Analysis Powerhouse: Autodesk Nastran In-CAD
In 2014 Autodesk purchased NEI Nastran. Why? Because they could. A few things made that purchase important:
Nastran is the household name in analysis; it’s powerful and respected
Nei developed a CAD embedded UI in Solidworks for the Nei Nastran solver, called Nastran In-CAD.
Autodesk has since adapted In-CAD for Autodesk Inventor® and now gives Inventor users far more analysis power than ever before. Essentially, if you wanted to use Nastran as your solver or simply wanted more than linear static analyses, but didn’t want to leave your Inventor interface, then Autodesk has the tool for you.
This enables Inventor users to use Inventor as their modeling software, as well as the pre- and post-processor for their Nastran studies.
I am writing this for companies using Inventor that are considering a Nastran purchase or have In-CAD and are wondering about how it works.
User Interface
The UI is divided between a Nastran In-CAD tab and the Browser.
Nastran In-CAD Ribbon Tab
This displays a new set of ribbon panels dedicated to the analysis model. These panels include settings, meshing tools, boundary condition applications, results plotting, and others.
Browser
The Browser is populated not only with the Model and Assembly component sets, but also three additional Nastran panels.
Nastran Model Tree
Nastran Model Tree is divided into the assembly and model groups. The model group accounts for all boundary conditions and templates defined in the model. The analysis group assigns these to individual analyses and subsets as the user dictates to accomplish different studies.
Nastran File
This gives users a look into the Nastran file data rather than trying to interpret everything through the CAD interface.
Nastran Output (Log)
The output window shows the progress of the Nastran run, including real-time convergence data. This browser window is displayed by default during the run process. Once solved, this output log can be reviewed as needed and the contents thereof are saved alongside the other Nastran model and results files.
From this window the analysis can be stopped, paused, and resumed.
Autodesk Nastran Solver
The Autodesk Nastran (formerly Nei Nastran) solver’s accuracy is routinely tested against the NAFEMS standards at every release. Mitch Muncy, product manager for Autodesk’s Nastran product, came along with the Nei purchase. He has stated that the company had spent countless hours verifying every detail of the solver to ensure that it met the advanced requirements of its customers in industries such as aviation and automotive.
Linear, Static Stress, Thermal, and Modal Analyses
- Prestress static
- Static fatigue – repeated loading cycles
- Heat transfer – conduction and convection heat in examination of temperature distribution
- Linear buckling – compression induced loss of stiffness
- Linear statics – stress, strain, and deformation from applied static loads and constraints
- Normal modes – component natural frequencies
Advanced Analyses
- Pre-stress normal modes – capture true stiffness when complex loading is present
- Frequency response – structural harmonic response based on frequency-dependent loads
- Random vibration fatigue – long-term structural robustness where operation must be characterized by power spectral density (PSD) inputs
- Transient response – response through a period of time under the influence of constant or time-dependent loads
- Random response – behavior due to random dynamic loads such as road vibration, wave cycles, engine vibration, and wind loads
- Nonlinear static and transient response – time-varying events including dynamic loading that result in resonant vibration or stress amplification
- Superior surface contact, impact analysis, and automated drop tests – includes nonlinearities of large deformations, sliding contact, and nonlinear materials
- Advanced material models – complex nonlinear phenomena including plasticity, hyperelasticity, and shape-memory effects
- Composites – straightforward complex ply data and progressive ply failure including Puck and LaRC02 algorithms
Element Types and Modeling
- 1D, 2D, and 3D element types open a whole new world of modeling capabilities at a fraction of runtime
- Automatic bolt connector modeling with preload – simplified setup
- Associative intelligent meshing
Using In-CAD
While I have had some experience with Siemens FEMAP interface for Nastran, I have had very little experience with Autodesk’s new In-CAD UI. I thought that this article would be a good opportunity to get in and try it from the perspective of a new user. (I should mention that I crashed an In-CAD seminar at Autodesk University for about an hour, so I did have an hour jump-start.)
