Dynamic Analysis Using Modal Synthesis

A modal synthesis method to compute the vibration characteristics of nuclear power plant structures and components is presented. The advantages and limitations of its application are considered. The convergence of natural frequencies and mode shapes to their true values are evaluated. The influence of using a truncated set of substructure modes in synthesizing the mode shapes and frequencies of the entire structure is studied. Numerical examples for typical nuclear power plant structure and piping are presented and the results obtained by the modal synthesis method are compared to those obtained using a direct method. It is concluded that the modal synthesis technique is both accurate and results in significant savings in computation costs. It is also concluded that the sum of all the substructure modes considered should be at least twice the number of modes required for the final analysis.