Research on a Rail Defect Location Method Based on a Single Mode Extraction Algorithm

Calculation of leaky Lamb waves with a semi-analytical finite element method

The enormous potential of Guided waves have a significant use for non-destructive evaluation(NDE) and structural health monitoring(SHM). It is common to use different solution approaches to predict dispersion curves depending on the material type, isotropic, transversely isotropic, or orthotropic, of the medium in which the wave propagates, shape of the waveguide, etc. Inability to model waveguides of arbitrary cross-section by existing matrix methods has led to development of Semi-Analytical Finite Element(SAFE) Method. In this study, rapid and accurate prediction of the propagation characteristics for guided waves in a wide range of structures has been performed by implementation of SAFE method. Damped and undamped waveguides of different shapes can be modelled. Wave propagation characteristics in both isotropic and anisotropic composite structures can also be studied. To benchmark the solution, a case study using Transfer Matrix Method (TMM) for composite plate has been evaluated. It was found that the element discretizaton plays an important role in accurate prediction of modes in SAFE method, neglecting which leads to loss of higher order modes.

Dispersion analysis of guided waves in the finned tube using the semi-analytical finite element method

In guided wave inspection, dispersion curves and wave structures are indispensable for designing inspection tools and analyzing waveforms. This report describes solutions of the dispersion curves and wave structures with a semi-analytical finite element method and discusses the applications of the dispersion curves and wave structures in guided wave inspection. Formularization of the semi-analytical finite element method revealed that external dynamic loading should be distributed in a shape similar to the wave structure of the desired mode and enabled the analysis of excitation potentials of desired modes with an angle beam transducer. Using a semi-analytical finite element analysis, guided wave tools for inspecting bottom-edges of rails were developed and gave good results for practical use.

Modeling lamb wave propagation in visco-elastic composite plates using a fifth-order plate theory

In this study, an output-only modal identification approach is proposed for decentralized wireless sensor nodes used for linear structural systems. The following approaches are implemented to achieve the objective. Firstly, an output-only modal identification method is selected for decentralized wireless sensor networks. Secondly, the effect of time-unsynchronization is assessed with respect to the accuracy of modal identification analysis. Time-unsynchronized signals are analytically examined to quantify uncertainties and their corresponding errors in modal identification results. Thirdly, a modified approach using complex mode shapes is proposed to reduce the unsynchronization-induced errors in modal identification. In the new way, complex mode shapes are extracted from unsynchronized signals to deal both with modal amplitudes and with phase angles. Finally, the feasibility of the proposed approach is evaluated from numerical and experimental tests by comparing with the performance of existing approach using real mode shapes.

The instrumented Canton Tower is a 610 m high-rise structure, which has been considered as a benchmark problem for structural health monitoring (SHM) research. In this paper, an improved automatic modal identification method is presented based on a natural excitation technique in conjunction with the eigensystem realization algorithm (NExT/ERA). In the proposed modal identification method, damping ratio, consistent mode indicator from observability matrices (CMI_O) and modal amplitude coherence (MAC) are used as criteria to distinguish the physically true modes from spurious modes. Enhanced frequency domain decomposition (EFDD), the data-driven stochastic subspace identification method (SSI-DATA) and the proposed method are respectively applied to extract the modal parameters of the Canton Tower under different environmental conditions. Results of modal parameter identification based on output-only measurements are presented and discussed. User-selected parameters used in those methods are suggested and discussed. Furthermore, the effect of environmental conditions on the dynamic characteristics of Canton tower is investigated.

Using a low frequency range in long-range inspection of a plate with Lamb waves, directivity of Lamb waves becomes weak and Lamb wave propagation is affected by the both sides of a plate. Thus, dispersion curves for a plate with a finite width should be used in nondestructive testing for it. Since dispersion curves for a plate with a finite width cannot be analytically obtained, guided wave calculation technique developed by authors using a semi-analytical finite element method is useful. In this study, therefore, theoretical dispersion curves for a plate with a finite width were derived using the calculation technique, and the characteristic of dispersion curves and the relationship between dispersion curves and vibration distributions were described. And also, the theoretical dispersion curves and vibration distributions obtained by the calculation were verified by experiments in which vibration distributions were obtained by measuring waveforms at many points with a laser interferometer

An accurate prediction for the response of civil and mechanical engineering structures subject to ambient excitation requires the information of dynamic properties of these structures including natural frequencies, damping ratios and mode shapes. Since the excitation force is not available as a measured signal, we need to develop techniques which are capable of accurately extracting the modal parameters from output-only data. This article presents the results of modal parameter identification using two time-domain methods as follows: the autoregressive moving average vector (ARMAV) method and the state–space method. These methods directly work with the recorded time signals and allow the analysis of structures where only the output is measured, while the input is unmeasured and unknown. The equivalence between ARMAV and state–space approaches for the problem of modal parameter identification of vibrating systems is shown in the article. Using only the singular value decomposition of a block Hankel matrix of sample covariances, it is shown that these two approaches give identical modal parameters in the case where the block Hankel matrix has full row rank. The time-domain modal identification algorithms have a serious problem of model order determination: when extracting structural modes these algorithms always generate spurious modes. A modal indicator to differentiate spurious and structural modes is presented. Numerical and experimental examples are given to show the effectiveness of the ARMAV or state–space approaches in modal parameter identification using response data only.

