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anb - anb is not best (README for the free lattice Boltzmann code 'anb')

Purpose

Starting with lattice gas/Boltzmann in 1992, I found it really hard to write a working code from the scratch only by the help of some papers. Now, years later, I find it really hard to show newcomers to our group the principles of lattice Boltzmann coding by the help of our large and complicated code BEST, which has been optimized for vector-parallel computers.

This is the reason, why I have written a rhichly documented self explaining lattice Boltzmann code, where I tried to make everything as clear and simple as possible. The code is called anb, what simply means anb is not best.

I hope, anb could be used for learning and teaching. It could and should not be used for 'real' computations, esp. not for time- and memory consuming runs on big (and expensive) machines ! Nearly every routine in anb could be coded more efficient, less memory consuming ... and less clear.

The source code for 'anb' is distributed under the terms of the GNU General Public License.

Code

anb is written is FORTRAN 77, and has been tested on various platforms (SUN, HP, SGI, Linux-PC, Fujitsu VPP, Cray T-90, NEC SX 4/5). It contains of the source code itself anb.f, one configuration file anb.par and one obstacle file anb.obs, which represents the geometry information of the flow domain. You can have a look at the source here !

Usage

Of course, you can just type f77 anb.f (or what ever the FORTRAN 77 compiler is called on your system ...) and then run the executable. You will see some messages written to stdout and - in the end - find some new files on your hard disk which are the results of the computation. If you have some visualization tool for post processing (like TECPLOT, for this you can get a temporarily free license at http://www.genias-graphics.de/) you can have a look at the flow you just simulated by the help of anb. Maybe you should do this, to see if everything works ... But then, you should do, what the code has been written for: read and try to understand the source of anb.f

anb-package

The package contains:

• anb.f: The source code in FORTRAN 77.
• anb.par: The configuration file for anb.
• anb.obs: The geometry information file.
• readme.htm This text.
• COPYING: The GNU General Public License.

You can dwonload the "zip"-package here: http://www.bernsdorf.org/research/anb.zip

The configuration files

• anb.par: The configuration file for anb. Example: 3000
0.1
0.005
1.85
10 Meaning:
  1. line: 3000 - number of iterations
  2. line: 0.1 - density per link
  3. line: 0.005 - acceleration
  4. line: 1.85 - relaxation parameter
  5. line: 10 - dimension for Reynolds number Have a look at the subroutine read_parameters in anb.f for more details !
• anb.obs: The geometry information file for anb. Example: 1 1
2 1
3 1 Meaning:
  x- and y-coordinates of occupied nodes are listed here, one line for each node. The order does not matter. Also the wall boundary nodes have to be defined in this way ! Have a look at the subroutine read_obstacles in anb.f for more details !

The result files

• anb_qx.out: The average velocity of the simulated flow. A good control if the simulated flow reached steady state is to monitor the average flow velocity at a certain cross section of the computational domain as function of time (iterations). You can watch this file for example with the free software xmgr. Example output: 26 1.7849222047450D-04
27 2.4511573992305D-04
28 3.1222702284171D-04
...
2999 3.2984900438651D-03
3000 3.2985335497016D-03
3001 3.2985335497016D-03 Meaning:
  The column is the iteration number, the second one the computed flow velocity.
• anb.dat: The results of the computation. Here, the velocity components, the local pressure and the obstacle information are stored. A header for the post processing tool TECPLOT is also written. If you have some other post processing tool, you should change the necessary things in anb's subroutine datout. Otherwise, it might be a good idea to get a free evaluation license for TECPLOT. Example output: VARIABLES = X, Y, VX, VY, PRESS, OBST
ZONE I= 30, J= 20, F=POINT
1 1 0. 0. 3.3333333333333D-02 1
2 1 0. 0. 3.3333333333333D-02 1
3 1 0. 0. 3.3333333333333D-02 1
4 1 0. 0. 3.3333333333333D-02 1
...
4 11 3.2778327874759D-03 2.4387587283551D-04 3.3355060665745D-02 0
5 11 2.7312371998704D-03 3.1218767491485D-04 3.3355269776544D-02 0
6 11 2.0203030622604D-03 3.6169210828650D-04 3.3357471944278D-02 0
... Meaning: Each line in the file anb.dat stands for one lattice node. The x- and y-coordinate of the node is stored in the first two columns, followed by the x- and y-component of the velocity, the local pressure and the information, if the considered node is occupied by an obstacle (1) or a fluid node (0).