A computer code for rapid calculation of bending frequencies of rotor blades
Akin, Hakki E.
Wood, E. Roberts
Couch, Mark A.
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This thesis provides a MATLAB (copyright) code and graphical user interface (GUI) which rapidly estimates the bending frequencies of rotating beams from the knowledge of bending frequencies of nonrotating beams. The approach is based on the Rayleigh energy method developed by Yntema. The beams may be rotating or nonrotating, cantilever or hinged, uniform or with linear mass and stiffness distributions, with or without root offsets from the axis of rotation; or uniform with or without tip mass. Especially, the frequencies of both nonrotating and rotating cases can be estimated for (a) beams with and without offset which have mass and stiffness distributions which can be approximated by linear relations and (b) beams with uniform mass and stiffness distributions plus a concentrated mass at the tip. Also, as a part of the MATLABÊ¼ code, the bending frequencies of rotating beams with arbitrary stiffness and mass distributions can be estimated given that the stiffness and mass distributions as well as mode shapes of the rotating beam are provided. In latter case, the mode shapes of nonrotating beams may be used to get rough estimations. The code also presents the nonrotating bending-mode shapes in conjunction with the bending frequencies. The code and GUI are intended for use as a subprogram of JANRAD computer program developed at the Naval Postgraduate School, but can also be used as a stand-alone MATLABÊ¼ program.
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