FAQ

This is the list of frequently asked questions for FElt 

last modified: 07-16-95 

 1. What is FElt? 
      What kinds of problems can FElt solve? 
      Can FElt solve my type of problem? 
      Can I modify FElt to make it solve my type of problem? 
      On that same note, can I add new kinds of elements? 
 2. Where can I get FElt? 
 3. What machines does FElt run on? 
      Is there a Windows interface to FElt? 
      What about a Motif or OpenLook interface? 
      Can I compile FElt using X11R4 (R3 ...) ? 
      Where can I get gzip to unpack the tar files on cs.ucsd.edu? 
 4. I think I found a bug, what now? 
 5. Is there a newsgroup or mailing list for FElt? 
      What kind of things should I post to the mailing list and what kinds of
      things should I contact the authors for? 
 6. Why do the FElt components have such stupid names? 

 1. What is FElt?

   FElt is a free system for introductory level finite element analysis. It is
   primarily intended as a teaching tool for introductory type courses in finite
   elements - probably in the mechanical/structural/civil fields. In a command
   line environment, FElt uses an intuitive, straightforward input syntax to
   describe problems. It also includes a graphical user interface for
   workstations that allows the user to set-up, solve and post-process the
   problem in a single CAD-like environment. 

   From the end-user point of view, FElt consists of six programs: felt, burlap,
   velvet, corduroy, patchwork, and yardstick. felt is the basic command-line
   application; burlap is an interactive Matlab-like environment for scripting
   your own elements and analyses; velvet is the primary GUI interface into the
   bulk of the functionality in FElt; corduroy is command-line program for
   automatic element generation; patchwork is a command-line application for
   file format conversion to and from the FElt syntax; and yardstick is a simple
   program for problem scaling and unit conversion. 

   Felt is the simplest - it takes a FElt input file and spits back appropriate
   ASCII based (tabular or ASCII graphics) results depending on the problem
   type. The command line application felt is the only interface of the three
   analysis engines (felt, velvet, burlap) that is available under DOS. 

   Velvet is the most powerful interface into the pre-programmed functionality
   of FElt - it allows for complete graphical problem definition through
   pulldown menus, popup dialog boxes and an interactive drawing area. It
   offers all of the capabilities of both felt and corduroy and has several options
   for post-processing, including color stress plots for planar elements, plots of
   the displaced structure, animation, graphical time-displacement plots for
   transient analysis problems, graphical frequency domain plots of transfer
   functions and output spectra for spectral analysis, and graphical plots of
   mode shapes for modal analysis problems. 

   Burlap is the most powerful interface in terms of raw FE computing power
   simply because you can make it perform analyses that are not otherwise
   available in FElt simply by scripting your own analyses algorithms in burlap's
   powerful Matlab-like syntax. You can also use burlap to try out new element
   definitions quickly and easily or to manipulate the results from one of FElt's
   pre-programmed analyses in a novel way that is otherwise not provided for. 

      What kinds of problems can FElt solve?

      As distributed, FElt can solve the classic problems in linear statics and
      linear dynamics for both structural and thermal mechanics (i.e.,
      problems of the form Kd = F, Md'' + Cd' + Kd = F , or Md' + Kd = F).
      It can also solve the generalized eigenvalue problem (K - lM)x = 0
      and use this information in modal analysis. It can do spectral
      (frequency domain) analysis of transient structural problems. The
      element library consists of truss, beam (Timoshenko and Euler),
      constant strain triangular, bilinear planar isoparametric, plate bending
      (selective reduced integration quadrilateral), isoparametric solid (eight
      node brick) elements, and rod and constant temperature gradient
      thermal elements. 

      Can FElt solve my type of problem?

      Unless it fits into one of the classes above there are no built-in solvers
      for your type of problem. You may be able to use burlap to write your
      own solver though. 

      Can I modify FElt to make it solve my type of problem?

      Probably, and we'd be happy to help. The only reason FElt cannot do
      more right from the start is partly because we don't have time and
      partly because it is very hard to keep everything simple,
      straightforward and intuitive if we support every different type of
      analysis and algorithm - especially because beyond the basics there
      are so many different possibilities. What may interest one person on
      the serious research level is probably not going to interest the majority
      of other users. 

