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Tutorial BATCH MESH SHELL MESHING Table of Contents 1. Introduction....................................................................................................................................2 1.1 Prerequisites............................................................................................................................2 1.2 Problem description..................................................................................................................2 1.3 Data files..................................................................................................................................2 2. Read and prepare the geometry.....................................................................................................3 2.1 Read and merge the parts........................................................................................................3 2.2 Check Geometry......................................................................................................................4 3. The Batch Mesh Manager...............................................................................................................6 3.1 Create the meshing scenario...................................................................................................6 3.2 Set the meshing parameters....................................................................................................7 3.3 Define quality criteria..............................................................................................................14 3.4 Keep important features.........................................................................................................15 3.5 Run Batch Mesh and view statistics.......................................................................................18 4. Mesh improvement........................................................................................................................19 4.1 Check mesh quality and correct violations.............................................................................19 4.2 Check and correct Penetrations.............................................................................................22 5. Conclusion....................................................................................................................................23 BETA CAE Systems S.A.

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Tutorial

BATCH MESH

SHELL MESHING

Table of Contents

1. Introduction....................................................................................................................................21.1 Prerequisites............................................................................................................................21.2 Problem description..................................................................................................................21.3 Data files..................................................................................................................................2

2. Read and prepare the geometry.....................................................................................................32.1 Read and merge the parts........................................................................................................32.2 Check Geometry......................................................................................................................4

3. The Batch Mesh Manager...............................................................................................................63.1 Create the meshing scenario...................................................................................................63.2 Set the meshing parameters....................................................................................................73.3 Define quality criteria..............................................................................................................143.4 Keep important features.........................................................................................................153.5 Run Batch Mesh and view statistics.......................................................................................18

4. Mesh improvement........................................................................................................................194.1 Check mesh quality and correct violations.............................................................................194.2 Check and correct Penetrations.............................................................................................22

5. Conclusion....................................................................................................................................23

BETA CAE Systems S.A.

Shell Meshing using the Batch Mesh Manager1. Introduction

The scope of this tutorial is to guide the user through the basic functionality of the Batch Mesh Manager in order to automatically mesh a model specifying the necessary meshing parametersand quality criteria. The tutorial mainly focuses in understanding why and how the meshing parameters must be set, according to the size and shape of features in the model, to get the best possible result.

The steps described in this tutorial are:

- Merge the ANSA databases containing the geometry- Check geometry- Create the meshing scenario- Set the parameters and quality criteria- Run the batch mesh- View statistics- Manual mesh improvement and final checks

! Note that the results that you will produce by the Batch Mesh may have some small variations compared with those presented in the pictures of this tutorial.

1.1 Prerequisites

It is highly recommended to have read the “Introduction & getting started” document as wellas to have performed the “basic ANSA” tutorial or to have basic meshing background.Also, User's Guide paragraphs §12.1 and §12.2 give a brief overview of the Batch Mesh Tool.The after_batch_mesh_practices.pdf document explains how the mesh can be improved after running the Batch Mesh.

1.2 Problem description

The model, a half frontal rail structure, consists of five parts saved in separate databases which need to be merged in one. Then the geometry must be checked before being meshedby the Batch Mesh Tool using a global element length of 8mm. The meshing parameters mustbe set in a way that the resulted mesh will only need minor manual improvements in order to fulfill all the defined quality criteria.

1.3 Data files

The files required for this tutorial are CrossLower.ansa, CrossUpper.ansa, Reinf.ansa, SideMemberInner.ansa and SideMemberOuter.ansa. The result file is batch_mesh_result.ansa. Also the mesh parameters and quality criteria can be found in 8mm.ansa_mpar and 8mm.ansa_qual respectively.

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Shell Meshing using the Batch Mesh Manager

2. Read and prepare the geometry

2.1 Read and merge the parts

Start ANSA and create a new empty database from File>New (Ctrl+N).

Then, select File>Merge to openthe File Manager.

Navigate and select all the files from Parts_To_Merge directory. Click on OPEN.

In Merge Parameters window leave the default settings and press OK.

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Shell Meshing using the Batch Mesh ManagerOpen the Part Manager (Ctrl+R)and switch to “Icon View”.

You can see the five merged Parts andan empty one named “untitled” which has tobe deleted.

To do so, right click on it and select “delete”.

Confirm and close the Part Manager.

2.2 Check Geometry

It is highly recommended before meshing the model to correct any geometrical problems which may exist.

Firstly, you must changethe CONS resolution to equalthe target element length

of 8mm. To do so, activate the Windows>Options (Ctrl+I).

Under the Settings, in Resolution, change the CONS Resolution to 8. Press APPLY, confirm and close the window.

Having all parts visible, activate from the D.UTIL group the CHECK>GEOMETRY.

Select all checks except the Unmeshed Macrosand Single Bounds and confirm.

