STRUCTURAL HEALTH MONITORING USING LINEAR AND NONLINEAR ULTRASONIC GUIDED WAVES

The dissertation addresses Structural Health Monitoring (SHM) using linear and nonlinear ultrasonic guided waves, with an emphasis on the development of analytical and numerical models of guided wave propagation and interaction with linear and nonlinear structural damage. An analytical model was developed based on the exact Lamb wave solution for the simulation of Lamb wave propagation and interaction with damage. The damage effects were inserted into the model using complex valued wave damage interaction coefficients (WDICs). The analytical procedure was coded as a framework into a MATLAB Graphical User Interface (GUI), and the software WaveFormRevealer (WFR) was developed as a general description of wave generation, propagation, interaction with damage, and detection. The WDICs were extracted from the harmonic analysis of small-size local finite element models (FEM) with non-reflective boundaries (NRB). By joining the analytical framework and the local FEM, a Combined Analytical/FEM Approach (CAFA) was developed for efficient simulation of Lamb wave propagation and interaction with damage. To model guided wave propagation in composite structures, the semi-analytical finite element (SAFE) procedure was investigated and coded with MATLAB, and the software SAFE-DISPERSION was developed to generate guided wave dispersion curves, mode shapes, and directivity plots for composites. Nonlinear ultrasonic SHM techniques were also examined because they have been reported to have remarkable sensitivity to incipient damage. An analytical model was developed to capture the nonlinear higher harmonic generation phenomena for localized damage. Also investigated was the nonlinear interaction between Lamb waves and breathing cracks using FEM through two specific simulation techniques: element activation/deactivation method and contact analysis. A damage index based on the nonlinear features of the sensing signal was proposed in order to identify the presence and severity of a breathing crack. Nonlinear ultrasonic SHM was also investigated for monitoring bolt tightness status of an aerospace bolted lap joint. The 3-D contact FEM simulation was carried out and compared with experiments using Scanning Laser Doppler Vibrometer (SLDV). The dissertation finishes with a summary of contributions followed by conclusions, and suggestions for future work

New Stability Criterion for Discrete-Time Genetic Regulatory Networks with Time-Varying Delays and Stochastic Disturbances

We propose an improved stability condition for a class of discrete-time genetic regulatory networks (GRNs) with interval time-varying delays and stochastic disturbances. By choosing an augmented novel Lyapunov-Krasovskii functional which contains some triple summation terms, a less conservative sufficient condition is obtained in terms of linear matrix inequalities (LMIs) by using the combination of the lower bound lemma, the discrete-time Jensen inequality, and the free-weighting matrix method. It is shown that the proposed results can be readily solved by using the Matlab software. Finally, two numerical examples are provided to illustrate the effectiveness and advantages of the theoretical results

N-(Quinolin-8-yl)quinoline-2-carbox­amide

In the title compound, C19H13N3O, the dihedral angle between the two quinoline systems is 11.54 (3)°. The mol­ecular conformation is stabilized by intra­molecular N—H⋯N and C—H⋯O hydrogen bonds, with N—H⋯N being bifurcated towards the two N atoms of the two quinoline rings. In the crystal, there are weak intermolecular π–π inter­actions present involving the quinoline rings [centroid–centroid distance 3.7351 (14) Å]

Sub-wavelength Coherent Imaging of a Pure-Phase Object with Thermal Light

We report, for the first time, the observation of sub-wavelength coherent image of a pure phase object with thermal light,which represents an accurate Fourier transform. We demonstrate that ghost-imaging scheme (GI) retrieves amplitude transmittance knowledge of objects rather than the transmitted intensities as the HBT-type imaging scheme does.Comment: 5 pages, 4 figures; Any comments pls. contact: [email protected]

PDHL-EDAS method for multiple attribute group decision making and its application to 3D printer selection

With the rapid development of 3D printing technology, 3D printers are manufactured based on the principle of 3D printing technology are more and more widely used in the manufacturing industry. Choosing high quality 3D printers for industrial production is of great significance to the economic growth of enterprises. In fact, it is difficult to select the most optimal 3D printers under a single and simple standard. Therefore, this paper establishes the probabilistic double hierarchy linguistic EDAS (PDHL-EDAS) method for the multiple attribute group decision making (MAGDM). Then the CRITIC model is introduced to derive objective weight and the cumulative prospect theory is leaded into obtain the cumulative weight of PDHLTS. In addition, what’s more, the PDHL-EDAS method is built and applied to the choice of high-quality 3D printer. Finally, compared with the available MAGDM methods under PDHLTS, the built method is proved to be scientific and effective. First published online 15 December 202