Research On Surface Morphology Sensing Based On Micro-cavity Array Fiber

With the rapid development of the aviation industry,various new types of aviation structures are constantly being developed and improved.In order to ensure the safe,reliable and stable operation of aviation structures,structural safety monitoring is a necessary process.During the flight of the aircraft,the wing is extremely susceptible to cross-interference from factors such as airflow,vibration,and alternating loads,resulting in strong deformation of the wing,which will cause the aircraft to break and fail to operate normally and even cause catastrophic accidents.Therefore,morphological perception of the shape of aircraft wings is critical.However,due to its complex working environment and susceptibility to electromagnetic environment interference,traditional methods cannot achieve online monitoring.Fiber gratings are widely used in structural safety monitoring due to their small size,resistance to electromagnetic interference,and freedom from complex environmental interference.However,most of the existing methods of reducing structural morphology use conventional Bragg fiber gratings with a length of 1 cm.Discrete curvature monitoring is performed,and the aircraft wing is susceptible to non-uniform strain resulting in FBG reflection spectra,which reduces the reduction accuracy,and because of the low spatial resolution,it is not possible to achieve high spatial resolution and high-precision curved surface morphology perception.In this paper,the existing optical fiber sensing-based curved surface morphology reduction technology has the problems of easy spectrum,low spatial resolution,and insufficient reduction accuracy.Based on the micro-cavity array structure fiber,combined with optical frequency domain reflection demodulation technology,a high Spatial resolution,high accuracy,and fully distributed spatial curvature monitoring;the use of a micro-cavity sensor network to construct a surface attitude model,and combined with a surface restoration algorithm,to achieve high-precision 3D surface pose restoration,the main research contents are as follows:(1)Research on the sensing mechanism of micro-cavity array fibers.Combining coupling mode theory and Bragg fiber grating spectral equations to establish a mathematical model for sensing micro-cavity array fibers.Simulation analysis and establishment of the equations for the changes in the micro-cavity unit spectrum with external physical quantities;research on sensing under non-uniform physical changes at different locations The spectral distribution characteristics of the unit,according to the parameters such as the width of the spectrum,the central wavelength,and the change in the shape of the spectrum,study the corresponding signal processing algorithms to achieve the demodulation of external physical quantities.(2)Research on surface morphology reduction algorithm based on micro-cavity array fiber.According to the experimental model studied and the finite element analysis method,the conversion relationship between the discrete strain and discrete curvature perceived by the micro-cavity array fiber is analyzed,and the continuous data of the curvature of the discrete points in the space is studied,and the difference algorithm is analyzed.The influence on the shape reduction of the space surface,the continuous curvature information acquisition of the surface of the space curved structure is realized,and based on the obtained continuous curvature information,the surface shape reduction algorithm based on the space curvature information is researched to realize the space surface shape perception based on the micro-cavity array fiber.(3)Research on high spatial resolution and high precision fully distributed demodulation algorithm based on micro-cavity array fiber.Set up a micro-cavity array fiber demodulation system based on optical frequency domain reflection,study the principles and methods of high spatial resolution and high precision sensor demodulation of fully distributed dense micro-cavity array fibers,and explore the degradation factors and suppression methods of spatial resolution,And high spatial resolution positioning algorithm of micro-cavity array;study the noise generation mechanism and compensation method in the demodulation system,analyze the nonlinear effects and correction methods generated by the optical components of the system,and establish a high-precision spectral reconstruction of the micro-cavity sensing unit Method to achieve a high-precision demodulation algorithm based on the spectral characteristics of the micro-cavity.(4)Experimental verification of surface shape reduction detection.Taking the safety inspection of aircraft wing structure as the main research object,a simplified model of composite aircraft wing deformation model was constructed and studied.Micro-cavity array optical fiber with grid length of 0.5 mm,interval of 0.5 mm,and reflectance of-45 d B was used as the sensing unit.In combination with optical frequency domain reflection technology,a high spatial resolution surface morphology sensing system is built.First,the sensor is calibrated under a known curvature model,and then the surface reduction effect under different curved surface conditions is tested to verify the microcavity array-based The feasibility of the optical fiber to realize the morphological sensing of curved structures.