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P. Helnwein, H.A. Mang:
"Parasitic Natural Frequencies of Circular Plates in Consequence of a Simplified Variational Principle";
in: "Proceedings of the International Conference on Computational Methods in Structural and Geotechnical Engineering", University of Hong Kong, 1994, Vol. III, 924 - 929.

The set of Euler equations resulting from application of the stationarity condition to the Hamiltonean functional for the problem of vibration of plates will contain relations concerning the physical identification of Lagrange multipliers, if geometric boundary conditions are not satisfied a priori. These equations are used to eliminate the multipliers, resulting in so-called Simplified Variational Principles. It is shown that such variational principles result in an infinite number of parasitic eigenvalues in addition to the correct eigenvalues.

Keywords: simplified variational principle, parasitic eigenvalues, Circular Plate, Natural Frequency, Variational Principle