von Estorff O., Petersen S.

When analyzing exterior acoustic problems employing the finite element method (FEM), special measures are needed to satisfy the Sommerfeld radiation condition. Within the last decade, infinite elements have become a viable tool for numerical simulations in unbounded media. Up to now, various formulations of these elements have been developed, where one of the best known are the so-called Astley-Leis elements. Similar to knowledge based concepts, these elements try to resemble the analytic solutions for the Helmholtz equation in an unbounded domain. For many problems, such as the sound radiation of slender structures, infinite elements with high approximation orders seem only necessary in local parts of the discretization. Hence, in order to reduce computational costs, it seems reasonable to vary the order of the infinite elements within the discretization. In this contribution an analysis procedure with infinite elements of variable order is presented. The applicability of common (and eventually modified) error estimators within the analysis process is discussed using representative numerical examples.