> simulations

SPH

simulations/sph·v1.5.1

IN:1 OUT:1

SUMMARY

The SPH operator turns the points of any POP into fluid particles that press toward a target density, drag each other along through viscosity and fall under gravity, using its own neighbor grid. It outputs a particle stream with the simulated P and PartVel.

Simple mode applies one solver step to the input every frame, while Advect runs a feedback loop (Initialize, Start, Play) with a Target Feedback Loop POP for forces downstream. The ground, a bounding box and a field collider act as fluid walls with friction, and Mesh Boundary samples a mesh collider so the fluid rests on it.

PARAMETERS

PAGESPH

[+]Solver Mode	Solvermode	Simple is stateless and recomputed from the input each frame. Advect runs a feedback loop, started with Initialize then Start.
Target Feedback Loop POP	Targetpop	A reference to a POP node downstream in the network whose data is retrieved one frame later. P, PartVel and PartForce are read back.
Substeps	Substeps	Number of solver substeps per 1/60 second. More substeps are more stable.
Iterations	Iterations	Number of pressure iterations per substep. More iterations make the fluid stiffer and less compressible.
Time Scale	Timescale	Speed multiplier on the time step. 0 freezes and 2 doubles.
Time Step	Timestep	The time step per frame in seconds, 1 divided by the cook rate (read-only). Time Scale multiplies it.
Initialize	Initializepulse	Initializes the POP from its input and parameters.
Start	Startpulse	Start the simulation from the initialized state.
Play	Play	Pause or play the feedback loop.
Step	Steppulse	Advance the simulation by one frame while paused.

PAGEProperties

Smoothing Radius	Smoothingradius	Kernel radius. Particles closer than this interact.
Target Density	Targetdensity	Sets the rest density the pressure drives the fluid toward. The useful range is about 0.05 to 0.3 with a Smoothing Radius of 0.05.
Pressure Multiplier	Pressuremulti	Scales the pressure force that holds the fluid at Target Density.
Near Pressure Multiplier	Nearpressuremult	Scales a short-range repulsion that stops particles clumping. Keep it small; 0 is the calm default.
Viscosity	Viscosity	Viscosity of the fluid: 0 is inviscid, 0.1 is water, 1 is honey.

PAGECollisions

Enable Ground Collision	Enablegroundcollision	Collide with an infinite ground plane.
Display Ground	Displayground	Display the ground plane.
[+]Ground Position	Groundposition	A point on the ground plane.
[+]Ground Direction	Grounddirection	Normal of the ground plane. 0 1 0 is a level floor.
Ground Collision Margin	Groundmargin	Distance the particles keep from the ground.
Enable Bounding Box Collision	Enablebboxcollision	Keep the particles inside the bounding box.
Display Bounding Box	Displaybbox	Enable drawing the bounding box.
[+]Bounding Box Center	Bboxcenter	Center of the bounding box, in collider space.
[+]Bounding Box Size	Bboxsize	Size of the bounding box, in collider space.
Lower Bounds	Bboxlowerbounds	Enable the lower walls of the bounding box in each axis.
Upper Bounds	Bboxupperbounds	Enable the upper walls of the bounding box per axis.
Bounding Box Margin	Bboxmargin	Distance the particles keep from the box walls.
[+]Collision Type	Collisiontype	Selects the collider: none, a POP mesh (ray traced, Windows only) or a field used as an SDF volume.
Display Geometry	Displaygeo	Enable drawing the collider, as the mesh or the field's zero surface.
Collision Passes	Geocollisionpasses	Number of collider solves per substep. More passes hold fast moving geometry.
Mesh Boundary	Meshboundary	Treat the POP collider surface as an SPH wall of boundary particles. When off, only the cheaper hard ray collision is used.
Boundary Samples	Boundarysamples	Sets the number of boundary particles sampling the collider mesh. Aim for a spacing near half the Smoothing Radius.
Collision POP	Collisionpop	The collider, either a mesh POP or an SDF field volume.
[+]Dist Attribute (SDF)	Distattr	For a field collider, the signed distance attribute of the Collision POP, negative inside.
Solid	Solid	When on, particles inside the collider are pushed out. When off, the collider is hollow.
Keep Inside	Keepinside	When on, the collider is hollow and every outside particle is pulled back in. When off, only escaping particles are caught.
Project	Project	Place every particle on the collider surface instead of colliding.
Collision Offset	Collisionoffset	Distance the particles keep from the collider surface.
Collision Damping	Collisiondamping	Velocity lost on contact. 0 bounces and 1 stops.
[+]Transform Order	Xord	Sets the transform order of the collider and the bounding box.
[+]Rotate Order	Rord	Sets the order of the rotations of the collider and the bounding box.
[+]Translate	T	Translate the collider and the bounding box in the three axes.
[+]Rotate	R	Rotate the collider and the bounding box around the X, Y and Z axes. Angles are given in degrees.
[+]Scale	S	Scale factor for each axis of the collider and the bounding box.
[+]Pivot	P	The pivot point for the rotate and scale of the collider and the bounding box.
Uniform Scale	Scale	Specifies a uniform scale factor for the collider and the bounding box.
[+]Display Color	Displaycolor	Sets the color of the displayed guides.

PAGEForces

[+]Gravity	Gravity	The gravity vector in units per second squared.
Gravity Multiplier	Gravitymultiplier	Multiplies the Gravity vector.
[+]Wind Direction	Winddirection	The direction the wind blows in. Its length does not matter.
Wind Speed	Windspeed	The wind acceleration along Wind Direction, in units per second squared.
Velocity Damping	Velocitydamping	Amount of damping applied to the velocity. 0 applies no damping.
Limit Velocity	Limitvelocity	Enable clamping the particle speed to Max Velocity.
Max Velocity	Maxvelocity	Sets the speed cap, the same at any frame rate. 100 gives 16.7 units per second.
Static Threshold	Staticthreshold	Sets the static friction coefficient. Contacts below it grip.
Dynamic Scale	Dynamicscale	Sets the kinetic friction coefficient that slows sliding contacts.

PAGECommon

Free Extra GPU Memory

Freeextragpumem

Free memory that has accumulated when output memory has grown and shrunk.

INPUTS

Input 0 POP - Particles In

OUTPUTS

Output 0 POP - Particles Out