Strain Measurement Of A Floating Raft Based On FBG Distributed Sensing

Floating raft isolation system can obviously restrain vibration from machine to the hull, thus has been widely applied in naval power machinery anti-vibration noise reduction fields. In the past, finite element method is used to model the raft system where a series of simplification was conducted; the simulation result cannot truly reflect the dynamic behavior of the system. Then it is necessary to verify the effectiveness of the model. Among many factors in isolation of the raft system which causes the raft elasticity of various modes that influencing the vibration system are not negligible. Therefore, the verification of effectiveness of the model and raft elastic deformation measurement for further research on improving the vibration characteristics of the floating raft isolation performance are of important significance.The dynamics analysis theory of the floating raft isolation system were detailedly derived. The finite element modal analysis method and the harmonic response analysis method were chosen to solve the dynamic characteristics of the floating raft system, and vibration grade fall was determined as the criterion to evaluate effectiveness of vibration isolation of the system. The distributed sensing principle of the fiber Bragg grating sensors were expatiated.Raft and floating raft three-dimensional finite element model were established, modal analysis was used to calculate the original vibration characteristics.To verify the effectiveness of the finite element model of the raft,7533 B&K modal test software was applied to hammering structure modal test. And through comparison of theoretical analysis results and the experimental results of a plate type raft structure of the modal, the feasibility of this method was verified, which laid a foundation for its further use to verify the effectiveness of such large-scale complex structure finite element model as floating raft and so on.A simplified calculation example of a raft model was built and finite element simulation of harmonic response analysis was calculated according to the analysis result of vibration magnitude distribution gap. Results show that the raft structure for the whole of the floating raft isolation system has great influence.Pointing against the influence on the raft floating vibration isolation effects brought by elastic modulus of the raft, it was proposed that to use fiber Bragg grating sensor for structure stiffness weak region of dynamic strain detection. Based on the theoretical analysis and test of plate type raft structure, a method to determine the fiber Bragg grating sensor installation location and number was proposed, and the feasibility of this method was verified through experiments, which provides the basis for its further use for distributed measurement of the complex structure elastic deformation.