Checking Element QualityI-DEAS Tutorials: Fundamental Skills
This tutorial covers techniques for checking elementquality, which may affect analysis accuracy.
Learn how to:
• calculate distortion and stretch• display distorted elements• fix distorted elements• use Auto Settings when meshing• graph quality statistics
2
Before you begin...
Prerequisite tutorials:
• Getting Started (I-DEAS Multimedia Training)
–or–
Quick Tips to Using I-DEAS–and–Creating Parts
• Introduction to Simulation• Managing Parts in Model Files• Free Meshing• Boundary Condition Sets• Displaying Results
3
Setup 1 of 4
If you didn’t start I-DEAS with a new (empty) model file,open a new one now and give it a unique name.
FileOpen
Open Model File form
Model File name: any unique name
OK
Make sure you’re in the following application and task:
Simulation
Master ModelerSet your units to mm.
OptionsUnits
mm (milli newton)
What: Sketch the shape to the dimensions shown.
Hint
1
Why: The dimensions of this part and the meshingparameters used later will result in distorted elements.
4
Setup 2 of 4
What: Extrude 50mm and name the part.
Hint
XXX
What: Create an FE model associated with the part.
Hint
Meshing
5
Setup 3 of 4
What: Turn off curvature-based refinement for allsurfaces.
Why: Surface attributes such as curvature refinementmust be defined on individual surfaces, not on thevolume definition.
Hint
All
Free Options...Curvature Based Length
None
What: Mesh the volume with 15mm elements.
Hint
Element Length: 15
Continued on next page...
6
Setup 4 of 4
Modify Mesh Preview form
Keep Mesh
Save your model file. File
Save
Warning! If you are prompted by I-DEAS to save your model file,respond:
NoSave only when the tutorial instructions tell you to––notwhen I-DEAS prompts for a save.
Why:If you make a mistake at any time between saves andcan’t recover, you can reopen your model file to the lastsave and start over from that point.
Hint To reopen your model file to the previous save, pressControl-Z.
7
Calculate distortion and stretch 1 of 3
Distorted elements may affect the accuracy of ananalysis. The seriousness of the effect depends on manyfactors, such as:
• the analysis type• the loading• where the distorted elements are located in the
model
There are several element quality checks you can make.In this section, you’ll learn how to make these checksand how to improve the model.
8
Calculate distortion and stretch 2 of 3
What: Calculate the distortion and stretch of theelements, listing the elements below selected thresholdvalues.
How:
All
Element Quality Checks form
Distortion
.8
Stretch
.4
(to generate report in I-DEAS ListWindow)
Dismiss
Check I-DEAS List . Examine the distortion and stretch values.
9
Calculate distortion and stretch 3 of 3
Things to notice Notice that the model appears unchanged, but that thereis information in the I-DEAS List window.
Values are normally between 0.0 and 1.0; withdistortion/stretch being worse as the value approacheszero. Severe distortion can even give negative values. Inthis mesh, with single elements around theninety-degree radius, you’ll have some severely distortedelements.
Notice, too, that the elements listed are stored in a groupcalled “output.”
10
Display distorted elements 1 of 7
What: Display the most distorted elements to see wherethey’re located.
How:
Use Group
Output
Things to notice Your mesh elements may not exactly match theelements shown above.
When you calculated the distortion values, the programautomatically created a group of elements resulting fromthe output of the calculation.
11
Display distorted elements 2 of 7
What: Create a group containing the part edges.
Why: To see where these elements are in the part, it willhelp to display them with the part edges.
How:
Filter
Selection Filter form
Edge...
Pick Only
All
name: Distorted Elements
12
Display distorted elements 3 of 7
What: Add the distorted elements to the group.
How:
Use Group
Output
What: Display the current group.
Using groups to display selected entities is a usefultechnique.
What: Display everything.
Close
13
Display distorted elements 4 of 7
A useful technique is to display a shaded contour plot ofthe distorted elements. It shows the location and thevalue of distortion.
