Blender Particle Fluids

• Blender Particle Fluids integrate into the existent powerful Blender particle system a fluid simulation tool that allows a wide range of fluids types, from steam to water to goo, slime and giggly fluids.

• The particle fluids inherit all the goodies of the base particle system, like baked simulations, scripting, etc.

In future releases will include also meshing particles

• Blender Fluid Particles uses a boundless interpolation technique to sample the fluids body called SPH (Smoothed Particle Hydrodynamics)

• Each particle could carry any fluid property: density, pressure, temperature, color, etc.

Smoothing radius is the most important parameter in the simulator, it controls the influence of each particle, and determines the performance and the type of the fluid simulated: for small scales of fluids (droplets, tiny water) use a relatively big smoothing radius (1.0) and for big scales fluids (sand, sea, rivers) use a small radius (0.2-0.1).

Mass controls the amount of fluid matter that each particle represent, it is important for multifluids interaction (denser and lighter fluids) and also for simulating different scales of fluids with the same amount of particles.

Viscosity controls the movement of the fluids making it more goo like and also more stable, is a factor that dampen the relative velocity of each particle.

Particle damping is a stabilization factor and control the absolute particle velocity, when a simulation seems to be out of control try to increase it or play with viscosity. It differs from viscosity because the second damp the relative particle speed.

Stiffness controls the surface tension on an external level, but internally is an attraction force in each particle smoothing radius. For small scale fluids use high stiffness values (1.0) and for large scale fluids use low to none value.

Repulsion factor has the opposite effect as stiffness factor, it repels particles from its neighbours to maintain an Equilibrium.

Collider damping affect the bouncing of the particle in the collision event, the more collider damping the more energy will loose the particle and stick to collider surface.

Collider particle friction affect the particle velocity as it travels over the collision object, increase its value to get realistic slipping liquid effects.

Rest density is an important parameter that set the density at which particles will try to maintain under a cero force field or rest state. Visually it controls the distance at what particles will be settled.

Tweak parameter is a time step tweak for the simulation, if a sim set up goes unstable first try to lower the time step by setting a fractional tweak. SPH simulators are not unconditionally stable: they are stable only for relative small time steps, that’s the reason why increasing the particle count without adjusting the rest of the parameters

could lead to exploding simulations The good news is that always will be a set of parameters that will make a desired simulation stable.

The particle integrator is the function that actually advance particles in time, they feature more fast and stable simulation, so correctly choosing the appropriate integrator is crucial. In general Midpoint is the most stable while Euler is the fastest and Verlet is more suited for fluid behaviours.

For Goo like fluids Spring is very important, is a force among pairs of particles that try to maintain them to a fixed distance, the rest length.

The rest length is the distance at what particles will try to be with a force proportional to the spring factor.

Brownian add a random movement to the particles, useful for small scale fluids or crazy FX’s

Collider stickiness control the force factor that try to stick particles to the collider surface, is great for slipping fluids.

Square viscosity is a second order viscosity factor, is used for advanced fluid for enhancing viscous behaviour.

Particles fluids could be rendered currently as billboards, simple dots, halos, instanced objects and volumetric distorted spheres in the pointdensity texture type.

While in the future they will be rendered as fluid isosurfaces.

There’s plenty of ways in particle fluids for interactions and advanced setups, and combinations of the parameters lead to non-linear behaviours so they are not the simply sum of effects. If you want to master particle fluids a good amount of experimentation is advised as well as a basic understanding on particle fluids theory. Raul Fernandez