1. SD in a few lines#

The sd_macr_elem_stat data structure represents a macro element that is in static substructuring.

A macro element is in a sense a finite element whose support mesh has any number of nodes. To « manufacture » it, we start from a finite element model and we « condense » it on some of these nodes (which we call « external »). This condensation takes place by eliminating the ddls carried by the internal nodes. This technique is described for example in the book by J-F. Imbert « Analysis of structures by finite elements » published by CEPADUES in 1991. At the end of this condensation, the macro element is represented by condensed matrices and charges. The matrices (stiffness, mass and damping) are solid and symmetric in size nddlesi nddleis the number of external ddls of the macroelement.

The data structure contains the following information:

  • definition of the external nodes of the macro-element,

  • « upstream » references to sd_mesh, sd_model, sd_cham_material and sd_cara_elem,

  • « upstream » references to sd_char_mecade kinematic conditions,

  • a condensed stiffness matrix,

  • a condensed mass matrix,

  • condensed loads.

It should be noted that these external nodes are not all « physical » nodes: because you can impose (dualized) kinematic conditions on an sd_macr_elem_stat, some nodes of the macro element are of the « Lagrange » type.

A macro element then behaves like a finite element that can only calculate certain options: RIGI_MECA, MASS_MECA, AMOR_MECA and CHAR_MECA.