3. Operating principles of the control#

The command takes a group of elements and a group of nodes as input and calculates and integrates the reaction of the nodes resulting from the efforts coming from the meshes.

The following operations are carried out:

  1. Calculating the field of nodal efforts on a subdomain using the CALC_CHAMP command and the FORC_NODA or REAC_NODA option. As indicated in [U4.81.04], we thus obtain the reaction of a subset on the rest of the model.

  2. The nodal reactions from the previous calculation are extracted and these nodal reactions are integrated to reduce them to a torsor at a given point via the command POST_RELEVE_T and the option EXTRACTION. The efforts are obtained in the global benchmark.

  3. A change of frame of reference is made in order to place the force twister in the local coordinate system entered by the user via the keywords AXE_X, AXE_Y and * AXE_Z. By default, the global coordinate system is used.

  4. If the user wishes to perform a modal-spectral calculation, the contributions of the modal torsors are then calculated and combined via the CQC method and then the contributions in the 3 directions are also combined. The method is largely based on the operations described in [U4.84.01] and [R4.05.03]

The user should pay particular attention to the mesh and node groups used. In fact:

  • To have a non-zero reaction, the nodes must be on the border of the domain defined by the cells entered,

  • If a node is « in the middle » of the domain, the internal forces cancel out and the calculated reaction will be zero.

  • If a node is on a free edge of the model (no boundary conditions and no external forces applied to this node), the reaction calculated at this node will be zero.

  • The torsor calculated with a specified group of elements including cells that are not in contact with the given nodes will be the same as the torsor calculated with the group of elements that is strictly limited to the cells of the group in contact with the given nodes because the internal forces in the group are compensated for. In terms of performance, however, it is preferable to limit the size of the group of elements.