Re-mesh the elements on the rib using the automesh panel. 1.
Go to the automesh panel.
2.
Ensure that you are in the size and bias sub-panel.
3.
Switch the entity selector to elems.
4.
Toggle to interactive.
5.
For element size=, type 3.5.
6.
Select one rib element from the graphics area.
7.
Select one element on the plane of elements perpendicular to the rib and in the same plane as the rib’s shortest edge as shown in the image below.
Example of elements to select
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8.
Select elems >> by face to complete the selection of elements as shown below.
Elements selected using by face 9.
Click mesh. The meshing module appears.
10. In the density sub-panel, change the element density on the rib’s hypotenuse edge to 9. 11. Change the element density on the rib’s shortest edge to 5.
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12. Keep all other element edge densities the same.
Adjusting element edge densities 13. Go to the mesh style sub-panel. 14. Under mesh method, set the last option to free (unmapped). 15. Under mesh method, select set all. 16. Click mesh to preview the mesh. 17. Go to the checks sub-panel, and check the jacobian, quads: min angle, and quads: max angle. 18. Notice that no elements fail the minimum and maximum angle checks. Only a couple of elements have a jacobian of less than 0.7. The smallest jacobian is 0.68, which can still be considered good quality. 19. Click return to accept the mes h and go back to the main menu.
Step 8: Remove the tria elements from the rectangular plane of re-meshed elements by first deleting the row of elements containing the trias. 1.
On the Tool page go to the delete panel.
2.
Ensure that elems is the active selector.
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3.
Select the elements as shown in the image below.
4.
Click delete entity.
5.
Click return.
Elements to delete
Step 9: Stitch the gap that resulted from deleting the row of elements using the replace panel. 1.
On the 2D page, enter the replace panel.
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2.
With the replace: node selector active, select node A as indicated in the image below.
3.
With the with: node selector active, select node B as indicated in the image below. Node A is replaced with node B.
Select nodes A and B
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4.
Repeat #2 and #3 for the other nodes along the gap. The resulting mesh should look like the mesh in the image below.
The mesh after replacing nodes on the bottom face 5.
Click return.
Step 10: Use the smooth panel to adjust the node placement on the rectangular plane of re-meshed elements. 1.
On the 2D page, enter the smooth panel.
2.
Go to the plates sub-panel.
3.
With the smooth: elems selector active, select an element on the rectangular plane of remeshed elements.
4.
Select elems >> by face.
5.
For iterations = specify 10.
6.
Switch the smoothing algorithm from autodecide to shape corrected.
7.
Click smooth.
8.
Click return.
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Step 11: Remove tria elements from another area of the model using the edit element panel, split and combine sub-panels. 1.
On the 2D page, enter the edit element panel.
2.
Go to the split sub-panel.
3.
With the splitting line: points selector active, click on four screen points as shown the image below. Temporary line segments are drawn to connect the points.
4.
You can right click to undo the last line segment drawn or you can click delete line to start over with selecting points.
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5.
Click split. Elements that have the line pass through them are split. The resulting mesh should look like the mesh below. There are two pairs of adjacent tria elements.
6.
Go to the combine sub-panel.
7.
Select two adjacent tria elements as indicated in the image below.
8.
Click combine.
9.
Repeat # 6 and # 7 for the other two adjacent tria elements.
10. Remain in the Edit Element sub-panel.
Trias to select
Combining trias into quads
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Step 12: Dynamically move nodes on the mesh area modified in the last step to improve element quality. 1.
Go to the cleanup sub-panel.
2.
Click cleanup. The element cleanup menu appears. It allows you to select various combinations of quality checks, specify a warning/unacceptable range for each check, and dynamically move nodes around to place them where you desire. Elements are colored as follows: •
No color; appear blank: element passes quality checks
•
Yellow: one or more quality check results falls into warning/unacceptable range
•
Red: one or more quality check results are beyond unacceptable
Among the group of elements you modified in the last step, Step 11, two quad elements are red and one quad element is yellow. 3.
Clear the warpage and jacobian check boxes.
4.
With the node selector active, click on an interior node of a red element and drag the node around until the element is no longer red.
5.
Repeat # 4 for the other red element.
6.
Click return.
Step 13: For the same area of elements you focused on in the last step, optimize element quality by simply clicking on nodes and elements. 1.
On the 2D page, go to the qualityindex panel.
2.
On the panel menu’s right side, switch view to optimize.
3.
With the node optimize selector active, click on a few nodes of the mesh area you modified. When a node is clicked on, it is reposition so that the elements attached to it have the best possible quality based on the criteria specified in the qualityindex panel.
4.
Click on the selector element optimize to make it active.
5.
Click on yellow and red elements in the same mesh area. When an element is clicked on, it is adjusted to have the best quality possible based on the criteria specified in the qualityindex panel. When you click on a red element, it may become yellow or black (no color assigned). When you click on a yellow element, it may become black.
6.
Click return.
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Step 14: Add a ring of radial elements around the smaller of the two holes. 1.
Click the Utility tab.
2.
On the Geom/Mesh page, click Add Washer.
3.
With the nodes selector active, select one node on the edge of the smallest hole as indicated in the image below.
Example node to select
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4.
Click proceed. A pop-up window appears as shown in the image below.
Add Washer macro dialog 5.
Toggle to Width, and specify 3.
6.
Select the Minimum number of nodes around the hole check box.
7.
In the Density: field, enter 12.
8.
Click Add.
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9.
Click Close. The mesh around the hole should look like the mesh in the image below.
Resulting mesh around the smallest hole
Step 15 (Optional): Save your work. With this exercise completed, you can save the model if desired.
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Measuring and Improving 2-D Quality using Quality Index - HM-3310 In this tutorial, you will learn how to measure and improve the quality of the mesh and how to eliminate manually fixing problem elements. The qualityindex panel is used to evaluate the quality of the mesh as well as improve local areas, while the smooth panel is used to achieve larger scale improvements to the mesh quality based on the quality index. The elem cleanup panel gives you an opportunity to clean up parts of the mesh in a more automated fashion. For example, you may have legacy models or a file from an external source that does not conform to current criteria. Checking mesh quality and correcting the mesh is an integral part of the meshing process. While the check elems panel in HyperMesh provides the tools to check a mesh against a user-defined value for a given quality criterion, it does not provide an overall measure of the quality of a mesh. This can be achieved in the qualityindex panel where the quality of a mesh can be gauged by a single number: the quality index (QI). HyperMesh functions based on the quality index offer more automated solutions for improving the quality of a mesh and helps eliminate the tedious task of correcting many elements by hand.
Tools - Quality Index The qualityindex and elem cleanup panel will be used in this tutorial. The qualityindex panel can be accessed by one of two methods: •
On the Checks menu, click Quality Index
•
On the 2D page, click the qualityindex panel
The qualityindex panel allows you to set quality criteria and evaluate your mesh against these quality criteria using a single number: the compound quality index (comp. QI) value. It also allows you to edit and optimize node and edge locations, improving the quality of your mesh by reducing the compound QI value. The compound quality index is a function of twelve quality criteria (organized in three pages) that are set in the panel, as well as the weight factors (comp wt) and penalty values associated with them (see figure below). Each criterion has five rating levels (ideal, good, warn, fail, and worst) and as the quality decreases, the penalty value increases. Therefore, the smaller the quality index value, the better the overall mesh quality for the criteria you set. The weight factor is a multiplier that can be used to bias the results and assigns more importance to some checks than others.
Criteria table In this panel, several QI values are computed: one for each element (not reported), one for each criterion turned on, and the compound QI value that represents the overall quality of the 2D elements displayed. Refer to the on-line help for the formulas used to compute these quantities. The compound quality index is the summation of all the element quality indexes, and also the summation of all the criteria quality indexes.
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To facilitate visual review of their quality, elements are displayed in the graphics region based on their individual element QI value, which is also based on selected criteria and their corresponding weight factors and penalty values. With the default colors, elements with a QI value over 10 are in the worst category and displayed in red. Elements with a QI value between 1 and 10 are in the fail category and displayed in yellow. Elements with a QI value between 0.8 and 1 are displayed in cyan and fall in the warn category, and elements with a QI value less than 0.8 are displayed in the background color (black) and considered good or ideal. Note
A quality index value is a relative value that is completely dependent on the quality criteria you use. The lower the quality index, the closer your mesh is to the quality criteria you defined.
