Using RBE3 elements with many legs and a mass element on the slave node can bring to a dense mass matrix. Since used numerical algorithms are optimized for sparse matrices, this can cause a slowdown of calculation time and even bring to calculation failure for the largest models.
In the attached example, which was developed in version 2206, we have a cube made of shell element at which center there is a conentrated mass; this mass is connected to all other nodes by means of an RBE3. A normal mode solution sol103 is taken. When the solution is launched, the following warning is thrown:
*** USER INFORMATION MESSAGE 22100 (LNNRIGL) The mass matrix is relatively dense. This could lead to a significant reduction in the computational performance in the analysis. This could be caused by a scenario where a few dependent DOFs with defined mass elements are associated with too many independent DOFs in the model. For example, a dependent DOF with CONM2 is connected to lots of independent DOFs by a RBE3 element.
If we change the Rigid element Method, by setting RIGID=LAGRAN in deck case control or Rigid Element Method as Lagrange multiplier in solution case control tab in Simcenter 3D interface (as depicted in the following figure), the previous warnig disappear and calculation time significantly decreases (from more then 4 minutes to 8 seconds in the attached example).