The 3ds Max software, released by Autodesk, allows users to model, animate, and render objects and systems with a large degree of freedom and accuracy. The Particle Flow program is a simulation system built into 3ds Max. It allows for non-linear events to drive the parameters of the system. Complex phenomena such as water, air, and photon-scale light behavior can all be modeled in the particle flow system.

MODULES

The system consists of various modules to modify simulation behavior. These include:

Emitter – The emitter is a geometry class object which represents the particle system in the viewport. This object controls particle counts/max and in the viewport and in the rendering, particle limits, ways to create a selection of particles and to run scripts.

Event – An event is a group of particle and the actions that affect the group of particles. Events can be linked using test actions or linked to events.

Birth Action – The birth actions generate new particles.

Operator – Operators change variables such as position, velocity, rotation or events such as rendering.

Test Action – Test Actions are a type of action which can script events

Source:  http://wiki.cgsociety.org/index.php/3ds_Max/Particle_Flow

Img Source: http://www.computerarts.co.uk/__data/assets/image/104975/varieties/7.jpg

Particle Flow FAQ:  http://wiki.cgsociety.org/index.php/Particle_Flow/FAQ

ECOLOGICAL SYSTEMS [ MODELED ]

Getting Started with Particle Flow:  http://www.escalight.com/tutorials/3dsmax-tutorials/getting-started-with-particle-flow-part-1.html

Modeling Ground Water Flow:   http://www.freeitsolutions.com/3ds/viewTutorial.aspx?id=3716

Modeling Particle Dispersion:  http://www.freeitsolutions.com/3ds/viewTutorial.aspx?id=4006

Modeling Grassland:  http://www.freeitsolutions.com/3ds/viewTutorial.aspx?id=3211

Video walkthrough creating a particle flow model interacting with terrain