# 3.2. Limitations of Subcycling

Subcycling is currently incompatible either in whole or in part with many other capabilities. The capabilities that have incompatibility with subcycling include but may not be limited to the following:

- Subcycling is incompatible with most capabilities that require an auxiliary region. This include representative volume elements (RVE), Gemini coupling, and multi-procedure analysis coupled via hand-offs or solution control.

- Subcycling currently does not work with implicit dynamics, implicit statics, or modal analysis.

- Subcycling is currently not compatible with rigid bodies.

- Subcycling is incompatible with any critical time step computation method other than the default element based time step calculation. This includes nodal based and Lanczos algorithm based time step computation methods.

Additionally several capabilities will not function correctly if that capability is operating at or near the boundary between the coarse and fine region. If such a capability is included in the subcycling analysis and that capability happens to cross the coarse/fine boundary, accuracy and stability problems may result. The capabilities known to be have restrictions when used with subcycling include but may not be limited to:

- Element death near the subcycling boundary may not be able to correctly determine when a node shared between the two regions goes inactive (leading to accuracy and stability issues).

- Contact between any surface in the fine region and any surface in the coarse region cannot be evaluated.

- Methods that define a force from an external load (such as CTH) can only be coupled to the deformation of the coarse.

- No non-local element or boundary condition can span the coarse to the fine boundary. This includes nodal based tetrahedra, MPCs, Spot Welds, Super Elements, Cylindrical Joints, and the J-Integral computation.

- Nodal output quantities at the coarse to fine boundary may not be displayed properly in plot files. Contributions to quantities such as nodal force may exist in both the fine and coarse region and the outputs would need to be summed from both.