What is SLFCFD?

SLFCFD stands for San Le's Free Computational Fluid Dynamics. It is a package of scientific software and graphical user interfaces for use in computational fluid dynamics. It is written in ANSI C by San Le and distributed under the terms of the GNU license.

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Like SLFFEA, you're keeping your name in the acronym. Sad.

Yeah, well. It's called name branding. Those of you who are bothered by this can think of it as SeLF-CFD as in Do-It-YourSeLF-CFD. Anyway, that's not really a question.

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What do I need to run SLFCFD?

To compile from source, you need GNU/Linux or some form of Unix.

Extraction tool, like tar xzvfp.
C compiler(you should know where your cc or gcc is located so you can define the CC macro in the makefiles. Just do a:
which gcc
or
which acc
and then put the path in the Makefile. For instance, when I do a "which gcc", I get:
/usr/bin/gcc
which is how my CC is currently defined.
Mesa-3.0 (OpenGL for the PC) or higher or Open GL. If you install it, you should put it in your /usr/local/ directory.

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What is SS-GUI?

SS-GUI stands for Self-Scaling GUI. If you resize the GUI window, all the text inside will rescale itself such that the text and color scale boxes maintain their proportions with the window, and it will also work the same as before. This is possible because the GUI is built on OpenGL rather than some packaged window manager.

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What is the P-Winston Motion Engine?

The P-Winston Motion Engine is about 300 lines of code written by Philip Winston which he has graciously and generously allowed me to use and modify for the GUI part of SLFCFD. The P-Winston enables you to use the mouse to rotate and translate the mesh, especially to refine rotations and translations done through hot keys or the GUI. It works like a trackball, but keeps the different types of motion separate. For example, holding down the left button and moving the mouse up and down will produce translation in Z. Moving it left and right with this same button held down will rotate it on the Z axis. The middle button controls translation in X and Y, and the right button, rotation in X and Y. While this seems more complex than a typical trackball, it has the advantage of isolating the movements for fine tuning of the position at which you want to view the object. Also, the P-Winston has much less computational overhead than a Mesa trackball.

Note that you have to have the Mesh Window active to have mouse control.

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What are your qualifications to write CFD code?

I claim no qualifications to write CFD code. Like all GNU software, you are using it at your own risk. That said, here is a bit of my academic history which you may use to judge my qualifications:

Academic History

Note that I'm not a PE and I have never taken the PE exam.

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What motivated you to write this?

I elaborate more on the page for SLFFEA, so I'll just say here that I enjoy working within the Free Software/Open Source Community and contributing my skills to it with these codes.

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There are so many free CFD codes. Why write another one?

In my survey of other codes like Gerris , Featflow , and OpenFoam I felt that SLFCFD could offer some things they lacked. First, I will say that I think the science of all these codes are much more sophisticated than SLFCFD, and you would do very well to download them yourself if you need a lot of functionality and are solving a very complex system. But here are the reasons to use SLFCFD:
1. The only real dependency SLFCFD has is Mesa which comes standard on most GNU/Linux, other Unices, and MS Windows distributions. For the other Free Codes that include graphics which I have tried out, there are often other packages which need to be installed. Sometimes, they even need very specific versions of the library, and all this makes installation a challenge. I hope that my code is standard enough that this isn't true about SLFCFD.
2. My control panel is built with Mesa, so there is no additional windowing library you need like GTK, Motif, QT, or Microsoft's Visual C++ API.
3. As related to the two points above, SLFCFD should be truly cross platform for all Unices, Microsoft Windows, and Apple OSX. This has been true of SLFFEA, which I have ported to/seen others port to the BSDs, Beos, OSX, Irix, and MS Windows(compiled with MS Visual C++ or under CYGWIN ) etc.
4. I break the code down between graphics and scientific. So if you only want to deal with the numerics, you can just focus on that.
5. Input and output data/graphics data have the same format. So it is possible to easily continue a calculation if more time steps are desired.
6. SLFCFD is, I hope, less resource intensive compared to others. Like SLFFEA, I develop on a Pentium II 233 MHz with 256 MB RAM + 128 MB swap.
7. Currently, the code is fairly simple so if your needs are limited, hacking SLFCFD might be less of a challenge than going through the other codes.
8. I am writing this also for my own edification and to take a break from FEA. There is also a possibility that I will do computations in the future requiring the merging of solid and fluid mechanics. I can customize SLFCFD and SLFFEA in preparation for that.
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Can you talk a little about the other codes you surveyed?
1. Gerris - This is an excellent code for incompressible fluids. It can handle both 2-D and 3-D meshes. It has a nice GUI and will make a video of the flow as it evolves over time. It does adaptive mesh refinement and has a multigrid solver. Also, calculations can be done independently of the graphics. One downside is that it requires a few other packages to compile.
2. Featflow - I have only installed the scientific part, but there is a graphics part as well. This code uses the finite element method to calculate incompressible 2-D and 3-D flows. It runs very well and has a nice mesh generator. If I add FEA to SLFCFD, I would like to base it on their solver. The few downsides of the code are that they are not clear about what Open Source License they are using, and this scientific part is written in Fortran. Here are some images of the work I have done with Featflow .
3. OpenFoam - I've downloaded OpenFoam, but have not installed it. Because it used to be a proprietary commercial code, I think it would be a very fully featured code. The reasons I have not installed it are that it has several dependencies which I currently don't want to install or update on my machine. They include, gcc-4.0.1, ParaView , and an implementation of Java. The sourcecode download is very big with the tarball 67 MB in size.
4. ParaView - ParaView is like OpenDX , a very powerful general graphics utility. It requires Tlc/Tk to run. It looks like it has very permissive redistribution terms, like the BSD license. The download is very big, about 44 MB.
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FEA can be applied to CFD. Will SLFCFD only include non-FEA methods leaving it for SLFFEA?
I don't think this will be the case. It was at University where I began to associate FEA with solid mechanics and finite difference/finite volume methods with fluid mechanics. While I have not seen non-FEA methods used in solid mechanics, I certainly have seen FEA applied to nearly every branch of computational physics. Because of the advantages of FEA(non-structured grids, arbitrary boundaries), I would like to use it as the core method of any other code I write including CFD.

