A lot of modern FE codes have an option called AUTOSPC. Examples are Nastran or Marc. I know that this option removes degrees of freedom to avoid a singular matrix system. But how to determine problematic DOF and how can they be removed without leading to a wrong result of the matrix system?

  • $\begingroup$ This is the first time I hear of this option. According to this document, it computes the eigenvalues and eigenvectors of the stiffness matrix and where the normalized eigenstifnesses are below a tolerance it constrains the DOF with the highest ratio in the eigenvector. It is suggested that you check the theory manual of Nastran (or the software you are using) to see how they implement this option. $\endgroup$ – nicoguaro Jul 24 '19 at 21:05

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