VDB fracture Test.

video

This was a simple test to fracture a wood object exploring methods for generating more interesting and complex fracture fragment shapes via the vdb fracture tool set within houdini. Used 3 fracture passes, first pass fractured the 3 major pieces, then the elongated pieces in the middle, then I re-fractured the elongated middle section pieces cutting them into less uniform more interesting pieces.

upped the rez here and added some shredding and sharpening, also added curl noise to the fluid source
smoke_twister_med_rez

smoke twister

did a little houdini test of some custom velocity feilds, this was the initial build driven by a pop net work as source for the velocity for the smoke.

smoke_test

particle version of similar test

particle_test_using_different_values

doing some tests with some houdini point clouds

https://vimeo.com/76930312

here is my final product
https://vimeo.com/58396702

L-systems

Before I can venture further with RBDs and fractureing I needed to create my flower seeds, leaves, and stem.

if you are unfamiliar with L-systems they are equal parts awesome and frustrating. Awesome in that you can create a blue print to grow CG plants,  geometric shapes, ect... however they are limited in that the L-system turtle commands can only take a limited number of variables, and they can quickly eat up large amounts of computing power, as L-systems maintain alot of history/data as they are grown/created.

for this project i needed three main components. first i needed a seed arrangement's for my flowering hands. Plant adhere to several laws for governing petal and seed arrangements and growth that fall under the heading of phyllotaxis .

for a description of phyllotaxis  check out the L-system help documents from sidefx. and this website:

http://www.selcukergen.net/ncca_lsystems_research/houdini.html

LEAVES:
here I created an L-system for the half of a leave. grouped it and then mirrored the geometry using the below values:

VALUES:

RULES:

STEM:
for this i needed a long stem similar to that of a rose stem with branching leave stems and thorns:


VALUES:

RULES:

after I have these rules set up i can then supply the leaves to the J and K leaf input nodes of the stem L-system and the result:

Next i needed to create a phyllotaxis rig that i could animate parameters to make the spiral structure rotate:

VALUES:

RULES:

with this in place i can now attach my arms to the appropriate leave input of the L-system with a transform node to align the orientation of that arm animation as needed the result:

deforming geometry fractures:

At this point i have the basics down and have R&D'ed the fracturing in a controlled manor. The next bit of R&D is to test a deforming piece of geometry.

The process outlined in the previous posts was replicated now with the deforming arm geometry as my fractured object.

the main difference here is in the solver type. FOR the geometry i need to stick together through out the sim(the arm before it fractures) I chose to use an RDB solver for this section due to its ability to handle more complex geometry shapes. Thus when the arm bends and shapes become distorted,  it  will have a higher likelihood of producing concave and or manifold shapes. The bullet solver(used in the tube example) although very fast and efficient, notoriously does not handle the aforementioned shapes with any real dignity. Using the bullet solver on deforming geometry, even with the penetration threshold cranked up: the piece shapes will remain rigid(not deforming per piece), and will try to maintain a minimum distance and position from each other resulting in an exploded view of the the animated geometry with unsightly gaps in what should look like a solid object.

However for the pieces that become active ( peices falling off the arm), i was able to use a second solver the bullet solver to speed simulation times, given the shot framing, ect... Another small trick to speed simulation times, is to set the merge node to "LEFT AFFECTS RIGHT" this dictates to dops that the falling pieces will be affected by the animated arm geo only.

the result of this test is deforming geometry that fractures in a controlled manor. This workflow gives the artist complete  control over which fractured pieces become active, by animating a attr transfer from say a simple sphere to static "T pose" or default pose of the geometry attr transfer as a blueprint for the deforming geometry.

here is an example of the result:
https://vimeo.com/57033954