printing _creating a 2-d mesh using batch mesher - hm-3160

Creating a 2-D Mesh using Batch Mesher - HM-3160

For this tutorial, it is recommended that you complete the introductory tutorial Getting Started with HyperMesh - HM-1000.

Geometry clean-up and meshing are often cited as the most time consuming aspects of finite element modeling. In HyperMesh, these tasks can be performed in batch mode (Batch Mesher), requiring minimum input and no user interaction.

In this tutorial you will learn how to generate a 2-D mesh on a part in batch mode and how to review and evaluate the results. As part of setting up the batch task, you will also learn how to create the custom criteria and parameter files used in batch mode.

The following exercises are included:

• Understanding the Batch Mesher process

• Gathering the input requirements and configuring the Batch Mesher

• Setting up and submitting a job to the Batch Mesher

• Reviewing the results

You can extend this process to mesh any number of parts in batch mode in a single step. Once you are satisfied with the mesh obtained, you can complete the modeling to generate appropriate solver decks.

This tutorial requires about 45 minutes to complete and uses files located in the <install_directory>/tutorials/hm/ directory. For detailed instructions on how to locate the installation directory <install_directory> at your site, see Finding the Installation Directory <install_directory>, or contact your system administrator.

The model file used for this tutorial is a floor panel (see figure below):

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Floor panel model

To understand the Batch Mesher process:

Batch Mesher is a process that generates a finite element mesh of a given CAD geometry without any user intervention. The objective of this process is to generate the best quality mesh while respecting the parameters set by the user, and with minimal deviation from the geometry.



Batch Mesher requires the following:

• Geometry data file in any CAD format that HyperMesh supports, or in a HyperMesh database file

• Parameter file - This text file defines the average element size, type of elements to be generated (quads or trias) and various options for geometry cleanup.

• Criteria file - This text file contains all the element quality requirements such as jacobian, warpage, etc. You can export this file from the qualityindex panel in HyperMesh after you update the settings to your requirements.

The quality of the mesh generated is measured with a quality index (QI) value which is derived from the individual element quality criteria defined in the criteria file. The Batch Mesher invokes HyperMesh in batch mode and performs a variety of predefined functions which include:

• Import the geometry file using the specified CAD translator.

• Perform a variety of geometry cleanup operations, such as closing internal slivers and removing duplicate geometry, to cure any inaccuracies in the geometry.

• Perform geometry simplification specified by the user such as removing pinholes, fillets, etc….

• Execute the geometry editing tools required to improve the regions to mesh.

• Determine the best combination of meshing algorithm and mesh parameters to generate the best quality mesh.

• Perform quality optimized meshing and node placement to meet the quality requirements (QI value).

• Save the resulting mesh and geometry as a HyperMesh database file.

You can launch the Batch Mesher function from a user interface or through the command line.

In this tutorial, we will work with the Batch Mesh user interface. You control the behavior of the Batch



Mesher by setting a variety of parameters and also providing the target element quality.

To gather the input requirements:

In this tutorial, mesh a floor panel (floor.iges) in batch mode with the following requirements:

• 10mm target element size

• Element size >3.0mm

• Warpage <20.0

• Jacobian >0.7

• The number of tria elements should not exceed 10% of the total number of elements

• All bolt holes with a diameter less than 8mm should be ignored and all others should be meshed with one row of washer elements

In this section, invoke the Batch Mesher user interface, and configure it to the requirements set above defining the appropriate criteria and parameter files.

1. Invoke the Batch Mesher user interface.

On PC:

- Click Start and go to Programs / Altair HyperWorks <version> / Altair Tools / Batch Mesher.

This launches a DOS window as well as the Batch Mesher interface.

Note On PC, you can also launch the interface by opening a command prompt and typing <install_directory>/hm/batchmesh/hw_batchmesh



On UNIX:

- Type the hw_batchmesh command at the prompt.

Note If you have difficulties launching the interface at your site, please contact your system administrator.

The user interface has four tabs:

Batch Mesh lets you choose the CAD geometry files to be meshed in batch mode and submit the jobs.

Run Status lets you check the status of runs that have been submitted to the Batch Mesher.

Configurations lets you specify the input parameters, such as the CAD geometry file format and file extension, desired element quality criteria file, parameter file, etc.

User Procedures lets you customize the Batch Mesher process to your needs.

The next step is to configure the Batch Mesher to your requirements. This step includes setting the geometry file type, and criteria and parameter file

2. Add a new Mesh Type using the Configurations tab.

- In the Batch Mesh window, go to the Configurations tab.

- Set Type of geometry: to IGES using the drop-drown menu.

- Set File filter: to IGES (*.igs, *.iges).

