# Control the Time Steps That Are Converted to FV-UNS

AcuTrans has access to all output data that AcuSolve writes during the simulation. For transient cases this typically includes many output steps.

Often times, you may only be interested in converting a subset of these time steps for visualization purposes. To provide this functionality, AcuTrans provides the -ts command line option. This option is used to provide a comma separated list of time steps for conversion. For example, "acuTrans -out -to fieldview -ts 24,25,26,27" produces a combined FV-UNS file for time step 24, 25 ,26 and 27. Each file is named with the time step identifier embedded within it:
mixingElbow_step000024.fv
mixingElbow_step000025.fv
mixingElbow_step000026.fv
mixingElbow_step000027.fv

When this data is read into AcuFieldView, it will automatically acknowledge the series of files as a transient sequence.

AcuTrans also allows specification of a range of time steps for each argument. The format of this range is as follows begin:end:increment, where end and increment are optional and assumed to be one if not provided by you. begin indicates the first step in the range, end represents the last step in the range, and inc represents the increment used to identify the values of interest ranging between begin and end.
Note: The letters "F", "L", and "A" can also be used to represent the "first", "last", and "all" keywords. "F" indicates that AcuTrans should select the first available step of data on disk, "L" indicates to select the last available step on disk, and "A" indicates selection of all steps on disk.
Examples of specifying time steps in this fashion include:
acuTrans -out -to fieldview -ts A
This converts all available time steps
acuTrans -out -to fieldview -ts 35,40:50:2,60
This converts steps 35, 40, 42, 44, 46, 48, 50, 60
acuTrans -out -to fieldview -ts 35,40:44
This converts steps 35, 40, 41, 42, 43, 44
acuTrans -out -to fieldview -ts F:L:20

This converts all steps in the range between the first and last output step with an increment of 20.

If you request a time step that is not available in the output database, AcuTrans gives an error and exits. This behavior can be overridden by providing the -imts or -ignore_missing_steps command line option. In this case, the missing steps are simply skipped and the remaining steps are converted.