Non intrusive beam-3D coupling for transient rotor dynamics applications

by M. Tannous (Ph.D. student at GeM, Ecole Centrale de Nantes supervised by P. Cartraud) and M. (EDF R&D), in collaboration with D. Dureisseix (LaMCoS, INSA de Lyon)

For rotor dynamics computations, a 3D model can properly take into account non-linear effects, at the expense of the computational cost. When nonlinearities are not taking place, a switch between a coarse beam-type model and the fine 3D model allows for a considerable gain in the global computational cost while preserving a good accuracy.

Thanks to the integrated and simple use of Python, Code_Aster enables non-intrusive switching from one model to the other during transient calculations.

Below an illustration of a pinned beam subjected to a sinusoidal dynamic excitation for 3s long. Dynamic computations begin with the beam-type model. At the chosen switch instant (2.4 s), displacements, velocities and accelerations of the beam neutral axis are collected. According to a rigid-body cross-section hypothesis, these fields are extruded in the thickness of the beam. The obtained deformations of the cross-section are corrected by operators handling matrices and fields.

Superimposed displacements of the beam-type model and the mixed model

Displacement of the node located in the middle of the bi-supported beam for different models (two reference models 1D and 3D, two 1D-3D mixed models with and without switch)

These results have been published in Eccomas international congress ([1]), and are under publication ([2]).

Outlooks :

For completeness of the methodology, the reverse switch from the 3D model to the beam model does not present any particular difficulty and work on it is under progress. The final switch from 1D to 3D and the reverse one from 3D to 1D is thought to potentially allow further CPU time and memory savings. Applications in nonlinear dynamics are under work in order to exemplify the relevance and effectiveness of the non intrusive suggested methodology. Moreover, the method is also being extended for rotor dynamic applications [3].

All these advanced features will be soon integrated to Code_Aster.

References :

– [1] M. Tannous, P. Cartraud, D. Dureisseix, M. Torkhani, A beam to a 3D model switch in transient dynamic analysis , Proceedings of the 6th European Congress on Computational Methods in Applied Sciences and Engineering, Eccomas 2012.

– [2] M. Tannous, P. Cartraud, D. Dureisseix, M. Torkhani, A beam to a 3D model switch in transient dynamic analysis, submitted to Computers and Structures, 2012

– [3] M. Tannous, P. Cartraud, D. Dureisseix, M. Torkhani, Bascule d’un modèle poutre à un modèle 3D en dynamique des machines tournantes, soumis au 11e colloque national en calcul des structures, CSMA 2013.