Prefs - Simulation (General)

The parameters you can see under “Options...” are the standard values for each new RealFlow. They can be overwritten to increase or decrease the defaults for the individual needs of your current project. We recommend determining the settings under “Preferences” globally and then altering them with “Simulation options” an a per-scene level. To open the “Simulation Options” dialogue, please click on the small triangle next to the “Simulation” button and choose “Options…”.

General

All values from the "General" section are global settings and should only be set once as long as you do not want to make fundamental changes. If you want to adjust these parameters on a per-project basis, this should always be done under “Simulation options”.

FPS Output

This value normally only needs to be set once and changes should always be made under “Simulation options” on a project level. The default value is 25, suitable for the PAL format.

Threads

“Threads” is adjusted automatically and normally equals the amount of detected processors or cores. Please note that RealFlow does not always use the maximum number of processors or threads, because this strongly depends on your scene. There are simulations which are better suited for multi-processor calculations, for example, projects with very large particle amounts. Other cannot completely utilize a computer’s power and therefore the processor load appears reduced. Most processes are multi-threaded, for example daemons and Caronte, the object dynamics solvers.

There is also a single-threaded process: Python. Whenever you run a script inside RealFlow, only one CPU or core is used. That is a principle matter of the Python programming language, not RealFlow, because Python can only support one CPU. Plugins, written in C++ can handle multiple processors.

Processors

Here you can see the number of available CPUs or cores in your system. RealFlow also detects active hyper-threading and displays an according number of processors.

Use max. threads

If you always want to simulate with maximum number of available processors, just leave the checkbox untouched. Please be aware though that it is much better to specify this number with each scene individually. Especially scenes with low particle counts can simulate faster with small thread settings. The maximum number of threads can be adjusted under “Simulation Options” for each scene individually.

Stepping

This section is of particular importance, because it is responsible for the number of substeps for Hybrido, HySPH secondary elements, particle fluids and body dynamics and describes a simulation’s accuracy. The more substeps, the better the result. The settings of the “Stepping” section control the number of substeps, RealFlow will finally use for a simulation – like a higher-ranking control instance. An example will help you to understand its functionality and mode of operation. Let’s say you have entered the following values under Hybrido > Hybrido Main Solver > Stepping: “MIN substeps” and “MAX substeps” are 1 and 3.

Under General > Stepping you have entered 1 for both parameters to create a fixed substep. In such a case, Hybrido will perform the simulation and needs (for example) 3 steps for the current frame, but the “Stepping” section under “General” says that the maximum is limited to 1 step. The final consequence is that Hybrido will use only 1 step instead of 3.

The relation between this “Stepping” section and “Caronte Solver” is probably not obvious, but there is a connection: the “Quality” slider can also be seen as a user-friendly way to determine the number of substeps and the actual number of steps is calculated internally.

For SPH particle emitters the mode of operation is the same as in previous RealFlow versions and exclusively controlled with the two parameters below.

MIN substeps

Here you can define the minimum number of time steps that will be used for a simulation. If you need more precision, it is sometimes better to raise “MIN substeps” than to alter the maximum number. In some cases it can even be necessary to use a “MIN substeps” that is very close to “MAX substeps”. Fixed time steps can be achieved by using the same values for both “MIN substeps” and “MAX substeps”.

MAX substeps

This is the particle fluid solver's upper limit of time steps. The final used number of steps will be between both values. In many simulations it is required to work with higher “FPS Output”. With higher settings, e,g. 100 FPS, you will most probably receive an error message, telling you that your “Choice of MAX substeps is too large”. Fortunately, the error message tells you the maximum substep you should use for the current settings directly, but you can also ignore this tip and start your simulation, though this may result in longer simulation times.

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Stop simulation on write error

When this checkbox is active RealFlow will stop the current simulation if it encounters write disk errors. This mainly happens when a disk is full and RealFlow is not able to store simulation data. A positive side effect is that your computer will not waste energy or resources when the simulation is aborted. You should enable this feature when you export Alembic data, because RealFlow might crash when there is no space left to store the ABC files.

Disk overflows can also be avoided with alternative paths under “Export Central”. With this feature, simulation files will be written to one or more alternative locations if the primary drive is full.