The check shows in green that there aren'tany geometrical errors present.

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Shell Meshing using the Batch Mesh ManagerYou must also check that single (red CONS) bounds are present only at the edges of each partand where holes are present.Deactivate from the Visibility group

the SHADOW, DOUBLE and HOT PNT flag buttons.

To visually check the Parts one by one, open the Part Manager and right click

on each one and select “show only”. You can confirm now that there no boundary problems.

When finished, activate SHADOW, DOUBLE and HOT PNT flag buttons.

Finally you can check for intersections by activating from the D.UTIL group the CHECK>PENETRATION>INTERSECTIONS

Click OK on the dialog to start the check.

There are no intersection errors.

! It is very important to have a model free of geometry errors before meshing it to get the best possible results. Geometry or intersection errors depend on the CONS resolution. Always check in resolution same as the target element length or finer.

Now you can proceed to the meshing process.

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Shell Meshing using the Batch Mesh Manager

3. The Batch Mesh Manager

3.1 Create the meshing scenario

Open the Batch Mesh Manager by clicking to its shortcut icon or by WINDOWS>BATCH MESH (Ctrl + B)

Create the meshing scenario by New>Meshing Scenario. The default session is automatically created. As all the parts are going to be meshed using the same parameters, no additional sessions need to be added.

The next step is to load the five parts intothe meshing scenario.

Double click on “0” in the Items column.The Contents window opens.

As you are only going to use the default session all parts will be added there.

Select all parts from the “Pending Items” listby clicking on the “select All” button and move them in the “Meshing Scenario” listby pressing the green arrow.

Confirm and close the window by pressing on OK.

All parts are automatically loaded now intothe default session.

Note:In case that more sessions and filterswere created, the parts would automaticallybe distributed to sessions according to these filters. See §12.3.7 of ANSA User's Guide.

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Shell Meshing using the Batch Mesh Manager3.2 Set the meshing parameters

The main and most important setting in the meshing parameters is the target element length.In addition, there are settings concerning the treatment of various features like holes, flangesand fillets. In order to correctly set up these, it is obligatory to know the violating limits of each quality criterion for the mesh that will be generated, especially the minimum and maximum element length.

It is already mentioned that the target element length is 8mm. The quality criteria to be usedare the following:

Aspect Ratio NASTRAN 3Skewness PATRAN 45°Warping IDEAS 12.5°Min Length 5mmMax Length 15mmMin Angle Quads IDEAS 60°Max Angle Quads IDEAS 120°Min Angle Trias IDEAS 30°Max Angle Trias IDEAS 120°

For more information on quality criteria definition see ANSA User's Guide §10.5.1

To edit the Mesh Parameters, whichare currently named “Untitled”, double clickon their name under the Mesh Parameters column. Alternatively, you can right click on it and select “Edit > Meshing Parameters”.

The Mesh Parameters Window opens with all options set to default values.On top, in the Name field optionally type “8mm”.

You can see that the parameters are dividedin tabs; the Shell Mesh, Defeaturing, Fillets, Flanges, Holes, Tubes and Fix Quality tabs.

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Shell Meshing using the Batch Mesh ManagerIn Shell Mesh tab, by default, the type of mesh is configured as General, Mixed with 1st order elements.

The target element length is automatically setto 8mm taken from the CONS resolution.

Distortion distance and Distortion angle are set by default to 20% and 0° respectively.

None of the options under “Remove triangle from:” is active.

Make sure that all these settings are set as shown in the picture on the left.

Also, in the Defeaturing tab leave all default settings making sure that the Defeaturing levelis set to “fine” and the “Join perimeters with distance <” is set to two thirds of minimum element length.

In this case (min length 5mm), perimeters with distance less than ~3.3 mm will be joined bythe Batch Mesh.

Switch to Fillets treatment and activatethe fillet and chamfer treatment by clickingon their flag buttons.

In the fillet treatment you can specify which fillets will be sharpened or split as well as how many rows of elements will be created.

Before setting, you will take some measurement on the model to get some information aboutthe present flanges and chamfers.

Middle click on the window title to minimize it.

Note:For recommended settings and optimum results refer to ANSA User's Guide §10.6.8

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Shell Meshing using the Batch Mesh ManagerActivate the Measure Toolby selecting MEASURE from the GEOMETRY group of functions.

In order to measure the width of fillets, activate the selection of CONS. Note also that you can toggle between the selection entities usingthe keyboard key “1”.

Note:You are able to use the MEASURE tool without leaving the Batch Mesh Manager.

Select two CONS that describe a fillet alongits length.

In the Results field. Change the resultto Distance to show the distance betweenthe two CONS.

Confirm the measurement by middle click.Proceed to measure other fillets by selecting pairs of CONS and pressing the middle mouse button to temporarily store the measurementfor each pair.

