Fluent Dynamic Mesh query
 

Hi,
I am new to using dynamic mesh

I would like to know more about the fluent dynamic mesh.
As far as i understand its a Lagrangian mesh which is being updated at every time step.

I have gone through some of the examples e.g falling box.
I see that it is using 2 meshes one around the box and other outside the boundary layer of the box.

& UDF is updating density and speed of sound with every time step.

I would like to know how exactly the simulation is working? How mesh is being updated by udf?