A MIXED FORMULATION FOR A BENDING DOMINATED KOITER SHELL WITH OBSTACLE

In this paper, we present a mixed formulation for a bending dominated Koiter shell with obstacle in order to avoid numerical locking or the deterioration of the convergence when the small parameter the thickness goes to zero. This formulation is a combination between the free locking mixed formulation presented in [1,10] and the Koiter’s model with obstacle for flexural shell proposed in [6].

A Posteriori Detection of Numerical Locking in hpq-Adaptive Finite Element Analysis

The proposed detection algorithms are assigned for the hpq-adaptive finite element analysis of the solid mechanics problems affected by the locking phenomena. The algorithms are combined with the M- and hpq-adaptive finite element method, where M is the element model, h denotes the element size parameter, and p and q stand for the longitudinal and transverse approximation orders within an element. The applied adaptive scheme is extended with the additional step where the locking phenomena are a posteriori detected, assessed and resolved. The detection can be applied to shear, membrane, or shear–membrane locking phenomena. The removal of the undesired influence of the numerical locking on the problem solution is based on p-enrichment of the mesh. The detection algorithm is also enriched with the locking assessment algorithm which is capable of determination of the optimized value of p which is sufficient for the phenomena removal. The detection and assessment algorithms are based on a simple sensitivity analysis performed locally for the finite elements of the thin-walled domain. The sensitivity analysis lies in comparison of the element solutions corresponding to two values of the order p, namely current and potentially eliminating the locking. The local solutions are obtained from the element residual method. The elaborated algorithms are original, relatively simple, extremely reliable, and highly effective.