- Use the icon, , to add a new entry in the table.

- In the blank field under Mesh Type, type in tutorial_meshsize10.



Configurations tab

We now need to assign a Criteria File and a Parameter File for this new Mesh Type. If we had such

files already, we could use the open file icon to browse for them. Here we will simply edit existing files from the installation and save them to our working directory before specifying them in the



Configurations tab.

3. Edit the nvh10.criteria file to define the criteria for the mesh.

- In the Configurations tab, select the Criteria File cell referencing the file nvh10.criteria.

- Click the edit icon to load this file into a text editor and edit it.

Disregard any message that is posted as we will save the edited file under a new name.

Note The file lists 12 criteria that can be turned on or off using the On column (0=off, 1=on). Specify various weight factors for the different criteria using the Wt column.



nvh10.criteria criteria file

- Leave the Ideal value for min length and max length untouched as it already matches our target element size.

- Change the Fail value for min length to 3.0.

- Turn on the warpage criterion, which is already set to the right Fail value of 20, by changing the 0 to a 1 in the On column.

- Change the Fail value of the jacobian to 0.7, and the Warn value to 0.75.

- Update the Fail value for % of trias to 10.0, and set the Warn value to 9.0.

- Set the weight factor in the Wt column to 2 for min length, warpage, jacobian, and % of trias as these are most important for us.

- Click Save, and save this criteria file to your working directory as tutorial_batchmesh.criteria.

- Close the criteria file.



tutorial_batchmesh.criteria criteria file

Note Criteria files can also be generated from the qualityindex panel located on the 2D page of HyperMesh. Refer to this panel help for complete information.

4. Specify the tutorial_batchmesh.criteria file in the Criteria File column of the Configurations tab for the Mesh Type we created using the open file icon.



5. Edit the nvh10.param file to define the parameters for geometry cleanup and mesh creation according to the following table:

Parameter and options: Action:

geometry_cleanup_flag

1 perform geometry cleanup such as equivalencing edges, suppressing features etc

0 no geometry cleanup

Leave at 1 to allow the Batch Mesher to perform any necessary geometry cleanup for better mesh quality

meshing_flag

0 Do not mesh (only cleanup if geometry_cleanup_flag = 1)

1 default mesh without any optimization

2 perform optimized mesh but does not optimize node across shared (green) edges

3 perform optimized mesh with node placement optimization across shared (green) edges

4 perform local area remeshing after optimized mesh with node placement optimization across shared (green) edges

5 perform local area remeshing and optimization as 4 does, and also reduces the number of trias in the mesh

Leave at 5 to allow the Batch Mesher to give the best mesh quality using all the options at its disposition

element_size

Element size for meshing and optimization

Leave at 10 to mesh this part with 10mm average element size



element_type

0 mesh with tria elements

1 mesh with quad elements

2 mesh with mixed (quads with trias at transitions)

Leave at 2 to obtain a quad mesh with use of triangles at transitions

surf_component

1 place the mesh in the surface's component

0 place the mesh in the current component (if none exists, one is created)

Leave at 1

feature_angle

Used in conjunction with meshing_flag. When meshing_flag is set to 3 or 4 the tool tries to move nodes on this free edge to its optimum position as long as the angle between the two surfaces that share the edge is less than the feature angle specified here.

Leave this at the current 30 degree setting

nodes_around_holes

Minimum number of nodes around a round hole (even when element size only allows for lesser number)

Set this to 5 elements around a hole

layers_around_holes

Number of concentric layers of washer elements around a hole

Leave at 1 to get one ring of washer elements

diameter_of_pinholes Set to 8 mm as per our



Removes all the pinholes in the model whose diameter is lesser than the value specified here

requirements

pinholes_in_solids

Removes all cylindrical holes in solid parts whose diameter is less than the value specified here

Since our part is a sheet representation of a stamped metal, this parameter can be ignored

keep_pinhole_center

Allows you to add a fixed point at the center of the pinhole being removed.

0 Does not add a fixed point

1 (non-zero value) retains the fixed point , useful for tracking the location of bolt holes, to apply constraints later

Leave at 0 so not fixed point is added

max_filet_radius

Removes all edge fillets whose radius is below the max value specified

Set this value to 0 - no fillet removed

minimal_bead_height

Suppresses all beads whose height is lesser than the specified value, thus ignoring the feature during mesh generation

Set this value to 4 mm

no_cleanup_comp

Name of component to which geometry cleanup functions should not be applied. Repeat it to provide

Remove this parameter as we wish to cleanup the entire model



multiple components. The geometry in these components will be meshed without performing any geometry cleanup

time_limit

Time limit for node optimization after meshing

To complete the batch mesh job quickly, add this parameter to the text file and set it to 10 minutes

6. Save the updated parameter file to your working directory as tutorial_batchmesh.param.



Updated parameter file

7. Specify the tutorial_batchmesh.param file in the Parameter File column of the Configurations tab for the Mesh Type we created.



