Numerical procedures for nonlinear static and dynamic analyses of shell systems of various sizes : doctoral dissertation
Numerični postopki za nelinearne statične in dinamične analize lupinskih sistemov različnih velikosti : doktorska disertacija

english

doktorska dela

2020

buckling   Built Environment   civil engineering   dissipative integration schemes in dynamics   doctoral thesis   energy-conserving/decaying and momentum-conserving schemes   mixed finite elements   shells   surface wrinkling

Univerza v Ljubljani, Fakulteta za gradbeništvo in geodezijo

The topics of the thesis are mixed(-hybrid) finite element formulations for shell-like structures, and implicit time-stepping schemes that preserve basic constants of the motion. The considered finite elements are based on two geometrically exact shell models, in particular, large rotation inextensibledirector model and rotation-less extensible-director model. The performance of the current state-of-theart mixed(-hybrid) shell finite element formulations is assessed by studying a large number of numerical examples. Some novel %near optimal% mixed-hybrid shell finite element formulations are proposed that allow for large solution steps, show near optimal convergence characteristics and display little sensitivity to mesh distortion. As for the non-linear shell elasto-dynamics, we revisit implicit dynamic schemes that belong to the groups of generalized-% methods and energy-conserving/decaying and momentumconserving methods. We compare their spectral characteristics, the tendency to overshoot and their accuracy. By performing a set of numerical tests for numerically stiff nonlinear shell-like examples, we assess how these features extend to nonlinear elasto-dynamics. We illustrate the ability of the considered schemes to dissipate the energy, to fully or approximately conserve the angular momentum, and we estimate the order of accuracy for nonlinear problems by error indicators. Novel energyconserving/decaying and momentum-conserving schemes are derived for the previously introduced novel mixed-hybrid shell formulations. The numerical examples demonstrate that the robustness and efficiency of the novel static formulations can be prolonged to dynamics. The final part of the thesis is related to the application of the derived formulations. In particular, the shell buckling process is studied by applying numerically dissipative schemes. The ability of these schemes to handle complex buckling and post-buckling processes is assessed. It is demonstrated that controlled numerical dissipation of higher structural frequencies is absolutely necessary for an efficient simulation of a post-buckling response. Finally, we apply the derived procedures to study the problem of surface wrinkling on curved stiff-shell/soft-core substrates, including the transition between the wrinkling modes.

25.02.2021