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Modal calculations easier and costless

19 November 2012

by O. Boiteau, EDF R&D / Sinetics

To study the vibrations of a structure or search its buckling modes, one must often solve a modal problem. Code_Aster offers several algorithms through different operators. Currently, these are the subject of a renovation to improve their ergonomics, robustness and performance (time and memory).

The first stage has just been completed. It provides time savings up to a factor of two with the operators INFO_MODE and MACRO_MODE_MECA. The use of INFO_MODE is easier in order to allow the chaining with MODE_ITER_SIMULT. The next step is to extend the parallelism in MACRO_MODE_MECA.

In a vibrations study, one have to size modal calculation with global parameters : strip search of eigenmodes as well as their number. Otherwise, the operator INFO_MODE provides this number of eigen-modes in a given interval. In all cases, the prior calibration of the model is very useful to define size intervals in order to optimize costs of further calculations.

Until now, users had to make several calls to INFO_MODE (one per band). Now one can carry in a single run since this operator accepts a list of frequencies (or critical loads). This ergonomic improvement comes also with big savings in computation time (up to a factor of 2) because each internal frequency is taken into account only once (instead of two).

These improvements have been declined in the modal operators calculation : MODE_ITER_SIMULT and MACRO_MODE_MECA. The first one can now reuse prior calibrations and not to repeat the same work as a pre-processing step. The second one had its algorithmic scheme completely redesigned. It is now costless in time (gain up to a factor of 2, cf. Tables 1 and 2) more robust (if eigenmode near a bound of a sub-band) and access parallelism (thanks to the linear solver MUMPS). This last point can save up to an extra factor of 2 in time but also in memory peak.

 Table 1. Comparaison of MACRO_MODE_MECA performances with the test-case perf013a (square plate with shell elements) : number of dofs=1.0M, 8 searching subbands on the interval[0Hz,4000Hz]. Version 11.4.
 Table 2. Comparaison of MACRO_MODE_MECA performances with a seismic analysis : number of dofs=0.7M, one searches 448 eigenmodes in the interval [0Hz,60Hz]. Version 11.4.