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How do you install Mesa?

For recent versions of GNU/Linux, you may not have to. (Mesa comes pre-installed on Slackware 7.1). All you need to do is add the following softlink:

   cd /usr/include/
   ln -s /usr/X11R6/include/GL/ GL

if it doesn't already exist.

If you would rather compile using the latest release of Mesa, you can do the following. From Section 16.0.0 of my GNU/Linux Installation Guide:

16.0.0 Installing Mesa(the OpenGL graphics library):


   16.1.0  For  recent  versions  of  GNU/Linux(like  Slack-
           ware-7.1), Mesa comes pre-installed.  All you need to do is  add  the
           following softlink:

                 cd /usr/include/
                 ln -s /usr/X11R6/include/GL/ GL

           if it doesn't already exist.

           There  are several places where you can get Mesa.  You can get it off
           the web at:

                 http://sourceforge.net/project/showfiles.php?group_id=3

   16.1.1  For  recent  versions  of RedHat you need to add the glut libraries
           from the RPMs on the installation disk(For RedHat 8.0, it is on the
           3rd disk, for RedHat 9.0, it is on the 2nd disk):

                 cd /mnt/cdrom/RedHat/RPMS
                 rpm -Uhv  glut-3.7-12.i386.rpm
                 rpm -Uhv  glut-devel-3.7-12.i386.rpm

   16.2.0  After getting the  tarfiles,  copy  them  to  the
           directory /usr/local/ and do:


                 tar xzvfp MesaLib*.gz
                 tar xzvfp MesaDemos*.gz


   16.3.0  Compiling Mesa Programs


        16.3.1 From the /Mesa-3.4.2/README:


                    To  compile  the library, first type 'make' alone to see the
                    list of system configurations currently supported.   If  you
                    see  your  configuration  on the list, type 'make '.
                    Most popular Unix/X workstations are currently supported.

               For my machine, I use:

                    make linux


        16.3.2 Header Files and Libraries

               From the /Mesa-3.4.2/docs/INSTALL:


                    Header and library files:
                       After you've compiled Mesa and tried the demos I recommend the following
                       procedure for "installing" Mesa.

                       Copy the Mesa include/GL directory to /usr/local/include:


                     mkdir /usr/local/include/GL
                     cp -r include/GL/* /usr/local/include/GL/


                       Copy the Mesa library files to /usr/local/lib:


                        cp -d lib/* /usr/local/lib



                            (actually, use "cp -d" on Linux to preserve symbolic
                    links)


        16.3.3 Install Widgets-Mesa Library

               You also need to install the Widgets-Mesa Library.  First:

                     cd  /usr/local/Mesa-3.4.2/widgets-mesa/

               The file /usr/local/Mesa-3.4.2/widgets-mesa/INSTALL tells you to:

                        ./configure
                        make
                        make demo.gl
                        make demo.mesa
                        make demo.ws
                        make demo.tea
                        make install

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Why am I getting the error GL/glut.h: No such file or directory?

Because Mesa is pretty standard on most GNU/Linux distributions, I think you are only lacking the glut libraries(and possibly some other include files) which usually aren't installed unless you install everything including development tools for Linux. I recommend that you check to see that the glut libraries are in:
```
   /usr/X11R6/lib
```
and that there is a directory:
```
   /usr/include/GL
```
containing all the necessary Mesa and glut files. See the next question for more information.

Sometimes, Redhat and Fedora have glut and glut development RPMs on their installation disk in the /RedHat/RPMS directories. You may have to look around to find it. For now, I will repeat what I say above:
```
   To install the glut libraries from the RPMs on the installation disk(For RedHat 8.0, it is on the
   3rd disk, for RedHat 9.0, it is on the 2nd disk):

         cd /mnt/cdrom/RedHat/RPMS
         rpm -Uhv  glut-3.7-12.i386.rpm
         rpm -Uhv  glut-devel-3.7-12.i386.rpm
```
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What does your /usr/X11R6/lib and /usr/local/include/GL look like?

