Simulation Options - General

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thomas (Unlicensed)
Last updated: 28 Apr, 2014
4 min read

The parameters you can see under “Options...” are the standard values from RealFlow’s “Preferences”. 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”. To open the “Simulation Options” dialogue, please click on the small triangle next to the “Simulation” button and choose “Options…”. Then you will see this window:

 

General

FPS Output

This option can be used either to adjust the frame rate to your local TV system or a certain cinematic frame rate. RealFlow’s standard “FPS Output” is 25 frames per second for PAL. You can enter any desired value, for example 30 for NTSC or 24 for HD, or other film formats. Please note that there is a connection between “FPS Output” and “Stepping”: when the number of frames per second is increased, accuracy can be decreased. RealFlow prints out a message when the amount of substeps is too low. The global “FPS Output” is determined under RealFlow's “Preferences”. This value is used to change the frame rate for the currently opened project.

“FPS Output” can easily be used for slow-motion effects. Another, very convenient, method to create slow-motion or time-lapse effects is RealFlow's "RetimeSimulation” tool, of course. Please have look at this example:

You enter a “FPS Output” value of 75 and simulate the scene. Once it is ready you import the simulation data into your 3D application, set the internal playback rate to 25 and render everything out . The result is a movie that is played back at just one third of the original speed of RealFlow. In other words, you have stretched time by a factor of three.

Threads

This is another parameter that also connected to RealFlow’s “Preferences” and is adjusted automatically. However, for simulations with lower particles counts, it is often better to reduce this value. The reason is that distributing simulation data to different CPUs or cores takes a certain amount of time and this process can take longer than the actual calculation step. Please make sure that the number of threads is not greater than the number displayed under “Processors”.

Processors

The total number of CPUs is automatically detected by RealFlow and displayed here. Please note that this is a read-only field. To change the number of processors used, uncheck “Use max. threads” and enter a new value under “Threads”.

Use max. threads

When this option is active, RealFlow always simulates with the maximum number of processors. Please bear in mind that using the maximum number of threads will not automatically boost simulation speed. It only means that RealFlow always uses all available processors. With low particle counts, simulations time can even increase, because it takes some time to prepare the simulation data and distribute the individual "packages" to the CPUs and cores.

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 5.

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 “Stepping” (General) 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

With this parameter you can change the solver's lower number of time steps. “MIN substeps” is of particular interest for SPH simulations with high “Viscosity” or “Surface tension” values. Due to the high forces these properties can create, you will most probably see “popping” and exploding particles. This behaviour can be reduced or even removed with higher “MIN substeps”.

MAX Substeps

If you want to increase accuracy, please change this value. To create a fixed number of substeps, simply use equal values for both parameters.