2.5.6.      Mass Weighted Effective Independence

The EI algorithm described in Section 3.4.5 has the advantage that it does not require calculation of static shapes or reduction of the mass matrix. Because of this it can be applied to large initial candidate sets (100,000+ DOF). An initial mass-weighting of the modes can be applied to guide the algorithm towards selecting DOF with high mass, but since the mass matrix is not reduced, the mass of the omitted DOF is not redistributed to the remaining DOF during application of the algorithm. The Mass Weighted Effective Independence (MWEI) algorithm combines the IGR and EI algorithms. It does a Guyan reduction at every step like the IGR algorithm, but uses the mass-weighted effective independence rather than the ratio of mass/stiffness to choose which DOF to eliminate. Its performance is very similar to the IGR algorithm, and it is limited to a maximum initial candidate set of 5,000 – 10,000 DOF because of the cost associated with the initial reduction.