HADDA, Nader (2016) UTILISATION DES TECHNIQUES SOUS-CYCLES ET MULTI-ÉCHELLES DANS DES SIMULATIONS CRASH AUTOMOBILE PFE - Project Graduation, ENSTA.

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Abstract

In explicit finite element simulation, the stable time step is bounded by the maximum natural frequency of the model -in practice, it’s estimated as the reciprocal of this frequency. That’s why, in models involving large spatial variation in mesh density (or material characteristics) the smallest elements dominate and impose theirs time step. All of this would increase computational cost for these models. Mass-scaling refers to a technique where a nonphysical mass is added to the small elements in order to achieve a larger explicit time step. Nevertheless, the added mass affects the result and generates nonphysical forces which lead to large plastic deformations –especially in a dynamic analysis and crash simulations where the ratio of the added mass in a specific part is very huge. This may lead to a contradictory nonphysical model or an uncompleted calculation. Subcycling and Multiscale are two techniques developed by LS-DYNA in order to reduce the calculation timing without adding such a huge amount of mass. The techniques consist in partitioning the model in levels of the characteristic time step of tis constituting finite elements. Each sub model is then integrated independently of the others using a time step that pertains to that specific sub model. Then, reducing the calculation timing will be achieved with a negligible added mass against the Mass Scaling case.

Item Type:Thesis (PFE - Project Graduation)
Uncontrolled Keywords:Mass-scaling, Subcycling, Multiscale, LS-DYNA, explicit finite element simulations, automotive, crash, simulations
Subjects:Materials Science, Mechanics and Mechanical Engineering
ID Code:6836
Deposited By:Nader Hadda
Deposited On:12 janv. 2017 11:22
Dernière modification:12 janv. 2017 11:22

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