Fluid simulations used to be purely scientific, but 3D artists can now use them too. Mike Griggs explores how
Fluid dynamics aren’t just about making things wet. They’re also about making things dusty, cloudy, smoky, fiery and very, very bloody. The major difference between fluid simulations and rigid and soft body dynamics is that instead of applying a simulation to a mesh, you’re applying it to a range of particles. These are then meshed in the case of liquid or can have 2D or volumetric sprites attached to them in the case of gases and clouds to allow your 3D software to render them.
The first thing to bear in mind when using fluid dynamics, especially with liquids, is that your simulations will probably not be 100 per cent physically accurate. The amount of processing power required to create a true simulation of a moving ocean that depicts both its surface and movement underneath the water is still in true supercomputer territory. In fact, most of the software that’s now used to create fluid sims was derived from early work in computation fluid dynamics after the Second World War in scientific institutions throughout the world.
Secondly, remember that for the majority of your shots you’re going to be asked to create simulations that have nothing to do with the real world. Whether it’s the fire emanating from a dragon’s mouth or animated dancers made out of water, you’re going to be creating simulations that have to be art directed – and therefore the need to be truly accurate becomes less important.
Both of these factors mean that you really need to break down your shots. There are various methods of solving simulations for fluids in various pieces of software, which range in price from free to the cost of a small car. Dependant on your core 3D application, find out if there are plug-ins that create fluids to save you having to round-trip to another app, because time is something your computer will tend to need to solve more complex simulations.
Some of these software solutions work well for small-scale simulations such as a product shot of some wine being poured, but this simulation method wouldn’t work as well for ocean waves crashing against rocks. Experiment with as many tools as you can; some of the more advanced software tools have a range of fluid solvers to help you find the best method for your shot.
01 How sticky is the liquid?
Not all liquids behave like water, and some solids can become liquids – wax, for example. Be aware of this when art directing your animation: the viscosity of your liquid material can give it all kinds of characteristics, especially when being applied when moving or interacting with other meshes. If you need to mix liquids, be sure your fluid solution can accommodate mixing different liquid materials.
02 Software options
Some fluid dynamics solutions are bundled directly within the 3D application, as in Softimage and Maya. Plug-ins that handle fluids are available for 3ds Max and Cinema 4D, while Houdini has a range of fluid systems along with its full dynamics setup. RealFlow and Naiad are standalone fluid applications that produce amazing results. Don’t dismiss Blender, though – it has for the money (free) an excellent fluid system that created the geometry for the main image in this tutorial.
03 Lighting and materials for simulations
Lighting is incredibly important for fluid simulations, especially clear liquids. HDR lighting solutions that can only be seen in reflections can be useful for bringing out the shape of a clear liquid. Also make sure that you’re using the correct refraction settings for your liquid because this shapes the light through the liquid to create realistic results. For gases, lighting is just as important – hiding lights in gas clouds is great for giving volume to your render.
04 Gases are fluids too
Fluid simulations aren’t just for liquid – they can also be used for flames and moving gases, either using standalone dynamics software or plug-ins such as Turbulence 4D, used to create this image in Cinema 4D. Both gases and liquids run off the same sets of equations, though to create liquids another stage of meshing the geometry created by the particles or creating the geometry to be moved in the fluid simulation needs to take place.
05 Model liquids for stills
Fluid simulations are an excellent way of creating natural forms for stills, but their computation time can be expensive. To minimise the time spent, simpler simulations can be run and the resulting meshes can be smoothed in sculpting software such as ZBrush. Alternatively, modelled liquid solutions such as the Splash Kit for modo come with modelled elements and lighting setups to enable you to create your liquid solutions as quickly as possible.
01 Create a world
Start by creating a cube and applying a modifier to act as a boundary for how far you wish your fluid simulation to extend.
02 Make the objects
Create simple geometry to act as obstacles as a receptacle and pourer, and create two spheres to be the fluid substance.
03 Run the simulation
Now, run the simulation. Some of the liquid misses the receptacle and splashes onto the edge of the cube boundary that was created at the start.
Mike Griggs is a freelance concept 3D, VFX and motion graphics artist working across TV, exhibition and digital design
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Posted on Thursday, November 8th, 2012 at 4:22 pm under Guides, Technique, Tutorials. You can subscribe to comments. You can leave a comment, or trackback from your own site.
Tags: 3ds Max, Blender, Cinema 4D, fluid simulation, Maya, ZBrush
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