Comparison of normal eigenmodes calculation methods based on identified complex eigenmodes

Three calculation methods were recently proposed to transform identified complex eigenmodes of a dissipative structure into normal eigenmodes of an associated conservative structure. These methods were first tested by running a large number of numerical examples and then applied to actual structures. This paper presents the basic ideas of each method. The difficulties encountered during the applications are also analyzed and comments are made on the results obtained. The application of these three methods to a test structure that has two close eigenfrequencies shows that the three results are sufficiently accurate. However, the first two methods use the orthonormality relations and thus require a precise estimation of the identified generalized masses, while the third method, which is iteratice in character, does not use the identified generalized masses and can be recommended for industrial applications.