Laser ultrasonic technology can provide a non-contact, reliable and efficient inspection of train rails. However, the laser-generated signals measured at the railhead are usually contaminated with a high level of noise and unwanted wave components that complicate the identification of defect echoes in the signal. This study explores the possibility of combining laser ultrasonic technology (LUT) and an enhanced matching pursuit (MP) to achieve a fully non-contact inspection of the rail track. A completely non-contact laser-based inspection system was used to generate and sense Rayleigh waves to detect artificial surface horizontal, surface edge, subsurface horizontal and subsurface vertical defects created at railheads of different dimensions. MP was enhanced by developing two novel dictionaries, which include a finite element method (FEM) simulation dictionary and an experimental dictionary. The enhanced MP was used to analyze the experimentally obtained laser-generated Rayleigh wave signals. The results show that the enhanced MP is highly effective in detecting defects by suppressing noise, and, further, it could also overcome the deficiency in the low repeatability of the laser-generated signals. The comparative analysis of MP with both the FEM simulation and experimental dictionaries shows that the enhanced MP with the FEM simulation dictionary is highly efficient in both noise removal and defect detection from the experimental signals captured by a laser-generated ultrasonic inspection system. The major novelty contributed by this research work is the enhanced MP method with the developments of, first, an FEM simulation dictionary and, second, an experimental dictionary that is especially suited for Rayleigh wave signals. Third, the enhanced MP dictionaries are created to process the Rayleigh wave signals generated by laser excitation and received using a 3D laser scanner. Fourth, we introduce a pioneer application of such laser-generated Rayleigh waves for inspecting surface and subsurface detects occurring in train rails.
A sol-gel based auto-combustion technique has been employed to synthesize polycrystalline La 0.1 Bi 0.9-x Pb x FeO 3 (x = 0.0, 0.05, 0.10, 0.20, 0.30) ceramics. The samples have been characterized by X-ray diffraction, scanning electron microscopy, an LCR-meter and a vibrating sample magnetometer for their structural and morphological features, as well as electrical and magnetic properties, respectively. The structural analysis revealed that when Pb was doped at Bi-sites in La 0.1 Bi 0.90 FeO 3 , the host retained the rhombohedrally distorted perovskite structure, attributed to the non centro-symmetric space group R3c. The surface morphological studies revealed that the grain size was increased and formed agglomerates at high concentrations of Pb contents. The dielectric parameters displayed conventional ferrite behavior depicting high values at low frequencies and decreasing with rise in frequencies, leading to constant values at still higher frequencies. The magnetic properties were changed nonmonotonically with increasing Pb concentration. This nonmonotonical behavior with increasing Pb could be attributed to the canting of the antiferromagnetic spins in BiFeO 3 based multiferroics.
An efficient adaptive wavelet method is proposed for the enhancement of computational efficiency of the Navier-Stokes equations. The method is based on sparse point representation (SPR), which uses the wavelet decomposition and thresholding to obtain a sparsely distributed dataset. The threshold mechanism is modified in order to maintain the spatial accuracy of a conventional Navier-Stokes solver by adapting the threshold value to the order of spatial truncation error. The computational grid can be dynamically adapted to a transient solution to reflect local changes in the solution. The flux evaluation is then carried out only at the points of the adapted dataset, which reduces the computational effort and memory requirements. A stabilization technique is also implemented to avoid the additional numerical errors introduced by the threshold procedure. The numerical results of the adaptive wavelet method are compared with a conventional solver to validate the enhancement in computational efficiency of Navier-Stokes equations without the degeneration of the numerical accuracy of a conventional solver.
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