Rigid Surfaces

The association of a rigid surface with part of the model is performed in a special way. BE2 variant 33 elements are used to model the actual rigid surface. Various IRS elements are then modelled as beam element variants which are attached to the edges of the relevant parts. The association of a particular part with a particular rigid surface is achieved by placing the FEMGEN geometry for both the part and the rigid surface into a set named RSn, where n is an integer between 1 and 99.

The rigid surface orientation ie. the direction of the surface normal, is implied by the rigid surface start and end points which in turn is implied by the order in which the user places lines into the RSn set. It is possible to specify the rigid surface start point directly by assigning a point element variant P-START (FEMGEN P-EL Variant 7) to the desired start point.

The interface will create a rigid body reference node number for each rigid surface and use it in the IRS element definitions. No *NODE data is created for this node and ABAQUS will issue a warning and set the coordinates to (0.0,0.0,0.0). The interface will automatically constrain such rigid body reference nodes.

It is possible to specify a rigid body reference node directly via a point element variant RB-REF (FEMGEN P-EL Variant 8). Such nodes will not be automatically constrained, and the user is free to constrain or load such nodes as appropriate.

Note that three-dimensional rigid surfaces are now supported as TR3 variant 12 together with the associated IRS elements (IRS3, IRS4, and IRS9). The three-dimensional rigid surfaces are defined as per the conventions for two-dimensional rigid surfaces. IRS9 elements (QU8 Variant 48) must be used in conjunction with one of the variable node solid element variants (see INTER9 elements) in order to generate the appropriate mid-face and mid-element nodes.

  

Figure 2.3: Example Rigid Surface Element Definition