The “Stepping” sections can be described as RealFlow accuracy. The more time steps, the better and more precise the simulation will turn out. The parameters already indicate that RealFlow uses an adaptive method to calculate the best number of steps within the specified range between “MIN and MAX substeps”. To achieve a fixed time step, "MIN substeps" and "MAX substeps" must be equal.
Stepping (Liquid - Hybrido
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Solver)
This section is responsible for RealFlow's Hybrido grid fluid solver. As you can see, there are also “MIN and MAX substeps” and they have exactly the same function as their particle fluids counterparts. Because of the used HyFLIP technology, our grid fluid solver can work with much lower “MAX substeps” to create stable fluids. The substeps are the number of subdivisions the solver performs in order to move the fluid. Higher settings will produce better and more accurate results. RealFlow's Hybrido solver does not need very high values, making it very fast.
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The substeps in RealFlow subdivide the simulation into portions of variable length. The solver calculates how fast the fluid will move within this time span. The number of steps depends on the maximum velocity of the fluid and the length of each grid cell. With a value of 1.0, the fluid will not move more than 1 grid cell in the current time step. With values smaller than 1.0, the fluid can cover a longer distance within a single step - the solver is less strict.
Pressure solver (Liquid - Hybrido
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Solver)
One of RealFlow’s grid fluid’s main characteristics is that the fluid is nearly incompressible. Incompressibility does not automatically imply that the fluid itself cannot be compressed. It means that density remains constant within a (very small) parcel of fluid which moves with the fluid’s velocity. This state can be achieved by making the velocity field divergence-free. Divergence is not so easy to explain in a physically correct way, but as an approximation we can say that the solver always tries to keep the volume of a fluid parcel constant. To achieve a constant volume, the Hybrido has to solve a complex system of linear equations using an iterative method – this is the number you enter under “MAX iterations”. The exactness of this process, on the other hand, is controlled with “Accuracy”. With a high value, the solution of the equation system is very precise and very close to the exact solution.
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This parameter ranges between 0 and 1. With 0, the pressure solver will quickly find a solution, but it will not be very accurate. A value of 1, on the other hand, will find a solution that is very close to the exact behaviour.
Viscosity Solver (Liquid - Hybrido
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Solver)
MAX iterations
In most cases, the default setting is sufficient, but under some circumstances it can be necessary to increase this value, for example when you see a warning message. Normally you will not see any misbehaving particles and you can proceed with the simulation. We recommend creating an OpenGL preview to see if the fluid behaves correctly.
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This value ranges between 0 and 1. With 0, the solver will quickly find a solution, but it will not be very accurate. A value of 1, on the other hand, will find a solution that is very close to the exact behaviour, but simulation time will increase. The default value of 0.2 represents a good balance between simulation speed and accuracy.
Transport (Liquid - Hybrido
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Solver)
RealFlow's HyFLIP technology also uses particles, for example to describe the grid fluid's surface. It is therefore necessary to move them through the grid. With this section's parameter you can control the quality of the process.
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This is the number of steps the solver uses to move the particles through the grid.
OpenCL (Liquid - Hybrido
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Solver)
RealFlow's Hybrido solver can exploit OpenCL-capable hardware to perform grid fluid simulations. OpenCL is not only restricted to graphics cards, but can also be used with CPUs; RealFlow even allows you to combine both devices. It will strongly depend on your hardware and computer setup whether OpenCL devices:
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This functions requires dedicated OpenCL-acceleration hardware and these devices have to be purchased separately. As long as your computer is not equipped with such an accelerator board this option is disabled.
Stepping (
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Liquid - Particles Solver)
With these settings you can easily control the accuracy of the secondary elements, for example splashes. Secondary elements are always considered dumb particles and therefore do not need very high “MAX substeps”. The default values should be sufficient for most applications. This solver is also called “HySPH”.
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