The qualityindex panel the following capabilities: The Criteria Setup includes: -
Turn criteria on and off.
-
Set good and fail values for each criterion.
-
Set criteria weight factors.
-
Choose display colors for each rating level.
-
Load and save criteria files.
-
Save a summary file of the results.
The Report Status includes: -
The percentage of elements that failed a given check.
-
The worst value found for the check.
-
The criterion Q.I. value.
-
The number of quads and trias.
-
The percentage of trias.
-
The total number of elements that failed.
-
The compound Q.I. value.
-
The editing options such as: place node and swap edge are available, as well as, the optimization functions: node optimize and element optimize
Additional options are available to fix the mesh. While the view setting does not provide any additional options, both the edit and optimize settings provide additional options for editing the mesh and improving its quality. These options will be discussed later in the tutorial. In this section, some of the concepts that govern the qualityindex panel were introduced. For complete details on this panel, refer to the Panels section of the on-line help, or click help while in a panel to display its context-sensitive help.
Tools - Element Cleanup The elem cleanup panel can be accessed by one of two methods: •
On the Mesh menu, click Auto Element Cleanup
•
On the 2D page, click the elem cleanup panel
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The elem cleanup panel allows you to amend and readjust the mesh to your criteria.
Strategy The list below provides best tips and practices:
•
Use the QI functionality on local models, not large structures with multiple parts
•
Use the qualityindex panel to check the quality of the mesh
•
Use the elem cleanup panel to amend and readjust the mesh
Exercise This exercise uses the model file, quality_index.hm. The model is of a bracket with various features such as holes and fillets. The bracket is meshed with a mixed mesh of tria and quad elements. You will evaluate the quality of this mesh based on its quality index and make any necessary improvements.
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Step 1: Retrieve the model file, quality_index.hm. 1.
On the File menu, click Open.
2.
In the Open File… window, browse to the file’s location and click Open.
3.
Click the Shaded Elements and Mesh Lines icon
.
Step 2: Evaluate the quality of the mesh. 1.
Go to the qualityindex panel. Note:
2.
By default, elements are color-coded based on the values currently defined for the quality criteria, the weight factors and the penalty values. These are used to compute individual element QI values.
Go to page 3 in the QI panel and click edit criteria to load the criteria file quality_index.criteria from the/tutorials/hm directory. The quality criteria defined in the file are automatically loaded and elements in the graphics area are color-coded based on their element QI values.
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3.
Review the quality criteria defined on pg1, pg2, and pg3. Pay close attention to the criteria that can be turned on and off, and the actual values assigned to them for the various threshold levels. The weighting factors can be adjusted for each criteria by accessing the edit criteria button on pg3 and toggling the Advanced Criteria Table checkbox. Several elements are displayed in yellow, meaning that their element QI values are between 1 and 10. The element QI value is computed as: (weighted average of penalties that pass) + (weighted sum of penalties that fail) Considering that all the weight factors are currently set to 1, it can be interpreted that these elements failed at least one of the checks currently turned on (fail rating). Hint:
To determine which quality check a specific element fails (fail or worst category) turn on each criterion separately (one at a time).
Note:
Elements are color-coded based on their QI values. The color-coding does not necessarily capture the outcome for each specific quality check, but it shows how elements fare against the entire set of criteria that are selected. In the end, elements displayed in red and yellow are elements for which the overall quality (defined by the criteria turned on) does not meet the requirements. Elements displayed in cyan are simply acceptable.
The fail value column lists the fail values set in the default panel for easy reference. The %fail column lists the percentage of element displayed that failed the given criteria, and the worst column lists the worst value found for the corresponding criteria. You can also review criteria QI values as they are listed in the Q.I. column, which can be accessed by the toggle switch. In this case, you will notice that the warpage quality check is the biggest contributor to the compound quality index. Maximum size has the smallest contribution, and would not warrant much attention when trying to decrease the compound quality index for a mesh. 4.
Write down the values for comp.Q.I. and # of failed =. Although these values are relative, they indicate how the mesh does against the set criteria. As you improve the quality of the mesh later in this tutorial, both numbers will decrease. In this section, you used the qualityindex panel to review the quality of the mesh based on quality criteria you set when loading the criteria file.
Step 3: Save and review criteria files. Various finite element applications call for different quality criteria and often, various meshed parts in the same model must meet different criteria. In such situations, the values assigned to the various quality criteria need to be changed in the qualityindex panel to match the new requirements for each mesh. While this can be done manually each time, HyperMesh allows you to limit this editing to a one-time operation by saving values set for the various quality checks in the qualityindex panel to a text file. The criteria file you used earlier in this tutorial has been prepared in a similar manner. In this section, change the values for some of the criteria in the qualityindex panel and save the quality criteria to a new file, starting your own library of criteria files. With a pre-defined set of criteria files you can then easily load the various criteria files for different applications.
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1.
In the qualityindex panel, go to pg3 and click edit criteria. The criteria file editor opens in a new window. This editor displays all of the element quality criteria with the values defined for each one, and allows you to change those values.
2.
Update the quality criteria listed to the values specified in the table below: Criterion:
Good value:
Fail value:
min length
5.5
3.5
max angle quad
120
140
min angle quad
60
40
After you modify the criteria, click "apply"; notice how elements in the model change color based on the new criteria. Note:
The element size elem size value used in the min size and max length checks is the target element size set in the global panel. This value can also be set by loading a criteria file. Alternatively, concentrate only on fail values if Advance Criteria Table if off. For example, worst cannot be greater than fail if looking at min size.
Warning:
When modifying criteria values, HyperMesh may reject some of the values you insert as there needs to be a logical progression in values. For example, the fail value for the min size check cannot be larger than the good value, so before increasing this fail value, you may need to first increase the good value.
3.
Select save as… from the criteria file editor’s file menu, and save the criteria file as quality_index_2.criteria to your working directory.
4.
Click the OK button in the criteria file editor to apply changes and close the editor.
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5.
Check the display summary legend checkbox to create a summary file. Next, click the browse… button to select a location to save the summary file. Once saved, you can view the summary file by clicking the summary button in the panel.
6.
Go to pg1 to review the comp.Q.I. = and # of failed = values and compare them to the values found for the criteria file loaded earlier. Both values have changed. The criterion on the minimum element size was tightened, while those on the minimum and maximum quad angles were loosened. The result is a slight decrease in the compound quality index value and a change in the number, and probably the actual elements, that fail our criteria.
In this section you experimented with changing values for the criteria in the quality Index panel. You reviewed how these changes affected the results for the mesh and the color-coding of elements, and exported a criteria file for the new criteria.
Step 4: Improve element quality using the edit functions. The edit tools (place nodes and swap edges panels) in the qualityindex panel, allows you to improve the quality of elements by letting you move nodes interactively and swap element edges. The place node function allows you move nodes manually on their surface while the color-coding of the elements sharing the node (indicating changes to their quality) is updated in real time. The swap edge function lets you swap the common edge between two elements to use different nodes, creating a new configuration that is automatically evaluated against the quality criteria and color-coding. In this section, experiment with both functions to improve some of the elements failing the quality criteria defined in the quality_index.criteria file. 1.
Load the criteria file quality_index.criteria from the/tutorials/hm directory.
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2.
Press V on the keyboard and click restore1 for View1.
3.
Use the place node function to drag the nodes shown in the figure below such that all the elements that share them fall in the good range.
Nodes to move Observe how the compound quality index value and the number of elements that fail both decrease as you fix this area of the mesh. The final mesh in this area should look similar to this:
Improved mesh 26 HyperMesh 8.0 Tutorials – Quality Proprietary Information of Altair Engineering
Altair Engineering
As you drag nodes, observe how the values for the results listed in the last columns of the results mode temporarily change to report the local effect of moving the nodes. The comp.Q.I. shows the compound quality index for these elements affected by the node being dragged (this helps in finding an optimal position); # of trias shows how many trias fail the criteria, and # of failed tells you how many of the elements involved in the current operation still fail the quality criteria. Note:
The place node function lets you move the node only on an inferred surface and not beyond its edges. Use the undo function at any time to undo the changes you have made to the mesh.
4.
Press V to restore View2.
5.
Use the swap edge function to improve the quality of some of the elements in this area (see figure below).
Edge to swap The common edge is changed (connectivity change) and produces two new elements from the nodes involved.