The coupling of various modes in centrifugal pumps renders the process of modal parameter identification through frequency response functions both time-consuming and labour-intensive. To accurately identify modal parameters, current modal testing typically requires the deployment of numerous measurements or excitation points. However, certain modal parameters may suffer from low SNR, leading to distorted modal shapes that deviate from reality. This study employs a semi-empirical approach to ingeniously design the excitation vector by leveraging the relationships among the centre of mass, inertial axes, and excitation points. During modal testing experiments, specific modes of the centrifugal pump are decoupled, significantly improving the SNR for the targeted modes. Experimental validation demonstrates that the proposed method markedly enhances the accuracy of modal parameters identification, thereby facilitating the analysis of its vibration characteristics. The findings enable rapid identification of modal parameters related to vibration issues in engineering applications, contributing to the swift localization and resolution of vibration problems.

Analysis of travelling waves in elastic waveguides with complex cross-sections, such as train rails, can only conveniently be performed numerically. The semi-analytical finite element (SAFE) method has become a popular tool for performing such analyses. This paper employs a hybrid SAFE-3D FE method to investigate the scattering of guided waves at discontinuities such as welds or cracks, in continuous welded train rails. The aim of the analysis is to predict transmission and reflection coefficients for a given incident wave and known discontinuity. This characterisation is useful for predicting the long-range transmission characteristics of transducers in non-destructive evaluation (NDE) and monitoring systems, such as the ultrasonic broken rail detector (UBRD) system developed by the Institute for Maritime Technology (IMT) and the Council for Scientific and Industrial Research (CSIR). Furthermore, we investigate an extension of the current UBRD system to detect cracks before complete breaks occur, which will require distinguishing between reflections from cracks and other reflectors such as welds, in order to avoid false alarms.

In order to identify the modal parameters of time invariant three-dimensional engineering structures with damping and small nonlinearity, a novel isometric feature mapping (Isomap)-based three-dimensional operational modal analysis (OMA) method is proposed to extract nonlinear features in this paper. Using this Isomap-based OMA method, a low-dimensional embedding matrix is multiplied by a transformation matrix to obtain the original matrix. We find correspondence relationships between the low-dimensional embedding matrix and the modal coordinate response and between the transformation matrix and the modal shapes. From the low-dimensional embedding matrix, the natural frequencies can be determined using a Fourier transform and the damping ratios can be identified by the random decrement technique or natural excitation technique. The modal shapes can be estimated from the Moore–Penrose matrix inverse of the low-dimensional embedding matrix. We also discuss the effects of different parameters (i.e., number of neighbors and matrix assembly) on the results of modal parameter identification. The modal identification results from numerical simulations of the vibration response signals of a cylindrical shell under white noise excitation demonstrate that the proposed method can identify the modal shapes, natural frequencies, and ratios of three-dimensional structures in operational conditions only from the vibration response signals.

Ultrasonic flaw detection is the most commonly used method in rail defect detection, and the defect judgment in flaw detection data is the most important link. The B-scan data of ultrasonic flaw detection vehicle is used for data analysis and recovery. A set of rail defect identification model based on BP neural network is established according to the channel distribution characteristics, digital combination characteristics and the arrangement and combination characteristics in time sequence of the recovered data. This method takes the 1–6 channel detection data as an example, and trains the model by extracting the rail head nuclear defect as the sample and making the training set, Experiments show that the model can effectively identify the defect data by setting a suitable threshold value, and give the location of the rail defect, help the flaw detection workers to improve the efficiency of rail defect detection, greatly reduce the labor intensity, and avoid the missed judgment of the rail defect.

This article studies optimization design of Vibratory stress relief (VSR) technology parameter for large welded components. The test is carried through a large welded truss. It first analysis key factor of the influence on VSR technology effect. And then by modal analysis, we’ve got the natural frequency and natural modes of the specimen , The optimization design is based on residual stress distribution and natural modes of component for VSR process parameters. Test pieces are treated by vibration. before and after vibration, residual stress of the specimens is measured by the method of blind hole.The results showed that vibration mode is a key factor in determining the effect of VSR. Stress distribution is more complex for large welded components.As accordance by selecting a few of vibration modes, for VSR main technical parameters design, it can get enough vibration displacement in the areas and directions of component with residual stress. Thus we can have a good effects to relief welding residual stress.Three major parameters (Excitation frequency, excitation point, support points) are related with vibration mode. They are decided by selecting vibration mode. Excitation force is decided based excitation frequency as well as the size of the exciter eccentric , to get the right excitation force by adjusting the size of the exciter eccentric under the condition of the selected excitation frequency.

Axial transmission ultrasonography, which uses a set of transmitting and receiving probes placed on the same waveguide’s surface, shows the potential clinical application for cortical bone quality assessment. In this work, a model-based parameter sweep inversion approach has been developed to estimate the thickness and elastic velocities of the cortex from the dispersive axially-transmitted snapshots. The inversion algorithm is formulated in the frequency-phase velocity (f-c) domain. To solve the inverse problem, i.e., to extract bone properties from ultrasound data, a forward modeling has been developed to simulate the f-c dispersion curves given a bone model. A semi-analytical finite element (SAFE) method is used to compute the dispersion curves for a complex structure of a cortical bone plate coupled with overlying soft tissues. A parameter sweep is used to seek within a range of values an optimized solution with the least misfit. The proposed method optimizes the mismatch between the measured and theoretically calculated dispersion curves with a least-square constraint. Numerical and in-vivo experimental data examples are presented to illustrate the technique’s performance.