Modal analysis of rotor on piecewise linear journal bearings under seismic excitationModal analysis of rotor on piecewise linear journal bearings under seismic excitation Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2015-11-071999enA rotor bearing system is expected to exhibit large vibration amplitudes when subjected to a large seismic excitation. It is possible that these vibrations can lead to large values the eccentricity of the bearings. Then the bearing is operated in highly nonlinear region because the stiffness and the damping coefficients are nonlinear as functions of the eccentricity. To solve this problem numerical integration must be performed with high cost in computer time. The idea of this paper was to divide the nonlinear area into more areas where the stiffness and damping coefficients could be considered to be constants. In other words the bearing coefficients are considered to be piecewise constant. The excitation due to the earthquake is modelled as a movement of the base of the bearings using the El Centro data for the acceleration. Then a simplified modal analysis for each of these piecewise linear regions can be performed. The equation of motion of the rotor contains rotational speed depended terms, known as gyroscopic terms, and terms due to base excitation. The response and the variation of the dynamic properties of this complicated rotor bearing system are investigated and presented.http://creativecommons.org/licenses/by/4.0/Journal of Vibration and Acoustics1212190-196 Gaganis Vasileios Γαγανης Βασιλειος Zisimopoulos, A Nikolakopoulos, Pantelēs Papadopoulos C. The American Society of Mechanical Engineers Automatic computers Automatic data processors Computer hardware Computing machines (Computers) Electronic brains Electronic calculating-machines Electronic computers Hardware, Computer computers automatic computers automatic data processors computer hardware computing machines computers electronic brains electronic calculating machines electronic computers hardware computer Quakes (Earthquakes) earthquakes quakes earthquakes