To keep a rigid body simulation together for exporting, you should put all the rigid body elements and its simulation environment into a model structure. Then when you export the model, it remembers all the elements that were in the simulation environment.
When you import the model into another scene, a separate simulation environment is created for it with all its elements intact. You can then merge this imported simulation environment with any existing ones in the scene.
Merging environments is useful for when you want to assemble a single rigid body simulation from the simulations contained in several models. You can have all rigid body elements from any number of models in a scene interact together in a single simulation. See Merging Multiple Environments for more information.
You can also store the cached simulation in an action source for exporting with the model. You can cache one action source per model, which lets you import and export models with their cached simulations intact.
For more information, see Models and Creating ICE Simulation Environment Cache Files.
