NASTRAN-95 vs MYSTRAN

[borges]

Based on my previous work with NASTRAN-95, I'd like to bring forward some information you might find useful in some way to keep this comparison correct and up-to-date.

Regarding NASTRAN-95's capabilities:

• NASTRAN-95 cannot allocate more than 14 million words (56 MB) to its open core. Any value of OCMEM above 14000000 will cause a fatal error to be issued.
  That makes it unable to load larger models, and limits the in-memory database size for medium-sized models, therefore hurting performance.
  
• Said limitation indeed makes the solver outdated by today's CPU architectures standards. IBM and COSMIC got it to alloc up to 2 GiB to itself, but that's still not enough for large models with a workable DBMEM... and they never relased the code for that AFAIK.
  
• It does, however, have a PSHELL card, but it works differently. Modern NASTRANs (e.g. Autodesk, Simcenter, MSC) use PSHELL for all "shell" elements, like QUAD4 and TRIA3, whereas NASTRAN-95's PSHELL can only be referenced by CQUAD4 cards.
  
• NASTRAN-95 does not have a CTRIA3 card. The closest you can get is CTRIA2, or maybe use a CTRSHL (similar to CTRIA6) with points 2-4-6 being merely the midpoints between 1-3-5 respectively. And you'd still have to change the PSHELL referenced by the CTRIA3 card into a PTRIA2/PTRSHL and, in the latter case, add three extra grid points.
  
• Due to string-size and encoding limitations, file names that contain special characters, spaces, or are too long (by 80s' standards) will cause crashes or otherwise weird behavior. You're forced to keep file paths mostly alphanumeric and short.
  
• Several undocumented error codes. Encountering error N but seeing the manual skip from error #(N-1) to #(N+1) is not uncommon.
  
• No BAILOUT parameter -- singularities force exits at NASTRAN's discretion.
  
• No BEAM element. Best you can do is convert to CBAR+PBAR and discard intermediate stations.
  
• AUTOSPC behaves differently from proprietary NASTRANs' in some warning/edge cases, leading to singularities.
  
• Less leniency on bulk data card format requires manual intervention/editing before running models generated by modern (proprietary) CAD/CAE applications.
  
• The top "Nastran" cards generated by said applications are completely incompatible. You will have to manually rewrite or comment them to have any hope of getting the model to even load.
  

Regarding compiling and using NASTRAN-95 in newer platforms:

• NASTRAN-95 actually can be compiled using open-source tools. There's a even a small toolset to compile, test and invoke it. I managed to get it running under x86_64, both Linux and Windows, and even cross-compile from Linux to Windows.
  Some devs have released compiled binaries for both platforms, but I never tried them -- I'm more comfortable building my own.
  
• These tools, however, are not perfect, nor do they work out-of-the-box; actually compiling the thing may require some developer intervention.
  
• In fact, all attempts to compile it with gfortran (gcc) versions other than 7 have produced nonworking binaries, and no one knows if it's a gfortran/libgfortran bug or some quirk/undefined behavior in the legacy F77 code.
  With ABI changes and more distros dropping support/packages for gcc-7, it's going to get harder and harder to compile NASTRAN-95 for modern targets, especially Windows.
  
• Invoking it is an absolute mess. Most options are passed through environment variables, so you will need a helper program to set up bootstrapping shell scripts.
  

In the interest of simplicity, I'd condense this information further into the following points:

• NASTRAN-95 has an open core memory hard limit of 56 MB
  
• NASTRAN-95 lacks support for BEAM and TRIA3 elements, and many others
  
• NASTRAN-95 has a different behavior for PSHELL cards
  
• NASTRAN-95 can be compiled for modern platforms using open-source tools... but it's a complex process, and may break in the near future
  
• NASTRAN-95 can be invoked in modern platforms, but you'll need a helper program due to the way it takes parameters
  
• NASTRAN-95 lacks or has different behaviors for many parameters
  
• NASTRAN-95 crashes on long file paths or special characters (and less leniency when parsing input in general)
  
• NASTRAN-95 has outdated behavior for the Nastran top card
  
• NASTRAN-95 has poorly or non-documented error codes (and hard-to-find documentation in general)
  

I hope this information can be useful and/or make this comparison richer.