After updating to Mesa-3.2.1,(Mesa-3.0 should still work), doing an ls -l in /usr/X11R6/lib gives:

-rw-r--r--  1 root root 678504 2005-01-23 20:45 libGL.a
lrwxrwxrwx  1 root root     12 2005-05-31 07:32 libGL.so -> libGL.so.1.2
lrwxrwxrwx  1 root root     12 2005-05-31 07:32 libGL.so.1 -> libGL.so.1.2
-rwxr-xr-x  1 root root 608015 2005-01-23 20:53 libGL.so.1.2
-rw-r--r--  1 root root 659352 2005-01-23 20:45 libGLU.a
lrwxrwxrwx  1 root root     13 2005-05-31 07:32 libGLU.so -> libGLU.so.1.3
lrwxrwxrwx  1 root root     13 2005-05-31 07:32 libGLU.so.1 -> libGLU.so.1.3
-rwxr-xr-x  1 root root 563990 2005-01-23 20:53 libGLU.so.1.3
-rw-r--r--  1 root root  27902 2005-01-23 20:45 libGLw.a
lrwxrwxrwx  1 root root     13 2005-05-31 07:32 libGLw.so -> libGLw.so.1.0
lrwxrwxrwx  1 root root     13 2005-05-31 07:32 libGLw.so.1 -> libGLw.so.1.0
-rwxr-xr-x  1 root root  26550 2005-01-23 20:53 libGLw.so.1.0
lrwxrwxrwx  1 root root     12 2005-05-31 07:22 libglut.so -> libglut.so.3
lrwxrwxrwx  1 root root     14 2005-05-31 07:22 libglut.so.3 -> libglut.so.3.7
-rwxr-xr-x  1 root root 215332 2003-08-20 14:24 libglut.so.3.7

and doing an ls -l in /usr/include/GL gives:

-r--r--r--  1 root root   7946 2005-01-23 20:45 GLwDrawA.h
-r--r--r--  1 root root   4433 2005-01-23 20:45 GLwDrawAP.h
-r--r--r--  1 root root   2309 2005-01-23 20:45 GLwMDrawA.h
-r--r--r--  1 root root   2311 2005-01-23 20:45 GLwMDrawAP.h
-r--r--r--  1 root root  89951 2005-01-23 20:44 gl.h
-r--r--r--  1 root root 306424 2005-01-23 20:44 glext.h
-r--r--r--  1 root root  15981 2005-01-23 20:44 glu.h
-r--r--r--  1 root root   9016 2005-01-23 20:44 glx.h
-r--r--r--  1 root root  29020 2005-01-23 20:44 glxext.h
-r--r--r--  1 root root   4257 2005-01-23 20:44 glxint.h
-r--r--r--  1 root root   2453 2005-01-23 20:44 glxmd.h
-r--r--r--  1 root root  71034 2005-01-23 20:44 glxproto.h
-r--r--r--  1 root root   8878 2005-01-23 20:44 glxtokens.h
-r--r--r--  1 root root   8349 2005-01-23 20:44 osmesa.h
-rw-r--r--  1 root root  20844 1998-08-07 17:18 glut.h
-rw-r--r--  1 root root   5150 1998-08-07 17:18 glsmap.h
-rw-r--r--  1 root root   7273 1998-08-07 17:18 fglu.h
-rw-r--r--  1 root root  10152 1998-08-07 17:18 fglut.h
-rw-r--r--  1 root root  60468 1998-08-07 17:18 fgl.h

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Does SLFCFD include mesh generators?

There are a few generators for specific meshes like the jet, bubble, and shock tube problems. Currently, SLFCFD is only for uniform, structured, finite difference meshes, so there's little advantage having a mesh generator at this point. If you download SLFCFD and look at the data you will see what I mean. Basically, the data is given in terms of i, j, k indices which also act as nodal coordinates. So i represents x , and i = 0 would be like the boundary at x = 0 . Associated with each nodal point are quantities such as pressure, temperature, density, etc. I think the data is highly understandable, but tedious to generate. For very big meshes, you will likely have to write a little program like the ones I have made. Also, the meshes tend to be rectangular at this point.

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What units does SLFCFD use?

For units, just be consistent. If using inches and lbs, then you would use psi for pressure. If meters and Newtons, then Pascals. So you can use any system of units you want.

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Why do I get "command not found" when I try the text executables in the data directories?

This is a common issue with Unices. For the incompressible flow, instead of just "qik", type in:
```
   ./qik
```
which means execute the code "qik" in your current directory. You can also add:
```
   export PATH=$PATH:.
```
or
```
   export LD_LIBRARY_PATH=.
```
in your ".bashrc" or ".bash_profile" (or whatever your Unix uses) to avoid having to type "./" before every executable. The reason this is not automatically done in Unix is for security reasons, so you may want to think about adding "." to your path.

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I'll add more Questions and Answers as they come.

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