New mesh after edge swapping Altair Engineering
HyperMesh 8.0 Tutorials – Quality 27 Proprietary Information of Altair Engineering
Hint:
6.
When using the swap edge function, the edge selected is re-positioned in the next possible way between the two elements. A single pick on the edge may or may not improve the quality, or produce the best improvement. Pick the edge again if the quality deteriorates. HyperMesh repositions the edge in all possible ways between the two elements in a cyclic process.
Use the swap edge function again between the pair of elements produced and cycle through all the pairs of elements possible by working with this common edge to select the one configuration that yields the lowest compound quality index. The configuration described in the figure above produces the lowest QI value.
7.
Use any combination of the place node and swap edge functions to ensure that all the elements in this area satisfy the quality criteria (see figure below for an example).
Improved area In this section, you used the edit tools and its various functions to manually and interactively improve one local area of the mesh. As you placed nodes and swap edges, you also monitored changes to the compound quality index to measure how this number decreases as the quality of the elements improves.
28 HyperMesh 8.0 Tutorials – Quality Proprietary Information of Altair Engineering
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Step 5: Improve element quality using the optimize feature. The optimize tool (node element) offers semi-automatic quality correction functions. The node optimize function finds the optimum position for the node you select so that the quality index for the elements sharing this node is lowest. With the element optimize function the same goal is sought; although HyperMesh works with all the nodes involved in this element at the same time, affecting a larger area. In this section, experiment with both functions from the optimize tool to improve the quality of the mesh in some local areas. You can monitor how changes are bringing the quality indexes down and improve the quality of the mesh. 1.
Press V to restore view3.
Elements to optimize 2.
Use the element optimize function to improve the quality of the elements in this area. Observe changes to the compound quality index value as you use this function. Note:
You may need to select multiple elements (not just the failing elements) multiple times to obtain the best possible quality as each operation only considers the element you select and the elements with which it shares nodes.
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The final mesh should look similar to this:
Improved mesh 3.
Press V to restore view4.
Nodes to optimize 30 HyperMesh 8.0 Tutorials – Quality Proprietary Information of Altair Engineering
Altair Engineering
4.
Use the nodes optimize function to improve the quality of the elements failing the checks. Observe changes to the quality index value as you optimize the location of various nodes. You should finish with a mesh similar to this:
Resulting mesh 5.
Correct any remaining bad elements by using one of the previously mentioned functions such as element optimize.
Final element after using element optimize Altair Engineering
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6.
Write down the values for comp.Q.I. = and # of failed = and compare these values to those with which you started. By now, these values have gone down, although they have decreased by only a certain percentage of the initial values. This is because there are still many other areas of our mesh that need attention.
Areas still requiring attention In this section, you experimented with the various tools available in the qualityindex panel for improving the quality of elements to ensure they meet quality requirements. While these tools are very powerful in improving the quality of a mesh, it may not always be practical to try to fix numerous elements in a model with this approach as only a few elements can be fixed at a time. These tools are more useful for local than global areas.
Step 6: Improve element quality using the smooth panel. The smooth panel from the 2D page can be used to smooth elements according to quality criteria. In this mode, it optimizes node locations so that the overall quality index of the elements selected is minimal. This allows you to work with large numbers of elements at one time.
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In this section, use the QI optimization mode of the smooth panel to improve the quality of the elements. Then go back to the qualityindex panel to review the quality of the resulting mesh. 1.
Use the smooth panel, QI optimization mode to optimize the elements based on the criteria defined in the qualityindex panel. -
From the 2D page, select the smooth panel.
-
Go to the plates sub-panel.
-
Use the switch to select the QI optimization mode.
-
Click elems and select displayed.
-
Set target quality index = to 0.2.
-
Ensure the time limit check box is cleared. Optimization time is not a concern with this small model.
-
Set the feature angle = to 30.0.
-
Set the toggle to use current criteria. Or, a criteria file can be specified.
-
Leave the lower toggle set to recursive optimization procedure.
-
Click smooth.
-
If a message displays, click Ignore.
HyperMesh smoothes the elements according to the specified quality criteria and returns the final quality index value in the header bar. Note: 2.
Refer to the on-line help for a complete description of all the options available in this panel.
Go to the qualityindex panel to review the quality of the mesh. The number of elements failing the quality criteria has been reduced to only a few.
3.
Compare the current values for the compound quality index and the number of elements that failed to the initial ones.
4.
Go to pg1 and use node optimize and the tools to fix any element that is still failing the quality criteria. While the smooth panel optimizes node locations so that the elements would yield the lowest compound quality index value, you still have the ability to work on local areas where only the local quality index is considered and will therefore often yield a different result.
5.
Use pg3 to save a summary file of the results to your working directory.
6.
Load this summary file into any text editor and review the information it contains.
Summary In this tutorial, you learned how to: •
Evaluate the quality of 2-D elements using quality indexes
•
Correct elements that fail the quality criteria
•
Use the smooth panel to address numerous elements needing improvement
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Penetration - HM-3320 In this tutorial, you will learn how to: •
Run the penetration check
•
Review the intersection results
•
Fix the intersection results
•
Interrogate the penetration results
•
Fix the penetration results
Tools The penetration feature can be accessed by: •
On the Checks menu, click Penetration
•
On the Tool page, go to the penetration panel
The penetration panel allows you to check the integrity of your model, visualize problem areas, and importantly fix the problem areas. The three entities that can be checked are elements, components and groups. Typically the group check would be for checking contact definitions (for example, Abaqus/Ls-Dyna).
This panel allows you to check components for element penetration and intersection. More importantly, you can correct your model. Penetration and intersection can be used individually or collectively. Penetration is defined as the overlap of the material thickness of shell elements, while Intersection is defined as elements that actually pass completely through one another.
Example of Penetration
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Example of Intersection
Strategy Use the following guidelines for conducting checks on models: •
Checks can be ran on both 2-D and 3-D elements, 2-D elements only, or 3-D elements only.
•
The include self interference option includes components that bend and pass through itself when checked on; this occurs rarely and is expensive when running the check. By default, this option is off.
•
The intersections only option or intersections and penetrations option is available.
•
The ignore penetrations option caters to some specific solvers that do not allow zero depth penetrations when initializing. By default, the check will always use the component thickness.
•
An additional option, specify thickness, allows you to assign a global thickness to all components.
•
An additional option, multiply thickness, allows you to multiply the existing thicknesses in the model.
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When the penetration check is invoked, a new penetration tab is invoked in the browser area.
The results are displayed in a tree format for ease of display and are split into intersections and penetrations with the number of components that are clashing in brackets. In the example above, two components are intersecting and eleven components have material penetration. Expanding each tree will provide more detail as to which components have failed. The columns (ID, Elems, Depth, Comps) provide valuable information on which components IDs are involved, the number of failed elements, the depth of penetration (not applicable for intersections), and number of components affected in the penetration/intersection. Each of the columns can be sorted by clicking on the column header. At the bottom of the tab area there is a message bar, which will detail: the status of the check, the number of failed elements, and any warnings and errors as the checks are invoked.
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Clicking the right mouse button can also access all of the options and tools within the penetration check. The context menu will invoke.
The options button allows for the configuration of the display, automatic fixing, and depentration vector and configuration of the tree display. The fixing of penetrations and intersections falls into two categories: automatic and manual. For penetration the fixing routine is automatic, for the intersections the fixing is manual. These capabilities will be discussed in more detail in the tutorial.
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Exercise This exercise uses the model file, penetration_check.hm.
Step 1: Retrieve the model file, penetration_check.hm 1.
Launch HyperMesh 8.0.
2.
On the File menu, click Open.
3.
Browse to the file, penetration_check.hm.
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4.
On the Preferences menu, click User Profiles. Select LsDyna. This model is an Ls-DYNA model, therefore, it is important to chose the appropriate user profile so that HyperMesh can access the actual thickness values of the shell components. The thickness values are required for material penetration check.
5.
Click the Shaded Elements and Mesh Lines icon.
.
Step 2: Run the penetration check. 1.
Go to the penetration panel.
2.
To invoke the penet ration check, select all the components by clicking comps.
3.
Click comps again, click all, and click select.
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4.
