Heylen W., Lammens S., Sas P., Modal Analysis Theory and Testing, KUL Press, Leuven, Belgium, 1997 (in Eng.)
2.
Frolov K. V., Mechanical engineering, Encyclopedia in 40 volumes, v. 2, Dynamics and strength of machines. Theory of mechanisms and machines, Mashinostroenie Publ., M., 1995, 624 pp. (in Russ.)