checking element quality · i-deas tutorials: fundamental skills this tutorial covers techniques...

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


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


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


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


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


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


What: Display the distortion and stress results.

Hint

Distortion Values

Display Results

Deformation Results: Clear

Stretch Values

Display Results

15


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


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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