Click check. Once the check has completed, the Penetration tab populates. In this example, there are two intersections and eleven penetrations. Expanding the tree the results will look like the following:
The tree is populated by a parent/child or master/slave relationship. As an example looking at the intersections, the top line shows the component, Rocker Fwd Top Panel RH (parent), and then below is component Rocker Inner Panel RH (child). It is important to understand that there is always a reciprocal relationship; the second entry is Rocker Inner Panel RH (parent) and then the component, Rocker Fwd Top Panel RH (child). In this case there is a one-to-one relationship. It is especially important to understand this when there is a one-to-many relationship (for example, Rocker Inner Panel RH under penetrations). Clicking on the parent component will always show that component plus all the components below (children). Clicking on a child component will show that component with the parent component only. Altair Engineering
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Step 3: Review the intersection results. 1.
Click the Intersections heading to view all the intersections. Based on which mode is chosen, certain components are displayed on the screen. Mode
Description Fit view to failed elements Displays all elements Display components with failed elements Display only failed elements
2.
Ensure that Display components with failed elements and Fit view to elements icons are selected.
3.
Under Intersections, click the component, Rocker Inner Panel RH. The screen will automatically fit to the failed intersecting elements.
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4.
Click the Review failed elements icon to review the other visualization modes. The contour and vector displays are only applicable to intersections. The intersecting elements display as follows:
Step 4: Fixing the intersection results. 1.
Under Intersections, click the component, Rocker Fwd Top Panel RH.
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2.
Click the Manual Fix Tools
icon to ensure that the intersecting entities can be fixed.
Additional buttons populate for intersection fixing.
3.
Ensure Elements from tree selection is selected – we will not pick any additional elements.
4.
Ensure Move in normal direction is selected for the direction of movement.
5.
Type 2 as the distance value.
6.
Click the left arrow button twice and notice the selected elements moving in the chosen direction. After the elements have been moved by a value of 4, they no longer intersect.
7.
Click recheck and notice there are no intersections. Only 11 penetrations remain. Important A dialog box displays that states: "Current results will be lost by rechecking the model. Would you like to continue?" Click Yes. The penetration tab needs to be refreshed.
Alternatively, you can use the automatic fixing tools: 1.
Load the file again, penetration_check.hm.
2.
Run the Check on all components.
3.
Highlight the Intersections directory in the penetration browser; notice that there are currently two intersections.
4.
Right -click to invoke the context-sensitive menu. Choose Automatic Intersection Fix – the wrenches will turn green indicating that the fix was successful.
5.
Run the Recheck – the intersections have been fixed.
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Step 5: Interrogating the penetration results. 1.
Expand the penetration tree.
2.
Click component, C-Pillar Bot Inner Panel RH.
The penetration results will look as follows:
3.
Click on the visualization options the penetration.
to view the different types of results display for
Remember that the columns can be sorted. For example, if you were only interested in the worst offending penetrations then sorting on the depth column will reorganize the tree structure (while still retaining the parent/child relationship). In this particular example, for component C-Pillar Bot Inner Panel RH there are 18 elements that have failed (parent and child), the maximum penetration depth is 0.159 and there is only one component penetrating.
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Step 6: Fixing the penetration results. Within the checking tool there is an automatic penetration fix that will remove the penetrations within the model. This works by physically moving the failed nodes to new locations to remove the material penetration. There are two options: automatic penetration fix or the automatic recursive penetration fix. Both will do the same thing, but the automatic option will take several passes, the iterative will do the fix in one go. The iterative option will take longer to complete. The user also has the option to either fix individual penetrations by clicking on a single parent branch of the tree, or the user can click and highlight the complete "Penetrations" tree and fix all the penetrations at once. In some circumstances there may be the need to lock or freeze a component that is sacred and cannot be adjusted or moved by the fixing tool. This can be achieved by clicking the right hand mouse and selecting "Lock Component". Once a component is locked a symbol will appear by the folder indicating that the component is locked.
In the example above component C-Pillar Bot Inner Panel RH was locked, notice how the lock symbol appears multiple times to correspond with the multiple references to the same component. To unlock, simply right click again and select "Unlock Component". For the purpose of this tutorial we will not be using the lock functionality. To fix the Penetrations in the model we will use the Iterative Fix: 1.
Click Penetrations at the top of the tree. See below.
2.
Right -click to bring up the menu and then click Automatic Recursive Penetration Fix. Important A dialog box displays that states: "Model changes to specific tree items are not possible once process is initiated. The Penetration tab will appear and disappear repeatedly during the process. Would you like to continue?" Click Yes. After the fixing has finished you will see that the penetrations have been fixed, there are now zero present.
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HyperWorks
Altair Engineering Contact Information Web site
www.altair.com
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Address: ftp.altair.com or ftp2.altair.com or http://ftp.altair.com/ftp Login: ftp Password:
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The following countries have distributors for Altair Engineering: Mexico, Romania, Russia, South Korea, Singapore, Spain, Taiwan and Turkey. See www.altair.com for complete contact information. © 2007 Altair Engineering, Inc. All rights reserved. No part of this publication may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated to another language without the written permission of Altair Engineering, Inc. To obtain this permission, write to the attention Altair Engineering legal department at: 1820 E. Big Beaver, Troy, Michigan, USA, or call +1-248-614-2400.
Trademark and Registered Trademark Acknowledgments ®
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Listed below are Altair HyperWorks applications. Copyright Altair Engineering Inc., All Rights Reserved for: ®
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HyperMesh 1990-2006; HyperView 1999-2006; OptiStruct 1996-2006; HyperStudy 1999-2006; ® ® ® HyperGraph 1995-2006; HyperGraph 3D 2005-2006; MotionView 1993-2006; MotionSolve 2002-2006; ® ® ® ® HyperForm 1998-2006; HyperXtrude 1999-2006; HyperOpt 1996-2006; HyperView Player 2001-2006; ® Process Manager™ 2003-2006; HyperWeb 2002-2004; Data Manager™ 2005-2006; Templex™ 19902006; Manufacturing Solutions ™ 2005-2006 All other trademarks and registered trademarks are the property of their respective owners.
HyperMesh 8.0 Tutorials Quality Checking and Editing Mesh - HM-3300 .......................................................................... 1 Measuring and Improving 2-D Quality using Quality Index - HM-3310................19 Penetration - HM-3320.......................................................................................................34
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Checking and Editing Mesh - HM-3300 In this tutorial, you will learn how to: •
Identify shell element connectivity problems
•
Correct shell element connectivity problems
•
Review the model’s shell elements to ensure connectivity problems were corrected
Re-mesh the elements along the rib
Tools The edges panel can be accessed: •
On the Checks menu, select Edges
•
On the Tool page, click edges
The edges panel allows you to find the free edges in a group of elements, find "T" or discontinuous connections in a group of elements (any edges connected to three or more elements), display duplicate nodes, and equivalence duplicate nodes. Free edges found in your model are displayed in red. You can use equivalence to remove the duplicate nodes, based on a tolerance which you specify. The preview equiv function is available to allow you to see which nodes are removed when the equivalence function is selected.
The normals panel can be accessed: •
Press the Shift + F10 key
•
On the Checks menu, select Normals
The normals panel allows you to display the normal of an element or surface, adjust the orientation of element normals, and reverse the normal of an element or surface. The normal of an element is determined by following the nodes of the element, in order, using the right-hand rule.
The check elems panel can be accessed: •
Press F10
•
On the Mesh menu, select Check Elements
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The check elems panels allow you to verify the basic quality of your elements and to verify the geometric qualities of those elements.
The automesh panel can be accessed: •
Press F12
•
On the Mesh menu, select AutoMesh
The automesh panel allows you to create meshes or re-mesh existing meshing interactively or automatically on surfaces or groups of elements. You can use the sub-panels to provide specific meshing parameters and manipulate surface edges and meshing fixed points (locations where the mesher is required to place a node).
Exercise This exercise uses the model file, cover.hm.
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Altair Engineering
Step 1: Retrieve and view the HyperMesh model file, cover.hm. Step 2: Review the model’s free edges to identify shell element connectivity problems. 1.
Go to the edges panel.
2.
With the comps selector active, select any element from the graphics area. The component containing the element is selected.
3.
Click find edges. Red, 1-D elements are displayed. They are organized into the new component named ^edges. A red 1-D element is created along each shell element edge that is free; one or more of the element edge’s nodes is not shared by the adjacent elements. Note:
For a component name whose first character is ^, the component and its contents is not written to the input file when the model is exported.
4.
On the View menu, click Utility Menu.
5.
Click the Shaded Elements and Mesh Lines icon
6.
