Computation of real normal modes from complex eigenvectors

A method for the computation of real normal modes from complex eigenvectors is described in this paper. The method is based on the exact eigensystem equations, which commonly cannot be used due the problem of modal truncation. A solution to this problem is achieved by a reduction transformation. The theory of the method is described in detail. With the purpose to demonstrate the applicability, a simulated vibration system is employed. In addition, experimental data from modal identification tests on an aircraft are used. It can be shown that the method is able to transform identified complex eigenvectors into real normal modes with good reliability and accuracy.