Impact Monitoring Technology Research Of Distributed Optical Fiber Based On Fractal Theory

In the field of Aeronautics and Astronautics,the damage caused by low energy impact on aerospace's structure is highly concealed,which will result in deterioration of structure over time and seriously affect the safety and reliability of spacecraft during its service.Thus it's vital to identify the position of low-energy impact timely and accurately.Optical fiber sensor has exclusive advantages.For instance,it has the small quantity,good flexibility,anti-electromagnetic interference,high sensitivity and it is also easy to build distributed sensor network etc.That's why it is widely used in the field of increasingly complex environment of aircraft service.Therefore,an impact monitoring technology of distributed optical fiber sensors based on fractal theory is presented for typical structure of aerospace plate.The paper will present the following aspects.Firstly,a de-noising method of impact signal in time-domain processing based on fractal theory,self-adapting and self-controlling is proposed.The relationship between the filtering result and parameters of its fuzzy-control is discussed in this paper.Based on above,the short-time fractal dimension of fractal theory is applied to correct the value of fuzzy-control' parameters so that the reduction of self-adaptive noise is realized.Secondly,an impact localization method of solving the full frequency band signal amplitude energy and inverse function is proposed for aluminum alloy plate structure with four clamped edges targeting at the meeting the requirement of instantaneity and convenience.The full frequency band amplitude energy of FBG impact response signal is selected as the characteristic parameter in order to realize the fast identification of impact load's position.Thirdly,a low energy impact position-identification method based on the calculation of correlational dimension and tri-circle model is proposed for Bragg grating sensing mode of low sampling rate fiber.Then,the correlational dimension is used as the characteristic parameter of the impact response signal,the impact load's position on aluminum alloy plate structure with four clamped edges is effectively identified by applying the combination of tri-circle model and reference weight.Finally,aiming at meeting the requirement of low energy impact localization of carbon fiber reinforced plastic plate structure,a fiber Bragg grating(FBG)sensor network is constructed and a novel method for impact localization based on Multifractal De-trended Fluctuational Analysis(MF-DFA)is proposed.This method applies MF-DFA to obtain the multi-fractal spectrum of impact signal data,selecting the extreme point as characteristic parameter.Distribution characteristics of the extreme point together with the distance between the impact point and the sensors are studied.In this way,the impact load's position is successfully identified.