Observe the red, 1-D elements (free edges).
7.
Try to identify gaps in the continuity of the mesh. Hint:
8.
Look closely at free edges interior to the model.
In the Model Browser, turn the display on and off for the component, shells, to continue to identify which red, free edges do not belong.
All red, free edges 9.
.
Red, free edges which belong
Turn on the display for the component, shells.
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Step 3: Correct the shell element connectivity problems using the edges panel. 1.
In the tolerance= field, type 0.01.
2.
Click preview equiv. The header bar displays the following message, "81 nodes were found". A sphere, is created on nodes having a distance between each other equal to or less than the specified tolerance.
3.
Notice that for this exercise’s model, a sphere is not created on every node along all of the red, free edges, which do not belong. A larger tolerance must be specified to identify the rest of the nodes.
4.
For tolerance =, increase its value until all 96 nodes are identified as shown in the image below. Be careful not to increase the tolerance value to too much. Although the 96 nodes will be identified, an excessively large tolerance value may collapse elements when the identified nodes are equivalenced.
The nodes identified with preview equivalence 5.
Click equivalence. The 96 coincident nodes are equivalenced.
6.
Rotate and observe the model to see that the mesh still looks as it should and no elements are collapsed.
7.
Click delete edges. The red, free edges and their component ^edges are deleted.
8.
Remain in the edges panel.
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Altair Engineering
Step 4: Review the model’s free edges again to confirm that all of the shell element connectivity problems have been corrected. 1.
Click find edges. Observe the red, 1-D elements (free edges). Are there any red, free edges that should not belong if the mesh were continuous or if all of the elements were connected? Hint:
2.
Only red, free edges should exist on the perimeter of the part.
Use the Model Browser, to turn the display off and on for the component shells to observe that all of the free, red edges belong.
Red, free edges which belong
Step 5: Display the element normals and adjust them to point in the same direction. 1.
Go to the normals panel.
2.
With the comps selector active, select one element from the graphics area. The element is highlighted briefly to indicate that the component to which it belongs is selected.
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3.
Click display normals. Arrows (vectors) are drawn from the element centroids and show the direction of the element normals. Notice the arrows do not all point from the same side of the part. For some analyses, the element normals should point from the same side.
4.
Click size = and type the size which the normal should be in model units and select display normals again. When size = is set to zero, the vector will be 10% of the screen.
5.
Toggle vector display normals to color display normals.
6.
Click display normals. The element normals are displayed using colors. The red side of the elements is the positive normal direction, while the blue side is the negative normal direction.
7.
Notice each side of the part shows red and blue.
8.
Click the orientation: elem selector to make it active.
9.
Select an element from the graphics area.
10. Click adjust normals. All elements on either side of the part are the same color, red or blue. The header bar displays the following message, "[X] elements have been adjusted." 11. Click return.
Step 6: Review the quality of the elements using the check elems panel. 1.
Go to the check elems panel.
2.
Go to the 2-d sub-panel.
3.
Verify that jacobian < field is set to 0.7.
4.
Click jacobian to determine if any elements have a jacobian of less than 0.7. Elements having a jacobian of less than 0.7 are highlighted.
5.
Notice that several elements on the triangular rib and around the smaller of the two holes have a jacobian of less than 0.7. The header bar displays a message indicating how many elements failed this check.
6.
In the graphics area, click on an element. A window displays that lists each quality check result for the element.
7.
Click any mouse button to close the pop-up window.
8.
On the right side of the panel menu, switch from standard to assign plot.
9.
Click jacobian to review again. A legend for jacobian values appears and each element is colored accordingly. The red elements have a jacobian less than the threshold, 0.7.
10. Verify that quads: min angle < is set to 45. 11. Click min angle to determine if any quad elements have an angle of less than 45.
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12. Notice that a couple of elements on the rib have an angle of less than 45. 13. Verify that the max angle >field is set to 135. 14. Click max angle to determine if any quad elements have an angle greater than 135. 15. Notice that several elements on the rib have an angle greater than 135. 16. Click return.
Step 7: Re-mesh the elements on the rib using the automesh panel. 1.
Go to the automesh panel.
2.
Ensure that you are in the size and bias sub-panel.
3.
Switch the entity selector to elems.
4.
Toggle to interactive.
5.
For element size=, type 3.5.
6.
Select one rib element from the graphics area.
7.
Select one element on the plane of elements perpendicular to the rib and in the same plane as the rib’s shortest edge as shown in the image below.
Example of elements to select
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8.
Select elems >> by face to complete the selection of elements as shown below.
Elements selected using by face 9.
Click mesh. The meshing module appears.
10. In the density sub-panel, change the element density on the rib’s hypotenuse edge to 9. 11. Change the element density on the rib’s shortest edge to 5.
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12. Keep all other element edge densities the same.
Adjusting element edge densities 13. Go to the mesh style sub-panel. 14. Under mesh method, set the last option to free (unmapped). 15. Under mesh method, select set all. 16. Click mesh to preview the mesh. 17. Go to the checks sub-panel, and check the jacobian, quads: min angle, and quads: max angle. 18. Notice that no elements fail the minimum and maximum angle checks. Only a couple of elements have a jacobian of less than 0.7. The smallest jacobian is 0.68, which can still be considered good quality. 19. Click return to accept the mes h and go back to the main menu.
Step 8: Remove the tria elements from the rectangular plane of re-meshed elements by first deleting the row of elements containing the trias. 1.
On the Tool page go to the delete panel.
2.
Ensure that elems is the active selector.
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3.
Select the elements as shown in the image below.
4.
Click delete entity.
5.
Click return.
Elements to delete
Step 9: Stitch the gap that resulted from deleting the row of elements using the replace panel. 1.
On the 2D page, enter the replace panel.
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2.
With the replace: node selector active, select node A as indicated in the image below.
3.
With the with: node selector active, select node B as indicated in the image below. Node A is replaced with node B.
Select nodes A and B
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4.
Repeat #2 and #3 for the other nodes along the gap. The resulting mesh should look like the mesh in the image below.
The mesh after replacing nodes on the bottom face 5.
Click return.
Step 10: Use the smooth panel to adjust the node placement on the rectangular plane of re-meshed elements. 1.
On the 2D page, enter the smooth panel.
2.
Go to the plates sub-panel.
3.
With the smooth: elems selector active, select an element on the rectangular plane of remeshed elements.
4.
Select elems >> by face.
5.
For iterations = specify 10.
6.
Switch the smoothing algorithm from autodecide to shape corrected.
7.
Click smooth.
8.
Click return.
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Step 11: Remove tria elements from another area of the model using the edit element panel, split and combine sub-panels. 1.
On the 2D page, enter the edit element panel.
2.
Go to the split sub-panel.
3.
With the splitting line: points selector active, click on four screen points as shown the image below. Temporary line segments are drawn to connect the points.
4.
You can right click to undo the last line segment drawn or you can click delete line to start over with selecting points.
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5.
Click split. Elements that have the line pass through them are split. The resulting mesh should look like the mesh below. There are two pairs of adjacent tria elements.
6.
Go to the combine sub-panel.
7.
Select two adjacent tria elements as indicated in the image below.
8.
Click combine.
9.
Repeat # 6 and # 7 for the other two adjacent tria elements.
10. Remain in the Edit Element sub-panel.
Trias to select
Combining trias into quads
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Step 12: Dynamically move nodes on the mesh area modified in the last step to improve element quality. 1.
Go to the cleanup sub-panel.
2.
Click cleanup. The element cleanup menu appears. It allows you to select various combinations of quality checks, specify a warning/unacceptable range for each check, and dynamically move nodes around to place them where you desire. Elements are colored as follows: •
No color; appear blank: element passes quality checks
•
Yellow: one or more quality check results falls into warning/unacceptable range
•
Red: one or more quality check results are beyond unacceptable
Among the group of elements you modified in the last step, Step 11, two quad elements are red and one quad element is yellow. 3.
Clear the warpage and jacobian check boxes.
4.
With the node selector active, click on an interior node of a red element and drag the node around until the element is no longer red.
5.
Repeat # 4 for the other red element.
6.
Click return.
Step 13: For the same area of elements you focused on in the last step, optimize element quality by simply clicking on nodes and elements. 1.
On the 2D page, go to the qualityindex panel.
2.
On the panel menu’s right side, switch view to optimize.
3.
