Floating raft is a special double-layer isolation system that reduces the level of noise and vibration, notably in vibrating machines. It has been widely applied to many kinds of ships. However, traditional floating raft as passive isolation system has two opposing constraints. On one hand, floating raft must support the static load of the machine; on the other hand, it must have a sufficiently low stiffness so that the mount frequency of the machine is considerably less than the operating frequency of the machine. Traditional floating raft alone cannot perform adequately when greater performance is required. In order to solve the problem, SUN Hongling of Key Laboratory of Noise and Vibration Research, Institute of Acoustics, in collaboration with partners of Department of Modern Mechanics, University of Science and Technology carried out a series of researches to improve the isolation performance of the traditional floating raft system.
The researchers introduce dynamic vibration absorber (DVA) into floating raft. The mathematical models of floating raft system consisting of beams are implemented by assembling the mobility matrices of the subsystems. Then the power flow transmission characteristics of the coupled system with/without the DVAs are investigated to evaluate the vibration reduction performance of DVAs. Numerical simulations are performed to explore the influence of several parameters, such as the setting positions, damping and mass of the passive DVAs, on the vibration reduction effects of DVAs. Moreover the vibration reduction performance of the semi-active absorber adjusting its stiffness adaptively is analyzed for the case of time-varying frequency excitation. In addition, the vibration reduction effects of semi-active DVAs under multi-frequency excitation are investigated.
A series of researches show that the proper placement of adaptive DVAs can significantly improve the isolation performance of floating raft system and the ratio of the power flow into the base of the coupled system with/without the adaptive DVAs is an effective performance index. The results were published on the recently issued journal of Applied Acoustics (Volume 71, Issue 3, March 2010, Pages 250-257).