Simcenter STAR-CCM+ How do I keep my .simh files to a reasonable size?

The solution history files (.simh) are very useful to record history of the solution and then create plots and scenes showing various stages in the simulation. However, it can easily get to very large file sizes as its recording data at every iteration/ timestep from the simulation. 

Here are few things that you can do to reduce the size of the .simh file.

1. If you are running a simulation where you don't need the history from the beginning, then record the solution history towards the end of the simulation.  Let the solution converge fully and at the end record the .simh file for the last few hundred timesteps. If you record the .simh file from the beginning of the simulation, it can get pretty big as it has to hold a lot of data for every time step.

2. The .simh file has the update option in the properties window. By default the frequency is set to record at every timestep. If the solution is not very dynamic and if you see that the data is not changing every time step, you can actually record every 10 timesteps instead of every timestep. This also reduces the amount of data and file size.

3. For the input part, it is more efficient to select only the boundaries of interest instead of the entire region. You can create plane sections or even constrained plane sections which are focused on areas of interest. This will reduce the file size and you will record data only where it is needed and not everywhere in the domain.

4. Further on, in the expert settings, you have the option for compression mode. If you change this to Lossy, it gives you the option to set the number of digits for the parameters. By default, STAR-CCM+ preserves upto 8 digits for all the functions. You can reduce this to 6 or 4. You might notice a change in accuracy depending on the type of simulation. You can check by doing couple of tests to see how much difference are you getting when you reduce the digits and choose the one that works for you. 

5. It is also good to create multiple .simh files instead of having one large .simh file with several boundaries and multiple field functions. Having too many input surfaces and field functions in one .simh file can lead to very large file sizes. When you import this file, it might lead to memory issues causing the STAR-CCM+ GUI to crash. Having multiple .simh files with smaller sizes work much better and prevents any memory issues or GUI crashes.