A counterrotating eccentric mass exciter shown in Figure is used to determine the vibrational characteristics of a structure of mass 181.4 kg.
At a speed of 900 rpm, a stroboscope shows the eccentric masses to be at the ~op at the instant the structure is moving upward through its static equilibrium position, and the corresponding amplitude is 21.6 mm.
If the unbalance of each wheel of the exciter is 0.0921 kg· m, determine
(a) the natural frequency of the structure,
(b) the damping factor of the structure,
(c) the amplitude at 1200 rpm, and
(d) the angular position of the eccentrics at the instant the structure is moving upward through its equilibrium position.