The setup workflow is the same as one would expect:
- Establish materials, boundary conditions, and loads
- Double-check everything
- Run the solution, which fails
- Adjust the model and rectify and oversights
- Run the solution – success
- Review the results
- … a laundry list of review and comparison to ensure that you are confident in the analysis model and results
Material Properties
Nastran In-CAD sorts components into material categories that are easily defined. It will pull in the material properties from the CAD model with the push of a button. In addition, it can import material properties from any of the Inventor or Autodesk material libraries, or allow users to create their own.
Setup
Constraints, contacts, and loads all use similar dialogs that permit faces and bodies to be selected and deselected as desired. Once selected, the particular conditions can be configured and applied as required.
The constraints dialog also contains buttons that identify limiting concepts (i.e., no rotation, free, symmetry, and others) that directly relate to the 6 degrees-of-freedom check boxes to which most analysts can relate.
Discerning between various surfaces is handled through the Inventor alternate surface explorer popup.
Five contact types are available: General, Slide, Welded, Rough, and Offset Weld.
Various limitations to contact proximity, penetration, and others are available to configure.
Loads can be applied statically, using basic magnitude fields and directions applied by:
- Individual component coordinate systems (X,Y,Z axes)
- Normal to face
- Geometric entity (by edge of selected geometry)
Dynamic loading is also available in an “advanced” expansion of the loads window. These can be applied through linear, linear equation, and quadratic methods.
Meshing
I have always loved Nastran’s adaptive meshing. It does it well and effortlessly. I often get mesh concentrations how I need them without a lot of manipulation.
Meshing is carried out with both global refinement settings and individual component settings. One feature I like is the mesh properties table, where all the component mesh settings are managed in one setting and are easily editable.
Nastran In-CAD also offers an element check, where In-CAD will inspect the model meshes for inconsistencies such as Skew, Aspect, and Jacobian limits. The results of these can be highlighted, making detection and adjustments much easier.
Nastran Editor
It has been brought to my attention that In-CAD does not give access to the Nastran Editor developed by Nei for their (now Autodesk’s) Nastran solver. This is unfortunate, and as the license fee for both In-CAD and Nastran are identical, I cannot see why it would be a financial imposition. I have no idea at this point whether this would be create a programmatic conflict, but I hope they will make that available to subscribers of In-CAD.
Results
I only ran through a simple linear static analysis for this test, but the results were consistent with what you would expect.
The standard array of plot types are available including displacement, Von Mises stress, principle stress, and more. XY plots can be configured by element or node.
Nodal information per result plot style can be reviewed by turning on the nodal display and passing the cursor over the nodes.
Tip: Remember to create a new Analysis subset! (Like a new Inventor “Scenario.”) Subsequent runs of the same analysis will overwrite the previous results. If you (like I just experienced) get a failure and overwrite your previous good results, you will feel quite foolish.
Closing Thoughts
Nastran is a fabulous analysis solution, no doubt. Having the ability to reach out to Nastran directly from Inventor is also a welcomed reality now. It is easy to learn and you can be up and running in less than an hour.
You will need some hardware in order to run In-CAD. Meshing can rapidly become quite complex without having to beg for it. While you may be accustomed to running Inventor comfortably on the machine, In-CAD will suck up resources quickly, depending on how carefully you limit your model DOF and mesh complexity.
In-CAD model setups will increase your assembly and model file size quite a bit as well. This is something that should be considered and a reasonable strategy should be imposed from the start.
There are some areas that need improvement, and a few glitches that should be addressed soon. While this UI is not tuned for analysts, I think In-CAD is a good tool to allow Inventor users (who don’t want to leave Inventor and learn a very complex interface) to have some access to the power that Nastran offers.
Companies purchasing Nastran should consider the type of pre- and post-processor they require. In areas where both CAD users and analysts will be using Nastran, the purchase of both Nastran and Nastran In-CAD licenses might be a wise choice, as the cost is the same, and users can access the Nastran Deck and Results files with either setup.
