Taking NASTRAN Input Files Into ANSYS Mechanical via External Model in ANSYS 16.0

nastran-ansys-external-model-tnI found another very nice enhancement to version 16.0 of the ANSYS Workbench/ANSYS Mechanical toolset.  If you happen to have a NASTRAN input file (.dat, .nas, and .bdf) that you need to get into ANSYS Mechanical, no longer do you have to use FE Modeler in ANSYS Workbench to perform the translation.  In fact, not only can you move the NASTRAN model into ANSYS Mechanical, but you get the existing mesh as well as newly-created geometry that can be used for boundary condition application, etc.  As with most translations from one FE tool to another, you can’t expect everything will be translated.  However, this new technique can be an incredible time saver in addition to giving us capabilities to continue and augment simulations that were previously performed in NASTRAN, now in ANSYS.

Here is an example of this new procedure.  (Note that we don’t have NASTRAN here at PADT, so I couldn’t create a generic sample of a NASTRAN model in NASTRAN.  Instead, I created a model in ANSYS, then converted it into NASTRAN using ANSYS FE Modeler to get a NASTRAN input file for the purpose of this exercise.)

Once I have the NASTRAN input file that I need to convert into ANSYS Mechanical, I launch ANSYS Workbench 16.0 and insert an External Model branch.  I then click the … button to browse to the NASTRAN input file.  In this case, the file is NASTRAN.nas.

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Next, I drag and drop a new analysis type block into the Project Schematic.  In this case, it was a modal analysis.  Note that you can’t drop this onto the Setup cell in the External Model block as you might expect.  You set it up as a separate block and establish the link in the next step.

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Next, we drag and drop the Setup cell from the External Model block onto the Model cell of the Modal analysis block.  This establishes the link from the NASTRAN model to the new Modal analysis.

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We also need to right click on the Setup cell in the External Model block and select Update to get a green checkmark in that cell:

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Notice that there is no Geometry cell in the resulting Modal analysis block.  If all goes well, there will be geometry within the Mechanical model that can be used for selection purposes (in addition to the mesh that comes in from NASTRAN). 

Next we open the Mechanical editor by double clicking on one of the cells in the Modal analysis blocks (other than the Engineering Data cell).  It may take several minutes to bring in the NASTRAN model depending on the size of the NASTRAN model.  The Mechanical window doesn’t really let you know that it’s working, but if it’s sitting there with nothing being displayed, it’s probably churning away at bringing in the NASTRAN mesh and creating surface geometry on it.

Here is what the Mechanical window looks like after the mesh is read in and geometry is automatically created.  This is the mesh from the NASTRAN file, but in this case both solid and surface geometry is also present.  It’s not guaranteed that everything will come across.  I’ve seen contact elements come through for certain types of contact but not for other types of contact for example.

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The next image shows that geometry was created that can be used for the purposes of inserting fixed supports, just as if the geometry had come in from a CAD system.  Note that the NASTRAN input file had NO geometry, just finite element entities.  ANSYS is creating the geometry for use in Mechanical from the information in the NASTRAN input file.

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Finally, after manually creating a needed contact region, I was able to solve the modal analysis, demonstrating that further simulation can be performed in ANSYS Mechanical from this model which originally came from NASTRAN.

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So, the main take away here is that with version 16.0 of ANSYS, we can take a NASTRAN input file and through the use of the External Model block, go directly into ANSYS Mechanical.  Not only do we get the nodes and elements as well as other finite element entities from the NASTRAN model, but if all goes well we get geometry that facilitates further processing within ANSYS Mechanical.

We certainly hope this new capability makes it easier for you to perform additional simulations in ANSYS when the starting point is a NASTRAN model.  The other formats documented for version 16.0 are ABAQUS, Fluent input files, and ICEM CFD input files.

ANSYS 16.0 License Manager – New Look and Feel, New Capabilities

ansys-license-manager-160-tnIf your role includes administering ANSYS licenses, you should be aware that the look and feel of the ANSYS license manager has changed somewhat at version 16.0.  The tasks that used to all be performed within the Server ANSLIC_ADMIN Utility have now been split pretty much between that tool and a new tool that runs within your browser called the ANSYS License Management Center.

