Research On Spatial Filter Based Structural Health Monitoring

At present, the method of structural health monitoring based on Lamb wave, which has goodapplication foreground, is one of the basic study of aircraft structure at home and abroad due to itssensitivity to small defects, active and passive monitoring and large area monitoring in plate structures.The spatial filter monitoring and imaging technology is a new method for structural health monitoring(SHM), which uses the sensors array to constitute spatial filter with space-wave number domainfiltering properties and uses the method of virtual rotation of spatial filter to realize themulti-directional scanning for the structure, identify the structural impact or damage and get theeffective mapped image of the recognition results. The goal of research in this dissertation is to detecteffective monitoring and damage information based on Lamb wave and spatial filter technology. Thisresearch lays the foundation for developing new technical means of impact and damage monitoring ofComposite Material structures in structural health monitoring.The main works and novel researches done in this dissertation include:(1) Discussing and analyzing multi-mode which lamb wave propagate, dispersion characteristicsand wave number characteristics of lamb wave, we have achieved the wave number dispersion curvesof lamb wave.(2) After researching the model, which is compounded by basic signal of linear sensor array, wecan get the dividing strip of near-field and far-field. After studying spatial filtering theory of lambwave signal deeply, we obtain the analytic expression and the scope of application of the ideal spatialfilter. The spatial filtering characteristics of the spatial filter have been discussed in detail. Theconventional imaging method of the spatial filter has been researched in theory and verified inexperiment. The feasibility of the spatial filter method testing structural damage has been verified inmetal structure. All above has provided theoretical and experimental basis for the improvement of thespatial filter in the following passage.(3) Improved imaging method of spatial filter structural damage based on Hilbert transform isproposed, the method uses Hilbert transform to construct the complex signal to participate in thesynthesis of spatial filtering signals. As it avoids the conventional use of structure parameters for thesimplified approach on the imaginary part, thus the spatial filter method is extended to the applicationof composite material structural damage diagnosis.(4) Improved imaging method of spatial filter structure, which is based on Shannon continuouscomplex wavelet transform has been put forward. The method can be applied not only to active damage monitoring but also to the passive impact monitoring，which makes up the disadvantage ofthe Hilbert transform. Thus the spatial filter method is extended to the application of the passiveimpact monitoring.(5) The nominal optimal damage imaging method based on the improved spatial filter has beenput forward to overcoming the error on signal attainment and the difficulties that the temperaturechanges make the baseline damage monitoring method difficult to carry out. The engineeringapplication of the structure health monitoring technology has been promoted by the method.(6) By taking the oil tank of the real aircraft as the research object, we have verified theimproved spatial filter method and the nominal optimal damage imaging methods that are proposed inthe paper.