Dynamic Analysis And Active Control Of The Floating Raft With Coupled Rigid And Elastic Motions

The application of floating raft isolation system can be a very effective way to depress thestructure-borne sound and mechanical vibratory energy transmission from vibration source to the shiphull, so it is widely used in large-scale rotating machinery of the vessel. The floating raft isolationsystem is a complicated and coupled system because it contains several sub-systems which aremulti-body vibration system with elastic coupling. The frequencies of excitation forces on the machinesare often within the low-frequency band, it will cause the floating raft isolation system fail to workproperly.This essay focuses on the study of the vibration control methods, taking advantage of the floatingraft isolation system. First, the dynamic model of the floating raft isolation system with the rigid orflexible raft is implenented by assembling the mobility matrices of subsystems when a combinedexcitation acts on the source. According to the relationship between the force and the velocity on eachsubsystem’s interfaces, the power flow expressions of the systems are derived, and the impact of thestructural parameters on the power flow transmitted into the subsystems of the isolation devices are alsoanalyzed. Second, creating a rigid floating raft isolation model by using the Automatic DynamicAnalysis of Mechanical Systems(ADAMS/View). Build the raft and basis flexible body model withfinite element software, and then import them to ADAMS get the Floating Raft with Coupled Rigid andElastic Motions. We can output the measurement point’s force and velocity response curve by thevibration response analysis. Through the power flow calculation method, we can get the power flowtransmitted into the foundation. The results show a great agreement with the theory. In order to improvethe performance of the vibration reduction in low-frequency domain, dynamic vibration absorbers(DVAs) are mounted on the raft subsystems of floating raft and the dynamic models of the floating raftisolation system with the dynamic vibration absorbers (DVAs) or adaptive vibration absorbers (AVAs)are derived respectively. Through the co-simulation of ADAMS and Matlab/Simulink, active controlcan be achieved. Finally, three different control strategies for minimization of vertical velocity, verticalforce and power flow are proposed, and compared their impact on the effect of depress the vibrationsound. Based on this, we build a floating raft isolation system with a complex raft and realize it’snecessary for raft shape research.