Vibration reduction of main hulls using semiactive absorbers
WEN-JENG HSUEH
Department ot Naval Architecture and Ocean Engineering, National Taiwan University, 73 Chow Shan Road, Taipei, Taiwan
Abstract： A semiactive-type absorber for vibration reduction of main hull girders was investigated. The semiactive absorber system includes a moving mass, support springs, dynamic dampers, and a control system. Only a small electrical power supply is needed for control of the damper valve and the operation of the control system. In this paper, the dynamics of the ship's hull and the constraints of the semiactive absorber are described first. Then, a suboptimal operation law is derived based on the properties of the absorber and the theory of optimal vibration reduction. The numerical simulation results show that the semiactive absorber is more efficient in hull vibration reduction than the passive absorber during critical periodical excitation from the propeller. The vibration caused by multifrequency excitation can also be suppressed by the semiactive absorber. In terms of effectiveness, the semiactive absorber is almost as effective as the active absorber. In particular, the performance of the semiactive absorber is excellent in the reduction of high-frequency fluctuations.
Key words： semiactive absorber, vibratron control hull vibration
Received for publication on May. 6,1997; accepted on Dec. 1,1997
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Introduction
The main hull vibration is an oscillation motion of the hull girder which is predominantly induced by repeated excitations from the propellers, the main engine, and the wave load. Since the high-pitch propeller and long-stroke diesel engine have become more widely used, widespread problems relating to main hull vibration require attention. The presence of such vibrations can affect the comfort of passengers and crew, damage the structure, and impair the fighting efficiency of war-ships. The first systematic investigation of ship hull
