Question about transient result output
 

Hi

I'd like to only record the history of one expression (could be done by monitor) and have a result that I can restart from. Which output option shall I choose at CFX-pre 'Output control'?

I do not understand your question. Have you got a monitor point which you want the data to continue after a restart? You control this in the solver manager settings.

I mean: how to set up so that I can have transient simulation with the full solution of the last time step saved?

And also if I want to continue the simulation in the future, i can also restart from the last time step.

Doesn't a normal stop of a transient run give you a result file with a full solution which can be used for a restart?

Yes. It can. But it occupy too much of my disk space. How to reduce the size of the file?

Have you looked at the results file options? You can control the compression and which variables get written. This can make the results file much smaller.

Hard drives are cheap, sounds like you need to buy another one. It is not worth your while fiddling with compression and making files smaller when you can buy lots of hard drive space for so little cash.

I checked it but confused about which option shall I choose. I don't need the solution in the middle. I only need the solution at the last time step. Which option shall I choose?

It is under the results tab in the output control object.

Typically when running large transients, I will use Output Trn Results at step time steps (every xx seconds) and use the option of selected variables (those that I am usually most interested in). This will create alot of small results files that cant be used as a restart, but are useful in post processing.

I also use Output Trn Results Option Standard at larger time steps (for example 50*xx seconds), which can be used for restarts. This limits the large data set (you can increase the 50 to what ever you are comfortable with).

In addition to that I use Backup Option of Essential at every yy step interval (dont confuse this with time [s]). This file can be used for restarts in case of crashes and what not. This file gets over written with every backup so it will not take up much diskspace.

May I suppose that if I set the timestep interval as 1000, the disk space will be saved by 999/1000 and I can still restart from a solution among the last 1000 time steps?

You will only be able to restart the solution (From the Backup) at the backup time step, which includes no other ones prior.

If you need a restart at an arbitrary time, you will need to do that from the transient results. If diskspace is a concern, use smallest as the choice, but that can still chew up alot of diskspace. It also might not be a totally clean restart depending on what physics you have going on.