Local modal analysis of unsteady discrete systems with nodal equations of unequal form

Finite element discretisations of higher order, applied to unsteady equations, generate nodal equations of unequal form. The stability analysis of a time-discretisation scheme for this system, by the local modal approach, therefore cannot be used. In this paper it is shown how, at the expense of a limited increase in numerical work, local modal analysis can be applied to these systems.