Controlling Fluid Simulations with Custom Fields in Houdini Master ...

1 AbstractThere are various dierent algorithms and techniques for uid simulation, bothphysical simulation and more artistic simulation. Some of these techniquesare available to the general public through existing 3d software packages. Thepurpose of this thesis is about developing a workow that provides more controlfor artistic uid simulation in Houdini. This workow consists of two mainelements, the development of a tool that helps with the creation of customvolumetric elds and the implementation of these elds in Houdini's dynamiccontext.2 IntroductionFluids and gaseous materials are hard to art direct. Physical simulation of reand smoke can result in realistic results, but can also make it harder to controlthem as they are bound by certain rules. For certain shots in lms a physicallyimpossible behaviour might be required and that is when artists need to be ableto truly direct where the smoke or re needs to go and how it needs to get there.In two dimensions it is straightforward to paint strokes on a canvas to denewhere certain densities, colours or other properties should be. In a 3D eld itbecomes a lot harder to dene these artistic strokes.Sometimes it is not the movement that needs to be dierent, but the look.There might be a demand to mix dierent types of smoke together, for instancea red gas and a blue gas forming purple gas when they mix. If this colourproperty is linked to the behaviour perhaps only the red gas is inammable, orperhaps they become inammable when they start mixing, similar to chemicalreactions. Because of this complexity in both look and behaviour, software thatcan handle this could be a useful tool. This project focuses on the developmentof a tool and workow that can provide this kind control in Houdini.3 Previous work3.1 IntroductionThere are several approaches to creating volumetric eects. The two mainapproaches are either using a large amount of very transparent particles asdeveloped by Frantic Films [1] and rendering them to an accumulation buer orusing a voxelgrid, ray-marching through the volume [8]. Both approaches couldbenet from additional user control through custom elds. However, most of thecurrent solutions are either part of visual eects studios proprietary software,or programmed in isolated simulators.Some of the uid solvers that are incorporated in mainstream 3d applicationsprovide not enough control to be able to create more advanced visual eects.A plug-in such as FumeFx for 3dsmax is basically a black box with little extracontrol beyond the provided parameters. Similarly the uid solver in Maya is3