Unlike the other motion types (linear, angular, combined, etc.), Free Motion allows for motion in any direction. This is the most flexible of the motion types, and can be used to simulate unconstrained (or partially constrained) movement of objects within an active flow field.
Free-Motion is always flow driven, and is defined by enabling or disabling any of the six degrees of freedom. Limits can be defined for each degree of freedom, but collisions with walls, static and other moving solids are automatically detected.
Forces can be applied to objects in free motion as well as gravity. Freely-moving solids can be subjected to initial linear and/or angular velocities as well.
Objects in free motion cannot pass through other solids, walls, symmetry or surfaces with periodic conditions. They can, however, pass through openings (such as fluid boundaries with specified velocities, flow rates, or pressure conditions).
Meshing Considerations
Care should be taken when defining the mesh for free motion analyses. For the constrained motion types, the path of the object is known, and the mesh can be refined within that path. This often reduces the mesh requirements on other areas of the model that do not directly influence the motion. In a free motion analysis, however, the path is often less certain, so a higher mesh density may be required throughout more of the model in order to adequately resolve the motion of the object.