EXACT EIGENVALUE CALCULATIONS FOR PARTIALLY ROTATIONALLY PERIODIC STRUCTURES

A computational method for calculating the exact eigenvalues of partia lly rotationally periodic structures is presented, where the eigenvalu es are the natural frequencies of undamped free vibration analysis or the critical load factors of buckling problems. In particular, the met hod can be used to find efficiently the eigenvalues of the following s tructural systems: (1) rotationally periodic structures with arbitrary boundary conditions; (2) rotationally periodic substructures which ca n be connected in any required way and at any number of connecting nod es to an arbitrary parent structure. The stiffness matrix method of st ructural analysis is used and an existing algorithm is employed to ens ure that no eigenvalues are missed. The successful combination of this algorithm with harmonic analysis and substructuring techniques makes the method presented very efficient. Finally, several non-trivial exam ples are given. (C) 1997 Civil-Comp Ltd and Elsevier Science Ltd.