The ANSYS License Management Center looks like this:

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This new License Management Center window is opened on Windows via Start > All Programs > ANSYS, Inc. License Manager > ANSYS License Management Center, and on Linux via /ansys_inc/shared_files/licensing/start_lmcenter.

This utility is where you now install license files, start and start the license manager, and also gather diagnostic information if something goes wrong.  You can also view the license .log files here as well as ANSYS licensing documentation.

The ‘old’ Server ANSLIC_ADMIN Utility is now smaller and does less than it did in prior versions.  This is what it looks like at version 16.0:

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This window is still useful in that you can click on View Status/Diagnostic Options to get information you can’t get in the new License Management Center, primarily Display the License Status to see what licenses are in use and are available.  This information is also available to clients via the Client ANSLIC_ADMIN Utility.  You can start the ANSYS License Management Center from here too.

One capability you won’t find in either utility is the ability to Reread the License Manager settings.  When you load a new license file, the License Management Center now automatically stops and starts the license manager so you shouldn’t have to do a reread after installing a new file, but just in case, it can still be done via the command line using these instructions:

On Windows, open a command prompt and move to:

C:\Program Files\ANSYS Inc\Shared Files\Licensing\winx64

Then issue the command:

ansysli_server –k reread

The same command works on Linux from the /ansys_inc/shared_files/licensing/linx64 directory.

Another important change is the location of the license files after they have been installed.  The new location is (on Windows):

C:\Program Files\Ansys Inc\Shared Files\Licensing\license_files

This means there is a new sub-folder named license_files that contains the license file(s).  File(s) is now plural since you can have both an ANSYS license file and an Ansoft license file in that folder, both running using the ANSYS License Management Center.  There is a new license file naming convention as well:

ANSYS License file name:  ansyslmd.lic

ANSOFT License file name:  ansoftd.lic

The path on Linux is:

 /ansys_inc/shared_files/licensing/license_files

When you install an ANSOFT license file, the license manager now does some edits to change the daemon to the ANSYS daemon in addition to renaming the file and placing it in the new location. 

One additional piece of information:  The license manager reads any .lic files that are located in the license_files folder, so it’s probably a good idea to ensure that only ‘good’ versions of ansyslmd.lic and ansoftd.lic reside in that folder. 

A major conclusion that can be drawn from all of this is that ANSYS license manager and Ansoft license manager license files can now be managed using a single licensing tool and single set of licensing software.  We’ve been waiting for this for some time and it’s nice to see it’s here and working successfully.

 

10 Useful New Features in ANSYS Mechanical 16.0

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PADT is excited about the plethora of new features in release 16.0 of ANSYS products.  After sorting through the list of new features in Mechanical, here are 10 enhancements that we found to be particularly useful for general applications.


1: Mesh Display Style

This new option in the details view for the mesh branch makes it easy to visualize mesh quality items such as aspect ratio, skewness, element quality, etc.  The default style is body color, but it can be changed in the details to element quality, for example, as shown here:

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Figure 1. A. – Mesh Display Style Set to Element Quality

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Figure 1. B. – Element Quality Plot After Additional Mesh Settings

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Figure 1. C. – Accessing Display Style in the Mesh Details


2: Image to Clipboard

How many times have you either done a print screen > paste into editing tool > crop or done an image to file to get the plots you need into tools such as Word and PowerPoint?  The new Image to Clipboard menu pick streamlines this process.  Now, just get the image the way you want it in the geometry view, right click, and select Image to Clipboard.  Or just use Ctrl + C.  When you paste, you’ll be pasting the contents of that view window directly.  Here’s what it looks like:

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Figure 2 – Right Click, Image to Clip Board


3: Beam Contact Formulation

This was a beta feature at 15.0, but if you didn’t get a chance to try it out, it’s now fully supported at 16.0.  The idea here is that instead of the ‘traditional’ bonded contact methods (using the augmented Lagrange or pure penalty formulation) or the Multi-Point Constraint (MPC) bonded option, we now have a new choice of beam contact.  This option utilizes internally-created massless linear beam elements to connect the two sides of a contact interface together.  This can be more efficient than the traditional formulations and can avoid the over constraints that can happen if multiple contact regions utilizing the MPC option end up generating constraint equations that tend to conflict with each other.

