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Spring assigns a mass to each point and simulates the effects of forces (gravity, wind, and/or turbulence) on the points. Edges act as springs which try to pull the points back to their original position.
Keep certain points in the mesh at fixed positions using a point group in the Fixed points parameter on the Nodes tab.
Apply directional force (gravity), wind (a directional force with a maximum speed), drag, and turbulence to the points using the parameters on the Forces tab.
Connect a Force SOP to the third input to let you attract or repel the points to/from metaball fields.
The greater the drag value, or smaller the mass, the faster the oscillation dies out.
The Spring SOP is useful for many situations, but for more sophisticated simulations use rigid body, cloth, or wire dynamics.
The Spring op will use point normals as initial node velocity if point normal attributes exist and there are no point velocity attributes in the incoming data. If you add velocity attributes to the points, the point normals are ignored.
Time at which the simulation resets.
Number of initial frames skipped.
Time per iteration.
Particles move more accurately.
How the attractor points affect particles
All points affect each particle
Single point per particle
Only one point affects each particle
Force of gravity on points.
Wind force acting on points.
Amplitude of turbulence along axes.
Inverse variance of turbulence over space.
Seed for random turbulence generator.
Group of points not to be moved by this operation.
Fixed Points go to Source Positions
Fixed Points are put to their positions in the Source.
Copy Groups from Source
All Source groups are copied at each frame. Useful if the Fixed Points group contents are animated.
Add Mass Attribute
Causes point mass to be calculated.
Relative mass of each point.
Add Drag Attribute
Causes drag coefficient to be calculated.
Drag of each point.
How the springs will behave
Use Hooke’s law. Force = displacement x spring constant.
Like Hooke’s law except displacement is normalized to the original length of the spring. (Behavior used in Houdini 2.5).
Stiffness of the spring
Initial spring tension before deformations.
+ Limit Plane, - Limit Plane
Points die or bounce off limit planes on contact. /limitposx … /limitposz, /limitnegx …
Whether particles die or bounce on limit planes.
Energy loss tangent to the collision.
Energy loss perpendicular to the collision.
The points to simulate, for example a polygon sphere or mesh.
(Optional) Geometry for the points to collide with. When the points hit this geometry, they can stick or bounce. If the collision object is deforming, collision detection may fail, causing some points to leak through the collision geometry.
(Optional) A Force SOP, which uses a metaball to create a field which attracts or repels the points.