Completed configurations

The Batch Mesher is now configured. You can save this configuration for future use using the Save Config… option from the File menu. The next step is to select the CAD files to be meshed.

To submit CAD geometry to the Batch Mesher:

In this section, choose the CAD geometry file(s) to be meshed in batch mode, and set the results directory where the Batch Mesher will save the resulting mesh files.

1. Use the Batch Mesh tab to set the Geometry source directory:.

- Go to the Batch Mesh tab.

- Click the open file icon next to Geometry source directory: and browse for the <install_directory>/tutorials/hm directory.

This is where the geometry file for this tutorial is located.

Warning Select the directory only, not the file.

2. Use the icon to select the file floor.iges to mesh in batch model.

A window is displayed with a list of all the files in this directory with the .iges extension, as specified



on the Configurations tab. While multiple selection is possible using the CTRL and SHIFT keys, we only select one file here.

The file name and path populate the Geometry File field, while the file type populates the Geom Type field.

3. Click the cell under Mesh Type and select tutorial_meshsize10 from the list.

4. Click the open file icon next to Result directory: and browse for your working directory as the directory where result files will be placed.

5. Click the icon to launch the Batch Mesher.

To monitor the status of the process and review the results:

Once the CAD geometry is submitted, the Run Status tab automatically displays. This is where you can check the status of the run(s). Each geometry file submitted is listed individually along with its current status (Pending, Working, or Done).

The results of the run are saved in a directory bm.xxxx within the specified result directory specified on the Batch Mesh tab where xxxx is randomly generated and varies for each run.

1. On the Run Status tab, click Details to load the content of the floor_res.txt file.

This file is generated by the Batch Mesher and shows the progress of the run.

It lists the file name being meshed in batch mode with the corresponding element size, criteria, and parameter files. It also lists the steps completed by the Batch Mesher along with time in seconds for each step. It also provides information such as:

- The total number of surface/faces in the model

- The number of surfaces that could not be meshed (#failed surfs)



- The number of surfaces whose mesh has poor quality (#badmsh surfs)

- The total number of elements in the model

- The % of trias

- The total quality index (QI) value of the model.

This information is only provided for some steps in the process.

2. Click Refresh to review the latest status of the run.

The final timing summary, along with the word COMPLETE, in the text file indicate the successful completion of the run. The status changes to Done on the Run Status tab. The Batch Mesher performs various numbers of steps for each model, as different models need varying extents of cleanup and meshing to achieve the target quality. The contents of the details are automatically saved in the result directory.An ERROR is printed when the run failed to complete successfully.

3. From the Run Status tab, click LoadMesh to load the resulting file into HyperMesh.

This invokes HyperMesh and loads the resulting HyperMesh database file that contains the final mesh along with the cleaned up geometry.



Final model

With the final result, we can compare the model obtained to the geometry that was supplied to the Batch



Mesher to better understand how the parameters we set affected the result. In the figure above are 6 areas we can zoom into to review the effect of the various parameters:

Area 1: Pinholes with a diameter less than 8mm were removed

Before

After

Area 2: Added (trimmed) layer of washer around pinholes with a minimum of 5 nodes (fixed points) along the free edges



Before

After

Area 3: Suppressed geometric edges which do not have a sharp feature and that are too close to other geometry causing elements smaller than specified element size



Before

After

Area 4: Bead patterns recognized and cleaned up



Before

After

Area 5: Fixed points (or trim lines) added to better align the mesh where surface edges are close to one another



Before

After

Area 6: Nodes moved off the surface edges (while still on surface geometry) to improve mesh quality



Finally, we can review the quality of the mesh using the qualityindex panel from the 2D page. You will find that some elements fail the quality criteria we set as many times, the Batch Mesher cannot improve the quality of some elements due to constraints imposed on it such as:

• Limit deviation from surface geometry

• Maintain feature angle and external edges

• Imposed minimum number of nodes around a hole

This concludes this tutorial. You may discard the files used of keep them in your working directory for your own reference.

In this tutorial we used the Batch Mesher to mesh an IGES model in batch mode. We defined specific



criteria for the quality of the elements to be generated, and also set some parameters as to what kind of geometry cleanup would be involved in the process. We experimented with various options and reviewed of these options would affect the final geometry and mesh.

See HyperMesh Tutorials for a complete list of tutorials.



printing _creating a 2-d mesh using batch mesher - hm-3160

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