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Figure 3 – Beam Formulation for Bonded Contact


4: Nonlinear Adaptive Region

If you have ever been frustrated by the error message in the Solution Information window that says, “Element xyz … has become highly distorted…”, version 16.0 adds a new tool to our toolbox with the Nonlinear Adaptive Region capability.  This capability is in its infancy stage at 16.0, but in the right circumstances it allows the solution to recover from highly distorted elements by pausing, remeshing, and then continuing.  We plan on publishing more details on this capability soon, but for now please know that it exists and more can learned in the 16.0 Mechanical Help.  There are a lot of restrictions on when it can work, but a big one is that it only works for elements that become overly deformed due to large and nonuniform deformation, meaning not due to unstable materials, numerical instabilities, or structures that are unstable due to buckling effects.

As shown in figure 4. A., a Nonlinear Adaptive Region can be inserted under the Solution branch.  It is scoped to bodies.  Options and controls are set in the details view.

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Figure 4. A. – Nonlinear Adaptive Region

If the solver encounters a ‘qualifying event’ that triggers a remesh, the solver output will inform us like this:

 

**** REGENERATE MESH AT SUBSTEP     5 OF LOAD STEP      1 BECAUSE OF
      NONLINEAR ADAPTIVE CRITERIA

 

 

 

 

AmsMesher(ANSYS Mechanical Solver Mesher),Graph based ANSYS Meshing EXtension,v0.96.03b
(c)ANSYS,Inc. v160-20141009
  Platform           :  Windows 7 6.1.7601
  Arguments          :  F:\Program Files\ANSYS Inc\v160\ANSYS\bin\winx64\AnsMechSolverMesh.exe
                     :  -m
                     :  G:\Testing\16.0\_ProjectScratch\Scr692\file_inpRzn_0001.cdb
                     :  –slayers=2
                     :  –silent=0
                     :  –aconcave=15.0000
                     :  –aconvex=15.0000
                     :  –gszratio=1.0000
  Seed elements      :  _RZNDISTEL block

– 17:6:17 2015-2-11

  ===================================================================
  == Mesh quality metrics comparison                                
  ===================================================================
  Element Average    :  ——–Source——–+——–Target——–
  ..Skewness(Volume) :    4.0450e-001             4.1063e-001        
  ..Aspect Ratio     :    2.3411e+000             2.4331e+000        
  Domain Volume      :    8.6109e-003             8.6345e-003        

  Worst Element      :  ——–Source——–+——–Target——–
  ..Skewness(Volume) :    0.8564  (e552     )      0.7487  (e2217    )   
  ..Aspect Ratio     :    4.9731  (e434     )      6.8070  (e2236    )   

  ===================================================================
  == Remeshing result statistics                                    
  ===================================================================
  Domain(s)          :   1      
  Region(s)          :   1      
  Patche(s)          :   7      
  nNode[New]         :   39      
  nElem[New/Eff/Src] :   79 / 92 / 2076      

  Peak memory        :   10 MB

– 17:6:17 2015-2-11
– AmsMesher run completed in 0.225 seconds

  ========================= End Run =================================
  ===================================================================

 **** NEW MESH HAS BEEN CREATED SUCCESSFULLY. CONTINUE TO SOLVE. 

Results item tabular listings will show that a remesh has occurred, as shown in figure 4. B.

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Figure 4. B. – Results Table Indicating a Remesh Occurred in the Nonlinear Adaptive Region

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Figure 4. C. – Before and After Remesh Due to Nonlinear Adaptive Region


5: Thermal Fluid Flow via Thermal ‘Pipes’

This has also been a beta option in prior releases, but nicely, at 16.0 it becomes a production feature.  The idea here is that we can use the ANSYS Mechanical APDL FLUID116 elements in Mechanical, without needing a command object.  These fluid elements have temperature as their degree of freedom in this case, and enable the effects of one dimensional fluid flow.  This means we have a reduced order model for capturing heat transfer due to a fluid moving through some kind of cavity without having to explicitly model that cavity.  The pipe ‘path’ is specified using a line body.

The line body gets defined with a cross section in CAD, and is tagged as a named selection in Mechanical.  This thermal pipe can then interact on appropriate surfaces in your model via a convection load.  Once the convection load is applied on appropriate surfaces in your model, the Fluid Flow option can then be set to Yes, and the line body is specified as the appropriate named selection.  Appropriate BC’s need to be applied to the line body, such as temperature constraints and mass flow rate, as shown in figure 5.

