# 3. Explicit Subcycling

This chapter describes how to setup an analysis to use explicit subcycling. Subcycling can be used to run different parts of the mesh at different time step sizes to improve speed.

Warning

Explicit subcycling is a capability still in the development stages. This capability is not yet recommended for general use.

Explicit subcycling can be used in an explicit transient dynamics analysis to run one part of the mesh at a small time step while running another connected part of the mesh at a large time step. Explicit subcycling can provide a substantial model speedup only if two properties hold. First, some region of the mesh must have a substantially smaller element critical time step than another region of the mesh. Second, the portion of the mesh with the small critical time step must contain a small fraction of the total number of elements used by the analysis.

Explicit subcycling divides the analysis domain into two regions: A coarse region iterating with a large time step and a fine region iterating at a smaller time step that is some integer fraction of the coarse time step. At the coarse mesh time step, both regions sync up to the same analysis time and exchange information. Using the standard analysis technique, every element must run at the same small time step. Testing has shown that an analysis run using subcycling can give equally accurate results as an analysis run without subcycling. The accuracy of the simulation is subject to several restrictions on cross region communication and compatible capabilities.