This document outlines different approaches to simulating fire, including physically-based methods using fluid dynamics equations, particle system-based methods, noise-synthesized methods, data-driven methods using real fire data, and geometry skeleton methods. It discusses challenges in realistic fire simulation and compares computational combustion discipline and computer graphics approaches. Future directions may include more controllable animation, real-time rendering, and applications for 2D/mobile devices.

1. Fire Simulation
Behanm Akbari
Dec 2014

2. Outline:
• Simulation & Fluid simulation.
• Fire.
• Fire simulation challenges.
• Fire simulation categories.
• Future direction of fire simulation.

3. Simulation:
• Simulation is the imitation of the operation of a real-world process or
system over time . The act of simulating something first requires that a
model be developed, this model represents the key characteristics or
behaviors/function of the selected physical or abstract system or process.
• Usually based on the rules of our real world.
• Some rules can be bent.
• Some rules can be broken.

4. Fluid simulation:
• Fluid simulation, or computational fluid dynamics , is a computer
graphics tool used to generate realistic animations of liquids such as water
and smoke. A fluid simulator emulates the motion of a described fluid,
making use of the Euler equations or Navier-Stokes equations which
describe the physics of fluids, or any simplified version of them. In computer
graphics, such simulations range in complexity from extremely time-
consuming high quality animations for film & visual effects, to simple real-
time particle systems, or Fourier synthesis used in modern games.

5. Navier-Stokes equations:
More recently, there has been an interest in using fluid dynamics, described
by the Navier-Stokes equation,to determine how the gas actually flows, and
to create effects such as swirling and vortices which can often be seen in
flames. The Navier-Stokes equation is a differential equation connecting the
force, velocity, viscosity and pressure at each point within a fluid.

6. Fire:
A fire is a set of physical and chemical phenomena, which include combustion
, fluid flows, and pyrolysis or evaporation. When the combustion occurs in
the gas phase, the luminous part of the gas is called the flame.

7. Fire simulation challenges :
• How to show fire color.
• Another difficulty in fire animation is
how to visualize fire and its lighting
effects on the environment.
• It is the very turbulent nature of fire that
makes it hard to produce a realistic
imitation , especially in real-time.

8. Fire simulation in CCD and computer graphics:
CCD is an interdisciplinary discipline concerning fire simulation in
computational physics. It replaces traditional experiments with numerical
simulation for experimental verification. Fire simulation in computer graphics
is for visual animation. Two fields share similar mathematical models and
numerical routines.
Differences:
•Different application fields.
•Different numerical accuracy.
•Different control strategy.
•Different fire scenarios.

9. visual simulation of fire can be loosely classified
into following taxonomy:
•Physically-based method.
•Particle system based methods.
•Noise-synthesized methods.
•Data-driven method.
• Geometry skeleton methods.

10. Physically-based method:
• Physically-based method becomes popular in past decades. Physical and
chemical models are developed to simulate the process of fire combustion.
Light transportation and visual adaption models are also considered in the
rendering phase.
• The fire elements.
• Flame profile.
• Hydrodynamic motion.
• Chemical reaction.

11. Physically-based method:
Chiba and Takahashi respectively presented fuel-driven models to simulate
propagating and animation of fire. Space is divided into grid cells and each
cell contains a certain quantity of fuel and heat.
A cell is ignited if the temperature reaches the specified flash point. Fire is
rendered by drawing geometry primitives around particle trajectories. It
causes artificial bumpy contours if particles are not adequate enough.
Xmpl:
Maya method.

12. Particle system based methods:
A particle system is a group of individual particles. The particles are given
simple rules that govern their interactions with each other and the
surrounding environment.
Particle-based methods are easy to implement and have low computational
overhead since they do not need to solve the underlying physical and
chemical model.
Besides, particles are not driven by physical model, the motion of flame does
not follow real fire. Particle-based methods are suitable for applications
without high visual quality requirements.

13. Particle system based methods:
Reeves was the first to model fire with particle systems. Fire was depicted by
a particle system of two-level hierarchy, one to model spreading of fire and
the other to simulate single explosion effect.

14. Noise-synthesized methods:
One distinguish feature of fire different from other fluid is its high fluctuation,
which is due to the turbulence of underlying flow motion. According to the
turbulence theory, these turbulent feature can be depicted with statistical
model, which is usually implemented in a noise-synthesized way.
Perlin presented noise-synthesized approach to capture turbulent features of
flames.

15. Data-driven method.
There are several methods to simulate fire based on existing data, such as
images from real scenarios or data set from third-part simulation software or
experimental measurements.
Roberts presented an image-based method to model candle flame. The flame
is simplified as a set of sphere balls. In atomographic method was advocated
to reconstruct volume presentation from photographs of real fire.

16. Geometry skeleton methods:
Geometry primitives are the most suitable presentation for modern
rendering pipeline in computer graphics. Several Geometry-based methods
are proposed to simplify the simulation. Flame is modeled as time-variable
geometry structures to depict its visual profiles, while the spreading of fire is
modeled as contours propagation on geometry surface.
Inakage introduced a simple laminar flame
model with textures mapped onto a flame
-like implicit primitives. The method has
the drawback of dealing with multiple and
animated flames.

17. Future direction of fire simulation:
• Feasible animation control.
• Real-time rendering.
• 2D HD & Mobile Device.