All of the simulation work we've done using Field3D has been proprietary, so unfortunately there is no real documentation to be found in regards to that...
But yes, it has definitely been physically based: the simulators we've implemented are all finite difference and particle-based fluid dynamics engines.
I have to say though that I'm not very familiar with the needs of robotics and robotic controllers.. What is your take on Field3D so far, based on looking at the code? Is it somewhat suitable for your needs?
Magnus