      FElt does offer a lot of basic support that would be useful in a broad
      class of finite element programs. If you do want to add your own
      analysis algorithms, the best place to start is to probably look at the
      source code for the felt driver program (bin/Felt/felt.c) and see how it
      handles switching between static, dynamic and modal analyses. Then
      take a look at the routines for static (lib/Felt/fe.c), dynamic
      (lib/Felt/transient.c), modal (lib/Felt/modal.c), and spectral
      (lib/Felt/spectral.c) problems to see how the different types of
      algorithms make use of the data structures and general routines to
      actually go about getting a solution. 

      Finally, we want people to know that our major motivation for
      creating burlap were questions just like this. With burlap you now
      have two options for performing analyses that don't already exist -
      you can modify and add to the FElt source as outlined above or you
      can script your algorithm in burlap. The latter is probably much easier
      and we encourage people to try it out. If we do end up with a lot of
      neat analyses scripted into burlap then perhaps we can start putting
      together a library of this functionality for general distribution. That
      kind of growth in functionality sounds a lot nicer to us because it would
      be a lot easier to maintain and distribute. 

      On that same note, can I add new kinds of elements?

      Absolutely, there's even a whole chapter in the user's manual devoted
      to this very topic. We'd be very interested if you did add a new
      element because we'd like to start putting a user contributed element
      library together for distribution with with regular sources. 

      Also, just like you can add your own new analyses through burlap,
      keep in mind that you can script new elements in burlap as well. This
      is a potentially much easier way to go about it. Whichever way you
      choose to go about it, let us know what you come up with - we'd like
      to hear whatever success (or horror) stories people might have. 

 2. Where can I get FElt?

   The latest version of FElt, in all its incarnations, is always available via
   anonymous ftp from cs.ucsd.edu. Once you have ftp'd to cs.ucsd.edu login as
   anonymous and give your email address as the password. cd to /pub/felt and
   grab whatever files you need for your particular situation. As of this update,
   the latest version is v3.00. Information (and hypertext access to the ftp site)
   is available via World Wide Web (e.g., Mosaic) at 

   http://www-cse.ucsd.edu/users/atkinson/FElt/felt.html 

   if you want to take a more serious look at some of FElt's capabilities before
   you actually take it for a test drive on your machine. 

 3. What machines does FElt run on?

   The complete version of FElt (including the X11 based graphical user
   interfaces) has compiled and tested on HPs, DECs, Suns, SGIs, 386/486s
   running Linux and SysV R3, and IBM workstations. It should do the same on
   any reasonable Unix system with X11R5 or R6. In general we provide
   binaries for Sparc stations running SunOS or Solaris and 386s with Linux, but
   there is no guarantee that the binaries are as up to date as the source code.
   When in doubt just grab the source code and build it yourself - really, it's
   easy. 

   DOS executables are available for the command-line applications felt,
   corduroy, yardstick, and patchwork. A simple graphical application, feltvu is
   also available. You need to have at least a 386 to use the DOS versions. 

      Is there a Windows interface to FElt?

      Not yet, and we're probably not the folks to write it as neither of us
      have much experience with Windows programming. If someone else
      would like to volunteer then I'd suggest starting with something like
      xfelt as it's really pretty simple. There may be people working on this
      - let us know if you're thinking about something like it and we'll try
      our best to make sure that people don't duplicate a lot of effort. 

      What about a Motif or OpenLook interface?

      Well we originally chose to work with the Athena widgets because
      the price is right and because they allow us to maintain FElt as a 100%
      free product. With the current set-up anyone (in theory at least) can
      get and build everything they need to get FElt up and running free. If
      we had worked in Motif then we at least would have had to shell out
      for Motif for Linux and people without Motif simply would be out of
      luck unless they happened to be working on one of the few machines
      that we could provide statically linked binaries for. We also recognize
      that we could maintain separate GUI interfaces, but we feel that our
      development time is better spent on functionality rather than on
      constantly keeping two or more separate interfaces up to date. In
      addition, it's our feeling that Motif or OpenLook or any other widget
      set would not offer us any significant additional capabilities that we
      haven't already worked out with the Athena widgets. 

      However, if you just want a slightly different look and feel than the
      stylized default look of velvet then please feel free to change it - that's
      what Xresources are for after all. The easiest way to get a slightly
      more Motif look (not really the feel though) is to switch to the 3d
      Athena widgets. I know that these are readily available as compiled
      libraries for Linux and should be for some other machines as well;
      they're also really easy to build yourself if you are so inclined. Once
      you have them all you have to do is swap them for your regular
      Athena shared library (or re-link if you don't use shared libs); the
      next time you run velvet everything should be 3d. There are some
      recommended changes to the app defaults for velvet if you do decide
      to go this route, they're at the bottom of Velvet.ad in src/Velvet. 