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Figure 5 – Thermal “Pipe” Line Body at Top, Showing Applied Boundary Conditions


6: Solver Pivot Checking Control

This new option under Analysis Settings > Solver Controls allows you to potentially continue an analysis that has stopped due to pivoting issues, meaning a model that’s not fully constrained or one that is having trouble due to contact pairs not being fully in contact. 

The options are Program Controlled, Warning, Error, and Off.  The Warning setting is the one to use if you want the solver to continue after any pivoting issues have occurred.  The Error setting means that the solver will stop if pivoting issues occur.  The Off setting results in no pivot checking to occur, while Program Controlled, which is the default, means that the solver will decide.

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Figure 6 – Solver Pivot Checking Controls Under Analysis Settings


7: Contact Result Trackers

This new feature allows you to more closely track contact status data while the solution is running, or after it has completed.  This capability uses the .cnd file that is created during the solution in the solver directory.  It is useful because it gives you more information on the behavior of your contact regions during solution so you can have more confidence that things are progressing well or potentially stop the solution and take corrective action if they are not.  The tracker objects get inserted under the Solution Information branch, as shown in figure 7. A.

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Figure 7. A. – Contact Trackers Inserted Under Solution Information

A large variety of quantities can be selected to track, such as Number Contacting, Number Sticking, Gap, Penetration, etc.

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Figure 7. B. – Contact Results Tracker Settings in the Details View

Contact results tracker quantities can be viewed in real time during the solution, as shown in figure 7. C.

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Figure 7. C. – Contact Results Tracker Showing Gap Decreasing as the Solution Progresses


8: Tree Filtering

For large assemblies or other complex models, there are useful enhancements in how the tree can be filtered, including the ability to create Groups.  Groups can consist of tree entities that are geometry, coordinate systems, connection features, boundary conditions, or even results.  Grouping is accomplished as easily as selecting the desired items in the tree, then right clicking to specify Group, as shown in Figure 8. A.

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Figure 8. A. – Grouping Displacements

A new folder in the tree is then created which can be named something useful.  Figure 8. B. shows the displacement boundary condition group (folder) after it was given a name.

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Figure 8. B. – Group of Displacement BC’s, Given a Meaningful Name

It’s easy to right click and Ungroup if needed, and there is also a Group Similar Objects option which allows you to select just one item in the tree and easily group all similar items by right clicking.


9: Results Set Listing Enhancements

In addition to the information on remeshing that we mentioned back in useful new feature number 4, there is a new capability to right click in the tabular listing of results and then right click to create total deformation or equivalent stress results.  This capability can make it faster to create a deformation or stress plot for a particular time point or result set of interest.

The procedure to do this is:

  • Left click on the Solution branch in the tree.
  • Left click on the desired Results set in Tabular Data
  • Right click on that results set and select Create Total Deformation Results or Create Equivalent Stress Results, as shown in figure 9.

The result of these steps will be a new result item in the tree, waiting for you to evaluate so you can see the new results plot.

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Figure 9 – Right Click in Solution Tabular Data to Create Deformation or Equivalent Stress Result Items


10: Explode View

We’ve saved a fun one for last, the new Explode View capability.  This allows you to incrementally ‘explode’ the view of your assemblies, making it potentially easier to visualize the parts and interaction between parts that make up the assembly.  To use this feature, make sure the Explode View Options toolbar is turned on in your View settings.  There are several options for the ‘explosion center’, such as the assembly center or the global or a user defined coordinate system.

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Figure 10. A. – The Explode View Options Toolbar

As you can see in figure 10. A., there is a slider that allows you to control the ‘level’ of view explosion.  Keep in mind this is just a visual tool and does nothing to the coordinates of the parts in your assemblies.

Figures 10. B. and 10. C. show various slider settings for the exploded view of an assembly.

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Figure 10. B. – Explode View Level 3

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Figure 10. C. – Explode View Level 4


This concludes our tour of 10 useful new features in ANSYS Mechanical 16.0.  We hope you find this information helps you get your ANSYS Mechanical simulations completed more efficiently.  There are lots and lots of other new features that we didn’t mention here.  The Release Notes in the Help covers a lot of them.  We’ll be writing more about some of the things we mentioned here as well as some of the other new features soon.