The position of the rigid body reference node is not important unless rotations are applied to the body or reaction moments about a certain axis through the body are desired. In either of these situations the node should be placed such that it lies on the desired axis through the body. In addition to the rigid body reference node, discrete rigid bodies consist of a collection of nodes that are generated by assigning elements and nodes to the rigid body. These nodes, known as the rigid body secondary nodes (see Rigid bodies), provide a connection to other elements. Nodes that are part of a rigid body are one of two types:
The rigid body node type is determined by the type of elements on the rigid body to which the node is attached. The node type also can be specified or modified when assigning nodes directly to a rigid body. For pin nodes only the translational degrees of freedom are part of the rigid body, and the motion of these degrees of freedom is constrained by the motion of the rigid body reference node. For tie nodes both the translational and rotational degrees of freedom are part of the rigid body and are constrained by the motion of the rigid body reference node. The nodes defining the rigid body cannot have any boundary conditions, multi-point constraints, or constraint equations applied to them. Boundary conditions, multi-point constraints, constraint equations, and loads can be applied, however, to the rigid body reference node. | |||||||