Global-Local Analysis (Submodeling)

Global-local analysis is a technique in which a full model is solved using two (or more) submodels; one submodel represents the full structure but at a lower accuracy (for example, a larger mesh size) and the second submodel represents only a part of the structure (for example, using a smaller mesh size).

The global structure is solved first and the displacements from the selected zone are interpolated and applied to the local structure. Global-Local Analysis is implemented with the use of the subcase specific modeling technique defined above.

Global-local modeling is only an approximation, and its use depends on the assumption that a more accurate local model will not significantly affect the displacements of the global structure. This process should not be used whenever small stiffness changes in the local submodel may have a large impact on the solution outside of it.

Motivation

Global-Local Analysis may help improve results in models with local stress concentrations. Parts of the structure with small details which require relatively higher accuracy can be modeled as local submodels with a fine mesh and the full structure can be modeled using a coarse mesh. This allows for faster solution times as only a part of the structure is being solved with a fine mesh.

Figure 1. Application of Global-Local Analysis

In Figure 1, an example building is illustrated wherein sections containing the pillar-roof joint are modeled as separate submodels with a refined mesh. The finer mesh allows for better accuracy at regions with high stress concentrations. Using the Global-Local Analysis capability, the results from the coarser global model are interpolated and applied to the finer mesh of the local model at the cut surface. This allows for the local model to be driven by the results of the global model.