On Some Problems Associated With Vibration Isolation of Ship Machinery

Vibration isolators of machines installed on ships are subject to both dynamic forces involved with the working of these machines and inertia forces resulting from the rolling of the ship. In order to illustrate this better, a solution of the vibration equation of a single mass system has been analyzed, the system being excited simultaneously by a dynamic force and a motion of foundation. It has been found that the larger the ratio of rotation speed is to natural frequency of vibration, the larger is the relative displacement of a machine mounted on vibration isolators. To obtain as small as possible a value of this ratio it might be necessary to use “hard” isolators, but such a solution is not one of the best, because forces transmitted to the foundation would then be larger than the dynamic forces causing the vibration of this machine. Thus the author recommends employing “soft” isolators, on condition, however, that the frequency ratio mentioned previously be chosen such that the elastic deformation of the isolators be within allowable limits.