Water Effects in Houdini 11

Taught by Jonathan Gilbert

Course Number:
Software Version:
Original Run Date:
July 2011 
11 hours 11 minutes 
This intermediate (pushing advanced) level course discusses fluid effects in Houdini. Profs Jonathan Gilbert and John Moncrief will help members become familiar with Houdini’s Dynamics Operators (DOPs) and the different fluid types: SPH, Voxel-Based and FLIP fluids. With this knowledge you will endeavor in a production oriented project to integrate a cg water fountain into a live action background plate. We will explore Houdini’s Rigid Body Dynamics (RBD) for collision detection, FLIP fluids for the bulk of the water effects, DOPs Forces for wind, foam and spray using some built in shelf tools (whitecaps) and lastly, lighting, shading, rendering and compositing the final image.

Gilbert is a freelance VFX artist with over six years of Houdini experience. He graduated with his MFA in 3D Animation and Visual Effects with a concentration in fluid dynamics from the Academy of Art University in San Francisco. He then worked at Side Effects Software Inc. building and teaching a series of basic and intermediate Pyro Effects classes in Santa Monica. More recently, Jonathan finished working on the last Harry Potter and the Deathly Hallows Part 2 as a Technical Director at Gradient Effects. He also is currently a Professor at the Academy of Art University in San Francisco, building and teaching Advanced Houdini.

Moncrief started working in VFX over ten years ago and has experience in Houdini, Maya, 3ds Max, After Effects, Shake, and just about every NLE you can think of. John just wrapped up 6 months working at Side Effects Software Inc. in Santa Monica where he created a library of Houdini training courses on FLIP fluids, DOPs and VOPs for industry professionals from various studios including Blizzard, Sony Entertainment and DreamWorks. He has one insane long-haired cat, horrible allergies, and is currently pursuing a Masters of Fine Art degree in Visual Effects at Savannah College of Art and Design in Atlanta.
Water Effects in Houdini 11
Watch our overview of the course

Class Listing

Class 1

Mainly theory and lecture. It lays down the foundation for understanding the more advanced properties of fluid simulations. We discuss the three types of fluid simulations available in Houdini, Voxel Based, SPH (particle), and FLIP. There is a complete breakdown of all three simulation methods including example scenes.

Class 2

You will build upon your fundamental theories and concepts that you learned already by learning how to set up volume, sph and FLIP fluid simulations. Also, you will explore the most common and useful parameters of each and gain some insight as to why FLIP is so powerful and the reason we'll be using it extensively in our project.

Class 3

Begin customizing the FLIP fluid simulation by first discussing different methods of emission, setting up clipping limits for efficiency and creating effective collision geometry. Discuss getting data in and out of DOPs and common work flows such as caching methods, writing out .sim data and/or .bgeos and where to find information about distributed simulation.

Class 4

Discuss some of the scene optimizations such as the .bgeo file format and only using one single piece of geometry for our fountain. Explore in detail different techniques and strategies for working with different scene scales in a fluid simulation by adjusting important parameters and using specific DOPs while analyzing the advantages and disadvantages for each of the setups. Cover methods to export .sim data and using an initial state. Quickly go over a couple simple VOP SOPs such as animated noisy volume and a velocity visualization tool.

Class 5

Explore a variety of ways to fill up our water fountain bowls by first using the particle fluid object's initial data option to turn geometry into particles as well as converting the geometry into our own set of points and using the particle field type for the initial data.

Look at working inside the popsolver to source particles from our geometry, the sculpted particle fluid shelf tool to take an initial reference surface and a terrain object to create a field of particles with it's own flip solver and fluid object and the method used in the first pass of the simulation, using another particle fluid emitter to emit particles from custom geometry.

Take a quick tour of the ripple solver and how it could be used to simulate the base water surface of the water fountain as an option to possibly save time by not having to simulate as many particles with flip.

Class 6

We cover some basic secondary effects for our fountain simulation. We float leaves on the water surface. First we show this on the ripple surface, and then demonstrate the technique using the mesh generated by the particle fluid surface. Instead of using shelf tools, we build our on set of custom DOPs nodes in order to push the leaves around in the water using the velocity field from the FLIP solver.

Class 7

We take a closer look at secondary effects for fluid simulations. First, a review of some reference footage so that we may get a better idea of what types of secondary effects we might need. Next we cover advanced DOPs techniques and build our own solver for calculating turbulence. We look at certain SOPs solutions for creating spray on a wave based on the curvature of the surface. We also check out the performance monitor and look at ways of optimizing the fountain scene to get a faster more efficient simulation.

Class 8

Briefly talk about the new simulation and the meshing parameters used to get our fluid mesh. Cover how to set up an environment light with an HDR that has been modified in COPs. Set up an area light for nicer lighting and shadows. Discuss the Mantra ROP and some of the important parameters to look at when rendering liquids and setting up Micropolygon Physically Based Rendering. Talk about Caustics and Photon Map generation. Then set up takes to separate out individual render passes and bring them into COPs where we composite them together. Look at some quick tricks to fake some shadows and lighting changes in our composite.

Class 9

We address the final touches to our fountain project. We take a closer look at the individual elements of a rendered fluid simulation. We discuss how to export out custom foam attribute as a separate image plane by creating custom renderable parameters inside the basic fluid shader. After that the footage is brought into Nuke for the final composite.

Class 10

A variety of methods for artistically controlling the motion of a fluid in Houdini are. These include creating custom velocity fields to use with the field force dop and gas particle to field dop, using a sop vector field with the gas calculate dop and using POPs attractors along with the ballistic attribute. With all of these different tools for controlling the motion of fluid simulations, pretty much any type of fluid effect can be achieved now.