“Alternative are / Conspicuously absent”, I concluded here, after outlining how to use HyperMesh to model enforced-motion for Nastran. I’ve since spent some time with Patran, and am modifying that conclusion a bit. Here’s the current mantra:
“GUI Alternatives are / Conspicuously absent / The best alternative is / Notepad++”
I think this is pretty much true of every CAE pro-processor on the market. For instance, I have spent a fair amount of time outlining Abaqus’ INP files in this Abaqus Workbook. I like Abaqus/CAE more than any other pre-processor I’ve used, but comes a time. I have a theory on why this is so, but that’s for later. For now, I’ll outline my way to setup and solve a transient problem using Nastran – using a text-editor to do the stuff that’s so hard for a GUI.
I’ll stay with enforced excitation for consistency with the earlier GUI-based description: the advantage of editing the text input file is stark. I think you’ll agree – it’s hard not to, once you’ve got the hang of it.
Note that this is only for direct-integration solutions of transient problems. That is, when the excitation is prescribed in the time domain and the period of interest is small. There are lots of other areas which are baffling, but one brick at a time.
The problem with using a GUI is that the solver’s terminology is bizarre. Why on earth should the same keyword be usable both in the case-control section and in the bulk-data section? Why on earth should the same “id” be usable across different items? Why …
The approach outlined uses these Nastran keywords: SPC (Case control), DLOAD (Case control), TSTEP (Case control), SPC1 (Bulk), SPCD (Bulk), TLOAD1 (Bulk), TABLED1 (Bulk), TSTEP (Bulk), PARAM/G and PARAM/W3.
You can look them up in the Quick-Reference Guide. (Can’t readily access your copy? MSC seems to have posted its manuals on the web – or the pirates have started masquerading as MSC.)
The article also shows why you should always setup a small problem first, to check your solution approach. There’s no other way to guard against keywords being interpreted the wrong way.
I’ve posted the article as a PDF – read it here.
Why not just insert the prose here? Because there’re quite a few figures, and I’ve used some fancy annotation that’s easier with a word-processor than with WordPress.
I thought of posting the Nastran data files (DBFs) but figured there’s not much point in doing so. You can copy the text from the PDF and paste them in your text-editor, can’t you? Let me know if you have trouble with that.