This section is concerned primarily with successful running of OpenFOAM
jobs and extends on the basic execution of solvers described in 3.3. When a solver
is executed, it reports the status of equation solution to standard output, i.e. the
screen, if the level debug switch is set to 1 or 2 (default) in DebugSwitches in the
$WM_PROJECT_DIR/etc/controlDict file. An example from the beginning of the
solution of the cavity tutorial is shown below where it can be seen that, for each
equation that is solved, a report line is written with the solver name,
the variable that is solved, its initial and final residuals and number of
iterations.
Starting time loop
Time = 0.005
Max Courant Number = 0 BICCG: Solving for Ux, Initial residual = 1, Final residual = 2.96338e-06, No Iterations 8 ICCG: Solving for p, Initial residual = 1, Final residual = 4.9336e-07, No Iterations 35 time step continuity errors : sum local = 3.29376e-09, global = -6.41065e-20, cumulative = -6.41065e-20 ICCG: Solving for p, Initial residual = 0.47484, Final residual = 5.41068e-07, No Iterations 34 time step continuity errors : sum local = 6.60947e-09, global = -6.22619e-19, cumulative = -6.86725e-19 ExecutionTime = 0.14 s
Time = 0.01
Max Courant Number = 0.585722 BICCG: Solving for Ux, Initial residual = 0.148584, Final residual = 7.15711e-06, No Iterations 6 BICCG: Solving for Uy, Initial residual = 0.256618, Final residual = 8.94127e-06, No Iterations 6 ICCG: Solving for p, Initial residual = 0.37146, Final residual = 6.67464e-07, No Iterations 33 time step continuity errors : sum local = 6.34431e-09, global = 1.20603e-19, cumulative = -5.66122e-19 ICCG: Solving for p, Initial residual = 0.271556, Final residual = 3.69316e-07, No Iterations 33 time step continuity errors : sum local = 3.96176e-09, global = 6.9814e-20, cumulative = -4.96308e-19 ExecutionTime = 0.16 s
Time = 0.015
Max Courant Number = 0.758267 BICCG: Solving for Ux, Initial residual = 0.0448679, Final residual = 2.42301e-06, No Iterations 6 BICCG: Solving for Uy, Initial residual = 0.0782042, Final residual = 1.47009e-06, No Iterations 7 ICCG: Solving for p, Initial residual = 0.107474, Final residual = 4.8362e-07, No Iterations 32 time step continuity errors : sum local = 3.99028e-09, global = -5.69762e-19, cumulative = -1.06607e-18 ICCG: Solving for p, Initial residual = 0.0806771, Final residual = 9.47171e-07, No Iterations 31 time step continuity errors : sum local = 7.92176e-09, global = 1.07533e-19, cumulative = -9.58537e-19 ExecutionTime = 0.19 s
The user may be happy to monitor the residuals, iterations, Courant number
etc. as report data passes across the screen. Alternatively, the user can redirect
the report to a log file which will improve the speed of the computation. The
foamJob script provides useful options for this purpose with the following
executing the specified <solver> as a background process and redirecting the
output to a file named log:
foamJob<solver>
For further options the user should execute foamJob -h. The user may monitor
the log file whenever they wish, using the UNIXtail command, typically with
the -f ‘follow’ option which appends the new data as the log file grows:
There are limitations to monitoring a job by reading the log file, in particular
it is difficult to extract trends over a long period of time. The foamLog script is
therefore provided to extract data of residuals, iterations, Courant number etc.
from a log file and present it in a set of files that can be plotted graphically. The
script is executed by:
foamLog<logFile>
The files are stored in a subdirectory of the case directory named logs. Each
file has the name <var>_<subIter> where <var> is the name of the variable
specified in the log file and <subIter> is the iteration number within the time
step. Those variables that are solved for, the initial residual takes the
variable name <var> and final residual takes <var>FinalRes. By default,
the files are presented in two-column format of time and the extracted
values.
For example, in the cavity tutorial we may wish to observe the initial residual
of the Ux equation to see whether the solution is converging to a steady-state. In
that case, we would plot the data from the logs/Ux_0 file as shown in 6.5. It can
be seen here that the residual falls monotonically until it reaches the convergence
tolerance of .
Figure 6.5:
Initial residual of Ux in the cavity tutorial
foamLog generates files for everything it feasibly can from the log file. In the
cavity tutorial example, this includes:
the Courant number, Courant_0;
Ux equation initial and final residuals, Ux_0 and UxFinalRes_0, and
iterations, UxIters_0 (and equivalent Uy data);
cumulative, global and local continuity errors after each of the 2
p equations, contCumulative_0, contGlobal_0, contLocal_0 and
contCumulative_1, contGlobal_1, contLocal_1;
residuals and iterations from the the 2 p equations p_0, pFinalRes_0,
pIters_0 and p_1, pFinalRes_1, pIters_1;
.
