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

Figure 4: The dierent states of target driven smoke using custom elds. Imagetaken from [7]3.3.2 Target driven smoke animationCustom elds can also be used to create target driven smoke animations, as in[7]. They introduce a driving force term that causes the uid to carry the smoketowards a particular target and they also add a smoke gathering term whichprevents the smoke from diusing too much due to numerical dissipation. Thecore concept behind this technique is using the gradient of a blurred densityeld of a target shape as direction vectors to advect the velocity eld of thesmoke. The resulting vector eld looks like all the vectors are pointing towardsthe target shape. Because the start and end shape might have dierent densitiesor the smoke might lose density along the way, density is added as it interpolatesbetween the two shapes as can be seen in Figure 4.3.4 A broader publicThe above approaches use custom elds and geometry to gain more controlover the simulation, but they are separate or proprietary software solutions.Because they are custom built they have the advantage that they will t withinthe pipeline of a particular company and are able to explore new hardwareplatforms such as the GPU. The drawback is that these tools are not veryportable and useable by a broader public.3.4.1 Node based dynamic simulationsOne company that is trying to change the way uid simulations are set upis Exotic Matter with their software called Naiad [5]. The creators are MarcusNordenstam and Robert Bridson who have both contributed greatly to thedevelopment of uid solvers over the past ten years. Robert Bridson has publishedseveral insightful papers and also the book Fluid Dynamics for ComputerGraphics [2]. At its core Naiad is a dynamics solver and a simulation framework.Naiad allows for the creation of a description of a simulation scene. Thisdescription can then be simulated. The description can be made through a nodebased interface which resembles that of node based compositing software as can6