Particle Nado

Hi All
This is the result of my latest R&D with particles in Houdini
My intention was to create a Tornado effect with particles, initially intended to be driven by some Curve Force POP but after a lot of testing it seemed to be uncontrollable with this kind of setup, so I ended up using some volume to advect the particles. Here's a little breakdown:

BREAKDOWN

This first part is about creating a line with some copies (the final shot was 50 copies). We generate some normals and the Curveu with a Resample node. Then we generate a big noise for general deformation and a small one with a randomized seed for each copy, recreate some Normal following the curve and an Id attribute. In the actual scene, the noise is very subtle (I increased it to show better the copies). Also, the noise is remapped along the Curveu to have no effect on the start of each line, so we don't end up moving the starting point.

All it goes inside a For Each Loop and iterates for each curve.
Inside the loop, a single point offset on the X axis is being copied on every point of the curve; and rotated by a certain amount of degrees with some Vex Code. An add code creates the final curves connecting the copied points.

Then I recalculated the Normals and the Curveu, and created a V attribute for velocity, along with a random Width value for the Polywire.
This is the output mesh:

I used a Volume Rasterize Attribute to create a Velocity field for the particle advection.

The Emitter is a simple flat donut created with two circles, where I can control and animate the shape deformation with a couple of Point Vop and some noises. I created some animated Density value and plugged it into a Pop Network.

Here in the PopNet the core force is the PopAdvectByVolumes, which uses the Velocity field to drive the particle position. Then I added some Pop Force to create additional movement, a Pop Kill with some boundaries, and another wrangle to kill particles if they stop. The final shot was done with around ten million particles at his peak.