DYNAMIC-RESPONSE OF A CRACKED ROTOR WITH SOME COMMENTS ON CRACK DETECTION

Bu considering time-dependent terms as external excitation forces, the approximate dynamic response of a cracked horizontal rotor is analyze d theoretically and numerically. The solution is good for small cracks and small vibrations in the stable operating range. For each steady-s tate harmonic component, the forward and backward whirl amplitudes, th e shape and orientation of the elliptic orbit, and the amplitude and p hase of the response signals are analyzed taking into account the effe ct of crack size, crack location, rotor speed, and unbalance. It is fo und that the crack causes backward whirl, the amplitude of which incre ases with the crack. For a cracked rotor the response orbit for each h armonic component is an ellipse the shape and orientation of which dep end opt the crack size. The influence of the crack on the synchronous response of the system can be regarded as an additional unbalance wher eupon, depending on the speed and the crack location, the response amp litude differs from that of the uncracked rotor. The nonsynchronous re sponse provides evidence of crack in the subcritical range, but is too small to be detected in the supercritical range. Possibilities for cr ack detection over the full-speed range include the additional average (the constant) response component the backward whirl of the response, the ellipticity of the orbit, the angle between the major axis and th e vertical axis, and the phase angle difference between vertical and h orizontal vibration signals.