The Research On Targeted Regulation Technology Of Floating-raft Isolation System Performance

The floating-raft isolation system is an important technology to control the vibration of warship's mechanical equipments at present.It plays an irreplaceable role in improving the acoustic stealthy of warships.In recent years,the new vibration isolation mechanisms and technologies for reducing total vibration level difference of floating-raft isolation system have attracted much attention,such as space truss floating raft isolation system,active control technology and so on.However,due to the limited space and energy of warships,these new technologies are difficult to apply in the engineering practice.Considering that the vibration energy of the mechanical equipment tends to focus on one or several frequency bands,improving the floating-raft isolation system performance in these frequency bands,rather than the whole frequency band will be more practical.Therefore,with the raft and isolator as the object of the research,this paper focuses on improving the floating raft isolation system in certain frequency band,without loss or small losses in total vibration level difference,to achieve targeted regulation of floating-raft isolation system performance.It can provide a new way to improve floating-raft isolation system performance.In the part of raft,keeping the floating-raft weight constant,the parametric finite element model of floating-raft isolation system was established by the floating-raft geometric parameters.The effects of floating-raft geometric parameters on isolation performance were numerically discussed.The results show that the effects of floating-raft geometric parameters on isolation performance are mainly reflected in the middle and high frequency area;the most important floating-raft geometric parameters impacting on isolation performance are floating-raft height,length-width ratio and the number of ribbed slab;choosing a set of proper floating-raft geometric parameters can improve the isolation performance of floating raft isolation system in the specified frequency band,and it can be used as one of the effective ways to achieve the target regulation of floating-raft isolation system performance.Finally,a set of model tests have been carried out to verify the correctness of the related conclusions.In the part of isolators,a model of one dimensional quasi-periodic phononic crystals with layer thickness arranged by TM sequence,with its geometric parameters arranged in quasi-periodic sequence,was proposed.Its band structure was investigated numerically using the transfer matrix method combined with the supercell method,then its band gap characteristics were compared with those of periodic-structure phononic crystals.Besides,the effects of filling rate and layer-thickness rate were also discussed.The results show: its first band gap start frequency decline nearly 50%,comparing to that in periodic-structure phononic crystals;Its bandgap-characteristics factors are more abundant,and the band gap adjustment is wider and more flexible,comparing to the phononic crystals with material parameters arranged in quasi-periodic sequence;arranging the material parameters,filling rate,and layer-thickness rate of the isolators based on the model of one dimensional quasi-periodic phononic crystals with layer thickness arranged by TM sequence is one of the effective ways to improve the floating raft isolation system in specified frequency band,using the low frequency band gap of elastic wave attenuation.Lastly,a set of model tests have been carried out to verify the correctness of the related conclusions.Finally,on the foundation of the previous two parts,introducing genetic algorithm,aiming at maximize the vibration isolation performance in the specified frequency band,and without loss or small losses in total vibration level difference,the targeted regulation technology of floating-raft isolation system performance is proposed,which can improve the floating raft isolation system in certain frequency band,by optimizing the geometric parameters of floating raft and using one dimensional quasi-periodic phononic crystal with the layer thickness arranged by the TM sequence isolators.At last,the targeted regulation technology of floating-raft isolation system performance was verified by simulation test.