This presentation was made at CAASE18, The Conference on Advancing Analysis & Simulation in Engineering. CAASE18 brought together the leading visionaries, developers, and practitioners of CAE-related technologies in an open forum, to share experiences, discuss relevant trends, discover common themes, and explore future issues.

Resource Abstract

Fatigue analyses are an example of engineering calculations that rely on accurate peak stress results from structural simulations. A refined finite element mesh is necessary to capture these peak values but can be challenging for models that have unfavorable aspect ratios of the features of interest relative to the global model size. Submodeling has been a technique used in finite element analyses for decades, but misconceptions about proper use limit the application of this powerful capability, and these will be the focus of the talk. The presentation will discuss (a) submodeling using 2D axisymmetric-to-3D solid submodels, (b) submodeling using buffer zones to capture features such as small fillets, and (c) submodeling when plasticity is present.

Plasticity in submodeling is perhaps the most controversial technique of the ones listed. An example problem will show the nuances of obtaining an accurate solution for these types of problems. Comparisons of the sub-modeled FEMs will be compared to a traditional, detailed, global FEM approach. An example of a mounting hole in a rib stiffener of a pressure vessel that includes material yielding will be used to illustrate all three of the aforementioned submodeling techniques. The example problem will show that the submodels make a finer mesh more feasible in critical areas while providing a numerical solution that is many times faster. Examples of implementation of submodeling on more complex ASME pressure vessel analyses will also be shown. Computational speedups become more dramatic on larger models. Naturally, there are tradeoffs, and the submodeling approach can take more time to document the results of analysis due to the increase in model numbers and the dependence on submodels to global models, for example.

As simulation capabilities becomes more powerful, the science and art of simplifying models into manageable "chunks" gets lost. Submodeling brings the skill of the engineer/analyst/scientist back into the equation and can make the use of powerful CAE more efficient.