With the node optimize selector active, click on a few nodes of the mesh area you modified. When a node is clicked on, it is reposition so that the elements attached to it have the best possible quality based on the criteria specified in the qualityindex panel.
4.
Click on the selector element optimize to make it active.
5.
Click on yellow and red elements in the same mesh area. When an element is clicked on, it is adjusted to have the best quality possible based on the criteria specified in the qualityindex panel. When you click on a red element, it may become yellow or black (no color assigned). When you click on a yellow element, it may become black.
6.
Click return.
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Step 14: Add a ring of radial elements around the smaller of the two holes. 1.
Click the Utility tab.
2.
On the Geom/Mesh page, click Add Washer.
3.
With the nodes selector active, select one node on the edge of the smallest hole as indicated in the image below.
Example node to select
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4.
Click proceed. A pop-up window appears as shown in the image below.
Add Washer macro dialog 5.
Toggle to Width, and specify 3.
6.
Select the Minimum number of nodes around the hole check box.
7.
In the Density: field, enter 12.
8.
Click Add.
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9.
Click Close. The mesh around the hole should look like the mesh in the image below.
Resulting mesh around the smallest hole
Step 15 (Optional): Save your work. With this exercise completed, you can save the model if desired.
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Measuring and Improving 2-D Quality using Quality Index - HM-3310 In this tutorial, you will learn how to measure and improve the quality of the mesh and how to eliminate manually fixing problem elements. The qualityindex panel is used to evaluate the quality of the mesh as well as improve local areas, while the smooth panel is used to achieve larger scale improvements to the mesh quality based on the quality index. The elem cleanup panel gives you an opportunity to clean up parts of the mesh in a more automated fashion. For example, you may have legacy models or a file from an external source that does not conform to current criteria. Checking mesh quality and correcting the mesh is an integral part of the meshing process. While the check elems panel in HyperMesh provides the tools to check a mesh against a user-defined value for a given quality criterion, it does not provide an overall measure of the quality of a mesh. This can be achieved in the qualityindex panel where the quality of a mesh can be gauged by a single number: the quality index (QI). HyperMesh functions based on the quality index offer more automated solutions for improving the quality of a mesh and helps eliminate the tedious task of correcting many elements by hand.
Tools - Quality Index The qualityindex and elem cleanup panel will be used in this tutorial. The qualityindex panel can be accessed by one of two methods: •
On the Checks menu, click Quality Index
•
On the 2D page, click the qualityindex panel
The qualityindex panel allows you to set quality criteria and evaluate your mesh against these quality criteria using a single number: the compound quality index (comp. QI) value. It also allows you to edit and optimize node and edge locations, improving the quality of your mesh by reducing the compound QI value. The compound quality index is a function of twelve quality criteria (organized in three pages) that are set in the panel, as well as the weight factors (comp wt) and penalty values associated with them (see figure below). Each criterion has five rating levels (ideal, good, warn, fail, and worst) and as the quality decreases, the penalty value increases. Therefore, the smaller the quality index value, the better the overall mesh quality for the criteria you set. The weight factor is a multiplier that can be used to bias the results and assigns more importance to some checks than others.
Criteria table In this panel, several QI values are computed: one for each element (not reported), one for each criterion turned on, and the compound QI value that represents the overall quality of the 2D elements displayed. Refer to the on-line help for the formulas used to compute these quantities. The compound quality index is the summation of all the element quality indexes, and also the summation of all the criteria quality indexes.
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To facilitate visual review of their quality, elements are displayed in the graphics region based on their individual element QI value, which is also based on selected criteria and their corresponding weight factors and penalty values. With the default colors, elements with a QI value over 10 are in the worst category and displayed in red. Elements with a QI value between 1 and 10 are in the fail category and displayed in yellow. Elements with a QI value between 0.8 and 1 are displayed in cyan and fall in the warn category, and elements with a QI value less than 0.8 are displayed in the background color (black) and considered good or ideal. Note
A quality index value is a relative value that is completely dependent on the quality criteria you use. The lower the quality index, the closer your mesh is to the quality criteria you defined.
The qualityindex panel the following capabilities: The Criteria Setup includes: -
Turn criteria on and off.
-
Set good and fail values for each criterion.
-
Set criteria weight factors.
-
Choose display colors for each rating level.
-
Load and save criteria files.
-
Save a summary file of the results.
The Report Status includes: -
The percentage of elements that failed a given check.
-
The worst value found for the check.
-
The criterion Q.I. value.
-
The number of quads and trias.
-
The percentage of trias.
-
The total number of elements that failed.
-
The compound Q.I. value.
-
The editing options such as: place node and swap edge are available, as well as, the optimization functions: node optimize and element optimize
Additional options are available to fix the mesh. While the view setting does not provide any additional options, both the edit and optimize settings provide additional options for editing the mesh and improving its quality. These options will be discussed later in the tutorial. In this section, some of the concepts that govern the qualityindex panel were introduced. For complete details on this panel, refer to the Panels section of the on-line help, or click help while in a panel to display its context-sensitive help.
Tools - Element Cleanup The elem cleanup panel can be accessed by one of two methods: •
On the Mesh menu, click Auto Element Cleanup
•
On the 2D page, click the elem cleanup panel
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The elem cleanup panel allows you to amend and readjust the mesh to your criteria.
Strategy The list below provides best tips and practices:
•
Use the QI functionality on local models, not large structures with multiple parts
•
Use the qualityindex panel to check the quality of the mesh
•
Use the elem cleanup panel to amend and readjust the mesh
Exercise This exercise uses the model file, quality_index.hm. The model is of a bracket with various features such as holes and fillets. The bracket is meshed with a mixed mesh of tria and quad elements. You will evaluate the quality of this mesh based on its quality index and make any necessary improvements.
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Step 1: Retrieve the model file, quality_index.hm. 1.
On the File menu, click Open.
2.
In the Open File… window, browse to the file’s location and click Open.
3.
Click the Shaded Elements and Mesh Lines icon
.
Step 2: Evaluate the quality of the mesh. 1.
Go to the qualityindex panel. Note:
2.
By default, elements are color-coded based on the values currently defined for the quality criteria, the weight factors and the penalty values. These are used to compute individual element QI values.
Go to page 3 in the QI panel and click edit criteria to load the criteria file quality_index.criteria from the
Color-coded elements (white background) 22 HyperMesh 8.0 Tutorials – Quality Proprietary Information of Altair Engineering
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3.
Review the quality criteria defined on pg1, pg2, and pg3. Pay close attention to the criteria that can be turned on and off, and the actual values assigned to them for the various threshold levels. The weighting factors can be adjusted for each criteria by accessing the edit criteria button on pg3 and toggling the Advanced Criteria Table checkbox. Several elements are displayed in yellow, meaning that their element QI values are between 1 and 10. The element QI value is computed as: (weighted average of penalties that pass) + (weighted sum of penalties that fail) Considering that all the weight factors are currently set to 1, it can be interpreted that these elements failed at least one of the checks currently turned on (fail rating). Hint:
To determine which quality check a specific element fails (fail or worst category) turn on each criterion separately (one at a time).
Note:
Elements are color-coded based on their QI values. The color-coding does not necessarily capture the outcome for each specific quality check, but it shows how elements fare against the entire set of criteria that are selected. In the end, elements displayed in red and yellow are elements for which the overall quality (defined by the criteria turned on) does not meet the requirements. Elements displayed in cyan are simply acceptable.
The fail value column lists the fail values set in the default panel for easy reference. The %fail column lists the percentage of element displayed that failed the given criteria, and the worst column lists the worst value found for the corresponding criteria. You can also review criteria QI values as they are listed in the Q.I. column, which can be accessed by the toggle switch. In this case, you will notice that the warpage quality check is the biggest contributor to the compound quality index. Maximum size has the smallest contribution, and would not warrant much attention when trying to decrease the compound quality index for a mesh. 4.
Write down the values for comp.Q.I. and # of failed =. Although these values are relative, they indicate how the mesh does against the set criteria. As you improve the quality of the mesh later in this tutorial, both numbers will decrease. In this section, you used the qualityindex panel to review the quality of the mesh based on quality criteria you set when loading the criteria file.