What: Create result sets containing distortion andstretch values.
How:
Post Processing
Distortion
Distortion Values
(accept defaults for all 5 id lines)
Stretch
Stretch Values
(accept all defaults)
Why: With the distortion and stretch values stored inresult sets, they can be displayed the same way asstress results.
14
Display distorted elements 5 of 7
What: Display the distortion and stress results.
Hint
Distortion Values
Display Results
Deformation Results: Clear
Stretch Values
Display Results
15
Display distorted elements 6 of 7
Remember Lower values of distortion and stretch areworse, shown as blue, not red as with stresses.
Things to notice Distortion tends to be worse in the area of the curvedfillet. Stretch tends to be worse in the area of the thinside wall.
You may define the color bar using model unitsinstead of percent of range to read distortion andstretch values directly off the color bar. To interpretactual values, you should display non-averagedvalues.
What: Display the distortion results on only the previousstored group of elements.
Why: Although distortion and stretch result sets containvalues for every element, it helps to see distortedelements inside the model by only displaying the valueson the group previously identified as the worst elements.
How:
Use Group
Distorted Elements
16
Display distorted elements 7 of 7
Result
Warning! Delete the result sets so you’ll be able tochange the mesh in the next step.
How:
All
Things to notice The I-DEAS List window indicates that the results sethas been deleted.
17
Fix distorted elements 1 of 1
What: Try to fix any elements with a distortion value lessthan the value set with Auto Settings.
How:
Meshing
Automatic Mesh Checking form
Improve distortion to: 0.5
OK
Check I-DEAS List . Look at the output from the Tetra Fix command. Ifany elements were found with distortion below thisvalue, the program will attempt to fix them.
Two other commands to repair distorted tetrahedralelements are Straighten Edges and MoveMid–Nodes. Both move mid-side nodes to improvedistorted elements, since distortion of tetrahedralelements is sensitive to the mid-node position.
18
Use Auto Settings when meshing 1 of 1
What: Generate the mesh again using automatic meshchecking and improvement options to fix the distortionduring the meshing process.
Hint
Improve stretch to: 0.3
Improve distortion to: 0.5
Hint
Things to notice If you calculate distortion values now, you’ll see that theelement quality is better.
Warning! The mesh improvement settings apply only to tetrahedralsolid elements, not to other element types.
19
Graph quality statistics 1 of 2
What: Generate a statistical graph of element distortion.
How:
All
Element Quality Statistics form
Generate statistics for: Distortion
(to update the display, if needed)
Things to notice Statistical values for distortion in all the elements aretabulated and graphed, which gives a picture of theoverall quality of the model. Most of the elements havevery little distortion.
20
Graph quality statistics 2 of 2
What: Generate a statistical graph of element stretch.
Hint
Generate statistics for: Stretch
What: Change the display to a cumulative Y-Axis graph.
Hint
Cumulative
Dismiss
These statistical quality functions are also availableusing Modify Mesh Preview and Quality Checks.
21
Tutorial wrap-up
You have completed the Checking Element Qualitytutorial.
You can delete the FE models and the part, or put themaway. Neither are used in any other tutorials.
See also...For additional information on the concepts covered inthis tutorial, see the following:
Help, Manuals, Table of Contents
Simulation: Finite Element Modeling User’s GuideSimulation Techniques and Examples
General Techniques and ExamplesUsing Simulation Tools
Selecting Simulation EntitiesUsing Groups
Meshing a ModelCreating a MeshUnderstanding Element Quality ChecksGenerating Element Quality Statistics
To quickly find definitions of terms used on forms, use: Help, On Context
What’s next?The remaining Fundamental Skills tutorials present moremodeling techniques. After completing these tutorials,use the Advanced Projects tutorials to get anintroduction to other element types and solutionmethods.
To exit this tutorial, select: File
Exit
Warning! Do not use the menu in the I-DEAS Icons window to exit.Use the File, Exit menu in the Acrobat Reader window.
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