Time and data input-output control

Time and data input/output control

4.3 Time and data input/output control

The OpenFOAM solvers begin all runs by setting up a database. The database controls I/O and, since output of data is usually requested at intervals of time during the run, time is an inextricable part of the database. The controlDict dictionary sets input parameters essential for the creation of the database. The keyword entries in controlDict are listed in Table 4.4. Only the time control and writeInterval entries are truly compulsory, with the database taking default values indicated by † in Table 4.4 for any of the optional entries that are omitted.





Time control

startFrom	Controls the start time of the simulation.
- firstTime	Earliest time step from the set of time directories.
- startTime	Time specified by the startTime keyword entry.
- latestTime	Most recent time step from the set of time directories.

startTime	Start time for the simulation with startFrom startTime;

stopAt	Controls the end time of the simulation.
- endTime	Time specified by the endTime keyword entry.
- writeNow	Stops simulation on completion of current time step and writes data.
- noWriteNow	Stops simulation on completion of current time step and does not write out data.
- nextWrite	Stops simulation on completion of next scheduled write time, specified by writeControl .
endTime	End time for the simulation when stopAt endTime; is specified.

deltaT	Time step of the simulation.

Data writing


writeControl	Controls the timing of write output to file.
- timeStep †	Writes data every writeInterval time steps.
- runTime	Writes data every writeInterval seconds of simulated time.
- adjustableRunTime	Writes data every writeInterval seconds of simulated time, adjusting the time steps to coincide with the writeInterval if necessary — used in cases with automatic time step adjustment.
- cpuTime	Writes data every writeInterval seconds of CPU time.
- clockTime	Writes data out every writeInterval seconds of real time.

writeInterval	Scalar used in conjunction with writeControl described above.

purgeWrite	Integer representing a limit on the number of time directories that are stored by overwriting time directories on a cyclic basis. Example of $t0 = 5s \relax \special {t4ht=$ , $Δt = 1s \relax \special {t4ht=$ and purgeWrite 2;: data written into 2 directories, 6 and 7, before returning to write the data at 8 $s \relax \special {t4ht=$ in 6, data at 9 $s \relax \special {t4ht=$ into 7, etc.
	To disable the time directory limit, specify purgeWrite 0;†
	For steady-state solutions, results from previous iterations can be continuously overwritten by specifying purgeWrite 1;

writeFormat	Specifies the format of the data files.
- ascii †	ASCII format, written to writePrecision significant figures.
- binary	Binary format.

writePrecision	Integer used in conjunction with writeFormat described above, 6† by default

writeCompression	Specifies the compression of the data files.

- uncompressed	No compression.†
- compressed	gzip compression.

timeFormat	Choice of format of the naming of the time directories.
- fixed	$� m.dddddd \relax \special {t4ht=$ where the number of $d \relax \special {t4ht=$ s is set by timePrecision.
- scientific	$� m.dddddde � xx \relax \special {t4ht=$ where the number of $d \relax \special {t4ht=$ s is set by timePrecision.
- general †	Specifies scientific format if the exponent is less than -4 or greater than or equal to that specified by timePrecision.

timePrecision	Integer used in conjunction with timeFormat described above, 6† by default

graphFormat	Format for graph data written by an application.
- raw †	Raw ASCII format in columns.
- gnuplot	Data in gnuplot format.
- xmgr	Data in Grace/xmgr format.
- jplot	Data in jPlot format.


Data reading

runTimeModifiable	yes†/no switch for whether dictionaries, e.g.controlDict, are re-read by OpenFOAM at the beginning of each time step.


Run-time loadable functionality

libs	List of additional libraries (on $LD_LIBRARY_PATH) to be loaded at run-time, e.g.( "libUser1.so" "libUser2.so" )
functions	List of functions, e.g. probes to be loaded at run-time; see examples in $FOAM_TUTORIALS


† denotes default entry if associated keyword is omitted.

Table 4.4: Keyword entries in the controlDict dictionary.

Example entries from a controlDict dictionary are given below:

17
18  application     icoFoam;
19
20  startFrom       startTime;
21
22  startTime       0;
23
24  stopAt          endTime;
25
26  endTime         0.5;
27
28  deltaT          0.005;
29
30  writeControl    timeStep;
31
32  writeInterval   20;
33
34  purgeWrite      0;
35
36  writeFormat     ascii;
37
38  writePrecision  6;
39
40  writeCompression off;
41
42  timeFormat      general;
43
44  timePrecision   6;
45
46  runTimeModifiable true;
47
48
49  // ************************************************************************* //

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User Guide

4.3 Time and data input/output control