Optionally you can isolate all the fillets of the model before measuring by activatingthe ISOLATE>RADIUS from the Focus group of functions and entering a value of 20°on the dialog box.

After taking the measurements you will notice that the fillets present in the model start froma width of about 1.4mm up to 15.5mm.

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Shell Meshing using the Batch Mesh ManagerAdditionally to the classic fillets, there are some features in our model having the shape of a half tube. These have a length of about 27mm.

Concerning the chamfers, the only presentin the model are located around the tubeon Part named CrossUpper.

Measure the width of the chamfer.

In addition, measure the angle by activatingthe nodes selection in measurement tooland selecting successively the three Hot Points as shown in the picture.

The width of the chamfer is about 2.75mm.The feature angle between the chamferand the face is about 45° (180°-135°).

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Shell Meshing using the Batch Mesh ManagerOpen the Batch Mesh Manager, the mesh parameters and switch to Fillets tab. In the Fillet treatment, fill the first

line so that Fillets having a Radius up to 1.5and Width up to 3mm to be treated by Sharpen.This will sharpen the Fillet exactly as the DACH function would do.

Click on the green cross to add more lines.

Set for Fillets with a width from 3 to 10mm to have one row of elements and for fillets from 10 to 20mm to have two rows of elements.Finally, set 4 rows for fillets 20 to 40mm.

For chamfers set the treatment so that any chamfers having a feature angle from 40 to 50°and a width up to 10mm to be sharpened.

When setting the number of rows according to the width ranges, take in account the minimum element length and also the maximum distance from perimeter used when fixing the qualityof the generated mesh. This will be set later at about 2.5mm. So, if one row of elements willbe generated on a fillet of 3mm, the elements will be resized at least at 5mm and they will not violate the minimum length criterion.

The next treatment in meshing parametersis the flanges treatment. Switch to Flanges tab and click on the flag button to activate it.

If not already set, activate the option to recognize the flanges by shape of faces.

If you do similar measurements as forthe fillets you see that the width of the flanges present in the model varies from about17 to 18mm.

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Shell Meshing using the Batch Mesh ManagerSet to create one row of elements on flanges up to width of 10mm and two rows of elements on flanges from 10 to 19mm.

Now switch to the Holes treatment tab.Enable the general holes treatment by clicking on its flag button.

Here, for various diameters ranges, the nodal distribution on the diameters and the creation of zones around them can be set.

Use MEASURE to get a reviewof the holes present in the model.

There are holes with diameter from about 6 to 50mm.

The small holes have to be filled because very small elements would be created around them. To do so, in the holes treatment list, set 7mm in the Diameter range field and select the option “Fill” in the Target Diameter field.

Press the green cross to one more line.

Then, for holes having a diameter up to 12mm set to have four nodes by selecting under the Node Number field the “expression” option and setting N=4

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Shell Meshing using the Batch Mesh ManagerCreate two more lines.

For diameters up to 24 and 36mm set the perimeter of the hole to havean element length of 5.5 and 6mm respectively using the L0= expression

Also set the creation of a zone for each one by using in the Zone field the expression W=5.5 and W=6 respectively.

Switch to Fix Quality tab.

Activate all flag buttons except the “Split remaining violating quads”.

Set the “Maximum distance from surface”to 5% of the target length (0.4mm) andthe “Maximum distance from perimeterto 50% of minimum length (2.5mm).

Refer to §12.4.7 of ANSA User's Guide for more information.

The meshing parameters,optionally,can be saved in a separate file (*.ansa_mpar) and loaded in other batch mess sessionsin the same or other ANSA databases.

Click on the Save icon.

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Shell Meshing using the Batch Mesh Manager

3.3 Define quality criteria

To open the Quality Criteria window double click on “Untitled”.

As it was seen in the Fix Quality partof the meshing parameters, by default,the Batch Mesh is set to automatically fixthe quality of the produced elements in orderto satisfy the corresponding threshold values defined in the Quality Criteria.

To have a satisfactory result, at leastthe minimum element has to be set.Here the criteria which were presented before, will be used.

Write “8mm” in the name field.Then activate the quality criteria using their flag buttons and set their limits in the Failed column.

Take care which calculated method is selected for each criterion.

As in meshing parameters, you can save the criteria under a separate file (*.ansa_qual).

Press OK to close the window.

Even if the the Meshing scenario is now ready to run, exit the Batch Mesh Manager by pressing ESC.

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Shell Meshing using the Batch Mesh Manager

3.4 Keep important features

You have already configured in the meshing parameters the defeaturing and feature treatment options according to our needs. Though, as a side effect, there may be in the model, some areas where you need to keep the geometry with higher accuracy. For this model, such an areacan be seen in the first picture. These features are important for example in a frontal crash analysis.