      Can I compile FElt using X11R4 (R3 ...)?

      Not really - you really should have X11R5 or R6. Compiled libraries
      should be available for most machines. If not, source code for the
      X11R5 distribution is available via anonymous ftp from ftp.x.org and
      pre- compiled libraries should be available from many places on the
      net. Now that X11R6 is available you should be able to use that just as
      well as R5. 

      If you really want to do it with X11R4, then you can try the following:
      from ftp.x.org get three header files from the untarred R5 or R6
      sources - Xfuncs.h, Xfuncproto.h, Xosdefs.h. Make a directory
      FElt-x.xx/inc/X11 and copy these three files into it. Then just do a
      regular make as described in the INSTALL file. See the notes on
      SGIs in the INSTALL file if you need a few more details. 

      Where can I get gzip to unpack the tar files on cs.ucsd.edu?

      Source code is available from prep.ai.mit.edu. Binaries for a wide
      variety of machines should also be available from various archives on
      the net. Building gnu binaries from source is really easy, just untar
      them, cd into the directory into which they unpacked, type configure
      and then type make. 

 4. I think I found a bug, what now?

   Send one of us email (jgobat@mit.edu or atkinson@ucsd.edu). Please,
   please, please, include as much information as possible in your report. Things
   that are absolutely essential: 
      version of FElt that you are using 
      the application that you think the bug is in (felt, velvet, everything,
      etc.), this is particularly helpful if the bug only shows up in velvet but
      not in felt (or the reverse) 
      type of machine and operating system (including the OS version) that
      you are using 
      if you are using a pre-built binary or if you are using a binary that you
      built yourself; if you built the binary, how did you build it (gcc, native
      cc, etc.) 
      and of course a detailed description of what went wrong and what you
      were doing when it went wrong. If possible send us the input file that
      causes the problem, if you can't do that then tell us what kind of
      analysis you are doing and any other relevant details specific to your
      problem. 

 5. Is there a newsgroup or mailing list for FElt?

   There is a mailing list. To subscribe to the list send a one line email message
   that says 

   subscribe felt-l 

   to listserv@mecheng.asme.org. To send a message to the list just send it like
   regular email to felt-l@mecheng.asme.org. Incremental release
   announcements and bug fixes will be posted to the mailing list. Major release
   announcements will be made to the following newsgroups:
   comp.os.linux.announce, sci.math.num-analysis, sci.engr, sci.engr.civil, and
   sci.engr.mechanical. So if you really want to keep up on new versions and
   capabilities, you should subscribe to the mailing list. 

      What kind of things should I post to the mailing list and what
      kinds of things should I contact the authors for?

      The list is generally for announcements, bug fixes, and questions that
      several FElt users might have an interest in (i.e., I'm trying to make
      FElt solve a problem like xxx, how have other people modeled this? or
      I really think that velvet should be able to do xxx, what does everyone
      else think?). We'd also like it to be a forum for discussion of what
      types of things people would like to see in FElt. 

      For bug reports that you think are specific to your machine or things
      that other users probably don't have an interest in, feel free to send
      email to one of us: jgobat@mit.edu or atkinson@ucsd.edu. See the 
      question on bugs for details on how to submit a bug report. 

 6. Why do the FElt components have such stupid names?

   Well, FElt is obvious, right? Finite ELemenT. felt the application came first -
   it's the most basic interface into the system. Now when it comes to fabrics,
   everybody knows that velvet is smoother than felt ... thus the slickest GUI
   interface is called velvet. xfelt is simply xfelt because it is nothing more than
   an encapsulator, with no real functionality beyond that provided by felt. 

   After this, we start to stretch because with the felt - velvet connection we
   have this fabric motif to keep up on. 

   - Burlap is rough but functional, just like its namesake fabric. It may not be
   as easy to use as velvet (or maybe it is if you like scripting in Matlab-like
   mathematical languages) but you can do an awful lot with it. 

   - Corduroy has that regular ripple effect so its sort of like a mesh ... 

   - Patchwork, well we figured that was better than convert simply to avoid
   conflicts. How many systems have some local app called convert to do
   whatever, or how many little hacks are there called convert. It seemed
   common enough to us that we figured we might as well call it something
   different. Patchwork implies a lot of different fabrics coming together so it
   seemed as good as anything else. 

   - A yardstick is used to measure fabric ... measuring implies some sort of
   units.