Step 3: Save and review criteria files. Various finite element applications call for different quality criteria and often, various meshed parts in the same model must meet different criteria. In such situations, the values assigned to the various quality criteria need to be changed in the qualityindex panel to match the new requirements for each mesh. While this can be done manually each time, HyperMesh allows you to limit this editing to a one-time operation by saving values set for the various quality checks in the qualityindex panel to a text file. The criteria file you used earlier in this tutorial has been prepared in a similar manner. In this section, change the values for some of the criteria in the qualityindex panel and save the quality criteria to a new file, starting your own library of criteria files. With a pre-defined set of criteria files you can then easily load the various criteria files for different applications.
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1.
In the qualityindex panel, go to pg3 and click edit criteria. The criteria file editor opens in a new window. This editor displays all of the element quality criteria with the values defined for each one, and allows you to change those values.
2.
Update the quality criteria listed to the values specified in the table below: Criterion:
Good value:
Fail value:
min length
5.5
3.5
max angle quad
120
140
min angle quad
60
40
After you modify the criteria, click "apply"; notice how elements in the model change color based on the new criteria. Note:
The element size elem size value used in the min size and max length checks is the target element size set in the global panel. This value can also be set by loading a criteria file. Alternatively, concentrate only on fail values if Advance Criteria Table if off. For example, worst cannot be greater than fail if looking at min size.
Warning:
When modifying criteria values, HyperMesh may reject some of the values you insert as there needs to be a logical progression in values. For example, the fail value for the min size check cannot be larger than the good value, so before increasing this fail value, you may need to first increase the good value.
3.
Select save as… from the criteria file editor’s file menu, and save the criteria file as quality_index_2.criteria to your working directory.
4.
Click the OK button in the criteria file editor to apply changes and close the editor.
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5.
Check the display summary legend checkbox to create a summary file. Next, click the browse… button to select a location to save the summary file. Once saved, you can view the summary file by clicking the summary button in the panel.
6.
Go to pg1 to review the comp.Q.I. = and # of failed = values and compare them to the values found for the criteria file loaded earlier. Both values have changed. The criterion on the minimum element size was tightened, while those on the minimum and maximum quad angles were loosened. The result is a slight decrease in the compound quality index value and a change in the number, and probably the actual elements, that fail our criteria.
In this section you experimented with changing values for the criteria in the quality Index panel. You reviewed how these changes affected the results for the mesh and the color-coding of elements, and exported a criteria file for the new criteria.
Step 4: Improve element quality using the edit functions. The edit tools (place nodes and swap edges panels) in the qualityindex panel, allows you to improve the quality of elements by letting you move nodes interactively and swap element edges. The place node function allows you move nodes manually on their surface while the color-coding of the elements sharing the node (indicating changes to their quality) is updated in real time. The swap edge function lets you swap the common edge between two elements to use different nodes, creating a new configuration that is automatically evaluated against the quality criteria and color-coding. In this section, experiment with both functions to improve some of the elements failing the quality criteria defined in the quality_index.criteria file. 1.
Load the criteria file quality_index.criteria from the
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2.
Press V on the keyboard and click restore1 for View1.
3.
Use the place node function to drag the nodes shown in the figure below such that all the elements that share them fall in the good range.
Nodes to move Observe how the compound quality index value and the number of elements that fail both decrease as you fix this area of the mesh. The final mesh in this area should look similar to this:
Improved mesh 26 HyperMesh 8.0 Tutorials – Quality Proprietary Information of Altair Engineering
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As you drag nodes, observe how the values for the results listed in the last columns of the results mode temporarily change to report the local effect of moving the nodes. The comp.Q.I. shows the compound quality index for these elements affected by the node being dragged (this helps in finding an optimal position); # of trias shows how many trias fail the criteria, and # of failed tells you how many of the elements involved in the current operation still fail the quality criteria. Note:
The place node function lets you move the node only on an inferred surface and not beyond its edges. Use the undo function at any time to undo the changes you have made to the mesh.
4.
Press V to restore View2.
5.
Use the swap edge function to improve the quality of some of the elements in this area (see figure below).
Edge to swap The common edge is changed (connectivity change) and produces two new elements from the nodes involved.
New mesh after edge swapping Altair Engineering
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Hint:
6.
When using the swap edge function, the edge selected is re-positioned in the next possible way between the two elements. A single pick on the edge may or may not improve the quality, or produce the best improvement. Pick the edge again if the quality deteriorates. HyperMesh repositions the edge in all possible ways between the two elements in a cyclic process.
Use the swap edge function again between the pair of elements produced and cycle through all the pairs of elements possible by working with this common edge to select the one configuration that yields the lowest compound quality index. The configuration described in the figure above produces the lowest QI value.
7.
Use any combination of the place node and swap edge functions to ensure that all the elements in this area satisfy the quality criteria (see figure below for an example).
Improved area In this section, you used the edit tools and its various functions to manually and interactively improve one local area of the mesh. As you placed nodes and swap edges, you also monitored changes to the compound quality index to measure how this number decreases as the quality of the elements improves.
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Step 5: Improve element quality using the optimize feature. The optimize tool (node element) offers semi-automatic quality correction functions. The node optimize function finds the optimum position for the node you select so that the quality index for the elements sharing this node is lowest. With the element optimize function the same goal is sought; although HyperMesh works with all the nodes involved in this element at the same time, affecting a larger area. In this section, experiment with both functions from the optimize tool to improve the quality of the mesh in some local areas. You can monitor how changes are bringing the quality indexes down and improve the quality of the mesh. 1.
Press V to restore view3.
Elements to optimize 2.
Use the element optimize function to improve the quality of the elements in this area. Observe changes to the compound quality index value as you use this function. Note:
You may need to select multiple elements (not just the failing elements) multiple times to obtain the best possible quality as each operation only considers the element you select and the elements with which it shares nodes.
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The final mesh should look similar to this:
Improved mesh 3.
Press V to restore view4.
Nodes to optimize 30 HyperMesh 8.0 Tutorials – Quality Proprietary Information of Altair Engineering
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4.
Use the nodes optimize function to improve the quality of the elements failing the checks. Observe changes to the quality index value as you optimize the location of various nodes. You should finish with a mesh similar to this:
Resulting mesh 5.
Correct any remaining bad elements by using one of the previously mentioned functions such as element optimize.
Final element after using element optimize Altair Engineering
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6.
Write down the values for comp.Q.I. = and # of failed = and compare these values to those with which you started. By now, these values have gone down, although they have decreased by only a certain percentage of the initial values. This is because there are still many other areas of our mesh that need attention.
Areas still requiring attention In this section, you experimented with the various tools available in the qualityindex panel for improving the quality of elements to ensure they meet quality requirements. While these tools are very powerful in improving the quality of a mesh, it may not always be practical to try to fix numerous elements in a model with this approach as only a few elements can be fixed at a time. These tools are more useful for local than global areas.
Step 6: Improve element quality using the smooth panel. The smooth panel from the 2D page can be used to smooth elements according to quality criteria. In this mode, it optimizes node locations so that the overall quality index of the elements selected is minimal. This allows you to work with large numbers of elements at one time.
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In this section, use the QI optimization mode of the smooth panel to improve the quality of the elements. Then go back to the qualityindex panel to review the quality of the resulting mesh. 1.
Use the smooth panel, QI optimization mode to optimize the elements based on the criteria defined in the qualityindex panel. -
From the 2D page, select the smooth panel.
-
Go to the plates sub-panel.
-
Use the switch to select the QI optimization mode.
-
Click elems and select displayed.
-
Set target quality index = to 0.2.
-
Ensure the time limit check box is cleared. Optimization time is not a concern with this small model.
-
Set the feature angle = to 30.0.
-
Set the toggle to use current criteria. Or, a criteria file can be specified.
-
Leave the lower toggle set to recursive optimization procedure.
-
Click smooth.
-
If a message displays, click Ignore.
HyperMesh smoothes the elements according to the specified quality criteria and returns the final quality index value in the header bar. Note: 2.
Refer to the on-line help for a complete description of all the options available in this panel.
Go to the qualityindex panel to review the quality of the mesh. The number of elements failing the quality criteria has been reduced to only a few.
3.
Compare the current values for the compound quality index and the number of elements that failed to the initial ones.
4.
Go to pg1 and use node optimize and the tools to fix any element that is still failing the quality criteria. While the smooth panel optimizes node locations so that the elements would yield the lowest compound quality index value, you still have the ability to work on local areas where only the local quality index is considered and will therefore often yield a different result.
5.
Use pg3 to save a summary file of the results to your working directory.
6.
Load this summary file into any text editor and review the information it contains.
