Identification of non-proportional modal damping matrix and real normal modes

Equations of motion for non-proportionally damped structures cannot be decoupled by using the real normal modes. For such structures. the complex normal modes are in common use for this purpose. but for the validation of finite element mass and stiffness matrices where physical damping matrices are not available. the related experimental real normal modes must be known, In previous publications. an identification theory using the real normal modes and the non-diagonal modal damping matrix for the nonproportionally damped system and some applications with the computer code ISSPA were presented. However, the theory cannot assure the symmetry of the identified modal damping matrix, which must be theoretically symmetric. In this paper, a method for identifying the symmetric non-proportional modal damping matrix using undamped modal parameters obtained from ISSPA is presented and the validity of the method is demonstrated through both numerical and experimental examples. (C) 2002 Publislied by Elsevier Science Ltd.