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

5 A workow for using and creating custom volumeelds in Houdini.5.1 IntroductionThe aim of this project was to get more and better control over uid simulationsusing custom elds. To be able to have this kind of control the problem isapproached from two sides. The rst side is by dening custom elds inside ofSOPS, the second side is by using microsolvers to integrate those custom eldswith existing solvers and perform certain mathematical calculations to solve therequired needs inside of DOPS.These custom elds are dened in SOPS and brought into DOPS. In orderfor them to work correctly they need to be inserted in a uid solver at theright place, some of this has been covered in section (4). Custom elds canadd any kind of data to the simulation. For example: add color, temperature,velocity, fuel, density, etc. Some of these attributes are already supported by thepreset solvers and can be easily modied. Others will need extra implementationthrough the use of microsolvers. There has already been done a lot of work in theeld of computational uid dynamics and some of the preset solvers in Houdinicover a lot of this functionality. The aim of this project is not to create a fulluid solver with a combustion model from the ground up, but rather to be ableto modify and augment existing solvers.By controlling the uid simulation through custom elds, depending on whatexactly is modied, some of the physical accurateness of the simulation will belost, but that is the whole point as by introducing custom elds (art-)directablesimulations are possible. The goal of this project is not to build a physicalsimulator, but rather to understand a physical simulator and then insert extraelds into it to augment the possibilities of the solver. Ideally the uid ow andturbulent behaviour is maintained within the modications, but if certain eldswill be overwriting other elds because this provides better visual results thenthis is considered an improvement.5.2 The implementation of an attribute transfer tool inSOPS to help dene custom volume elds.There are a few microsolvers inside DOPS that will allow to bring data fromSOPS into DOPS already:• The Sop Scalar/Vector eld microsolver which can bring in a fog volumethat has been dened in SOPS through an iso-oset sop.• The Gas Particle To Field microsolver allows point attributes from particlesto be copied into a eld, after the particle geometry has been denedinside a SOP Geometry dop. This microsolver allows for most of the requiredfunctionality, but it is in dops which requires the simulation to cookup to the current frame as soon as a change is made.20