Recently I reviewed the features that Autodesk Nastran In-CAD offered to inventor users that wanted a lot more simulation power. 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 time 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)
It should be noted here that Autodesk is selling In-CAD directly with Autodesk Inventor, as if to say “Here is our Nastran solver with an Inventor front end”. I am however writing this for everyone’s benefit, including existing Inventor users that are considering a Nastran solver.
The setup workflow is the same as one would expect:
- Establish materials, boundary conditions, and loads.
- Double-check everything
- Run the solution which fails [beat head on desk]
- 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
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.
Tip: Non-linear material types are supported, but will need to be created as these definitions are not in the existing Inventor Library (as far as I know).
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, etc.) that directly relate to the 6 degrees-of-freedom check boxes that most analysts relate to.
Discerning between various surfaces is handled through the Inventor alternate surface explorer popup.
5 Contact types are available: General, Slide, Welded, Rough, and Offset Weld.
Various limitations to contact proximity, penetration, etc. are available to configure.
Tips: Autodesk suggested using Welded for ‘Bonded’ types, and General for most other applications.
Load applications are equally simple. Load direction is applied by:
- Individual component coordinate systems (X,Y,Z axes)
- Normal to face
- Geometric entity (by edge of selected geometry)
Tip: boundary conditions such as constraints and the like can be applied to different subsets
I have always loved Nastran’s adaptive meshing. It does it well and effortlessly. I typically (not always but often) get mesh concentrations how I needed 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.
I liked this a lot. 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 in the model, making detection and adjustments much easier.
Tip: In-CAD will allow you to return to Inventor to work as normal. Be very aware that once component geometries that are connected with an In-CAD study are altered, anything applied to meshes, including constraints and contacts will be fouled and subsequent runs will require the boundary conditions to be meticulously corrected unless very broad automatic detection settings are imposed (which can be costly in run time)
I chose to setup a simple linear static analysis for this article, so that it would solve quickly and I could get a feel for basic activities. Additionally, we were using a Lenovo P500 Thinkstation CAD platform provided by Lenovo for these “CAD user” type evaluations in order to frame this in a “CAD user” perspective for solve times. While most companies purchasing a Nastran license will be mating that to a serious workstation, I wanted to understand how the solving would fare on their existing workstations, should they want to hold off on an upgrade until later.
My first run was shoddy, and I was getting Jacobian warnings and an unexpectedly long run-time. I found one surface contact that was left to the system to determine, as well as some poorly defined mesh areas. I increased the density slightly, defined the last contact manually (which I prefer to do in Nastran), and added another constraint. The subsequent runs were cleaner with a speed that was on par with an upscale 16 GB CAD platform.
Tip: Watch the convergence in the Output panel. This is a clear indication how Nastran is handling your model setup. If the convergences won’t get close to 100% and the iterations keep rising (within a reasonable amount of time) you may want to cut your losses and stop the analysis (and possibly reduce the model DOF).
Results to Come
Setup was quite easy to pick up on. The UI has been simplified in such a manner that it takes little review in order to setup what you want. Experienced users will get it immediately, and new users should find these methods quite easy to learn.
After the review I realized that I really need to spend a couple hours setting up a simple transient analysis with some alternate elements in order to get a better feel for the setup procedure, accessibility, and capabilities. We’ll do that in the future.
In the mean-time, I will return with the post-processing and results of this review, as well as an overall perspective for adopting this software.