Shape Sensing of Thin Shell Structure Based on Inverse Finite Element Method

Shape sensing as a crucial component of structural health monitoring plays a vital role in real-time actuation and control of smart structures,and monitoring of structural integrity.As a model-based method,the inverse finite element method(iFEM)has been proved to be a valuable shape sensing tool that is suitable for complex structures.In this paper,we propose a novel approach for the shape sensing of thin shell structures with iFEM.Considering the structural form and stress characteristics of thin-walled structure,the error function consists of membrane and bending section strains only which is consistent with the Kirchhoff–Love shell theory.For numerical implementation,a new four-node quadrilateral inverse-shell element,iDKQ4,is developed by utilizing the kinematics of the classical shell theory.This new element includes hierarchical drilling rotation degrees-of-freedom(DOF)which enhance applicability to complex structures.Firstly,the reconstruction performance is examined numerically using a cantilever plate model.Following the validation cases,the applicability of the iDKQ4 element to more complex structures is demonstrated by the analysis of a thin wallpanel.Finally,the deformation of a typical aerospace thin-wall structure(the composite tank)is reconstructed with sparse strain data with the help of iDKQ4 element.

2D and 3D Shape Sensing Based on 7-Core Fiber Bragg Gratings

A fiber-optic shape sensing based on 7-core fiber Bragg gratings(FBGs)is proposed and experimentally demonstrated.The investigations are presented for two-dimensional(2D)and three-dimensional(3D)shape reconstruction by distinguishing bending and twisting of 7-core optical fiber with FBGs.The curvature and bending orientation can be calculated by acquiring FBG wavelengths from any two side cores among the six outer cores.And the shape sensing in 3D space is computed by analytic geometry theory.The experiments corresponding of 2D and 3D shape sensing are demonstrated and conducted to verify the theoretical principles.The resolution of curvature is about 0.1 m^(-1) for 2D measuring.The error of angle in shape reconstruction is about 1.89°for 3D measuring.The proposed sensing technique based on 7-core FBGs is promising of high feasibility,stability,and repeatability,especially for the distinguishing ability on the bending orientation due to the six symmetrical cores on the cross-section.