In this case, if you run the batch mesh as it is right now, due to defeaturing, some Perimeterswill be joined (see orange perimeters in second picture) and the resulted mesh will not completely match the initial geometry.

Refer to paragraph §12.4.3. of ANSA User's Guide for more information on defeaturing by the batch mesh algorithm.

You can indirectly instruct the Batch Mesh not to join these Perimeters by including their respective CONS in a SET.

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Shell Meshing using the Batch Mesh Manager

If not already open, show the Database Browser by pressing the F12 key. Right click on empty space and create a new SET.

In the window that opens, expandthe GEOMETRY group by clicking on its arrow and select CONS.

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Shell Meshing using the Batch Mesh Manager

Zoom in the area and select the CONS as shown in the picture.While selecting in “In SET” column the number of selected CONS is shown in red.Note that all selected CONS are 60. Confirm by middle click, give a name to the set and close its card.

The contents of the SET can be reviewed anytime by activating the “Highlight” flag and selecting the SET from the SET list.

These CONS which belong to a setare respected by the Batch Mesh andthey will not be joined during mesh generation.

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Shell Meshing using the Batch Mesh Manager

3.5 Run Batch Mesh and view statistics

Open the Batch Mesh Manager.Make sure the scenario and the session are checked and press RUN.

Batch Meshing starts. It will take a coupleof minutes to complete. Check the progressin the Status column.

When finished the Status of the sessionis “Error”. Double click on it to see the report window.

Here you can see analytically why the statusof the session is “Error”.In this case four of the parts are violatingthe quality criteria.

For more details select all the partsand click on statistics.

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Shell Meshing using the Batch Mesh ManagerANSA creates a report which can be saved as a text or html document. It gives information for each part separately as well as for the whole session.

To save, select the type of document and press the save icon.

Press ESC twice to return to Batch Mesh Manager.

4. Mesh improvement

4.1 Check mesh quality and correct violations

Right click on Default Session and select“Copy to Global Settings > Meshing Parameters and Quality Criteria”.

This will copy the quality criteria to the F11 window.

Also the meshing parameters will be copiedto the meshing options so that can be used later by the mesh improvement functions.

Close the Batch Mesh Manager and switchto Mesh menu.

Press F11 to open the Quality Criteria – Presentation Parameters window.

Check that the quality settings are now setin this window.

Click on Presentation Parameters tab.

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Shell Meshing using the Batch Mesh ManagerFor being able to view all detailsindependently from the viewing distanceslide the “Detail on Demand Effect” barto the left end.

Press OK to to close the window.

At this point optically examine the generated mesh and see how each area and featurewas treated.

Meshed model Fillet Sharpening

Chamfer Sharpening Zone around hole

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Shell Meshing using the Batch Mesh ManagerAs it was shown in the Batch Mesh Report, some elements are violating the quality criteria.These need to be located and corrected manually.

Activate the HIDDEN flag button from the visibility group.

All the failed elements are now drawn in color according to the criterion they violate.

Also on the screen the number of violating elements is reported.

To quickly correct some ofthe violating elements usethe FIX QUALITY algorithm located in the SHELL MESH group of functions.

Automatically, only the areas around the violations are selected. Confirm the selectionby middle click.

A preview is shown.Accept the changesby clicking on OK.

To isolate the Macroareas containing violating elements press EXTREME, located in the Focus group of functions.

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Shell Meshing using the Batch Mesh ManagerThe next steps would be to fix all the remaining violating elements. The techniques for doing so are not going to be presented in this tutorial as all cases of violating elements you may encounter are presented in after_batch_mesh_practices.pdf document. You can also refer to ANSA User's Guide §10.7

4.2 Check and correct Penetrations

Due to the fact that the minimum element length does not allow some elements to lie exactlyon the geometry, it is possible to have intersections or penetrations between two parts speciallyin areas where there are flanges.

Make all visible and use CHECK> PENETRATIONS>PROPERTY THICKNESS

Leave the factor to oneand press ENTER to startthe check.

Intersections and penetrations are found.Select them and press Show Only to see them.

For information and guidelines on how to fix intersection and penetration problems refer to ANSA User's Guide §10.8.3

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Shell Meshing using the Batch Mesh Manager

5. Conclusion

This tutorial presented shortly the most commonly used shell meshing scenario using the Batch Mesh manager. It was shown how the model should be prepared before meshing and how to set the meshing parameters and the quality criteria. The case where different mesh density is needed for different model areas by the addition of more meshing session it was not presented as for each one, the same techniques can be used. Other features like setting ranges in the quality criteria can always be studied using ANSA's User Guide chapter 12.

Finally, some techniques for the mesh improvement and the checks to be performed after meshing were referred. For more information use after_batch_mesh_practices.pdf documentand ANSA's User Guide §10.6, §10.7 and §10.8.

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