Using Iterated IRS Model Reduction Techniques to Calculate Eigensolutions

Static or Guyan reduction is widely used to reduce the number of degrees of freedom in a finite element model but it is exact only at zero frequency. The Improved Reduced System (IRS) method makes some allowance for the inertia terms and produces a reduced model which more accurately estimates the modal model of the full system The IRS method may be extended to produce an iterative algorithm for the reduction transformation. On convergence this reduced model reproduces a subset of the modal model of the full system. An iterative version of the IRS method based on dynamic reduction has also been derived. This paper considers the possibility of using the iterated IRS method to calculate the eigensolutions of a structure. The method is compared to subspace iteration and a plate example given to evaluate its efficiency.