Summary In this tutorial, you learned how to: •
Evaluate the quality of 2-D elements using quality indexes
•
Correct elements that fail the quality criteria
•
Use the smooth panel to address numerous elements needing improvement
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Penetration - HM-3320 In this tutorial, you will learn how to: •
Run the penetration check
•
Review the intersection results
•
Fix the intersection results
•
Interrogate the penetration results
•
Fix the penetration results
Tools The penetration feature can be accessed by: •
On the Checks menu, click Penetration
•
On the Tool page, go to the penetration panel
The penetration panel allows you to check the integrity of your model, visualize problem areas, and importantly fix the problem areas. The three entities that can be checked are elements, components and groups. Typically the group check would be for checking contact definitions (for example, Abaqus/Ls-Dyna).
This panel allows you to check components for element penetration and intersection. More importantly, you can correct your model. Penetration and intersection can be used individually or collectively. Penetration is defined as the overlap of the material thickness of shell elements, while Intersection is defined as elements that actually pass completely through one another.
Example of Penetration
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Example of Intersection
Strategy Use the following guidelines for conducting checks on models: •
Checks can be ran on both 2-D and 3-D elements, 2-D elements only, or 3-D elements only.
•
The include self interference option includes components that bend and pass through itself when checked on; this occurs rarely and is expensive when running the check. By default, this option is off.
•
The intersections only option or intersections and penetrations option is available.
•
The ignore penetrations option caters to some specific solvers that do not allow zero depth penetrations when initializing. By default, the check will always use the component thickness.
•
An additional option, specify thickness, allows you to assign a global thickness to all components.
•
An additional option, multiply thickness, allows you to multiply the existing thicknesses in the model.
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When the penetration check is invoked, a new penetration tab is invoked in the browser area.
The results are displayed in a tree format for ease of display and are split into intersections and penetrations with the number of components that are clashing in brackets. In the example above, two components are intersecting and eleven components have material penetration. Expanding each tree will provide more detail as to which components have failed. The columns (ID, Elems, Depth, Comps) provide valuable information on which components IDs are involved, the number of failed elements, the depth of penetration (not applicable for intersections), and number of components affected in the penetration/intersection. Each of the columns can be sorted by clicking on the column header. At the bottom of the tab area there is a message bar, which will detail: the status of the check, the number of failed elements, and any warnings and errors as the checks are invoked.
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Clicking the right mouse button can also access all of the options and tools within the penetration check. The context menu will invoke.
The options button allows for the configuration of the display, automatic fixing, and depentration vector and configuration of the tree display. The fixing of penetrations and intersections falls into two categories: automatic and manual. For penetration the fixing routine is automatic, for the intersections the fixing is manual. These capabilities will be discussed in more detail in the tutorial.
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Exercise This exercise uses the model file, penetration_check.hm.
Step 1: Retrieve the model file, penetration_check.hm 1.
Launch HyperMesh 8.0.
2.
On the File menu, click Open.
3.
Browse to the file, penetration_check.hm.
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4.
On the Preferences menu, click User Profiles. Select LsDyna. This model is an Ls-DYNA model, therefore, it is important to chose the appropriate user profile so that HyperMesh can access the actual thickness values of the shell components. The thickness values are required for material penetration check.
5.
Click the Shaded Elements and Mesh Lines icon.
.
Step 2: Run the penetration check. 1.
Go to the penetration panel.
2.
To invoke the penet ration check, select all the components by clicking comps.
3.
Click comps again, click all, and click select.
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4.
Click check. Once the check has completed, the Penetration tab populates. In this example, there are two intersections and eleven penetrations. Expanding the tree the results will look like the following:
The tree is populated by a parent/child or master/slave relationship. As an example looking at the intersections, the top line shows the component, Rocker Fwd Top Panel RH (parent), and then below is component Rocker Inner Panel RH (child). It is important to understand that there is always a reciprocal relationship; the second entry is Rocker Inner Panel RH (parent) and then the component, Rocker Fwd Top Panel RH (child). In this case there is a one-to-one relationship. It is especially important to understand this when there is a one-to-many relationship (for example, Rocker Inner Panel RH under penetrations). Clicking on the parent component will always show that component plus all the components below (children). Clicking on a child component will show that component with the parent component only. Altair Engineering
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Step 3: Review the intersection results. 1.
Click the Intersections heading to view all the intersections. Based on which mode is chosen, certain components are displayed on the screen. Mode
Description Fit view to failed elements Displays all elements Display components with failed elements Display only failed elements
2.
Ensure that Display components with failed elements and Fit view to elements icons are selected.
3.
Under Intersections, click the component, Rocker Inner Panel RH. The screen will automatically fit to the failed intersecting elements.
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4.
Click the Review failed elements icon to review the other visualization modes. The contour and vector displays are only applicable to intersections. The intersecting elements display as follows:
Step 4: Fixing the intersection results. 1.
Under Intersections, click the component, Rocker Fwd Top Panel RH.
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2.
Click the Manual Fix Tools
icon to ensure that the intersecting entities can be fixed.
Additional buttons populate for intersection fixing.
3.
Ensure Elements from tree selection is selected – we will not pick any additional elements.
4.
Ensure Move in normal direction is selected for the direction of movement.
5.
Type 2 as the distance value.
6.
Click the left arrow button twice and notice the selected elements moving in the chosen direction. After the elements have been moved by a value of 4, they no longer intersect.
7.
Click recheck and notice there are no intersections. Only 11 penetrations remain. Important A dialog box displays that states: "Current results will be lost by rechecking the model. Would you like to continue?" Click Yes. The penetration tab needs to be refreshed.
Alternatively, you can use the automatic fixing tools: 1.
Load the file again, penetration_check.hm.
2.
Run the Check on all components.
3.
Highlight the Intersections directory in the penetration browser; notice that there are currently two intersections.
4.
Right -click to invoke the context-sensitive menu. Choose Automatic Intersection Fix – the wrenches will turn green indicating that the fix was successful.
5.
Run the Recheck – the intersections have been fixed.
44 HyperMesh 8.0 Tutorials – Quality Proprietary Information of Altair Engineering
Altair Engineering
Step 5: Interrogating the penetration results. 1.
Expand the penetration tree.
2.
Click component, C-Pillar Bot Inner Panel RH.
The penetration results will look as follows:
3.
Click on the visualization options the penetration.
to view the different types of results display for
Remember that the columns can be sorted. For example, if you were only interested in the worst offending penetrations then sorting on the depth column will reorganize the tree structure (while still retaining the parent/child relationship). In this particular example, for component C-Pillar Bot Inner Panel RH there are 18 elements that have failed (parent and child), the maximum penetration depth is 0.159 and there is only one component penetrating.
Altair Engineering
HyperMesh 8.0 Tutorials – Quality 45 Proprietary Information of Altair Engineering
Step 6: Fixing the penetration results. Within the checking tool there is an automatic penetration fix that will remove the penetrations within the model. This works by physically moving the failed nodes to new locations to remove the material penetration. There are two options: automatic penetration fix or the automatic recursive penetration fix. Both will do the same thing, but the automatic option will take several passes, the iterative will do the fix in one go. The iterative option will take longer to complete. The user also has the option to either fix individual penetrations by clicking on a single parent branch of the tree, or the user can click and highlight the complete "Penetrations" tree and fix all the penetrations at once. In some circumstances there may be the need to lock or freeze a component that is sacred and cannot be adjusted or moved by the fixing tool. This can be achieved by clicking the right hand mouse and selecting "Lock Component". Once a component is locked a symbol will appear by the folder indicating that the component is locked.
In the example above component C-Pillar Bot Inner Panel RH was locked, notice how the lock symbol appears multiple times to correspond with the multiple references to the same component. To unlock, simply right click again and select "Unlock Component". For the purpose of this tutorial we will not be using the lock functionality. To fix the Penetrations in the model we will use the Iterative Fix: 1.
Click Penetrations at the top of the tree. See below.
2.
Right -click to bring up the menu and then click Automatic Recursive Penetration Fix. Important A dialog box displays that states: "Model changes to specific tree items are not possible once process is initiated. The Penetration tab will appear and disappear repeatedly during the process. Would you like to continue?" Click Yes. After the fixing has finished you will see that the penetrations have been fixed, there are now zero present.
46 HyperMesh 8.0 Tutorials – Quality Proprietary Information of Altair Engineering
Altair Engineering
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