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[FAQ]

*CONSTRAINED_BEAM_IN_SOLID (CBIS) has been developed to constrain beam elements into solid elements. In this case, there are no nodes shared between the beams and the solids. CBIS constrains the nodes of the beams to the nodes of the adjacent solids so that these nodes end up with the same velocity and acceleration fields. CBIS works best when the length of the beam elements is similar to the edge length of the adjacent solids. If the size of the beam elements is larger, additional coupling points need to be to introduce with the NCOUP field. For example, for beam elements with twice the size of the solids, NCOUP should be set to 1 to introduce an additional coupling point at the middle of the beam. This will result in a tributary beam length at the coupling points that is similar to the edge length of the solids. Having beam elements much smaller than the solids does not imply more accurate results in terms of coupling. Note that CBIS ensures conservation of mass and momentum at the expense of kinetic energy loss. The latter is more evident in transient problems involving high loading rates. The kinetic energy loss due to the coupling in CBIS is included in the “sliding” energy component of glstat. *CBIS_PENALTY invokes a penalty-based coupling. This conserves kinetic energy much better in transient problems, however, it does not support the CDIR and AXFOR fields. The spring energy done by the coupling force is included in the “sliding” energy component.