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

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Figure 1: Separate user dened elds combined into a nal velocity eld, createdby Rhythm and Hues using FELT. Image taken from [6]also limited in terms of control. These solvers will provide good results quickly,but are not able to be extended or internally modied by users for more specicrequirements.3.2 Proprietary Systems3.2.1 Rhythm and Hues' Field Expression Language ToolkitAn example of a proprietary system that helps dene 3d scalar and vector eldsis a tool developed by Rhythm and Hues. They create and combine user denedvector elds using FELT, their Field Expression Language Toolkit as can beseen in Figure 1. The resulting velocity eld is used to drive particles for themovie The Incredible Hulk [6].3.2.2 ILM's directable, high resolution reILM has created high detailed re for the movie Harry Potter and The HalfBlood Prince, using particles that were rst advected by a low resolution uidsimulation and then were used to ll up eld information such as temperature,velocity for high resolution 2d elds [10]. Those elds are then processed bya uid solver solving velocity, density and temperature. The particles are projectedon 2d slices perpendicular to the camera, similar to the way sprites facethe camera as can be seen in Figure 2. Because the slices are 2d, the resolu-4
Figure 2: High resolution 2d uid containers controlled by information fromprojected particles created by ILM. Image taken from [10]Figure 3: Advecting the simulation with curl noise where turbulent energy isdetected. Image taken from [14]tion can be raised quite high. The interesting part is that the relatively smallamount of particles are used as a way to dene the high resolution elds. Theparticles represent a custom eld, this hints towards the idea that the customeld does not need to have a very high resolution as some of the simulationsonly used 20.000 to 100.000 particles.3.3 Research3.3.1 Introducing noise in the velocity eldAnother example of the use of a custom eld to give more interesting resultsin uid simulation is the introduction of curl-noise for procedural uid ow [3].They generate turbulent velocity elds based on Perlin noise. This type of noiseis procedural but could just as well be added to uid simulations, which is whatis being done in [14] with the additional condition that the curl noise is notadvecting the velocity everywhere, but only where their physically motivatedenergy model dictates it as can be seen in Figure 3.5
Page 1 and 2: Controlling Fluid Simulations with
Page 3: 1 AbstractThere are various dierent
Page 7 and 8: Figure 5: The node based operator g
Page 9 and 10: sets, which means they are built fr
Page 11 and 12: • as an axis aligned plane that s
Page 13 and 14: Figure 7: The node tree for the upd
Page 15 and 16: Figure 8: The node tree showing the
Page 17 and 18: Figure 9: The node tree in Houdini
Page 19 and 20: 4.4 Up Res techniqueIn Houdini 10 a
Page 21 and 22: • The nal option is with a Gas Fi
Page 23 and 24: Figure 12: Premultiplication proble
Page 25 and 26: Figure 14: The preset smoke solver
Page 27 and 28: Figure 16: A helix curve emitting d
Page 29 and 30: Figure 19: A few stages of the adve
Page 31 and 32: Figure 21: Top: The stages of the a
Page 33 and 34: and pyrosolver work took time. This
Page 35: [10] Christopher Horvath and Willi

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