Scene : Solver

Owned by thomas (Unlicensed)
Last updated: 27 Sept, 2019 by Alex Ribao
3 min read

This is the place where the simulation preferences are defined. 



The "Solver" tab is subdivided into two sections:

Global

Number of Threads

Here you specify how many computer processors and cores you want to use with your simulations.

Auto

When this option is checked RealFlow | Cinema 4D will always use the maximum number of threads.

Time Scale

Values smaller than 1.0 will decelerate the fluid; settings greater than 1.0 have an acceleration effect. “Time scale” works as a factor: 2.0 means that the fluid will be two times faster.

Stepping Strictness

RealFlow | Cinema 4D calculates how fast the fluid will move within a simulation step (aka "time step" or "substep", see below):

  • With a value of 1.0, the fluid will not move more than 1 grid cell in the current simulation step.
  • With values smaller than 1.0, the fluid can cover a longer distance within a single step – the solver is less strict.
Use Geometry Velocity

When enabled RealFlow | Cinema 4D will adjust the simulation's substeps to get a correct fluid-object interaction behaviour:

  • Imagine an animated object falling into a container with calm water.

  • Here, RealFlow | Cinema 4D uses very large substeps to speed up the simulation.

  • Due to these large steps the interaction between the object and the fluid is delayed.

  • With “Use Geometry Velocity” the interaction will happen in time again.

Maximum Deformation Allowed

This is the threshold used to consider if an object with a RFCollider is being deformed or just transformed. A bigger value would recompute less often the colliding geometry, thus providing a better performance. However, if the value is too high there might appear differences between the real object and the geometry "seen" by RealFlow. If the value is too small, some objects that are just animated (or parented) may be considered deformed just because of precision errors, decreasing the simulation performance greatly. 

The value represents a percentage of the distance between every vertex and the center of mass of every object. The default value of 0.5% should work for most parented objects.

Auto Params

When enabled, RealFlow | Cinema 4D applies default settings. These default values work for most projects with PDB or SPH fluids, but for other materials (granular, viscous, etc.) it is normally necessary to apply custom settings. This also applies to simulations with collision geometry involved.

Min | Max Substeps

Here you find the minimum and maximum numbers of simulation steps. Substeps play an important role for collision detection. If you see particles going through a solid object

  • decrease the object's "Cell Size" in the "Volume" tag
  • enable "Continous Collision Detection" in the "Volume" tag
  • try do reduce the particles speed with a "Drag Force" daemon
  • if possible, make the collision object thicker.
  • If you see popping particles while the fluid settles try to increase "Min Iterations" and/or "Min Substeps".

Substeps should also be increased when you see distorted polygons in conjunction with rigid or elastic particles and the "Skinner" daemon.

Min | Max Iterations

These two parameters are important for the rigidity of elastic, granular, viscous, and viscoelastic materials:

  • The higher the values, the more rigid the material will finally be.
  • Iterations are applied per subset, so with substeps value a materials rigidity will also increase.
  • For the materials, mentioned above, a fixed number of iterations often works well, e.g. 20 | 20 or 40 | 40.
  • If you see popping particles while the fluid settles try to increase "Min Iterations" and/or "Min Substeps".
Accuracy

In most cases this value can be kept. This parameter ranges between 0.0 and 1.0. With

  • 0.0 RealFlow quickly finds a solution, but it will not be very accurate
  • 1.0 RealFlow finds a solution that is very close to the exact behaviour, but simulation time will increase.
Interpolate sub-frame

Sometimes emitters and daemons have some of their parameters are animated. If this option is checked, interpolated values between frames are transferred to the simulation.

GPU

Use GPU

To speed up simulation by 3-8x (depends on your graphic card and CPU) compared to the CPU, enable this feature:

  • Gaming cards like the GeForce series perform very well with RealFlow | Cinema 4D. 
  • The amount of VRAM determines the size of the simulation and there is currently no fallback on the mainboard's RAM.
  • Old and low-performance graphic cards normally do not have any effect on simulation time or might even slow down the simulation.
  • For more information visit the → "GPU-Acceleration" page.
Device

When "Use GPU" is active you will see a drop-down menu with all available graphic boards. Multi-GPU simulations are currently not possible.