When an object is turned into fragments RealFlow groups all these new nodes under a single, so-called MultiBody. MultiBodies are containers which contain large amounts of elements. These individual parts no longer appear in the “Nodes” panel or “Relationship Editor” as accessible and adjustable nodes, but as one object. All transformations of a MultiBody will be applied to its elements as well. This way it is, for example, possible to create splinters: simply downscale the original object in one direction, then fracture it. Now rescale the MultiBody to pull apart the pieces and elongate them.
But, MultiBodies do not only occur in combination with fractured objects. They are also very convenient when you have to import hundreds or thousands of objects, because the import process is very fast in this case. RealFlow does not have to add, manage, and draw all the individual elements of the different panels, but everything is treated as one object. Internally, the objects still exist and keep properties like volume and shape, of course. In terms of simulation data export, the objects are also treated as one node and all transformations are written to a single file.
MultiBodies can be defined as passive and active rigid bodies, or soft bodies. The according “Node Params” panels are very similar to their counterparts of “normal” objects, but with one main difference: there is no “@ mass”, but a “@ density” parameter instead. When an object is created or imported RealFlow determines its volume and calculates its mass from this value. With MultiBodies, on the other hand, there are many objects with completely different volumes and – as a consequence – different masses.
Density is defined as mass per volume unit or, in SI units, kilograms per cubic metre. Since RealFlow knows the volume of each node inside a MultiBody, and density is given as 1,000 kg/m3, by default, it is easy to calculate the objects' individual masses. This is what you do in a MultiBody's rigid and soft body panel: you simply decrease or increase “@ density” to alter the masses of the nodes.
Otherwise, MultiBodies are treated the same way as single objects, and you will find exactly the same parameter sets for both node types.
You can see the physical properties of a MultiBody's nodes under:
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