A New H-Adaptive Method for Shell Elements in LS-Dyna

University essay from Lunds universitet/Väg- och vattenbyggnad (CI); Lunds universitet/Byggnadsmekanik

Author: Ivan Oskarsson; [2006]

Keywords: Technology and Engineering;

Abstract: This thesis describes the development of a new h-adaptive method for shell elements in the explicit FE-code LS-DYNA. Adaptivity is used to obtain accurate results for large deformation analyses to a low computational effort. However, the present adaptive method available in LS-DYNA is based on a geometrical simplification. When the mesh is refined, the bending deformation of the shell is not considered. This simplification makes the strains and strain distribution improper in for example hydro-forming simulations with the adaptive method. The new method is based on an improved description of the updated geometry. This is made by approximating the shape of the deformed structure and inserting new nodes on the approximated surface. Re-meshing is performed based on the new geometry and the simulation is restarted. The method was applied in two hydro-forming simulations and results from the present adaptive method were compared to results from a reference analyses with a fixed mesh. The conclusions of the new method for the analysed examples are: • Improved accuracy in terms of strains compared to the present methods. • Improved strain distribution compared to the other present adaptive methods. • Probably more effective than the present two-pass method. That is improved accuracy in terms of strains to a lower computational effort. • The method results in a loss of internal energy which leads to inaccurate stresses.

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