Pulga Physics Lite

Functionality

This node creates simulations from input parameters, it is meant to be used in form-finding purposes. It creates the simulation using the inputted vertices as spherical particles that react to applied forces.

The node is a basic NumPy implementation of basic physics system heavily inspired in “The Nature of Code” by Daniel Shiffman and the Kangoroo Plug-in for Grasshopper. Due the nature of the algorithm it can get very intensive, handle with responsibility

Input & Output

Input	Type	Description
Initial_Pos	Vertices	Vertices in original state
Iterations	Integer	Number of iterations of the process
Springs	Strings	Edges referenced to vertices
Springs Length	Strings	Specify spring rest length, 0 to calculate it from initial position
Springs Stiffness	Strings	Springs stiffness constant
Pins	Strings	Indexes of vertices with fixed position, accepts a vertices mask and index number
Pins Goal Position	Vertices	Final position of pinned vertices
Radius	Strings	Radius of virtual sphere, used to calculate intersections, mass and surface
Self Collision	Strings	Collision force. Applied when vertex distance < sum Radius
Self Attract	Strings	Attract force magnitude. Applied when vertex distance > sum Radius
Self Attract Decay	Strings	attract force decay with distance (power) 0 = no decay, 1 = linear, 2 = quadratic…
Grow	Strings	Radius variance factor. Shrink when they intersect, Grow when don’t.
Min Radius	Strings	Minimum radius limit
Max Radius	Strings	Maximum radius limit
Pols	Strings	Pols referenced to vertices. (used to calculate inflate force)
Inflate	Strings	Inflate force magnitude (per surface unit)
Initial Velocity	Vertices	Initial vertices velocity
Max Velocity	Strings	Maximum vertices velocity
Drag Force	Strings	Movement resistance from environment
Attractors	Vertices	Attractors origins
Attractors Force	Strings	Attractors Force magnitude
Attractors Clamp	Strings	Attractors maximum influence distance
Attractors Decay	Strings	Decay with distance 0 = no decay, 1 = linear, 2 = quadratic…
Random Seed	Strings	Random seed number
Random Force	Strings	Random force magnitude
Random Variation	Strings	Random force variation
Density	Strings	Particles Density
Gravity	Vectors	Constant forces that are mass independent
Wind	Vertices	constant forces that are mass dependent
Bounding Box	Vertices	Limits of the system. It will work with the bounding box of the given vectors (min. two)
Obstacles	Vertices	Obstacles vertices
Obstacles Pols	Strings	Pols referenced to obstacles vertices. (they must be triangles)
Obstacles Bounce	Strings	Obstacles Bounce force

Accumulative:

When activated every nodeTree update will use the previous update as the starting point. The update can be triggered by the Update button or by any other event that triggers regular updates (like playing animation or changing any value).

It offers some options:

• Reset: Takes back the system to the initial state.

• Update: Runs one Node-Tree update.

• Pause: Pauses nodes calculations and ignores ui changes.

Examples

Arranging circles with attraction and collision.

Tensile structures can be studied with collisions and pinned points.

Traction structures can be converted to compression structures with inverted gravity.

Using the caternary as a structural modeling tool:

Variable spring stiffness can be used to simulate sewing springs inflatable structures.

Trajectories can be traced by supplying the desired iterations as a list.

Shooting particles to a attractors field.

The “Pins Reactions” output supply the resultant force on the pins. It can be use to model auxiliary structures.

Notes

When using accumulative mode the node uses one text-block (called pulga_memory + NodeTree name + Node name .txt) to save the current state when you hit pause in order to be maintained in case of closing the program.