Investigation Into The Structural Style Design Of Naval Vessel's Floating Raft With Horizontal Grillage

The equipment vibration and noise are closely related to naval vessel safety and comfort.Vibration and noise induced by vibration will make crews feel uncomfortable,reduce the reliability of the naval vessel equipment,and cause fatigue damage of hull structure,further seriously affect the battle performance of warship.The MSC91 of International Maritime Organization(IMO)issued a proposal of amendment(No.338)in terms of International Convention for Safety of Life at Sea(SOLAS),which aimed at the non-mandatory Code on Noise Levels On-board Ships passed in 1981(A.468(XII)proposal),improved the control requirements of noise level in engine room,living room for crew,working room and other rooms.Recently,the research work on the vibration noise reduction of naval vessel mainly focuses on the application of damping material,noise reduction of propeller and vibration isolation of mechanical equipment,etc.With the development of light and high power equipment,considering the maximum utilization rate of equipment space and load of naval vessel,double-deck vibration isolation is difficult to meet the requirement.The floating raft isolation system is widely applied in this field due to its excellent vibration isolation performance,smaller additional quality and installation space.Previous research on the floating raft system mostly focused on the influence of foundation stiffness,vibration isolator stiffness,damping and distribution principle,and the mass ratio of raft body on the vibration isolation performance,the studies on the raft structure form are less.This paper focuses on the effect of raft structure form on the vibration isolation performance with low and medium frequency characteristics.The main research contents in this thesis are summarized as follows:(1)Classification of vibration control,vibration analysis method,dynamic modeling methods,and assessment methods include their advantages and disadvantages were introduced.(2)Finite Element Method(FEM)was used to simulate the floating raft isolation system.A Y2-200L1-2 motor is taken as an example for modeling of dynamic mechanical model of floating raft isolation system with horizontal grillage,and the vibration isolation performances are analyzed.(3)Vibration severity and vibration level difference were used to evaluate the vibration isolation performance of floating raft system.The influence of raft structure form on the vibration isolation performance are performed,which includes raft body mass,thickness of plate,locations of web,additional stiffener,web with hole,and partly cut raft body.(4)Combined effect of each improvement was investigated.The improved FE model was modeled and its vibration isolation performance was analyzed.